Freitag, 14. Juli 2017 - 22:00 Uhr

Raumfahrt - LISA-Pathfinder Mission-Update-2



 Under control of the mission team at ESOC, LISA Pathfinder discarded its propulsion module on 22 January 2016.
After a six-week journey, LISA Pathfinder arrived at its destination today, an orbit around a point of balance in space where it will soon start testing technologies crucial for exploring the gravitational Universe.
LISA Pathfinder is testing the key elements that could be used for a future mission to detect gravitational waves – ripples in spacetime predicted by Albert Einstein in his General Theory of Relativity.
To this end, it will release two test masses into near-perfect free fall and measure their motion with unprecedented accuracy.
LISA Pathfinder was launched on 3 December 2015 and arrived today in its orbit around ‘L1’, the first libration point of the Sun-Earth system, a virtual point in space some 1.5 million km from Earth towards the Sun.
LISA Pathfinder’s arrival came after a final thruster burn using the spacecraft’s hard-working propulsion module on 20 January. The small, 64-second firing was designed to slightly change its speed and just barely tip the craft onto its new orbit about L1.
Since launch, the propulsion module raised the orbit around Earth six times, the last of which kicked it towards L1.
“We had planned two burns to get us into final orbit at L1, but only one was needed,” says Ian Harrison, Spacecraft Operations Manager at ESA’s ESOC operations centre in Darmstadt, Germany.
Separation after arrival 1.5 million km away
The propulsion module separated from the science section at 11:30 GMT (12:30 CET) today after the combination was set spinning for stability.
“Heat and vibration from the regular, hot thrusters on the propulsion module would cause too much disturbance during the spacecraft’s delicate technology demonstration mission,” notes Ian. “Primary propulsion during the rest of the mission will be provided by cold-gas microthrusters to keep us at L1.”
These small thrusters were used in the hours after separation to kill the spin and stabilise the spacecraft.
Today’s operations were monitored by the mission control and science teams at ESOC in real time via the Agency’s deep-space station at Malargüe, Argentina.
During this evening, the craft will be slowly turned to point towards Earth and, around midnight, establish a full communications link via ESA’s New Norcia ground station, Australia.
Next week, LISA Pathfinder’s trajectory will be fine-tuned with a series of three microthruster bursts, taking it onto its final orbit, a 500 000 × 800 000 km orbit around L1.
L1 was chosen because it is a quiet place in space, far away from large bodies such as Earth and is ideal for communications.
Quelle: ESA
Update: 17.02.2016
Freely floating in space
ESA’s LISA Pathfinder has released both of its gold–platinum cubes, and will shortly begin its demanding science mission, placing these test masses in the most precise freefall ever obtained to demonstrate technologies for observing gravitational waves from space.
Launched on 3 December, LISA Pathfinder reached its operational location on 22 January, some 1.5 million km from Earth in the direction of the Sun.
As tests on the spacecraft and its precious payload continue, a major milestone was reached today. For the first time, the two masses – a pair of identical 46 mm gold–platinum cubes – in the heart of the spacecraft are floating freely, several millimetres from the walls of their housings. The cubes sit 38 cm apart linked only by laser beams.
Throughout LISA Pathfinder’s ground handling, launch, the burns that raised its orbit, and the six-week cruise to its work site, each cube was held firmly in place by eight ‘fingers’ pressing on its corners.
The interior layout of LISA Pathfinder's science module.
At the heart of the science module lies the LISA Technology Package. This contains inertial sensors, an optical metrology system, the payload computer and a diagnostic system. The inertial sensors and optical metrology system provide signals to the Drag-Free and Attitude Control System, which in turn commands three clusters of cold-gas micronewton thrusters, as well as feeding back to the inertial sensors.
The solar array (shown here as partly transparent for illustrative purposes) provides the spacecraft with solar power and shields it from the Sun.
On 3 February, the locking fingers were retracted and a valve was opened to allow any residual gas molecules around the cubes to vent to space.
