SpaceX aims for another rocket landing experiment Sunday

Artist's concept of a Falcon 9 booster after landing on SpaceX's ocean-going platform. Credit: Jon Rosszlsa
Artist’s concept of a Falcon 9 booster after landing on SpaceX’s ocean-going platform. Credit: Jon Ross

Keeping with its mantra of fly, fix and fly again, SpaceX says its engineers have resolved an engine valve problem that kept one of its Falcon 9 boosters from successfully touching down on a barge in the Atlantic Ocean in April, ahead of another landing attempt planned after a launch from Cape Canaveral scheduled for Sunday.

The landing tests are classified by SpaceX as purely experimental maneuvers, but they have garnered wide attention from launch industry competitors and space enthusiasts around the world.

SpaceX says the experiments should lead to the reusability of Falcon 9 booster stages, an achievement that engineers say will cut launch costs and open up access to space to more companies, governments and universities with lean budgets.

Sunday’s launch — set for 10:21 a.m. EDT (1421 GMT) — will be the third time SpaceX has tried to recover a Falcon 9 first stage on a specially-outfitted ocean-going barge. Landing attempts in January and April got close, but the rockets landed too hard — and at tilted angles — and disintegrated in fireballs.

On both attempts, the rocket’s first stage flipped around after separating from the Falcon 9’s upper stage, which continued into orbit with Dragon cargo ships heading for the International Space Station.

The boosters fired three of their nine Merlin first stage engines for two burns — first to guide the booster back toward the landing zone downrange from Cape Canaveral, then to slow down for re-entry into the atmosphere. A third ignition of the rocket’s center engine is supposed to brake for landing.

Engineers blamed the first crash landing in January on insufficient hydraulic fluid for the 14-story booster’s aerodynamic grid fins used to steer the rocket during descent.

In April, the first stage descended toward the landing barge and the rocket fired for its final braking maneuver, but a stuck valve thwarted the touchdown.

“That controlled descent was spectacular, but about 10 seconds before landing, a valve controlling the rocket’s engine power (thrust) temporarily stopped responding to commands as quickly as it should have,” SpaceX said in a post on its website Thursday. “As a result, it throttled down a few seconds later than commanded, and — with the rocket weighing about 67,000 lbs and traveling nearly 200 mph at this point — a few seconds can be a very long time.

“With the throttle essentially stuck on ‘high’ and the engine firing longer than it was supposed to, the vehicle temporarily lost control and was unable to recover in time for landing, eventually tipping over,” SpaceX said.

SpaceX released a new video — longer than a video clip initially posted on YouTube in April — from an aerial drone Thursday showing the rocket’s fall through the sky, ignition of the booster’s Merlin main engine and deployment of the booster’s four landing legs.

The footage starts with the rocket flying at about 10 kilometers — or 6 miles — in altitude, according to SpaceX.

“Last-second tilt aside, the landing attempt happened pretty much exactly as planned,” SpaceX said.

The rocket executed the pre-programmed flyback burns as designed, then steered toward the landing barge.

“Our atmosphere is like molasses to an object traveling at Mach 4, and the grid fins are essential for landing with precision,” SpaceX wrote on its website. “The final landing burn ignited, and together the grid fins, cold gas thrusters and steerable engines controlled the vehicle, keeping the stage within 15 meters (49 feet) of its target trajectory throughout the landing burn. The vehicle’s legs deployed just before it reached our drone ship, ‘Just Read the Instructions’, where the stage landed within 10 meters (33 feet) of the target, albeit a bit too hard to stay upright.”

SpaceX said post-launch analysis showed the throttle valve was the sole cause of April’s failed landing.

“The team has made changes to help prevent, and be able to rapidly recover from, similar issues for the next attempt,” SpaceX said.

The next landing try will use a different vessel than SpaceX’s earlier descent maneuvers.

Called drone ships by SpaceX, the vessels have thrusters to maintain position in the sea to provide a stable platform for rocket landings.

The football field-sized ship assigned to Sunday’s launch is based in Jacksonville, Florida, and is named “Of Course I Still Love” in a nod to giant starships featured in science fiction novels by Iain M. Banks.

The drone ship will be stationed in the Atlantic Ocean about 200 miles northeast of Cape Canaveral for Sunday’s flight.

SpaceX has not said why officials switched landing platforms for the next mission, but the company plans to stage a drone ship off Southern California for a Falcon 9 launch from Vandenberg Air Force Base in early August.

Falcon 9 launch operations from both coasts of the United States dictate requirements for at least two landing platforms.

The drone ships are emblazoned with a giant bullseye, a stylized “X” representing SpaceX’s logo and the vessel’s name.

Space'x new drone ship, named "Of Course I Still Love You," is ready for Sunday's launch. Credit: SpaceX
Space’x new drone ship, named “Of Course I Still Love You,” is ready for Sunday’s launch. Credit: SpaceX

If SpaceX succeeds in landing the booster, the accomplishment will be the first step in the company’s bid to field a reusable rocket for space launches. Engineers plan detailed inspections and tests of the recovered booster before committing it to another launch into orbit.

The prime objective of Sunday’s launch from Cape Canaveral is to dispatch a commercial Dragon cargo craft to the space station. More than 4,000 pounds of gear, provisions and experiments are packed inside the capsule.

The weather forecast is favorable.

U.S. Air Force forecasters predict a 90 percent chance of acceptable weather for Sunday morning’s instantaneous launch opportunity, calling for a few clouds at 2,500 feet, scattered clouds at 22,000 feet, southwest winds at 12 to 17 mph, and a temperature of 84 degrees Fahrenheit.

It is the seventh launch of SpaceX’s 15-flight contract with NASA to carry supplies to the space station. The Dragon capsule is due to arrive at the complex Tuesday, assuming an on-time launch.

If the launch does not occur Sunday, SpaceX has a backup opportunity Monday at 9:58 a.m. EDT (1358 GMT).

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Follow Stephen Clark on Twitter: @StephenClark1.