Satgen 215  Hubble Space Telescope - Lessons   by GM4IHJ      8th May 93
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NASA recently published a new plan for the repair of the visual impaired
Space Telescope. The December 93 mission has grown and grown ever since
the original discovery that the telescope's major optical system did not
focus properly. Hubble's troubles have several useful lessons for Radio
Amateur Satellite builders.
Firstly and perhaps , lost, in the press reports at this time , is the
fact that even if the scope focus problem had not occured, Hubble would
have required a rescue mission at this time because it is running out of
operational inertia wheel stabilisers. It started with 6. A pair for each
of its X ,Y and Z axes. But it now only has 3 , and one of them is taking
excess drive current suggesting imminent failure. If it fails before Dec
93, Hubble will have to shut down, because it must stabilize extremely
accurately in all 3 axes if it is to take steady pictures of distant stars
and galaxies. Amateur Radio satellites due to be launched with inertia
wheel stabilization, look very dodgy in light of their failure in almost
every satellite in which they have been fitted. Mir, Hubble and Solar Max
Mission have all had mission critical failures of inertia wheels.
Fortunately it has been possible to replace the duds in these sats, but
this will not be possible in Amateur Radio Satellites. May be Amateurs
will build wheels with long lives - but I would not bet on it.
Another big problem on Hubble which could influence the design of Amateur
Radio sats, is the satellite wobble introduced as Hubbles large solar
panels emerge out of Earth shadow and warmed by the sun, expand and move
about. With 15 sunsets a day this recurrent wobble can be a very big
nuisance.
Both the above faults have come close to rendering Hubble inoperable. But
the lens focus is still the biggest job for the December repair crew.
Radio Amateurs do not have repair crews, so perhaps this warns us to be
very very careful with pre launch checks. It is difficult to sympathise
with Hubble's builders, however we should not forget. That Amsat Oscar 10
went for a mystery tour of the Van Allen Radiation Belts, and was thereby
subject to radiation damage which severely impaired its usefullness. As
far as I know, the best explanation for why Oscar 10's rocket motor
refused to obey ground control, was a possible wrong connection on inter
frame to motor wiring . Eg plug wired 1.2,3,4, socket wired 2,3,4,5. Phase
3D's motor wiring will hopefully be treble checked.
Meanwhile NASA has had to lengthen the Hubble Repair Mission from 8 to 11
days - something now possible with the improved Shuttle Electrical
supplies, in order to meet the increasing work load on the 4 space walking
crew members. Lets hope all goes well for them.
Unfortunately the Hubble orbit does not bring it above the latitude of the
Channel Islands. So UK ops will probably not be able to monitor the very
interesting EVA radio traffic unless they take a December holiday in
Gibraltar. Which is not a bad idea to close on. 73 de GM4IHJ @ GB7SAN