Each cube remained in the centre of its housing held by a pair of rods softly pushing on two opposite sides.
The rods were finally released from one test mass yesterday and from the other today, leaving the cubes floating freely, with no mechanical contact with the spacecraft.  
“This is why we sent the test cubes into space: to recreate conditions that are impossible to achieve in the gravitational field of our planet,” says Paul McNamara, ESA’s project scientist.
“Only under these conditions is it possible to test freefall in the purest achievable form. We can’t wait to start running experiments with this amazing gravity laboratory.”
It will be another week before the cubes are left completely at the mercy of gravity, with no other forces acting on them. Before then, minute electrostatic forces are being applied to move them around and make them follow the spacecraft as its flight through space is slightly perturbed by outside forces such as pressure from sunlight.
On 23 February, the team will switch LISA Pathfinder to science mode for the first time, and the opposite will become true: the cubes will be in freefall and the spacecraft will start sensing any motions towards them owing to external forces. Microthrusters will make minuscule shifts in order to keep the craft centred on one mass.
Then the scientists will be in a position to run several months of experiments to determine how accurately the two freely-flying test masses can be kept positioned relative to each other, making measurements with the laser that links them.
Roughly speaking, the required accuracy is on the order of a millionth of a millionth of a metre.
Quelle: ESA
Update: 21.02.2016
Testmassen von LISA Pathfinder schweben frei
Entscheidender Meilenstein auf dem Weg zum wissenschaftlichen Missionsbetrieb im März
Die LISA Pathfinder-Missionswissenschaftler haben erfolgreich erstmals beide würfelförmigen Gold-Platin-Testmassen im Satelliten freigesetzt. LISA Pathfinder wird diese Würfel im präzisesten jemals erreichten freien Fall vermessen, um Kerntechnologien für die Beobachtung von Gravitationswellen im Weltraum zu demonstrieren.
LISA Pathfinder startete am 3. Dezember 2015 ins All und erreichte sein Ziel – rund 1,5 Millionen Kilometer von der Erde entfernt in Richtung Sonne – am 22. Januar 2016. Die erste Komponenten der wissenschaftlichen Nutzlast wurden erfolgreich zwischen dem 11. und 13. Januar in aktiviert, gefolgt von weiteren Inbetriebnahmeschritten.
Nun wurde ein Meilenstein auf dem Weg zum wissenschaftlichen Missionsbetrieb erreicht, der am 1. März beginnen soll. Erstmals wurden die beiden Testmassen von LISA Pathfinder – zwei identische 46 mm große Würfel aus einer Gold-Platin-Legierung – von ihren Haltemechanismen freigegeben und schweben nun frei innerhalb des Satelliten. Ein Laserinterferometer vermisst den Abstand zwischen den Massen mit höchster Präzision.
„LISA Pathfinder arbeitet weiterhin perfekt! Das Freilassen der Testmassen erforderte etwas Lernen, aber das Team hat dann schnell eine elegante Lösung gefunden. Mit dem erfolgreichen Betrieb eines Laserinterferometers im Weltraum zwischen zwei freischwebenden Testmassen liefert LISA Pathfinder eine echte Weltneuheit!“, sagt Prof. Karsten Danzmann, Director am Max-Planck-Institut für Gravitationsphysik und Direktor des Instituts für Gravitationsphysik der Leibniz Universität Hannover. „Wir stehen nun kurz vor dem Beginn der wissenschaftlichen Mission, die Schlüsseltechnologien zur Beobachtung von Gravitationswellen im Weltraum demonstrieren wird.“
Während der Vorbereitung des Satelliten am Boden, während des Starts und der Bahnmanöver, die LISA Pathfinder nach einer sechswöchigen Reise zum Lagrangepunkt L1 brachten, wurden beide Würfel fest mit acht „Fingern“ an den Ecken fixiert. Am 3. Februar wurden diese Haltefinger gelöst, gleichzeitig wurde ein Ventil geöffnet, um die Restmoleküle aus der Vakuumkammer um die Testmassen zum Weltraum zu entlüften.
Ein Paar von Druckstäben, die die Würfel beidseitig feinfühlig fixierten, hielt die Testmassen bislang in der Mitte der Einhausungen fest. Diese Druckstäbe wurden nun gestern von der einen Testmasse und heute von der anderen gelöst. Nun schweben die Würfel frei im Abstand von einigen Millimetern von den Wänden der Einhausung ohne mechanischen Kontakt zum Satelliten.
Präzisionsmessungen mittels Laserinterferometrie
