Space | 21. September 2018 | posted by Michael Maibaum

What will happen in the MASCOT control room before and during the landing?

Michael Maibaum vor jeder Menge Daten
Credit: DLR (CC-BY 3.0)
Lots of data: The MASCOT teams receive the lander's data via the Japanese Hayabusa2 space probe

MASCOT will begin its main and also final mission phase on 3 October 2018. Early in the morning, at 03:58:15 local time, MASCOT will separate from Hayabusa2 and land on the surface of Ryugu a few minutes later. It will already begin to conduct scientific measurements before starting its descent, and will continue doing so after landing, right up until its battery runs out. Standing on the surface, MASCOT will observe its surroundings and carry out various measuring sequences, depending on whether it is night or day at the landing site at the time. A day on Ryugu is only 7:38 hours, meaning that MASCOT will land in the early afternoon, local asteroid time.##markend##

In order for MASCOT to be able to carry out its scientific measurements, the MASCOT Operations Team has undertaken many months of intensive preparations at the control centre in Cologne. The requests and inputs of the scientific and MASCOT system teams have been analysed, coordinated and then converted into appropriate command sequences, before being fully tested on the ground reference model of MASCOT.

After these preparations have been completed, a final overall test will be carried out on the ground reference model. These tests will be followed by the Operations Team from the MASCOT control centre. In doing so, not only the command sequences, but also the control centre computers and their configurations are tested. Additionally, the Operations Team will use this test as an extra training session and as a final verification of all tools and monitoring software to be used during the landing.

Credit: DLR.

All of the command sequences can now be uploaded to MASCOT. For this purpose, a special event will be carried out a few days before the landing. As with all of the previous flight events, the Operations Team will follow and monitor the execution from the control centre, intervening if necessary. The actual commands are issued by JAXA, as is always the case for Hayabusa2, but all of the required command sequences have previously been created and tested in Cologne.

MASCOT's status and the progress of its activities will be monitored by the Operations Team, based on telemetry that MASCOT transmits to the ground via Hayabusa2. This telemetry  can be roughly divided into three categories: events, housekeeping and scientific data. Events are generated by special actions or conditions, so they do not occur on a regular basis. Housekeeping data, in contrast, are generated at regular intervals and show the current condition of a unit, with its configuration and status. Housekeeping data include current and voltage readings, temperatures, status bits and modes, and pressure. Data from a unit are only generated if the unit is switched on. Housekeeping data from systems are generated on an ongoing basis. These include data from the power systems, thermal control and system software. Scientific data are generated only by scientific units and contain data such as images, magnetic field values, temperature ranges and frequency spectra.

Only housekeeping data and events will be generated and sent to the control centre during the flight event for uploading the on-asteroid sequences. Some of the Operations Team members will monitor MASCOT's state using the housekeeping data, while others will focus on the events in particular, as these report the correct execution of the commands, the storage of the sequences in the corresponding memory areas and, most notably, register checksums that need to be exactly right for the upload to be deemed a success.

The actual flight event for the landing begins with a further battery depassivation. This is necessary in order to get the battery ready for use after the separation from Hayabusa2, having been in storage ever since MASCOT’s launch. Following that, a final check of all units and systems will be carried out. Serious problems could lead to aborting the separation, so there is the possibility of making repairs, although in this phase of the mission this can only be done by uploading software or during operations. Both activities again generate housekeeping data and events, which are continuously downloaded by the Operations Team for evaluation and monitoring. If the results are positive, the Operations Team will issue a "Go" to the Hayabusa2 team to initiate the descent of Hayabusa2.

Housekeeping data and events from Hayabusa2 and MASCOT are continually downloaded by their respective control centres throughout Hayabusa2’s entire descent phase. A special evaluation of all systems will be carried out about one hour before the planned separation of MASCOT, and the MASCOT Operations Team will issue another "Go" to the Hayabusa2 Team to initiate the separation procedure of MASCOT. By this point, MASCOT will already be at the temperature required for separation, the MARA and MAG science units will have begun conducting measurements, and the software will have been been set to 'Wait for separation' status.

Credit: DLR.

From this point onwards, the Operations Team and all of the other MASCOT teams can only sit back and watch, as the actual separation is performed autonomously by Hayabusa2. The orbiter will continue to descend until it detects that it is about 60 metres from the asteroid’s surface. It will then begin its freefall phase, lasting 2 minutes and 20 seconds, by the end of which MASCOT will have separated. MASCOT will then descend to the surface on its own and will autonomously determine whether it has landed upright. If not, it will automatically initiate an uprighting sequence, before conducting the pre-programmed scientific measurements. As the orbiter will also be generating huge quantities of data during this phase, and the bandwidth of the link to Earth is relatively low, only a few events and housekeeping readings will be received from MASCOT. The Operations Team must use these to determine the lander's status and the progress of its activities. During this phase, MASCOT will, however, continue to send its scientific data to Hayabusa2, but for the time being it will simply be cached there. The scientific data generated by MASCOT will only be downloaded over the next few days. By then, the individual teams will be back at their workplaces, where they will be able to download the data from the control centre server and start to analyse it.


About the author

Michael Maibaum is a member of the operations team in the MASCOT project and is responsible for the thermal system in particular. to authorpage

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