Space Shuttle.

[Oz Lander[_2_]]

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?

--
Oz Lander.
Straight and Level Down Under Forum.
http://www.straightandleveldownunder.net

[Oz Lander[_2_]]

Oz Lander wrote:

> 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?

Perdon the typo! Columbia!

--
Oz Lander.
Straight and Level Down Under Forum.
http://www.straightandleveldownunder.net

[Bob Noel]

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?

--
Bob Noel
(goodness, please trim replies!!!)

[Oz Lander[_2_]]

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?

--
Oz Lander.
Straight and Level Down Under Forum.
http://www.straightandleveldownunder.net

[Bob Noel]

In article >,
"Oz Lander" > wrote:

> > 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?

It would require a large amount of fuel, way more than we can currently
afford to put into orbit.

--
Bob Noel
(goodness, please trim replies!!!)

[Oz Lander[_2_]]

Bob Noel wrote:

> In article >,
> "Oz Lander" > wrote:
>
> > > 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?
>
> It would require a large amount of fuel, way more than we can
> currently afford to put into orbit.

Question answered. Thanks.
I guess that's where the solar sail technology might one day come in
handy.

--
Oz Lander.
Straight and Level Down Under Forum.
http://www.straightandleveldownunder.net

[Steven P. McNicoll]

"Bob Noel" > wrote in message
...
>
> How do you propose to slow the shuttle down from orbital velocity?
>

The shuttle does slow from orbital velocity to re-enter.

[Morgans[_2_]]

>Oz Lander" > wrote > Question answered. Thanks.
> I guess that's where the solar sail technology might one day come in
> handy.

Not really.

The whole idea behind a solar sail, is to exert a tiny force on a spacecraft
for a very long time, and accelerate it for a long trip between planets.

It would be able to do nothing for slowing down for re-entry.

Really, the ONLY answer is a thrust with tons of force exerted over a very
short time period. Right now, that is chemical burning of something,
and........ that's it!

The other thing left is aero braking, which is what we do now, and have done
for all past programs, and has been done by the Soviets.
--
Jim in NC

[[email protected]]

Steven P. McNicoll > wrote:

> "Bob Noel" > wrote in message
> ...
> >
> > How do you propose to slow the shuttle down from orbital velocity?
> >

> The shuttle does slow from orbital velocity to re-enter.

Yeah, by a tiny fraction of it's total horizontal velocity.

Then there is that inconvenient energy of position which gets
converted to energy of motion as it falls back to Earth.

--
Jim Pennino

Remove .spam.sux to reply.

[WolfRat]

Wolfgang Schwanke wrote:
> "Oz Lander" > wrote in
> :
>
>> What would it take to slow
>> the shuttle down whilst in orbit, enough to allow it to re-enter at a
>> slower speed?
>
> The same amount of fuel that was needed to accelerate it in the first
> place, plus lots more to get that extra fuel up. To avoid all that,
> spacecraft use the atmosphere for braking. They've been doing that
> since the beginning of manned spaceflight, it's not specific to the
> shuttle. They just accept the risk associated with that method as a
> tradeoff against the extra complication of carrying those enormous
> masses of fuel all along.
>
> Regards
>


They could aero-brake from orbit slower but it would take
forever. If they launched an unmanned fuel source, docked
and then transfered fuel it could be done.

Keep it simple the new Orion(Apollo on steroids) will work
just fine. The Russians have done a good job with safe and
repeated journeys from orbit

[Ron Lee[_2_]]

>
>The same amount of fuel that was needed to accelerate it in the first
>place, plus lots more to get that extra fuel up.

Actually not the same amount...not even close. You only have to lower
the perigee such that you reenter on the proper trajectory whereas
going up you have to get into a circular orbit

Ron Lee

[Ron Wanttaja]

On Fri, 28 Dec 2007 12:27:44 +0000 (UTC), "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?

You have to understand what "orbit" is: A balance between velocity and gravity.
Here's a simplified explanation.

