I like asking questions, and where better than a place like this?

So here's one... Mars Climate Orbiter burned up during a too-low pass through the atmosphere. So where would its debris have fallen?

This ought to be a fairly straightforward question to answer. We presumably know, or can find, the details of its trajectory as it approached Mars. We know the orientation of Mars at the time. The location of periapsis in Mars coordinates ought to be easy to find. This might be buried in a technical report somewhere, or it might be possible to figure it out with one of the solar system simulator type programs. Can anybody help answer this?

(if so, we can extend it to Pioneer Venus and Magellan later in a separate thread)

Phil

Could be simulated with Orbiter if you knew the right info.

Thinking out loud - how much of it might it thru to the surface - perhaps the prop tanks ( Delta II 2nd stage prop tanks make it to the ground here on earth ) - but not a lot else I'd imagine.

Doug

Unfortunately, the official report indicates that we're not even sure it DID crash on Mars -- its remains may not have lost enough velocity even to avoid continuing into solar orbit, let alone going into orbit around Mars. So the short answer is: we'll never know, and it may well be scattered over a large part of the planet.

Indeed phil is right this is a great place for questions,
here is mine.
Mars observer another lost spacecraft is belived to have sufferd a fuel line explosion as it neared a flyover of the martian north pole.(where on the space craft was the fuel line in relation to its line of flight? The accident board tells of the space craft being in solar orbit (2) would not this place the space craft in an orbit just "south" of the plane of the ecliptic? (3) how much delta vie would an explosion have imparted on mars observer?
a large enough explosion would have left mars observer scatterd all over the martion polar regions perhaps.or itself melted and skipped of the atmoshere and back into space.but then a fuel line located on the space craft facing downward towards the planet on its line of flight would have alterd the orbit higher.
As for the climate orbiter was it intended orbit a polar one as well?

I with jonathen mcdowell at harvard have an interest in this subject as history of space flight.I had a conversation with him years ago about some conversations I had in the mid 90's with atrodynamics/mission design folks at JPL in reguards to the locations of the voyager and pioneer solid upperstages.I think these are in solar system escape orbits.

steven

I think it's probably sensitively dependent on the state of the martian upper atmosphere, which we don't know, and on the breakup dynamics of the spacecraft, which would be very hard to predict. As was pointed out, it's not even known if MCO debris fell on Mars or ended up in solar orbit.

The most likely outcome stated by the Coffey board in 1993 was that MO was spun up to a high rate by helium expelled from a blown propellant line. The delta v this would impart could end up averaging to near-zero. I tried to get people to seach for MO in 2000 when it would have approached to about 0.2 AU from the Earth, but it was very dim, and I couldn't interest anyone in spending telescope time on such a long shot.

A paper written in 2001 by Carl Guernsey of JPL, though ( http://www.klabs.org/richcontent/Reports/F...y_a01-34322.pdf )
suggests it was more likely that MO suffered contamination in the He pressure regulator and that the oxidizer tank just exploded, which would have blown the spacecraft into pieces.

If I may provide yet another advance ad for my "Astronomy" article: those upward and downward jumps in Martian upper-atmosphere density have turned out to be so big, hard to predict, and dangerous for landers (and maybe for aerocaptured craft) that their study is turning into a major theme in the near-future Mars program -- as an engineering necessity.

I'd like to thank everybody for these comments. Very useful.

Leaving aside the question of whether or not any fragments of MCO fell to the surface, let me rephrase my question: Where in Mars lat/long was the closest approach? So if it just sailed on by, where was it at its lowest altitude? Do we know that? That, I suppose, is what I was thinking of initially when I said it ought to be fairly easy to find or figure out.

Phil

So does this translate into another Mars Climate Orbiter or would a pack of small static long life MET station type probes be better suited to the task?

Maybe instead we should use entry systems with more margin against these sorts of problems. I don't know how much of what Bruce is saying about Spirit is reality and how much engineering conservatism, but it's always been understood that MER had fairly poor robustness in the face of some environmental factors. There are two engineering responses to this: ask "the scientists" for better environmental data, or design proper margins into the system based on the uncertainties (probably losing capability in the bargain.) One is looking for the proper mix, but it's likely not on one end or the other of this spectrum.

