Senkrechtstarter mit WasserstoffantriebMetro Skyways will fliegendes Auto entwickeln
Das Tochterunternehmen Metro Skyways Ltd. von Urban Aeronautics beginnt mit der Entwicklung eines senkrechtstartenden Autos für vier Passagiere.
Mit einer Kapazität für vier Passagiere, keinen freiliegenden Rotoren und keinen Batterien an Board entspricht das geplante Design des fliegenden Autos der Größe nach einem Kompaktwagen.
Angetrieben wird der ursprüngliche Entwurf mit herkömmlichen Kerosin. Nach Angaben von Metro Skyways Ltd. soll die Möglichkeit bestehen, den Senkrechtstarter, welcher den Namen CityHawk trägt, mit Wasserstoff zu betreiben. Je nach kommerzieller Machbarkeit wird entweder flüssiger oder auf 700 bar komprimierter Wasserstoff verwendet. Der Wasserstoff soll ein herkömmliches Turbinentriebwerk antreiben. Dieses revolutionäre Antriebskonzept ist hinsichtlich der FAA/EASA Zertifizierung der kritischste Punkt.
Das Rotorkonzept basiert auf der Fancraft-Technologie von Urban Aeronautics. Der CityHawk wird zunächst von einem Menschen gesteuert. Für die Zukunft sollen das Flugkontrollsystem und das Flugmanagementsystem aber autonom arbeiten. Die Automatisierung ist von dem israelischen Unternehmen Tactical Robots entwickelt worden und wird derzeit in deren bereits autonom fliegenden Prototypen namens Cormorant getestet. Der CityHawk entspricht in Größe und Form dem Cormorant.
Im Notfall einer kritischen Flugsituation ist der CityHawk mit einem Notfallschirm-System ausgestattet, das das Fluggerät kontrolliert auf den Boden zurückbringt.
Für die Entwicklung des CityHawks gibt Metro Skyways Ltd. einen Zeitraum von fünf Jahren an. Derzeit führt Urban Aeronautics aber noch Gespräche mit potentiellen Geldgebern für das CityHawk-Projekt.
Int'l coalition set up to promote space cooperation
XI'AN, A coalition was established Sunday in northwest China's Shaanxi Province to promote innovation and cooperation on space exploration under the the Belt and Road Initiative.
The coalition, set up in the provincial capital of Xi'an, encompasses 48 universities, research institutes and academic organizations at home and abroad. It was initiated by the Chinese Society of Astronautics and Xi'an-based Northwestern Polytechnical University.
Tian Yulong, secretary-general of China National Space Administration, said the alliance will boost exchanges on space innovation between its members and help joint training of high-caliber professionals.
China designated April 24 as Space Day last year to mark the anniversary of the country's first satellite launch Dongfanghong-1 in 1970.
Xi'an, home to more than 200 aerospace research centers and enterprises, will hold major celebrations on Monday.
Der Ursprung des Jets aus der nächsten Umgebung des zentralen Schwarzen Lochs einer aktiven Galaxie
Die große Radiogalaxie M87 in nur ca. 50 Millionen Lichtjahren Entfernung enthält ein supermassereiches Schwarzes Loch von sechs Milliarden Sonnenmassen in ihrem Zentrum. Sie ist berühmt für ihren leuchtkräftigen Jet, der aus ihrem Zentralbereich abgestrahlt wird und das beobachtete Spektrum über einen Frequenzbereich von 10 Größenordnungen dominiert. Aufgrund ihrer Nähe, des ausgeprägten Jets und des sehr massereichen Schwarzen Lochs im Zentrum stellt M87 ein ideales Laboratorium dar, um die Entstehung, Beschleunigung und Bündelung der Materie in relativistischen Jets zu erforschen. Ein Team von Forschern unter der Leitung von Silke Britzen vom Bonner Max-Planck-Institut für Radioastronomie zeigt in einer aktuellen Veröffentlichung wichtige Hinweise darauf, dass turbulente Prozesse die Akkretionsscheibe und den Jet dieser Galaxie miteinander verbinden. Dies liefert neue Erkenntnisse für das lange bestehende Problem des Ursprungs von astrophysikalischen Jets.
Supermassereiche Schwarze Löcher in den Zentren von Galaxien sind eines der rätselhaftesten Phänomene in der modernen Astrophysik. Ihr gewaltiger Energieausstoß wird im Allgemeinen auf die Umwandlung von Gravitationsenergie in Strahlung zurückgeführt.
Aktive Schwarze Löcher produzieren Strahlung über das Ansammeln (“Akkretion”) von Materie. Es entsteht eine sogenannten Akkretionsscheibe, die die Zentralquelle umgibt. Ein deutliches Anzeichen für den Akkretionsvorgang im Zentralbereich von Galaxien stellen Jets von enormer Ausdehnung dar, die sich über etliche Millionen Lichtjahre Entfernung vom Galaxienzentrum aus erstrecken und damit weit über den sichtbaren Bereich der Galaxie hinausragen.
M87, die Zentralgalaxie des Virgo-Galaxienhaufens in Richtung des Sternbilds “Jungfrau” liegt in einer Entfernung von 17 Megaparsec (das entspricht ungefähr 50 Millionen Lichtjahren). Sie stellt die zweitnächste Galaxie mit einem aktiven Galaxienkern („Active Galactic Nucleus“, AGN) dar und enthält in ihrem Zentrum ein aktives Schwarzes Loch mit einer Masse von rund sechs Milliarden Sonnenmassen. M87 war die erste Galaxie, bei der ein Jet gefunden werden konnte, und zwar bereits in optischen Beobachtungen am Lick-Observatorium vor rund 100 Jahren: „ein bemerkenswerter geradliniger Materiestrahl, der mit dem Galaxienkern verbunden scheint“ (Heber Curtis, 1918).
Der Jet von M87 ist einer der am sorgfältigsten untersuchten astrophysikalischen Jets. Er ist über das gesamte elektromagnetische Spektrum - von Radiowellen bis zu Röntgenwellen - sichtbar. M87 stellt ebenfalls die erste Galaxie dar, für die Signale selbst bei den höchsten Gammastrahlungsenergien im Teraelektonenvolt (TeV-) Bereich nachgewiesen werden konnten.
Trotz einer Fülle von Beobachtungsmaterial ist die genaue Art und Weise, wie der leuchtkräftige Jet an das akkretierende Schwarze Loch koppelt, unbekannt. Die Forscher sind dieses Problem dadurch angegangen, dass sie interferometrische Radiobeobachtungen von M87 mit dem „Very Long Baseline Array“ (VLBA) analysiert haben. Das VLBA verbindet Radioteleskope von Hawaii bis zu den Virgin Islands miteinander. Dadurch kann bei einer Frequenz von 15 GHz (bzw. 2 cm Wellenlänge) eine Winkelauflösung von nur 0,6 Millibogensekunden am Himmel erreicht werden, das entspricht gerade mal 0,16 Lichtjahren oder 84 Schwarzschildradien für M87.
Obwohl bereits mehr als hundert Jets von aktiven Schwarzen Löchern detailliert untersucht werden konnten, bietet nur M87 die Möglichkeit, die unmittelbarste Nachbarschaft des zentralen Schwarzen Lochs zu erforschen.
Die Radiobeobachtungen wurden im Rahmen des MOJAVE-Projekts (“Monitoring of Jets in Active galactic nuclei with VLBA Experiments”) durchgeführt. „Wir haben diese Daten erneut analysiert, um so einen Einblick in die komplexen Prozesse zu gewinnen, die den Jet und die Akkretionsscheibe von M87 miteinander verbinden“, sagt Silke Britzen vom Bonner Max-Planck-Institut für Radioastronomie (MPIfR), die Erstautorin der Veröffentlichung. „Soweit wir wissen, ist dies das erste Mal, dass die Vorgänge im Zusammenhang mit dem Fußpunkt des Jets, also seinem Entstehungsort, und dem Aufladen des Jets mit Material untersucht werden konnten.“ Schnelle turbulente Prozesse bei denen magnetische Rekonnektion ein wichtige Rolle spielt, wie man sie im kleineren Maßstab von Vorgängen auf der Sonnenoberfläche her kennt, bieten die beste Möglichkeit zur Erklärung der Beobachtungsergebnisse (vgl. Abb. 1).