Imagine a vehicle 100 miles in space with no velocity. It immediately starts
falling straight down, accelerating at 32 feet/second per second until it hits
the Earth.

Imagine the same vehicle at 100 miles with a horizontal velocity (e.g., tangent
to the Earth) of 1000 miles per hour. It now falls at a slant. But it takes a
bit longer to actually hit the ground, because the Earth is curved... it's
"curving away" from the oncoming vehicle. The vehicle want to travel in its
original direction, but gravity keeps pulling it toward the center of the Earth.
The velocity vector (imagine an arrow pointing in the direction the vehicle is
traveling at any given moment) alters until it intersects the ground, and the
object hits downrange of the release point. Because the Earth is round, that
downrange point is a bit further away, and the time to drop is a bit longer than
the no-velocity release.

But...what happens if you give your vehicle a fast enough speed that it "misses"
the Earth? If you give it *just* enough speed, you're in orbit...the forward
velocity balances the effect of gravity to hold you at a near-constant altitude.

The velocity is critical: If it's too low, the vector will sag downward. If
the velocity vector intersects the Earth, the vehicle will impact. Even if the
vector doesn't dip below the horizon, if the vehicle gets too low, the drag of
the atmosphere will further reduce its velocity...and the velocity vector drops
even further.

At 100 NM, a vehicle in a circular orbit is doing about 25,500 feet per second.
If it slows down just 150 feet per second (a bit more than 100 mph), it *will*
impact the Earth...and the atmosphere only makes matters worse!

The upshot, to a pilot, is that space objects cannot do "slow flight." There's
nothing "holding you up" other than your spacecraft's velocity...if you reduce
velocity, you're going down. There's really only a small range of speed you can
play around before the top of the atmosphere starts slowing you down and lets
the Earth suck you in. Unfortunately, the upper reaches of the atmosphere are
too thin to generate any appreciable lift unless you have very long
wings...which aren't the thing you want, hitting atmosphere at Mach 25.

You can add "lift" to your vehicle to maintain your altitude while it slows, but
there's only one way to do it: Add lift by firing rocket engines downward. This
is analogous to a Harrier transitioning to hovering flight. In fact, if you
could run a Harrier's engines in space, it probably would do quite nicely for a
low-speed return to Earth.

The problem is, this would take a *lot* of fuel. As others have posted, about
as much as it took to put the spacecraft into orbit to start with. The trouble
is, each pound of "return fuel" that you want to put into orbit takes about 15
pounds of launcher fuel to GET it there!

Until we develop antigravity, or highly-efficient engines that can put out the
thrust levels needed to hover, we're stuck with the high-speed reentry process.

Ron Wanttaja

[Morgans[_2_]]

"WolfRat" > wrote
>
> They could aero-brake from orbit slower but it would take forever.

Not really. If you slow down gradually, the effect of gravity takes hold,
and you start falling faster. Mush of the speed is picked back up in that
manner.

> If they launched an unmanned fuel source, docked and then transfered fuel
> it could be done.

You still have to pay to get all of that fuel up there. That is not cheap,
let alone the fueling station cost, and the weight to get that up there.

> Keep it simple the new Orion(Apollo on steroids) will work just fine. The
> Russians have done a good job with safe and repeated journeys from orbit.

I would have more of a warm fuzzy feeling, if that were true. The Russians
have lost a couple crews on the whole re-entry landing procedure, I believe.
At least one, I am positive.

The Orion will be/should be more reliable, because of more simplicity, and
the fact that it will be above the whole rocket, and the fact that it does
not need to be made reusable.
--
Jim in NC

[Ron Wanttaja]

On Fri, 28 Dec 2007 13:53:06 -0500, "Morgans" > wrote:

> > Keep it simple the new Orion(Apollo on steroids) will work just fine. The
> > Russians have done a good job with safe and repeated journeys from orbit.
>
> I would have more of a warm fuzzy feeling, if that were true. The Russians
> have lost a couple crews on the whole re-entry landing procedure, I believe.
> At least one, I am positive.

