In article <1993Apr30.145450.1@stsci.edu> hathaway@stsci.edu writes: >..  >>  >> After all the space walking,  they are going to  re-boost the HST's >> orbit.  I think right now  it's sitting  at 180 miles up, >> they would like  220.  I don't know the exact orbit numbers. 					^^^^^^^^^^^^^^^^^^^^^^ > >As Ben says - this re-boost idea is all news to us here.  Do you know  >something we don't?  Please supply a source - it would be nice for  >the schedulers of observations to know where the thing is going to  >be.  These altitude numbers are also way off.   > >My best source has:  >"Minimum ST ALTITUDE in the PMDB is:    573 Kilometers" >"Maximum ST ALTITUDE in the PMDB is:    603 Kilometers" >"Delta   ST ALTITUDE in the PMDB is:      3 Kilometers"  > >(PMDB is Proposal Management Data Base - used to schedule observations.)  >.. >  I am sure your numbers are far better then mine.  As i said above, i don't have exact numbers.  >> In order to perform the re-boost of the HST, the OMS engines >> will be fired for a long period.  Now the shuttle is a heavy >> thing.  THe HST isn't light either.  THe amount of OMS fuel >> needed to fly both up is substantial.   a small booster >> carried up and used to boost HST on it's own will weigh significantly >> less then the OMS fuel required to Boost  both HST and SHUttle, >> for a given orbital change.   >>  > >Could you supply some calculations?  You might check some recent  >postings that explained that 'a small booster' as suggested does  >not now exist, so comparing the mass of something that doesn't  >exist to the mass of the OMS fuel seems impossible.  The contamination  >threat also remains.   >  How different would the contamination threat of a small manuevering tug be from that of the Shuttle and it's OMS engines??????  I know that no small manuevering tug exists,  but maybe  one could soup up a Bus 1.   Does anyone out there have the de-clasified specs on hte BUS 1?  would it be able to provide enough  control force to balance the HST,  and  still have the rocket thrust to hurl her into a decent high orbit?  >..  >>  >> or the HST could even get placed into  some sort of medium orbit. >> The reason they want a high orbit, is less antenna pointing, >> and longer drag life. >>  >  Longer drag life I can understand, but could you explain the  >antenna pointing?    Sorry,  that should be intrument pointing.  > >> Whatever it is,  the problem in the tilt array is a big constraint >> on HST ops. > >Tell me about it.  Although the arrays can be (and are) moved perfectly  >well utilizing the second electronics box.  Getting them both working  >is much desireable so as to reclaim redundancy.    Plus, if the second box gets fritzy, you could be in shitter ville real fast.  > >I don't mean to jump on you - helpful suggestions are always welcome  >and we all know the more ideas the better, but I do want the true  >situation to be described clearly and correctly, lest some get  >confused.  > >Regards,  >Wm. Hathaway   The problem is no-one seems to have the exact numbers.  When the mission was planned originally at 3 spacewalks,  and 3 astronauts,  there was enormous concern over the mass margins for the flight.  THey have now planned for 5 EVA's,  an 11 day mission and have 2 reserve EVA's and an emergency EVA.  Obviously that is coming from somewhere. My guess is the OMS burn  fuel,  or  re-boost  margin.     I just figured, if GOldin wants to really,  prove out faster, cheaper better,   have some of the whiz kids  slap together an expendable space manuevering tug  out of a BUs1,  and use that for the re-boost. it has to be better then using the Discovery as a tow truck.