Space Shuttle.

wrote:

Ron Lee wrote:
wrote:
How do you get rid of all the velocity than builds up as you decend
through near vacuum and your energy of postition becomes energy of
motion?

Yes potential energy becomes kinetic energy and that is taken care of
by friction during reentry.

And thus we have come full circle and forgotten the original question,
which was why does the shuttle have to land so fast.

Jim here is the original post. Has nothing to do with landing:

"Just watched a show on the Columbis disaster, and a question came to
me.

Why does the shuttle have to be travelling so fast to re-enter the
atmosphere?"

Ron Lee

Ron Lee wrote:
wrote:

Ron Lee wrote:
wrote:
How do you get rid of all the velocity than builds up as you decend
through near vacuum and your energy of postition becomes energy of
motion?

Yes potential energy becomes kinetic energy and that is taken care of
by friction during reentry.

And thus we have come full circle and forgotten the original question,
which was why does the shuttle have to land so fast.

Jim here is the original post. Has nothing to do with landing:

"Just watched a show on the Columbis disaster, and a question came to
me.

Why does the shuttle have to be travelling so fast to re-enter the
atmosphere?"

If the shuttle re-enters the atmosphere, what maneuver is it going to
performing other than landing since at that point it has little to no
fuel, is a brick until the air gets thick, a glider thereafter, and
nowhere to go but down?


--
Jim Pennino

Remove .spam.sux to reply.

On Dec 29, 1:27 am, "Oz Lander" wrote:
Bob Noel wrote:
In article ,
"Oz Lander" wrote:

Why does the shuttle have to be travelling so fast to re-enter the
atmosphere?

How do you propose to slow the shuttle down from orbital velocity?

That I guess answers my question then. I was not aware that such high
speeds were required to just stay in orbit. What would it take to slow
the shuttle down whilst in orbit, enough to allow it to re-enter at a
slower speed?


Orbital velocity is about 8km/s I think. That's what all that fuel is
for -to accelerate it to that speed and raise it to orbital height.
Most fuel is burnt just lifting fuel... Getting down is a fine
balance, too fast (steep) and the shuttle can't dissipate it's energy
as radiated heat and it will burn up. Too slow (shallow) and it is
likely to skip off the atmosphere which will then rob the shuttle of
energy and lead to a very steep descent the next time it comes down
(and it will as it does not have escape velocity). At least that's how
I understand it.

Cheers

If the shuttle re-enters the atmosphere, what maneuver is it going to
performing other than landing since at that point it has little to no
fuel, is a brick until the air gets thick, a glider thereafter, and
nowhere to go but down?

Jim, the original question is as stated previously. That the Shuttle
will land after reentry is not the point.

Ron Lee

Ron Lee wrote:

If the shuttle re-enters the atmosphere, what maneuver is it going to
performing other than landing since at that point it has little to no
fuel, is a brick until the air gets thick, a glider thereafter, and
nowhere to go but down?

Jim, the original question is as stated previously. That the Shuttle
will land after reentry is not the point.

Ron Lee

And once again we have been saved from the horrors of paraphrasing by
the courageous Captain Semantics and his trusty sidekick The Punctuation
Kid.

Having been suitably chastised, I scurry in search of a multi-windowed
newsreader to ensure every turn of a phrase, nay every letter and comma,
is 100% pristine in any followup.

Once the shuttle pilot hits the button to start the retro burn, you can
call it a de-orbit burn, reentering the atmosphere, landing, going down,
or break out the skillet and pork chops mom 'cause I'm coming home.

--
Jim Pennino

Remove .spam.sux to reply.

On 2007-12-28 04:05:46 -0800, "Oz Lander" said:

Just watched a show on the Columbis disaster, and a question came to me.
Why does the shuttle have to be travelling so fast to re-enter the
atmosphere?

The Shuttle's orbital velocity is dependent on the altitude of the
orbit and the mass of the planet that is being orbited. Consider an ice
skater that is spinning in place. If she extends her arms she will spin
much more slowly than if she folds her arms close to her side. This is
the law of conservation of momentum.

A typical Shuttle orbit is at 300 km. The orbital velocity at 300 km is
7.73 km/sec. for an orbital period of 90.52 minutes. At the lowest
possible stable orbit of 185 km the orbital velocity is 7.79 km/sec.
and the orbital period is 88.19 minutes. A lower orbit requires a
higher orbital velocity due to the stronger pull of gravity exerted on
it.

So the thing is, the closer the Space Shuttle is to the earth, the
faster it must travel in order to maintain a stable orbit.

Now, in order for the Shuttle to descend, the most efficient method is
to accelerate the Shuttle in a direction opposite the direction of
orbit (the Shuttle could also be made to descend by accelerating it in
the direction of the orbit, but that would require more fuel).
Accelerating the Shuttle straight down is essentially accelerating it
forward.

In order for the Shuttle to re-enter the earth's atmosphere at a
relative zero velocity the Shuttle would have to be in a geo-centric
orbit; that is the orbit would have to be of the same period as the
earth's rotation. That would imply an altitude of about 35,786 km and
the orbit would have to be exactly above the equator. But the Shuttle's
orbit is always inclined to the equator by at least 28.5 degrees. So,
even if there were no east/west motion of the Shuttle, there would be
north/south motion. The Shuttle does not carry even a large fraction of
the fuel needed to reach a geo-centric orbit and even if it managed to
get up there we would be left with the problem of getting back down.

