BepiColombo Earth flyby enables unique instrument scan of Moon
As early as 9 April, with its Earth-facing side illuminated by the Sun, the Moon will be observed for the first time in the thermal infrared and examined for its mineralogical composition using the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument, developed and built at DLR.
Space exploration missions require precision of the highest order. In the early hours of 10 April 2020, the European Space Agency's (ESA) BepiColombo spacecraft will fly towards Earth at over 30 kilometres per second. At 06:25 CEST it will make its closest approach, over the South Atlantic, at an altitude of 12,677 kilometres. The spacecraft will then fly further towards the centre of the Solar System, travelling somewhat more slowly than when it arrived. This is a unique opportunity for planetary researchers and engineers at the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) and the Institute for Planetology at the Westphalian Wilhelms University of Munster to conduct a unique experiment, where they will study the Moon.
As early as 9 April, with its Earth-facing side illuminated by the Sun, the Moon will be observed for the first time in the thermal infrared and examined for its mineralogical composition using the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument, developed and built at DLR. This will be possible because there will be no absorption by Earth's atmosphere. At Mercury, MERTIS will investigate the composition and mineralogy of Mercury's surface and investigate the planet's interior. The scientific evaluation of the data will then be carried out jointly at participating institutes in Munster, Berlin, Gottingen and Dortmund, as well as several locations in Europe and the USA.
The main purpose of the Earth flyby is to slow down BepiColombo somewhat without expending propellant, in order to bring the spacecraft onto a trajectory towards Venus. During its flight towards Earth, on its spiral orbit through the inner Solar System, it will travel at a speed of 30.4 kilometres per second. As it moves away from Earth, BepiColombo be travelling at a speed of approximately 25 kilometres per second.
With two subsequent close flybys of Venus (the first flyby will take place on 16 October 2020), BepiColombo will then be on a trajectory that will take it to the final destination of the six-year journey, an orbit around Mercury, the innermost planet of the Solar System. Due to the enormous gravitational field of the Sun and the limited transport capacity of the available launchers, planetary missions to the inner and outer Solar System can only be accomplished by following very complex trajectories.
Unique possibility to observe the Earth-facing side of the Moon
"Observing the Moon with our MERTIS instrument on board BepiColombo is a one-of-a-kind opportunity," says Jorn Helbert from the DLR Institute of Planetary Research, who is a Co-Principal Investigator for MERTIS. "We will examine the Earth-facing side of the Moon spectroscopically in the thermal infrared for the first time. Without any absorption by Earth's atmosphere, the view from space will provide a valuable new data set for lunar research.
This is also an excellent opportunity to test how well our instrument works and to gain experience in preparation for operations in Mercury orbit." The current situation with the Coronavirus pandemic is also putting the team to the test. "Our team will support the MERTIS instrument from our home offices and process and evaluate the data there," Helbert adds. "This has been tested several times over the last few days and 'data evaluation at the kitchen table' seems to work well."
MERTIS has two uncooled radiation sensors. Its spectrometer covers a wavelength range from seven to 14 micrometres, and its radiometer to a wavelength range from seven to 40 micrometres. It will identify rock-forming minerals in the mid-infrared at a spatial resolution of 500 metres.
"We will not be able to obtain such a detailed resolution when observing the Moon," explains Gisbert Peter, MERTIS Project Manager at the DLR Institute of Optical Sensor Systems, which was responsible for the design and construction of MERTIS. "Having the Moon in the spectrometer's field of view before the flyby is partly an astronomical or geometric 'coincidence' and, above all, due to good planning. MERTIS will observe the Moon from distances of between 740,000 and 680,000 kilometres for four hours." Here, the instrument, which is very compact at 3.3 kilograms, will be able to demonstrate its unique optical properties for the first time in orbit. Three small cameras on the exterior of the BepiColombo spacecraft will also acquire images of Earth during the approach.
"The Moon and Mercury are not dissimilar in size, and their surfaces resemble one another in many ways," explains Harald Hiesinger from the University of Munster, Principal Investigator for the MERTIS experiment. After decades of lunar research, he is particularly looking forward to the new measurements.
"We will obtain new information on rock-forming minerals and the temperatures on the lunar surface and will later be able to compare the results with those acquired at Mercury. The Moon and Mercury are two important bodies that are fundamental to enhancing our understanding of the Solar System," Hiesinger adds: "I am anticipating many exciting results from the observations with MERTIS. After about 20 years of intensive preparations, the time will finally come on Thursday - our long wait will be over, and we will receive our first scientific data from space."
Third mission to Mercury
BepiColombo was launched on 20 October 2018 on board an Ariane 5 launch vehicle, which lifted off from the European spaceport in French Guiana. It is the most extensive European project to explore a planet in the Solar System. The science component of the mission consists of two spacecraft that will orbit Mercury at different altitudes - the ESA Mercury Planetary Orbiter (MPO) and the Japan Aerospace Exploration Agency (JAXA) Mercury Magnetospheric Orbiter (MMO). Two NASA missions - Mariner 10, in the mid-1970s, and MESSENGER, which orbited Mercury from 2011 to 2015 - are the only other spacecraft to have studied the planet that is closest to the Sun.
While MPO is designed to analyse the planetary surface and composition, MMO will explore its magnetosphere. Further goals of the mission are the investigation of the solar wind, the internal structure and the planetary environment of Mercury, and its interaction with the near-solar environment. Scientists also hope to gain insights into the formation of the Solar System, and Earth-like planets in particular. Until they reach Mercury orbit, the two spacecraft will travel as part of the Mercury Composite Spacecraft (MCS).
This includes the Mercury Transfer Module (MTM), which supplies the orbiters with power and protects them from the extreme temperatures as they approach and fly past Mercury. MCS is also equipped with the Magnetospheric Orbiter Sunshield and Interface Structure (MOSIF), which will further protect the MMO before it enters orbit. Surface temperatures on Mercury range between 430 degrees Celsius on the day side and minus 180 degrees Celsius on the night side. On 5 December 2025, after six flybys of Mercury, the MPO, MMO and MOSIF will enter an initial capture orbit.
Juggling gravity and velocity
Flyby manoeuvres, also referred to as 'Gravity Assist Manoeuvres', have become routine for space missions. They are used to change the flight trajectory and speed of spacecraft without using propellant, by employing the gravitational fields of planets. Leaving Earth's gravitational field and reaching a distant destination in the Solar System requires a great deal of energy for acceleration, for changes of direction, and also for deceleration at the destination. Carrying this energy in the form of propellants for engines or thrusters is expensive in terms of mass and would inevitably reduce the science payload that can be carried or simply make the mission technically unfeasible.
Close flybys of planets enable an elegant technical solution. If a spacecraft approaches a planet, that planet's gravitational attraction prevails over that of the Sun at a certain distance, influencing its movement. In a sense, a flyby is the juggling of two forms of energy - the kinetic energy of the spacecraft and the planet's potential energy, which, with its much greater mass, attracts the small spacecraft during its approach. With this juggling, depending on the spacecraft's velocity and proximity to the planet, energy can be transferred from the planet to the spacecraft, or vice versa.
The visitor then either begins to travel faster (and the planet slows down imperceptibly) or, with kinetic energy being transferred from the spacecraft to the planet, the craft slows down (and imperceptibly accelerates the planet in return). The speed of the spacecraft does not change in relation to the planet; its overall velocity and trajectory are only modified. However, since the planet is in orbit around the Sun, this change in the trajectory of the spacecraft causes it (and minimally the planet) to accelerate or slow down on their orbits around the Sun.
The ingenious trajectory solution proposed by Giuseppe 'Bepi' Colombo
For the first time, flyby manoeuvres along a planetary orbit were used on the Mariner 10 mission to allow two more close flybys after the first flyby of the planet Mercury. The calculations were made by the Italian engineer and mathematician Giuseppe 'Bepi' Colombo. In 1970, Colombo, a professor at the university in his hometown of Padua, was invited to a conference at NASA's Jet Propulsion Laboratory in Pasadena, California, held in preparation for the Mariner 10 mission.