Soyuz 1 and Soyuz 11. The first due to a parachute failure, the second due to
failure of a valve.

http://en.wikipedia.org/wiki/Soyuz_1

http://en.wikipedia.org/wiki/Soyuz_11

Ron Wanttaja

[Robert M. Gary]

On Dec 28, 4:05*am, "Oz Lander" > wrote:
> 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?

Think of it this way. The shuttle isn't moving fast, its landing on a
fast moving object. Landing on the earth is like a carrier landing,
the earth is spinning around and the shuttle has to match to it.

-Robert

[[email protected]]

WolfRat > wrote:
> Wolfgang Schwanke wrote:
> > "Oz Lander" > wrote in
> > :
> >
> >> What would it take to slow
> >> the shuttle down whilst in orbit, enough to allow it to re-enter at a
> >> slower speed?
> >
> > The same amount of fuel that was needed to accelerate it in the first
> > place, plus lots more to get that extra fuel up. To avoid all that,
> > spacecraft use the atmosphere for braking. They've been doing that
> > since the beginning of manned spaceflight, it's not specific to the
> > shuttle. They just accept the risk associated with that method as a
> > tradeoff against the extra complication of carrying those enormous
> > masses of fuel all along.
> >
> > Regards
> >


> They could aero-brake from orbit slower but it would take
> forever. If they launched an unmanned fuel source, docked
> and then transfered fuel it could be done.

And put it in what and do what with it?

It took the jettisoned external tanks and engines to provide the
energy to get up in the first place and would take an equivelant
amount of energy to kill all your velocity and energy of position
in orbit to get down slowly.

--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

Ron Lee > wrote:
> >
> >The same amount of fuel that was needed to accelerate it in the first
> >place, plus lots more to get that extra fuel up.

> Actually not the same amount...not even close. You only have to lower
> the perigee such that you reenter on the proper trajectory whereas
> going up you have to get into a circular orbit

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?


--
Jim Pennino

Remove .spam.sux to reply.

[Bob Noel]

In article >,
"Steven P. McNicoll" > wrote:

> > How do you propose to slow the shuttle down from orbital velocity?
>
> The shuttle does slow from orbital velocity to re-enter.

It slows only slightly, enough to get its orbit to dip into the atmosphere
where it then uses aerodynamic braking. Avoiding the need for
aerodynamic braking was, I believe, the whole point of the original
question.

--
Bob Noel
(goodness, please trim replies!!!)

[Steven P. McNicoll]

"Bob Noel" > wrote in message
...
> In article >,
> "Steven P. McNicoll" > wrote:
>
>> > How do you propose to slow the shuttle down from orbital velocity?
>>
>> The shuttle does slow from orbital velocity to re-enter.
>
> It slows only slightly, enough to get its orbit to dip into the atmosphere
> where it then uses aerodynamic braking. Avoiding the need for
> aerodynamic braking was, I believe, the whole point of the original
> question.
>

The short answer to your follow-up question is the Orbital Maneuvering
System. The shuttle uses the OMS for both orbital maneuvering and to slow
from orbital velocity for reentry.

[Bob Noel]

In article >,
"Steven P. McNicoll" > wrote:

> The short answer to your follow-up question is the Orbital Maneuvering
> System. The shuttle uses the OMS for both orbital maneuvering and to slow
> from orbital velocity for reentry.

I know how the shuttle de-orbits. My follow-up question was directed at
the OP.

In the context of the original question, the OMS is entirely inadequate.

--
Bob Noel
(goodness, please trim replies!!!)

[Steven P. McNicoll]

"Bob Noel" > wrote in message
...
>
> I know how the shuttle de-orbits.
>

Of course you do, I just explained it.


>
> My follow-up question was directed at the OP.
>

It should have been clear to you that he had no idea.

[Bob Noel]

In article >,
"Steven P. McNicoll" > wrote:

> > I know how the shuttle de-orbits.
> >
>
> Of course you do, I just explained it.

oh my, you are so precious. LOL

> >
> > My follow-up question was directed at the OP.
>
> It should have been clear to you that he had no idea.

