Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Throttle up to 104%
Message-ID: <1990Jun5.033740.8218@utzoo.uucp>
Organization: U of Toronto Zoology
References: <990@gazette.bcm.tmc.edu>
Date: Tue, 5 Jun 90 03:37:40 GMT

In article <990@gazette.bcm.tmc.edu> skywalker@dino.qci.bioch.bcm.tmc.edu (Timothy B. Reynolds) writes:
>On all the shuttle flights @ around 50 + MET into
>the flight, Houston gives the command to go at throttle up
>to 104%. My question is how can you throttle up past 100% ???

The percentages are with respect to the original nominal thrust of the
engines, not to what they are rated for today.  I believe 104% is the
highest power currently cleared for flight, although in pre-Challenger
days NASA was hoping to operate at 109% routinely by now.

>ALso what is MAX-Q

Maximum aerodynamic pressure.  As a rocket climbs, it is picking up speed
(increasing the aerodynamic forces on it) but the air density is also
falling off with altitude (decreasing the forces).  In general there is
a specific point, fairly early in flight, where aerodynamic forces hit
a maximum, and this is one of the worst-case design points for the rocket.

The shutttle throttles back some, early in flight, to avoid building up
too much speed early on while the air is still thick and worsening Max Q.
-- 
As a user I'll take speed over|     Henry Spencer at U of Toronto Zoology
features any day. -A.Tanenbaum| uunet!attcan!utzoo!henry henry@zoo.toronto.edu