Rockets of Today


It’s an old idea: the “rockoon”. Since rockets lose a lot of energy by fighting their way through the atmosphere, and engine bells which work well at high altitude can’t be used at sea level, use a balloon to lift the rocket up into the stratosphere before it even starts firing. It doesn’t impart some horizontal velocity like an airplane does, but on the other hand, helium balloons can reach a higher altitude than any affordable plane, and of course are also a lot cheaper. The makers of Bloostar, a Spanish company called Zero 2 Infinity (or Z2I or 0II) already have balloons that can lift instrument packages to altitudes of thirty kilometers, where the air density is only a fiftieth of what it is at sea level. At such altitudes, rockets can use large vacuum-optimized bells even on the first stage. And they’re building such a rocket. They tout that this balloon-based approach significantly lowers the environmental impact of a launch. The rocket is tiny — no bigger than the Vector would have been, if you don’t count the balloon, but with (they hope) twice the capacity. And by starting with this concept, they have come up with one of the most unique and original rocket designs ever.

Bloostar has three stages, but it doesn’t look like any other three stage rocket. It’s wider than it is tall! From the side, with the fairing up, it looks a bit like a VW Beetle. The stages are not cylinders stacked end to end, but toroid shapes — the first two stages have hollow centers. The first stage is a ring with six small “Teide 2” engines (which I presume they’ve made in-house) spaced around it. (Teide is the name of a volcano in the Canaries.) They burn liquid methane with lox. They’re fed by pressurized tanks, which keeps them simple and cheap because they don’t need any turbines, but does limit the performance, because the combustion chamber pressure cannot exceed the remaining tank pressure. In fact, they are currently planning to limit the chamber pressure to a measly 10 bar (about the pressure of a skinny bicycle tire). The second stage is a smaller copy of the first, which nestles inside the outer ring. It has six “Teide 1” engines, which are about half the size of the first stage engines, also burning methane. These engines stick out of the hole in the center of the first stage. Finally, the third stage is of a conventional shape, and has a single Teide 1 engine. This topper weighs under half a ton, and is about the size of a wine barrel balanced on a wastebasket.

The fairing is attached to the outer ring of the first stage, and opens like an eyelid, with accordion pleats. They say that since it’s common for satellites to be wider than they are tall, this shape helps satellite makers avoid having to do as much folding and unfolding as they usually need to do.

Why this crazy donut shape? Well, it allows them to run all three sets of engines at the same time. Others have talked about using propellant crossfeed, or “asparagus staging”, but they’ve actually gone and done it. (Or maybe this counts more as “onion staging”.) When the rocket lights up, all 13 engines ignite, but the fuel comes only from the first stage tanks. When it drops off, the second stage tanks are still full. And likewise, the third stage engine burns fuel from the second stage tanks until it drops off. Why bother with all the plumbing and valves required for this trick? I guess the answer is that the Teide 2 engines just don’t have enough thrust, because of their low pressure. But they claim there is enough thrust so that if an engine outage occurs on either the first or second stage, and the engine on the opposite side has to shut down to balance it out, it can still reach orbit.

Both the balloon and the rockets may be reusable, though they’re not counting on it. They’ll put parachutes on the first two stages, and hope to recover them both. One advantage of the fat torus shape is to slow down faster on reentry. The balloon would be set loose at sea, probably from near the Canary Islands (which belong to Spain), so the parts will come down at sea and they can have boats waiting.

Their only test flight that’s been done so far consisted of taking up the second stage with no first stage under it, dropping it, and firing it just long enough to make sure that it could aim itself correctly, then recovering it after it descended on chutes. A long time later, I learned that this test didn’t even use the Teide engines: they just stuck a solid motor on it to simulate them, so the only test was of the guidance stuff. And unfortunately, it seems the company has gone rather quiet since that test. They are now concentrating on their profitable balloon business and apparently putting rocketry plans aside for a while. It’s sounding more and more like this company is long on hype and short on hardware, and realistically, the Bloostar project might already be shelved permanently.

They also plan to offer tourist rides to the stratosphere in a capsule carried by a really big balloon. This craft is simply named “Bloon”. It won’t fly as high as a New Shepard or a SpaceShipTwo, but it can spend hours at high altitude rather than just a few minutes.

(One other small company which is taking the rockoon approach is called Stofiel Aerospace. Brian Stofiel is a home inventor who says he has come up with a formulation that will allow him to 3D-print a rocket motor out of plastic! I find that somewhat difficult to believe.)

There’s another rocket company from Spain — one which started out with a lot less hype but is now looking a lot more credible. They are called PLD Space.

Bloostar: mass 5 t, diam 2.9 m, thrust 90 kN, imp 3.4 km/s, pressure-fed (methane), payload 0.14 t (2.8%), cost unknown.