[FPSPACE] planetary orbiting relaystations

[LARRY KLAES]

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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