Rockets being passé, China is working on using an electromagnetic railgun to launch crewed spacecraft the size of a Boeing 737, weighing 50 tonnes, into orbit. This remarkably ambitious project is even more ambitious than it seems at first glance.
Call it a railgun, a catapult, or a mass driver, the idea of replacing rockets with an electromagnetic accelerator is a very attractive option. Instead of lifting off on chemical rockets that have to carry fuel and fuel to lift the fuel and fuel to lift the fuel and the additional fuel, it makes more sense to keep as much of the launching system on the ground while leaving the vehicle as light as possible.
The principle behind such a space railgun is simple, but the details are surprisingly complex and the numbers involved very quickly become daunting. If China can carry off using such a system to launch a spaceplane as part of its Tengyun project that began in 2016, it would be one of history's major engineering achievements.
According to the Chinese official media, the plan is to build an electromagnetic launch track that would be able to accelerate a spaceplane to a speed of Mach 1.6 or even as high as Mach 5. Once airborne, the vehicle would then fire its onboard rocket engines and continue to accelerate to orbital velocity.
This not only means creating a spacecraft that is compatible with such a railgun, but also a launcher that is able to keep its g-forces, vibrations, and other variables to within safe tolerances for human passengers. Similar systems have been studied by NASA, though these concentrated more on robust dumb and robotic payloads that can take a lot of punishment.
The new system is being developed by the China Aerospace Science and Industry Corporation’s (CASIC) Flight Vehicle Technology Research Institute, which has reportedly built a two-kilometer (1.2-mile) test track in Datong, Shanxi Province. From the description, it's about the same size as the Hyperloop test track that used to sit in Nevada outside Las Vegas and is sealed inside a similar vacuum tube. At present, the track can attain a speed of 620 mph (1,000 km/h) and will be extended to be five times faster.
To develop this into a proper space launch system will be daunting to say the least. It won't just be a matter of scaling the technology up, it will require major advances across the board not only in the railgun itself, but in its control systems, the means of powering it, and even in how to build the components that make it up.
One problem is that for a railgun that can reach Mach 1.6 with passengers aboard, it will have to be about at least five-miles (8-km) long. And a lot longer if it's to reach Mach 5. That's not only a lot of electromagnets, which may need to be cryogenically cooled, it will also need to be sealed in the largest vacuum chamber ever constructed that will need enormous pumps to maintain that vacuum. This tubular chamber will also need a very special airlock so the vehicle can exit at supersonic speed. If this doesn't work perfectly, there could be any of a number of very nasty accidents involving energies in the neighborhood of a tactical nuclear weapon.
Then there is that matter of power. The railguns used to launch fighter planes from the aircraft carrier USS Gerald R. Ford use 121 megajoules to accelerate the plane to 150 mph (241 km/h). To accelerate a similar mass to Mach 5, the Chinese railgun would need a staggering 50,000 megajoules. And the proposed spaceplane is supposed to weigh in at least 10 times more.
That means the space railgun would require a nuclear power plant generating a gigajoule per second to run it and it would need a whole new generator of supercapacitors to store the energy. The Hochfeld-Magnetlabor Dresden- Dresden High Magnetic Field Laboratory has a state-of-the-art capacitor bank that can handle 50 Megajoules, a world record. The Chinese railgun would need to improve this by a thousand.
This will require not only remarkable basic advances in some already advanced engineering, but the construction of a whole new industrial infrastructure capable of building such machines. And this doesn't even address the sensor and computer systems needed to monitor and control all of the subsystems of the railgun in real time.
The Chinese claim that if the railgun is successful, it will reduce launch to orbit costs to US$60/kg. That's a revolutionary reduction even on SpaceX's $3,000/kg.
However, as the saying goes, first catch your rabbit.
Source: South China Morning Post
