From: prb@access.digex.net (Pat)
Subject: Re: HST Servicing Mission Scheduled for 11 Days
Organization: Express Access Online Communications USA
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NNTP-Posting-Host: access.digex.net

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.

pat