“Es gibt gute Gründe anzunehmen, dass die Oberfläche der Akkretionsscheiben sich ähnlich verhält wie die Sonnenoberfläche – blubberndes heißes Gas mit ständiger magnetischer Aktivität wie Rekonnektion und Strahlungsausbrüchen“, fügt Christian Fendt vom Heidelberger Max-Planck-Institut für Astronomie (MPIA) hinzu, Ko-autor der Studie und ein Experte für die die theoretische Modellierung von Jets. Während nahe der Oberfläche der Akkretionsscheibe eher kleinskalige magnetische Strukturen die Massenübertragung in die Jets dominieren, bleibt über größere Distanzen hin nur das globale spiralförmige Magnetfeld bestehen und dirigiert die Bewegung des Jets.
In Zukunft werden Beobachtungen bei noch höheren Frequenzen und somit besserer Winkelauflösung im Rahmen des Event-Horizon-Teleskops (EHT) es ermöglichen, sich den supermassereichen Schwarzen Löchern in den Zentren von aktiven Galaxien noch weiter zu nähern. „Es gibt nur zwei Zielobjekte, die es uns erlauben, den Ereignishorizont selbst als Schatten in den Radiobeobachtungen abzubilden“, stellt Andreas Eckart von der Universität zu Köln fest. „Das zentrale Schwarze Loch in der Galaxie M87 und dasjenige im Zentrum unserer Milchstraße. Beide sind sehr unterschiedlich, sowohl in der Aktivität als auch in ihrer Masse. Aber auch in ihrer Entfernung von uns sind sie verschieden. Dadurch erscheint in beiden Objekten das Schwarze Loch in vergleichbarer Winkelauflösung am Himmel und es sollte auch bei beiden ein dunkler Schatten von ähnlicher Größe sichtbar werden.“
Vladimir Karas (Astronomical Institute of the Czech Academy of Sciences) betont, dass die Beobachtungsergebnisse für M87 als Grundlage für weitere Untersuchungen sowohl von Beobachtungen als auch von der Theorie her dienen könnten. Die direkte Umgebung eines Schwarzen Lochs umfasst einen sehr interessanten als „Ergosphäre“ bezeichneten Bereich, der aber noch jenseits der Auflösung der derzeitigen Generation von Teleskopen liegt.
Die Beobachtungen im Rahmen des EHT-Projekts mit der höchsten derzeit verfügbaren Winkelauflösung haben in den ersten beiden Aprilwochen 2017 stattgefunden. Die Ergebnisse dieser Beobachtungen könnten dazu beitragen, das in der vorliegenden Arbeit präsentierte Modell weiter zu verfeinern und die Verbindung zwischen Jets und supermassereichen Schwarzen Löchern in den Zentren von Galaxien besser zu verstehen.
Beobachtung des Jets im Zentralbereich der aktiven Galaxie M87 mit dem Weltraumteleskop “Hubble”. Das Inlet zeigt die Zentralregion in der der Jet in einem turbulenten Prozess entsteht und durch ein großskaliges Magnetfeld gebündelt abgestrahlt wird.
Zum Forscherteam gehören Silke Britzen, Christian Fendt, Andreas Eckart, und Vladimir Karas.
Der Schwarzschildradius wird definiert als Radius einer Kugelsphäre bei der, wenn die Gesamtmasse innerhalb dieses Radius konzentriert wird, die Fluchtgeschwindigkeit an der Kugeloberfläche gleich der Lichtgeschwindigkeit wäre. Dieser Radius ist benannt nach Karl Schwarzschild, der im Jahr 1916 die erste exakte Lösung für Einsteins Feldgleichungen für ein nichtrotierendes sphärisch-symmetrisches Objekt gefunden hat.
Der Ereignishorizont im Rahmen der Allgemeinen Relativitätstheorie ist eine Begrenzung in der Raumzeit, jenseits der Ereignisse keine Auswirkungen mehr auf Beobachter von außen haben können. Dabei ist der Schwarzschildradius der Radius des Ereignishorizonts um ein nicht rotierendes Schwarzes Loch. Der Schwarzschildradius von Sgr A* hat eine Größe von 12 Mio. km, entsprechend 10 Mikrobogensekunden. Bei der Galaxie M87 erscheint der Ereignishorizont aufgrund der größeren Masse des Zentralobjekts, aber auch der wesentlich größeren Entfernung geringfügig kleiner, mit einem Wert von etwa 4 – 7 Mikrobogensekunden am Himmel. Jedoch wird vorhergesagt, dass der tatsächlich sichtbare Ereignishorizont größer erscheint, verursacht durch einen Gravitationslinseneffekt des eigenen Gravitationspotentials. Der Durchmesser des beobachteten Schattens sollte ca. 1 bis 5mal größer sein als der Schwarzschildradius.
Die hier analysierten VLBA-Beobachtungen ermöglichen die Untersuchung des Jets von M87 in einem Bereich von ungefähr 30 bis 3500 Schwarzschildradien Abstand von der Zentralquelle. Das VLBA (Very Long Baseline Array) Netzwerk von Radioteleskopen umfasst insgesamt 10 Radioteleskope von jeweils 25 m Durchmesser in den Vereinigten Staaten – von Hawaii bis zu den Virgin Islands.
A black hole has been "beating" about every 5 to 10 million years, pumping material and energy into its environment.
This black hole is at the center of a large elliptical galaxy located within the core of the Centaurus Cluster of galaxies.
Data from Chandra and other telescopes show evidence for repeated bursts, or eruptions, from the black hole.
These bursts created cavities within the hot, X-ray emitting gas that pervades the cluster.
At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.
New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.
In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.
By examining the details of the X-ray data from Chandra, scientists have found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.
This composite image contains X-ray data from Chandra (red) that reveals the hot gas in the cluster, and radio data from the NSF's Karl G. Jansky Very Large Array (blue) that shows high-energy particles produced by the black hole-powered jets. Visible light data from the Hubble Space Telescope (green) show galaxies in the cluster as well as galaxies and stars outside the cluster.
Cavity processing scale: This image shows a larger field of view than the main composite image above and is about 122,000 light years across. This image has also been rotated slightly clockwise to the main composite image above.
Astronomers employed special processing to the X-ray data (shown above) to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.
The researchers estimate that these black hole bursts, or "beats", have occurred every five to ten million years. Besides the vastly differing time scales, these beats also differ from typical human heartbeats in not occurring at particularly regular intervals.
A different type of processing of the X-ray data reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole's repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate. (Note that both images showing the labeled cavities and this image are rotated slightly clockwise to the main composite.)
The features in the Centaurus Cluster are similar to the ripples seen in the Perseus cluster of galaxies. The pitch of the sound in Centaurus is extremely deep, corresponding to a discordant sound about 56 octaves below the notes near middle C. This corresponds to a slightly higher (by about one octave) pitch than the sound in Perseus. Alternative explanations for these curved features include the effects of turbulence or magnetic fields.
Curved processing scale: This image also shows a larger field of view than the main composite image and is about 550,000 light years across. This image has also been rotated slightly clockwise to the main composite image.
The black hole bursts also appear to have lifted up gas that has been enriched in elements generated in supernova explosions. The authors of the study of the Centaurus cluster created a map (shown above) showing the density of elements heavier than hydrogen and helium. The brighter colors in the map show regions with the highest density of heavy elements and the darker colors show regions with a lower density of heavy elements. Therefore, regions with the highest density of heavy elements are located to the right of the black hole. A lower density of heavy elements near the black hole is consistent with the idea that enriched gas has been lifted out of the cluster's center by bursting activity associated with the black hole. The energy produced by the black hole is also able to prevent the huge reservoir of hot gas from cooling. This has prevented large numbers of stars from forming in the gas.
A paper describing these results was published in the March 21st 2016 issue of the Monthly Notices of the Royal Astronomical Society and is available online. The first author is Jeremy Sanders from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Aerojet Rocketdyne Achieves 3-D Printing Milestone with Successful Testing of Full-Scale RL10 Copper Thrust Chamber Assembly
SACRAMENTO, Calif., April 03, 2017 (GLOBE NEWSWIRE) -- Aerojet Rocketdyne, a subsidiary of Aerojet Rocketdyne Holdings, Inc. (NYSE:AJRD) has successfully hot-fire tested a full-scale, additively manufactured thrust chamber assembly for the RL10 rocket engine that was built from a copper alloy using selective laser melting (SLM) technology, which is often referred to as 3-D printing.
