[Isocops] Orbit 109/110 Sun Precession maneuver

Mark Tapley mtapley at swri.edu
Fri Jan 21 10:57:48 EST 2011


At 1:00 PM -0600 1/19/11, Reno, Michelle wrote:
>Hello,
>
>Tim verified in last night's 0600 pass that the sun precession 
>maneuver executed and the spacecraft is nominal. We are still in a 
>100% outage so two tasks remain:
>1) verify the off-sun pointing angle is less than 7.25 when the 
>payload descends (info from 1/21 0230 pass), and

We are good to go.

I tried both  the quaternion 
0.41869900,0.70158400,-0.28378800,0.50193100 (yellow) and the "spin 
axis" vector 0.466650,-0.818519,-0.335059 from Tim's email (purple) - 
same answer (good).

Sun angle at the 15 Re descending crossing on the 26th very near 
all-balls would be a problem:

[tapley at ena ~]$ ibex_rotate -o -u 0.466650,-0.818519,-0.335059 -w 
ibex-sun -t 2011-01-26T00:00:15.740Z
Quaternion    +0.000000,+0.000000,+0.000000,+0.000000
  points axis  +1.000000,+0.000000,+0.000000
  towards ECI  +0.466650,-0.818519,-0.335059
  which is     R.A. +299.688 Decl. -19.576
  missing      R.A. +307.852 Decl. -18.920 (ibex-sun)
  error is     R.A.   +8.164 Decl.  +0.656
  for a total  7.734 deg

But at the time we have the PL coming down 13 hours earlier on the 
25th we will be OK:

[tapley at ena ~]$ ibex_rotate -o -u 0.466650,-0.818519,-0.335059 -w 
ibex-sun -t 2011/01:25:10:32:44Quaternion 
+0.000000,+0.000000,+0.000000,+0.000000
  points axis  +1.000000,+0.000000,+0.000000
  towards ECI  +0.466650,-0.818519,-0.335059
  which is     R.A. +299.688 Decl. -19.576
  missing      R.A. +307.253 Decl. -19.067 (ibex-sun)
  error is     R.A.   +7.565 Decl.  +0.509
  for a total  7.156 deg

All clear on that issue, I believe.


-- 
						- Mark     210-379-4635
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Large Asteroids headed toward planets
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