We’ve all marveled at the videos of SpaceX rockets returning to their point of origin and landing on their spindly deployable legs, looking for all the world like something pulled from a 1950s science fiction film. On countless occasions founder Elon Musk and president Gwynne Shotwell have extolled the virtues of reusable rockets, such as lower operating cost and the higher reliability that comes with each booster having a flight heritage. At this point, even NASA feels confident enough to fly their missions and astronauts on reused SpaceX hardware.
Even so, SpaceX’s reusability program has remained an outlier, as all other launch providers have stayed the course and continue to offer only expendable booster rockets. Competitors such as United Launch Alliance and Blue Origin have teased varying degrees of reusability for their future vehicles, but to date have nothing to show for it beyond some flashy computer-generated imagery. All the while SpaceX continues to streamline their process, reducing turnaround time and refurbishment costs with each successful reuse of a Falcon 9 booster.
But that changed earlier this month, when a helicopter successfully caught one of Rocket Lab’s Electron boosters in midair as it fell back down to Earth under a parachute. While calling the two companies outright competitors might be a stretch given the relative sizes and capabilities of their boosters, SpaceX finally has a sparing partner when it comes to the science of reusability. The Falcon 9 has already smashed the Space Shuttle’s record turnaround time, but perhaps Rocket Lab will be the first to achieve Elon Musk’s stated goal of re-flying a rocket within 24 hours of its recovery.
Catch and Release
Unfortunately, while the helicopter was able to catch the booster as it returned to Earth, it wasn’t able to hold onto it for long. The pilots noted that the behavior of the captured rocket at the end of the tether was inconsistent with that of the mass simulator they had used during the practice runs, and rather than risk a deadly situation, they made the decision to cut it loose.
It’s still not clear why the flight characteristics of the real rocket were different, but one theory is that its fuel and oxidizer tanks were not fully empty, and the sloshing liquid introduced unexpected oscillations. You might think the answer would be to simply run the first stage’s nine Rutherford rocket engines until all propellants were expended, but allowing the turbopumps to run dry would likely lead to significant internal damage, if not complete destruction.
Should it be determined that unburned propellants were to blame, the solution would likely be to vent the fuel and oxidizer tanks into the upper atmosphere after main engine cutoff (MECO) and stage separation at an altitude of approximately 75 kilometers (46 miles); thus ensuring the rocket is empty and in a safe configuration long before the helicopter enters the capture area.
Even though the helicopter wasn’t able to bring the rocket back down to the ground safely, all was not lost. As luck would have it, the booster’s parachute reinflated after it was released from the tether, and it ultimately made a controlled splash down in the ocean. While it obviously had a far rougher ride than anticipated, Rocket Lab CEO Peter Beck has hinted that the rocket may still be in good enough condition to reuse. Pictures he tweeted from the recovery ship appear to show that the rocket and its valuable engines are in remarkably good shape, though a thorough internal examination will naturally be required before any decisions can be made about using the hardware on a future flight.
Faster isn’t Always Cheaper
It’s worth noting that Rocket Lab’s rationale for attempting to reuse their Electron rockets isn’t quite in line with that of SpaceX. Being a far smaller and cheaper rocket than the Falcon 9, the cost of recovery, especially this early in the program, likely exceeds the value of the hardware itself. But that’s not the point. The unique construction of the Electron, with its carbon composite fuselage and 3D printed engines, means it currently takes a month to produce each rocket. When your competitors are flying every two weeks, that’s simply not good enough.
As Peter Beck explained when he first announced the company’s plan to make Electron reusable in 2019, the hope is that a recovered rocket can be refurbished in less time than it takes to construct a new one. Even if the recovery and refurbishment ends up being more expensive, in the long-term, the increased launch cadence will be better for Rocket Lab’s bottom line. By reusing each rocket just once, they will double the number of missions they can fly in a year.
While SpaceX has used reusability to slash their operating costs, Rocket Lab sees it as an alternative to setting up a second Electron production line. Whether it will be as successful for them as it has been for SpaceX is yet to be seen, but one thing is clear: single-use rockets are becoming an increasingly quaint concept among this new breed of aerospace companies.