Aerojet Rocketdyne has actively been working over the last decade to incorporate 3-D printing technology into the RL10 and other propulsion systems to make them more affordable while taking advantage of the inherent design and performance capabilities made possible by 3-D printing. This recent testing was enabled by the Defense Production Act Title III program management office located at Wright-Patterson Air Force Base near Dayton, Ohio.
"Aerojet Rocketdyne has made several major upgrades to the RL10 to enhance the engine's performance and affordability since it first entered service in the early 1960s," said Aerojet Rocketdyne CEO and President Eileen Drake. "Incorporating additive manufacturing into the RL10 is the next logical step as we look to make the engine even more affordable for our customers."
"We believe this is the largest copper-alloy thrust chamber ever built with 3-D printing and successfully tested," said Additive Manufacturing Program Manager Jeff Haynes. "Producing aerospace-quality components with additive manufacturing is challenging. Producing them with a high-thermal-conductivity copper alloy using SLM technology is even more difficult. Infusing this technology into full-scale rocket engines is truly transformative as it opens up new design possibilities for our engineers and paves the way for a new generation of low-cost rocket engines."
The 3-D printed RL10 copper thrust chamber would replace the current RL10C-1 model design that uses a very complex array of drawn, hydroformed stainless steel tubes that are brazed together to form a thrust chamber. The new chamber design is made up of only two primary copper parts and takes just under a month to print using SLM technology; reducing overall lead time by several months. The part count reduction of greater than 90 percent is significant as it reduces complexity and cost when compared with RL10 thrust chambers that are built today using traditional manufacturing techniques.
Another key benefit provided by 3-D printing is the ability to design and build advanced features that allow for improved heat transfer. For many rocket engine applications, this enhanced heat transfer capability enables a more compact and lighter engine, which is highly desirable in space launch applications.
"This full-scale RL10 thrust chamber test series further proves that additive manufacturing technology will enable us to continue to deliver high performance and reliability while substantially reducing component production costs," said RL10 Program Director Christine Cooley. "Now that we have validated our approach with full-scale testing of a 3-D printed injector and copper thrust chamber, we are positioned to qualify a new generation of RL10 engines at a much lower cost; largely attributed to the additive manufacturing capabilities we have developed and demonstrated. With the next generation of RL10 engines, we aim to maintain the reliability and performance that our customers have come to expect, while at the same time making the engine more affordable to meet the demands of today's marketplace."
Aerojet Rocketdyne is applying 3-D printing technology to many of its other products, including the RS-25 engines that will help explore deep space, and the company's new AR1 booster engine that is being developed to replace Russian-built RD-180 engines by the congressionally-mandated deadline of 2019.
Since its first operational flight in 1963, more than 475 RL10 engines have flown in space to help place numerous spacecraft into Earth orbit and propel others to explore every planet in our solar system.
Aerojet Rocketdyne is an innovative company delivering solutions that create value for its customers in the aerospace and defense markets. The company is a world-recognized aerospace and defense leader that provides propulsion and energetics to the space, missile defense and strategic systems, tactical systems and armaments areas, in support of domestic and international markets. Additional information about Aerojet Rocketdyne can be obtained by visiting our websites at www.Rocket.com and www.AerojetRocketdyne.com.
Aerojet Rocketdyne recently completed successful hot-fire testing of a full-scale, additively manufactured thrust chamber assembly for the RL10 rocket engine at its West Palm Beach, Florida facility
Aerojet Rocketdyne Successfully Completes Qualification Tests on Reusable Engine to Support Next Era of Human Spaceflight from the United States
SACRAMENTO, Calif., Aerojet Rocketdyne, Inc., a subsidiary of Aerojet Rocketdyne Holdings, Inc. (NYSE:AJRD), has successfully completed hot-fire qualification tests of an engine that demonstrates the ability to meet reusability requirements for Boeing's Crew Space Transportation (CST)-100 Starliner crew module propulsion system. The tests were conducted on Aerojet Rocketdyne's MR-104J hydrazine monopropellant engine in Redmond, Washington. For NASA service missions to the International Space Station, Boeing's Starliner spacecraft will carry up to four astronauts and time-critical scientific research.
"Our engineers have incorporated a unique design that will allow the MR-104 engine to be used on multiple missions, providing the reliability, cost-efficiency and reusability our customer needs to be competitive in the current commercial space environment," said Aerojet Rocketdyne CEO and President Eileen Drake. "We look forward to delivering the engines for the crew module and continuing our proud heritage of enabling astronauts to fly to the International Space Station from U.S. soil."
The Starliner crew module propulsion system will use 12 MR-104J engines for reaction control to orient the vehicle during re-entry into the Earth's atmosphere. Prior to re-entry, attitude control is provided by the Service Module Engines, also provided by Aerojet Rocketdyne.
The MR-104J, designed by Aerojet Rocketdyne, was developed and tested under the company's Commercial Crew Transportation Capability (CCtCap) subcontract to Boeing. Similar to other reaction control system engines, the MR-104J includes additional features to increase redundancy that meet critical requirements and improved strength to withstand multiple shocks at operating temperatures. The engine upgrades also provide reusability for Boeing as it certifies Starliner crew modules for multiple missions.
Under the CCtCap subcontract to Boeing, Aerojet Rocketdyne will provide propulsion system hardware that includes Crew Module Reaction Control engines; Launch Abort Engines, Orbital Maneuvering and Attitude Control thrusters, and Service Module Reaction Control System thrusters. Boeing will assemble propulsion hardware into the Starliner spacecraft at its Commercial Crew and Cargo Processing Facility at NASA's Kennedy Space Center in Florida.
Aerojet Rocketdyne is an innovative company delivering solutions that create value for its customers in the aerospace and defense markets. The company is a world-recognized aerospace and defense leader that provides propulsion and energetics to the space, missile defense and strategic systems, tactical systems and armaments areas, in support of domestic and international markets. Additional information about Aerojet Rocketdyne can be obtained by visiting our websites at www.Rocket.com and www.AerojetRocketdyne.com.
A simulated galaxy is pictured, showing the main ingredients that make up a galaxy: the stars (blue), the gas from which the stars are born (red), and the dark matter halo that surrounds the galaxy (light grey)
Further evidence of the existence of dark matter – the mysterious substance that is believed to hold the Universe together – has been produced by Cosmologists at Durham University.
Using sophisticated computer modelling techniques, the research team simulated the formation of galaxies in the presence of dark matter and were able to demonstrate that their size and rotation speed were linked to their brightness in a similar way to observations made by astronomers.
One of the simulations is pictured, showing the main ingredients that make up a galaxy: the stars (blue), the gas from which the stars are born (red), and the dark matter halo that surrounds the galaxy (light grey).
Until now, theories of dark matter have predicted a much more complex relationship between the size, mass and brightness (or luminosity) of galaxies than is actually observed, which has led to dark matter sceptics proposing alternative theories that are seemingly a better fit with what we see.
Most cosmologists believe that more than 80 per cent of the total mass of the Universe is made up of dark matter – a mysterious particle that has so far not been detected but explains many of the properties of the Universe such as the microwave background measured by the Planck satellite.
Alternative theories include Modified Newtonian Dynamics, or MOND. While this does not explain some observations of the Universe as convincingly as dark matter theory it has, until now, provided a simpler description of the coupling of the brightness and rotation velocity, observed in galaxies of all shapes and sizes.
The Durham team used powerful supercomputers to model the formation of galaxies of various sizes, compressing billions of years of evolution into a few weeks, in order to demonstrate that the existence of dark matter is consistent with the observed relationship between mass, size and luminosity of galaxies.
Long-standing problem resolved
Dr Ludlow said: “This solves a long-standing problem that has troubled the dark matter model for over a decade. The dark matter hypothesis remains the main explanation for the source of the gravity that binds galaxies. Although the particles are difficult to detect, physicists must persevere.”
Durham University collaborated on the project with Leiden University, Netherlands; Liverpool John Moores University, England and the University of Victoria, Canada. The research was funded by the European Research Council, the Science and Technology Facilities Council, Netherlands Organisation for Scientific Research, COFUND and The Royal Society.
Expedition 51 flight engineer Thomas Pesquet of the European Space Agency (ESA), working with commander Peggy Whitson of NASA, captured the John Glenn using the space station's Canadarm2 robotic arm at 6:05 a.m. EDT (1005 GMT).
"We are very proud to welcome on board the S.S. John Glenn," Pesquet said.
With the Cygnus in grasp, flight controllers at NASA's Mission Control Center in Houston will take over from Pesquet and Whitson and to guide the spacecraft to a berthing on the Earth-facing port of the space station’s Unity module, where it will remain attached for the next 85 days.