Zwischen den zwei Testmassen, die rund 38 Zentimeter von einander entfernt sind, befindet sich ein Laserinterferometer, das die Positionen und die Ausrichtung der beiden Testmassen relativ zum Satelliten und zueinander mit bisher unerreichter Genauigkeit von etwa zehn Pikometern (hundertmillionstel Millimeter) bestimmt. Dieses optische Präzisionsmesssystem wurde unter Federführung und mit maßgeblicher Beteiligung von Forschenden des Max-Planck-Instituts für Gravitationsphysik und von der Leibniz Universität in Hannover entwickelt und gebaut.
Die Testmassen werden derzeit durch elektrostatische Kräfte von den Elektrodeneinhausungen kontrolliert. Dies sorgt dafür, dass die Testmassen den Bewegungen des Satelliten folgen. In einer Woche soll LISA Pathfinder erstmals im wissenschaftlichen Messbetrieb laufen. Dann werden die Testmassen im vollständigen Freifall sein und der Satellit wird ihren Bewegungen mittels seiner Mikronewton-Triebwerke folgen.
Datenanalyse in Hannover
Nach einer Woche letzter Überprüfungen wird die wissenschaftliche Mission von LISA Pathfinder am 1. März beginnen. Diese wird Schlüsseltechnologien für den Nachweis von Gravitationswellen im Weltraum demonstrieren und validieren. So wird die Mission den Weg für zukünftige Gravitationswellen-Observatorien im All – wie eLISA – ebnen.
Forschende der Max-Planck-Gesellschaft und der Leibniz Universität in Hannover sind führend an der Entwicklung der Auswertungssoftware beteiligt, die eine zentrale Rolle beim Extrahieren der entscheidenden Information aus den Messdaten spielt. Dafür betreibt das Institut einen Kontrollraum in Hannover. Da eine unmittelbare Auswertung der Daten für die Konfiguration der Folgeuntersuchungen entscheidend ist, besetzen Forscher des Instituts außerdem rund um die Uhr Schichten im Darmstädter Kontrollzentrum (ESOC) der europäischen Weltraumagentur ESA.
LISA Pathfinder ist eine Mission der ESA. Daran beteiligt sind europäische Raumfahrtunternehmen unter der Systemverantwortung von Airbus DS, Forschungseinrichtungen aus Frankreich, Deutschland, Italien, den Niederlanden, Spanien, der Schweiz, und Großbritannien sowie die NASA.
LISA Pathfinder wird aufgrund eines Beschlusses des Deutschen Bundestages vom Bundesministerium für Wirtschaft und Energie über das Deutsche Zentrum für Luft- und Raumfahrt (DLR) gefördert.
Wegbereiter für eine neue Astronomie
LISA Pathfinder ist Wegbereiter für eLISA, ein großes Weltraumobservatorium, das eines der am schwersten fassbaren astronomischen Phänomene direkt beobachten soll – Gravitationswellen. Der Nachweis dieser von Albert Einstein im Jahr 1916 vorhergesagten winzigen Verzerrungen der Raumzeit erfordert eine sehr empfindliche und hochpräzise Messtechnik. Kürzlich gelang mit den erdgebundenen Advanced LIGO-Detektoren der erste direkte Nachweis. Weltraumobservatorien wie eLISA werden Gravitationswellen mit Frequenzen im Millihertz-Bereich nachweisen, wie sie Paare extrem massereicher schwarzer Löcher oder Doppelsternsysteme aus weißen Zwergen aussenden. So ergänzen sie irdische Detektoren wie GEO600, aLIGO und Virgo, die bei höheren Frequenzen (im Audiobereich) Gravitationswellen von weniger massereichen Objekten aufspüren sollen. Im Zusammenspiel mit anderen astronomischen Methoden werden diese Gravitationswellen-Observatorien bisher noch unbekannte Bereiche beobachten, gleichsam die dunkle Seite des Universums. Mit eLISA wollen die Forscher in 20 Jahren verfolgen, wie massereiche schwarze Löcher entstehen, wachsen und miteinander verschmelzen. Und auch die Entwicklung von Galaxien während der gesamten Vergangenheit des Universums wird sich erfassen lassen. Außerdem soll eLISA Vorhersagen der Allgemeinen Relativitätstheorie überprüfen und nach bisher unbekannter Physik suchen.
Das hochempfindliche Messsystem von LISA Pathfinder
In den zwei separaten Vakuumtanks der wissenschaftlichen Nutzlast von LPF sollen während des Missionsbetriebs jeweils eine würfelförmige Testmasse von zwei Kilogramm (nahezu) frei von allen inneren und äußeren Störkräften schweben und so die präzise Vermessung einer kräftefreien Bewegung im Raum demonstrieren. Eine spezielle Gold-Platin-Legierung sorgt dafür, dass auf die Massen keine magnetischen Kräfte wirken; eine berührungslose Entladung mit Hilfe von UV-Strahlung stellt sicher, dass keine elektrostatische Aufladung erfolgt. Eine besondere Herausforderung stellt dabei der sogenannte Caging-and-Venting-Mechanismus dar, der die Testmassen während der heftigen Vibrationen beim Start von LISA Pathfinder sichert, sie kontrolliert freigibt und sie