Rockets of Today

VULCAN — USA, 2024

The United Launch Alliance, having been caught somewhat flat-footed by the new competitiveness in the launch market, and aware of tensions with Russia which they knew might halt the supply of Atlas V motors, has been putting together a modern rocket to replace Atlas: the Vulcan. Uncle Sam contributed to the development effort. The intent is to cut the Atlas’s launch cost in half, and also to launch a lot more frequently, on a more mass-production basis. It also needs to replace the discontinued Delta IV, which was too expensive to make, except for the few who were willing to cough up for the Delta IV Heavy, which by the time the Vulcan project was half done, was the only Delta model they still offered. Once the Vulcan is given a full complement of strap-on boosters, it should pretty well match the capacity of the Delta IV Heavy.

ULA partnered with Blue Origin (see the New Glenn article) to use their BE-4 staged combustion methane engine, which may soon be ready for full production... or maybe not — though ULA was supposed to get the first engines, ahead of Blue Origin’s own rocket, they were so delayed that they ended up holding up the whole Vulcan program. In 2021 a government report found that issues with the engine may be threatening the readiness of the Vulcan, and therefore risking noncompliance with the federal mandate to stop using Russian engines for national security launches by 2022. And 2022 did indeed come and go with no Vulcan, as they did not receive the engines until late October.

They called the BE-4 engine a codevelopment effort, but I have not heard of any engineering contribution coming from the ULA side. Aerojet Rocketdyne was lobbying to have their proposed AR1 engine used instead (and yes, “lobbying” meant they were getting members of Congress to try to put a thumb on the scale in the selection process), but their experience with expensive engines such as those in the Space Shuttle has apparently left them ill-prepared to compete on cost per flight, so they didn’t have a suitable motor anywhere near as ready as the BE-4 appeared to be... the Air Force has paid Aerojet-Rocketdyne around a quarter billion to develop one, and after years of pressure to stop American companies buying from Energomash, their AR1 replacement still had yet to be test fired. It was to be a fairly direct replacement for the RD-180, being a high performance staged combustion kerosene burner, but it would be two separate engines instead of a single unit with two nozzles. But in the fall of 2018 ULA finalized their choice to use two BE-4 engines instead. Either one would give it a capacity upgrade over the Atlas, but the BE-4 has the edge in thrust, as well as having better specific impulse thanks to using methane as the fuel.

The rest of the Vulcan is apparently a mishmash of existing Atlas and Delta parts, some of which are to be updated later. They are planning to use up to six solid boosters around the base to augment lift when needed. These boosters are designated as “GEM 63XL”, and they are lengthened versions of the GEM-63 boosters which Atlas switched to a few years prior to the Vulcan’s debut. But the thing with solid motors is that the fuel cylinder is hollow, which means that the burning surface area is proportional to length, which means that a stretched booster doesn’t burn any longer than the short version, but instead increases its power output. And on top of that, Northrop Grumman (who make the GEM series) actually shortened the burn time of the XL from 94 seconds to 84, which compined with the 10% length increase means it now has over 2000 kilonewtons of thrust — a 22% increase over the Atlas booster. The peak thrust is over 2200 kilonewtons, which is nearly a match for one of the BE-4 core engines. Without side-pipes the Vulcan actually has to underfill its fuel tanks a bit, but adding one pair gives it plenty of grunt, and using three pairs makes it able to hoist some truly hefty payloads.

Though positioned primarily as a replacement for Atlas, which is much more heavily used than Delta is, the Delta IV tooling is apparently what gets repurposed to make the Vulcan’s core stage, which is slightly bigger around than the Delta’s five meter diameter. Cost savings relative to the Delta should be huge, they say, though I wonder about that because the Vulcan tanks are made with the same “isogrid” technique as the Delta IV tanks were — a process in which thin tank walls are machined out of thick slabs of aluminum, so that internal ribs are part of a single piece with no welds. That does not sound cheap.

