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. The makers of Bloostar, a Spanish company called Zero 2 Infinity (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 quite small — no bigger than the Vector would have been, if you don’t count the balloon, but with (they hope) twice the capacity.

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. It 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.

There’s another Spanish company in the game now too, called PLD Space. They are working on a single stage suborbital rocket which was to be called Arion 1 but has now been renamed as Miura 1, to be followed by an Arion 2 Miura 5 version a few years later. They’ve got a kerosene/lox engine more or less working, they say. It was called “Neton 1”, then “Teprel-1B”, but now it’s called “Teprel-B”. The Miura 5 will graduate to a “Teprel C”, and add one (or optionally two) more stages, with five engines at the bottom, to create a rather conventional small-satellite lifter roughly the size of the Electron. (The Miura 1 is much smaller — just 2.5 tons.) The B engine is pressure-fed but they plan to go gas-generator for the C. So far they have only gotten the B into operational condition on the test stand.

The launch pad is to be built in the Canaries. They also hope to recover the booster by parachute, and this is something they hope to perfect with the initial Miura 1 suborbital rocket. They are telling customers that they will retrieve and return their suborbital payload. (They also claim they will work on propulsive landing in the future.) This venture is getting some support from the European Space Agency, as well as backing from private investors. The first orbit might come around 2022 under ideal circumstances. The Miura 5 will get its own section at some point, if it moves forward as hoped and develops more definite specs. All I know so far is that their planned payload capacity is between 300 and 500 kilograms. So far they have done drop tests for the splashdown and recovery, but have not shown a working booster, or even its engine. Once again, the company seems to be going rather quiet.

There are a lot of companies entering the competition to launch small satellites cheaply, but few of them are counting on reusability, which is the one thing that would allow them to separate from the pack and avoid the coming shakeout as the less successful companies fail. This simple addition of parachutes by Bloostar and Miura is the nearest we’ve seen to a reuse plan from most of these startups, at least before 2021 or so. Zero 2 Infinity also say that one reason they’re using methane instead of kerosene is that the absence of soot would make it easier to clean up and reuse a stage, should they manage to recover it.

(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!)

The one company that was really working on a highly reusable small launcher was not any disruptive new startup, but Boeing, with the Phantom Express spaceplane they were building for the Pentagon. Unfortunately, they abandoned the project.

ULA plans to recover Vulcan engines by snagging the parachute out of the air with a helicopter. It occurs to me that when the rocket is small enough, the same technique could work for the entire booster. That simple approach, involving no new technology, could be what lets someone disrupt the small launch market in the same way that SpaceX disrupted the large one. It could finally bring prices down to a level well below those of solid-fuel missiles. But it wouldn’t produce any semi-monopolies, as the barriers are much lower than with propulsive landings. If the technique works, it could be applied to other little rockets — and indeed, Rocket Lab now says they will try it with their Electron.

PLD Space is going for an even cruder approach with the Miura boosters: they plan to let them hit the ocean, and just add reinforcement and waterproofing so they can survive the splashdown. The chute would be on the back end so the nozzles don’t absorb the impact. That’s a better plan for reusability than most of their competition has, but there’s room for improvement where some other company could have lower reuse costs.

Speaking of people who speak Spanish, the government of Argentina is also working on a kerosene-burning launcher, with a three engine booster and a hypergolic second stage. They call it Tronador (Thunderer) II. This is larger, like 67 tons, though still with only a half ton target capacity — a less ambitious figure than many solid rockets in that size range.

They hope to do better than Brazil, which after decades of effort (with some Ukrainian help) built a big solid-fueled satellite launcher called VLS, but never managed to reach space with it. They suspended the program after the rocket blew up in 2003, killing 21 workers and destroying their launch complex... but recently they said they plan to resume the effort, and also work on a smaller rocket called VLM. The VLS had four solid rockets as the first stage while the VLM will use just one. The project is controversial because it involves pushing a large group of poor rural people off their land — not a great look for a dictatorship already in trouble for utterly failing to manage covid. But now maybe they’re backing down and just hiring Virgin Orbit.

Another hopeful country, which doesn’t fit anywhere else, is Turkey. Their UFS national program is developing a liquid-fueled engine for a small launcher with side boosters, known during development as Mikro Uydu Firlatma Sistemi... or maybe for its successor. They’ve previously built a solid-fueled sounding rocket.

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.

(no specifics yet for Miura 5)