Descent into the unknown: MASCOT starts the final countdown for its asteroid landing

"In the hours leading to the separation, the Japanese Hayabusa2 space probe will be operating at a relative height of only 60 metres above the asteroid’s surface," explains Tra-Mi Ho, Project Manager of the German-French lander MASCOT at the DLR Institute of Space Systems in Bremen. "Just before the landing, Hayabusa2 will go into a freefall phase, at the end of which – after just 2 minutes and 20 seconds – MASCOT will be separated." Once the separation is complete, MASCOT will fall, completely unpowered, tumbling down onto the asteroid. The low gravitational pull will gently accelerate the lander to a speed of up to 20 centimetres per second. By comparison, normal walking speed is seven times faster. Five to 10 minutes after separation, MASCOT will already touch down on the selected landing zone on Ryugu for the first time, and then bounce several times before coming to rest.

"We are anxious to see whether MASCOT will slide out of its supporting frame smoothly", as we have planned and tested so extensively,” Ho says. “A smooth descent is crucial, otherwise MASCOT will bounce back up from the asteroid like a rubber ball due to the low gravitational pull, and be lost in space.” In addition, the researchers will be watching with excitement in the minutes and hours after touchdown, as it is impossible to predict how MASCOT will move on the surface according to the laws of physics alone. "We do not know in which direction and for how long MASCOT will bounce around after the initial touchdown, and we are of course hoping that it will not end up on terrain that is too soft or get stuck in a crevice, where it could not straighten itself," explains DLR's MASCOT Operations Manager Christian Krause. "However, we are optimistic because we ran through numerous scenarios on the ground and have sent the corresponding command sequences to MASCOT."

The lander will operate autonomously while on the asteroid and must operate robustly using the prepared command sequences, so that all of the measurements can be carried out according to plan. During the mission, MASCOT will decide how and when to initiate these sequences. An in-built autonomy manager will then determine when MASCOT has come to rest and can start to conduct measurements.

Landing and jumping between 30 metre-high boulders

It is planned that MASCOT will land in the southern hemisphere of the 950-metre-diameter Ryugu asteroid, at 315 degrees east and 30 degrees south. This location has a favourable day and night cycle, and a temperature range of around +47 to –63 degrees Celsius, which is neither too hot nor too cold for the lander. The rocks around the landing site are not too big, but there are numerous boulders measuring up to 30 metres in height, which present an additional challenge.

After MASCOT has uprighted itself autonomously, if necessary, and carried out the initial measurements autonomously for a few hours, the scientists in the MASCOT control centre in Cologne will decide whether the lander should hop to another measuring point using its built-in swing arm. "In the final tests before the landing, we estimated that we would probably only let MASCOT perform one jump of less than 10 metres, in order to preserve the battery life and ensure the optimal execution of the measurements and data transfer," Ho explains. "What is more, recent images suggest that the surface of Ryugu has a rather uniform composition everywhere, so we do not need to perform big jumps."

First images after a few days

A total of four instruments are installed within the 30 x 30 x 20 centimetre lander, which weighs only 10 kilograms. A DLR radiometer and camera, together with a spectrometer from the Institut d'Astrophysique Spatiale and a magnetometer from TU Braunschweig, are set to examine the mineralogical and geological composition of the asteroid’s surface and gauge its surface temperature, as well as the asteroid's magnetic field. Upon landing on Ryugu, MASCOT will only be reachable during a few time windows, whereby sending a command to the lander and receiving a response back on Earth will take more than 30 minutes. Therefore, MASCOT will be left largely to its own devices during the 16-hour-long measurement operation planned on the surface. As the orbiter will also be generating huge quantities of data during this period and the bandwidth of the link to Earth is relatively low, only a few status updates from MASCOT will be transmitted to the control centre in Cologne. The scientific data and images are expected to arrive a few days after the landing, at which point they will be analysed.

About the Hayabusa2 mission and MASCOT

Hayabusa2 is a

Japanese space agency

(Japan Aerospace Exploration Agency; JAXA) mission to the near-Earth asteroid Ryugu. The German-French lander MASCOT on board Hayabusa2 was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and built in close cooperation with the French space agency CNES

(Centre National d'Etudes Spatiales). DLR, the

Institut d'Astrophysique Spatiale

and the

Technical University of Braunschweig

have contributed the scientific experiments on board MASCOT. The MASCOT lander and its experiments are operated and controlled by DLR with support from CNES and in constant interaction with the Hayabusa2 team.

The

DLR Institute of Space Systems

in Bremen was responsible for developing and testing the lander together with CNES. The

DLR Institute of Composite Structures and Adaptive Systems

in Braunschweig was responsible for the stable structure of the lander. The

DLR Robotics and Mechatronics Center

in Oberpfaffenhofen developed the swing arm that allows MASCOT to hop on the asteroid. Das

DLR Institute of Planetary Research

in Berlin contributed the MasCam camera and the MARA radiometer. The asteroid lander is monitored and operated from the MASCOT Control Center in the

Microgravity User Support Center (MUSC)at the DLR site in Cologne.