Reduced ground station allocation compared to the baseline and our predictions for LTP12 and LTP13 means that SOC were not convinced that the level of data return predicted in Mission Level Planning of NMP Segment 2: Initial Analysis is in fact possible. Here we present a more refined analysis taking into account the output of LTP11 long term planning (i.e. the amount of data in the SSMM at the end of LTP11) and the confirmed pass schedule for LTP12 and LTP13. Note this will not be as accurate as the simulations done during the long term planning process since the proportion of the downlink reserved for spacecraft housekeeping and other MOC activities is calculated differently, but it is more representative than the mission level planning simulations performed to date.
Simulating the Current Instrument Timelines Using the Realistic Pass Schedule
If no data generation is removed from the plan and a simulation run with the current timelines (4 and 5x EID-A in RSWs, 0.5xEID-A synoptics, in situ in high rates within 0.8 AU), the plan is not feasible. A total of 32594 GiB are lost due to SSMM overruns as follows:
The amount of spare space in the SSMM at its peak fill state is ~14000 MiB so these overruns cannot be solved by reallocating the downlink between instruments to handle peaks of generation.
Reduced Synoptics, Realistic HIS generation
If synoptics are reduced to the level planned for the end of LTP11 throughout LTP12 and before the start of the RSWs in LTP13, and HIS high rates reduced to a more realistic estimate of current data generation (2x EID-A), the plan can be made to work with no overruns. However, this requires extreme reallocation of downlink between instruments and results in SSMM fill states of 95% for some stores (notably EUI and Metis). In this situation the loss of one pass would result in overruns, and there would be no scope for adding any e.g. calibration campaigns at LTP. SOC do not consider this feasible.
Reduced Synoptics, Realistic HIS generation, RSWs all with 4x EID-A Volume
This represents a slight reduction in RSW generation when compared to the initial analysis but does result in a feasible plan, with sufficient margin for mission level planning. It does still require extreme reallocations of downlink between instruments, to the extent that data latencies are uneven. This is particularly the case for SWA, because in order to make the plan work we need to use the SSMM as efficiently as possible. This means filling the SWA store to 80%. Given post-launch SWA data generation is a lower proportion of the total than assumed pre-launch, their SSMM store is oversized, and thus if we need to let it fill to this extent, they necessarily will receive less downlink during constrained times and have a higher data latency.
Simulation results below. Note that the downlink allocation via the TDR is not optimised at this point so fill sates and latency could be equalised somewhat, but not to the extent that everything is even.
SOC consider this feasible, with some small margin for increased generation at LTP should our assumptions about the downlink turn out to be conservative.
Comparison with LTP09 RSWs
The plan currently approved by the SWT is to "do the same as" the remote sensing windows from LTP09 in LTP13. At mission level, during LTP09 We proposed 2xEID-A 3x EID-A and 3x EID-A as the baseline data generation in the remote sensing windows, together with 0.5X EID-A synoptics. What was actually planned during the remote sensing windows at LTP generated 72213 MiB, compared to a total EID-A volume for 3 RSWs of ~28000 MiB. Note this does not include PHI (and STIX) data that were flushed later than the 30 days of remote sensing window. So with the reduced downlink and reduced synoptics, SOC believes a similar programme is also feasible, while leaving some margin that can be assessed at LTP.
Thus, our proposal for H2 2023 is the following:
- LTP11-like synoptics in LTP12 and until the start of the remote sensing windows in LTP13. Higher synoptics after the RSWs
- In situ high rates within 0.8 AU (i.e. change on 20 August). Note we assume functional maximum generation for HIS of 2 x EID-A
- A remote sensing window programme equivalent in TM generation to LTP09 as planned at LTP.
This should leave margin for calibration activities, small increases in generation here and there or spending downlink to even out latency, the scope of which will be clearer once we receive the formal planning products for LTP12 and LTP13 from MOC.