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Why SpaceX is Taking Its Next Rocket Landing Back Out to Sea

January 15, 2016, 8:40 PM UTC
The first stage of the SpaceX Falcon 9 rocket returns to land at Cape Canaveral Air Force Station in Florida
The first stage of the SpaceX Falcon 9 rocket returns to land at Cape Canaveral Air Force Station, on the launcher's first mission since a June failure, in Cape Canaveral, Florida. December 21, 2015. The rocket carried a payload of eleven satellites owned by Orbcomm, a New Jersey-based communications company. REUTERS/Joe Skipper Tags: SCIENCE TECHNOLOGY TRANSPORT - RTX1ZP2K
© Joe Skipper / Reuters REUTERS

Last month, SpaceX made history by launching and then landing a Falcon 9 rocket booster on land at Cape Canaveral, Fla. On Sunday, Elon Musk’s commercial space cargo company will try to the same thing at sea, after two previous failed attempts.

The effort to land on a ship in the Pacific Ocean should make for another nail-biter that could mark yet another historic milestone for Space X. But with its success on land, why is the company trying again with a method that ended in fiery crashes in the past?

The simple reasons are all practical, chief among them the fact that SpaceX doesn’t have a landing pad on the West Coast—or at least a place where it has government clearance. Last month’s historic launch and landing took place on the East Coast; the Falcon 9 lifted off from Cape Canaveral and landed just a few miles away. Sunday’s scheduled launch, however, will originate from Vandenberg Air Force Base in California. This time around, SpaceX didn’t have time to obtain the proper approvals from the Federal Aviation Administration to land at Vandenberg, so any landing had to take place somewhere else.

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Those FAA clearances are related to safety, among other considerations, and landing at sea is one way to solve the problem. But to say Sunday’s maritime landing attempt is all about safety and bureaucratic red tape is to miss something larger. Though more difficult to execute, at-sea landings would allow SpaceX to efficiently recover rockets that are moving heavier payloads into higher orbits with less safety risk. That explains why the company has confirmed that its next few missions—not just Sunday’s launch—will attempt landings on drone ships rather than dry land.

The reason is linked to the reality that rockets fly in a parabolic arc rather than straight up. By the time a first stage booster like the Falcon 9’s separates from the second stage and payload, it has traveled many miles horizontally as well as vertically. To land near its launch site like in December’s landing, the booster must burn extra fuel while it backtracks through the atmosphere.

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Additionally, the heavier the rocket and the faster it’s traveling, the more fuel it must burn to decelerate for its gentle landing. Therefore, the rocket must carry extra fuel at liftoff, which itself adds more weight.

In the rocket business, fuel and weight have a huge impact on cost. So for missions like December’s in which the Falcon 9 was delivering relatively light-weight communications satellites into low earth orbit, a return to a terrestrial landing made sense. But for rockets carrying heavier payloads—and especially those accelerating to the speeds necessary to reach higher orbits—the economics of a return-to-origin turn less favorable.

SpaceX’s autonomous drone ships, however, can go wherever the combination of the rocket’s trajectory and gravity are already taking it by moving underneath it the way a center fielder tracks down a fly ball. The rocket can launch with less fuel to help it further trim cost. Given that the whole point of developing reusable rockets centers on cutting space launch costs, figuring out how to land at sea is critical to SpaceX’s core mission of going faster and bigger for less money.

Sunday’s launch will carry NASA’s Jason-3 satellite—a research satellite that will monitor global ocean surface temperatures—into a lower orbit, so it very well could’ve been a candidate for a second terrestrial landing. But the mission will prove a good trial run for the weeks ahead in which SpaceX is slated to launch a communications satellite into a higher geostationary orbit and make a potentially heavy cargo run to the International Space Station. SpaceX hasn’t detailed any rocket-landing plans for those missions, but either or both could help its engineers hone their at-sea landing skills.

That’s assuming Sunday’s launch goes as planned. Air Force meteorologists have given a “100 percent chance of favorable weather” at the launch site on Sunday. We’ll soon find out whether that translates into a favorable conditions for landing a rocket as well.