h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

What quantity of fuel is necessary to put 1 kilo into space?

How much does that cost at the moment?

Is the quantity a constant, irrespective of climate and manner of transport?

How does the cost compare to an equivalent in crude oil?

Does anybody care?

I care. I just don't know the answer.

Ask NASA? Can't say I know.

I know that ordinary fuels such as petrol produce insufficient energy to lift there own mass into orbit, let alone the mass of a rocker.
So very powerful propellants are used that are essentially major explosives. Isn't a hydrogen/oxygen mix used to blast the shuttle into space?
Hydrazine and hydrogen peroxide were used in early rocket engines (in the last world war). I don't think there's much issue with carbon dioxide release anyway since neither of these mixtures will produce any.

Someone like SoRB might have better knowledge on this subject than I.

Don't know either, but I've googled a few facts and figures.

A figure of $10,000 per lb payload is mentioned more than once. That's overall cost though.

From wiki, for a single-stage vehicle: "88.4 % of the initial total mass has to be propellant. The remaining 11.6 % is for the engines, the tank, and the payload. "

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

It is only a constant figure for the same fuel in the same type of vehicle. Most of the fuel is needed to lift the weight of fuel, so multi-stage rockets don't need to carry so much as they shed weight on the way up. Systems that don't need to carry any fuel at all, such as space elevators or electromagnetic rail guns would be far more efficient.

To use the shuttle as an example, though not a very good one, I found the following figures:

Max payload - 22,700 Kg.
Fuel in main tank (hydrogen and oxygen) - 730,400 Kg
Fuel per SRB (aluminium and stuff) - 526,727 Kg

That gives a very rough figure of about 78 Kg fuel per Kg payload, ignoring the fact it uses different types of fuel. But as I said, the shuttle isn't a very good example because it needs to carry wings and people and toilets and all sorts of unnecessary stuff, so I looked at Ariane 5 instead:

Max payload - 10,500 Kg.
Main stage - 132,000 Kg oxygen and 26,000 Kg hydrogen.
Booster (x2) - 138,000 Kg (aluminium)
Upper stage (don't know) - 9,700 Kg.

Giving about 42 Kg fuel (and oxidiser) to 1 Kg payload. That's to a much higher orbit than the shuttle though. Lots of ifs and buts applicable to those calculations, as I fully suspect someone will point out in due course...

All very detailed and helpful so far, thank you

<...such as space elevators or electromagnetic rail guns would be far more efficient>

Space elevators OK, mindbending but imaginable (just, and only after reading a bit).

But Rail Guns? I've just had a quick look on google and for an application of this magnitude it's completely counter-intuitive, so must look further...

A railgun would be a realistic launch technology for cargo getting off the moon. There are four main obstacles for using one to get people off earth:

1. Atmospheric drag. It as, as the name suggests, a GUN. The payload starts DEcelerating the moment it leaves the "muzzle", and it's moving, by definition, through the thickest bit of the air, i.e. the bit near the ground. Air friction would also make it HOT, so you'd need a heat shield that worked *really* reliably for exit as well as reentry. Look how robust the Shuttle's shields are - they fall apart quite regularly, apparently, during the relatively sedate speeds and accelerations of a rocket launch. They'd be shredded by supergun delta-v's.

2. Gravity. This is a deep gravity well, so you'd need some serious velocity to get out of it even if you didn't have the complication of atmospheric drag to overcome.

3. Acceleration. The big advantage of a railgun is the colossal accelerations they can achieve. This is of course, ahem, "inconvenient", for any potential passenger. You don't want to smear your astronauts in a pink layer a millimetre thick on the back wall...

4. Minor concern, but where would you put one? It would have to be miles and miles long, perfectly straight, etc. You'd need some pretty specific location for that.

A more realistic tech for getting stuff (not people) into orbit is a supergun. Indeed, that's what Saddam Hussein's "supergun" was for. As a weapon of war it would be next to completely useless - large, conspicuous, entirely immobile and next to impossible to aim. But as a launcher for satellites... now you're talking. That was why it had to be stepped on. Nobody seriously cared if he got a big gun - he had lots of guns, and missiles, already. But the US couldn't tolerate him having the capacity to put things in orbit.

