China is building a railgun that can hurl crewed spacecraft into orbit

China is building a railgun that can hurl crewed spacecraft into orbit
Artist's concept of China's spaceplane
Artist's concept of China's spaceplane
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Artist's concept of China's spaceplane
Artist's concept of China's spaceplane

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

Great article. Fascinating stuff
Rick O
Sounds like a good idea until you start doing the physics and math
The financial cost will never be paid back. Also when the 'rocket' exits the end of the launch tube it will run into a brick wall of air. This idea is crazy.
Why would it need to be inside a vacuum tube? None of the space rockets so far have been inside a vacuum tube during launch...
These numbers aren't significantly worse than the numbers for a chemical rocket, it's just that we're used to burning tons of fuel per second. Which Himalayan peak are they planning to run up the side of?
windykites said what I was thinking too. Once you leave that vacuum, bam.
Robert A. Heinlein would be thrilled, since he "invented" this a LONG time ago, but...

It is indeed an instructive exercise to do the physics and math. Suppose the target speed is 500 m/sec (approximately Mach 1.5), and the acceleration is one gravity, 10 m/sec^2. It takes 50 seconds to reach the target speed, in which time it goes 1/2 x 10 x 50^2 = 12.5 km. That's 8 miles of tunnel kept at a vacuum IF one can figure out a way of getting it out of the vacuum and through the resulting turbulence as your 1.5 mile tunnel explosively refills with air. Alternatively, one can accelerate it in open air (Heinlein's design) but now you have to overcome drag forces that scale like v^2. To minimize these, you move it to the Himalayas -- China does have some very high mountains but still have to increase the magnetic force accelerating your big ship, and have to design it to make it through the sound barrier without being shaken apart, which in turn means that you can't be near ANY reflective surface or your own shockwave will bounce back chaotically and hit the ship itself. Magnetic fields being effectively short range, this is a problem.

This leaves one with another problem -- mach 1.5 is a joke compared to orbital speed, which is around 8 km/sec. OK, so try for mach 5 (2.5 km/sec) (which STILL leaves one the 5+ km/sec to obtain from the rocket burn). Now 1 g implies 250 seconds, and your track has increased to 190 miles long and vacuum or not, that's seriously expensive. So fine, you say -- humans can stand higher g-forces in the accelerating frame. Standard rocket acceleration is 2g, opposing the earth's gravity producing 3g in the accelerated frame. One can do most of the mass driver acceleration horizontally, so let's make it 3 g! Now the track only needs to be 63 miles long to reach mach 5 -- still a no-go, especially if one tries to use a vacuum in a tunnel that long (built in an earthquake-prone part of the world, BTW). Even going to 10g and only mach 5, the tunnel or open air track needs to be 20 miles long, and frankly, humans probably would be badly damaged by 25 seconds of "weighing" approximately one ton -- blindness, ruptured organs, strokes -- the crew would most likely be crippled.

I've worked through this a lot of times and never once found a way that it could work for people. Shooting up building materials, sure. Building a ballistic cannon as a weapon perhaps. But EVEN mach 5 is a factor of 3 less than low earth orbital speed or intercontinental long range ballistic speed.
RGBatduke pretty much described the human downside. I didn't do any physics, but as a long time Naval Aviator, quickly figured out what a sustained miles long "cat" (catapult) shot would do to human passengers. Could it work for cargo only? Possibly.

I am closely watching the Japanese with their rail guns right now. US put many millions into that program and couldn't make it work. Hopefully our allies the Japanese do.
I can imagine that a combination of current rocket power assisted by a railgun launch system would be a happy hybrid median.
Terrific idea, although likely impractical. The one on the Ford doesn't work very well either.
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