16 avril 2020 |
International,
Aérospatial
Irene Klotz
The first Falcon 9 rocket to land successfully after dispatching a payload into orbit stands on permanent display outside SpaceX headquarters in Hawthorne, California, a testament to the perseverance of founder, CEO and chief engineer Elon Musk, who wants a fleet of fully reusable spaceships to reduce the cost of colonizing Mars.
The vision is shared by fellow tech entrepreneur Jeff Bezos, whose Kent, Washington-based Blue Origin space company is developing a series of reusable vehicles, beginning with the New Shepard suborbital passenger transport system. The New Shepard made 12 uncrewed flight tests over the last five years, with more to come before commercial flights begin.
Bezos also has pumped $2.5 billion into developing the New Glenn, a reusable system powered by seven BE-4 methane-fueled engines designed to carry nearly 50 tons to low Earth orbit. “That is the smallest orbital vehicle we are planning to build and launch,” says Clay Mowry, Blue Origin vice president of sales, marketing and customer experience.
But the first BE-4s to power a rocket to orbit may not be aboard the New Glenn. United Launch Alliance (ULA) is buying the engines to power the first stage of its Vulcan rocket, an expendable booster—at least for now—which, like the New Glenn, is slated to debut next year.
At some point, ULA may decide to recover and reuse just the BE-4 engines, a pair of which will fly on each Vulcan. The idea is for the engine compartment to disengage after launch and fall back through the atmosphere protected by an inflatable hypersonic shield. A helicopter would be positioned to snag the engine section midair as it makes a parachute descent. ULA calls the approach its Sensible Modular Autonomous Return Technology, or SMART.
“It does not impact, in any significant way, the overall performance of the launch vehicle because you don't have to save fuel to fly home with,” ULA CEO Tory Bruno tells Aviation Week. “You still get to burn up all your fuel, separate your engine, which is the most expensive piece, and recover it.”
“We have not really changed our assessment over the last couple of years because we have yet to see the other forms of reusability—flyback or propulsive return to Earth—demonstrate economic sustainability on a recurring basis,” Bruno says. “It's pretty darn hard to make that actually save money. . . . We've seen nothing yet that changes our analysis on that.”
SpaceX currently is the only launch company reflying orbital rockets. SpaceX launched its final version of the workhorse Falcon 9 booster, called the Block 5, in May 2018. Within two months, the company was flying Block 5s exclusively. The upgrade includes higher-thrust Merlin engines, stronger landing legs and dozens of upgrades to streamline recovery and reuse.
Block 5s were designed to fly 10 times with minimal maintenance between flights, and up to 100 times with refurbishment. SpaceX President and Chief Operating Officer Gwynne Shotwell says the company no longer expects to need to fly a Falcon 9 more than 10 times.
“We don't have to ramp up our production, at least for boost phases, like we thought we were going to,” Shotwell said on March 10 at the Satellite 2020 conference in Washington.
“From a reliability perspective, we want to know the limits of Falcon 9, so we'll push them, but . . . some government customers want new vehicles—I think over time, they will come to flight-proven vehicles as well,” she added. “But if I have to build a couple of new ones every year, or 10 new ones a year, that adds to the fleet, and I don't know that I'll have to push a rocket more than 10 [flights.]”
With regard to how much the company has been able to cut costs by reflying rockets, Shotwell would only say, “We save a lot of money.”
As a privately held company, those operating expenses are not publicly available, but the Block 5 flight record is. So far, SpaceX has flown 14 Block 5 core boosters over 31 missions, including two Falcon Heavy flights, which use three cores apiece.
Of those 14 boosters with flight history, five remain part of the operational fleet. The rest were expended—several after multiple missions—due to payload performance requirements or unsuccessful landings. One booster was intentionally destroyed as part of a Crew Dragon capsule launch abort flight test.
SpaceX's fleet leader flew five times before failing to land on a drone ship stationed off the Florida coast on March 18. SpaceX has not said if the botched landing was related to a premature engine shutdown during the final phases of ascent. The rocket's remaining eight Merlin engines compensated for the shutdown, and the payload—a batch of 60 SpaceX Starlink broadband satellites—reached its intended orbit.
While it continues to fly the Falcon 9 and Falcon Heavy for NASA, national security and commercial missions, SpaceX is developing a fully reusable, human-class deep-space transportation system called Starship at its own expense.
Another company testing the waters of reusability is Rocket Lab, which builds and flies the Electron small-satellite launcher.
“For a long time, I said we weren't going to do reusability,” Rocket Lab CEO Peter Beck said in August 2019, when he announced the new initiative. “This is one of those occasions where I have to eat my hat.”
Electrons do not have the performance for a propulsive return like SpaceX's Falcons do, so Rocket Lab is pursuing a midair, helicopter recovery system to snare the booster's first stage. The intent is not to reduce costs per se but to increase flight rates without having to boost production. The company currently is producing one Electron rocket about every 30 days. “We need to get that down to one a week,” Beck says.
“We view [rocket reuse] as sort of a journey,” ULA's Bruno adds. “We're going to start with the engines because we're pretty sure we can save money with that and pass those savings on right away. As we learn more by doing, we'll continue to assess other valuable parts of the rocket, and we may discover that we can do that there as well.”
“There is one funny thing about reusability,” he adds. “As you make your rocket less expensive, and you make parts of your rocket less expensive, it's harder to close a business case on reuse because the thing you're recovering isn't as valuable. There's a balance there.”
https://aviationweek.com/shows-events/space-symposium/economics-rocket-reuse-still-air
