[Isocops] Goat Herder for Sept 15 2018

Mon Sep 17 09:31:42 EDT 2018

Those numbers sound fine to me. Again with the knowledge that we’ll have to change them again. Probably in another 2 years or so:

[cid:image004.png at 01D44E64.A29C10A0]

The solid black line is my addition showing a trend for the minimum values. The telemetry values vary by intervals of 0.105 psi, so everything in this plot is a significant variation as opposed to random noise at the bit level.

I’ll point out that the initial “mini-panic” on this one was because I looked back at the previous month’s data and never saw a number below 106, but in looking at the longer term data above, it turns out that we did see some numbers <106 the month before that. It’s really just a combination of timing of when various heaters throughout the propulsion system turn on and how that makes propellant and gas of varying temperatures flow around the system, and that combination just didn’t happen to occur last month whereas it did the month before as well as this last weekend.

So if we like the strategy we used last time around that led to this “mini-panic” a few years later—as preferable to not having a yellow to note a slow leak—then we can go ahead and apply the same strategy again and go with 104/102 as suggested. We should probably plan to change them at regularly scheduled intervals. We lose about 0.5 psi per year, so maybe we should proactively plan to drop the limits by another psi every 2 years.

There’s no hurry to change the limits so long as we understand what they mean. It’s just a yellow limit. Doesn’t cause anything to happen. We should just do it sooner rather than later so we don’t become too accustomed to seeing and not caring about yellow limit violations.

-Ryan

From: Angold, Nigel G. (GSFC-444.0)[Johns Hopkins University Applied Physics Lab] [mailto:nigel.angold at nasa.gov]
Sent: Sunday, September 16, 2018 1:01 AM
To: Bobbett, James <James.Bobbett at OrbitalATK.com>; Bret Hautamaki <bhautama at gmail.com>; Chubin, Eric <Eric.Chubin at OrbitalATK.com>; Colin Joyce <colin.joyce at unh.edu>; Dreyer, Sean <Sean.Dreyer at OrbitalATK.com>; Fleming, Ed <Ed.Fleming at OrbitalATK.com>; IBEX Operations <ibexops at gmail.com>; IBEX-FDG <IBEX.fdg at applieddefense.com>; ISOC at New Hampshire <isocops at lists.sr.unh.edu>; Cavallo, John <John.Cavallo at OrbitalATK.com>; Ken Fairchild <fair-play at comcast.net>; Lockwood, Robert <Robert.Lockwood at OrbitalATK.com>; Tyler, Ryan <Ryan.Tyler at OrbitalATK.com>; Wesley, Sheral <Sheral.Wesley at OrbitalATK.com>; Regiec, Thomas <Thomas.Regiec at OrbitalATK.com>; Zirnstein, Eric <ezirnstein at swri.edu>; Reisenfeld, Daniel Brett <dreisenfeld at lanl.gov>; Perry, Timothy <Timothy.Perry at OrbitalATK.com>
Subject: EXT :Re: Goat Herder for Sept 15 2018

The tank pressures were up at ~106 psi during tonight’s contact. The +X tank pressure yellow limit (106.3 psi) was toggling but the -X pressure was now above 106.3 psi. Tim dumped the back orbit data and plotted the prop temps and tank pressures for the last day or so (see attached). The pressures look like they track the tank temps pretty well so I suspect that the -X tank pressure yellow limit violation that we saw earlier today coincides with a period where heaters were off.

In any case, both tank pressures are close and stable i.e. within the usual variation range, and at around the yellow limit. But since the tank pressures continue to slowly drop, it’s time to change the limits. The 2016 study suggested 104 psi for the yellow limits and 102 psi for the red limits which sounds good to me.

Comments?

Thanks,
Nigel

All,
    The support was nominal for CMD and TLM. The Inertial maneuver was successful. We did have a yellow low limit violation. The Minus X Tank pressure (ACT ActSoh.TankPressureMX) is 105.7 PSI. The current yellow low limit is set at 106.3. Razor #I100-647 “Minus X Tank Pressure is Low Yellow” has been written. Ryan Tyler has been contacted and a follow on contact has been scheduled for tonight @ 02:30gmt on Haw02.

Q1 -0.52422300 ActNor.EstInrToBdy[0]
Q2 -0.43584200 ActNor.EstInrToBdy[1]
Q3 0.47773800 ActNor.EstInrToBdy[2]
Q4 0.55407400 ActNor.EstInrToBdy[3]
GPS sec 1221040882.000 ActNor.EstTime
MPS Diff 0.567
MPS Cmd Vector X -0.984344000
MPS Cmd Vector Y 0.165517000
MPS Cmd Vector Z 0.060596000
CSS Angle TLM 0.773037
CSS Sun-Pointing Angle 1.546074
  10 Sept 18 @1600
CSS Angle TLM 0.395648
CSS Sun-Pointing Angle 0.791296
  15 Sept 18 @1000
Pre-Burn
Thruster 1 5264 10 Sept 18 @1600
Thruster 2 5136
Thruster 3 5680
Thruster 4 5808
Post-Burn
Thruster 1 5536 15 Sept 18 @1000
Thruster 2 5408
Thruster 3 5968
Thruster 4 6096
Number of Pulses
Thruster 1 272
Thruster 2 272
Thruster 3 288
Thruster 4 288
Thruster Pairs
Thruster 1 & 2 544
Thruster 3 & 4 576

Timothy E. Perry
CRS, IBEX, OCO-2 & TESS
Mission Operations
Tim.perry at ngc.com<mailto:Tim.perry at ngc.com>
Office (703) 406-5976
Cell (301) 606-1430

<image002.png>

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