Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Speed and altitude
Message-ID: <1988Oct1.224618.10990@utzoo.uucp>
Organization: U of Toronto Zoology
References: <790@nosc.NOSC.MIL> <23004@tut.cis.ohio-state.edu>
Date: Sat, 1 Oct 88 22:46:18 GMT

In article <23004@tut.cis.ohio-state.edu> pritch@tut.cis.ohio-state.edu (Norm Pritchett) writes:
>>While listening to the launch broadcast this morning I noticed that as
>>the shuttle's velocity increased, its altitude seemed to decrease.  
>>At some where around 15000fps the altitide was 65 nautical miles 
>>and then a few seconds later around 19Kfps it sounded like the 
>>controller called out the altitude as 61 n.m.  Did I mis-hear this?
>
>... I heard it mentioned that this was done to insure
>proper ditching of the external tank into the ocean rather than having
>it go into orbit.

The early shuttle missions flew a dip maneuver to put the ET into the
Indian Ocean.  The later ones used a direct-ascent trajectory which did
away with the dip and put the ET into the Pacific.  I don't know which
trajectory this flight is using, offhand.

Another possible reason for the dip is simply that the shuttle is
accelerating horizontally and the small loss in altitude is unimportant.
*Velocity* is the main requirement for getting into orbit; any fuel spent
on maintaining altitude is unproductive overhead.  Some such overhead is
necessary, since the shuttle has to get out of the atmosphere to do its
accelerating, but the less fuel spent on it, the better.  The shuttle
may simply have been starting to fall back to Earth, with no attempt made
to stop it since orbital velocity was not far away anyhow.
-- 
The meek can have the Earth;    |    Henry Spencer at U of Toronto Zoology
the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu