Newsgroups: sci.space
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Shuttle fuel reserves
Message-ID: <1990Jan18.060556.2168@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1990Jan17.233050.3044@helios.physics.utoronto.ca>
Date: Thu, 18 Jan 90 06:05:56 GMT

In article <1990Jan17.233050.3044@helios.physics.utoronto.ca> neufeld@physics.utoronto.ca (Christopher Neufeld) writes:
>...one of the shuttle's forward thrusters fired accidentally last night...
>   So, was the thruster which fired one of the ones used to break orbit?

A 'forward thruster' will be an RCS thruster, used for attitude control
and minor maneuvering.  I *think* they normally use the OMS for retrofire.

>What is the fuel reserve on the shuttle? Are there similar thrusters on the
>stern, which would not deorbit the shuttle, but could burn so much fuel
>that the shuttle would no longer be able to break orbit?

Fuel reserves are substantial, and although I don't have a shuttle plumbing
diagram handy, it is normal to split such multi-thruster systems into two
entirely separate subsystems, with separate tanks, each capable of doing
any crucial jobs.  This guards against massive malfuction in one subsystem.
(For example, a thruster which cannot be turned off except by shutting
down an entire subsystem -- it happened to Gemini 8.)

> Does the shuttle
>always fly with the nose pointing along the orbit (ie. forward)?

No.  Shuttle attitude is determined by what it's doing (i.e. whether the
cargo bay wants to point in some specific direction) and a variety of
other minor issues.

>   While we're on the subject of fuel, does the shuttle exhaust all its
>fuel before landing, or does it land with some fuel left in the tanks?

The latter.  That's why the first ground crews around a landed shuttle
are wearing protective gear -- the fuel and oxidizer are very toxic.

>Also, are the shuttle's thrusters powered by hydrogen-oxygen, hydrazine, or
>something else?

Oxidizer is nitrogen tetroxide, fuel is one of the hydrazine family (I
think it's monomethyl hydrazine but I could be wrong).  They're toxic
and corrosive and vile in other ways, but they don't need refrigeration
and they're hypergolic (ignite on contact --> no ignition system).
-- 
1972: Saturn V #15 flight-ready|     Henry Spencer at U of Toronto Zoology
1990: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