There, he saw the original mission plan and realised that, with a highly precise first flyby, two more close flybys of Mercury were possible. The current European-Japanese mission to Mercury was named in his honour.
Of the 15 instruments on board the two orbiters, three were largely developed in Germany: BELA (BepiColombo Laser Altimeter), MPO-MAG (MPO Magnetometer) and MERTIS. The DLR laser experiment BELA will only be operated when the spacecraft reaches its destination.
The magnetometer is already being used to carry out measurements during the flight through Earth's magnetosphere, which extends far into space. Funded by the DLR Space Administration, it was developed and built at the Institute for Geophysics and Extraterrestrial Physics at TU Braunschweig in collaboration with the Graz Space Research Institute and Imperial College London.
Last chance to see 'Bepi' - but not in Europe
Space enthusiasts are, of course, interested in knowing whether they will have the opportunity to see BepiColombo one last time, during the flyby, before it leaves on its way to the inner Solar System. The answer is indeed yes.
However, this will only be possible south of 30 degrees north over the Atlantic, in South America, Mexico and, with some restrictions, over Texas and California. The solar panels, illuminated by sunlight, will probably be most visible above the European Southern Observatory in the clear air of the Chilean Andes. In Central Europe, the consolation remains that on the night of 7 to 8 April, there will be an exceptionally large full Moon, commonly referred to as a 'supermoon'.
BEPICOLOMBO TO FLY BY EARTH ON APRIL 10TH
BepiColombo, the joint ESA/JAXA mission that’s ultimately bound for Mercury, will swing by Earth on Friday.
When it comes to solar system exploration, flybys are easy; it’s arriving and staying at a planetary destination that is hard. On Friday, April 10th, the joint Japanese/European BepiColombo mission pays Earth a visit, making its sole flyby past our planet on its long trek towards its final destination: Mercury.
Closest Earth approach will occur on Friday, April 10th, at 12:22 a.m. EDT (4:22 UT). The spacecraft will fly at 7,900 miles (12,700 kilometers) from the surface of the Earth over the South Atlantic. That’s just over a third of the distance to the ring of satellites in geostationary orbit. The flyby will provide an opportunity to test and calibrate instruments while the sensors and cameras are looking at Earth and the Moon.
SPACE OPERATIONS IN THE TIME OF COVID-19
The flyby comes during the COVID-19 pandemic, a time when many space agencies around the world are shuttered or at minimal staffing. The team at the European Space Agency (ESA) will work to guide BepiColombo through the critical phases of Friday’s flyby, all while using physical distancing measures for personnel working at the European Space Operations Centre in Darmstadt, Germany. (Those who can will be working remotely from home.)
“The Earth swing-by is a phase where we need daily contact with the spacecraft,” says Elsa Montagnon (ESA) in a recent press release. “This is something we cannot postpone. The spacecraft will swing by Earth independently in any case.”
GETTING TO MERCURY
BepiColombo will be the second mission to orbit Mercury after NASA’s Messenger mission, which terminated its successful stay by crashing into the innermost planet on April 30, 2015. In addition to this week’s Earth flyby, BepiColombo will make two flybys past Venus, the first of which is later this year on October 15th, and six preliminary flybys past Mercury before settling into orbit on December 5, 2025.
Launched atop an Ariane 5 rocket on October 20, 2018, BepiColombo is actually composed of two spacecraft: ESA’s Mercury Planetary Orbiter (MPO) and Japan's Mercury Magnetospheric Orbiter (nicknamed Mio, Japanese for "waterway"). Both are stacked atop ESA’s Mercury Transfer Module, and the two missions will separate into their respective orbits once they arrive around Mercury.
The early design phase of the mission also called for a Mercury lander and rover, options that were cut to reduce complexity and meet cost constraints.
Mio sits behind the transfer module’s protective sunshield, but will still have a portion of its sensors switched on during Friday's flyby. The transfer module will also partially block some of the MPO’s sensors during the flyby, though mission planners expect to collect data from eight of the spacecraft’s 11 science packages.
