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 now they’re saying that the Adeline recovery trick will have to wait for Ariane 7.

Ariane 6 should still be substantially cheaper than Ariane 5, though... or at least that was the intent, though they’re now admitting it’s unlikely that the costs will work out the way they’d hoped. 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 are HTPB and aluminum in a single piece, encased in carbon fiber 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 eith 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. 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 programs to develop a more advanced and inexpensive generation of hardware hadn’t been forgotten. Besides the complicated scheme for recovering the booster engine 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. It would not require any change to the rocket under it, at least for uncrewed use, and would remain compatible with Ariane 7, and with a future large reusable rocket they hope to build.

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 some kind of 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.

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. And in parallel with the development of the ADELINE trick, another project will (if they get the funding) be building a test booster to try to fly back and land vertically like the Falcon 9 does. This experimental hopper will be called “Themis”, and will also use the Prometheus engine. 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.

Or that was the ESA plan, anyway. In 2021, the government of France, frustrated by ESA budget cuts and slowness, 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.

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