Rockets of Today

CTS-100 STARLINER— USA, 2022?

This is a traditional conical capsule which looks a lot like an Orion, only smaller and with fewer windows — one big square one and two little round ones, one of which is on the door. It also comes from a ULA partner, but the two have less in common than you’d expect. As hinted by the “liner” name, this comes from Boeing (the part which in a former life was mostly McDonnell Douglas)... but they got it from a smaller aerospace company named Bigelow, who started from a project originally called “Orion Lite” (which got early assistance from Lockheed’s Orion team) and diverged from there. So yeah, they may not have much in common, but originally they were supposed to have. They reached a point where they decided to throw out the Orion heritage and start clean; that was the best way to achieve lite-ness.

(Bigelow is a name we might have heard a lot more from. They were planning and designing the first private, for-profit space station! They have tested a small scale version of it as a module on the ISS. It’s inflatable! And then they wanted to put one in orbit around the moon. Robert Bigelow also runs a hotel chain, and his eventual goal is to own hotels in space. There’s a rumor that he may be a UFO believer. The plan was to lift their station on a Vulcan — ULA would apparently be some sort of partner in the venture. One claimed advantage of the soft inflatable material is that it should be much better at blocking both radiation and micrometeorites than sheet metal is, though the tests of this in the small test version on the space station failed to bear out any claimed benefits on the radiation level. Unfortunately Bigelow laid off its entire workforce during the COVID-19 pandemic. They claim they will rehire them someday, but many are not believing this.)

Unlike the Orion or the Dragon, this has no stated ambitions to go any further from Earth than the space station. It could ride on any appropriately sized launch vehicle, and seat up to seven people in an 11 cubic meter cabin... as far as NASA is concerned, IIS flights would have been limited to four seats, just as with the Dragon 2, but Boeing talked them into adding a fifth seat, which they can sell to an IIS tourist. The size and dry mass and interior volume are roughly similar to those of the Dragon, though the shape is shorter and wider. It’s a bit roomier overall, but the layout gives less subjective feeling of space, at least to my eye.

It has a service module which is also short and wide, with four semi-large rocket nozzles sticking out, solar cells on the back between the nozzles, and heat radiators around the sides. The four nozzles are angled slightly outward — I don’t know why. The service module actually has three different sizes of motors: tiny for reaction control, moderate for orbital maneuvering, and the bigger four for launch escape (which look undersized for the job), all sharing the same fuel supply. The reason the launch escape is divided into four is that the service module is hollow, with a little trunk area under the solar cells. The midsized orbital motors have a lot more muscle than the Dragon’s tiny thrusters, allowing it to quickly make orbit-change maneuvers which in a Dragon take many minutes. All of these minor thrusters are mounted in four rectangular “doghouse” boxes that stick out from the sides of the service module... and they’ve been been the most trouble-prone parts of the spacecraft. Total mass with the service module fuelled is about 13 tons, just a hair more than the Dragon. (I don’t know the dry mass without the service module but I’m guessing around 7 tons.)

They hope the capsule can be reusable for up to 100 flights, whereas the Orion is only trying for ten at the most. For the near term, they’ll launch the Starliner with an Atlas V, then presumably switch to a Vulcan. They use airbags for landing on dirt. Unlike the Orion’s proposed bags, which would have had to wrap awkwardly around the sides, the Starliner’s approach is to jettison the heat shield while suspended by the parachutes, so the airbags can come right out the bottom. I guess replacing the heat shield each time is a pretty good way to make a capsule last for a hundred flights.

Once docked, they could use the maneuvering thrusters to boost the station’s orbit, because the service module and its fuel are going to be discarded anyway. This needs doing on a fairly regular basis, and other service modules, notably the one used on the ATV cargo canister and since given to the Orion, have performed this orbit-raising service in the past. In theory it might be possible for the Dragon to also perform this service, but they have not pursued the option. In fact, I’ve heard a claim that they could not spare the fuel, as its total supply of fuel is apparently quite a bit smaller than that of the Starliner. Boosting the station while docked to the American end would first require using its gyros to turn the whole station over so it’s facing backwards. The station also has its own orbit-raising motors in the Russian section, so the job could be done by simply delivering fuel for them instead of by actively pushing the station, but these are disused and possibly no longer functional, so nowadays they always use an attached craft. If nothing better is available they’ll use the tiny reaction-control thrusters on a Progress capsule, though this is inefficient and tedious. All it all, it needs about four tons a year of propellant to keep the station from falling down, which is about one percent of its total mass. It used to need seven, due to being in a lower orbit so the Shuttle could dock with it. If they ever replace the Soyuz maybe it could go higher, but the current plan is to retire the ISS, because it may be increasingly unsafe as parts wear out.

