[FPSPACE] planetary orbiting relaystations

Fri Jun 6 23:23:25 EDT 2008

While searching through my archives I could not find absolute proof that 
Mars 6 crashed (just a lot stories it did, but no true references!).

What we DO know is that it was descending at 61 m/sec when the signal 
cut off (ref Brian Harvey, "Russian Planetary Exploration", page 159), 
however the transmitter was designed to cut off when the soft landing 
rocket was ignited (ref Perminov page 45). Furthermore, the descent 
speed under parachute was designed to be maximal 65 m/sec (ref. Perminov 
page 45), so basically what we do know is that on firing of the soft 
landing rocket engine (when the transmitter was cut off) the craft was 
descending at its intended descent rate. Apparently up to that moment 
everything was still working as planned. What happened afterwards we 
will never know.

The solid propellant softlanding rocket was designed to be fired at 
16-30 mtr above the surface, as measured by the radar altimeter, however 
this also depended on the descent speed, so a correction was applied if 
the craft was descending slower or faster then intended. Once the 
descent speed dropped to 6.5 m/sec the lander was cut free from the 
'backshell' and dropped to the surface. The lander was tested to 
withstand a vertical touch-down speed of 12 m/sec and a horizontal speed 
of 28.5 m/sec, with a maximum of 180G on touch-down, so the craft was 
quite sturdy. The parachute system was tested several times on earth 
using high altitude sounding rockets (similar to the Viking parachutes, 
however contrary to Pathfinder, MER, MPL and Phoenix who never did a 
parachute test under "true" conditions).

The calculated landing spot of Mars 6 (the Samara Valley at 23-54 S 
19-25 W) has recently been imaged by HIRIS, but no sign of the Mars 6 
lander has been found as yet. However, with the uncertainty in its 
position it would require hundreds or maybe thousands of HIRIS images to 
cover the whole landing elips, and even then chances of finding a lander 
(or more likely its parachute) after so many years of marsian dust are 
very, very small. Hopefully some astronaut will accidentally stumble on 
it (or the Mars 3 lander) in the far future, and then remember the story 
of the poor lander which was left without a relay...

As a side note, the story of the Argon reading is also more complicated: 
during descent a mass spectrometer analyzed the atmospheric composition, 
however this data was not included in the live transmission (intended to 
be transmitted later, after landing). Data transmission was at a slow 
datarate and the whole EDL is very fast so there was simply no time to 
transmit that much of data. Only pressure, temperature, light-intensity, 
and G-forces were transmitted, as well as the power drawn by the pump of 
the mass spectrometer. Descent speed and windspeed were measured from 
the doppler shift of the signal I presume, they are mentioned but there 
is no clear reference on how they were obtained. The transmitted 
measurements were valuable and conform later data from other probes, 
however the power drawn by the pump of the mass spectrometer was higher 
then expected, and this was interpreted as evidence that there was far 
more inert gas (possibly argon) in the atmosphere then expected. Later 
analysis showed this interpretation was incorrect (ref. 'Robotic 
Exploration of the solar system', Paolo Ulivi / David Harland, page 
167). Once again, I can not find any valid reference for the often heard 
story that the Mars 6 lander was transmitting only 'garbage' and not 
functioning as intended, instead all references seem to indicate 
everything was more or less proceeding as planned and the published 
descent-data is conform data of later probes. There is no way to be 
certain what happened after the signal was cut off on firing of the 
landing rocket, if the soft landing rocket did indeed fire it might very 
well have survived touch down, however with no orbital relay nobody was 
able to receive its signal and the whole landing was doomed from the 
very start.

Regards,

Geert.

