Rockets of Today

I will briefly list here some capsules which are being used for space station freight, and aren’t intended to carry astronauts:

  • Progress (Прогресс) — Russia, 1978: Basically a Soyuz with all the unnecessary bits stripped out, this had already been supplying Russian space stations for decades before the ISS was put together. Over 150 of these have been launched. Early versions had a heat shield but nowadays that’s omitted, along with the ability to separate the modules. It is capable of returning very small payloads to Earth with a mini-capsule that it ejects. The service module has a pair of solar panel wings. Only the forward module is pressurized; the bell part where the seats would be in a Soyuz is now just a set of extra propellant tanks, which allow it to either refuel the station it’s attached to, or elevate the station’s orbit using its own thrusters. Aside from this it carries no unpressurized cargo. Its capacity is just 2.4 tons.
  • Automated Transfer Vehicle — EU, 2008: This large expendable cargo carrier is on hiatus due to its high cost. I’ve heard some talk of bringing it back, and maybe giving it some reusability, but I doubt there’s any will to do that. It’s a question of whether other nations can get the EU to do more, or whether they can get away with substitute contributions. The ATV (which originally stood for Ariane Transfer Vehicle) was made primarily by Airbus and flown on an Ariane 5. It not only lifted plenty of supplies — it can handle a whopping 7.6 tons — but its engine was also used to boost the space station, counteracting its orbital decay. To do this, it docks to the station’s back end, using a Russian docking port which is incompatible with those on the American end, which most of these other vessels use. The ESA flew several of these as their contribution to keeping the ISS running, with each one named after a historical European associated with space, such as Jules Verne and Johannes Kepler. Now its back end is being repurposed as the service module for Orion, this being one of the substitute contributions they prefer to make in lieu of further flights. But the shuttle OMS engine that’s incorporated into the Orion version was not part of the original ATV design; it just had four tiny nozzles. And they’re still there in the Orion version — in fact, there are now eight of them. I don’t know how they crammed all these engines into there; it’s not like there was a hollow center like in the Starliner service module. It has four skinny solar panel wings, giving it a look reminiscent of a Star Wars X-Wing. The ATV might return in a variant form called ATV-X, which will service not the ISS but the Lunar Orbital Platform-Gateway.
  • H-II Transfer Vehicle, a.k.a. Kōnotori ( / こうのとり) — Japan: 2009: An even larger cylinder (10 meters long) which includes an integrated service module, this flies on an H-IIB. In fact, it’s the whole reason the H-IIB was built — the H-IIA couldn’t lift it. The capacity is about six tons, and it can bring big items since it berths to the large square CBM ports on the international side of the ISS, rather than to a docking hatch. It cannot return cargo to Earth, but they are working on a replacement that can, called the HTV-R, which in turn would be followed up by a crewed capsule. These would be three part designs, with a cone, a large unpressurized trunk section, and a small service module. The cone is intended to have 15 cubic meters of pressurized space. For heavy loads, most bulk cargo would have to go in the trunk. This isn’t as bad as it sounds: despite its monolithic cylindrical shape, a lot of the current HTV is already unpressurized. A large hatch allows the Canadarm to reach inside this part. Solar cells cover the exterior on one side; no wings stick out. Before the HTV-R they will first fly a minor upgrade called the HTV-X, atop an H-III. (“Kōnotori” is a species of stork.)
  • Dragon — USA, 2012: SpaceX’s original freight capsule was basically just a development prototype for their crewed version, the Dragon 2, but it did quite well at making deliveries, and it was fully reusable except for the trunk. Being much simpler than the crewed craft, it weighed barely over four tons dry. They stopped making more of these a couple of years before the Dragon 2 was ready, finishing the craft’s remaining jobs with reused capsules. The trunk is often left mostly empty; when it separates from the second stage, you can look right up into it. This original version made its last flight in 2020. From then on they delivered cargo in seatless Dragon 2 capsules, though these can’t deliver large interior fittings as the docking hatch is quite a bit narrower than the berthing port used by the old Dragon was.
  • Cygnus — USA, 2013: This was from Orbital ATK, and now from Northrop after the acquisition. It can launch on either their Antares or an Atlas, with the latter allowing a heavier load than the old Antares did. With that Antares now retired, they sometimes have to launch on a Falcon, until the new Firefly-built replacement for the Antares is ready. There have been two sizes, a short version which they stopped using years ago, and “enhanced”, with the latter being quite substantial in size with 27 cubic meters of pressurized space — not far off from the interior size of a standard shipping container — but still having only 3.5 tons capacity. The shape is a corrugated cylinder, like a can of beans. Actually, Northrop doesn’t even build the can, only its little service module. The can is built by Thales Alenia Space in Italy. It has no reusability. Each one gets named after a famous astronaut of the past. It has two circular solar panels that unfold like fans. (This has had one minor failure in 2022 when one of the circular solar panels was unable to open.) It berths to the large CBM port. They considered some variations for other roles such as unpressurized cargo, but none have been built yet. This could be entering other roles in the future: one proposal for the Artemis program was that a Cygnus service module would be used for orbital transfer of a lunar lander between the Lunar Orbital Platform-Gateway and low orbit, but this fell through. A Cygnus version to resupply the Gateway may still be forthcoming.
  • Tianzhou (天舟) — China, 2017: This made only one flight before their space station went up in 2021, in which it practiced docking repeatedly with their Tiangong 1 orbital laboratory testbed, and pumped fuel across the connection. The two are variations of the same design. Now the successor Tianzhou 2 model is supplying the new Chinese space station. It has the usual cylindrical cargo area up front, and a service module which is long and narrow, with two large solar panel wings. It can haul 6.5 tons, and is not reusable. It sounds like the partition between pressurized and unpressurized cargo space can be adjusted from one mission to the next.
  • Dragon XL — USA, 2024?: After saying that they would do no more development on the Dragon line of spacecraft, with all future work going into Starship, SpaceX reversed itself and announced that they would build a new cargo capsule for NASA called Dragon XL, to deliver freight to the Lunar Orbital Platform-Gateway. Launched on a Falcon Heavy, it would carry five tons or more of pressurized and unpressurized cargo to the LOP-G, with no return to Earth. As sketched out so far, it’s a big cylinder, with a hatch on the front and a trunk with folding solar panel wings in the back, like the original Dragon and unlike the Dragon 2. It may have no propulsion other than Draco RCS thrusters — we don’t know yet. It will go up inside a regular Falcon fairing, maybe oriented hatch end down. But maybe this won’t be built — NASA may be looking for a way to do this job with Starship instead, or at least is asking SpaceX if that’s what they’d rather try. But Starship may not be safe to attach to the Gateway as it’s so heavy, and may not be capable of staying parked there for months, as is normal practice with any other cargo vessel, due to its use of entirely cryogenic propellants.

