Spitzer Oversight, day 2

Today was the second day of the Spitzer Oversight Committee meeting. Far and away the highlight for me was a presentation by Sean Carey (IPAC) about the overall health of the spacecraft and the imaging instrument. He showed the photometric throughput of the system as a function of time, which has been amazingly constant (sub-percent level), and yet showing a consistent and repeatable trend (of less than one mmag per year, ish?). He showed the bad pixel count, which has risen linearly with time, but only to a few hundred (and many of those are nonetheless still calibrated and useful pixels). He showed the astrometric wobble and drifts, associated with spacecraft thermal events. These are substantial, but changing, as the spacecraft goes through more and more extreme solar-angle events to downlink its data to the Deep Space Network. Spitzer is in an Earth-trailing orbit, so as time goes on, it has to point at worse and worse Sun angles to send its data home.

The latter point is very interesting: Carey showed that the batteries are still just as good as new, but that the spacecraft draws 11 A (yes, 11 Amps at 300 Volts!) on average (don't ask why), and when it is in downlink to Earth, the solar panels are not getting enough insolation to cover it. This leads to non-trivial scheduling in which the spacecraft must point near-orthogonal to the Sun vector for a while (hours) after downlink. This complexity is handled without issues by the non-trivial scheduling systems, and the overall spacecraft health is excellent. The mission can run until March 2019, when it is cut off, both by funding and by these Sun-angle issues. Carey also showed the long-term performance of the solar panels. This also declines linearly with time, but is easily within spec to keep the mission running (barring any severe micrometeorite hit). Knock wood!

It has been a great two days, with an absolutely great team, working on an absolutely great mission.

1 comment:

  1. Surely not 300 volts. I expect that was 30 Volts, giving 330 Watts power.