Launched atop a United Launch Alliance (ULA) Atlas 5 rocket from the Cape Canaveral Air Force Station in Florida on Tuesday (April 18), the S.S. John Glenn could have arrived at the space station earlier, but held off its approach (referred to by NASA as "station-keeping") to allow Russia’s Soyuz MS-04 spacecraft to dock with crewmembers Jack Fischer of NASA and Fyodor Yurchikhin of the Russian federal space corporation Roscosmos on Thursday.
With the arrival of the Cygnus came the delivery of more than 7,600 lbs. (3,500 kilograms) of cargo, including the research materials to support dozens of new and ongoing science investigations. The delivery will enable studies on cancer-fighting drugs and crystal growth.
Also aboard the S.S. John Glenn is equipment to be installed outside the space station during a spacewalk scheduled for May 12, 38 CubeSats (many built by university students from around the world) to be deployed from the station’s Japanese airlock (or from the Cygnus itself) and a new advanced plant growth habitat.
"A big difference in this system, compared to [the plant growth chamber] Veggie, is that it requires minimal crew involvement to install the science, add water and perform other maintenance activities," said Bryan Onate, the habitat's project manager, in a NASA interview. "We are learning how plants grow in space and what levels of commodities, such as light and water, are required so we can maximize our growth with the least resources.”
Once emptied of its deliveries, the space station's crew will refill the S.S. John Glenn with spent equipment and other refuse to be destroyed during the spacecraft's destructive re-entry into Earth's atmosphere in July. Prior to that plunge — but after the Cygnus departs from the space station — the cargo freighter will support the third in a series of experiments into how fire burns in microgravity.
The spacecraft’s namesake, John Glenn, died on Dec. 8, 2016, at the age of 95 and was interred at Arlington National Cemetery on April 6. A Marine Corps Colonel and four-term U.S. Senator from Ohio, Glenn was the last of NASA's Mercury astronauts to die. In addition to being the first American to orbit Earth, Glenn became the oldest astronaut to fly in space at age 77 on space shuttle Discovery in 1998 (a record he still holds).
The bright landing platform left behind by NASA's Mars Exploration Rover Opportunity in 2004 is visible inside Eagle Crater, at upper right in this April 8, 2017, observation by NASA's Mars Reconnaissance Orbiter. Image Credit: NASA/JPL-Caltech/Univ. of Arizona
A new observation from NASA's Mars Reconnaissance Orbiter (MRO) captures the landing platform that the rover Opportunity left behind in Eagle Crater more than 13 years and 27 miles (or 44 kilometers) ago.
A series of bounces and tumbles after initial touchdown plunked the airbag-cushioned lander into the crater, a mere 72 feet (22 meters) across, on Jan. 25, 2004, Universal Time (Jan. 24, PST).
The scene includes Eagle Crater and Opportunity's nearby parachute and backshell, from the April 10, 2017, observation by MRO's High Resolution Imaging Science Experiment (HiRISE) camera.
This is the first color view from HiRISE of the Eagle Crater scene. Mars Reconnaissance Orbiter began orbiting Mars more than two years after Opportunity's landing. One of the first images from HiRISE in 2006 showed Opportunity at the rim of a much larger crater, Victoria, nearly 4 miles (about 6 kilometers) south of the landing site. The camera also recorded a monochrome view of Eagle Crater that year.
Eagle Crater is at the upper right of the new image. The lander platform's job was finished once the rover rolled off it. The parachute and backshell are at the lower left.
The smattering of small craters on a broad plain is a reminder of the amazement expressed in 2004 about Opportunity achieving a "hole-in-one" landing. When the lander's petals opened and Opportunity sent home its first look at its surroundings, it provided the first-ever close-by view of sedimentary rocks on Mars, in Eagle's rim.
After leaving the lander and exploring Eagle Crater, the rover recorded a look-back viewbefore departing the scene. Opportunity remains active more than 13 years later.
HiRISE, the most powerful telescope ever sent to Mars, is operated by the University of Arizona, Tucson, and was built by Ball Aerospace & Technologies Corp. of Boulder, Colorado. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the MRO Project and Mars Exploration Rover Project for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the orbiter and collaborates with JPL to operate it. JPL built the rover.
Artist’s concept of Cassini’s final orbits between the Saturn’s innermost rings and the planet’s cloud tops. This set of orbits will consist the last leg of Cassini’s mission, called “The Grand Finale,” which will culminate with a plunge on Saturn’s atmosphere in September 2017. Image Credit: Image Credit: NASA/JPL
It has become something of a hackneyed phrase, but in the case of NASA’s Cassini spacecraft it is rather fitting: an epic mission of exploration of Saturn that has single-handedly changed our view of the ringed planet, its moons, and their potential habitability, yet like all good things it must come to an end. Having nearly completed two full decades in space, Cassini has now entered its final 18 months around Saturn on what has been a tremendously successful and productive mission, full of unexpected and ground-breaking discoveries. Last week the mission’s science team officially began the one-year countdown toward the start of Cassini’s “Grand Finale,” which will culminate with an end-of-mission daring plunge on Saturn’s cloud tops on Sept. 15, 2017.
Launched on October 1997, Cassini undertook a seven-year journey of 3.5 billion km which included two flybys of Venus, one of Earth, and one of Jupiter, before finally arriving and entering orbit around Saturn in July 2004, becoming humanity’s first ever robotic spacecraft to do so. Since that time, Cassini has literally made history with every covered mile of space around the ringed giant planet and its assortage of fascinating moons, while slowly uncovering many of their long-held secrets and returning hundreds of thousands of images of unparalleled beauty. While the mission’s overall science results are too many to mention, highlights include the dispatch of the European-built Huygens probe which made humanity’s historic first soft-landing on the surface of the moon Titan, the ground-breaking discovery of water ice geysers erupting from Enceladus, the discovery of seas and lakes of liquid ethane and methane on Titan, as well as the detailed study of Saturn’s atmosphere and rings, just to name a few.
A diagram showing the orbits that Cassini will follow around Saturn during the Grand Finale. The green-colored orbits represent the first phase of the Grand Finale when Cassini will reach as close as 10,000 km from Saturn’s outermost visible ring. The blue-colored orbits represent the second phase when Cassini will be positioned inside Saturn’s rings during closest approach to the planet. Image Credit: NASA/JPL
Having completed its initial four-year primary mission in 2008, Cassini was given the go-ahead by NASA for an extended mission called the Cassini Equinox Mission and a third and final extension in 2010 called the Cassini Solstice Mission. The names for these extended missions weren’t arbitrary. Since one Saturnian year equals 29.4 Earth years, Cassini has been able to study the planet and its moons essentially through half of its orbit around the Sun, allowing planetary scientists to have a first close-up view of how the change of seasons affects the climate and atmospheric circulation on both Saturn and its largest moon Titan.
Yet, now more than a decade after it entered orbit around the ringed giant, Cassini has spent almost all of its onboard fuel which allowed it to maneuver through the Saturn system by way of hundreds of close flybys of its largest moon Titan. Cassini’s mission planners had been preparing for the inevitable end ever since the conclusion of the spacecraft’s primary mission in 2008, while evaluating several scenarios as to the exact way with wich Cassini would make its farewell. Some of the options that were considered for Cassini’s end of mission by ground teams included an escape from Saturn toward Uranus or Neptune, an escape toward a heliocentric orbit, or an aerobraking and eventual placement in a stable orbit around Titan. All of these options were evaluated against certain factors like the time needed for the completion of each scenario, the delta-v required for the orbital changes, the fuel that would be available, as well as the best overall science return for each option. In the end, the only options that satisfied all of the required criteria were either an impact on one of Saturn’s icy satellites, or an impact on the giant planet itself. In the best interests of planetary protection, Cassini’s science team eventually chose the latter, in order to prevent the biological contamination of Saturn’s moons from any terrestrial microorganisms that could have been carried from Earth onboard the spacecraft.
