I’ve long been a fan of the idea of the space elevator ever since Bradley Edwards published his famous feasibility study, but his elevator is not the only game in town when it comes to alternative systems for launching cargo and people into orbit.
Gizmag has just published an article about the Startram launch vehicle, which is based on the tried and tested magnetic levitation (maglev) propulsion system, albeit amped up to a speed some 50 times faster than the top speed of today’s maglev trains. But unlike the space elevator, which is still awaiting the advent of carbon nanotubes that are strong enough and long enough to be spun into a ribbon thousands of miles long, the Startram system could be built entirely from technology that exists today.
Of course, if it was easy, we would already be building it. Needless to say, there are some complications:
The scope of the project is challenging. A launch system design for routine passenger flight into LEO should have rather low acceleration – perhaps about 3 g’s maximum, which then requires 5 minutes of acceleration to reach LEO transfer velocities. In that period, the spacecraft will have traveled 1,000 miles (1,609 km). The maglev track must be 1,000 miles in length – similar in size to maglev train tracks being considered for cross-country transportation.
That’s a maglev track that is 100 miles longer than Texas is east to west or Britain is north to south. And it’s not as simple as just building a track:
Like a train, the Startram track can follow the surface of the Earth for most of this length. Side forces associated with the curvature of the surface can be accommodated by the design, but not the drag and sonic shock waves of a craft traveling at hypersonic velocity at sea level – the spacecraft and launching track would be torn to shreds.
To avoid this, the Startram track must be contained inside a vacuum tube with vents to allow air compressed in front of the spacecraft to escape the tube. A vacuum equivalent to atmospheric conditions at an altitude of 75 km (about 0.01 Torr) should suffice for the efficient operation of the Startram launch system. Rapid pumping to achieve this pressure will be provided by a magnetohydrodynamic vacuum pump.
If the entire Startram tube is at sea level, on exiting the tube the spacecraft will suddenly be subjected to several hundred g’s due to atmospheric drag – rather like hitting a brick wall. To reduce this effect to a tolerable acceleration, the end of the Startram vacuum tube must be elevated to an altitude of about 20 km (12 miles). At this height, the initial deceleration from atmospheric drag will be less than 3 g’s, and will rapidly decrease as the spacecraft reaches higher altitudes.
Estimates for the cost of the launch system range from $20 billion for a cargo-only system that could be built in 10 years, to a $60 billion system capable of launching people into orbit within 20 years. That doesn’t sound a lot when compared to the $3.5 trillion the US government spent last year, or even the $680 billion spent on the military budget alone, but it is still a huge chunk of change. NASA’s entire budget for 2012 is less than $20 billion.
And it’s also a lot of money to spend on an unproven engineering project of such a massive scale. Thus the reality is that there would need to be a seismic shift in government policy before the Startram system had any chance of becoming reality, something that perhaps only a new Cold War (with China) or the imminent threat of an asteroid strike could bring about–not that anyone would wish for either of those things!
Still, I have no doubt that one day we will need a way into space that is cheaper, faster, safer, and more reliable than strapping people to the top of a massive firework, and some long-forgotten group of scientists who toiled in obscurity for years on one alternative launch system or another will suddenly be hailed as the visionaries who revolutionized our access to space. Let’s hope that time comes sooner, rather than later.