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Posted by: Phil Stooke Nov 15 2005, 02:47 AM

I will ask here the same question I asked a few days ago concerning Mars Climate Orbiter in another thread:


Both Pioneer Venus and Magellan ended their missions by entering the atmosphere and burning up. I am absolutely sure I saw, once, somewhere, a lat-long position for the re-entry location - of one of them, I forget which. Not very helpful, I know.

I don't want to worry about whether any part of them might survive to the surface. But just supposing some bit of frame or tank made it down, where would it be? So what I'm interested in is a rough location for the atmospheric entry points for these missions. If the orbit details could be tracked down a solar system simulator or orbit program might give the results, or they might be hidden in a tech report somewhere. In practice we might only need a latitude of periapsis for the final orbits, and a longitude from the orbit orientation and time... for a rough result.

Can anyone help?

Phil

Posted by: tasp Nov 15 2005, 02:12 PM

I am just speculating, but it seems during entry into the Venusian atmosphere Magellan would not have had its dish pointed towards earth.

The Pioneer Venus craft (IIRC) had an antenna that was despun to the main probe body and at least potentially, could have remained in contact with earth during the early stages of burning up.

-however-

Pioneer Venus could have been on the far side of Venus when this occured.

I am assuming if the craft was in contact with the Deep Space Network at entry interface, we would have a better idea of where the event occured.

I'll see if I can find my Pioneer Venus Nasa SP today.

Posted by: Phil Stooke Nov 15 2005, 05:53 PM

I'm afraid the NASA SP on Pioneer Venus will not help. It would be bureid in the tech. reports. Or it will have to be figured out from ephemerides etc.

Phil

Posted by: tedstryk Nov 15 2005, 06:24 PM

I doubt that this could be determined. It is quite possible that atmospheric drag both craft's ability to transmit before the final plunge (especially with Magellan). Given the precision with which the drag properties of the Venusian upper atmosphere are known, I doubit either craft can be precisely pinpointed.

Posted by: Phil Stooke Nov 15 2005, 07:57 PM

Ted, I'm not worried about trying to track fragments to the surface, just an approximate atmospheric entry point on the last orbit.

Since we know (or could presumably find) the time and latitude of the last periapsis, and the orientation of the orbit plane and of Venus at that time, we ought to be able to say within a few degrees of lat and long where the spacecraft began to disintegrate. We don't need tracking data.

Even within 500 km would be OK by me. No, even 1000 km... just so one could say something like 'Magellan burned up over Ovda Regio' or whatever.

Can this be done?

Phil

Posted by: JRehling Nov 15 2005, 09:16 PM

NSSDC says:
"Magellan began its final descent into the Venus atmosphere on 11 October 1994. On 12 October radio contact was lost, and the spacecraft presumably burned up in the atmosphere on 13 or 14 October 1994."

That sure sounds like we don't know. At the best, you could say that Magellan's path followed a great circle route over the slow-rotating Venus, and say that you know that it burned up somewhere on that circle route. Given that radio contact was lost, the only way to pinpoint the time of "burn up" would be to model the process rigorously! Now, if you were content to know where it was at the time of loss of radio contact, you'd have a chance.

NSSDC only pins down the demise of Pioneer Venus to August 1992.

Posted by: Bob Shaw Nov 15 2005, 09:46 PM

Perhaps the phrase '...contact was lost over XXX at 19:28 UT on XX/XX/XX...' will be the best possible finale!

So, is it an article, Phil?

Bob Shaw

Posted by: Phil Stooke Nov 15 2005, 09:49 PM

JRehling said:

"NSSDC only pins down the demise of Pioneer Venus to August 1992."

They are mistaken. It was October 8th 1992 (NASA/Ames press release 93-51).

If the orbit was fairly elliptical the latitude of burn-up would be known to within a few hundred km. Pioneer Venus was lost on the side facing away from Earth at the time according to contemporary reports. Things can still be narrowed down a lot more.

For Pioneer Venus I know this so far: The orbit was near polar, moving nearly along a meridian near the equator. The orbit periapsis was 150 km, apoapsis 66000 km, near the end - the last few periapses were as low as 90 km. Periapsis latitude was 10 degrees south (just found that). So now all I need is the longitude of periapsis on the last day and I've got it. I don't have that yet, but it must be around. Oh ye of little faith! Basically it's just simple geometry, you don't need tracking.

Magellan's orbit was similar, near-polar but not so elliptical. The low point was near a pole, probably the north but I have to check.

I will persevere on this - I want to put, if not a point, then at least a big ellipse, on a map!

(edited)

Phil

Posted by: BruceMoomaw Nov 23 2005, 11:06 AM

Alas, for Pioneer 12 you'll never be able to. Today I stumbled across a JPL Technical Report -- http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/35720/1/93-1445.pdf -- which says (pg. 9) that they lost contact with Pioneer 12 (apparently due to overheating) during the low pass of an orbit where the drag braking was still low enough that it can't possibly have entered on that pass, and they don't quite know how many more orbits it survived before finally burning up. (I'm looking for the data on Magellan.)

Posted by: BruceMoomaw Nov 23 2005, 12:07 PM

Hmph. Even an uncertainty of several days would allow you to nail down the longitude of final periapsis pretty well, wouldn't it? Unfortunately, I haven't been able to find out any more about either mission -- except that the latitude of Magellan's periapsis during its final low gravity-mapping orbits ranged between 4 deg N and 28 deg N, and that contact was lost with it due to battery depletion at about 3 AM Oct. 11, 1992, with entry thought certain to have occurred some time within the next 58 hours ( http://www2.jpl.nasa.gov/magellan/status941013.html ).

Posted by: Phil Stooke Nov 23 2005, 02:24 PM

Many thanks for this, Bruce. As you say, an uncertainty of a few days doesn't matter too much. But every bit of information is useful here.

Phil

Posted by: JRehling Nov 24 2005, 05:38 AM

Take a look at the gravity maps generated from Magellan data. Particularly, the uncertainty map.

http://www.windows.ucar.edu/tour/link=/venus/images/mgngr40e_image.html

Also see:

http://jules.unavco.org/Voyager/Docs/Venus

Is there any greater factor governing the uncertainty other than the shape of Magellan's final orbit? Going on the assumption that the final periapsis was at the place where the gravity data was the most precise, that would place it at about (E longitudes here) 110E, 10N. Of course, whoever had the data used to compute these maps would have your answer, I think. Check out papers on Venus's gravitational field, and THEIR references, and you're probably going to find out the final orbit.

Posted by: Richard Trigaux Nov 24 2005, 07:33 AM

Thse work of searching earthborne objects on other planets may have an unexpected utility, in some tens or hundreds of years, if one day we explore these planets and stumble on some wrecket spaceship:

not to confuse Earthborne spaceships with spaceships of other civilizations!!

On Moon, Mercury, Titan, Mars, wrecks can remain identifiable for thousand of years and more, and offer markings and logos to read. But on Venus, it is very likely that any metallic structure quickly turns into a heap of oxydes. Only ceramics or precious metal parts would allow some identification of an Earth origin, if their dimentions are metric (dimentions in inches would indicate a near-Earth origin).

Otherwise we may find, one day, in a venusian plain, something which would be obviously a completelly burned spaceship part, but which identification as an Earthborne spaceship would be really difficult, resulting into completelly pointless speculation about a possible extraterrestrial origin. (or on the countrary an extraterrestrial spaceship would be confused with a terrestrial one, and we would miss an unequaled evidence).

This is why, especially with Venus, landing locations are very useful, together with archives (plans and models) of the spaceships which landed there.