To that end and after shifting through a list of names that were submitted by more than 2,000 members of the public, the mission’s science team chose to appropriately name the final leg of Cassini’s trek around Saturn “The Grand Finale.” The latter is comprised of two parts. The first one, which will begin this year on Nov. 30 following the spacecraft’s penultimate Titan flyby, consists of a set of 20 elongated polar orbits around the planet which will bring Cassini within 10,000 km of Saturn’s F ring (the planet’s outermost discrete ring). This will be followed by The Grand Finale’s second phase beginning on April 22, 2017, when Cassini will use its final Titan flyby in order to change its orbital orientation and execute a daring loop that will bring it just 3,800 km above Saturn’s cloud tops, thus positioning it inside the planet’s entire ring system! From this vantage point, Cassini will complete a total of 22 highly elliptical polar orbits around Saturn before finally plunging onto the gas giant’s atmosphere on Sept. 15, 2017, putting an end to its spectacular 20-year mission.
One of the reasons that this scenario was chosen for Cassini’s end of mission was that it would return the most science compared to all the other options that had been evaluated. In fact, for Cassini’s science team, The Grand Finale represents an entire new mission on its own, which hadn’t even been considered as a possibility when the spacecraft was still on the drawing board back in the 1980s. One of the mysteries that have remained unresolved to this day involve the composition of Saturn’s internal structure as well as the planet’s exact rotation rate, which has not been measured to a great precision. Cassini’s position inside the main ring system during the second phase of The Grand Finale will allow the spacecraft to make very detail measurements of Saturn’s gravity and magnetic fields which will help scientists to better answer the remaining questions regarding the planet’s interior and overall rotation. Furthermore, a different spacecraft, Juno, which is scheduled to arrive on Jupiter this summer, will be making similar measurements regarding Jupiter’s interior at the same time, which will provide planetary scientists with great insights as to the inner workings of the Solar System’s gas giant planet’s during the same point in time. “We’ll have a much better understanding of how the planet works,” says Dr. Jonathan Fortney, a professor of astronomy at the University of California, Santa Cruz, who is part of the science team that has been selected by NASA to coordinate Cassini’s Grand Finale mission. “We really don’t know what their interiors are like. What’s great is that, in the space of a year, we’ll have once-in-a-lifetime data sets for both Jupiter and Saturn.”
One other important set of science results expected to come during Cassini’s Grand Finale is the exact mass determination of Saturn’s ring system. For the entire duration of its mission to date, the spacecraft has operated solely outside of Saturn’s rings which has limited its ability to determine their mass, since it had to take into account the gravitational effects of the giant planet on the ring system. By positioning itself inside the rings, Cassini will be able to differentiate between these gravitational effects and the mass of the rings themselves. In addition, Cassini will have an unprecedented close-up view at the rings’ overall structure and composition, which might help scientists shed more light on their age and determine whether they have formed late in the planet’s history or have the same age as Saturn itself.
NASA has already set officially the countdown clock ticking toward the start of Cassini’s Grand Finale, as announced late last week by Ron Baalke, a planetary scientist at the Jet Propulsion Laboratory in Pasadena, Calif., with a post on his Twitter account. This countdown marks the final 18 months of life for Cassini, which for many has been the epitome and highlight of NASA’s Planetary Science Division for the last two decades.
Both Cassini and Juno will end their missions around the same time, with the latter scheduled to make a final plunge onto Jupiter’s cloud tops in February 2018. After that, and save for the Europa Clipper mission which is still in the conceptual stage, no other missions toward the outer Solar System exist in the NASA pipeline for the foreseeable future. This unfortunate reality, which is a result of cuts in the space agency’s planetary science budgets in recent years, means that we can probably not expect to see another dedicated probe toward the outer planets for the next couple of decades. This doesn’t mean that there hasn’t been a lack of proposals from the planetary science community, including mission concepts for the exploration of the ice giants Uranus and Neptune, both of which have been largely neglected ever since the Voyager 2 fly bys of the 1980s. Yet, as things stand at the moment, with the coming conclusion of the Cassini mission in 2017 and Juno in early 2018, the outer Solar System will likely remain out of reach for at least the next couple of decades.
NASA’s Cassini Mission Prepares for 'Grand Finale' at Saturn
This illustration shows NASA’s Cassini spacecraft above Saturn's northern hemisphere prior to one of its 22 grand finale dives.
NASA's Cassini spacecraft, in orbit around Saturn since 2004, is about to begin the final chapter of its remarkable story. On Wednesday, April 26, the spacecraft will make the first in a series of dives through the 1,500-mile-wide (2,400-kilometer) gap between Saturn and its rings as part of the mission’s grand finale.
"No spacecraft has ever gone through the unique region that we'll attempt to boldly cross 22 times," said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "What we learn from Cassini’s daring final orbits will further our understanding of how giant planets, and planetary systems everywhere, form and evolve. This is truly discovery in action to the very end."
During its time at Saturn, Cassini has made numerous dramatic discoveries, including a global ocean that showed indications of hydrothermal activity within the icy moon Enceladus, and liquid methane seas on its moon Titan.
Now 20 years since launching from Earth, and after 13 years orbiting the ringed planet, Cassini is running low on fuel. In 2010, NASA decided to end the mission with a purposeful plunge into Saturn this year in order to protect and preserve the planet's moons for future exploration – especially the potentially habitable Enceladus.
But the beginning of the end for Cassini is, in many ways, like a whole new mission. Using expertise gained over the mission's many years, Cassini engineers designed a flight plan that will maximize the scientific value of sending the spacecraft toward its fateful plunge into the planet on Sept. 15. As it ticks off its terminal orbits during the next five months, the mission will rack up an impressive list of scientific achievements.
"This planned conclusion for Cassini's journey was far and away the preferred choice for the mission's scientists," said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. "Cassini will make some of its most extraordinary observations at the end of its long life."
The mission team hopes to gain powerful insights into the planet's internal structure and the origins of the rings, obtain the first-ever sampling of Saturn's atmosphere and particles coming from the main rings, and capture the closest-ever views of Saturn's clouds and inner rings. The team currently is making final checks on the list of commands the robotic probe will follow to carry out its science observations, called a sequence, as it begins the finale. That sequence is scheduled to be uploaded to the spacecraft on Tuesday, April 11.
Cassini will transition to its grand finale orbits, with a last close flyby of Saturn's giant moon Titan, on Saturday, April 22. As it has many times over the course of the mission, Titan's gravity will bend Cassini's flight path. Cassini's orbit then will shrink so that instead of making its closest approach to Saturn just outside the rings, it will begin passing between the planet and the inner edge of its rings.
"Based on our best models, we expect the gap to be clear of particles large enough to damage the spacecraft. But we're also being cautious by using our large antenna as a shield on the first pass, as we determine whether it's safe to expose the science instruments to that environment on future passes," said Earl Maize, Cassini project manager at JPL. "Certainly there are some unknowns, but that's one of the reasons we're doing this kind of daring exploration at the end of the mission."
In mid-September, following a distant encounter with Titan, the spacecraft's path will be bent so that it dives into the planet. When Cassini makes its final plunge into Saturn's atmosphere on Sept. 15, it will send data from several instruments – most notably, data on the atmosphere's composition – until its signal is lost.
"Cassini's grand finale is so much more than a final plunge," said Spilker. "It's a thrilling final chapter for our intrepid spacecraft, and so scientifically rich that it was the clear and obvious choice for how to end the mission."
Cassini mission’s final performance a fiery plunge to Saturn
NASA has revealed plans to send the Cassini spacecraft into a death spiral,allowing it to capture new data and images of Saturn and its rings, writes Richard A. Lovett.
NASA’s 20-year-old Cassini mission is about to make a final orbit correction that will cause it to crash into Saturn and burn up in September.
Before it meets its fiery demise, however, the long-lived spacecraft, which left Earth in 1997 and first entered Saturn orbit in 2004, will make a series of 22 close flybys, diving within 2,000 km of the giant planet’s cloud tops. Its final passes, in fact, would be so close that it would be able to sample the outer fringes of the planet’s atmosphere, Cassini project manager Earl Maize said at a press conference on April 4 in Pasadena, California.
This Grand Finale, as NASA is dubbing it, begins on April 22 when the spacecraft makes a flyby of Titan, using that moon’s gravity to turn toward Saturn. There it will dive through the gap between the innermost of Saturn’s rings and the giant planet’s atmosphere.
At each of these close approaches, the spacecraft will be traveling 122,000 km/h – fast enough that hitting anything more substantial than a speck of dust could damage it irreparably. “We would never take a flagship mission on that kind of course at any other time in the mission except when it’s about to end,” Maize said.
Cassini’s mission is about to end one way or another, because the spacecraft is on the verge of running out of maneouvring fuel. Project leaders decided years ago that they did not want to leave the spacecraft drifting without maneouvring power, for fear it might eventually crash into one of Saturn’s moons, potentially contaminating it with microbes that had hitchhiked all the way from Earth.
