Here’s another prospect to add to the list of alternatives to rocketry, if only for launching inert and non-fragile stuff like fuel or water into orbit. It’s a dirty great air-gun, basically:

At the Space Investment Summit in Boston last week, Hunter described a design for a 1.1-kilometre-long gun that he says could launch 450-kilogram payloads at 6 kilometres per second. A small rocket engine would then boost the projectile into low-Earth orbit.

While humans would clearly be killed and conventional satellites crushed by the gun’s huge g-forces, it could lift robust payloads such as rocket fuel. Finding cheap ways to transport fuel into space will lower the cost of keeping the International Space Station in orbit, and in future it may be needed to supply a crewed mission to Mars.

The gun would cost $500 million to build, says Hunter, but individual launch costs would be lower than current methods. “We think it’s at least a factor of 10 cheaper than anything else,” he says.

A factor of ten is a lot of money, meaning that initial investment could probably be recouped pretty fast. But is a Jules Verne-style cannon a sexy enough idea to attract the funding? It’s limited range of cargo will probably count against it, for a start.

Meanwhile, the Ad Astra company is making strides with its prototype VASIMR plasma engine, which will hopefully be way more efficient than traditional thruster designs. Fitting one to the ISS could save literally tonnes of orbit-adjustment fuel expenditure per year, and (once the tech is scaled up) plasma engines could get a spacecraft to Mars in little over a month. Here’s a brief video if the VASIMR being tested:

It’s a bit quieter than a regular rocket, isn’t it? But still more exciting than a big air-gun… which may partly explain the enduring romance of rocketry.