Getting to space without rockets

After the launch of Rocket Lab’s Electron a few weeks ago we had a look at the price range to launch stuff into space here. One of the comments that someone made was that we are not going to see any real magnitude change in the price of getting to space unless there’s a a way of overcoming our reliance on chemical rockets. So at milky-way.kiwi we thought we would have a look at what research and thinking is going on around the world to find a replacement for the current way of getting stuff into space.

Project HARP

Over the years there have been some quite interesting suggestions on how we might get objects into space without the use of rockets, these range from huge guns to space elevators. Back in the 1960s, during the development of Intercontinental Ballistic Missiles, a collaborative programme between Canada and the United States, called Project HARP designed a huge gun that was supposed to punch re-entry vehicles into space and test their re-entry characteristics. The gun was adapted from a 16” naval gun and though the programme never reached full maturity due to a variety of reasons, it did manage to launch a 180kg projectile to an altitude of 180km, over the 100km Kármán Line but still not a very useful height. The design did have it’s limitations such as a very narrow firing tube which limited what could be fired.

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Project HARP Gun

Hypersonic Airplane Space Tether Orbital Launch

Other ideas mooted over the years have included hooks flying at huge speeds, launching rockets from high altitude aircraft, building enourmous towers and space elevators.

The space hook concept essentially involves having a hook dangling down from a orbital structure that stuff can be loaded onto by high flying aircraft. The concept was investigated by Boeing, which they called Hypersonic Airplane Space Tether Orbital Launch (HASTOL) and provided their assessment on the feasibility in a report in 2001. Basically a satellite in orbit has a tether that rotates around, when the tether is at it’s lowest point it is loaded with whatever needs to be flung into orbit by a fast flying aeroplane or rocket. The load is then flung into space as the tether rotates around the satellite, the picture below explains it quite well and is from the report linked above.

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This concept was found to be feasible but had a number of challenges including the design of the procedure to intercept the tether and the required energy to lift the tether satellite back up to operational orbit, after it’s flung the payload away. Boeing found that material that existed back in 2001 could do the job though they were worried that the tether may corrode quickly. The final report covered a design that would have to intercepted at 150km in altitude by a rocket flying at Mach 17, the tether would be a few hundred kilometres long. It would be interesting what the same study would conclude now with the different materials available and the different propulsion options around. This could be a feasible way of achieving a magnitude change in the price of getting stuff into space – and not into the too distant future.

The MAGLEV launch

This report from 2011 covered the options of using magnetic levitation to accelerate a spacecraft to a speed fast enough to propel it into space. Basically the theory goes that you can launch something by accelerating above 8km/s then just give it a boost with a rocket for the rest of the way, greatly reducing the cost. The expensive bit is in the infrastructure of the MAGLEV which would need to be many hundreds of kilometres long to achieve the speed required without creating such a strong acceleration that the passengers would be killed. The promising thing with this concept is that it is possible – doesn’t require any yet to be invented technology. It just required many many $billions to build it.

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The Startram concept 

The concept claims that 40ton spacecraft could be launched multple times per day costing as little as $43 per kilo. If this is correct then the magnitude difference in cost from the $10k – $20K per kg today would be a significant game changer. It will be interesting if this idea ever comes to fruition. Another interesting combination could be the Startram and HASTOL combined, with a smaller more affordable MAGLEV track built to accelerate something to the 3.5km/s required to intercept the HASTOL.

Space Elevator

The next concept, and probably the most popular, is the idea of a super strong cable extending from the surface of the Earth into space that can be used to climb up and insert stuff into orbit. The challenge in this concept is building the cable of a material that is sufficiently strong enough, carbon nanotubes might help solve the problem. Basically the long cable is tethered to a base on the Earth’s surface and a counterweight is at the other end in space. The counterweight keeps the cable taught and stuff is hauled up and down the line. Of all the examples here this is probably the most difficult with respect to currently available technology. The featured image comes from Liftport.

Economics will ultimately drive the development of alternatives to get things into space. None of the methods described above are fanciful, they are real and potentially can occur, though the gun option is probably not that useful. The inhibitor is mainly the huge infrastructure cost not the vehicle. At the moment the vehicle and propulsion is the main cost. The real change in the reducing the cost to space will be when each shot is very cheap and quick to recycle.