“For example, the Probing of the Hermean Exosphere by Ultraviolet Spectroscopy instrument (PHEBUS) will use the Moon as a calibration target to the produce better data once at Mercury,” says Johannes Benkhoff (ESA). “We also want to make some measurements of the solar wind and its interaction with Earth’s magnetic field. The main purpose of having the instruments on at this stage is testing and calibration.”
The German Aerospace Center also plans on making thermal infrared observations of Earth’s moon using the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) during the flyby.
ESA must also prepare the spacecraft to prevent battery discharge during the crucial 33 minutes when the Sun is eclipsed by Earth’s shadow. Its main solar electric propulsion unit, draws electric power from solar arrays to power four QinetiQ T6 ion thrusters — the most powerful ion engines fielded on a spacecraft to date.
BepiColombo is named after 20th-century Italian mathematician and engineer Giuseppe “Bepi” Colombo, who proposed the gravitational assist maneuver for Mariner 10, the first successful Mercury flyby mission in 1974.
At its closest approach on Friday, BepiColombo will appear as an 8th- to 10th-magnitude "star"moving at a leisurely one degree (twice the diameter of a full Moon) per minute across the sky. Though South America gets the very best view, Europe and the western half of Africa should see BepiColombo on approach at dawn. Observers in southeastern North America have a chance to see the spacecraft low to the south just after its closest approach, while it's exiting Earth's shadow in the early morning hours. BepiColombo enters Earth’s shadow for 33 minutes starting at 1:01 a.m. EDT (5:01 UT).
The BepiColombo Italian outreach site has a calculator for observing prospects based on latitude and longitude. Heavens-Above also offers flyby prospects. Catching BepiColombo will be similar to nabbing satellites fainter than naked eye: simply note when the spacecraft will pass by a given star, use a service such a WWV Radio on AM shortwave radio to call out the precise time in the background, aim your telescope at the suspected field, and wait for the spacecraft to pass through the field at the appointed time.
Heavens-Above offers a great tool to aid this method, as it allows you to see a plot of the satellite's pass against the starry background. Note, however, that you'll also have a waning gibbous (92% illuminated) Moon to contend with on Friday morning.
If you’ve got clear skies, be sure to join with humanity and catch a last glimpse of the BepiColombo spacecraft en route to Mercury.
BepiColombo closing in on Earth ahead of flyby
BepiColombo closing in on Earth ahead of flyby
A sequence of images taken by the MCAM selfie cameras on board of the European-Japanese Mercury mission BepiColombo as it neared Earth ahead of its gravity-assist flyby manoeuvre in April 2020. Images in the sequence were taken in 10-minute intervals from 11:25 UTC until 15:00 UTC on 9 April 2020, less than a day before the closest approach. As BepiColombo approached the planet at a speed of more than 100 000 km/h, the distance to Earth diminished from 281 940 km to 230 000 km during the time the sequence was captured.
In the image Earth appears behind the spacecraft structure and above the high-gain antenna, and moves slowly to the centre of the image.
The manoeuvre, first of an overall nine flybys but the only one at Earth, helped steer the spacecraft towards Venus as it gradually closes in on its target orbit around Mercury. During its seven-year cruise to the smallest and innermost planet of the Solar System, BepiColombo will twice use the gravity of Venus and six times that of Mercury to break against the gravitational pull of the Sun. This constant need to break requires either a lot of fuel or a complicated trajectory with many flybys, otherwise BepiColombo would not be able to enter the correct orbit around Mercury.
BepiColombo takes last snaps of Earth en route to Mercury
The ESA/JAXA BepiColombo mission completed its first flyby on 10 April, as the spacecraft came less than 12 700 km from Earth’s surface at 06:25 CEST, steering its trajectory towards the final destination, Mercury. Images gathered just before closest approach portray our planet shining through darkness, during one of humankind’s most challenging times in recent history.
Launched in 2018, BepiColombo is on a seven-year journey to the smallest and innermost planet orbiting the Sun, which holds important clues about the formation and evolution of the entire Solar System.
Today’s operation is the first of nine flybys which, together with the onboard solar propulsion system, will help the spacecraft reach its target orbit around Mercury. The next two flybys will take place at Venus and further six at Mercury itself
While the manoeuvre took advantage of Earth’s gravity to adjust the path of the spacecraft and did not require any active operations, such as firing thrusters, it included 34 critical minutes shortly after BepiColombo’s closest approach to our planet, when the spacecraft flew across the shadow of Earth.
