Talk:Colonising Space/Access to space

Notes removed, but have valuable info for a proper write-up of the topic of access to space

...we need an efficient, reliable way of getting large amounts of material beyond the Earth's gravitational pull. While incremental improvements in rocket technology may suffice, several very different ways of getting off the planet have been proposed.

• Multi-stage rocket
• Aircraft piggy-back
• Scramjet  / rocket hybrid, such as the single stage to orbit  (SSTO) Skylon  launch vehicle

• Space elevator . Picture a satellite tethered to the Earth — a large weight in geosynchronous orbit is attached by a strong, long, light cable to an anchor-point on the planet's surface. Robots could climb this cable, carrying payloads into space. This is expected to reduce the cost of transporting a pound of material into space to $100 ^[1], which would completely open up space to all kinds of new ventures. However, there are still many challenges to be overcome before a space elevator is viable: the robots that ascend the cable need a reliable power source, there are dangers of the cable being snapped by lightning strikes, asteroids or orbiting debris and there is doubt as to whether carbon nanotube cables can be made strong enough to withstand the tension generated by such an enormous structure.
• A launch loop  (illustrated here) is perhaps more feasible than a space elevator as it requires no new materials. It is essentially a conveyor belt to space. It consists of a loop of iron cable anchored on the surface of the Earth at one end, and at a height of 125km above the Earth at the other end. The loop passes through electromagnetic bearings at each end. These bearings spin the cable at high speeds, which creates a centrifugal force that lifts the cable up into an enormous loop, the top half of which is in space. Payloads can use magnets to attach themselves to the cable and ride it into space.
• Space guns like HARP .
• Linear motor assisted launch from high altitude terrain

The most promising non-rocket launch method is the 'space gun'. Anything propelled upwards at a speed over 11.2 kilometers per second will escape Earth's gravitational pull and get into space. One of the most straightforward ways to reach this fantastic speed is by firing things out of an enormous hydrogen-powered gun. This would provide a very cheap and practical way of putting materials in space, but the large g forces involved would make it unsuitable for humans. A space gun holds all the promise of a space elevator or launch loop (i.e. cheap, rough-and-ready access to space) but requires none of the unlikely engineering of either of those two proposals. Quicklaunch Inc. have designed this 1100m-long, hydrogen-powered floating gun that can launch 1000lb payloads into space every few hours for $250/lb. See this Google talk for more detail.

About the space gun

A large fraction of the weight of a manned vessel is fuel. If we launch this fuel (and any other bulky stuff) cheaply from a giant gun, astronauts can travel in smaller rockets. The less mass that is launched by rocket, the cheaper manned spaceflight becomes. This is the primary market that Quicklaunch Inc are targeting; theey want to launch fuel payloads to be picked up in orbit by other spacecraft. --Balatro 21:57, 17 April 2012 (CEST)

Yes that is quite interesting, I had only heard about it vaguely. Presumably it would make the most difference for missions beyond Earth orbit - rockets just to get into Earth orbit are still pretty massive (and mostly fuel), not sure it will help those ones.

For going further out into the solar this kind of thing could make a big difference. Although I'm personally more of a fan of a maglev-type electric rail-gun/maglev going up through a mountain. Could have a much longer launch tube (much less G - important even for cargo) and would exit above the majority of the Earth's atmosphere (by mass) at the top of a high mountain (one hopefully near the equator where gets an extra 1000mph of velocity from the Earth's rotation).

We should gather together a page on launch systems, focusing on the ones with the top potential, including this. CharlesC 02:14, 22 April 2012 (CEST)

The Quicklaunch website claims "Quicklaunch reduces the overall cost of manned exploration of Mars and the Moon by more than a factor of 10". They calculate propellant costs for a 10-man, 3-year mission to Mars at $50bn without their technology, or $5bn with it. Of course, this is a biased source and something doesn't quite add up: at one point they claim the "overall cost of manned exploration" comes down tenfold, but in the Mars metric, it seems that just propellant launch costs are coming down that much. Anyway, I am sure the reductions will be significant.--Balatro 19:32, 22 April 2012 (CEST)

A 'propellant mass fraction' of 80-90% is typical, meaning 80-90% of the mass launched is fuel. If there were fuel depots in orbit (launched by a gun), a rocket would only need enough fuel to get it to the depot. I'm not sure how much of the fuel is needed for takeoff; it seems to be somewhere around half. --Balatro 20:34, 25 April 2012 (CEST)