The Grand Finale does more than simply dump the spacecraft safely into Saturn’s atmosphere, where conditions are unsuitable for Earth life. It would also produce some exciting science, said Linda Spilker, the mission’s project scientist: “I would not be surprised if some of the discoveries will be the best we’ve obtained.”
One goal is to measure the mass of the rings more accurately than has previously been possible. That can help determine how old they are because ring material is being constantly eroded away by micro-meteorite bombardment from outside the ring system. Massive rings survive longer than less-massive ones, and thus might also be older.
It would also be possible, Spilker said, to determine what the rings are made of by studying the impacts of harmless, smoke-sized dust particles with Cassini’s cosmic dust analyser. “We know they are 99% water ice,” she said, “but we’re not sure about the other 1%. What is it? Iron, silicates, organics, a mix of all three, or something else we’ve not thought of?”
There will also be the best-yet close-up views of Saturn’s poles, which have giant hurricanes and a mysterious hexagonal feature Spilker called a “six-sided jet stream, two Earth diameters across”.
Some of the passes will even come close enough to measure trace constituents in Saturn’s upper atmosphere.
Measurements of Saturn’s gravity field will also allow the scientists to peel back its atmosphere and determine the size of its rocky core.
“The Grand Finale is like a brand new mission,” Spilker said.
Even on the final dive into the atmosphere, the spacecraft will continue to return data as it fights to keep its antenna pointing in the right direction. Not that it will be able to do this for long, because this is a flight for which it was never designed. Eventually, Maize said, it will lose contact, break up and vaporise.
There is, of course, a risk that Cassini will hit something big enough to damage it. Maize put the odds of successfully completing all 22 passes at 98.8%, based on the best models of the density and size of dust particles in the not-entirely-empty gap. “Our most dire models put us at 97%,” he said.
“If we get surprised, we have a bunch of contingency plans,” he added. Even if the spacecraft is knocked entirely out of commission, it is not at risk of hitting a moon, because from the moment it lines up for its upcoming Titan flyby, its orbit is determined by the laws of physics. “Cassini will still end up as planned, but we’ll get less science,” Maize said.
When the end comes, it’s going to be an emotional moment for the project team. “I’ve worked on it for almost three decades,” Spilker said of the mission. “My oldest daughter started kindergarten when I started working on Cassini. Now she’s married and has a daughter of her own. It’s really going to be hard to say goodbye to this plucky, capable spacecraft that has returned all of this great science.”
Cassini had also made its mark in the planning for other missions, added Jim Green, director of NASA’s Planetary Science Division. Just to start with, he said, the upcoming Europa Clipper mission (scheduled for launch in the 2020s) would use an approach similar to that which Cassini used to study Titan. Rather than orbiting Europa, the Europa Clipper will spend as little time as possible in Jupiter’s dangerous radiation belts by instead making repeated flybys of Europa.
“We’re taking a page out of Cassini’s book,” Green said.
NASA will destroy a $3.26 billion Saturn probe this summer to protect an alien water world
An illustration of the Cassini spacecraft over Saturn's north pole with its hexagon-shaped storm.NASA/JPL-Calte
The Cassini spacecraft, which launched toward Saturn in 1997, is running low on fuel.
To avoid accidentally crashing into and contaminating a nearby moon that may harbor alien life, NASA is going to destroy the robot.
But before Cassini perishes, it will fly between Saturn and its rings and record as much new data as possible.
For nearly three decades, researchers have worked to design, build, launch, and operate an unprecedented mission to explore Saturn.
Called Cassini-Huygens — or Cassini, for short — the golden nuclear-powered spacecraft launched in October 1997, fell into orbit around the gas giant in July 2004, and has been documenting the planet and its dizzying variety of moons ever since.
But all good things must come to an end. And for NASA's $3.26 billionprobe, that day is Friday, September 15, 2017.
During a press conference held by the US space agency on April 4, researchers explained why they're killing off their cherished spacecraft with what they call the "Grand Finale." The maneuver will use up the fleeting reserves of Cassini's fuel and put the robot on a collision course with Saturn.
"Cassini's own discoveries were its demise," said Earl Maize, an engineer at NASA's Jet Propulsion Laboratory (JPL) who manages the Cassini mission.
Maize was referring to a warm, saltwater oceanthat Cassini found hiding beneath the icy crust of Enceladus, a large moon of Saturn that spews water into space. NASA's probe flew through these curtain-like jets of vapor and ice in October 2015, "tasted" the material, and indirectly discovered the subsurface ocean's composition — and it's one that may support alien life.
"We cannot risk an inadvertent contact with that pristine body," Maize said. "Cassini has got to be put safely away. And since we wanted to stay at Saturn, the only choice was to destroy it in some controlled fashion."
But Maize and a collaboration of researchers from 19 nations aren't going to let their plucky probe go down without a fight.
They plan to squeeze every last byte of data they can from the robot, right up until Cassini turns into a brilliant radioactive comet above the swirling storms of Saturn.
'We're going in and we're not coming out'
Long before Cassini began orbiting Saturn in 2004, mission managers carefully plotted out its orbits to squeeze in as many flybys of the gas giant planet, its moons, and its expansive icy rings as possible.
Their goal: Get lots of chances to record unprecedented new images, gravitational data, and magnetic readings without putting the spacecraft into harm's way or burning up too much of its limited propellant.
But after 13 years of operation at nearly 1 billion miles (1.45 billion kilometers) away from Earth, Cassini's tank is running close to empty.
Skye Gould/Business Insider
"We're coming to the end. As it runs out of fuel, the things it can do are quite limited — until we decided on a new approach," Jim Green, the leader of NASA's planetary science program, said during the press conference.
NASA could have propelled Cassini to some other planet — perhaps Uranus or Neptune. In 2010, however, mission managers decided to keep it around Saturn, reasoning they could squeeze more science out of the mission there. But this effectively doomed the spacecraft to a fiery death.
Cassini's death spiral will officially begin on April 22, 2017. That's when it will, for the last time, fly by Titan: an icy moon of Saturn that's bigger than our own, has a thick atmosphere, seas of liquid methane, and even rain.
Titan's gravity will slingshot Cassini over Saturn, above the planet's atmosphere, and — on April 26 — through a narrow void between the planet and the innermost edge of its rings.
"That last 'kiss goodbye' will put Cassini into Saturn," Maize said. "This is a roller-coaster ride. We're going in, and we are not coming out — it's a one-way trip."
The void between Saturn and its rings is about 1,200 miles wide, or roughly the distance from northern Washington state to the southern tip of California.
"As we're skimming close to the planet, we'll have the best views ever of the poles of the planet," Linda Spilker, a Cassini project scientist and a planetary scientist at NASA JPL, said during the press briefing. "We'll see the giant hurricanes at the north and south poles."
During its final orbits above Saturn, Cassini will get its closest-ever views of the hexagon-shaped feature of Saturn's north pole, which Spilker said is "two Earth diameters across" yet poorly understood.
"Perhaps by getting close with Cassini, we'll answer the question, 'What keeps the hexagon there in this particular shape?'" she said.
Spilker said Cassini will also photograph the auroras of Saturn's poles, measure how massive the planet's rings are, sample the icy material they're made of, and even probe deep below its layers of thick clouds.
Sensitive magnetic and gravitational measurements that Cassini couldn't make before may also answer lingering questions about the internal structure of Saturn, including how big its rocky core is, plus how fast a shell of metallic hydrogen around it spins.
"How fast is Saturn rotating?" Spilker asked. "If there's just a slight tilt to the magnetic field, then it will wobble around and give us the length of a day."
Hours before it takes its final plunge on September 15, 2017, Cassini will beam back its last batch of images — then prepare for the end.
The fiery end of a longtime robotic friend
Cassini is a 2.78-ton robot with delicate instruments that was not designed to ram into icy ring material at 70,000 mph. It also wasn't made to plunge into the thick atmosphere of a gas giant and live to tell the tale.
Nevertheless, scientists behind the mission say they are going to do their best to protect its instruments from damage and keep the data flowing until the moment it dies.
The Cassini spacecraft being prepared for flight in 1997.NASA
They'll do this primarily by using the cone-shaped primary antenna as a shield for its camera and other important parts.