Is it going to be rated for human passengers? Yes. Is it going to be reusable? A little bit. The plan is that the engine section would detach itself from the first stage, reenter with an inflatable heat shield, and descend on parachutes. As with the ADELINE plan from Arianespace, the idea is for everything expensive to go into that bottom piece. The original idea was that it would then be snatched up by helicopters before it hits the ocean, but later they dropped that and decided to just have the engines splash down and bob around on the surface. If successful, this would be relatively inexpensive to build — a lot less complicated than ADELINE, and more fuel-efficient than landing the entire booster, though the recovery operation would certainly have some expense, and losing the rest of the booster would allow it to save at most about two thirds of the cost of the first stage. Two thirds isn’t bad, but on the other hand, they aren’t going to put this capability into the first Vulcan version. And that heat shield is going to have its work cut out for it, as the Vulcan booster, like that of the Atlas before it, will get to unusually high speeds and altitudes before cutting the second stage loose. The reentry would take place many times further out to sea than those from a Falcon 9 or anything that copies it. ULA dubbed this detachable engine plan as SMART Reuse, for Sensible Modular Autonomous Return Technology (the S being completely gratuitous).

Centaur V

The whole program was originally designed to evolve incrementally away from the Atlas one step at a time; using the BE-4 engines and methane tanks is one big step, but lots of smaller ones would come later, such as replacing the Centaur second stage, as the old one was undersized for it. They wanted the new one to be able to remain fueled and active for weeks rather than hours after it reaches orbit. The working name for the new one was ACES, and it wasn’t scheduled to fly until a few years after the first Vulcans. It would have a modular design so it could be made in various lengths, with one, two, or four engines. The motor they use would, at least for a while, be some version of the venerable Aerojet Rocketdyne RL10 hydrogen-burner, like they’ve been using all along for their Atlas and Delta second stages, but they considered switching to the Blue Origin BE-3U (which has quite a bit more thrust than the RL10).

But the ACES plan was shelved. With the BE-4 engine delayed, they managed to fix up the old Centaur enough so that it could be the permanent second stage for the Vulcan. They widened it to 5.4 meters, got an improved version of the RL10-C engine, and gave it two of them. The new upper stage will now be called Centaur V, and though it will use some ACES ideas to increase its endurance and reusability, it is not a full redesign. They still say it might eventually be able to do missions with 500 times the duration that the old Centaur could handle, but for early versions the increase in endurance will be modest. (They may also design a third stage, for cases where you need to send a big load to a far destination.)

One odd feature of the ACES was that it would meet its needs for electric power not with solar panels or fuel cells, but with a six cylinder internal combustion engine which burns the vapors from the hydrogen and oxygen tanks. (A piston engine has never gone into space before. I would think a fuel cell made more sense.) The engine’s heat would be used for keeping the fuel pressurized. It’s part of a system which is designed to eliminate many of the secondary fluids and energy sources which other rockets have to lug around with them to make all the little parts work — for instance, the old Centaur had separate hydrazine tanks for steering thrusters, whereas the new one will use small hydrogen burners. This piston engine idea is not used in the Centaur V... yet. It might come back when they tackle the problem of refrigerating the hydrogen for those long missions.

With a hypothetical bigger upper stage and six side boosters, they think a Vulcan could hoist up to 36 tons — enough to compete very directly with the Falcon Heavy and the New Glenn — but with Centaur V the limit would be 27 tons. There’s been some loose talk of them making a triple-booster Vulcan Heavy, but no such plan will be pursued for some years yet. If they do build one, it would be a lot more capable than the Falcon Heavy. Even the single-stick Vulcan should be fairly competitive with the Falcon Heavy in both capacity and cost, especially for cislunar and interplanetary missions, where hydrogen upper stages outperform kerosene ones... unless SpaceX cuts their prices, which they probably could. And the Vulcan would from the start offer a larger fairing capacity than the Falcon Heavy, with even bigger fairings coming along — they’re planning to go wider than five meters.

space trucks

They’re also tackling reusability from another angle. For missions beyond low or geosynchronous orbit, rockets usually need a third stage added, but they envision avoiding this by making a future Centaur V reusable, which would give them something they call a “space truck”. A few of them could be parked in low orbit, and the launch vehicle would rendezvous with one, fuel it, hand over the payload, and tell the truck where to take it. After completing the job, the truck could return to its parking place. This would not only save building expendable third stages, it would save the weight of lifting it along with large payloads; you’d only need to lift the fuel. But the fuel is the heaviest part (or to be more exact, the lox is), and this system would be of little use in cases where a lower orbit is the final destination of the payload, as it quite often is... and orbital transfer just isn’t the costly part of the average mission. So this plan might not have much impact for most commercial work, though for lunar or interplanetary missions, this sort of refueling might yield extra delta-V. On the other hand, if you want to bring the truck back to low orbit, that increases the fuel requirement again, so its weight may be no better than sending up an expendable stage. In the near term, a reusable truck doesn’t sound very helpful to me... an orbiting fuel depot to top up expendable stages seems like it would be more broadly useful.