gegebenenfalls auch wieder einfängt. Mittels Laserinterferometrie werden die Positionen und die Ausrichtung der beiden Testmassen relativ zum Satelliten und zueinander mit bisher unerreichter Genauigkeit von etwa 10 Pikometern (ein hundertmillionstel Millimeter) gemessen. Darüber hinaus werden die Positionen über kapazitive Inertialsensoren mit geringerer Genauigkeit erfasst. Die Messdaten werden dazu verwendet, mit Hilfe eines „Drag-Free Attitude Control System (DFACS)“ die Sonde so zu steuern, dass sie gewissermaßen stets auf eine der Testmassen zentriert bleibt. Die eigentliche Lageregelung des Satelliten erfolgt dabei durch Kaltgas-Mikronewton-Triebwerke. Diese ermöglichen eine extrem feine und gleichmäßige Regelung des Antriebschubs. Die Schubkräfte liegen im Bereich von Mikronewton – dies entspricht der Gewichtskraft eines Sandkorns auf der Erde.
Quelle: Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)
Update: 6.06.2016
Livestreaming of the media briefing on the first results from ESA’s LISA Pathfinder mission will begin on 7 June at 09:30 GMT (11:30 CEST). LISA Pathfinder is a technology demonstrator for the observation of gravitational waves from space.   
Programme outline
09:30–09:40 GMT / 11:30–11:40 CEST
Opening up the gravitational Universe for ESA’s Science Programme
Fabio Favata, Head of the Coordination Office, ESA Directorate of Science
09:40–09:50 GMT / 11:40–11:50 CEST
LISA Pathfinder: A new way to look at our Universe
Paul McNamara, ESA LISA Pathfinder Project Scientist
09:50–10:00 GMT / 11:50–12:00 CEST
LISA Pathfinder optical metrology performance
Martin Hewitson, LISA Pathfinder Deputy Primary Investigator, University of Hanover
10:00–10:10 GMT / 12:00–12:10 CEST
LISA Pathfinder first results
Stefano Vitale, LISA Pathfinder Primary Investigator, University of Trento
10:10–11:00 GMT / 12:10–13:00 CEST
Question and Answer sessions and opportunity for individual interviews
Quelle: ESA
Update: 7.06.2016
ESA’s LISA Pathfinder mission has demonstrated the technology needed to build a space-based gravitational wave observatory.
Results from only two months of science operations show that the two cubes at the heart of the spacecraft are falling freely through space under the influence of gravity alone, unperturbed by other external forces, to a precision more than five times better than originally required.
In a paper published today in Physical Review Letters, the LISA Pathfinder team show that the test masses are almost motionless with respect to each other, with a relative acceleration lower than 1 part in ten millionths of a billionth of Earth’s gravity.
The demonstration of the mission’s key technologies opens the door to the development of a large space observatory capable of detecting gravitational waves emanating from a wide range of exotic objects in the Universe.
LISA Pathfinder performance
Hypothesised by Albert Einstein a century ago, gravitational waves are oscillations in the fabric of spacetime, moving at the speed of light and caused by the acceleration of massive objects.
They can be generated, for example, by supernovas, neutron star binaries spiralling around each other, and pairs of merging black holes.
Even from these powerful objects, however, the fluctuations in spacetime are tiny by the time they arrive at Earth – smaller than 1 part in 100 billion billion.
Sophisticated technologies are needed to register such minuscule changes, and gravitational waves were directly detected for the first time only in September 2015 by the ground-based Laser Interferometer Gravitational-Wave Observatory (LIGO).
This experiment saw the characteristic signal of two black holes, each with some 30 times the mass of the Sun, spiralling towards one another in the final 0.3 seconds before they coalesced to form a single, more massive object.
The signals seen by LIGO have a frequency of around 100 Hz, but gravitational waves span a much broader spectrum. In particular, lower-frequency oscillations are produced by even more exotic events such as the mergers of supermassive black holes.
With masses of millions to billions of times that of the Sun, these giant black holes sit at the centres of massive galaxies. When two galaxies collide, these black holes eventually coalesce, releasing vast amounts of energy in the form of gravitational waves throughout the merger process, and peaking in the last few minutes.
Quelle: ESA
Update: 10.09.2016
An artist's drawing of LISA measuring gravitational waves in space

