e-Printse-PrintsThere're some details on Mars 96 mission events based on Monday news conference in the Russian Space Agency. The mission was more difficult (and interesting) than we could think.
Short info: Proton-K launch vehicle with Block D-2 upper stage and Mars 96 spacecraft (a.k.a. Mars 8) was launched from Baykonur on Nov.16/20:48:53 UT. Mars 96 with its small stations, penetrators and radioisotopic generators reentered early on November 17 on orbit 3 near perigee, presumably in the Southern Pacific [JEO: about 4 hrs 20 min after launch]. Block D-2 reentered at approx. November 18/01:13 UT [JEO: about 28 hours 25 minutes after launch] and parts of it fell into the Southern Pacific at 18/01:20 UTC at 50.9S, 168.1W.
More details: Proton-K (8K82K) worked perfectly and Block D-2 (11S824F) first burn was made successfully. Initial circular 160 km orbit was deduced from measurements from ground stations during LEO insertion and part of orbit 1.
The planned second burn of 3150 m/sec [JEO: 529 seconds] by Block D-2 engine was not achieved [JEO: Ignition was planned at MET 1:08:52, over 25S 30W]. Instead, some 20 m/sec in wrong direction was given by Block D-2 resulting in Block D-2 orbit of 145.7x171.1 km. This was object 1996-064A [USSPACECOMM identification] and it lasted for 28.5 hours. [JEO: The absence of a tracking ship in line-of-sight of the burn may have been a critical factor, since it could have sent backup commands -- but the Russian space program can no longer afford tracking ships (this was their first interplanetary mission attempted without them) and in fact the ship was recently sold for scrap]
On orbits 2 through 5, telemetry from Block D-2 was received. Then the upper stage was not in sight from Russian ground stations and by evening of November 17, chemical batteries were depleted and communications from Block D-2 was not restored. It barely missed Australia and ended in the Pacific. [JEO: THIS was the object tracked by USSPACECOMM, but misidentified, which led to the White House's "plutonium panic" and Clinton's phone call to Australia].
Mars 96 separated from Block D-2 after unsuccessfull second burn in the beginning of orbit 2. Solar battaries and external elements were deployed and the spacecraft tried to catch the required velocity by its own engine, the ADU. This was impossible because the spacecraft had not enough fuel to make a 3700 m/sec delta-V. So, this burn was not successful either. Moreover, it effectively killed Mars 96 [JEO: ..since the burn apparently was made at a large angle to the horizontal, thereby fatally lowering the perigee with the burn's radial component].
On orbit 2, telemetry from Mars 96 was recieved at Yevpatoriya ground station in Crimea from 16/22:19:14 till 1622:26:55 [JEO: about seven minutes]. Ussuriysk station also received signal from Mars 96 from 16/22:55 to 16/22:57. Different transmitters were used on Mars 96 and Block D-2 so the controllers can say for sure which object they tracked.
The spacecraft was found in a kind of orbit of 87x1500+some km. [JEO: This orbit would require about 350 meters per second delta-V, apparently a lot more than the pre-planned Mars-96 insertion burn, so this suggests its autopilot tried to make up the D-2 deficit and may even have burned to depletion. The initial realization that the spacecraft had achieved a high apogee probably led to the early claims that it had a 30-day lifetime, but this was before it was realized that the off-level burn had lowered the perigee].
[JEO: A crucial question is what was the new 'argument of perigee', that is, where was the new low point in the spacecraft's orbit relative to the equator. Based on the estimated point where the burn occurred, and assuming that the burn was made slightly 'upwards', I'd guesstimate that the new perigee was very close to the northbound equator crossing point. Apogee would then be over the mid-Pacific]
It survived the first perigee [JEO: This is astounding] and was tracked by the Russian Center for Space Surveillance on orbit 3, some 100 minutes after orbit 2 [JEO: This would have been about 16/23:50]. By this time, flight controllers were ready to command Mars 96 to maneuver to some stable LEO orbit for possible future use in Earth research [JEO: Or recovery by the US Space Shuttle]. Unfortunately, flying at 87 kilometers proved to be too bad. On orbit 3, Mars 96 wasn't transmitting already and cannot be commanded. [JEO: I interpret this to mean that although they had skin track, there no longer was any comm directly from the spacecraft -- perhaps aero effects had tumbled it, or over-heated it, but it was dead].
[JEO: My back-of-envelope figures for rev 3 shows equator crossing at 16/23:36 at 32 degrees W, with ground track across Morocco, Corsica, northern Italy, Hungary, Ukraine, southern Russia (where it was tracked), Kazakstan, central China, Taiwan, New Guinea, skirting the NE coast of Australia, New Zealand, and then across the far southern Pacific to northern Chile, Bolivia, Amazonian Brazil, French Guiana, then across the Atlantic to overfly Paris, central Germany, Warsaw, and on to Russia, where it was not tracked. It came down somewhere on this pass, somewhat short of perigee, but exactly where remains a mystery]
[JEO: Rev 4 would have begun about 17/01:04 at about 55 degrees W, over the Amazon basin south of Surinam. I'm putting the spacecraft perigee near this point as well. This suggests to me that the likeliest impact point is over South America, not the eastern Pacific. The Moscow press conference on Monday put the range of entry times as 00:30 through 01:30, which begins over the Pacific, brackets South America, and finishes over the Atlantic]
Mars 96 was not tracked on orbit 4 and the conclusion was that it reentered in orbit 3 perigee somewhere in Southern Pacific.[JEO: I differ on where this perigee would have been located].
[JEO: Had Mars-96 completed rev 4 it would have passed within range of Eglin AFB, Florida, where the south-facing phased array radar would have spotted it along with the 4th stage. Earlier passes near US sensors such as Kwajalein were either before the probe had separated, or were at unexpected times and angles during periods when the sensors may have had other tasks to concentrate on. The USSPACECOMM failure to observe the probe is just bad luck due to geographic accidents, but is still embarrassing]
[JEO: USSPACECOMM needs to go back and review the DSP (Defense Support Program) infra-red tracks for that period and that area, to see if the Mars-96 entry fireball was observed, either over the eastern Pacific or over South America. Also, it would be helpful to check South American wire stories to see if observers in Chile or Bolivia reported a southwest to northeast fireball about 17/00:50 or so, which would be early Saturday night with a good dark sky].
[JEO: My conclusion is that the optimistic (and self-serving) Russian claim that the probe and its plutonium impacted safely in the Pacific is not sufficiently convincing. I think the orbital data strongly suggests that the probe could have come down over South America about 17/01:00, or 8 PM EST Saturday night.]
[JEO: It's clear the Russians were confused by these events but they
had good tracking data and knew by early Sunday morning (Moscow Time)
that the spacecraft had separated and had subsequently entered. They
made no announcement about this, either as a pre-entry warning or as a
post-entry search advisory. By the time the White House was calling
Australia to warn them about the possibility of a plutonium impact
(mid-afternoon DC time), and claiming in its press release that it had
been "in close contact" with the Russian government, the Russians
already had known for more than twelve hours that the real probe was
down. Their inability to 'come clean' on this nuclear-related accident
smells like reversion to Chernobyl-style coverup, and is not an
encouraging sign that our new partnership really has changed their
thinking.]