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The purpose of this page is to collect ideas about cruise phase science that the in situ instruments could do, and provide information about trajectory, telemetry return etc. that will be useful in planning the cruise phase.

Cruise Phase Trajectory

  • Orbit plots for the February 2019 Trajectories (including cruise phase) can now be found here: Orbit Plots
  • CReMA 4.0 and associated OEM files and SPICE kernels are here: Solar Orbiter SPICE Kernels

About the Feb 2019 Cruise

For the first 18 months we stay relatively close to Earth and therefore have good comms. This is also handy for cross-calibrating EPD with other spacecraft. The next year is terrible for comms.

During cruise we will have 3 comms passes a week, plus extras for the remote sensing checkout windows. It's still not completely clear what the comms performance per pass will be, but based on current information we're assuming it won't be significantly worse than during nominal phase, this means for in situ operations in cruise we'll get about 35% of the equivalent NMP/EMP rate for the entire payload (I think this is still quite a conservative estimate). Recall the total EID-A rate for in situ is 25 kbps

The white/grey shading on the plots marks when we'll be able to generate at the following rates without significantly filling the SSMM, so this represents a lower limit on data rate. As usual with SSMM usage and data latency the devil is in the details so consider this a rule of thumb.

> 0.35 * EIDA RSW Instantaneous Rate = 42 kbps 
> 0.35 * EIDA Orbit Average Rate = 14.5 kbps
> 0.35 * EIDA In Situ Only rate = 8.75 kbps
< 0.35 * EIDA In Situ Only rate = 8.75 kbps

These figures represent what will be available to the in situ payload. Downlink for RS checkouts is handled separately.

We're working on a full downlink analysis for cruise so should be able to refine these numbers soon and create an initial telemetry corridor for the entire cruise phase.

We've tentatively scheduled the remote sensing checkout windows during the cruise, though these are likely to change.

Comms roll information isn't there yet, I'll update that as soon as I can. For communications roll strategy we're assuming the following:

  • Outside of RS checkout windows, when necessary, we roll for the pass then roll back to nominal attitude.
  • Inside of RS checkout windows, if comms rolls are needed we maintain a stable roll angle for the 7 days (any RS calibration rolls notwithstanding), then return to nominal attitude at the end of the window.

The exact dates of MTP periods will change so they contain an integer number of STP periods. STP periods in cruise are likely to be 3 weeks, not 1 week.

Planning for the First E2E Test

As mentioned at SOWG 9, the first E2E test will cover a six month planning period during cruise, that contains at least one checkout window. We've decided to plan the period Jan - Jul 2020 (i.e. MTP 3) from the Feb 2019 In Trajectory. For remote sensing instruments we'll plan one checkout window. For in situ we'd like to plan the whole six months at LTP level but will only expect one week's worth of IORs for the test proper. The period actually contains 3 checkout windows (preliminary locations) so we'd like to plan the in situ operations as if all three checkouts were happening.

To set some boundary conditions and determine exactly how much telemetry would be available to you we need to do the equivalent to mission level planning. As a first iteration we suggest the following:

  • Ensure the SSMM stores are empty at the end of the planning period to prepare for the next year of bad downlink.
  • TBC pending the more detailed downlink analysis this means generating on average 42kbps total for the in situ payload until ~8 June, 14.5kbps thereafter.
  • Outside of RS checkout windows data are split pro rata between the in situ instruments.
  • MAG calibration roll scheduled on or around Tuesday 31 March, exact times TBC depending on the pass schedule.
  • Inside of RS checkout windows, MAG and (maybe) RPW get more so they can burst throughout for EMC characterisation.
    • For the Extra Cold and Cold windows this could mean giving MAG 13 kbps, RPW 26 kbps and SWA and EPD  as much as we can support so that the stores are empty on time (this will mean focussing generation in the windows and reducing rates a bit after each window). Scope TBC pending downlink analysis.
    • For the warm window (which is the one we'll plan for the RS instruments) more careful planning of burst modes during specific activities and tradeoff against normal mode will be needed. Details TBC pending downlink analysis.
  • Recall that the SSMM will not be configured to support selective downlink at this point.

Any comments or suggestions welcome!

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