Roll Program
dane_arnold
program, but here is some of what I know:
The shuttle launch pads are the same as those used during the
Apollo program, hence their configuration and orientation were
defined long before theshuttle was ever designed. Hence, the
orientation of the Shuttle vehicle on the pad was fixed (on pad A,
the tail of the vehicle points roughly south). After liftoff, the
vehicle must assume a proper launch azimuth upon clearing the tower in
order to achieve the desired orbital inclination. Therefore, it has to
roll in order to do so. You may notice that flights to high inclination
orbits appear to roll more than those to the usual 28.5 deg. inclination.
The Apollo/Saturn vehicles also had a roll profile early in first stage
(at least there was a voice call to that effect, but I'll be darned if I
can see it from the videotape that I have). I don't think it had
anything to do with allowing the crew to see the horizon as the windows
were covered by a boost protection cover during first stage flight. I'm
guessing it had to do with aligning the vehicles navigation base with
some desired azimuth.
Maybe somebody else can tell me why we fly heads down vs. heads up.
Maybe its structual loading.
Michael Guzzo
>: Maybe somebody else can tell me why we fly heads down vs. heads up.
>: Maybe its structual loading.
> Or may just pure aerodynamics? Seems the stack would cut through the air/
>atmosphere better heads down than up. Anyone know?! Interesting thread! Love
>this kind of stuff!
>Tom
I believe the traditional reason for heads down was to allow the crew to
acquire the horizon for orientation purposes. Technically, you can fly heads
up or heads down, you would have to recertify the ET to allow exposure to
heating on the "backside."
________________________________________________________________________
Michael S. Guzzo msg...@srqa01.jsc.nasa.gov
The FutureBasic FAQ is almost here....
Tom Randall
: I am only going from my own knowledge of why there is a roll
Or may just pure aerodynamics? Seems the stack would cut through the air/
Gert-Jan Bartelds
SNIP SNIP....
>The Apollo/Saturn vehicles also had a roll profile early in first stage
>(at least there was a voice call to that effect, but I'll be darned if I
>can see it from the videotape that I have). I don't think it had
>anything to do with allowing the crew to see the horizon as the windows
>were covered by a boost protection cover during first stage flight. I'm
>guessing it had to do with aligning the vehicles navigation base with
>some desired azimuth.
I have a copy of "Apollo 12 Lunar Trajectory Notes", also known as MSC
Internal Note 69-FM-305, which discusses all aspects of this lunar
flight. This is what it has to say on the launch, including the
Roll Program:
" After launch, the vehicle rises approximately 43 feet vertically to
clear the launch umbilical tower. During the vertical rise, a yaw
maneuver is executed to increase the lateral distance between the
vehicle and the tower. After the tower is cleared vertically, the pitch
and roll programs are initiated. The roll program alined the vehicle
body axis with the computed flight azimuth. The pitch prpgram provides a
trajectory that satisfies vehicle performance, heating, and load
requirements."
As I understand it, the launch azimuth changes during the launch window
because of the rotation of the Earth, about 15 degrees per hour. Thus
the amount of "roll" should also change within the launch window. This
comes about because the spacecraft needed to be put into a precise
plane, defined by the vector to the Moon's position (at arrival) and the
vector to KSC, taking the center of Earth as the origin for these
vectors. (It's hard to describe this in words, drawing a picture might
help...)
I think, but am not sure, that for a Shuttle launch the azimuth
*doesn't* change within the launch window, because there's no need to be
in a plane with the Moon. Anybody comment on this?
Gert-Jan Bartelds
Jack Frillman
|> In article <36aif7$1g...@admaix.sunydutchess.edu> ran...@cygnus.sunydutchess.edu (Tom Randall) writes:
|>
|> >: Maybe somebody else can tell me why we fly heads down vs. heads up.
|> >: Maybe its structual loading.
|>
|> > Or may just pure aerodynamics? Seems the stack would cut through the air/
|> >atmosphere better heads down than up. Anyone know?! Interesting thread! Love
|> >this kind of stuff!
|>
|> >Tom
|>
|> I believe the traditional reason for heads down was to allow the crew to
|> acquire the horizon for orientation purposes. Technically, you can fly heads
|> up or heads down, you would have to recertify the ET to allow exposure to
|> heating on the "backside."
|>
This is correct. Last night on The Learning Channel there was an episode
of Scientific Frontiers that was about the shuttle. The pilot of the flight
stated that they flew heads down so they could "look up" and see the horizion
for reference. This was also true for Apollo where the commanders side window
was uncovered during launch.