"If we get surprised, well, we've got a bunch of contingency plans ... We'll milk the best out of this," Maize said. He added that even if icy bits take out Cassini's ability to talk to Earth, the spacecraft "will still finish out exactly where we planned, but we'll have a little less science than we hoped for."
When Cassini begins its final plunge, it will use its last propellant to fight atmospheric drag and keep the antenna pointed at Earth. During that time, it will sniff Saturn's atmosphere as it descends into the gases, broadcasting its readings of the gases' composition in real time back to satellite dishes on Earth.
But the measurements won't last long.
"It will break apart, it will melt, it will vaporize, and it will become a very part of the planet it left Earth 20 years ago to explore," Maize said.
While members of the Cassini team said they're looking forward to the Grand Finale, they weren't without remorse.
"It's really going to be hard to say goodbye ... to this plucky, capable little spacecraft that has returned all of this great science," Spilker said. "We've flown together a long time."
Plateaus Up Close
Saturn’s C ring isn’t uniformly bright. Instead, about a dozen regions of the ring stand out as noticeably brighter than the rest of the ring, while about half a dozen regions are devoid of ring material. Scientists call the bright regions “plateaus” and the devoid regions “gaps.”
Scientists have determined that the plateaus are relatively bright because they have higher particle density and reflect more light, but researchers haven’t solved the trickier puzzle of how the plateaus are created and maintained.
This view looks toward the sunlit side of the rings from about 62 degrees above the ring plane. The image was taken Jan. 9, 2017 in green light with the Cassini spacecraft’s narrow-angle camera.
Cassini obtained the image while approximately 194,000 miles (312,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 67 degrees. Image scale is 1.2 miles (2 kilometers) per pixel.
Cassini finds final ingredient for alien life in Enceladus’s sea
By Leah Crane
Enceladus is ripe for life. In one final pass through the icy moon’s liquid plumes, NASA’s Cassini spacecraft found molecular hydrogen, which indicates favourable conditions for life in Enceladus’s subsurface sea.
For over a decade, Cassini has been exploring Saturn and its moons, sending back the best pictures and measurements we’ve ever had of the system. It dropped off the Huygens probe at hazy Titan, scrutinised the structure of Saturn’s rings, and revealed that Enceladus was much stranger than anyone expected.
Enceladus’s south pole has strange, warm fractures, and plumes of liquid water coming from an internal ocean many believed was impossible in such a small, cold world. The plumes also contain enticing compounds like organics and carbon dioxide, all necessary for life as we know it on Earth.
Those things represent tantalising hints of habitability. But there was no evidence for an energy source to feed potential life, until now. In extreme environments on Earth, hydrogen can play that role.
“What was missing to complete the story of habitability was an energy source,” says Chris McKay at NASA’s Ames Research Center in California. “This completes that story.”
Candy for microbes
Cassini did detect hydrogen in early trips through the plumes, but there was no way to determine if it came from the moon itself or from inside the instrument. When particles from the plumes entered the spacecraft’s Ion and Neutral Mass Spectrometer (INMS), they interacted with its titanium walls, producing the same sort of hydrogen as hydrothermal processes would produce under Enceladus’s ocean.
“We didn’t know we were going to do this experiment when we launched Cassini,” says Hunter Waite at the Southwest Research Institute (SwRI) in Texas. So to look for hydrogen, Waite and his team had to put the INMS instrument in a new mode that measured the molecules without allowing them to touch the walls.
Finally, they found the molecular hydrogen they were looking for – and a lot of it. Their findings indicated that there was too much hydrogen to be stored in tiny Enceladus’s ice shell or ocean. That means it must be continuously produced there, probably by hydrothermal reactions similar to those that occur near hot vents at the bottom of Earth’s oceans.
Near those vents on Earth, there is life. Some of Earth’s oldest microorganisms, called methanogens, are often found near hydrothermal vents where, deprived of light and oxygen, they convert hydrogen and carbon dioxide to methane.
“If you were to take methanogens from Earth’s ocean and transport them to Enceladus, they would have all the food they need,” says Waite. “This is like candy for microbes.” If Earth microbes could exist on Enceladus, maybe it could have homegrown life, too.
Between its liquid water, organic molecules, and hydrogen, Enceladus is looking more and more like our best bet for finding extraterrestrial life. “If we’re looking for life in the solar system, then Enceladus has a lot of potential to be the place that we could find it,” says Kelly Miller at SwRI, who was part of the team that discovered Enceladus’ molecular hydrogen.
Signs of life?
Showing Enceladus is habitable is one thing, finding life is quite another.
“Just because a place is suitable for life doesn’t mean that life is present, because we don’t understand the origin of life at all,” McKay says.
Some believe that life is inevitable, given the right conditions. Others think that it is rare and requires a great deal of luck. Right now, our sample of definitely habitable worlds has only one: Earth. But pairing observations of Enceladus with our own planet could help astrobiologists figure out the likelihood of life existing elsewhere in the universe.
“The message is in the molecules,” says Christopher Glein, another member of Waite’s group at SwRI. “We just have to keep measuring the molecules in that plume, and that’s going to tell us about what we cannot see.”
We won’t have any more molecules from Enceladus’s plumes for a long time, though. Cassini is running low on fuel, and if it were to crash into Enceladus it might destroy any extraterrestrial ecosystem living there. To protect potential life on Saturn’s ocean moons, we have to destroy the only tool we have to find it. The spacecraft will crashinto Saturn on 15 September.
Even if an Enceladus mission is selected in NASA’s next round of New Frontiers funding, to be announced in 2019, it wouldn’t reach the Saturn system until the late 2020s or early 2030s.
“To address whether there is life, we’ll have to go back,” McKay says. “Two decades can go by pretty fast.”
The Grand Finale: Cassini prepares for final mission
Nearly 20 years after launch and almost 13 years at the majestic ringed planet, the Cassini spacecraft is about to enter the final phase of its historic mission. The Grand Finale of Cassini’s mission will begin Sunday morning, setting up a series of close-proximity ops to the planet as Cassini dives between the innermost edge of Saturn’s rings and the planet itself to prepare for atmospheric entry into Saturn and the end of its mission on 15 September 2017.
The Grand Finale:
The grand finale to Cassini’s mission is set to begin at 03:46 GMT on 23 April – 23:46 EDT on 22 April) when the spacecraft reaches aposaturnium, the farthest point in its orbit of Saturn – which will mark the commencement of the first of the final 22 orbits of the craft.
The commencement of the grand finale will be aided days earlier by the spacecraft’s 126th and final close flyby of Saturn’s moon Titan on 22 April at 06:08 GMT (02:08 EDT).
The encounter with Titan will allow Cassini to gather the last bits of information possible about the atmosphered moon while simultaneously using Titan’s gravity to alter its trajectory to “leap over the planet’s icy rings.”
This will be the first of 22 weekly ring crossings for Cassini in the final five months of its mission.
During this first ringplane crossing, Cassini’s orientation will allow the craft’s High Gain Antenna to act as a shield to protect the instruments and the spacecraft from possible ring particle impacts.
Moreover, the trajectory of each of the 22 ring crossing orbits is not identical, as each is specifically designed to allow Cassini to investigate different aspects of the planet and its rings as the final weeks of scientific data are collected.
Overall, the grand finale to Cassini’s mission carries unique mission objectives, including: detailed mapping of Saturn’s gravity and magnetic fields to reveal how the planet is arranged internally and to potentially solve the mystery of how fast Saturn is rotating; to improve knowledge of how much material is in Saturn’s rings and to help better understand and reveal their origins; to sample the icy ring particles being funneled into the atmosphere by Saturn’s magnetic field; and to take close-up images of Saturn’s rings and upper atmospheric clouds.
To successfully complete these mission objectives, the final 22 orbits will see Cassini’s distance from Saturn differ greatly, with some orbits allowing the spacecraft to skim the outer edges of the atmosphere while others will take the spacecraft farther out to skirt the very inner-most sections of the ring system.
The farthest into one of the rings Cassini will go will occur on the 6th ring crossing on 28 May. During this passing, Cassini will sample Saturn’s innermost ring, the D-ring, while being shielded by its high-gain antenna.
This will be followed by a second close venture into the D-ring on 4 June that will again allow Cassini to sample the D-ring material.
A third venture into the D-ring will then occur on 29 June followed by the fourth and final ring dive on 6 July.
On 14 August, Cassini will begin the first of five dives into Saturn’s atmosphere, sampling the gas giant’s atmosphere for the first time in history.
The first atmospheric sampling dip will occur on the 18th orbit of the grand finale mission.
