Health check for asteroid lander MASCOT
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DLR
Space travel is no easy task – first comes the stressful launch with vibrations, then the long flight through the bitter cold and the vacuum. The Mobile Asteroid Surface Scout (MASCOT) has been travelling on board the Japanese Hayabusa2 spacecraft for the last one-and-a-half years, and is currently at approximately 65 million kilometres from Earth. On 14 July 2016, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) engineers in the Lander Control Center (LCC) in Cologne switched the shoebox-sized lander and its four German and French-built instruments back on, and will spend the next few days finding answers to two questions: How is MASCOT's state of health? And how are the experiments on board? "We do a check-up once a year to find out whether all system components and instruments are still in good working order," explains Christian Krause from the Lander Control Center team at DLR.
A complete package for a primitive object
The Hayabusa2 spacecraft by the Japanese space agency JAXA set off on its mission on 3 December 2014, carrying the French-German MASCOT lander. One year later, the duo zipped round the Earth to gain momentum and sent back photos from our planet before continuing on toward the asteroid Ryugu. The spacecraft will venture deeper into space until the summer of 2018, when it will enter orbit around the celestial body that DLR planetary researcher Ralf Jaumann refers to as a 'beautifully primitive object'. "During this mission, we will be investigating primordial material from the solar nebula; it has remained practically unchanged in its 4.5 billion years of existence." Then, while the Hayabusa2 spacecraft measures and analyses the asteroid from its position in orbit, MASCOT will descend to its surface to conduct scientific measurements. The Japanese spacecraft will also take on soil samples that it will bring back to Earth in 2020. "This is a complete package. There has never been anything like this before: we will be observing and mapping remotely, measuring the asteroid, analysing its surface and bringing the samples back to Earth." But this complete package requires the concerted efforts of engineers and scientists from Germany, France and Japan who have joined forces in an international cooperation.
Like the dwarf planet Ceres, the asteroid that the scientists have targeted – Ryugu – belongs to the C class of carbon-rich asteroids. Observations from Earth suggest that water could be bound in the asteroid's regolith . In addition, the celestial body, named after a submerged palace described in Japanese mythology, belongs to the Apollo group of asteroids that cross Earth's orbit. Even though Ryugu will never pose a risk to Earth, learning more about this type of asteroid will be helpful to prepare for future defence missions. Hayabusa2 and MASCOT will cooperate as a team on this mission: Hayabusa2 will deliver the data to locate a suitable landing site for MASCOT. Then the lander will analyse the asteroid's surface and send information and data on the location of the soil samples that Hayabusa2 will eventually bring back to Earth.
Training for independence
The team at the DLR Microgravity User Support Center (MUSC) are training with a ground model of the lander to ensure that everything runs like clockwork. "Once on the ground, MASCOT will have to operate its four instruments as autonomously as possible," explains Christian Krause from the DLR Mascot Control Center. The vast distance from Earth simply does not permit control in real time, so the engineers must program software that the lander will need as 'knowledge' on its mission. In total, four instruments are fitted to the interior of the lander, which measures 30 by 30 by 20 centimetres. The instruments include a DLR radiometer and a camera, a French spectrometer and a magnetometer by TU Braunschweig. Together they are designed to analyse the mineralogical and geological composition of the asteroid surface and to measure its surface temperature and magnetic field.
After landing, MASCOT will deploy its sensors to ascertain whether it is standing upright on the asteroid surface, or whether it has ended up on its side. An internal swing arm can then automatically provide the right impulse to restore MASCOT to its correct position. After conducting the first measurements, the lander will use the swing arm to hop to the next measurement point. "We are planning as well as we can, although we know that we must expect the unexpected," says Christian Krause from DLR. Ryugu has a diameter of approximately 900 metres, and it only possesses around 1/60,000th of the Earth's gravitational field. One day lasts rapproximately 7.6 hours. But these values were measured from Earth, and the MASCOT team will have to wait until Hayabusa2 enters orbit around Ryugu to find out whether and how much their estimates deviate from reality.
Heat, measure, transmit
But first of all, the MASCOT team will put the lander through its paces until 16 July 2016. To do this, the team heated the lander back up to operating temperature following its lengthy travel through space at around -30 degrees Celsius. After switching the lander on, the first step will be to upload the correct command sequences for MASCOT to perform its health check. Even now, two years before arrival, each signal takes three minutes to travel in one direction. Therefore, the team at the LCC will have to wait approximately seven minutes after sending a message to MASCOT before they can expect a response.
In addition to the data that MASCOT will be asked to send on its own state of health, the engineers and scientists on the ground will also assess how well the four instruments are working and whether they show changes in parameters after their journey so far. Light-emitting diodes will be switched on, a photograph taken, and the swing arm carefully set in motion. "We cannot leave all this equipment unused for years. It needs to be activated repeatedly until it is time to land," emphasises Krause. "We also plan to test the interaction between the Hayabusa2 orbiter and the lander to make sure that everything is prepared for the science phase on the asteroid. When that time comes, MASCOT's data will be beamed via the orbiter to the Japanese Control Center and from there to its counterpart at DLR.
The team at the DLR MASCOT Control Center will make contact with its lander on several occasions before the mission reaches its culmination in October 2018. They will occasionally check the lander's state of health, as well as calibrate the instruments to ensure that the data can be analysed accurately after landing. The Control Room team around Krause has their eyes fixed firmly on the objective for the coming two years: "We only want to intervene after landing if something goes wrong – otherwise MASCOT will simply proceed autonomously with its scientific programme, without our help," says Tra-Mi Ho, Mascot Project Manager at the DLR Institute of Space Systems.
DLR's participation in the Hayabusa2 mission
The DLR Institute of Space Systems developed the lander and tested it under space conditions during parabolic flights, in a drop tower, on a shaker and in a thermal vacuum chamber. The DLR Institute of Composite Structures and Adaptive Systems was responsible for the stable structure of the lander. The DLR Institute of Robotics and Mechatronics developed the swing arm that MASCOT will use to 'hop' on the asteroid. The To the Institute's website managed the development of the MASCAM camera and the MARA radiometer. The asteroid lander is being monitored and controlled from the Microgravity User Support Center (MUSC) in Cologne.