Dec 02 2021
Recently on the SGU we talked about a new company, SpinLaunch, which just conducted a test of their system to hurl satellites into orbit by spinning them up to high speeds then releasing them. We also did a follow up discussion on the show which will release this Saturday. It’s an interesting case study in how to assess the plausibility and viability of potential new technology.
The basic idea is a good one. Right now rockets are the way we get into space. The technology works, and reusable rockets have brought down the cost considerably. In the space shuttle era the cost of getting stuff into Earth orbit was about $100,000 per pound. Today SpaceX is below $2,000 per pound and hoping to get the cost under $1,000. Because the rockets themselves are now reusable, much of the cost is in fuel. Fuel use is governed by the rocket equation – it takes fuel to carry the fuel to carry the fuel you need to get the payload into orbit. The vast majority of the fuel, therefore, is used just to get the rest of the fuel up.
But perhaps there is another way. From the first conception of Earth orbit, the notion was that a very powerful canon would project something into orbit. This view held sway until the early 20th century when rocket technology became feasible. Even still, the idea persisted. In the 1960s the US and Canada developed the HARP (high altitude research project) system, which is essentially a giant gun that projected probes into the upper atmosphere for weather research. This system worked, and was canceled mainly for political reasons, not scientific ones.
For various reasons you cannot get something into orbit directly by shooting it from the surface of the Earth. In order to get into an orbit you will need rockets to get into the correct vector. But shooting a payload into the upper atmosphere at high velocity could essentially serve as the first stage, with rockets then taking over to get the payload into a stable orbit. This would dramatically reduce the fuel needed to get into orbit. The basic concept is to use an external source of power to accelerate the payload most of the way in order to avoid carrying all the power with the payload and therefore falling prey to the rocket equation.
The idea of SpinLauch is to accomplish this without a gun but rather to use an electric motor to spin up the payload in a vacuum chamber and then release it through a launch tube. If you watch the animations from the company it all looks very compelling. And again, the basic concept is sound. But the technology is an extreme engineering challenge, and that is where the skeptics come in.
First, we have to note that the demonstration of the technology was a scaled down version. The payload was only spun up to about mach 1, and it does not seem as if the chamber was evacuated, so no vacuum. The payload was successfully released, but it was not very straight and did tumble. Still, you might argue that this is version 1.0 and any new technology will have kinks that have to be worked out. This is fair. But scaling up to the speeds they claim they are shooting for is not just a matter of making a bigger SpinLaunch system. New engineering challenges come into play when you try to get to faster velocities. The company says they will get their payloads up to 5,000 mph and 10,000 Gs of force. This would require a near perfect vacuum, and they have not yet demonstrated they can do this with their design. Further, the vacuum is kept in place with a membrane that the payload can break through on launch, so it has to be strong enough to hold in a vacuum yet brittle enough that the payload can break through without damage or losing too much velocity. There is reason to be skeptical that this is even possible.
Being generous, we can imagine that the SpinLauch would be built on a mountain top, so the atmospheric pressure would be lower (say, 40-60% depending on altitude). Perhaps they can use a series of membranes with progressive pressure changes. This all adds complexity and cost, and also extends the time between launches. If they use liquid fuel in the payload they will also need additional rocket to accelerate the rocket and get the fuel at the bottom toward the engines, something not included in their original designs. Or, they could use solid fuel. These are all probably solvable engineering problems. But even if they can solve them, it raises the separate question of will it be worth it? If at the end of the day the system works but costs more than reusable rockets, then no one will use it.
YouTuber Thunderfoot has produced two videos where he outlines his criticisms of the SpinLaunch system if you want some more details. I mostly agree with him, but feel he ignores possible solutions to some of the challenges he raises and also is somewhat unfair in putting down the company itself. Sure, they are producing slick promotions hyping their technology while glossing over the negatives, but I take that as par for the course for any technology company seeking funding. It does not mean the technology can’t work. Didn’t SpaceX do the same thing? I am still critical of companies for doing that, but I just don’t think it predicts that the technology is bogus or the company a complete scam. Legitimate companies do it too.
At this point I think it is more likely than not that this company will not be able to solve all the engineering challenges. I think they will fail when they try to scale up, mainly because of the need for a vacuum in the chamber. But even if they do succeed I think the company will still fail for two reasons. The first is risk – spinning at 10,000 Gs is extremely risky. If anything goes wrong the result is likely to be catastrophic, like a rocket blowing up on launch. When a rocket blows up, however, you lose that one rocket, and there are many more to take its place. If the SpinLaunch fails you lose the entire thing. There are no others, and the majority of the cost in the system is building the giant SpinLaunch chamber. Losing the chamber would likely bankrupt the company, whereas SpaceX planned on blowing up lots of rockets while developing the technology.
The second fatal flaw is that solving all the engineering problems will likely result in a cost to orbit that exceeds the declining cost of reusable rockets. While the fuel savings would be great, that may not be enough to warrant the higher risks and costs.
As an example, the US has been developing a rocket alternative that involves an electromagnetic rail of two miles that accelerates a ram jet. Once launched the ram jet (which is now going fast enough for the ramjet itself to work) blasts into the upper atmosphere at Mach 7. From there it can launch payloads into low Earth orbit. It then flies down and lands, and can be launched again in a day. Such a system will probably work, and the underlying technology is already proven. Railguns work, and there are proposals to use railguns to shoot payload partly into orbit. The HARP system could also be resurrected. All these methods are viable, and likely would be cheaper, safer, and more reliable than SpinLaunch. But they all suffer a lack of enthusiasm for investing in them because SpaceX has brought the cost of getting payloads into orbit down so much. The financial incentive has narrowed.
So while the idea of getting around the tyranny of the rocket equation remains compelling, no one has managed to develop an alternative to rockets that is safe, reliable, and cost effective. I still think it is likely that some such system may come into existence, especially for small satellites like cubesats. I don’t think SpinLaunch will be it. If I had to bet, my money is on some kind of railgun system. There may be some other entirely new technology developed as well – anything that uses external energy to get partly into space. Something like SpinLaunch might work well on the Moon, where there is no atmosphere, so it is still useful to develop the basic technology. Further, as we try to get to net zero, reducing rocket fuel use may become a greater incentive for developing alternatives, even if there is no cost advantage.
Predicting future technology is extremely difficult, and this one example shows many of the reasons why this is the case. The technology itself is only one factor, and even if we can do something it may never come to fruition because of relative economic and other factors.