Orbit 19 will see another dip into Saturn’s atmosphere, while orbit 20, on 27 August, will see the third and lowest of the dips into the atmosphere.
Orbits 21 in orbit 22 on 2 September and 9 September, respectively, will see the fourth and fifth dips into the atmosphere.
After this, on 11 September, Cassini will perform a final, distant flyby of Titan that will give the spacecraft just enough of a gravitational nudge – what’s being called the “goodbye kiss” – to send Cassini into its 293rd and final orbit of Saturn.
Cassini will reach its final aposaturnium on 12 September at 05:37 GMT – a moment that will mark the start of Cassini’s plunge into Saturn’s atmosphere.
On 15 September at 10:44 GMT (06:44 EDT), Cassini’s thrusters will fire to maintain attitude control for a roughly 60 second burn that will enable the final transmission of expected mission data back to Earth.
The spacecraft, during its fiery death plunge, will be commanded to continue relaying telemetry back to Earth until the spacecraft’s destruction.
Based on atmospheric entry parameters, the last signal from Cassini is expected to be transmitted from the spacecraft on 15 September 2017 at 10:45 GMT (06:45 EDT).
The signal is expected to arrive at Earth through the Deep Space Network 1 hour 23 minutes later at 12:08 GMT (08:08 EDT).
Cassini – 20 years on:
It was a mission slated to last only four years.
Following a flawless launch from the Cape Canaveral Air Force Station aboard a Titan IV (401) B rocket, Cassini spent seven years performing multiple gravity assist maneuvers and flybys of various planets before entering orbit of Saturn on 1 July 2004.
Even its arrival at Saturn was daring.
To insert Cassini into the proper orbit, mission controllers had to fly the vehicle through the gap between the planet’s F- and G- rings, something that caused a bit of concern due to the relatively unknown nature of how debris-free the ring-gap was.
Despite the fears, Cassini threaded the needle perfectly and entered orbit of the ringed planet for a mission that, at that point, was scheduled to end on 30 June 2008.
On 14 January 2005, the Huygens lander successfully entered Titan’s atmosphere, performing a 2.5 hour descent via parachute and subsequent landing on the surface of the moon.
The Huygens landing remains to this day the most-distant landing of a human-built craft and the only landing thus far attempted in the outer solar system.
Huygens functioned for 90 minutes after landing, returning images and scientific data of the landing site near the Xanadu region.
While Huygens touched down on land, the possibility of a methane lake landing was accounted for in its design.
On 15 April 2008, Cassini received the 27 month mission extension for 60 additional orbits of Saturn, 21 close flybys of Titan, and seven close encounters with Enceladus.
The extended mission was named the Cassini Equinox Mission and allowed the spacecraft to observe Saturn’s transition through Equinox, which occurred in August 2009.
The first mission extension came to an end in August 2010 and was succeeded by a second and final extension – a seven year mission extension out to the maximum operating time for Cassini based on its RTG (Radioisotope Thermoelectric Generator) power source.
The mission was subsequently named the Cassini Solstice Mission as it would allow Cassini to monitor Saturn’s transition through the solstice, which will occur on 24 May 2017.
The solstice mission allowed 155 more orbits of Saturn, 54 additional flybys of Titan, and 11 more close encounters with Enceladus.
Throughout the course of its nine and a half years of mission extensions, Cassini has helped unlock startling revelations about Saturn, Titan, and Enceladus.
Chief among Cassini’s discoveries regarding Enceladus was last week’s ground breaking announcement of the discovery of possible life-supporting hydrothermal vents on the surface of Enceladus’ subterranean salt-water ocean.
It’s time to start actively removing space debris from orbit or risk disaster, says the European Space Agency
t was on 23 August at 17:07 GMT that spacecraft operators at the European SpaceAgency’s (ESA) control centre in Darmstadt, Germany, noticed something was going wrong. Their flagship Earth observation satellite, Sentinel-1A, had suddenly jumped into a slightly different orbit and a slightly different orientation.
More seriously, the electrical power had dropped, and was not returning to normal. The spacecraft was only in its third year in orbit. Activating on-board cameras that had been used two years earlier to monitor the deployment of the solar panels, the operators found the problem.
It was enough to make an engineer’s blood run cold. There was a 40-centimetre-wide damaged area on one of the solar panels.
The spacecraft had been hit by a piece of space debris. Subsequent computer simulations of the damage indicated that the solar panel had been hit from behind and that the size of the impacting object was no more than just a few millimetres.
It packed such a punch because it was travelling at orbital velocities, which are measured in kilometres per second. It was lucky that the debris wasn’t any larger. If it had been, the entire solar panel could have been shattered and the mission ended. Worse, the fleck could have struck the main body of the satellite.
In that case, “the outcome might have been much more severe,” said Holger Krag this week at the opening of the 7th European Conference on Space Debris, which was held at ESA’s Space Operations Centre (ESOC) in Darmstadt, Germany.
Krag is Head of the ESA Space Debris Office. His team monitors the 10 satellites that ESA currently operate in low Earth orbit to protect them from the swarm of human-made debris that now surrounds our planet.
On average there is a high risk alert of a potential collision every week, and every ESA satellite has to be manoeuvred to avoid a collision once or twice a year. “It’s just normal life now,” says Krag.
Radar stations track 18,000 objects in orbit. Of these, only 7% are operational satellites. The rest is space debris. And radar only sees the big stuff.
Using observations and computer models, Krag estimates that there are around 5,000 objects larger than 1m, 20,000 objects larger than 10cm, 750,000 larger than 1cm (he calls these “flying bullets”), and a whopping 150 million larger than 1mm (or about the size of the piece that damaged Sentinel-1A).
Space debris comprises spent rocket parts and fragments from defunct spacecraft: old batteries can explode, leaks can occur in coolant systems that solidify into pellets, occasionally satellites actually collide. Worryingly each collision produces more fragments and exacerbates the problem.
And it’s not just satellites that are at risk. So too are human lives. The conference was addressed by ESA astronaut Thomas Pesquet, via a satellite link from the International Space Station (ISS).
Just like other satellites, the space station has been manoeuvred out of harm’s way in the past. Chillingly, however, if the collision alert comes with less than 24 hours warning, there is nothing that can be done.
Pesquet described how the astronauts must close all the hatches between the various modules and then wait in their Soyuz spacecraft, ready to perform an emergency evacuation to Earth if needed.
This procedure has been enacted four times in the 19-year history of the ISS. The latest was in July 2015, when the three man crew received just 90 minutes warning that a collision was possible. Thankfully, the space debris sailed cleanly by and to date no catastrophic debris strike has taken place.
But it’s set to get worse. So called mega-constellations of satellites are planned by companies such as One Web, Boeing, SpaceX and Samsung to bring Internet access to all sectors of the globe. These will loft more than ten thousand satellites into orbit.
By way of comparison, since the launch of the world’s first spacecraft, Sputnik One, in 1957, only 7000 spacecraft in total have been launched in the entire 60-year exploration of space.
The nightmare scenario that space debris experts contemplate is called the Kessler syndrome, after American astrophysicist Donald Kessler. In 1978, while working for Nasa, he published an analysis that showed frequent collisions exponentially increased the amount of space debris, leading to many more collisions, leading to much more debris until we lose the use of certain orbits because anything we put there would certainly be hit.
Krag showed the conference a graph of the radar-tracked fragments and said that since 2002, “The growth has entered into the more feared exponential trend.”
There can be absolutely no doubt that the time to do something about space debris has arrived, and this is what the experts have spent the week discussing. At the conclusion of the conference today, Jan Wörner, ESA Director General, committed the Agency to leading European activities to combat space debris.
This includes detection, tracking, and development of automatic collision avoidance systems for satellites, and new binding guidelines on satellite design. He went further saying that there had to be a concerted effort to reduce and remove the space debris that is already there.
ESA knows this is challenging. Their own debris removal mission, called e.deorbit, failed to get the backing of enough European governments last year and so was not funded.
Addressing this point at the conference, Brigitte Zypries, German Federal Minister for Economic Affairs and Energy, said that the mission would be re-tabled at the next ministerial meeting in four years time.
Wörner also said that he would not tolerate any excuse for non-participation. Clearly there is palpable determination in the agency, and a growing interest around the world. For the first time in its history, the conference was oversubscribed, and had to turn researchers away.
But unless a global community comes together quickly to tackle this problem, it will inevitably end up being too little too late.