Rockets of Today

ARIANE — EU, 1979

This is the signature rocket of the European Space Agency. Though developed by an intergovernmental initiative, it was the first orbital rocket system to be operated for commercial profit (though with substantial governmental support), by Arianespace SA in France, which for a while also sold some Soyuz launches. The first Ariane flew in 1979. Versions 1 through 4 were based on France’s Diamant rocket, after Britain withdrew its Blue Streak booster. It was the first rocket whose design was primarily guided by the mission of launching commercial satellites, particularly geostationary ones, in direct competition with the Space Shuttle. The Arianes pioneered the technique of launching more than one satellite per flight — even Ariane 1 could do two geostationary satellites per flight if they were small enough. The Ariane 4 had a long run: 116 launches with just three failures.

The current Ariane 5 is an all-new design, dropping much of the legacy of models 1–4. It’s bigger than a Proton, though not as big as a Long March 5. Like the space shuttle, the “Vulcain 2” main engine is hydrogen fueled, and it is always launched with a pair of very large solid-fuel boosters on the sides. (The old Arianes used hypergolic fuel.) The Vulcain’s thrust is low: less than a tenth what the pair of solid boosters puts out. The boosters use aluminum bound in HTPB and have steerable nozzles. They’re built in three segments and use a steel casing.

The second stages originally used hypergolic fuel (monomethylhydrazine), but lately they’ve come up with a much bigger one that burns hydrogen, called ESC-A (Etage Supérieur Cryotechnique de type A), or just ECA for short. It was first used on Ariane 4. So far they only use this for single payloads to GTO, as its engine is not restartable, so they also modernized the hypergolic stage for low-orbit work. This version is called ES. The majority of launches now use ECA, as the Ariane in general tends to specialize in geosynchronous launches. These toppers are basically kick stages, as the hydrogen core can reach orbit on its own with typical payloads (though of course they drop it just short of that for safe disposal). As with the shuttle, the hydrogen engine stays lit all the way up — in rocketry jargon, this is called a “sustainer engine”.

The Ariane 5 is rated for human flight, but has never been used for this purpose. The cancelled Hermes spaceplane was supposed to be launched with it, and that was one of the main reasons for the 5 being developed in the first place. With no Hermes, the 5 was somewhat oversized. The 5’s success rate started out rough, but they’ve been nearly spotless since 2002 — the worst “failure” being a guidance error made on the ground which resulted in a slightly wrong orbit.

Arianes do not launch from Europe. The spaceport they use is in French Guiana, near the equator, on land that used to be part of the notorious prison colony there. The big solid boosters are manufactured right there at the launch center. This equatorial launch site gives them an advantage with equatorial and geostationary orbits that helps mitigate the otherwise high cost (which is driven in part by intra-European politics, which require that all the contributing countries get a piece of the budgetary pie even if the alternative would save money). Because of the rocket’s large size, geostationary launches routinely carry two satellites, which also helps with costs. That’s its main business, in fact.

Ariane 6

Ariane 6 is in development, and aims to be much more competitive in cost per payload ton. They announced plans for it to have a main engine section that can detach itself from its tanks and land on a runway with little wings, thus recovering the majority of the money spent on the first stage. It would have little propellers and wheels tucked away inside it. This idea is known as “Project ADELINE” (a tortured acronym not worth spelling out). But then they said that the Adeline recovery trick will have to wait for Ariane 7... and after Ariane 6 was delayed several years, that gave them time to rethink ADELINE and change their minds. Now they want to go with vertically landing the whole thing for more complete reuse, like SpaceX does with the Falcon 9.

Ariane 6 should still be substantially cheaper than Ariane 5, though... or at least that was the intent. For starters, it’s smaller — particularly the solid boosters, which will have the option of being used as a pair or a quad, so as to match the 5’s capacity. These shorter side boosters are a variant of the “P120” first stage of the Vega C, and burn HTPB and aluminum in a single piece carbon fiber case 25 centimeters thick. The nozzle is an update of the one from the old booster, and and it’s assembled and filled at the same facility in Guiana. They plan to soon upgrade these to a “P120C+” version for a bit more payload capacity.

The Ariane 6 will use an ESC-B upper stage, updated with a new “Vinci” engine which is restartable up to five times. It burns hydrogen in an expander cycle (the first European engine to use that cycle), and has a telescoping bell extension. It supposedly has substantially more thrust than the classic American RL10 expander, without being any heavier or any less efficient. They also want to make the second stage out of carbon fiber.

