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From: lohof@buast5.bu.edu (Alan Lohof)
Newsgroups: sci.space.shuttle
Subject: Re: Shuttle Status for 02/22/91 (Forwarded)
Message-ID: <75803@bu.edu.bu.edu>
Date: 28 Feb 91 08:36:43 GMT
References: <1991Feb22.223855.6112@news.arc.nasa.gov> <1991Feb27.123109.540@axion.bt.co.uk>
Sender: news@bu.edu.bu.edu
Organization: Boston University
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>>                        STS-39/DoD - DISCOVERY (OV 103) - PAD A
>>                                  LAUNCH - MARCH 1991
>> 
>>           WORK IN PROGRESS:
>>           - Evaluation of cracks in hinges for the external tank right  and
>>           left doors.
>		 ^^^^^
>Anyone able to say what these are ? Hard to imagine what kind of doors a tank
>can have.
>

Recall how the orbiter is attached to the external tank? the orbiters 
engines get hydrogen and oxygen from the external tank via large pipes
connecting the tank and the orbiter's underside. when the orbiter 
separates from the external tank, the pipes drop away from the valves
on the orbiter and the above mentioned doors closed over the valves to 
seal the underside of the orbiter.  The orbiters 'belly' must be sealed
with the protective tiles for re-entry. A problem would arise if these
valve hinges with the cracks would break away or be unable to close,
thus exposing an area to the heat or re-entry. 

alan lohof
lohof@buast5.bu.edu
Boston Univ. Astro Dept.