--
\ /
\ /
------------------+ ( ) +------------------
Jack Frillman | ^ " Carrots are devine you | Mead Data Central
ja...@meaddata.com | *\/|\ get a dozen for a dime, | P.O. Box 933
(513) 865-6800 | |/ it's magic! | Dayton, Oh 45401
EXT. 4812 | | -Bugs Bunny |
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-- --
George Rachor
>>: Maybe somebody else can tell me why we fly heads down vs. heads up.
>>: Maybe its structual loading.
>> Or may just pure aerodynamics? Seems the stack would cut through the air/
>>atmosphere better heads down than up. Anyone know?! Interesting thread! Love
>>this kind of stuff!
>>Tom
>I believe the traditional reason for heads down was to allow the crew to
>acquire the horizon for orientation purposes. Technically, you can fly heads
>up or heads down, you would have to recertify the ET to allow exposure to
>heating on the "backside."
>________________________________________________________________________
>Michael S. Guzzo msg...@srqa01.jsc.nasa.gov
One more factor was so radio signals from ground to air didn't have to
go through the ET to get to the orbiter (Just one more hunch... Does anyone
really know?)
George Rachor
Aloha, OR
--
George L. Rachor Jr.
Prefered mail address:
geo...@endeavor.intel.com
Len Struttmann
|> DaneArnold wrote:
|> : Maybe somebody else can tell me why we fly heads down vs. heads up.
|> : Maybe its structual loading.
|>
|> Or may just pure aerodynamics? Seems the stack would cut through the air/
|> atmosphere better heads down than up. Anyone know?! Interesting thread! Love
|> this kind of stuff!
|>
|> Tom
|>
From the NSTS 1988 News Reference Manual:
"The orbiter flies upside down during the
ascent phase. This orientation, together with trajectory shaping,
establishes a trim angle of attack that is favorable for aerodynamic loads during the region of high dynamic pressure, resulting in a net positive
load factor, as well as providing the flight crew with use of the ground
as a visual reference. By about 20 seconds after lift-off, the
vehicle is at 180 degrees roll and 78 degrees pitch."
Len
--
==========================================================================
| Len Struttmann - Rockwell Collins Avioncs |
| lmst...@cca.rockwell.com |
==========================================================================
Dean Lopez
> One more factor was so radio signals from ground to air didn't have to
> go through the ET to get to the orbiter (Just one more hunch... Does anyone
> really know?)
I'm a little late on this thread, but I've heard of another reason why the
Shuttle flies heads-down that hasn't been mentioned yet. In fact, it was
supposedly a *big* reason.
It has to do with the thrust force vector, and how it must be centered through
the ET. Structurally, this means its easier to *push* the ET than *pull* it.
Anyone else care to comment on this one?
--
+--------------------------------------+------------------------------+
| Dean Lopez | |
| SAIL DPS Engineer | dlo...@sailsun.jsc.nasa.gov |
| Rockwell Space Operations Co. | dean...@aol.com |
| JSC Shuttle Avionics Integration Lab | dean_...@maclair.sccsi.com |
+--------------------------------------+------------------------------+
#include <standard_disclaimer.h>
/* The opinions expressed are all mine.
RSOC doesn't speak for me and I don't speak for RSOC
After all, I'm only an engineer - what do I know? */
Michael Guzzo
>From: geo...@ornews.intel.com (George Rachor)
>Subject: Re: Roll Program
>Date: 28 Sep 1994 13:50:36 -0700
>msg...@srqa01.jsc.nasa.gov (Michael Guzzo) writes:
>>>Tom
In a heads up attitude you could use TDRS for comm.
