Not so very long ago, orbital rockets simply didn’t get reused. After their propellants were expended on the journey to orbit, they petered out and fell back down into the ocean where they were obliterated on impact. Rockets were disposable because, as far as anyone could tell, building another one was cheaper and easier than trying to reuse them. The Space Shuttle had proved that reuse of a spacecraft and its booster was possible, but the promised benefits of reduced cost and higher launch cadence never materialized. If anything, the Space Shuttle was often considered proof that reusability made more sense on paper than it did in the real-world.
But that was before SpaceX started routinely landing and reflying the first stage of their Falcon 9 booster. Nobody outside the company really knows how much money is being saved by reuse, but there’s no denying the turn-around time from landing to reflight is getting progressively shorter. Moreover, by performing up to three flights on the same booster, SpaceX is demonstrating a launch cadence that is simply unmatched in the industry.
So it should come as no surprise to find that other launch providers are feeling the pressure to develop their own reusability programs. The latest to announce their intent to recover and eventually refly their vehicle is Rocket Lab, despite CEO Peter Beck’s admission that he was originally against the idea. He’s certainly changed his tune. With data collected over the last several flights the company now believes they have a reusability plan that’s compatible with the unique limitations of their diminutive Electron launch vehicle.
According to Beck, the goal isn’t necessarily to save money. During his presentation at the Small Satellite Conference in Utah, he explained that what they’re really going after is an increase in flight frequency. Right now they can build and fly an Electron every month, and while they eventually hope to produce a rocket a week, even a single reuse per core would have a huge impact on their annual launch capability:
If we can get these systems up on orbit quickly and reliably and frequently, we can innovate a lot more and create a lot more opportunities. So launch frequency is really the main driver for why Electron is going reusable. In time, hopefully we can obviously reduce prices as well. But the fundamental reason we’re doing this is launch frequency. Even if I can get the stage back once, I’ve effectively doubled my production ratio.
But, there’s a catch. Electron is too small to support the addition of landing legs and doesn’t have the excess propellants to use its engines during descent. Put simply, the tiny rocket is incapable of landing itself. So Rocket Lab believes the only way to recover the Electron is by snatching it out of the air before it gets to the ground.
Reusability on SpaceX’s Falcon 9 comes at a considerable price. Between the additional hardware required and the propellants that need to be kept in reserve for the reentry and landing burns, the payload capacity of the rocket is reduced by as much as 40%. To accommodate this without compromising on the vehicle’s useful payload capacity, SpaceX has gradually been enlarging and upgrading the design. When it first flew in 2010, the Falcon 9 was 47.8 m (157 ft) tall and had a liftoff mass of 333,400 kg (735,000 lb); the version flying today has been stretched to 70 m (230 ft) in length, and tips the scales at 549,054 kg (1,210,457 lb).
For SpaceX, who have their eyes on the medium and heavy lift markets, this kind of vehicle expansion aligns well enough with their goals. But Rocket Lab isn’t looking to compete with vehicles of that scale. With a length of just 17 m (56 ft) and a maximum payload capacity of 225 kg (496 lb), their Electron rocket is of an entirely different class. The company is laser focused on providing bespoke launch capabilities for the so-called “smallsat” market. These smaller satellites would be considered the second or even third priority if they were launched on a larger rocket, but on Electron, they’re the primary mission.
Unfortunately, the reality of operating such a small rocket is that there’s precious little wiggle room for vehicle modifications. Every ounce of additional hardware they add to the rocket will reduce their already minuscule payload capacity. Even if the Electron could spare the propellants to perform a propulsive landing burn, the mass penalty for deployable landing legs would be unacceptable. If Rocket Lab can squeeze a bit more thrust out of their 3D printed Rutherford engines they’ll have some breathing room, but not much. Any modifications to the Electron for recovery purposes will therefore need to be exceptionally minimal.
This early in the program, Rocket Lab is reluctant to say what those modifications would entail. We can tell from the rendered video they’ve posted to their YouTube channel that the first phase will use a ballute decelerator to bring the Electron down to subsonic speeds, at which point a parafoil will be deployed to further slow the rocket. This is not entirely unlike SpaceX’s now defunct plans for recovering the second stage of the Falcon 9. But what we don’t see is what kind of thermal shielding will be required for Electron to survive the intense heat of reentry, or what method of stabilization and guidance it will use on its way back down; likely because Rocket Lab themselves don’t quite know yet.
Snagging a Falling Rocket
Even assuming Rocket Lab upgrades the Electron to the point it can survive reentry and deploy its deceleration devices, they still need to figure out a way to get it down on the ground in one piece. As shown in the rendered video, the plan right now is to snatch the Electron out of the air by flying a helicopter over the descending rocket and grappling it. This might sound like something out of a James Bond movie, but in reality it’s arguably the easiest aspect of Rocket Lab’s entire scheme.
In fact, it would appear that this part of the plan has already been completed. In 2017, Lockheed Martin (a strategic investor in Rocket Lab since 2015) partnered with a PDG Aviation Services to conduct a little-publicized mid-air helicopter recovery of a mock rocket stage, and the similarities are hard to ignore. The device used to snatch the leader cable behind the rocket’s parafoil shown in Rocket Lab’s rendering appears to be identical to the one seen in video of the Lockheed Martin test, which really makes the whole thing look like a low-key dress rehearsal.
One element of the recovery process that’s unclear after comparing both videos is how the Electron will safely be lowered to the ground. During the Lockheed Martin test the “rocket” was dropped rather unceremoniously on its faux engines, but that obviously won’t work with actual flight hardware. The fact that the official Rocket Lab video fades out before the Electron is actually brought back down to the waiting ship may mean the company still hasn’t sorted that part out yet. Though if you have the technical wherewithal to launch and recover an orbital rocket, figuring out how to softly lower it onto the deck of a ship shouldn’t pose much of a challenge.
Faster and Cheaper
The fundamental goal of any reusable launch system is for subsequent reflights to be more economical and less time consuming than simply building a new booster for each mission, and in such a demanding field, even relatively minor gains are generally considered a success. But ideally the less time and money spent between launches, the better. To that end, the unique nature of the Electron may make it particularly well suited for so-called “rapid reuse”: a concept wherein a rocket is reflown nearly as often as a commercial aircraft, needing only to be inspected and refueled before being sent on its next mission.
The Electron does away with the complex gas generator and turbine arrangement traditionally used in liquid rockets, and instead uses electrically-driven pumps for the fuel and oxidizer. Combined with its relatively simplistic 3D printed engines and how small the vehicle is, there’s simply not as much that needs to be checked out between flights. A smaller team can go over every inch of the Electron in a fraction of the time it would take a much larger crew to thoroughly examine the Falcon 9, for example.
SpaceX has so far demonstrated a turnaround time of a little over two months from landing to reflight, but Rocket Lab may be poised to reduce that time to a few weeks. Considering both companies have stated an ultimate goal of reflight within days of recovery, they’ve got their work cut out for them. But even if they never quite hit that lofty goal, it seems clear the days of crashing used rockets into the ocean are coming to a close.