Well, I not surprised that you didn't understand the purpose
of the question.

Have a wonderful New Year.

--
Bob Noel
(goodness, please trim replies!!!)

[Steven P. McNicoll]

"Bob Noel" > wrote in message
...
>
> Well, I not surprised that you didn't understand the purpose
> of the question.
>

I certaimly understood what you wrote, if your intent was something else you
misspoke.


>
> Have a wonderful New Year.
>

Likewise!

[Mike Noel]

As long as were on the subject of getting into and out of orbit, anyone want
to discuss the space elevator concept?

--
Best Regards,
Mike

http://photoshow.comcast.net/mikenoel


"Robert M. Gary" > wrote in message
...
On Dec 28, 4:05 am, "Oz Lander" > wrote:
> 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?

Think of it this way. The shuttle isn't moving fast, its landing on a
fast moving object. Landing on the earth is like a carrier landing,
the earth is spinning around and the shuttle has to match to it.

-Robert

[Ron Wanttaja]

On Fri, 28 Dec 2007 15:52:55 -0700, "Mike Noel" > wrote:

> As long as were on the subject of getting into and out of orbit, anyone want
> to discuss the space elevator concept?

Great once it's in place (except for the risk from terrorists) but kinda tough
to build....

Ron Wanttaja

[Jim Logajan]

"Mike Noel" > wrote:
> As long as were on the subject of getting into and out of orbit,
> anyone want to discuss the space elevator concept?

Wont work - the banal music will keep people from using it.

[[email protected]]

Mike Noel > wrote:
> As long as were on the subject of getting into and out of orbit, anyone want
> to discuss the space elevator concept?

It has been discussed to death on sci.physics, sci.space.policy,
sci.space.shuttle and for some strange reason soc.culture.zimbabwe,
though a lot of it is babbling drool by Brad Guth and associates.

--
Jim Pennino

Remove .spam.sux to reply.

[Roger (K8RI)]

On Fri, 28 Dec 2007 07:34:38 -0500, Bob Noel
> wrote:

>In article >,
> "Oz Lander" > wrote:
>
>> > 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?

They can slow down, but the more they slow down the steeper the
re-entry and the more power it would take to slow them at that stage.
Currently they slow just enough to drop out of orbit. Orbital speed
doesn't let them break free of earth's gravitational field. They are
continually falling around the earth.

>
>It would require a large amount of fuel, way more than we can currently
>afford to put into orbit.
Or even have the technology to lift.

Yup. Just think of a take off in reverse. They'd need enough fuel to
do the opposite of the take off which means they'd have to put
everything they now use for a takeoff, into orbit. They'd have to use
many times the fuel they now use to launch that extra weight. Much of
the initial lifting is done with those large solid propellant boosters
so they'd need to launch not only every thing they do now, they'd need
to power to put the shuttle, an external fuel tank, and two boosters
into orbit.

It sorta makes those old sci-fi movies where they used retro-rockets
to land appear in a different light. We don't have that kind of
power...yet. <:-))

Roger (K8RI)

[Bertie the Bunyip[_19_]]

John Smith > wrote in
:

> In article >,
> "Mike Noel" > wrote:
>
>> As long as were on the subject of getting into and out of orbit,
>> anyone want to discuss the space elevator concept?
>
> What is going to be used as the counter-mass in space?
> Is someone going to trap the proper sized rock in the asteroid belt
> and haul it back to the desired Earth orbit to attach to the top of
> the elevator tube?
>

We could use anthony. We'd have to check as to his exact mass, but I bet
it's in the ballpark.


