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Not quite finished yet. Will be done by Monday.


Optimisation Carried Out Prior to SWT 24

At the mini-SWT during SOWG13 SOC took the action to try and optimise the in situ data return for the cruise phase. Here we present the results of that optimisation, the optimised plan can be found on the SOOP Kitchen: MLP Feb 2020 as of SWT24.

The optimisation was carried out with the goal of minimising the amount of time that the instruments would have to operate with a reduced cadence or resolution of normal mode data, while maintaining a reasonable amount of burst mode and without filling the packet stores more than approximately 90%. Recall that selective downlink will be unavailable during the cruise.

The plan was constructed using only observations definitions that SOC are sure are accurate, i.e. no GENERIC type observations were used. Observations of duration 7 days were added to the plan as follows:

  1. Normal mode only at standard cadence and resolution throughout the cruise. This resulted in packet store overruns!
  2. Reduced cadence, "low rate" observations replace the default normal mode observations for periods subsequent to the first perihelion when the spacecraft was further than 0.8 AU from the Sun, apart from the end of cruise when the spacecraft will approach Earth.
  3. Some minutes per day of burst mode were added to each observation, commensurate with the default amount of burst mode for that observation type according to the observation definition.
  4. For RPW and MAG, an additional 8 hours of burst mode (EQUAL128 for MAG) per day were added during each of the Remote Sensing Checkout Windows to allow for detailed EMC characterisation of RS instrument operations.

The plan is then as follows:


The following observations were used, minutes per day of burst mode in brackets:


RateEPDMAGRPWSWA-EASSWA-PASSWA-HIS
Nominal (R<0.8)EPD_CLOSE_BURST (15)MAG_NORMAL_BURST (120)RPW_DEFAULT_COLD (10)SWA_EAS_NOMINAL_BURST (10)SWA_PAS_NORMAL7_BURST7 (5)SWA_HIS_NORMAL_BURST (5)
Low (R>0.8)EPD_FAR_BURST (5)MAG_LOW_BURST (30)RPW_LOW1_COLD (10)SWA_EAS_LOW_BURST (10)SWA_PAS_NORMAL11_BURST11 (5)SWA_HIS_LOW_BURST_HALF (5)

Note that for RPW and MAG different observations were used during RS Checkout Windows.


Downlink was shared pro rata between the instruments according to EID-A allocations. This results in the following output data rates and packet store fill states:
EPD MAG RPW SWA
There is still some limited scope for increasing SWA data rates in the good periods.

Scope for Further Optimisation & Target Fill states at the End of LTP 01

Packet stores only start to fill during the first RSCW (17 June 2020) so there is scope for some additional burst mode up to and including the first perihelion. Exact amounts cannot be calculated without knowing the exact times of the communications passes and the true spacecraft trajectory, however the unused downlink drops dramatically as the spacecraft approaches perihelion so the vast majority of this will have to be earlier. Some burst can be added during LTP.


If significant additional burst mode is deemed to be desirable during the first perihelion, this could be achieved through increasing the time spent in low rate mode later, or indeed through reducing the amount of burst mode scheduled after 1 July. Conversely, because SSMM stores start to fill so late in the planning period, there is almost no scope to reduce data production during LTP01 in order to increase production later during the cruise and hence minimise the amount of time in low rate mode. However, Should the SWT decide to further minimise the amount of time in Low rate mode later in the cruise. This can be accomplished by sacrificing burst mode. For example, according to the currently scheduled observation definitions, the following tradeoffs are possible.

  • EPD
  • MAG: Sacrificing 360 minutes of BURST64 buys 1 day to be changed from LOW to NORMAL
  • RPW
  • SWA

Similarly, 

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