[Ibex-maneuver-engineering] Biased repointing vector for post-spindown
Mark Tapley
mtapley at swri.edu
Thu Jun 16 14:21:14 EDT 2011
All,
At 6:09 +0000 6/16/11, fair-play at comcast.net wrote:
>I commented out all the lines in the orbit 129 STF e vector is
>
>0.042788,0.92168,0.385584
I have generated another pointing vector to use after the spin-down.
The objective is to point the spin axis at where the sun was
2.5 days before the perigee happening 21-Jun at 14:43:31 Z.
Using ibex_rotate on ena, I think that vector is
RA: 87.219
Dec: 23.378
which is the same as
+0.044536,+0.916826,+0.396795
[tapley at ena ~]$ ibex_rotate -o -r 87.219 -d 23.378 -w ibex-sun -t
2011-06-19T02:43:31.000Z
Quaternion +0.000000,+0.000000,+0.000000,+0.000000
points axis +1.000000,+0.000000,+0.000000
towards ECI +0.044536,+0.916826,+0.396795
which is R.A. +87.219 Decl. +23.378
missing R.A. +87.219 Decl. +23.378 (ibex-sun)
error is R.A. +0.000 Decl. +0.000
for a total 0.000 deg
To get this as the result, I think we need to tell ADC to point at
RA: 86.6211699309974
Dec: 23.076131027330046
which is the same as
+0.0542216, +0.918386, +0.391954
A mathematica model showing what I think will happen is
attached, both as a mathematica notebook and as a .pdf printout of
the notebook.
The first part of the notebook shows a model of our repoint
to get to the Delta-V pointing. This should compare reasonably to the
standalone simulation Jim Bobbett described in his "Notes ... " word
document, Figure 3.
Note that to get this to match, I used a Control-loop delay
of 1.0 seconds (vs. the nominal single loop of 0.5 seconds). After
talking with Jim, this seems somewhat reasonable, given filter
(analog and digital) and processing delays.
The second part of the notebook shows what should happen
given the same ADC parameters but the target vector I suggest. The
orange dot shows the desired final spin vector, the blue dots show
the history of the maneuver, and the final line shows the error in
the pointing at the conclusion of the maneuver.
Comments are most welcome!
--
- Mark 210-379-4635
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