________________________________________________________________________
Michael S. Guzzo msg...@srqa01.jsc.nasa.gov
fis...@skylab.enet.dec.com
In article <bartelds....@ruunat.fys.ruu.nl>, bart...@fys.ruu.nl
|>I have a copy of "Apollo 12 Lunar Trajectory Notes", also known as MSC
|>Internal Note 69-FM-305, which discusses all aspects of this lunar
|>flight. This is what it has to say on the launch, including the
|>Roll Program:
|>
|>" After launch, the vehicle rises approximately 43 feet vertically to
|>clear the launch umbilical tower. During the vertical rise, a yaw
|>maneuver is executed to increase the lateral distance between the
|>vehicle and the tower. After the tower is cleared vertically, the pitch
|>and roll programs are initiated. The roll program alined the vehicle
|>body axis with the computed flight azimuth. The pitch prpgram provides a
|>trajectory that satisfies vehicle performance, heating, and load
|>requirements."
|>
|>As I understand it, the launch azimuth changes during the launch window
|>because of the rotation of the Earth, about 15 degrees per hour. Thus
|>the amount of "roll" should also change within the launch window. This
Yes, this makes sense, but does not explain the real question: Why do you have
to roll a Saturn V to hit a particular azimuth. Given that it is approximately
symmetrical, it should not matter in terms of aerodynamics (as it does with the
shuttle).
I think that the real answer to "Why Roll" is still either (or both) "to orient
the crew in a particular direction relative to the horizon", or "to make it
easier on the relatively primitive navigation/gimballing etc hardware and
software.
Burns
Marc Brett
: In article <36ckus$k...@ornews.intel.com> geo...@ornews.intel.com (George Rachor) writes:
[deletia]
: >One more factor was so radio signals from ground to air didn't have to
: >go through the ET to get to the orbiter (Just one more hunch... Does anyone
: >really know?)
[]
: In a heads up attitude you could use TDRS for comm.
Story I heard was that spacecraft sit on the pad for days with
telemetry antennas operating at low power, pointed away from ocean
where Russian spy trawlers may be lurking. Once in the air, these same
antennas are more useful running at full power, pointed at the ground.
Any truth to this spin (pun intended) on the story?
--
Marc Brett Marc....@london.waii.com
Western Geophysical Tel: +44 81 560 3160
Henry Spencer
>...makes sense, but does not explain the real question: Why do you have
>symmetrical, it should not matter in terms of aerodynamics (as it does with the
>shuttle).
I can't find a definitive statement, but I do find strong implications that
the purpose is to align the navigation axes with the flight path. The roll
maneuver definitely did *accomplish* that -- the yaw angle was normally zero
throughout the rest of the flight.
I don't think the "view of the horizon" argument holds water for Apollo,
because the view out from within the CM was poor at best, and virtually
zero with the crew in their couches and the protective cover on the CM.
--
Justice for groups that doesn't include justice | Henry Spencer
for individuals is a mockery. | he...@zoo.toronto.edu
T.E.Thack...@lesueloc.com
> I'm a little late on this thread, but I've heard of another reason why the
> Shuttle flies heads-down that hasn't been mentioned yet. In fact, it was
> supposedly a *big* reason.
> It has to do with the thrust force vector, and how it must be centered
through
> the ET. Structurally, this means its easier to *push* the ET than *pull* it.
> Anyone else care to comment on this one?
I believe the original reason was abort safety. An RTLS abort only requires
a pitcharound. If flown heads-up then a pitcharound and a roll is required.
The ET must be jettisoned downwards to avoid recontacting the orbiter when
it tries to pull out of it's reentry dive.
BTW: They are considering a heads-up ascent now. It seems that because of
thrust vector geometry that the slight up-lift generated from a heads-up
ascent (versus down-lift for a heads-down ascent) would add something like
2000 lbs to payload performance. (The throttle to 65-67% is to negate this
little lift so max-Q doesn't shred the wings).
T.E.Thack...@lesueloc.com
> Yes, this makes sense, but does not explain the real question: Why do you
have
> to roll a Saturn V to hit a particular azimuth. Given that it is
approximately
> symmetrical, it should not matter in terms of aerodynamics (as it does with
the
> shuttle).
