Rocket Lab has made improvements to the first stage of the Electron Rocket to make it more resistant to ocean water, improvements that will be tested with tonight’s launch.

The “Baby Come Back” mission will launch from the company’s launch complex on the Māhia Peninsula, New Zealand, with a launch window opening at 7:30 pm EST. The main goal of the mission is the delivery of four satellites for NASA, two weather intelligence satellites for Spire Global and a demonstration satellite for the Canadian satellite communications company Telesat.

NASA’s four-cubesat mission, called Starling, will test the satellites’ ability to autonomously coordinate their movements, or “swarm,” in orbit. The satellites will also demonstrate the ability to plan and execute movements without guidance from human mission controllers.

After launch, the first stage will descend to Earth under a parachute and splash down in the Pacific Ocean. Rocket Lab’s recovery ship will lift the propellant out of the water and return it to a company production facility for analysis.

Rocket Lab has taken early stages out of the ocean before, but this time the stage will include new designs to make some key engine and avionics components even more waterproof. There will be a few other changes to the entire recovery process, Rocket Lab CEO Peter Beck said, including a lighter parachute and a different method of getting the stage out of the water.

The company has been working to make Electron’s first stage reusable since late 2018, the year it began launching payloads into orbit. The following year, Rocket Lab announced that it would pursue methods of recovery: by ditching in the ocean and by capturing the first stage in the air with a helicopter.

Rocket Lab has attempted the capture with a helicopter twice, with the first attempt ending in partial success after the helicopter briefly caught and then released the propellant. The second attempt was canceled entirely due to a loss of stage telemetry data; but this turned out to be a positive turn of events, Beck told investors earlier this year.

“Electron survived oceanic recovery in very good condition, and in many cases its components actually pass requalification for flight.”

Encouraged by these results, Rocket Lab appears to have moved away from helicopter capture entirely. While Rocket Lab has yet to fly a booster again, it plans to reuse a Rutherford engine on a mission later this year.