LISA, on the drawing boards for decades, may now launch earlier than 2034.

Albert Einstein Institute/Milde Marketing/exozet; GW simulation: NASA/C. Henze

NASA moves to rejoin sped-up gravitational wave mission

Earlier this year, scientists announced the detection of gravitational waves—Einstein’s ripples in spacetime—for the first time on Earth. Those ripples are now reverberating through NASA, nudging the agency to mend fences with the European Space Agency (ESA) and rejoin an ambitious mission, called the Laser Interferometry Space Antenna (LISA), to study gravitational waves from space.

This week, at the 11th LISA symposium in Zürich, Switzerland, a NASA official said he was ready to rejoin the LISA mission, which the agency left in 2011. Meanwhile, ESA says it is trying to move the launch of the mission up several years from 2034. “This is a very important meeting,” says David Shoemaker, a gravitational wave physicist at the Massachusetts Institute of Technology in Cambridge. “It feels like a turning point.”

Plans for LISA date back more than 2 decades. Three separate spacecraft, flying millions of kilometers apart from each other at the vertices of a giant triangle, would precisely measure their mutual separations using sensitive lasers, and thus be capable of detecting low-frequency ripples in spacetime. The objects causing these low-frequency ripples—such as orbiting supermassive black holes at the centers of distant galaxies—would be different from the higher frequency ripples, emitted by collisions of much smaller black holes, that have so far been detected on Earth.

Originally, LISA was conceived as a joint ESA-NASA mission. Both partners would pay 50% of the mission cost, estimated at some $2 billion. But in April 2011, NASA dropped out of the collaboration because of budgetary problems, and the program was almost killed. “The next year, the LISA symposium felt like a funeral,” recalls astrophysicist Paul McNamara of ESA’s space research and technology center ESTEC in Noordwijk, the Netherlands.