“This eclipse phase was the most delicate part of the flyby, with the spacecraft passing through the shadow of our planet and not receiving any direct sunlight for the first time after launch,” said Elsa Montagnon, BepiColombo Spacecraft Operations Manager for ESA.
To prepare for the scheduled eclipse, mission operators fully charged the spacecraft batteries and warmed up all components in advance, then closely monitored the temperature of all onboard systems during the period in darkness, between 07:01 and 07:35 CEST.
“It is always nerve-wracking to know a spacecraft’s solar panels are not bathed in sunlight. When we saw the solar cells had restarted to generate electrical current, we knew BepiColombo was finally out of Earth’s shadow and ready to proceed on its interplanetary journey,” added Elsa.
Space operations are never routine at ESA’s mission control centre in Darmstadt, Germany, but today’s flyby had one extra challenge. The manoeuvre, programmed long in advance and impossible to postpone, had to be prepared with limited on-site personnel, amid the social distancing measures adopted by the Agency in response to the ongoing coronavirus pandemic; but the restrictions had no impact on the operation’s success.
As BepiColombo swung by our planet, most scientific instruments on ESA’s Mercury Planetary Orbiter – one of the two science spacecraft that make up the mission – were switched on. Several sensors were also active on the second component of the mission, JAXA’s Mercury Magnetospheric Orbiter, also known as Mio.
Scientists will use the data gathered during the flyby, which include images of the Moon and measurements of Earth’s magnetic field as the spacecraft zipped past, to calibrate the instruments that will, as of 2026, investigate Mercury to solve the mystery of how the scorched planet formed.
“Today was of course very different to what we could have imagined only a couple of months ago,” said Johannes Benkhoff, ESA’s BepiColombo Project Scientist, who followed the operation from his home in the Netherlands, along with the many scientists from the 16 instrument teams that comprise the mission, scattered between Europe and Japan.
“We are all pleased that the flyby went well and that we could operate several scientific instruments, and we are looking forward to receiving and analysing the data. These will also be useful to prepare for the next flyby, when BepiColombo will swing past Venus in October.”
“There is a great interest in Japan in the BepiColombo mission. Thus, after the successful flyby we are looking forward to the science at Venus and Mercury,” said Go Murakami, BepiColombo Project Scientist at JAXA.
Our home from space
On 9 April, ahead of the flyby, and then again today, just before closing in, the BepiColombo monitoring cameras snapped a series of images of Earth from space, picturing our planet in these difficult times for humans across Europe and the world.
“These selfies from space are humbling, showing our planet, the common home that we share, in one of the most troubling and uncertain periods many of us have gone through,” said Günther Hasinger, ESA’s Director of Science, who also followed the event remotely from home, in Spain.
“We are scientists who fly spacecraft to explore the Solar System and observe the Universe in search of our cosmic origins, but before that we are humans, caring for one another and coping with a planetary emergency together. When I look at these images, I am reminded of the strength and resilience of humankind, of the challenges we can overcome when we team up, and I wish they bring you the same sense of hope for our future.”
Join us on ESA Web TV on 10 April at 17:00 CEST for a live streamed conversation featuring ESA mission experts and scientists from some of the instrument teams, reflecting on the flyby and presenting data gathered by the different instruments: https://esawebtv.esa.int
For updates on the science data obtained during the flyby and images to be taken by the BepiColombo monitoring cameras as the spacecraft moves away from Earth on 10 and 11 April, follow the mission on Twitter via: @ESA_Bepi, @ESA_MTM, and @BepiColombo
BepiColombo flies by Earth, completing first leg of journey to Mercury
Working with a reduced staff due to coronavirus-related restrictions, European Space Agency flight controllers monitored the BepiColombo spacecraft during a flyby of Earth on Friday, a maneuver that used our planet’s gravity to steer the mission on a course toward Mercury.