For years we were in suspense waiting to see which would carry passengers first, the Starliner or the Dragon 2. Originally the Dragon was scheduled much earlier, but SpaceX’s scheduled dates were, as always, more expressions of hope than of confidence. At the beginning of 2019, the two looked to be roughly neck and neck... then Dragon was the first to pull off an unmanned flight to the space station, and shortly after, rumors started to emerge of further delays for the Starliner, so it might not be ready for crewed flight before the end of the year. But then a static test of the SuperDraco motors on the used Dragon capsule caused an explosion that destroyed the entire craft. So at this point it looked like the odds favored the Starliner being the first to carry astronauts. But it had its own delays, and some of them were also due to difficulty with the launch escape system, which like that of the Dragon uses hypergolic fuel, because the people who run the Space Station don’t approve of docking solid rockets to it. They are not safe in an environment which is being alternately baked and frozen sixteen times a day. Apparently Boeing’s escape rockets have suffered from fuel leaks.

After resolving the escape rocket issues, their launch abort test had a chute that didn’t open, and an excessive release of hypergolic fuel, which is too toxic to tolerate leaks of. And then, once they finally launched it to orbit uncrewed, to catch up to where the Dragon got to the previous spring, it went off course and didn’t reach the space station, due to a software error in the service module that threw off its clock and caused it to waste fuel. Then they spotted another software issue in the nick of time, which without a quick patch, would have made it unsafe to detatch the service module for reentry.  Upon later scrutiny it also came out that a few of the reaction control thrusters had not worked right, again due to software, which apparently had an incorrect map of which thruster was which. NASA found that the whole QA process at Boeing was substandard — an issue that also played a part in the 737 Max scandal, as the entire company had undergone a shift toward trying to cut too many corners. For a while the possibility stayed open that once debugging was completed, the next flight attempt would be crewed, but eventually Boeing decided to redo the test launch at their own expense, which pushed the crewed flight out to 2021. By the time all this was settled, the Dragon had flown two test pilots to the station and back without incident, and before that second test flight went up, Dragon launched two full crews of four.

And then, when the second test launch rolled out to the pad, they had to scrub because sensors reported an incorrectly set valve. They tried to quickly resolve this, but it turned out to be not one wrong valve, but thirteen of them. They had to roll the whole rocket back to the assembly building and unstack it. They then spent days coaxing one valve after another back into operation, using “mechanical, electrical, and thermal techniques”, which does ’t sound reassuring for how reliable the unjammed valves would be in the future. Finally they had to ship the whole capsule back to the factory. They fussed over the service module for weeks and in the end junked it entirely, mating a new one to the capsule in order to retry the flight. This finally went up in the spring of 2022... and had two more maneuvering thrusters quit working during orbital insertion, and apparently two little reaction jets also took some time off (though they became usable again later) before it finally approached the ISS... at which time they had trouble with a balky docking ring. There was also some issue with the cooling system for the cabin. At least the landing went smoothly, though an unconfirmed story says another reaction jet failed during reentry, this time one on the capsule itself rather than on the service module.

From the bad escape-motor test to the glitch on the nominally successful docking flight, the thing that has repeatedly given them trouble has been the valves that send hypergolic propellant to the motors. When they tore open the bad service module, they found corrosion in them. A trace of leakage, combined with Florida humidity, ended up producing nitric acid, among other nasty byproducts. Boeing pointed the finger at the valve builder, Aerojet-Rocketdyne, who pointed back at Boeing’s design. Apparently neither had thought to test the valves in humid conditions. This specific issue did not recur in flight, but it’s clearly not the only way the hypergolic propellant flow is failing to start and stop reliably.

Trouble with hypergolic leakage is historically not rare, and a cargo Dragon recently also had an issue where some toxic smells escaped and set off alarms. But the frequency and severity of issues on the Starliner service module definitely stands out.

At this point, the Starliner is looking like a clusterfuck. Sure, 99% of it is fine, but in aerospace being 99% right gets people killed. If they don’t redo these propellant valves, that service module will continue to be a danger to anyone who rides it, and to any station it docks to. SpaceX once had a valve problem like this on their escape motors, and it blew up the whole capsule during a test firing. They fixed it with burst discs, which positively stop all leakage. But that fix probably isn’t applicable to maneuvering thrusters, only to escape rockets that normally go unused.

In the end, NASA bought additional flights from SpaceX to carry most of the astronauts that were supposed to go up on Starliners. They aren’t giving up on Boeing entirely, but they clearly have decided not to count on them either. They may also be reopening opportunities for other spacecraft projects such as Dream Chaser to bid on making crewed flights.