Then, in 2013, a trimmed-down, €1 billion version of LISA was selected by ESA as its L3 mission—the third large mission in its Cosmic Vision 2020 program. Called eLISA (where the “e” euphemistically stands for “evolved”), it would have less capability and sensitivity than the original design. Launch was foreseen for 2034. NASA expressed interest to become a minor partner, providing technological support.

But things have changed a lot in the past few years. ESA’s technology demonstrator LISA Pathfinder, launched in December 2015, has performed flawlessly, says McNamara, who is the mission’s project scientist. Then, in February, the ground-based Laser Interferometer Gravitational-Wave Observatory experiment announced that it had bagged its first direct detections.

In June, a NASA-appointed L3 Study Team presented its interim report, suggesting ways for the agency to rejoin the program as a senior partner. And on 15 August, a midterm assessment of the National Academy of Sciences’s (NAS) 2010 Decadal Report, which reviews U.S. priorities for astronomy and astrophysics, strongly recommended NASA to restore support to the space observatory this decade, and to help restore the mission to its original full capacity.

It now looks like the recommendations are taking effect. At the Zürich meeting, Paul Hertz, the director of NASA’s astrophysics division, said: “2011 saw the dissolution of our original LISA partnership. But I’m here to move forward from that.” NASA’s contribution may not get back to 50%, but according to the NAS report, what’s required is “a significantly larger U.S. contribution than the $150 million […] currently being considered”.

Meanwhile, ESA’s Director of Science Alvaro Giménez in Madrid announced that the call for mission concepts for eLISA will be brought forward from 2018 to next month. “We want to make your dreams come true,” he told the gravitational-wave scientists at the meeting. “Although 2029 is probably too optimistic, we might be able to launch the mission a few years earlier, somewhere in the early 2030s.” According to Giménez, not restoring a much stronger partnership with NASA is now almost unthinkable.

Scientists at the meeting were pleased. “When we launch 14 or 15 years from now, this meeting will be seen as the rebirth of LISA,” says Karsten Danzmann of the Albert Einstein Institute in Hannover, Germany, who is LISA Pathfinder’s co–principal investigator.

Adds Shoemaker: “Let’s drop the ‘e’ in eLISA from now on. There’s only one LISA again.”

Quelle: Science


Update: 20.11.2016


Artist's concept of the European Space Agency's LISA Pathfinder spacecraft
Cluster of four colloid thrusters
This cluster of four colloid thrusters, part of the Disturbance Reduction System developed by NASA/JPL, helps keep the LISA Pathfinder spacecraft extremely stable. › Larger view

A next-generation technology demonstration mission has just passed a big milestone. 

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a system of thrusters, advanced avionics and software managed by NASA's Jet Propulsion Laboratory, Pasadena, California. It has been flying on the European Space Agency's LISA Pathfinder spacecraft, which launched from Kourou, French Guiana on Dec. 3, 2015 GMT (Dec. 2 PST). As of Oct. 17, the system had logged roughly 1,400 hours of in-flight operations and met 100 percent of its mission goals. 

Most thrusters are designed to move a spacecraft, but ST7-DRS has a different purpose: to hold Pathfinder as perfectly still as possible. This allows the spacecraft to test technologies used in the detection of gravitational waves, whose effects are so miniscule that it requires extreme steadiness to detect them.

Just how steady is that? Steady enough that "position noise" -- subtle vibrations in Pathfinder's position -- won't exceed 2 nanometers. That's about the diameter of a DNA helix. This kind of precision is needed to counteract the biggest disturbance to Pathfinder: the pressure from sunlight pushing on the spacecraft (about 25 micronewtons).

"Here's another way of thinking about it: when the thrusters fire at full throttle, they produce a maximum force of 30 micronewtons -- equivalent to the weight of a mosquito landing on the spacecraft," said John Ziemer of JPL, ST7-DRS systems lead. "To maintain our precise position, the thrusters can be controlled in 0.1 micronewton increments, equivalent to the weight of that mosquito's antenna."

