Newbie query: _How_ is the shuttle roll manoeuvre performed?

On Fri, 29 Aug 2003 15:13:13 +0100, Trust No One® wrote:

Before anyone flames me I'm not asking WHY the shuttle roll is performed but
rather HOW the manoeuvre is executed.

I did find an reference in the book "Voyage into History" by James Harwood
to the effect:

"The shuttle's computers moved the booster nozzles in opposite directions to
roll Challenger about its vertical axis so as the ship climbed toward space,
the shuttle would be positioned below the external tank with the crew upside
down relative to Earth and the shuttle's wings level in relation to the
horizon"

Is the author referring to the SRB nozzles?

Yes. Attitude control on ascent is by gimbaled nozzles.

http://www.spaceflight.nasa.gov

--
Chuck Stewart
"Anime-style catgirls: Threat? Menace? Or just studying algebra?"

Trust No One® wrote in message
...

Before anyone flames me I'm not asking WHY the shuttle roll is performed
but
rather HOW the manoeuvre is executed.

Been through the FAQ for the newsgroup, Google searches and a couple of
books and while the WHY is explained, there is precious little on how it
is
actually done.

I did find an reference in the book "Voyage into History" by James
Harwood
to the effect:

"The shuttle's computers moved the booster nozzles in opposite directions
to
roll Challenger about its vertical axis so as the ship climbed toward
space,
the shuttle would be positioned below the external tank with the crew
upside
down relative to Earth and the shuttle's wings level in relation to the
horizon"

Is the author referring to the SRB nozzles?

Would very much appreciate if the one of the many experts on the newsgroup
could take time out to explain the HOW of the manoeuvre or point me to a
reference.

One of those questions I've always wanted to ask in my months of lurking,
but have only now plucked up the courage. Bit of a break from the "Maxson
wars" LOL

Thanks & Best Wishes

Here's a starting point: http://www.moog.com/Space/ .

--
John Thomas Maxson, Retired Engineer (Aerospace)
Author, The Betrayal of Mission 51-L (www.mission51l.com)

Is the author referring to the SRB nozzles?

Yes.

Jan

Trust No One® wrote:

Before anyone flames me I'm not asking WHY the shuttle roll is performed
but rather HOW the manoeuvre is executed.

Been through the FAQ for the newsgroup, Google searches and a couple of
books and while the WHY is explained, there is precious little on how it
is actually done.

I did find an reference in the book "Voyage into History" by James
Harwood to the effect:

"The shuttle's computers moved the booster nozzles in opposite directions
to roll Challenger about its vertical axis so as the ship climbed toward
space, the shuttle would be positioned below the external tank with the
crew upside down relative to Earth and the shuttle's wings level in
relation to the horizon"

Is the author referring to the SRB nozzles?

Would very much appreciate if the one of the many experts on the newsgroup
could take time out to explain the HOW of the manoeuvre or point me to a
reference.

One of those questions I've always wanted to ask in my months of lurking,
but have only now plucked up the courage. Bit of a break from the "Maxson
wars" LOL

Thanks & Best Wishes



Hi Trust No One,

Shuttle first stage guidance is basically a table lookup. A table of roll,
pitch and yaw vs velocity. When the Shuttle lifts off from the launch pad,
it hold that attitude, until it crosses the next velocity point in the
table. The values of roll, pitch and yaw at the tower clear velocity is the
attitude that the Shuttle needs to be at the end of the Single Axis
Rotation (SAR). This attitude is very different from it's current attitude
that it has been at since liftoff. It's like having a huge attitude error,
so flight control computes the necessary rotation that the vehicle needs to
perform to get from it's post SAR attitude that guidance commanded. Flight
control also limits the rate of change of the attitude during first stage,
so the vehicle rolls, pitches and yaws at it's maximum rates to get to the
new guidance commanded attitude.

There really is no "Roll Program" in the flight software other that the
vehicle commands having a step change in the vehicle's attitude at tower
clear. And, flight control just figures out how to move the engines to
roll, pitch and yaw the vehicle to this new attitude.

I hope this helps,

Craig Fink

Jan C. Vorbrüggen wrote:
Is the author referring to the SRB nozzles?

Yes.

Jan

Thanks. The paragraph i quoted does answer the question, but did not do much
to help my understanding of the concept. I was struggling to wrap my head
around of the concept of the SRB nozzles "moving in opposite directions".

Following the replies to my post, it is only now hit me that the the
movement refers to swivelling of the SRB nozzles. Seems to make perfect
sense. I'm sure there is much more to it but at least this is a start

My original searches in Google was along the lines of "Shuttle roll
program", but i've now refined them to "Shuttle SRB steering" and "Shuttle
SRB gimbal" and I've now unearthed a mountain of information catering to
levels of expertise from raw newbie to rocket scientist

Thanks to all who replied.

--
Peter X-Files Fan
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John Maxson wrote:

Here's a starting point: http://www.moog.com/Space/ .

John,

Thanks for the link. It certainly did give me a kick-start in the right
direction (see my other post).

Best Wishes

--
Peter X-Files Fan
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