Space Shuttle.

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 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

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!!!)

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

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!!!)

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

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

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)

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

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