[Isocops] Static Z Rate Discussion on ISOC Call

[Reno, Michelle]

Let's discuss this, from Ryan :


Somewhat related, as I mentioned on the call yesterday, I still think there’s an issue with setting (or, more specifically, not setting) the static Z rate following a sun maneuver at apogee. See the following scenario from a little over a year ago (I just picked a random month and looked at the trending data):

[X]

As you can see, this was a normal sun pointing maneuver with no spin-down (things are worse with a spin down). When the maneuver happens the star tracker is still the only thing used by the estimator but as soon as the static Z rate is added to the estimator the spin rate (and therefore spin pulse) is decidedly wrong, in 2 different regimes, for what could be several days (it’s not as long in this case).

So my suggestion is that the apogee contact be taken shortly after the sun maneuver. If the percent valid is high (i.e., static Z rate is not being used currently) then go ahead and set the static Z rate per the estimator. Otherwise, use the attached spreadsheet to take a guess at the new static Z rate so that you’re more likely to get an easily-despinnable solution.

You enter the before and after thruster counts and if there was no spin down then you estimate the new static Z rate given the number of thruster pulses. If there was a spin down then it asks for a collection of accel data (intended to be performed during the same pass) and suggests a spin rate based on that data. Because you’d only be using the accel data after a spin down you expect to be in the range where accel data is a useful predictor of actual spin rate. Coarse sun sensors could be used as well, but this tool doesn’t go there because it doesn’t assume that you have a high enough data rate to get usable CSS data.

-Ryan



--
Chelle Reno
IBEX Mission Operations Manager
Juno/JADE Deputy Project Manager
Austin Mission Consulting
(210) 478-7337
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