ERIS — Australia

Australia has never had its own space program before, but its abundance of sparsely populated deserts and coastlines has attracted a number of hopeful visitors to try to base their launch attempts there. Several different spaceports are now under construction — or at least under promotion — on the northern and southern coasts, with various interested parties at home and abroad hoping they can have their rockets ready enough to try their luck at one of them. And the inland spaceport of Woomera has in fact launched a satellite, when Britain’s Black Arrow rocket managed a successful launch on its final attempt in 1971, as the UK government was in the middle of shutting the program down.

With that legacy in the history books, and so much hype and venture capital in the air in the 2010s, of course there are native Aussie startup companies with their own rocket designs to enter into the international market... and one of them is now ready to try an orbital shot. It was founded by brothers Adam and James Gilmour, so it’s called Gilmour Space. They’ve done some messing about with suborbital tests, and have now built a three stager that’s nearly ready to light up. They call it Eris, after the minor Greek goddess of disorder and disagreement who is mythically blamed for starting the Trojan War. This name seems very inauspicious in a business where any chance of success depends on being very damn orderly, but there are people who think Eris is a cool name because back in the Space Race era, a couple of hippies created an amusingly bizarre parody religion around the goddess, which was then popularized by some mindbending novels known as the Illuminatus! Trilogy, and then was a key influence in the founding of the one true mind control cult, the Church of the SubGenius. Praise “Bob”!

So this sounds pretty cool but then when we look at the actual rocket, the disappointment sets in. Because it’s based on a “hybrid” motor — a setup in which the oxidizer is gaseous but the fuel is solid. And I’m sorry, but I’m pretty convinced that this approach sucks. It’s a design which is favored by those whose engineering skills are not up to building a real rocket engine, and whose chemical knowhow is insufficient for formulating a good solid fuel mix. It is not going to perform as well as either a good solid rocket or a decent hypergolic liquid one, let alone a proper cryogenic rocket engine like the ones produced by the leading rocket builders. If you’re trying your very first starter back yard rocket engine, this is a good place to begin. It’s how the Mythbusters tried to make their own rockets, and why so few of them worked. No hybrid tocket has ever gotten anywhere near orbit.

Typical hybrid engines use something like compressed nitrous oxide as the gas, and some form of plastic or rubber as the fuel. Nitrous oxide liquifies easily when compressed, so volume isn’t a problem, and nothing needs to be chilled to difficult temperatures. Hydrogen peroxide can also be used.&ensp:It’s possible to use actual liquid oxygen in a hybrid, but people who can handle liquid oxygen will generally want to feed it to a proper liquid-fueled emgine. In theory it is possible for a hybrid engine to outperform a solid one, but achieving this in practice seems unlikely. You’re always going to be struggling with non-optimal mix ratios and uneven fuel consumption, losing some unburned ocidizer, and with most designs, paying the costs of a pressure-fed system, where the walls all have to be thick and heavy, and you need either an excess of propellant or a separate tank of helium to push all of it into the combustion chamber.

The Sirius motor that Gilmour has developed uses peroxide. This does help with one problem with other hybrid oxidizers, which is difficulty with getting it ignited. With peroxide it can be self-igniting, and therefore restartable. But peroxide is heavy, which reduces performance. Because peroxide is a liquid, Gilmour went with an electric pump instead of helium to push the juice into the combustion chamber, so they don’t need heavy walls in the liquid part of the motor, only the solid part. Their solid fuel is some secret family recipe, but I would bet it’s probably based on the same sorts of polymers that are common in solid fuel, such as hydroxyl-terminated polybutadiene (HTPB) — a type of urethane. The Sirius is probably the most advanced hybrid engine yet built... as it would have to be, to stand any chance.

The first stage of the initial “block 1” Eris rocket has four Sirius motors according to most sources, but some probably outdated material says it only has three. The second stage uses one Sirius, which presumably has shorter and wider chambers, and a large bell for use in vacuum. The second stage is one and a half meters in dameter, which is half a meter less than the first. A small liquid-fueled kick stage sits on top and is apparently mandatory. The fairing is also 1.5 meters wide, giving it more room than that of an Electron. This comparison matters because Eris is targeting the same 300 kilogram payload. But when their block 2 update targets a full ton in a couple of years, they may want something roomier. I don’t know to what degree the block 2 will be bigger or heavier than block 1. After that they want to make an Eris Heavy with three main stages and target a capacity of four tons.

They have their own little spaceport in Queensland named after the nearby town of Bowen, and it’s a lot closer to the equator than Cape Canaveral is.

They’re trying to launch by the end of 2024. If they make it, they’ll beat all the European startups like RFA and PLD and Skyrora and Isar.

Eris: mass 35 t, diam 2.0 m, thrust 460 kn, imp unknown, hybrid (peroxide and proprietary solid mix), payload 0.3 t (1.0 t in next revision), cost unknown.