Bertie

[Oz Lander[_2_]]

Ron Wanttaja wrote:

>
> Until we develop antigravity, or highly-efficient engines that can
> put out the thrust levels needed to hover, we're stuck with the
> high-speed reentry process.
>
> Ron Wanttaja

An excellent explanaition. Thankyou!;-)

--
Oz Lander.
Straight and Level Down Under Forum.
http://www.straightandleveldownunder.net

[Oz Lander[_2_]]

Robert M. Gary wrote:

> Think of it this way. The shuttle isn't moving fast, its landing on a
> fast moving object. Landing on the earth is like a carrier landing,
> the earth is spinning around and the shuttle has to match to it.
>
> -Robert

That makes sense! Thanks!

--
Oz Lander.
Straight and Level Down Under Forum.
http://www.straightandleveldownunder.net

[Capt. Geoffrey Thorpe]

"Ron Wanttaja" > wrote in message
...
<...>
> The upshot, to a pilot, is that space objects cannot do "slow flight."

What about when they let John Glen ride a couple years ago? I heard they
wouldn't let him drive because they were concened that he would end up
orbiting the earth at 25 miles per hour with the turn signals on...

--
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.

[Ron Wanttaja]

On Fri, 28 Dec 2007 19:31:44 -0500, "Capt. Geoffrey Thorpe" <The Sea Hawk at
wow way d0t com> wrote:

> "Ron Wanttaja" > wrote in message
> ...
> <...>
> > The upshot, to a pilot, is that space objects cannot do "slow flight."
>
> What about when they let John Glen ride a couple years ago? I heard they
> wouldn't let him drive because they were concened that he would end up
> orbiting the earth at 25 miles per hour with the turn signals on...

And they had the engine igniters wired to a "Clapper".... :-)

Ron Wanttaja

[Bertie the Bunyip[_19_]]

John Smith > wrote in
:

> In article >,
> Bertie the Bunyip > wrote:
>
>> John Smith > wrote in
>> :
>>
>> > In article >,
>> > "Mike Noel" > wrote:
>> >
>> >> As long as were on the subject of getting into and out of orbit,
>> >> anyone want to discuss the space elevator concept?
>> >
>> > What is going to be used as the counter-mass in space?
>> > Is someone going to trap the proper sized rock in the asteroid belt
>> > and haul it back to the desired Earth orbit to attach to the top of
>> > the elevator tube?
>> >
>>
>> We could use anthony. We'd have to check as to his exact mass, but I
>> bet it's in the ballpark.
>
> Mass (definition) - anything that has weight and takes up space.
>
> While Anthony does take up space in these forums, I think most would
> agree that what he writes carries no weight.
>

I was thinking more of the pile of Krispy Kreme boxes in the corner of his
bedrom and where their contents have gone.

Bertie

[Ron Lee[_2_]]

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.

Ron Lee

[brtlmj]

> > What about when they let John Glen ride a couple years ago? I heard they
> > wouldn't let him drive because they were concened that he would end up
> > orbiting the earth at 25 miles per hour with the turn signals on...
> And they had the engine igniters wired to a "Clapper".... :-)

Don't forget about the trifocal windshield... ;-)

[[email protected]]

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 Pennino

Remove .spam.sux to reply.

[Maxwell]

> wrote in message
...
> 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.
>
>
> --

We are certainly getting better at dragging discussions off topic. In the
old days it used to take as much as a hundred posts to come full circle, but
today we can accomplish it in as little as dozen or so.

People that live in reality have things like "speed dating", here we are
limited to things like "speed drifting".

[Bob Noel]

In article >, 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.

The original question was answered way back earlier in the thread.

--
Bob Noel
(goodness, please trim replies!!!)

[[email protected]]

Bob Noel > wrote:
> In article >, 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.

> The original question was answered way back earlier in the thread.

Yes it was, and the above is part of the answer.

As I said, we have come full circle.

--
Jim Pennino

Remove .spam.sux to reply.

[Ron Lee[_2_]]

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

[[email protected]]

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.

[WingFlaps]

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

[Ron Lee[_2_]]

>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

[[email protected]]

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.

[C J Campbell[_1_]]

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

[Bertie the Bunyip[_19_]]

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

[terry]

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

[Capt. Geoffrey Thorpe]

"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.

[Roger (K8RI)]

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)