>
> I think that the real answer to "Why Roll" is still either (or both) "to
orient
> the crew in a particular direction relative to the horizon", or "to make it
> easier on the relatively primitive navigation/gimballing etc hardware and
> software.
The roll program was exceedingly primitive by today's standards. The
practice of rolling to the correct axis simplifies the guidance problem
into a simple pitch in a 2-D plane. The software of the time had very
limited computational ability & it greatly simplified computations to
pitch solely about one vehicle axis. It also helped prevent the dreaded
axis lockup. At certain attitudes (where the gimbal axes would all align),
the gyro gimbals would "freeze" - resulting in total gyro loss of alignment.
The danger of this was lessened if the vehicle could roll, then pitch.
Also, rolling onto the right azimuth meant that steering commands need
only command one or two engines into a single-pitch direction. up-down,
or left-right. It was way beyond those computers to figure a spherical
pitch equation.
Also-squared, the first stage boost was a simple pitch-profile. No
iterative guidance until SII boost. The roll component merely lined up
the stack in preparation for the simple pitch profile.
ANDREW SCHWERIN
about certain subjects, but I tend not to know what the name of the subjects
are. If anyone could briefly describe the roll program, perhaps I have some
useful information.
-Andrew Schwerin
... Battelstar Galactica- Science Fiction meets Comedy
___ Blue Wave/QWK v2.12
ANDREW SCHWERIN
The roll is performed, to the extent of my knowledge, to alleviate pressure
on the shuttle orbiter. It seems that the payload bay doors and the area
on the top of the shuttle are not as well equipped to take such pressures
as are the ET, SRBS, and the belly of the shuttle.
As to why the Saturn V would make use of a role manuver, I cannot say.
Perhaps it had some function in aligning the rocket on a navigational
axis.
Well, maybe
Andrew Schwerin
... RAM = Rarely Adequate Memory
___ Blue Wave/QWK v2.12
Michael K. Heney
<T.E.Thack...@lesueloc.com> wrote:
>
[...]
>
> BTW: They are considering a heads-up ascent now. It seems that because of
>thrust vector geometry that the slight up-lift generated from a heads-up
>ascent (versus down-lift for a heads-down ascent) would add something like
>2000 lbs to payload performance. (The throttle to 65-67% is to negate this
>little lift so max-Q doesn't shred the wings).
Can you provide a bit more detail on this? Who are "they", and how far
along has the "considering" part gotten? I can see this helping on the
Ralpha assembly flights - boosting performance to a 51.8 degree orbit
would make life somewhat easier ...
----
Mike Heney | Senior Systems Analyst | Reach for the
mhe...@access.digex.net | Space Activist / Entrepreneur | Stars, eh?
Silver Spring, MD 20901 | Working for SSAI at NASA/GSFC |
T.E.Thack...@lesueloc.com
> I seem to have picked up what the roll program is since my last post.
> The roll is performed, to the extent of my knowledge, to alleviate pressure
> on the shuttle orbiter. It seems that the payload bay doors and the area
> on the top of the shuttle are not as well equipped to take such pressures
> as are the ET, SRBS, and the belly of the shuttle.
>
Not so. The roll program does not affect pressure on the bay doors. That is
solely a function of Pitch. Pitch during boost is only affected by SSME
throttle settings (Thrust Vector Pitch).
The roll program rotates the vehicle about the vertical axis while it is
ascending straight up so that the pitchover onto the orbital path is neatly
aligned with the orbiter's belly or backside. This makes for simpler and
easier guidance algorithms. Although the gyros can have any attitude, they
had to choose a reference "up" - and this was chosen to be the classical
aircraft "up". It needs an "up" so the guidance equations have somewhere to
begin calculating from. Apollo's "up" was chosen such that the astronauts
in their couches would be sitting "upright".
In the case of the Saturn, any old axis would do as "up" and they had to
choose one. Saturn's "up" was such that it pointed due south at the moment
of launch and was rolled to the right anywhere from 38 to 140 degrees.
