Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed

Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed

In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and
accepting the performance penalty), I saw some
remarks that the current ascent trajectory is
actually an innovation introduced for Mir and ISS
orbital inclinations, to regain some performance
lost by the higher inclination. Is that true -- and
what were the performance consequences?

Does this make the higher-Q (and higher aero
stress on TPS) another 'benefit' of the Russian
partnership? Or am I more confused than usual?

Thanks!

Jim O

In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and
accepting the performance penalty), I saw some
remarks that the current ascent trajectory is
actually an innovation introduced for Mir and ISS
orbital inclinations, to regain some performance
lost by the higher inclination. Is that true -- and
what were the performance consequences?

I seem to remember changing the angle of attack so that
there was actually some lift from the wings during ascent.
That certainly was to increase performance for the high-
inclination and weight-limited launches. How much of a
difference that makes I dunno.

Jan

Jan Vorbrüggen wrote:

: In recent discussions about lowering the Q on the
: 121 ascent profile, to the 'Lo-Q' trajectory (and
: accepting the performance penalty), I saw some
: remarks that the current ascent trajectory is
: actually an innovation introduced for Mir and ISS
: orbital inclinations, to regain some performance
: lost by the higher inclination. Is that true -- and
: what were the performance consequences?
:
:I seem to remember changing the angle of attack so that
:there was actually some lift from the wings during ascent.
:That certainly was to increase performance for the high-
:inclination and weight-limited launches. How much of a
:difference that makes I dunno.

I would think this would actually DECREASE performance, since you
would then be deliberately putting the vehicle into a 'draggier'
attitude (lift creates drag) and losing energy to that drag.

Orbit isn't about HEIGHT. It's about SPEED.

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

On Tue, 09 May 2006 14:27:06 GMT, Fred J. McCall
wrote:

Jan Vorbrüggen wrote:

: In recent discussions about lowering the Q on the
: 121 ascent profile, to the 'Lo-Q' trajectory (and
: accepting the performance penalty), I saw some
: remarks that the current ascent trajectory is
: actually an innovation introduced for Mir and ISS
: orbital inclinations, to regain some performance
: lost by the higher inclination. Is that true -- and
: what were the performance consequences?
:
:I seem to remember changing the angle of attack so that
:there was actually some lift from the wings during ascent.
:That certainly was to increase performance for the high-
:inclination and weight-limited launches. How much of a
:difference that makes I dunno.

I would think this would actually DECREASE performance, since you
would then be deliberately putting the vehicle into a 'draggier'
attitude (lift creates drag) and losing energy to that drag.

The delta increase in drag from an epsilon increase in lift isn't that
big if you can use the lift to get higher quicker. There's less drag
at higher altitudes. There's also less lift, but the reduction in
drag is bigger because parasite drag is reduced, too, not just
induced.

Orbit isn't about HEIGHT. It's about SPEED.

But speed can be about height. Drag is, so speed is.

Mary
--
Mary Shafer Retired aerospace research engineer
We didn't just do weird stuff at Dryden, we wrote reports about it.
or

On Mon, 08 May 2006 14:06:24 +0000, Jim Oberg wrote:

Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed

In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and
accepting the performance penalty), I saw some
remarks that the current ascent trajectory is
actually an innovation introduced for Mir and ISS
orbital inclinations, to regain some performance
lost by the higher inclination. Is that true -- and
what were the performance consequences?

Does this make the higher-Q (and higher aero
stress on TPS) another 'benefit' of the Russian
partnership? Or am I more confused than usual?


No, I wouldn't blame the Russian for how NASA decides to the increase
performance of the Space Shuttle.

Yes, higher Q increases loads on the vehicle including TPS.

As for the performance gain, they should have been quoting a performance
loss in their presentations. HighQ to LowQ with the NominalQ in between.
I'd imagine it would be around a 1000 lbs, maybe more, but you need to
look at their recent presentations for a better number.

--
Craig Fink
Courtesy E-Mail Welcome @

On Tue, 09 May 2006 08:17:56 -0700, Reunite Gondwanaland (Mary Shafer)
wrote:

On Tue, 09 May 2006 14:27:06 GMT, Fred J. McCall
wrote:

Jan Vorbrüggen wrote:

: In recent discussions about lowering the Q on the
: 121 ascent profile, to the 'Lo-Q' trajectory (and
: accepting the performance penalty), I saw some
: remarks that the current ascent trajectory is
: actually an innovation introduced for Mir and ISS
: orbital inclinations, to regain some performance
: lost by the higher inclination. Is that true -- and
: what were the performance consequences?
:
:I seem to remember changing the angle of attack so that
:there was actually some lift from the wings during ascent.
:That certainly was to increase performance for the high-
:inclination and weight-limited launches. How much of a
:difference that makes I dunno.

I would think this would actually DECREASE performance, since you
would then be deliberately putting the vehicle into a 'draggier'
attitude (lift creates drag) and losing energy to that drag.

The delta increase in drag from an epsilon increase in lift isn't that
big if you can use the lift to get higher quicker. There's less drag
at higher altitudes. There's also less lift, but the reduction in
drag is bigger because parasite drag is reduced, too, not just
induced.

Orbit isn't about HEIGHT. It's about SPEED.

But speed can be about height. Drag is, so speed is.


