Difference between revisions of "Talk:Colonising Space/Access to space"

Latest revision as of 22:31, 26 July 2013

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.

• Multi-stage rocket - These are currently very expensive, but need not necessarily be so. Jeff Greason of XCor argues very persuasively here that rockets are not expensive because of the technology. "Rockets are built out of aluminum, just like airplanes. They're not built out of diamonds." The expensive thing is the 3000-person assembly line and 10,000-person team of mechanics. If we build the same technologies we are building now, but mass-produce them or open-source them, they could be radically cheaper. Anything mass-produced, digitally fabricated, or open-sourced is bound to be cheaper than something tailor-made. We have been tailoring rockets. The various private space companies propose mass-producing them. Copenhagen Suborbitals are working on an open-source rocket. Unreasonable Rocket is a project to 3D print a rocket. July 2013: 3D printed rockets look like they're gonna work out: [1]. This will slash costs.
  Reusability is another factor. The more reusable the rocket is, the lower the cost per launch. XCor have already flown a rocket seven times in one day.
• Aircraft piggy-back - SpaceShipOne piggy-backed on an aircraft to 13km, then got to 112km. It was retired straight after the X Prize and the company that built it, Scaled Composites, have teamed up with Virgin Galactic to form The Spaceship Company, which will be making SpaceShipTwo.
• Scramjet  / rocket hybrid, such as the single stage to orbit  (SSTO) Skylon  launch vehicle. Skylon is very promising. Though it doesn't work yet, the key components have been demonstrated and everyone agrees they are technically feasible. According to their FAQ, a Skylon flight to launch 15,000kg will cost $30m to 40m. This is $2000-$2667 per kilogram launched. This is the initial cost; amortization could cause it to fall to $2m per payload, which is $133 per kilogram. It can deliver 15 tonnes to 300km orbit or 11 tonnes to 800km.
• Space guns like HARP .
  

  Anything propelled upwards at a speed over 11.2 km per second will escape Earth's gravity and reach space. A straightforward way to achieve this fantastic speed is to fire 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. 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.
• Linear motor assisted launch from high altitude terrain
• http://en.wikipedia.org/wiki/Laser_propulsion
• StarTram, essentially a vactrain angled up the side of a mountain. The top of the tube is open, but it uses 'magneto hydrodynamic' pumps to maintain the vacuum.
• 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 ^[2], 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.

Assessment of these technologies

The elevator and launch loop are not gonna happen. It would be nice if they did, but they're way too far removed from reality. Long before it is possible to build them, other equally effective methods will have matured.

The private and open-source space race - XCor, Virgin, The Spaceship Company, Unreasonable Rocket, Hermes, Copenhagen Suborbitals, etc. - are focusing on conventional rockets. Whether launched from the ground or piggy-backed on planes, they have one important thing going for them - they really work. This is the only proven launch technology, and the progress that needs to be made is incremental, not revolutionary. Rockets definitely will become cheaper in the decade ahead; we will do thousands of launches and come up with a reliable, reproducible launch protocol.

Scramjets are promising. Skylon is streets ahead of any other project. It will work if they get the funding, and they probably will get the funding eventually, though it will cause delays.

The space gun is equally promising. It is definitely technically feasible. If funded, it will happen.

Startram is technologically feasible, but will be outcompeted. It has a lower Ridiculousness Quotient than the space elevator or launch loop, but still higher than rockets, scramjets or space guns. It is just too big and too expensive.

It is a three-horse race. Cheap rockets, scramjets or guns - one of these will open up space soon. If one of them reaches maturity first, the others may fail to get investment. Skylon say they need funding of $9-12bn. Quicklaunch are looking for $562m over 8 years. Startram are looking for $20bn to build a version that will launch cargo, or $60bn for one that can launch people as well. That is exactly why I think Startram will never be built, and why Quicklaunch is so promising. Skylon's figure may sound high, but they have the sort of credibility needed to raise that money.

I don't know enough about laser propulsion or mass drivers to comment on those. --Balatro 02:20, 1 May 2012 (CEST)

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)