SoRB

Wouldn't the same problem that causes the astronaut's pink smear also cause the destruction of any delicate electronics within a satellite launched by this sort of system?

It strikes me that anything that is remotely functional in terms of moving parts is screwed and also anything remotely compressible. After all, the pink smear includes mashed bone presumably.

What you need is some good old inertial dampers within

Not necessarily. Packed properly, solid objects can be subjected to really quite, ahem, suprising accelerations without damage. Why would you suppose electronics - entirely solid state systems, remember - would suffer from acceleration?

It wan't the objects themselves that concerned me, it was the bits that connect them together that might weaken under a sudden accelerating force. But I guess if, as you say, you pack them properly they might be OK.

The aerospace industry already tests electronics modules to hundreds of Gs. Even the hard disk in my desktop PC, complete with moving parts, can allegedly withstand 200G for short periods. The advantage of the rail gun is that it can sustain a controlled acceleration all the way up to escape velocity without ever exceeding the payload's design parameters. A conventional gun would have to do that in a far, far smaller timeframe, and less controlled manner, meaning higher accelerations and more rugged payloads.

Granted it'd be useless for launching people; conventional rockets already approach human limits and they need the full distance-to-orbit to get up to speed.

Aaaahh, I think I was mistaking a railgun for - well - a gun.

Forgivable, I think, given the name. It's a gun that fires rails, inni'?

what's a super gun?

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

For anyone that may not know, a railgun differs from a conventional gun in accelerating its projectile using magnetic coils rather than the explosive expansion of chemical propellants.

They have been proposed in the past as a possible method of escaping a comparitively small gravity well, such as that of the moon. Indeed, artists impressions have been produced by NASA showing railguns, (or mass drivers, to give them their 'propulsion' name,) being used to throw rock from the moon's surface and out of its gravity well, presumably to be 'caught' at a predetermined point and used for construction purposes.

Mass drivers have also been proposed as an propulsion system for vehicles, specifically spacefaring asteroids. The idea is that you find a suitably sized asteroid and then start hollowing it out, firing the extracted rock out the back of the 'ship' using a few suitably-sited mass drivers. According to Newton's third law of motion, for every action there is an equal and opposite reaction, so by firing rock out the back of your asteroid, it will start to move the asteroid in the other direction. Movement will be slow at first, but as long as time isn't an issue then the acceleration will gradually increase, especially as every chunk of rock launched will decrease the mass that needs to be accelerated. By the time your asteroid arrives at wherever it needs to be, you'll be left with a big, hollow shell of rock, which can itself be used for construction purposes or even as a living space in its own right.

None of which answers the original question, of course, but what would you expect?

The supergun is a much better bet for launching stuff into orbit, as shown by the fact that Gerald Bull, the designer of the Iraqi supergun, allegedly briefed western security services that the gun was designed solely to launch satellites. In this the weapon would have been helped by the extra 'kick' that a weapon fired in the opposite direction to the rotation of the earth would receive.

If the launch tube in question is a conventional, single charge device, then there would indeed be a big problem with the tremendous and almost instantaneous accelerative forces affecting the projectile, but one way round that would be to use a 'multi-chamber' device, as experimented with by the Germany in WWII. In such a launcher, instead of being fired by one big bang, it would be accelerated by a timed series of detonations as it travelled up the barrel, each one imparting an extra charge of acceleration. Although this would still be too violent a process for humans to withstand, it would at least reduce the forces involved to series of large bangs, instead of just one very big bang indeed.

Hope that's of some help to someone.

I used a railgun for years in Quake II and never knew how it was powered!

You know Gnomon, I never pictured you as a Quake II type of guy!

It's essentially a specialised linear motor, the same type of technology that powers magnetic levitation trains.

Anyone who has played a lot of 'Mechwarrior' games on the PC will know it as a Gauss Rifle.