It sounds like the real point of the Space Truck is that they are making a long term bet on the possibility that someday they will have a facility for making hydrolox fuel away from Earth, such as at the lunar south pole. ULA has called for the government to work toward this goal, which if achieved would give Centaurs the ability to go anywhere.

The Russians, on the other hand, are hoping to build an orbital truck with nuclear-powered ion engines. They’ve had plans for this on paper for about a decade. It would be covered on the sides with big hinged radiators to disperse about three megawatts of heat. They call it the Transport and Energy Module, or the Nucleon. This would move slowly because it would only have about 18 newtons of thrust, but it would cut the mass of needed propellant down to a tiny amount, like no heavier than the payload. This thing could, like, make repeated trips to Mars orbit and back, or explore asteroids. And they want to build a substantial fleet of them.

getting it operational

Unless the government gets more heavily behind this, I don’t know if ULA will even hold together... they’ve laid off many workers, though apparently they are still turning a profit. And in May 2018, their machinists’ union went on strike against them. Even if they succeed with this project, a 50% price drop may not save them. Some governmental launch customers, such as the Air Force, have requirements that there be two American providers for any rocket they need, so they might prop up ULA for a while (as they are currently propping up the Delta 4 Heavy though ULA would rather drop it)... but if one of the other startups qualifies, ULA might eventually be out in the cold. But on the other hand, it may turn out that none of the upstarts is capable of building something as good as the Vulcan, and its prices may be reasonable for its quality level. This rocket might end up a real winner. Their Atlas V has been the safest and most dependable rocket ever built, and if they can continue that record with the Vulcan, it may not matter much that SpaceX underprices them. And Blue Origin’s New Glenn may not be any cheaper, nor ready anywhere near as soon at the rate they’ve been going.

I will say this about ULA: after the nonstop barrage of specious timelines and self-promotional bluster from all the wannabe disruptors in the New Space crowd, it’s downright refreshing to hear innovative plans coming from authentic old-school aerospace experts who don’t bullshit you.

Unfortunately, their ability to complete these innovations on a predicted schedule is just as prone to go wrong as anyone else’s. Once they finally got the first pair of BE-4 engines in the fall of ’22, and finished the first Vulcan in the winter, a series of niggles delayed the initial launch from spring into summer...and then a Centaur V upper stage got blown up on a test stand. At first the news didn’t seem bad, as the issue was just that something had leaked hydrogen into the shedlike enclosure around the stand, but then the source of the leak, which they had hoped might be in ground equipment, turned out to be about the worst scenario imaginable: a failure of the balloon tank. This lightweight tank, which holds its shape only when pressurized, is the foundation of the whole Centaur design... and they had decided that improved steel would allow them to make the walls thinner than before — too thin, it turned out. They worked out a way to add reinforcement, but they might need to re-engineer the whole tank for a longer-term fix. The original Vulcan had to be unstacked so its Centaur could be patched, pushing the launch back by probably another six months.

And then, just when that news was sinking in, a BE-4 being tested for the second Vulcan went kerplooey on the stand. And worse, though the news was new, the anomaly was not — it had been kept quiet for weeks. But Tory Bruno of ULA says he’s fairly confident that this particular engine was “a lemon” and it probably means nothing bad for the other engines.

Fortunately for the Youtuber who bet a tattoo that Vulcan would complete a successful mission before Starship managed an orbit, the first two Starship launches ended in destruction. And Vulcan finally went up in January 2024, sending a small commercial lander to the moon. (It didn’t get there, but that was its own fault.) This mission included Centaur relights to achieve that trajectory, and they went off perfectly. ULA’s record of flawless launches remains unbroken.

Vulcan 401 (no side boosters): mass 430 t?, diam 5.4 m, thrust 4900 kN, imp ~3.4 km/s?, staged combustion (methane), payload 10.7 t (2.6%?), cost hopefully under $5M/t, record 1/0/0 through April 2024.