I don't recall seeing specific analyses of the trajectory based on final tracking data, though it certainly exists in some form. In the pre-launch mission plan, closest approach was over about 30N, 170W and the spacecraft was moving southward; the orbit was near-polar (inclination 92.93 deg) but I don't know if the closest approach coordinates varied with actual day of launch.

I don't think either would work; conditions in the upper atmosphere can only be assessed to the needed accuracy by entry probes at the time of entry.

*Maybe* atmospheric sounding, such as will be provided by MCS on MRO, will give some insight, but I don't think to the desired level.

Another reason that building systems that can handle the variations in real time would be better than trying to characterize and predict conditions in advance.

This is the right design. It would avoid any future surprises.

It should have implemented to Hayabusa's spacecraft for its control in releasing Minerva and also in releasing the right moment a fire balls before landing to the Itokawa surface in order to suck samples by its long trumpets.

The software algorithm must be accopled to external sensors (altimeter, spectrometer, imagery, etc.) to handle the real time conditions.

This must also be implemented for the MSL Crane for its search a better place to drop the thettle.

Rodolfo

Giving away another article secret in advance: what Jay Bergstralh talked about at length at the meeting was the serious need for a Mars orbiter to observe both high-altitude density variations and low-altitude winds in more detail than the sounder on MCO (and MRO) can do. This has been talked about earlier on the Web (I believe MEPAG has recommended it), but it's likely that more work needs to be done on the instrumentation, although apparently IR sounders and limb sounders are capable of it. (There was one Mars Scout proposal for a pair of orbiters exchanging radio-occultation signals with each other all over Mars, but I'm told that this would require a dedicated mission rather than experiments that could piggyback on other orbiters -- ultrastable oscillators are lightweight, but their lock-on receivers are not.)

As Bergstralh also said, though, in the longer run we do need a weather network on Mars' surface (which is in the new NASA Mars plan) -- and for manned landings, at least, we'll definitely need landed weather sensors near the landing site itself for real-time observations. In addition, as Mike Caplinger says, obviously we'll need lander designs robust enough to cope with such fluctuations, especially for precision landings. Guided entries will obviously help a lot (although that experiment has now been removed from Phoenix due to lack of funds -- it will be attempted, at least "to some degree", with MSL.)

One thing we apparently DON'T need -- at least Jeffrey Hall was very forceful on this -- is a test of aerocapture at Mars. According to him, an Earth-orbital aerocapture test of the sort proposed for ST-9 will be fully adequate (along with continued ground-based studies) to verify not only Mars aerocapture but the outer-planet type (although the latter will need radically remodelled aeroshells).

Doug:

I suspect that the dynamics of atmosphere entry on Mars are quite dissimilar to Terrestrial ones, and that debris might well survive to the surface. Most objects entering our atmosphere survive largely intact to *below* the equivalent pressure level of the Martian surface - for example, Columbia. Perversely, the terminal velocity on Mars for low-density objects might well be higher than we'd see on our own planet, despite the 1/3 G environment.

Bob Shaw

One possible at least partial solution to the entry problem would be to include a relatively small limb scanning radiometer/spectrometer on the cruise stage for an entry mission, and to have somewhat more capability than current entry vehicles to adjust lift/drag during entry.

A dedicated single-purpose limb scanning instrument operating up to maybe 5 minutes before entry interface should be able to profile temperature structure, solve for the density profile automatically, and generate commands to vary entry-vehicle orientation (like Apollo) to optimize lift/drag. It's nice to be able to jettison a cruise stage well before entry, but there's no essential reason it can't be done later, nearly at the last minute.

If you KNOW the entry profile before hitting the atmosphere, you can probably go in at a shallower angle as well, giving more entry margin. That increases the along-track landing ellipse length, but if you know the entry profile and can steer the entry, you counter that effect and can probably reduce the landing ellipse length below an unguided entry.

We don't right now, but will eventually want to land packages at higher altitudes than we have on Mars. Certainly we'll want to deploy geophysical payloads (seisometers, magnetometers, meteorology) well up on the Tharsis bulge, and landers limited to a kilometer or two altitude don't hack it.