What keeps the space shuttle from going to the moon?

Or for that matter, to Mars?

Well, not down to the surface of the moon, because the shuttle needs a runway to land on. But how about a fly-by? Then we could get some good close-up pictures of the neighborhood, not to mention some photos of the alleged leftover lunar lander junk from 1969.

And as long as we’re at the moon, why not zip on over to Mars & finally get some real experimentation accomplished. Landing a robotic mini-lab on Mars would be easier (methinks) from a high orbit than would blasting one off from the earth.

Another advantage would be that Earth-bound scientists wouldn’t need to wait 9 minutes for the radio transmissions to make their round trip travel between a Mars rover & main mission. The space shuttle in a high orbit over Mars could do the job more efficiently.

What are the rea$ons, if any?

WAG (IANARS): Fuel. They haven’t been able to design something able to hold enough to go to Mars AND back. The apollo missions were designed specifically to go to the moon and back. The shuttle is just meant to orbit the earth, and was made only to do so. Look how much fuel is required just to lift off from the earth. I imagine it also takes a massive amount to launch towards mars even when using the slingshot around the earth. To break orbit from mars and accelerate back to earth int the same manner would probably require massive amounts of fuel.

Well there are several.

One the shuttle is an Orbitor. (sp?) Meaning it was built to orbit the earth. It takes quite a bit of power to get to orbit. To LEAVE orbit and go to the moon takes another huge burst of power. The shuttle does not have that much power left after it gets into orbit. Then of course there is the matter of consumables. Air and Food. Sure you could fill up the bay with this stuff if you just wanted to fly by the moon and take pictures but to go all the way to Mars the shuttle couldn’t possibly pack enough Air to get there much less sustain scientist to remotely operate a lab on the planet.

So the three basic reasons are a lack of power, food and air.

It takes about as much energy to go from the surface of the Earth to orbit as it does to get from orbit to the Moon. The problem is, you need to lift the fuel up as well, so you need more fuel, and then you need even more to lift that fuel, etc. This gets to be a problem pretty quickly. Getting the Shuttle to the Moon would require a LOT more fuel than it could ever carry. And remember, it has to get back, which means carrying even more fuel. So it was never designed to do anythin gbut get into orbit. It is really impossible for it to get much higher than a few hundred kilometers up.

Couldn’t they stockpile fuel in orbit? Make a few trips, fuel up in orbit and off they go!

I’m surprised that no one’s mentioned it yet… CAPITALISM. Most of the shuttle missions are funded for very specific research. Joyriding to the Moon to photograph the leftover junk we left behind just doesn’t interest anybody enough to cough up the dough for such a mission. I think the shuttle could possibly get to the moon and back, but I suspect we’d need to use a conventional launch vehicle to get some extra fuel into orbit first - don’t think you want to fill the cargo bay with extra fuel - too dangerous.

As mentioned, a trip to Mars is probably out of the question with shuttle technology.

Even with a runway or a relatively smooth surface, the shuttle couldn’t land on the Moon. It glides back to the Earth’s surface, which needs air.

Any attempt at landing on the Moon would just be a crash. You couldn’t even steer the shuttle for a landing. You could try using the manuevering thrusters, but they’d be pretty ineffectual coming in for a landing.


Aw, c’mon. You’re not thinking out-of-the-box… I have visions of the shuttle starting it’s descent, quickly turning about so that it’s coming in ass-first, then firing the retros at just the right moment to lightly touch down inside a nice cooshy crater… a la Starsky and Hutch. Maybe we can have the pilot jump out and slide across the hood of the shuttle right after they land… just for effect.

[just kidding… not sure if I needed to point that out]

With regard to GEO satellites, they seem to have no trouble staying in orbit with the assistance of centrifugal force. They do this at an altitude of 35,887.4 km (the Clarke orbit) which seems to be the “just right” zone between gravity & centrifugal force generated from their orbital velocity of 11,080 kph (6,885 mph). For this figure I am relying on Monty Python data, specifically The Galaxy Song:


It seems to me that there must be some point at which the planetary gravity becomes a non-issue, or at least much less of an issue. At the half-way point (or a little past the half way point, since the Earth has about 9 times the mass of Mars) the shuttle could switch its engines off and contiunue on momentum. With no resistance, why would the shuttle need any fule once it escapes Earth gravity?

I guess the question is more about escape velocity. I had always heard that escape velocity was 7 miles per second but now as I think about it, I wonder at what point a vehicle actually escapes the Earth’s gravity enough that momentum is an effective method of propulsion.