The shuttle had an additional constraint to ensure even forces on the
wings - but the Saturn philosophy suited this just fine. The only major
change was that the X and Z axes were switched due to the Saturn being
at home upright and the Shuttle at-home horizontal.
BTW: There is no difference in force on the vehicle if the shuttle is
heads-down or up. Head-down improves an RTLS abort's geometry but heads-up
adds 2,000 lbs to performance.
T.E.Thack...@lesueloc.com
> > BTW: They are considering a heads-up ascent now. It seems that because of
> >thrust vector geometry that the slight up-lift generated from a heads-up
> >ascent (versus down-lift for a heads-down ascent) would add something like
> >2000 lbs to payload performance. (The throttle to 65-67% is to negate this
> >little lift so max-Q doesn't shred the wings).
>
> Can you provide a bit more detail on this? Who are "they", and how far
> along has the "considering" part gotten? I can see this helping on the
> Ralpha assembly flights - boosting performance to a 51.8 degree orbit
> would make life somewhat easier ...
>
there is a small crab angle that the shuttle thrusts into relative to
the vehicle longitudinal axis. The wind forces during early ascent on this
small angle generates a small amount of side force as well as the much
larger axial force. Throttling down at max-Q reduces this crab angle and
reduces the stress on the orbiter wings.
Flying the shuttle heads-up causes this small side force to be a lofting
force instead of a diving force. This allows the ascent trajectory to be
slightly depressed to attain the same injection targets. This depression
improves the horizontal thrust component such that an extra 2,000 lbs payload
can be lofted.
I remember seeing this as I was reading NASA technical articles in a
Federal Repository library. (Most any University library is a Federal
Repository library. If not just ask them where one is).
BTW: Can any FDO's out ther confirm this one:
I have performed an iterative computation showing that shuttle performance
would improve by about 5,000 to 7,000 lbs by delaying throttle-up until PC-50
which occurs about T+120 seconds. Keep the same trajectory as if no such
delay occurred (In other words, don't "react" to the lack of throttle-up).
In other words, 100% from T+0 to T+10, 104% from T+10 to T+30 or so,
67% from T+30 to T+120 (and not T+60), back to 104% from T+120 to stack
mass of 488,800 lbs at about t+450 or so, the continuous 3G throttle until
MECO.
The swing between 5,000 and 7,000 lbs is because I don't have the exact
SRB thrust profile nor the exact STS pitch profile. I got a candidate SRB
profile from various NASA tech articles and adjusted the STS pitch profile
until the computed targets started matching what NASA has in their press kits
under Trajectory Sequence of Events.
So could a NASA FDO out there plug my 67%-thru-Pc50 into the actual profile
and see what improvement it yields?
Philip D Bridges
>would improve by about 5,000 to 7,000 lbs by delaying throttle-up until PC-50
>which occurs about T+120 seconds. Keep the same trajectory as if no such
>delay occurred (In other words, don't "react" to the lack of throttle-up).
One factor to keep in mind is that the shuttle trajectory is optimized
not only for performance but also for abort boundaries. As I recall from
my work as an RTLS guidance/control engineer, the second stage guidance
produces a more lofted trajectory than one would expect from an optimal
solution in order to make sure the shuttle can always perform a
successful abort. To produce the lofting, the second stage guidance is
told that an engine failure will occur at some point in the flight. The
guidance solution thus produces a more lofted orbit. At some point
in the second stage, the guidance algorithm is told that it will
have all three engines for the rest of the trajectory, with the result
being the trajectory flattens out for the remainder of the flight.
The first stage guidance is also non-optimal for performance due to
shaping the trajectory to achieve maximum load relief within the
constraints of the ascent trajectory. In fact, the first stage
guidance is open-loop, and only flies commanded body angles. The
flight control system does active load relief using the elevons and
can override the guidance command to ensure the wings aren't overstressed.
So, yes, you probably can get more performance out of the ascent
trajectory. However, you may not be able to do a successful abort if
an engine fails at the wrong time.
Phil Bridges
Dept. of Aerospace Engineering
Miss. State University