On 2021-10-22, Spin Launch successfully launched a sub-scale demonstrator payload from its test centrifuge at Spaceport America in New Mexico. Spin Launch, which has raised US$ 80 million in funds from venture capital heavy-hitters including Kleiner Perkins, John Doerr, and Google Ventures, plans to develop a 100 metre diameter centrifuge which will mechanically accelerate its payload to a velocity of 2.2 km/second, flinging it to an altitude of 61 km, where a small rocket motor accelerates it to orbital velocity.
Launch cost is estimated at US$ 500,000, which is around a factor of 20 less than small satellite launches by conventional rockets. The company estimates it could launch five payloads a day with the system. Here is an explanation of how the launcher works and the engineering challenges it presents.
It seems odd that their patent does not illustrate the rupturable membrane or whatever lets them maintain the vacuum at the “exit port”:
“The exit port 115 may comprise any system or structure that can provide adequate sealing when the circular mass accelerator structure 150 is under vacuum and that can be opened at a high rate of speed, or alternatively pierced by the launch vehicle 105 . In various embodiments, the exit port 115 may comprise a fast-actuating door or shutter. In other embodiments, the exit port 115 may comprise one or more sheets of a polymeric material such as Mylar which may be pierced by the launch vehicle 105 upon launch.”
They may be using just the rupturable membrane on the sub-scale demonstrator, allowing air to rush in after the launch, as they’ll have to inspect the centrifuge arm and mount the next payload, which will surely not be done in a vacuum for these test shots.
The question of designing a fast-acting door to allow the projectile to exit without losing (much) of the vacuum in the launch tube is discussed in the design for StarTram (my review) and in the technical paper [PDF] describing the system. That was a much more ambitious system which used magnetic levitation to accelerate payloads to 8 km/sec, whose cost was estimated to be around US$ 20 billion.
Another issue I did not see discussed in the patents or mentioned in the video is recovery of the kinetic energy in the centrifuge after the payload is released. It’s obviously necessary to stop the rotation in order to mount the next payload, and just dissipating that energy as heat then cranking it up again for the next launch is going to be expensive. I wonder if they might use a scheme such as spinning down the launch centrifuge by running a generator which powers the motor on an energy storage flywheel. Then, after the next payload is attached and ready to go, that flywheel runs a generator that spins up the launcher part of the way, needing only a top-off from grid power.
Handling the G-forces is challenging but entirely doable. Proximity fuzes for anti-aircraft artillery have been in use since World War II, and they have to survive being shot from a cannon with something like 20,000 Gs and a spin of 30,000 RPM. These were built using vacuum tubes until transistors became available. Several of the SpinLaunch patents cover rugged reaction wheels, solar panels, and avionics for payloads launched by their system.
Incredible! Especially when I think of how carefully we handled vacuum tubes when I was a kid. They seemed to fail and/or break pretty easily. I guess those produced under military contract can be made to be far more rugged.
Over the years, there has been intermittent discussion about the kinder, gentler approach of using a balloon to lift a rocket high above much of the atmosphere before dropping & igniting it. Clearly preferable for delicate cargoes. I wonder about the comparative economics of helium balloons versus large diameter vacuum centrifuges? While helium is currently a rather expensive commodity, there are reports that new developments in Qatar and Russia could significantly increase global supply.
The good news is that entrepreneurs are exploring many different approaches to getting to space, beyond the expensive throw-away single-use rocket. NASA’s administrators, and their Congressional overlords, should be ashamed of themselves.
Use hydrogen. It’s dirt cheap (easily made from natural gas) and completely safe in a closed balloon with no ignition sources. When the rocket fires, the hydrogen burns to water vapour in the thin atmosphere. And, hydrogen gives you around 8% more lift per volume of balloon than helium.
Thunderfoot rightly tears this apart pretty significantly. In particular, note how they hid the HQ video of the projectile tumbling over and over as it exited? Also, the likelihood of a vacuum chamber at full scale is pretty unlikely to be accomplished, especially given what little we saw of the acceleration chamber in the demo.