Escape speed is, indeed, the issue here. The Space Shuttle does not reach escape speed, and doesn’t need to, since it’s staying in orbit around the Earth. As far as energy goes, low Earth orbit is considered “halfway to anywhere”: In other words, the amount of energy to get from the surface to orbit is the same as the energy to reach escape speed, once in orbit, which is enough to get you anywhere… eventually. If you had a couple of solid rocket boosters and a full external tank already floating around up in orbit, and some way of redezvousing with them, then you would theoretically have enough fuel to reach the Moon or Mars or whatnot (although I suspect that it’d be a technical nightmare). However, it’d be almost impossible to lift all that fuel all at once from the surface, and even with multiple trips, it’d still take a while. We could do it (although probably with a custom-designed vessel, not the Shuttle), and when we finally go to Mars, we probably will refuel in orbit, but the major obstacle there is keeping your crew alive for the several years needed for a round trip.

Staying in orbit is never a problem, unless you’re so low that you’re actually getting atmospheric drag (as most non-geosynch sattelites do).

Attrayant et al

Correct me if I’m wrong,I’m sure you all will,(big grin) but isn’t the moon in orbit around the earth. That means that it is held in place by the earths gravity. Sooo you wouldn’t ever actually get out of earths gravity in a trip to the moon.
Outside of that I believe I have heard that one of the reasons for the space station was the possibile exploration of space. The proverbial jumping off place.

If you really want to indulge in this, I have a book to recommend. Back to the Moon by Homer Hickam Jr. (you saw the movie October Sky, that’s the guy). It’s a story of a guy (a good guy, really) who hijacks a space shuttle, and flies it to the moon. Key details are the use of fuel and an engine which have been placed in orbit. It includes a jury-rigged lander, and heroic rescue. It’s sort of a James-Bond meets junkyard wars story.

Mr. Hickam is an ex-NASA engineer (who I happen to see at the gym once in awhile here in the Rocket City).

Now, as for the “escape earth’s gravity” idea - the earth’s gravity falls off as 1/r^2 as you fly away from earth, you never really get “out” of it. The issue is speed. If you achieve escape velocity (which is a function of altitude) then you’ll have enough kinetic energy to get as far away from earth as you please. If you don’t get up enough speed, you’ll be comming back around in orbit.

Neglecting atmospheric drag, a ship traveling at escape velocity (or more) would be essentially free of earth’s gravity even at treetop altitude.

I’ve said this before in another thread…

There is only one force keeping an object in orbit. That force is gravity. Actually, the centripetal force (the force that accelerates an orbiting object such that it moves in a circular path) is gravity!

Attrayant wrote:

The shuttle burns up almost all of its fuel in the first few minutes. There’s no way it could keep burning the main engines for the day or two it takes to get halfway to the moon. It would instead need to burn enough fuel, for a few more minutes, to get near escape velocity. The problem is as The Bad Astronomer described - it takes a lot more than twice the fuel to go twice as fast, because you’re having to move the extra fuel too.

No matter how far you get away from the earth, (or anything else for that matter) you will always be subjected to some gravitational pull from it, but if you get far enough away, It’ll get so small it won’t matter.

I’ve heard that the SOHO solar telescope is located where the Sun’s and earth’s gravaties are equal, about a million miles away from earth, so Earth is still pulling, even a million miles away.

Well then take a gander at yon web site which, in the last diagram, shows the orbit of GEO satellites. They don’t come right out and say it, but the diagram strongly implies that the Clarke orbit is the Goldilocks point between gravity and centrifugal force.

Is the diagram in error?

What’s keeping the space shuttle from taking a trip to the moon?


YOU gonna pay for it?

What would we get out of the deal…couple of photos?

The diagram is in error. This is one of those cases where the introduction of “centrifugal force” to explain something just gets people screwed up. Think about this, if gravity and cf were the only two forces on an object, and they were balanced, what kind of path would the object take? The answer is: a straight line, at constant speed. Obviously, satellites don’t behave this way, their paths are curved (ellipses, in general). Gravity is what keeps the orbit closed (for objects moving under escape velocity).

The “goldilocks” feature of the Clarke orbit is that it matches the period of the earth’s rotation. (Let’s talk circular orbits here, in the plane of the equator) Anything orbiting at a lower radius (in the CCW direction, as most satellites do) moves faster than the earth, covering ground from west to east. An orbit higher than the Clarke orbit would lag behind the earth’s rotation, covering ground from east to west.

Here is a good link to show you how much fuel was needed to get to the moon and back.

When will it end.

Oh my gosh, yes, the diagram is in error. I don’t need to repeat kellymccauley’s explanation, but look up “satellite motion” and/or “centripetal force” in any physics book. A similar diagram in any physics book would shown only one force (gravity).

Here is a site with a decent explanation that also includes a discussion of the fictitious “centrifugal force.” They say that the explanation involving centrifugal force is “confusing.” I think they are being generous; it is simply wrong. The key issue is that no forces are cancelling out; the satellite is constantly being accelerated.

Here is more in-depth explanation of geosynchronous satellites (with a picture).