Catch a falling rocket and bring it back to shore…
On Tuesday, Rocket Lab, a small company with a small rocket, accomplished the first half of that feat on its latest launch from the east coast of New Zealand.
After sending a payload of 34 small satellites into orbit, the company used a helicopter to catch the spent 39-foot-long booster stage of the rocket before it crashed into the Pacific Ocean.
“Pretty, pretty epic day,” Rocket Lab CEO Peter Beck said at a press conference hours later. “The difficulty of capturing a stage is quite extreme.”
In the future, Rocket Lab hopes to refurbish a salvaged booster and then use it for another orbital mission, a feat only one company has managed so far: Elon Musk’s SpaceX.
A video feed showed a long cable hanging from the helicopter with cloudy skies below. Then the propellant appeared suspended under the parachute.
“Here we go, we’ve got a first look at it,” said commentator Murielle Baker on the Rocket Lab show. The grappling hook at the end of the helicopter cable snagged the parachute line before the captured thruster swung out of view of the camera.
Cheers from Rocket Lab Mission Control confirmed a successful take.
However, the company later provided an update that qualified the success. Mr Beck, said the helicopter pilots reported that the thruster was not hanging under the helicopter in quite the same way as during testing and they let go.
“If the drivers were unhappy at any point, that’s what they had to do,” Mr Beck said. “Then the stage continued under parachute at a low rate of descent and crashed into the ocean.”
A Rocket Lab ship lifted the thruster out of the water. Eventually, the company would like the helicopter to carry a taken booster to dry land and avoid salt water damage.
Mr. Beck did not rule out the possibility that it could be reused. “It is always my hope that you will see this vehicle on the platform again,” he said.
Rocket Lab gives most of its missions fancy names. This one was called “There and Back Again,” a nod to the encore recovery as well as the subtitle of JRR Tolkien’s novel “The Hobbit.” Director Peter Jackson’s Hobbit film trilogy was filmed in New Zealand.
Rocket Lab’s Booster Socket is the latest advancement in an industry where rockets were once expensive single-use disposable items. Reusing all or part of an element reduces the cost of delivering payloads into space and could speed up the launch rate by reducing the number of rockets to be manufactured.
“Eighty percent of the rocket’s cost or thereabouts are actually in stage one,” Beck said in a previous interview. “So the economy for us is really good. It is certainly worth doing.
SpaceX pioneered a new era in reusable rockets and now regularly lands the first stages of its Falcon 9 rockets and flies them again and again. Falcon 9 second stages (as well as Rocket Lab’s Electron rocket) are always thrown away, usually burning up as they re-enter Earth’s atmosphere. SpaceX is designing its next-generation super rocket, Starship, to be fully reusable. Competitors like Blue Origin and United Launch Alliance, as well as Chinese companies, are also developing rockets that would be at least partially reusable.
NASA’s space shuttles were also partially reusable, but required extensive and expensive work after each flight, and they never lived up to their promise of airliner-like operations.
For the Falcon 9, the booster fires multiple times after it separates from the second stages, slowing it en route to a smooth landing on a floating platform in the ocean or on land.
As a much smaller rocket, the Electron must use all the propellant to lift the payload into orbit. This ruled out the possibility of propulsive landings like Falcon 9 boosters.
Instead, Rocket Lab engineers came up with a more fuel-efficient approach, adding a system of thrusters that expel cold gas to steer the thruster as it falls, and thermal shielding to protect it from temperatures exceeding 4 300 degrees Fahrenheit.
The booster separated from the second stage at an altitude of about 50 miles. It then continued to climb another 10 miles before starting to fall, accelerating to 5,200 miles per hour.
“If you don’t have the stage perfectly oriented with the heat shield down, then basically when the reentry process starts, it’s like a big ball of plasma,” Beck said. “It’s going to basically shred the scene.”
The friction of the atmosphere acted as a brake. About 7 minutes and 40 seconds after liftoff, the thruster’s sink rate slowed to less than twice the speed of sound. At this point, a small parachute called the drug deployed, adding additional drag. A larger main parachute further slowed the rappel to a more leisurely pace.
Rocket Lab had demonstrated in three previous launches that Electron boosters could survive re-entry. But on those missions, the boosters splashed down in the ocean and were later pulled out for examination.
This time, a Sikorsky S-92 helicopter hovering in the area encountered the booster in flight at an altitude of 6,500 feet, dragging a cable with a grappling hook across the line between the drug and the main parachutes.
With almost all of its propellant expended, the propellant was much lighter than at launch. But it was still a heavy piece of metal – a cylinder four feet in diameter and about as tall as a four-story building and weighing nearly 2,200 pounds or one metric ton.
Mr Beck said he expected the unexpected charging issue to be resolved with more drop testing. The Sikorsky is capable of lifting up to five metric tons, far more than the weight of the booster. “It’s a small detail,” he said.
Eventually, Rocket Lab would like to nab boosters for about half of its missions, Beck said. Some missions cannot use a reusable booster because the payloads are too heavy. The added weight of thrusters, parachutes, and thermal protection reduces the 550-pound payload by 10-15 percent.
Other missions have constraints like an instant launch window or night launch that make capturing the booster impractical.
The next two electrons directed to the launchpad do not include the apparatus needed to retrieve the booster. This includes the rocket to launch CAPSTONE, a NASA-funded but privately operated mission that will study a highly elliptical trajectory around the moon that will be used by a future US lunar space station.
But there is another Electron with a reusable booster on the factory production floor that could be used soon, Beck said.
“For sure today gave us extreme confidence to continue,” he said.