Mission simulator to be revamped after 20 years

A TDE activity with Telespazio VEGA in Germany and a consortium of other companies has established a plan for revamping the software used to simulate different space and ground segment activities.

Currently, the simulations are used to train the operations team at ESA’s European Space Operations Centre (ESOC) for different satellites and missions. The simulations can introduce errors and scenarios to make sure the team are prepared for any possible eventuality.

The current infrastructure is comprised of ~3 million lines of code, with systems originally built around twenty years ago. With upgrades, a re-design and changes to the operating system, it has served its purpose well. But now, both space craft and computing systems have improved to such a level the current simulator is beginning to reach a point where its performance cannot be improved any further.

In particular, the simulator was struggling on new missions coming forward to replicate scenarios in real time (where one second in the simulation is the same as one second in real life). Once a  simulation is unable to imitate reality it becomes obsolete.  

The activity developed recommendations for design changes and a series of nine prototype systems to see how much functionality could be improved and whether it was necessary to rewrite all of the code, or whether parts of the system could be licensed from suppliers running similar simulations. The prototypes were able to demonstrate simulation models executing anywhere from three to 25 times faster than the current system. 

Quickly it became clear that the existing infrastructure needed more than just polishing. Especially when it came to one specific technology – the emulator. A key element inside an operational simulator is the on-board software emulation. Often, a simulation will use a mission’s real on board software in the core simulation while other parts of the spacecraft are being modelled in a functional manner. This enhances the overall realism of the simulation and allows for further verification and validation of the on board software. This is executed by a microprocessor software emulator; the emulator is the most computationally intensive model within the simulation environment.

If the emulator runs slowly then everything else in the simulation will run slowly or not work. The activity included a trade off analysis of developing the current emulator vs rewriting the entire emulator vs using a commercial emulator. The study found that in terms of performance, instead of rewriting the code it may be more efficient to use a commercially available emulator in a future simulator.

Each of the nine prototypes provide different functionalities to the future simulator. One, called Digital Twin, prototyped replicating the simulator (on ground) with a copy of the flying spacecraft status for a particular subsystem (thermal). This will enable the operators to compare the evolution of the real spacecraft to the theoretical evolution and also allows profiling of failure cases and recoveries with minimal setup.

The entire simulations infrastructure has been incrementally improved slowly over time but rewriting from scratch is more efficient. As such, the other 2 million lines of code are being re-written internally with the support of external companies and the first changes are now being implemented. 

T709-502GI completed in 2019 but the final documentation was received in September 2020.