Unfortunately, they made the same mistake with the Ariane 6 that NASA made with the shuttle: they scheduled the end of life for the old rocket before the new one was ready. Ariane 6 was originally supposed to fly around 2020, but when delays slid that to 2023, they found themselves with a gap, as the final Ariane 5 was in July. The 6 was still in the phase of testing separate parts and modules, and even those tests were hitting repeated delays. It became clear they eould not launch until the next spring... and the Vega C was also grounded at the time. And at the same time, they were forced to admit that the hoped-for cost savings were not happening, and the 6 eould not save very much compared to the 5. The Ariane 6 program had pretty much become a fiasco, exemplifying numerous ways that a bureaucratic noncompetitive aerospace program can fail when it isn’t getting a full level of enthusiastic support.

In November they decided that the ESA could not continue the old model of having rockets built to government specifications, which wasn’t going to bring down launch costs to anywhere near acompetitive level for many years. It was time to embrace commercial launch services. But they also got some agreements to reinvest in fully modernizing Ariane, in line with a plan known as Ariane Next. This would be based on a reusable methane-burning engine, which would be used in clusters on both the core and the side boosters. The core diameter and fittings would stay consistent, so the boosters can be replaced before the core or after — whichever works out easier. Both would have the same style of landing legs we’re familiar with from the Falcon: four triangular flaps that fold out hydraulically.

Above this new core they could put a lightweight second stage made of carbon fiber, which would be expendable. I don’t know what engine it would use. But they might also have a reusable top stage, which could sit on top of the small second stage rather than directly on the core, if any extra oompf is needed:


In parallel with ADELINE, they were also studying a plan to add reusability at the other end, by replacing the fairing with a craft capable of reentry — something that might even carry people. It is provisionally called SUSIE — Smart Upper Stage for Innovative Exploration. It would not require any change to the rocket under it, at least for uncrewed use.

SUSIE’s preliminary design is a lifting body with heat shield tiles, kind of squarish in cross section. This approach resembles the small “Space RIDER” experimental craft that they are now working on. That will launch on a Vega and land on a runway under a parafoil chute, but it sounds like for SUSIE they are thinking about propulsive vertical landing. Both steer in the atmosphere with air-brake flaps at the rear. Space RIDER has only a rather minimal cargo hatch, but the interior of SUSIE would be quite roomy — they say forty cubic meters, which would put it at a nice middle point between a normal sized crew capsule and a giant Starship. The thing would end up functioning a lot like Starship, except probably without much in the way of orbital refueling. I have not yet seen any details about what kind of propulsion SUSIE would have. Doesn’t sound like it’s going to have much delta-V once in orbit.

Themis, Callisto, and Maïa

For the rockets after Ariane 6, the new reusable first-stage engine is going to be called “Prometheus”. It will be cheaply 3D-printed, and burn methane. One early project using this will be a test booster to try to fly back and land vertically like SpaceX does. This experimental hopper will be called “Themis”. This will persumably happen some time after they do some initial flyback experimenting with a much smaller “Callisto” hopper which they announced earlier. This baby hopper will let them make their first efforts at flyback landing more inexpensively, without waiting for the Prometheus engine.

In 2021 the government of France, frustrated by ESA’s slowness and the budget cuts it was getting at the time, decided to move more aggressively toward a reusable commercial launcher. Their plan is to put a single Prometheus engine at the bottom of a small reusable booster called Maïa, and have it ready to fly by 2026 — maybe even 2025. It would have a half ton payload capacity with reuse, one ton without. It’s being built by a startup called MaiaSpace, but ArianeGroup, and hence the ESA, is their main financial backer. This might well be ready earlier than any Prometheized Ariane is, and alongside various commercial outfits such as Rocket Factory Augsburg, allow Europe to develop a decent selection of launch options without depending on ArianeSpace.

Ariane 5 ECA: mass 780 t, diam 5.4 m (width 11.5 m), thrust 13000 kN, imp 4.2 km/s (core), gas generator (hydrogen) and solid fuel, payload 19.3 t (2.5%), cost $7M/t, record 113/0/4 for “5” (final — 137/0/7 for 1-4).
Stage name EAP-E EPC H173 EPS L10 * ESC-A
Role (pos) count booster (S) ×2 core (1) upper (2) upper (2)
Diameter (m)   3.06   5.40   5.40   5.40
Liftoff mass (t) 273    185    11.2 19.4
Empty mass (t) 33   14.7  1.2  4.5
Fuel mass (t) ~72    ~22    ~3.4 ~2.4
Oxidizer mass (t) ~169     ~151     ~6.6 ~12.2 
Fuel type HTPB+aluminum hydrogen MMH hydrogen
Engine EAP P241 Safran
Vulcain 2
Aestus Snecma
Power cycle solid gas gen pressure-fed gas gen
Chamber pres. (bar) 100    11   37  
Ox./fuel ratio   2.3?   6.70   1.90   5.00
Thrust, vac max (kN) 6470     1350     27   67  
Thrust, SL initial (kN) 5975     960   
Spec. imp, vac (km/s)   2.70   4.24   3.18   4.38
Total imp, vac (t·km/s) 1312     737    31.3 63.5