Why do all space vehicles travel at about 17K per hour?

Merlin5 · 3 Jun 2010 at 20:34

ISS travels at about 17,500 miles per hour. Space shuttle does as well I think. The Saturn V was 17,432mph. They're talking about the old Sputnik satellite on TV and how it travels at 17K per hour. Although google says 18,000 mph.

So these are orbiting speeds right? It's probably a very simple answer, but for you space enthusiasts, I guess it's all to do with escape velocity is it? So it's possible is it to have even faster orbiting speeds in the future?

Tefal · 3 Jun 2010 at 20:37

stop it falling back to earth

Glaucus · 3 Jun 2010 at 20:38

Iirc 17k is around the escape velocity.

Which is also the speed required to maintain orbit, although varies slightly with height.

Force of mavity has to be equalled out by speed, meaning the resulting force is zero.

Greenlizard0 · 3 Jun 2010 at 20:40

I think it's the speed required at that height to avoid flying off into space or back to Earth.

orderoftheflame · 3 Jun 2010 at 20:42

I'm no rocket scientist, but I'd guess that it's just the speed required for orbit at a certain height above the earth.

Any slower and you begin to drift back to earth, any faster and you begin to escape.

I'd guess that as all those craft all orbit in LEO they'd all be similar speeds.

Heliospherez · 3 Jun 2010 at 20:42

Don't think it's anything to do with escape velocity as they all have different fuels and weights/shapes.

At that height, it's a perfect orbit. 17,000 is a perfect Low earth orbit. And possibly 17,000 is the rough max speed we can handle (with regard to heat shielding) with current technology with chemical fuels. 17,000 or there abouts is all we can realistically achieve (on earth) with the chemicals we have.

And I believe voyager reached over 40,000 mph when it left our solar system.

ChroniC · 3 Jun 2010 at 20:43

I would imagine (and I'm sure some one more knowledgeable will be able to explain better) but 17-8k mph is probably the speed necessary to maintain orbit.
As in, if your travelling slower than that you would essentially fall back into the path of the moving earth, however at speed above it, you fall slightly past it constantly and are kept constant by mavity.

As has now be said about 5 times

PMKeates · 3 Jun 2010 at 20:45

It goes 17,000 MPH because there's little resistance to it's movement and there's a giant planet sucking it towards it.

Glaucus · 3 Jun 2010 at 20:46

PASONIX said:
Don't think it's anything to do with escape velocity as they all weigh differently.

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

look for orbit section.

orderoftheflame · 3 Jun 2010 at 20:47

/facepalm

ignore.

Mik3 · 3 Jun 2010 at 20:52

AcidHell2 said:
Iirc 17k is around the escape velocity.

Which is also the speed required to maintain orbit, although varies slightly with height.

Force of mavity has to be equalled out by speed, meaning the resulting force is zero.

This. There's a good explanation on this site: http://www.gma.org/surfing/sats.html#stay

yermum · 3 Jun 2010 at 20:56

if you look on the heavens above website, you can see the height of the iss falls gradually and has to be boosted from time to time.

Heliospherez · 3 Jun 2010 at 20:59

Apollo 11 travelled at 25,000 mph - Why not any faster ?

willhub · 3 Jun 2010 at 21:01

I thought these space things would be able to travel much faster than 25,000mph, that's slow for space terms.

Merlin5 · 3 Jun 2010 at 21:09

Thanks for the answers. You're right guys about 25,000 mph for apollo. It seems the Saturn V went faster than the 17K per hour I thought, to achieve it's mission to the moon. In this article it says 7 miles per second. I work that out to be 25,200 miles per hour.

http://www.wwheaton.com/waw/mad/mad3.html

PhillyDee · 3 Jun 2010 at 21:14

willhub said:
I thought these space things would be able to travel much faster than 25,000mph, that's slow for space terms.

And the reason why our technology has not taken us very far past the moon!

RavenLunatic · 3 Jun 2010 at 21:14

I think its got something to do with the distance the ISS is from the earth. The further an orbiting object is from the earth the faster it has to move to counter act mavity pulling it back down to earth.

Inquisitor · 3 Jun 2010 at 21:21

It depends on the orbital radius. 17,000 mph is simply the natural tangential speed of a body orbiting the Earth at a particular radius/altitude. As the radius increases, the tangential speed decreases.

Dave M · 3 Jun 2010 at 21:21

It's the speed it falls round the planet - orbit.

Imagine driving a car off a building like in james bond - drive faster and you'll fall further, drive slower and you'll fall closer.

In a round planet that is constantly pulling you in to it, if you go fast enough you'll shoot off into space in a straight line, go too slow and you'll fall into the planet. Get it just right and you'll fall round it forever.

Inquisitor · 3 Jun 2010 at 21:29

Telescopi said:
It's the speed it falls round the planet - orbit.

Imagine driving a car off a building like in james bond - drive faster and you'll fall further, drive slower and you'll fall closer.

In a round planet that is constantly pulling you in to it, if you go fast enough you'll shoot off into space in a straight line, go too slow and you'll fall into the planet. Get it just right and you'll fall round it forever.

Pretty much, except it's possible for an object to follow a non-circular orbit (i.e. an elliptical orbit). In fact, a circular orbit is a special case that requires an object to have a single, exact kinetic energy. Any slight deviation from that particular energy causes an elliptical orbit, so any naturally occurring orbit is clearly elliptical rather than circular.

See orbital eccentricity: a circular orbit corresponds to an eccentricity of precisely zero.