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From: glenn@LL-VLSI.ARPA (Glenn Chapman)
Newsgroups: sci.space
Subject: Phobos II failure analysis - hit near Phobos?
Message-ID: <8904230642.AA26812@ll-vlsi.arpa>
Date: 23 Apr 89 06:42:59 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 52


    The USSR has declared the Phobos II probe dead in orbit according to 
Radio Moscow (Apr. 18/19).  A commission has been set up to study the 
failure, but some information is now available.  On Mar. 27th at 3:59 p.m. 
Moscow Time (7:59 am EDT) the probe was ordered to turn towards the Phobos 
for almost the final picture set.  Phobos II, which does not have its 
antenna mounted on a separate pointing platform, was to turn back to the 
Earth for signal transmission by 6:59 - 7:05 p.m. (AW&ST Apr. 17) However, 
no radio source was at time on earth, though at 8:50 p.m. they regained the 
signal for 13 min.  Indications are that it was not a transmitter failure 
as was first thought, though this is the backup 5 Watt radio, not the 
main 50 Watt one which failed in January.  Instead, in an interview with 
Roald Segdeev (former director of the Institute for Cosmic Research (IKI)), 
it was revealed that the probe has been found to be rotating unexpectedly. 
The Russians suggest the probe probably collided with something near  
Phobos, either particles in orbit near the moon, or possibly debris from 
the separated main propulsion section (suggested by Jonathan McDowell at 
Harvard).  Another possibility not mentioned by the Soviets was simply a 
hydrazine thruster failed (either stuck on or off).  They are worried 
that the probe may crash onto the Martian moon as this current orbit 
is unstable, according to James Oberg (Soviet Aerospace Apr. 3).
   A latter short wave report stated that the Phobos II mission had 
achieved 75% of the intended studies of Mars.  The probe 
made excellent studies of the Martian magnetic field, the plasma  
density around the planet and infrared observations of the surface. 
However, originally it was to stay in the original orbit with a 
closest approach to the planet of 800 Km. (500 mi.) for 25 days,  
but only 14 days were spent before the orbit was raised to 6300 Km 
(3940 mi.)  This considerably reduced the accuracy of Mars observations.   
The probe did obtain pictures of Phobos from less than 100 Km (63 mi.) much 
closer than the Viking orbiter did at 480 Km (300 mi.).  The Soviets 
claim these are the best photos so far of the Martian moon.  There is  
some uncertainty in this as Viking had better cameras, but clearly 
Phobos II took more pictures.  In all the probe obviously obtained much data, 
but probably it not three-quarters of the original planned mission. 
Never the less, this was the most successful of the USSR's Mars  
missions.
   Indications are that the Russians are considering using the ground 
test vehicle as a full system and launching it for a duplicate mission 
in 1992.  The next two launch windows open in Sept. 1990 and Oct. 1992. 
Unfortunately, 1988 was the best launch window until 2001 (taking the 
least energy).  Probably they would have to use what is called a type II 
Hohmann transfer orbit, which is slower but takes less energy just to 
be able to run a similar mission.  Skipping the 1990 mission probably 
is necessary just to do the checkout of this craft, and to do the 
programming to prevent the problems that killed the Phobos I probe 
in Sept. '88.
   As Groucho Marx used to say "Close but no cigar" for this Soviet 
Mars mission.

                                                Glenn Chapman
                                                MIT Lincoln Lab