LARRY KLAES wrote:
> An interesting and scary analysis from the point of view of losing an entire
> mission for want of a relay.  Let us be glad that Phoenix has three 
> functioning
> orbiters to choose from for calling to and receiving from Earth.
>
> Just out of curiousity, would Mariner 9 have been able to relay data from
> the Mars 3 lander assuming both sides agreed to such a thing?  I know
> that Mariner 9 had long stopped functioning when Mars 6 arrived in 1974,
> but it probably would not have mattered anyway since that lander apparently
> hit the Martian surface at a high rate of speed - in other words, it 
> crashed.
> And the argon reading it did send back while descending turned out to be
> erroneous.  Plus I believe the computer chips on all the Mars 4-7 probes
> were infected with a virus but the Soviets sent them anyway and hoped
> they would last long enough to do some good.
>
> It still amazes me how the Soviets had so much better luck at the much
> more nasty planet Venus, but then again, maybe if they built their Mars
> probes to be as tough as the Veneras, there might have been a few
> more successes.
>
> Larry
>
>
>   
>> From: Geert Sassen <geert at navtools.nl>
>> Reply-To: geert at navtools.nl
>> To: fpspace <fpspace at friends-partners.org>
>> Subject: [FPSPACE] planetary orbiting relaystations
>> Date: Fri, 06 Jun 2008 11:32:44 +0200
>>
>> Sometimes you can find little jewels of snaps of information in your 
>> archives which apparently you overlooked for a long time.
>>
>> Based on the problems Phoenix is having with the data relay via MGS and 
>> Odyssee, I checked out the history of other landers which relied completely 
>> on orbiting relay stations, and so arrived at the Soviet landers of '71 and 
>> '73. Back in those days two landers (Mars 3 and Mars 6) seemed to have come 
>> quite intact through EDL, only to lose all connections on touchdown or 
>> shortly afterwards (Mars 3 lost contact a few minutes after touch-down, 
>> Mars 6 lost contact on touch-down).
>>
>> In his very interesting booklet 'The difficult road to Mars' ( 
>> http://klabs.org/richcontent/Reports/mars/difficult_road_to_mars.pdf ) V.G. 
>> Perminov gives first-hand information about both missions. Quite apart from 
>> several interesting insights into Mars 3, he describes on page 61 how, 
>> after the experiences with Mars 3 (which was not designed to transmit any 
>> science data during EDL) an additional radio system was installed on the 
>> lander backshell, which would transmit data during the parachute descent. 
>> This data was relayed to earth by the main bus of the spacecraft, which 
>> continued on a flyby trajectory. Shortly prior landing the backshell was 
>> released and the automatic landingstation was released. This lander was 
>> more or less identical from Mars 3. Then, on page 65, Perminov notes: "The 
>> additional channel was operative only during the descent of the lander. 
>> Information from the Martian surface had to be transmitted by the main 
>> radio channel to the Mars 5 spacecraft".
>>
>> In other words, apparently the main bus of the craft (Mars 6) only 
>> functioned as a relay during the descent, after touch-down the relay 
>> function was taken over by the Mars 5 orbiter, working on a different radio 
>> channel. However... all contact with Mars 5 was lost on February 28, while 
>> Mars 6 only arrived on March 12. With no functional orbiting relay station 
>> (and apparently no method to transmit surface data via the main Mars 6 
>> craft), all surface activities of Mars 6 and 7 were doomed from the very 
>> start. The only hope they could have was getting some descent information 
>> via the main bus (which more or less worked). The Mars 6 lander might very 
>> well have survived touch-down and run his complete set of surface 
>> activities, but with no-one listening to its signal we will never know...
>>
>> The MER rovers, as well as Viking, are equipped with a direct-to-earth 
>> connection to back up the data transmissions relayed from orbit, this 
>> requires more expenses and more complicated equipment but at least you do 
>> not run the risk that problems with the orbiting relay spoil your day. The 
>> Soviet landers, as well as MPL and Phoenix, relied only on the orbiting 
>> relay and did not have a direct-to-earth link. At least on Mars 6, but 
>> probably also on Mars 3, this resulted in loss of the mission.
>>
>> --
>> Geert Sassen
>>
>> Mobile Netherlands: +31646402502
>> Mobile Thailand: +66833273833
>>
>>     
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-- 
Geert Sassen

Mobile Netherlands: +31646402502
Mobile Thailand: +66833273833

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