Rockets of Today

DAWN — Netherlands / New Zealand ...and AURORA — Germany

Everybody likes spaceplanes and wants to see them start replacing rockets, but who does anything about it? Not Boeing — their Phantom Express project was cancelled as part of the general shitstorm that has embroiled the whole company in the period around 2020. Not NASA — their VentureStar project was killed off over a decade ago, and they’ve never looked back. Not Reaction Engines Ltd — their Skylon idea is just a paper concept to generate interest in their half-built SABRE engine... nothing is going to use that engine for probably a decade, and when it does it will probably look nothing like the sketches. Not their Pacific Northwest rivals Radian, whose SSTO plane concept is some of the most naive and implausible visionary guff I’ve ever heard, in a business where that sort of hype is already way past what’s normal elsewhere. Not ARCA, whose spaceplane idea sounded great, but who abandoned it when it became obvious that to build such a thing was way beyond their modest capabilities. Not Aevum, whose plane is just an ordinary supersonic jet with no pilot — a fairly minor upgrade over the subsonic platforms used by Virgin Orbit and Stratolaunch.

But there are some spaceplane projects in development. These need to be separated into two categories: spaceplane orbiters launched by bigger rockets (like the shuttle) and spaceplane boosters that launch smaller rockets (like Phantom Express). The former is pretty easy if done on a small scale, as with Sierra Space’s Dream Chaser, or the Boeing X-37B. There are projects now making more of these, such as the European Space Agency’s experimental little Space RIDER, a lifting body that would land under a parawing. China and India also have spaceplane orbiter projects in the works.

But little reusable orbiters like those don’t replace rockets — or rather, they don’t replace the launchpad and tower complexes that rockets require on the ground. For that, what we want is a plane which takes off from an ordinary runway. That would gain the ability to launch on any day in any direction from any non-polar latitude in almost any weather, like Virgin Orbit or the Pegasus could do, but unlike them, also being capable of reaching space from the ground with the plane, so that the rocket they launch from it can be substantially smaller and cheaper, perhaps only one stage.

Dawn Aerospace is the one company making real progress on giving us such a plane. They’re a Dutch company, but their engineering is being done in New Zealand. Their approach is a perfectly straightforward idea: make a supersonic drone but put a rocket engine into it instead of a jet engine. This would allow it to get above the atmosphere and achieve hypersonic speeds without any great aerodynamic difficulty. Then drop an upper stage or two from it.

And Dawn has already built a plane. It isn’t full sized, and it doesn’t have an upper stage to carry, but it should have the capability to fly small instrument packages into space for a few minutes of microgravity. At least, they say it does. So far they’ve only flown it at lower altitude with temporary jet engines. It’s called Aurora, or just Mark II. They have not given a proper name yet to the bigger Mark III followup plane. When they do we’ll have to rename this article. And even the little version of the plane, for taking a few kilograms of instruments above the atmosphere, should have ongoing usefulness for gathering scientific data.

When finished, the Aurora will powered by a rocket nozzle burning kerosene with high-test peroxide. These propellants may not be super high performance, but since they can be stored long term at room temperature, it should not be too hard to set up fueling at different airports. And because the mix is fairly close to hypergolic, the engine is quickly restartable. They also tout the fuel as “green”, but that’s in comparison to conventional hypergolics, which are horrible toxins. And just because the peroxide doesn’t pollute doesn’t mean it’s anywhere near safe to handle. Refueling is not an operation you would leave to ordinary airport workers; the guys handling the hoses should probably be wearing heavy suits.

The high-test peroxide can also be used as a monopropellant. It sounds like they’ll do this in their side thrusters.

They have not said what kind of fuel feed or power cycle their engine uses. Pressure-fed? Gas generator? No idea. In any case, their big plane should operate the same way as the little one, but with the capacity to carry an upper stage instead of just a little instrument bay. And it should be highly reusable. The goal is to be able to fly it more than once per day. And the plane itself is a nice simple design: a pointy cylinder with wings and a vertical tail, and just one engine, so it shouldn’t be very expensive to build several of them.

Is anyone else building a first stage spaceplane? There is a Chinese project to put an orbital spaceplane on top of a first stage spaceplane, to make both halves reusable. It’ll be interesting to see what comes of that, if anything.

But more appropriately to this page (and weirdly linked by the coincidental fact that Jared Isaacman’s vanity civilian spacewalk flight is named Polaris Dawn) is that a small German company named Polaris is building an aerospike-powered booster plane named MIRA. They’ve managed one flight of a small-scale demonstrator plane, but it crashed before they could light up its main engine. So as yet, the world’s first true flight under aerospike power is still in the future. And if you’re going to use an aerospike, this is definitely the correct aoplication for it — not on anything that actually goes to orbit.

No, wait — they’re talking up the idea that they’re going to achieve SSTO — single stage to orbit — which would impress people, and also simplify a lot of design challenges, but I would say is not the right answer to how to lift satellites. It depends on pushing the wet-to-dry weight ratio to an extreme, which greatly penalizes the payload capacity it can achieve, and also makes it twice as hard to give it a decent heat shield. Also, it’s specifically bad for an aerospike: the point of that kind of engine is that it adjusts itself for all levels of the atmosphere, but that breaks down once you’re in full vacuum. But it’s early days yet; they can figure all that out after they get a test plane into working condition, and see how it actually performs.

The rocket engine is called AS-1 and burns kerosene and lox. The MIRA test article also has four small jet engines running off of the same kerosene, for the lower altitudes and speeds. For efficient fuel use they will want to push it as fast as possible with the jets before lighting the aerospike. And wait a minute... the self-adjusting quality of an aerospike is needed mainly in the lower altitudes, but it isn’t even used there?

The intended orbital spaceplane is called Aurora (another coincidental collision with Dawn Aerospace) and would have dual aerospike engines in addition to the jets. It would offer the option of in-flight refueling like a military plane, which might help a bit with the payload capacity, but not much. The payload would deploy out a hatch in the back, like a rear-facing torpedo tube in a submarine, so you could stick an upper stage in there. The upper stage would be about 10 tons in size, which is their targeted capacity for suborbital or hypersonic flight. They hope for one ton in SSTO mode... and I guess it does make some sense to pursue that, because though the payload becomes much smaller that way, it also allows the craft to be 100% reusable, decreasing the cost just as much. I doubt that will work, though.

Of course, like everybody, they say that once Aurora is working, they’ll build something a lot bigger.

(No meaningful stats exist yet for either spaceplane, as both companies are still working out small scale test versions.)