[Isocops] [Ibexlo] CAR : New P/L DESCENDING commands
Eberhard Moebius
eberhard.moebius at unh.edu
Mon Jun 28 18:57:16 EDT 2010
Dear Chelle:
Thanks! I commend your wise decision. Thanks for asking! That prompted me to go back and dig out the plot and what I did back then.
Regards
Eberhard
Eberhard Möbius
Space Science Center and Department of Physics
Department Chair
University of New Hampshire
Morse Hall, 8 College Road
Durham, NH 03824
Phone: 1 603 862 3097
Fax: 1 603 862 0311
On Jun 28, 2010, at 6:40 PM, Reno, Michelle wrote:
> Hello All,
>
> Eberhard pointed out that the actual sun angle margin will be closer to 0.23 when you take into account a 2-D sun. See below.
>
> Given this I would like to upload new DESCENDING commands and delete the ones onboard. Mark, please generate an STF that has us in HVSTANDBY by a predicted angle of 7.4 degrees. Attached is a partial CAR with the commands to be deleted and a spot for the ATS filename - Tim, please edit and redistribute.
>
> This orbit we will descend early. At an ISOC telecon we should discuss again (with feeling, as Nathan says) the reason for the prediction error prior to the burn and the actual off sun pointing planning limit.
>
> Thanks,
> Chelle
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Chelle Reno
> Austin Mission Consulting
> 106 E. 6th St. Ste. 939
> Austin, TX 78701
> (512) 704-3394 (o)
> (210) 478-7337 (c)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> From: Eberhard Moebius [mailto:eberhard.moebius at unh.edu]
> Sent: Mon 6/28/2010 4:45 PM
> To: Reno, Michelle
> Cc: Eberhard Moebius
> Subject: Re: [Ibexlo] Quaternions post pointing burn
>
> Hi Chelle:
>
> The maximum angle is 8.12o. Please see the figure attached, which I produced at the time of the design. We raised the height of the cover over a certain angular range on the Sunward side so that the angle is guaranteed even if the spin axis is off in ecliptic latitude.
> However, it just occurs to me that the actual safe range for partial illumination by the Sun is only 7.87o (8.12 - 0.25) adjusted for the size of the Sun's disk in the sky of 0.5 degrees. That is why we went with 8 degrees + in the first place. SO, we are a little closer than I said, 0.23 degrees to the limb of partial illumination!
>
> As long as we stay away from that we are safe, but we shouldn't get closer. There is no additional margin beyond that, except that a little partial illumination will probably not immediately lead to a big jump in something, but we never tried that!!
>
> We should definitely take a look whether anything is changing in the sensor HK data when we approach this extreme angle. What has been the maximum that we actually went to up to now?
>
> With best regards
> Eberhard
>
> Eberhard Möbius
> Space Science Center and Department of Physics
> Department Chair
> University of New Hampshire
> Morse Hall, 8 College Road
> Durham, NH 03824
>
> Phone: 1 603 862 3097
> Fax: 1 603 862 0311
>
>
> From: Reno, Michelle
> Sent: Mon 6/28/2010 4:06 PM
> To: Mark Tapley; isocops at lists.sr.unh.edu; ibexhi at lists.sr.unh.edu; ibexlo at lists.sr.unh.edu
> Cc: michelle.reno at swri.org
> Subject: RE: Quaternions post pointing burn
>
> Thanks Mark. I agree we should leave the current DESCENDING times; 7.64 degrees off sun pointing is higher than desired (7.5 degree planning limit) but less than the actual max limit of 8.0 degrees.
>
> Hi or Lo, please speak up by noon 6/29 if you are uncomfortable with this. The only planned opportunity to change these is the apogee contact early on 6/30.
>
> Chelle
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Chelle Reno
> Austin Mission Consulting
> 106 E. 6th St. Ste. 939
> Austin, TX 78701
> (512) 704-3394 (o)
> (210) 478-7337 (c)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> From: Mark Tapley [mailto:mtapley at swri.edu]
> Sent: Mon 6/28/2010 2:05 PM
> To: isocops at lists.sr.unh.edu
> Cc: michelle.reno at swri.org
> Subject: Quaternions post pointing burn
>
> All,
> Chelle asked me to look at the pointings subsequent to
> delivery of the quaternion resulting from the sun-pointing burn.
>
> From the Goat Herder orbit 82 which Tim emailed:
>
> Q1 -0.15279000 ActNor.EstInrToBdy[0]
> Q2 -0.52037700 ActNor.EstInrToBdy[1]
> Q3 -0.78616500 ActNor.EstInrToBdy[2]
> Q4 0.29632300 ActNor.EstInrToBdy[3]
>
> Checking how close the maneuver was to pointing at the sun:
>
> [tapley at ena ~]$ ibex_rotate -o -z
> -0.15279000,-0.52037700,-0.78616500,0.29632300, -w ibex-sun -t
> 2010-06-27T10:55:12.782Z
> Quaternion -0.152790,-0.520377,-0.786165,+0.296323
> points axis +0.000000,+0.000000,+1.000000
> towards ECI -0.068163,+0.908755,+0.411726
> which is R.A. +94.290 Decl. +24.313
> missing R.A. +96.080 Decl. +23.340 (ibex-sun)
> error is R.A. +1.791 Decl. +0.974
> for a total 1.906 deg
>
> this agrees with the Goat herder, which says 1.901 degrees.
> Hmmm, not very close.
> If we look at the situation at the time of descending macros,
> taking that time from the STF (looking at the last of the commands),
>
>
> [tapley at ena ~]$ ibex_rotate -o -z
> -0.15279000,-0.52037700,-0.78616500,0.29632300, -w ibex-sun -t
> 2010-07-03T15:10:51.000Z
> Quaternion -0.152790,-0.520377,-0.786165,+0.296323
> points axis +0.000000,+0.000000,+1.000000
> towards ECI -0.068163,+0.908755,+0.411726
> which is R.A. +94.290 Decl. +24.313
> missing R.A. +102.498 Decl. +22.926 (ibex-sun)
> error is R.A. +8.209 Decl. +1.387
> for a total 7.647 deg
>
> 7.647 degrees should still be OK, though close. I would say let it
> ride, unless -Hi or -Lo teams are not happy with that big an angle.
>
> --
> - Mark 210-379-4635
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