BepiColombo sailed by Earth at a distance of around 7,900 miles (12,700 kilometers), about one-third the distance of geostationary communications satellites, at 0425 GMT (12:25 a.m. EDT) on Friday.
The BepiColombo spacecraft is made up of European and Japanese orbiters that will survey Mercury in tandem. A solar-powered ion propulsion module is accompanying the two science orbiters during the flight to the solar system’s innermost planet.
Some of BepiColombo’s 16 science instruments were switched on and gathered data on the Earth and the moon during the flyby, providing an opportunity to calibrate sensors before the mission reaches Mercury. Small cameras mounted outside the spacecraft also captured ethereal views of the Earth on BepiColombo’s approach Friday.
“These selfies from space are humbling, showing our planet, the common home that we share, in one of the most troubling and uncertain periods many of us have gone through,” said Günther Hasinger, ESA’s director of science, in a statement.
A reduced team of engineers at the European Space Operations Center in Darmstadt, Germany, monitored the progress of BepiColombo during Friday’s flyby maneuver. Scientists and managers, who would have normally been at the control center, tracked the flyby and analyzed data from their homes due to restrictions on gatherings of people adopted by ESA and government authorities.
“We are scientists who fly spacecraft to explore the solar system and observe the universe in search of our cosmic origins, but before that we are humans, caring for one another and coping with a planetary emergency together,” Hasinger said. “When I look at these images, I am reminded of the strength and resilience of humankind, of the challenges we can overcome when we team up, and I wish they bring you the same sense of hope for our future.”
BepiColombo’s flyby of Earth on Friday completed the first leg of the mission’s seven-year journey before entering orbit around Mercury in December 2025.
The $1.8 billion mission launched from French Guiana aboard an Ariane 5 rocket in October 2018. BepiColombo’s two orbiters will become the first European and Japanese spacecraft to enter orbit around Mercury, and will become the second mission to ever orbit the solar system’s innermost planet, following NASA’s MESSENGER spacecraft.
“Since it is very hard to go to Mercury, it’s quite a long tour to make,” said Johannes Benkhoff, ESA’s project scientist for the BepiColombo mission. “It’s a seven-year cruise which we have to go through, so we need the help of planetary flybys.”
During each flyby, BepiColombo will use gravity to slow down and reshape its orbit. Without the gravity assist maneuvers, BepiColombo would have had to launch on a much more powerful rocket.
BepiColombo executed Friday’s flyby sequence according to plan, according to Elsa Montagnon, ESA’s BepiColombo spacecraft operations manager. The spacecraft required no thruster firings during the pre-targeted flyby.
Shortly after its closest approach to Earth, BepiColombo passed through Earth’s shadow for 34 minutes.
“This eclipse phase was the most delicate part of the flyby, with the spacecraft passing through the shadow of our planet and not receiving any direct sunlight for the first time after launch,” Montagnon said in a statement.
ESA said the spacecraft’s batteries were fully charged to prepare for the eclipse. Ground teams also ensured all components were warmed up.
“It is always nerve-wracking to know a spacecraft’s solar panels are not bathed in sunlight. When we saw the solar cells had restarted to generate electrical current, we knew BepiColombo was finally out of Earth’s shadow and ready to proceed on its interplanetary journey,” Montagnon said.
“We are all pleased that the flyby went well and that we could operate several scientific instruments, and we are looking forward to receiving and analyzing the data,” Benkhoff said. “These will also be useful to prepare for the next flyby, when BepiColombo will swing past Venus in October.”
The encounter with Earth was the first of nine planetary flybys planned during BepiColombo’s journey before it enters orbit around Mercury. The mission’s next flyby is scheduled for Oct. 15, when BepiColombo will make its first encounter with Venus.
Another Venus flyby is planned in August 2021, followed by six flybys of Mercury before BepiColombo finally enters orbit around the solar system’s innermost planet on Dec. 5, 2025.
Once at Mercury, the European Mercury Planetary Orbiter and the Japanese Mercury Magnetospheric Orbiter will separate to enter their own orbits and perform independent measurements.
BepiColombo’s European-built science orbiter will map Mercury and study the planet’s geologic history, while the Japanese component of the mission will observe the solar wind’s influence on Mercury.