Finally I have to mention the X-37B — USA, 2010: this is a small (5 ton) reusable spaceplane owned by the US Air Force. It resembles the Dream Chaser except it’s not nearly as pretty, and is unmanned. Like a miniature space shuttle, this has cargo bay doors on its back. It performs secret missions of long duration, like eight months at the shortest, and not much else is known about it. The Air Force’s official position is that it’s just a testbed for new technology and a platform for zero gravity experiments. It has a single rocket nozzle on the back end, which apparently reacts kerosene with peroxide — a fuel combination which, like hypergolics, can be stored for a long time without refrigeration. On its fourth flight they added an experimental ion engine, for orbital maneuvering on those long flights. SpaceX got to launch the fifth and seventh ones; the other flights were on Atlases. The cargo bay is about 1.2 meters in diameter and just 2.1 meters long, and has deployable solar panels. On recent flights they’ve added an extension to carry more payload, like the Shooting Star on Dream Chaser. The Space Force has two of these spaceplanes but they don’t put them both up at the same time.

Boeing said they were thinking about building an X-37C, which looks very similar but is quite a bit bigger, and would be able to carry passengers in a cargo capsule. But nothing new has been heard since they announced the idea back in 2011.

Meanwhile, China has been working on a military spaceplane which appears to be more or less an imitation of the X-37B. They may be calling it the Shenlong Space Plane (神龙 — usually translated as “divine dragon”, but nowadays you might as well just say “space dragon”). They’ve been working on it for several years, and first sent a small test version to orbit in 2020 (suborbital tests date back to 2011). They’ve also announced that they’re also soon going to build a much bigger plane, possibly called Tengyun, for suborbital flights with passengers. We don’t really have to concern ourselves with that one. So it sounds like it’s a bigger, badder SpaceShipTwo... but they apparently intend to make it a lot more practical, as a means of quick intercontinental transportation.

See the Vega article for a description of the ESA’s experimental Space RIDER.