The object during first stage is to not break the wings/tail off during
ascent. It's really a constraints problem with a little optimization
within those constraints. The Orbiter in first stage is flying above it's
manuvering speed. During high Q, it's flying a negative angle of attack to
reduce loads on the wings. It must fly within an angle-of-attack/dynamic
pressure (QAlpha) and QBeta tunnel, so to speek. Any optimization within
this tunnel would put the Orbiter at the edge of the "acceptable" tunnel,
as opposed to fly down the center of the tunnel. And, some small amount
of performance would be gained.

In the case of the Shuttle, it's flying upside down with a negative angle
of attack. A more positive angle of attack increase performance, while
more negative angle of attack decrease performance. A more negative angle
would actually produce more lift in the up direction. So, it really about
gaining speed downrange, letting the flight path angle fall off with time,
not fighting gravity with lift.

--
Craig Fink
Courtesy E-Mail Welcome @

Craig Fink wrote in
news
On Mon, 08 May 2006 14:06:24 +0000, Jim Oberg wrote:

Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed

In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and
accepting the performance penalty), I saw some
remarks that the current ascent trajectory is
actually an innovation introduced for Mir and ISS
orbital inclinations, to regain some performance
lost by the higher inclination. Is that true -- and
what were the performance consequences?

As for the performance gain, they should have been quoting a performance
loss in their presentations.

I think Jim knew that - the "regain some performance" was in reference to
the switch *to* high-Q.

HighQ to LowQ with the NominalQ in between.
I'd imagine it would be around a 1000 lbs, maybe more, but you need to
look at their recent presentations for a better number.

1000 lbs is about right for the loss from high-Q to low-Q. 121 could spare
it because they had around 1900 lbs margin. 115 and other performance-
critical flights will need some other solution.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Jim Oberg wrote:
Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed

In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and
accepting the performance penalty), I saw some
remarks that the current ascent trajectory is
actually an innovation introduced for Mir and ISS
orbital inclinations, to regain some performance
lost by the higher inclination. Is that true -- and
what were the performance consequences?

try
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=2248&start=1

1000 lbs is about right for the loss from high-Q to low-Q. 121 could spare
it because they had around 1900 lbs margin. 115 and other performance-
critical flights will need some other solution.

The other quesions is: What problem does this solve? OK, so there is less
aero stress on the orbiter including its TPS. How does that influence the
chance that any foam from the tank actually impacts the TPS? It seems to
me the mechanism could actually work in the other direction: higher Q could
mean less chance of hitting the orbiter with debris. So what's actually the
case and the rationale?

Jan

On Tue, 09 May 2006 17:47:40 -0500, Jorge R. Frank wrote:

Craig Fink wrote in
news
On Mon, 08 May 2006 14:06:24 +0000, Jim Oberg wrote:

Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed

In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and
accepting the performance penalty), I saw some
remarks that the current ascent trajectory is
actually an innovation introduced for Mir and ISS
orbital inclinations, to regain some performance
lost by the higher inclination. Is that true -- and
what were the performance consequences?

As for the performance gain, they should have been quoting a performance
loss in their presentations.

I think Jim knew that - the "regain some performance" was in reference to
the switch *to* high-Q.

Well, the performance gain from a "Nominal" Q to High Q probably would
have been something like 300-400 lbs. At the performance Optimal Q the
derivative dWT/dQ is zero, by definition. Like being at the top of a hill,
varying Q and loads doesn't change performance. As Q is increased from
"Nominal" Q the gain dWT/dQ becomes less and less, so High Q doesn't gain
that much. Essentially, gaining less and less performance while steadily
increasing Q/loads.


HighQ to LowQ with the NominalQ in between. I'd imagine it would be
around a 1000 lbs, maybe more, but you need to look at their recent
presentations for a better number.

1000 lbs is about right for the loss from high-Q to low-Q. 121 could
spare it because they had around 1900 lbs margin. 115 and other
performance- critical flights will need some other solution.

Included in DOLILU I software was an input variable Delta Meco WT, which
would have allowed the Shuttle to use excess margin to decrease dynamic
pressure and loads on the Day of Launch. Trading excess performance for
decreased loads in first stage. So in the case of the next flight, on the
Day of Launch, -1900 lbs delta Meco WT could have been entered and vehicle
would fly a much lower Q.

But, you say, all the ISS mission have zero margin. Well, that's not quite
true. To be able to launch on any given day, in the flight performance
reserve, some amount of performance must be included to cover the worst
performance case. In this case, a large head wind. But on the actual day
of launch, a large head wind is rarely the case. It could be a large tail
wind and we really wouldn't know it until the day of launch. So, on the
day of launch, we have additional information about the winds and in
almost every cases some amount of excess performance. This excess
performance improves abort boundaries a little, but is essentially thrown
away with the tank at MECO.

If you look at performance vs loads tradeoff dWT/dQ becomes smaller and
smaller as dynamic pressure in increased from "Nominal" Q to High-Q to
Optimal-Q. Essentially zero at Optimal-Q. The inverse of this derivative,
dQ/dWT, is what would have been important on the day of launch. At
Optimal-Q, dQ/dWT is infinity, at High-Q it's less but still large and at
"Nominal"-Q even less... At Optimal-Q a little tiny decrease in
performance is a hugh decrease in Q/loads and it's still somewhat true for
High-Q. It doesn't cost much performance to get large reductions
in Q and loads.

Flying High-Q is a very poor way to gain a little bit of performance.

--
Craig Fink
Courtesy E-Mail Welcome @