NEUTRON — New Zealand / USA

Rocket Lab had excellent success with their little Electron, but the market for launching small satellites turned out to be more limited than it had seemed a decade ago, and founder Peter Beck (who had once pronounced that they had no interest in ever building bigger rockets) saw the huge crowd of new companies trying to build small rockets to compete with it, and figured that eventually one or more strong competitors would emerge from the pack. So for Rocket Lab to grow — and maybe just to survive — he saw that they would have to move up from small rockets and enter the mainstream. Which would mean competing directly against the emergent 363 kilogram gorilla of the launch market, SpaceX.

Nobody in the first world wanted to do this. Nobody else was trying to target SpaceX’s main bread-and-butter customers and compete on cost. New rockets like the Vulcan and the Ariane 6 were looking for smaller volume markets which to SpaceX counted as niche use cases, based on some combination of fairing volume, high orbit capability, and government favoritism. In other markets such as China, it could make sense to try to just copy the Falcon 9 to have it available locally, but that wouldn't work in the USA. The only way to do it would be to come up with a rocket genuinely better than SpaceX’s.

Fortunately, there was an opportunity to do just that, because SpaceX had ceased to improve the Falcon and was putting all its development into the Starship, which was not likely to have very much impact on the market for launching individual sats of moderate size. The Falcon had a lot of older technology in it, and Rocket Lab had strengths in areas that SpaceX had not explored much, such as carbon fiber and 3D printing. So the Rocket Lab engineers were able to come up with a design which took maximum advantage of those strengths, which might well be able to outperform a Falcon in a free market. And in 2021 they made the announcement, and gave the new rocket its name: Neutron. Its target capacity was originally going to be eight tons to low orbit, with reuse of the booster. And despite having no current plans to develop anything like a crew capsule, they would make sure the rocket is human rated.

design

The key idea is to make the upper stage as flimsy and lightweight as possible, by enclosing it in a five meter fairing which is part of the booster and gets reused. (Five meters is a very standard fairing diameter for larger rockets.) Normally, a significant part of the dry weight of a second stage is a sturdy outer wall to support everything stacked above it, but on the Neutron that wall goes back down with the first stage, so the second is basically just bare tanks, hanging suspended from the support platform that the payload rides on. The walls can be thin, supported largely by internal gas pressure. (An existing rocket with a bare second stage somewhat like this is the Astra Rocket 3.) And since the fuel is methane, it will have the specific impulse to send stuff to high orbits, and even do interplanetary missions if they’re small enough — something that SpaceX is not well optimized for.

The main stage is much more robustly constructed. It consists of a sleek and complex shape laid down by a sophisticated robot that paints stripes of carbon fiber weave onto moulds. It has long narrow fins down the sides, and a bit of a taper to its profile. In early versions the fins were wider and doubled as landing legs, giving it a look like something from an old pulp magazine cover, but just as SpaceX had done before, they ended up dropping this idea. Actual legs will have to fold out. The main purpose of the long fins is not for steering during ascent but for gliding a bit during descent, so they’re better called strakes. The booster of the New Glenn has a pair of strakes for the same reason. The Neutron has four, but they soon decided that two would be minimal, mainly just there to hide legs in. Then they decided that big strakes were not necessary and made all four of them minimal.

At the front of the booster, the fairing was originally going to be divided into four leaves, with hinges near the bottom of the payload area, but then they reduced it to two and made them shorter, so the second stage has to go through a bit of a tunnel when departing. Just beind the fairing are four steerable vanes for guidance during descent. These should have less drag than SpaceX’s grid fins, though also less ability to change the rocket’s course aerodynamically. They might not need as much; since SpaceX’s rockets are a lot longer and thinner than the comparatively fat and stubby Neutron design, they might need a much firmer push to keep things straight. Making it short and wide actually saves weight, as there is less surface area per unit volume and therefore less material used in construction, but the tradeoff is a bit more drag during ascent. Most of the width is accounted for by the fairing, which at its base seems to be more than the nominal five meters across.

So yes, the first stage will land vertically, like a Falcon. At first Beck said it would always go back to the launch site — no sea landings because ships are expensive — but later they admitted that this was a mistake and they would use a landing barge, as the payload capacity gets much worse if you have to turn it around to head back to where it started. Their hope is that the carbon fiber at the bottom end is tough enough that it can do its suborbital reentry without needing to do any braking burn first, and since they’ve already done this with the Electron, they ought to know what they’re talking about. This would enable them to reuse the booster while carrying a payload almost 90% of what they could do expendably. (SpaceX tried to do the same thing with their Super Heavy booster, which is made of steel, and found the heat unexpectedly difficult to cope with.) They won’t launch the Neutron from New Zealand, but only from MARS — Mid-Atlantic Regional Spaceport, that is — on Wallops Island, Virginia. (Wallops is a place where rockets were being launched years before anything got started in Florida).

Despite the design which seems sized for larger satellites, and the human rating, Beck says the Neutron will be mainly intended for launching swarms. Their existing customers are still people with small satellites, but some of them want to launch them in batches. This role may evolve. Their goal is to fly it cheaper than a Falcon 9, which is probably doable, but they don’t expect to beat the Falcon’s price per ton. Bigger rockets always win on that metric, but that doesn’t matter unless you have a payload that uses the rocket’s entire capacity.

progress

The Neutron’s methane-burning engines are being newly developed. They originally went for a conventional gas generator cycle, as the electric pumps in the Rutherford don’t scale up to that size nearly as well as turbines do. Beck wanted this engine to be “boring”. But then they switched the approach to a fuel-ruch staged combustion cycle like the Blue Origin BE-4. They also changed the booster’s engine count from seven to nine at this time (in the earliest drafts they had intended to use just four), and bumped the payload capacity to thirteen metric tons, which makes the idea of putting a crew capsule on it more plausible. (It’s still only eight tons if it flies back to the launch pad area.) The engine, now dubbed “Archimedes”, breathed its first fire in mid-2024.

Rocket Lab started bidding the Neutron for government launches, and promising them that it would be ready within the time frame of other competitors, which meant they’d have something flying by the end of 2024. The government took a look at this assertion and didn’t buy it. An internal report accused Rocket Lab of a “campaign to misrepresent their launch readiness in an effort to gain competitive advantage”, and it leaked, as well it should. Beck has said that they are “tracking [the deadline] pretty closely”, meaning that even the maximum possible amount of startup optimism left no room for anything to slip. This plan had them reaching orbit in ten months when the first engine hadn’t even reached the test stand yet.

With engines now blasting away and working through a complete test program, the first flight is still supposed to be about ten months out. They will probably at least have a complete main stage on the test stand in 2025, hopefully by midyear.

Neutron: mass 480 t, diam 7 m, thrust 6600 kN, imp 3.58 km/s, staged combustion (methane), payload 13 t (2.7%) with reuse, cost unknown.