MGS in Trouble, Formerly: MGS in safe mode Options

[mcaplinger]

HiRISE attempts to image the predicted locations might be futile, resulting in huge amounts of data of empty space.

Maybe they're planning on using some other instrument on MRO with a wider field of view first. Gee, which one could it be?

[djellison]

"We'll use HiRISE on Friday"
"We'll use CTX on Wednesday then HiRISE on Friday"
"We'll use a long exposure with HiRISE on Wednesday then a targetted observation on Friday"

The usual suspect media outlets have all reported one or more of those.....so it's been a bit confusing for the layperson.

Doug

[mcaplinger]

The usual suspect media outlets have all reported one or more of those.....so it's been a bit confusing for the layperson.

Well, I'm afraid I have nothing definitive to tell you. Note that there are lots of players and we may not know, or need to know, what other teams are doing. Plans may be changing from day to day, and the media often misquotes sources anyway. Even I might not know for sure what my own instrument will be doing and when. I'd believe that images were taken when you see the images.

[nprev]

Or maybe it's just time the DSN got the investment it deserves to install multiple 70m assets at each station, or the arrays of mass produced 12m dishes suggested at IAC.
http://www.iac-paper.org/abstractcd/2006/a...-06-B3.1.03.pdf
Doug

Not to beat a deceased equine excessively, but maybe this is a partial answer:

http://www.unmannedspaceflight.com/index.php?showtopic=3227

[mcaplinger]

Not to beat a deceased equine excessively, but maybe this is a partial answer...

How would you propose to fly antennas many tens of meters in diameter, much less duplicate, in flight-qualified form, the sensitive receivers and megawatt transmitters used by DSN stations? After all, these orbital comm relays would in general be little closer to Mars than Earth, and would then have to send the data to Earth.

[nprev]

Good questions. I'm not sure if it would be feasible with RF unless 1) we can successfully develop & deploy very large collapsable antennae (the Galileo experience was instructive), 2) advanced DSP on the receiving end of all terminals involved could compensate for much lower transmitter power outputs, and 3) flight-qualified ultra-stable transmitters with very fine output frequency resolution could be developed.

This idea would work better with lasers; something like an MTO for at least each of the inner planets would provide the necessary link between active exploration missions & the new network. This network would be used almost exclusively for data return & housekeeping, freeing up the DSN for critical activities such as resolving the current MGS anomaly, early mission support, and tracking during cruise.

EDIT: Apologies if anyone saw a smiley instead of 2) above; this was not intended as a shot against Galileo, the message board just interpreted by original use of a letter plus a parenthesis as a smiley.

[RichardLeis]

What's so difficult about it? Lookheed-Martin designs the slew and they tell you when to start imaging. At least, that's how the Odyssey image by MGS was done. Doesn't sound too hard to me.

Teeny-tiny spacecrafts, great big universe.

Ephemeris data for Mars is pretty good, though we require more recent updates prior to sending final commands to make sure our targeting is correct. Spacecraft-to-spacecraft ephemeris is not so good because of the variable atmosphere, dynamics of the Sun-Mars-MGS-MRO system, and other factors.

Sure, it can probably be done, but it will be hard, especially when there is a regular science mission ongoing with other timely observations required, and a million little things just waiting to go wrong somewhere in the complex process.

If the Odyssey imaging by MGS was easy, then wow.

[RichardLeis]

"We'll use HiRISE on Friday"
"We'll use CTX on Wednesday then HiRISE on Friday"
"We'll use a long exposure with HiRISE on Wednesday then a targetted observation on Friday"

The usual suspect media outlets have all reported one or more of those.....so it's been a bit confusing for the layperson.

Agreed. The media provides a snapshot of what things were like at a specific moment in time. The situation is dynamic, however, with scores of people and several teams involved, all in addition to the team members who really want to hear back from their pride and joy. The situation is confusing, and everyone is trying to do what they can.

[mcaplinger]

Sure, it can probably be done, but it will be hard, especially when there is a regular science mission ongoing with other timely observations required, and a million little things just waiting to go wrong somewhere in the complex process.

Sorry, not buying this. We had little difficulty imaging Odyssey with MGS, and MRO should be better in every respect than MGS (HiRISE has a wider FOV than MOC, MRO pointing control is much more accurate/stable, etc, etc.) Maybe it'll take a couple of tries, but it shouldn't be that big a deal. LMSS does most of the work anyway; they just tell you when to start imaging, no?

[tuvas]

Sorry, not buying this. We had little difficulty imaging Odyssey with MGS, and MRO should be better in every respect than MGS (HiRISE has a wider FOV than MOC, MRO pointing control is much more accurate/stable, etc, etc.) Maybe it'll take a couple of tries, but it shouldn't be that big a deal. LMSS does most of the work anyway; they just tell you when to start imaging, no?

MGS had one thing that MRO doesn't, the exact knowledge of the spacecraft to photograph. THAT is the largest problem, which the space.com article got correct.

Also, I, who work with the HiRISE team, and have been paying really close attention to what's happening, honestly can say I don't know when the picture will take place, or which instrument will do it. I'd be willing to bet that either CTX or HiRISE will be the photographers, but there again, it's a big universe and a small spacecraft.

[edstrick]

Unless Global Surveyor's done a lot of attitude gas jetting, it's on-orbit location should be pretty well known. I don't, however, have a clear idea of how the along-orbit uncertainty spreads with time. What's not known at all and is the object of investigation is MGS's ATTITUDE.

Of course, if they spot a Klingon bird of Prey next to it.......

Now if we could just get something other than random noise (and fullsome self-praise) from the remote-viewing pseudo-psychics....(sigh)

[ugordan]

The along-track uncertainty is likely the principal uncertainty here. The exact orbit need only be slightly higher/lower for significant timing differences to be accumulated on a time scale of days. These would manifest as a change in when the spacecraft passes a certain point in its orbit, with respect to the (practically identical) reference orbit. Given the speed these things move, even a couple of seconds worth of timing error means they move quite far along track. As to how much of a contributor the possible thruster firings are (ideally, they should not be one at all) or how significant the atmospheric friction is in lowering the orbit is open to question.

[edstrick]

Assuming no net thruster firings, it's a relatively simple <and probably documented somewhere in published mission navigation papers, like AAS Advances in Navigation, or AAS Advances in Communication and Control type volumes in engineering libraries>, how the along track knowledge degrades with time following a normal orbit solution.

[djellison]

When I started this place a couple of years back - I never thought I'd see a debate between MOC/CTX and HiRISE people over the relative difficulty of photographing spacecraft - what a very very sureal thing to read over ones cornflakes

Doug

[ugordan]

A very back-of-the envelope calculation, could be very wrong, but still I think it's illustrative:
Assuming a 118 minute orbit, 3800 km orbital radius, 3.37 km/s orbital velocity here. That amounts to 122 orbits in 10 days. Let's suppose we change the orbital radius by just 100 meters, from 3800 km to 3800.1. Given the ratio of orbital periods T1/T2=SQRT(R1^3/R2^3), that gives me around 0.9999605 T ratio. Multiply (1- 0.9999605) by 118 minutes, that amounts to a difference of about 0.28 seconds per orbit.
Now, 122 * 0.28 s * 3.37 km/s = 115 kilometers in along-track drift. Not exactly peanuts. It's not getting any smaller as time passes, either. Note how even a small, 100 meter radial change in orbit radius results in an 3 orders of magnitude larger change in along-track position.