# How might SpinLaunch actually spin something fast enough to launch it into orbit?

Ars Technica's Edition 1.34 of the Rocket Report! says:

SpinLaunch signs deal with Spaceport America. Spaceport America has announced that SpinLaunch has signed a lease to conduct tests at the facility in southern New Mexico and that the company will invest up to $7 million in facilities there, Parabolic Arc reports. The company considered several locations for the test site, but the New Mexico-based site provided the best mix of affordability and location. A novel approach ... SpinLaunch is developing a kinetic-energy launch system that would spin in a circle at up to 5,000 miles per hour before it is released to fly to space. The system would not use any propellants, and the company has reportedly raised$40 million in venture-capital funding. We're intrigued but will remain skeptical until we see some test flights. (submitted by Ken the Bin)

That's 2222 meters/sec so I'm guessing they are only talking about building a suborbital demo? Or does it have a propulsive "2nd stage"?

The Wikipedia article SpinLaunch doesn't say much about how this is going to work:

Technology

SpinLaunch intends to develop a space launch technology that aims to reduce dependency on traditional chemical rockets. Instead, a novel technology will use a large centrifuge to store energy and will then rapidly transfer that energy into a catapult to send a payload to space at up to 4,800 kilometres per hour (3,000 mph). If successful, the acceleration concept is projected to be both lower cost and use much less power, with the price of a single space launch reduced to under US\$500,000.[2] The speed required to maintain Low Earth orbit is 27,000 kilometres per hour (17,000 mph).

The last sentence is a bit unusual as it seems to be a disconnected factoid, as if it wants to remind us that the company's numbers are deeply sub-orbital without coming out and saying "their current speed is way too low to go to orbit!"

Their website doesn't seem to address the issue either.

Is there any engineering information out there on the feasibility of spinning something to orbital launch velocity while on the ground and then letting it go? I don't need the blueprints, but at least an informed discussion or educated speculation.

• I note that at no point in the article is the word “orbit” used. – Russell Borogove Jan 29 '19 at 16:10
• Even if they launched at 8km/s the payload would try to return to the launch point, without some kind of circularization burn at apogee. – Russell Borogove Jan 29 '19 at 16:26
• It's not clear if their catapult is mechanical or electromagnetic. They might just be using a flywheel instead of the more common capacitor banks to power some form of railgun or coilgun. – Steve Linton Jan 29 '19 at 16:46
• I've quoted this a couple of times before, but: "Many novel launch schemes need some amount of help from rockets. What kills a lot of them is doing a tradeoff study of just enlarging the rocket part and getting rid of the non-rocket part. Surprisingly often, that works out to be better and cheaper." --Henry Spencer – Russell Borogove Jan 29 '19 at 17:57
• @RussellBorogove That quote about novel launch schemes could not be quoted too often. – Uwe Jan 29 '19 at 20:35

There is lots of information on spinning things fast. The main problem is that at high speeds, the centrifugal force exceeds the tensile strength of the material.

The Bloodhound SSC team ran into this limit when designing the wheels for their car. At 1600 km/h, the wheel rims (with a diameter of 900 mm) experience 50,000 G. SpinLaunch wants to go 5 times faster than that?

Smaller objects can go faster: you can get ultracentrifuges that operate at 1 MG.

There's also a balance problem. An ultracentrifuge has to be finely balanced, or it'll break up. When you launch an object from a spinning contraption, your contraption instantly becomes unbalanced and starts wobbling.

• To avoid disbalance, two oblects of equal mass should be launched simultaneously in opposite direction. One up into the sky and the other one down into a deep hole into the ground. – Uwe Jan 29 '19 at 18:41
• "a novel technology will use a large centrifuge to store energy and will then rapidly transfer that energy into a catapult to send a payload to space" No launch of an object from a spinning contraption but from a catapult driven by the spinning wheel. – Uwe Jan 29 '19 at 19:57
• A catapult that will take the form of an arm that rotates on an axis. An arm that has to reach 5000 mph according to their claim. So, an object that rotates at 5000 mph. – Hobbes Jan 29 '19 at 20:03
• But there may be linear catapults too, for instance aircraft catapults used on aircraft carriers. – Uwe Jan 29 '19 at 20:25
• I think you are mixing up tangential velocity (mph) with angular velocity (rpm). If angular velocity is fixed, centrifugal force scales linearly with radius, thus smaller is better. For SpinLaunch, tangential velocity is fixed, and centrifugal force scales inversely with radius, so the much longer (I assume) catapult arm will not be under such high centrifugal force. – Lex Jan 31 '19 at 2:13