Now we begin to see the problem. Low earth orbit demands high orbital
velocity and any deceleration causes us to 'fall' into the atmosphere
at near orbital velocity. The Shuttle actually depends on drag from the
atmosphere to slow it down; it does not have enough fuel to slow it
down significantly relative to the atmosphere. It barely has enough
fuel to accelerate it against the orbit enough to cause it to enter the
atmosphere in the first place. Furthermore, the g forces generated by
decelerating the Shuttle enough to make a slow entry into the
atmosphere would cause the astronauts inside to be squished like bugs
on a windshield.

--
Waddling Eagle
World Famous Flight Instructor

wrote in :

Ron Lee wrote:

If the shuttle re-enters the atmosphere, what maneuver is it going to
performing other than landing since at that point it has little to no
fuel, is a brick until the air gets thick, a glider thereafter, and
nowhere to go but down?

Jim, the original question is as stated previously. That the Shuttle
will land after reentry is not the point.

Ron Lee

And once again we have been saved from the horrors of paraphrasing by
the courageous Captain Semantics and his trusty sidekick The Punctuation
Kid.

Having been suitably chastised, I scurry in search of a multi-windowed
newsreader to ensure every turn of a phrase, nay every letter and comma,
is 100% pristine in any followup.



vEry wsie

Bertie

On Dec 30, 4:37*pm, C J Campbell
wrote:
On 2007-12-28 04:05:46 -0800, "Oz Lander" said:

Just watched a show on the Columbis disaster, and a question came to me.
Why does the shuttle have to be travelling so fast to re-enter the
atmosphere?

The Shuttle's orbital velocity is dependent on the altitude of the
orbit and the mass of the planet that is being orbited. Consider an ice
skater that is spinning in place. If she extends her arms she will spin
much more slowly than if she folds her arms close to her side. This is
the law of conservation of momentum.

A typical Shuttle orbit is at 300 km. The orbital velocity at 300 km is
7.73 km/sec. for an orbital period of 90.52 minutes. At the lowest
possible stable orbit of 185 km the orbital velocity is 7.79 km/sec.
and the orbital period is 88.19 minutes. A lower orbit requires a
higher orbital velocity due to the stronger pull of gravity exerted on
it.

So the thing is, the closer the Space Shuttle is to the earth, the
faster it must travel in order to maintain a stable orbit.

Now, in order for the Shuttle to descend, the most efficient method is
to accelerate the Shuttle in a direction opposite the direction of
orbit (the Shuttle could also be made to descend by accelerating it in
the direction of the orbit, but that would require more fuel).
Accelerating the Shuttle straight down is essentially accelerating it
forward.

if you accelerated in the direction of the orbit , my understanding is
you would just turn a cicular orbit into an elliptical orbit. ie you
would go out further from the atmosphere on the other side of the
orbit and come back to the original ht where you first accelerated.
this would not result in the shuttle descending at all.
terry

"terry" wrote in message
...
On Dec 30, 4:37 pm, C J Campbell
wrote:
...
if you accelerated in the direction of the orbit , my understanding is
you would just turn a cicular orbit into an elliptical orbit. ie you
would go out further from the atmosphere on the other side of the
orbit and come back to the original ht where you first accelerated.
this would not result in the shuttle descending at all.

As long as we are picking nits...

You pass through the point (and at the same velocity and direction) where
you LAST accelerated (assuming something else doesn't get in the way)

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On Sun, 30 Dec 2007 02:50:59 -0800 (PST), terry
wrote:

On Dec 30, 4:37*pm, C J Campbell
wrote:
On 2007-12-28 04:05:46 -0800, "Oz Lander" said:

Just watched a show on the Columbis disaster, and a question came to me.
Why does the shuttle have to be travelling so fast to re-enter the
atmosphere?

The Shuttle's orbital velocity is dependent on the altitude of the
orbit and the mass of the planet that is being orbited. Consider an ice
skater that is spinning in place. If she extends her arms she will spin
much more slowly than if she folds her arms close to her side. This is
the law of conservation of momentum.

A typical Shuttle orbit is at 300 km. The orbital velocity at 300 km is
7.73 km/sec. for an orbital period of 90.52 minutes. At the lowest
possible stable orbit of 185 km the orbital velocity is 7.79 km/sec.
and the orbital period is 88.19 minutes. A lower orbit requires a
higher orbital velocity due to the stronger pull of gravity exerted on
it.

So the thing is, the closer the Space Shuttle is to the earth, the
faster it must travel in order to maintain a stable orbit.

Now, in order for the Shuttle to descend, the most efficient method is
to accelerate the Shuttle in a direction opposite the direction of
orbit (the Shuttle could also be made to descend by accelerating it in
the direction of the orbit, but that would require more fuel).
Accelerating the Shuttle straight down is essentially accelerating it
forward.

if you accelerated in the direction of the orbit , my understanding is
you would just turn a cicular orbit into an elliptical orbit. ie you
would go out further from the atmosphere on the other side of the
orbit and come back to the original ht where you first accelerated.

That's why it takes two burns to move to a circular orbit farther out.
The confusing part is when docking accelerating to move out will cause
you to drop back IF I understand correctly.

this would not result in the shuttle descending at all.
terry

Roger (K8RI)