Balancing all the disturbances on the spacecraft allows Pathfinder's instruments to stay in near-perfect free fall. This lays the groundwork for a future Pathfinder-type mission, which will need this kind of stability to cancel out any force other than the subtle tug of gravitational waves, produced by supermassive objects like black holes. 

"This achievement represents the last hurdle for this microthruster technology development, which the project has been chartered to perform," said JPL's Phil Barela, project manager for ST7-DRS. "Our successful development and demonstration of this electrospray technology will pave the way for future gravitational wave missions, or other missions requiring precise control of spacecraft position and pointing."

Large space observatories and spacecraft formation-flying missions could both benefit from this technology, Barela added.

ST7-DRS is a system of eight thrusters positioned on either side of the Pathfinder spacecraft. Each thruster emits microscopic liquid droplets called a colloid electrospray, which are created and charged through an electric field. These ionized droplets are accelerated by a second electric field with an opposite charge, which pushes them out of the thruster. The force of that reaction provides the "thrust" that steadies the spacecraft.

The electrospray microthrusters were developed by Busek Co., Inc., Natick, Massachusetts, with technical support from JPL.

"The success of the ST7-DRS mission emphasizes the enormous benefit of one of NASA/JPL's key charters: to mature high-risk technology that can benefit future space exploration," Barela said. "The collaborative relationship between NASA/JPL, ESA, Busek and Goddard Space Flight Center has been the key enabler for this project's success." 

The Pathfinder spacecraft was built by Airbus Defence and Space, Ltd., United Kingdom. Airbus Defence and Space, GmbH, Germany, is the payload architect for the LISA Technology Package.

Caltech in Pasadena, California, manages JPL for NASA.

Quelle: NASA


Update: 14.07.2017



LISA Pathfinder operating in space

The final days of the LISA Pathfinder mission are some of the busiest, as controllers make final tests and get ready to switch off the gravitational pioneer next Tuesday.

Following 16 months of scientific effort, LISA Pathfinder completed its main mission on 30 June, having demonstrated the technology needed to operate ESA’s future LISA space observatory to study gravitational waves – ripples in spacetime predicted by Albert Einstein in his General Theory of Relativity.

The LISA mission will comprise three spacecraft orbiting some 2.5 million km apart in a triangular formation, with their ‘test masses’ isolated from all external forces bar gravity and linked by laser beams.

With the required sensitivity fully proven by LISA Pathfinder, teams are now using the spacecraft’s last days to conduct a series of technical tests on components and devices, making full use of every remaining minute.

LISA Pathfinder mission controllers conducting flight operations at ESA’s ESOC mission control centre, Darmstadt, Germany, on 27 June 2017
LISA Pathfinder flight controllers

“These tests will give us a better grasp of the craft’s behaviour and provide valuable feedback to the manufacturers about the characteristics of their equipment, in both routine and unusual conditions,” says spacecraft operations manager Ian Harrison.

“The gravitational wave detectors work by measuring the changing separation of two cubes that are in free-fall. Changes in the spacecraft’s state or any movement may interfere with the measurements, and we want to better understand these for the future mission.”

In addition to satellite movement, the delicate cubes on LISA Pathfinder can be influenced by variations in their environment, such as in temperature and magnetic interference.

Baking, rattling and rolling

Inside LISA Pathfinder, with narration

Working at ESA’s mission control centre in Darmstadt, Germany, the controllers have been conducting daily tests since the mission formally ended its normal phase on 30 June. These could not be performed before because meeting the science goals required a very stable and ‘quiet’ environment.

Engineers have commanded the craft to turn to assess thermal effects on its systems, particularly the micropropulsion system, from solar illumination.

Repeating thermal tests previously performed on the ground will help to improve procedures for the future LISA mission.

Quelle: ESA



Tags: Raumfahrt - LISA-Pathfinder Mission-Update-2 Raumfahrt