Why does the shuttle throttle on ascent?

Jose, if in space, the foam, when it detached, would be going the same
speed as the rocket, and the only incremental change in velocity would
be that cause by the rocket between the time it detached until it hit.
If the rocket was at say 3 Gs and the foam had 50 feet before it hit,
it would 'fall' for t = (2 * 50 / (3 * 32))^.5 or about a second.
Impact speed would be 100 feet a second or so or about 70 miles an
hour. It's light stuff, probably wouldn't hurt.

Because it's light stuff though, it probably had aerodyamic breaking to
about zero speed when it shed off in the atmosphere, and that would
mean a hypersonic impact. That would hurt -- and did.




On Jan 7, 10:35 am, Jose wrote:
Yes, and it is also why the shedding foam can only do serious damage within
the lower atmosphere, as the drag cannot decelerate the chunks enough to
strike with enough force to do harm at that altitude.Uh... even with no atmosphere, the rocket is accelerating wrt the
detached foam. I'm not convinced this is insignificant.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

You airn't never been lost until you've been lost at Mach 3. I learned
that bit of wisdom from an air force jock. I can get lost at 150 kts.


On Jan 6, 11:31 pm, "Danny Deger" wrote:
"Danny Deger" wrote in m...

Why does the shuttle throttle to 3 Gs on ascent?The answer is:

So Navy Fighter pilots can fly the shuttle :-)

Danny Deger

P.S. I was an Air Force figher pilot.

If you've got a few hours to kill:

http://spaceflight.nasa.gov/shuttle/...hutref/events/

Sounds like essentially what Dudley said:

To keep the dynamic pressure on the vehicle below a specified level, on
the order of 580 pounds per square foot (max q), the main engines are
throttled down at approximately 26 seconds and throttled back up at
approximately 60 seconds. This also reduces heating on the vehicle.

"Jim" wrote in message
et...
SSME's are "rated" at a certain thrust. However, the thrust rating has a
minimum, average and maximum. The "rated" thrust is the average. Therfore,
the engines can be run to an amount greater than "rated" thrust. I am not
an engineer or NASA personel, but I have read that during the nominal
acent the engines are throttled from 64% to 104% but can be throttled to
109% of rated thrust if necessary.

You are correct. For 2 engine out aborts, the last engine can be throttled
to 109%.

Danny Deger

"Danny Deger" wrote in message
...

Why does the shuttle throttle to 3 Gs on ascent?


The 3 G throttling is done late in the flight (about 7:30)and has nothing to
do with dynamic pressure. It was designed in to allow "regular" people fly
the shuttle.

While in the atmosphere the main engines are throttled back to reduce the
maximum aerodynamic pressure. The grain in the SRB is also designed to have
them go through a period of reduced thrust at about the same time.

Danny Deger

"Tony" wrote in message
ps.com...
You airn't never been lost until you've been lost at Mach 3. I learned
that bit of wisdom from an air force jock. I can get lost at 150 kts.


I have never been lost in an airplane. Though, I have suffered from
temperary disorintation due to poorly designed maps :-)

Danny Deger

On Sun, 07 Jan 2007 07:42:46 GMT, "Jim" wrote:

BTW "go at throttle up" is, as I understood, is simply a radio call to
confirm communication with the vehicle, same as the "roll program" call. Is
that correct?

No, throttling high performance rocket engines is still somewhat
difficult and risky, despite the Shuttle making it look easy. NASA has
always worried that the Mains won't throttle back up as they are
intended, which would mean the crew would be going for a swim.
This risk is such that at one time, the now-cancelled Advanced Solid
Rocket Motor was going to eliminate the need for the early
throttle-down/up during SRB burn completely.

So the "Go at throttle-up" tells the crew that the engines did
throttle up as expected and the flight is "go" to proceed. One less
thing for the crew to worry about.

Brian

In article ,
Brian Gaff wrote:
But the actual thrust abilities of the smes was increased over the life of
the Shuttle, I'm sure I read that.

Correct -- originally 100% was to be tops (surprise, surprise), but later
the engines were qualified for 104%, and at the time of Challenger there
were plans to qualify them for routine operation at 109%, and possibly
more. Those plans got scaled back in the post-Challenger safety rethink.

There is nothing particularly unusual about this; most rocket engines grow
in thrust as experience builds up and small improvements are made. It
attracted attention on the shuttle only because of how it was expressed:
numbers above 100% sound vaguely alarming to the ignorant. The RS-27A
first-stage engine on modern Delta IIs runs at 153% of its original thrust
rating. The H-1 first-stage engines on the Saturn IBs that launched ASTP
were running at 124% of the thrust of the first H-1s, and even those were
110% upgrades of the S-3D Thor/Jupiter engines, which were themselves
substantially more powerful than still-earlier versions. Had there been a
second production batch of Saturn Vs, almost certainly the first-stage
engines would have been F-1As, running at 120% of the original F-1 thrust.

That said, the SSMEs are cranky, marginal engines, and taking *them* up to
120% (as was once intended) is much more iffy than doing the same for
robust engines like the H-1 or F-1.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

You, like any other truthful person, talk about a temp disorientation
(because of badly designed maps? -- I like that!).

This is way off topic but it makes me smile and I hope it does that for
you, too.

A church was having a yard sale, and had big box of golf balls for
sale. The sign over the balls?

"I was lost, but now I'm found."

In that context, I'm still lost.




On Jan 7, 12:16 pm, "Danny Deger" wrote:
"Tony" wrote in glegroups.com...

You airn't never been lost until you've been lost at Mach 3. I learned
that bit of wisdom from an air force jock. I can get lost at 150 kts.I have never been lost in an airplane. Though, I have suffered from
temperary disorintation due to poorly designed maps :-)

Danny Deger

In article om,
Tony wrote:
You airn't never been lost until you've been lost at Mach 3. I learned
that bit of wisdom from an air force jock. I can get lost at 150 kts.


The first time I took my wife for a ride in a J-3 Cub we had a stiff
headwind that had us making 37 knots across the ground. We were over
territory she's flown 100 times in faster planes but didn't recognize
any of it because we were going so slow. She was convinced we were
drifting into controlled airspace 50 miles away.

--
Scott Post