Falcon 9 landing attempt number two: ‘Excess lateral velocity,’ says Musk
After Tuesday’s CRS-6 mission left the ground to go carry supplies to the International Space Station (ISS), aerospace enthusiasts held their collective breath as they watched the booster’s progress rather than the spacecraft’s. Several minutes after liftoff, the second Falcon 9 landing attempt by Space Exploration Technologies (SpaceX) ended with the target being hit, but evidently a little too hard.
The CRS-6 mission, as is usual for Commercial Resupply Services missions, had a single-second window for the launch to happen. Monday saw a scrub due to weather, but liftoff occurred successfully on Tuesday, the next opportunity for launch.
Just under three minutes after liftoff, the first stage separated from the rest of the vessel. After that, nitrogen thrusters flipped the vehicle into the proper direction for landing and then a boost-back burn brought it into the correct trajectory for the landing site. A re-entry burn combined with atmospheric drag worked to slow it down, after which its four hypersonic grid fins deployed to control the lift vector. Finally, a landing burn was performed, which was meant to slow the rocket down enough for it to touch down softly and safely. During this, the landing legs deployed, which are made of carbon fiber with aluminum honeycomb.
The booster did hit its football-field-sized target – the company’s autonomous spaceport drone ship with the unusual name “Just Read the Instructions” after a ship from author Iain M. Banks’ “Culture” book series. However, this was not quite the desired soft touchdown.
“Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post landing,” tweeted SpaceX CEO and founder Elon Musk in the aftermath.
Despite the sub-optimal landing and subsequent fireball, which can be viewed in the video below, the barge is nearly undamaged, according to Musk. “Droneship is fine. No hull breach and repairs are minor. Impact overpressure is closer to a fast fire than an explosion,” he tweeted on Wednesday.
The attempt to land the Falcon 9 booster rocket’s first stage in order to recover it and use it again is part of a goal to make space travel less expensive and more accessible. Currently, rockets are used once and then discarded – left behind to burn up when they re-enter Earth’s atmosphere. Stabilizing one for a safe re-entry is a task that SpaceX describes as “trying to balance a rubber broomstick on your hand in the middle of a wind storm.”
“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred,” Musk has said. “A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space.”
The company tested their rocket landing concepts using a 10-story-tall Vertical Takeoff, Vertical Landing (VTVL) vehicle they called the Grasshopper. It consisted of “a Falcon 9 first stage, a single Merlin 1D engine, four steel landing legs with hydraulic dampers, and a steel support structure,” according to SpaceX. The vehicle did see eight flight tests with successful landings in 2013, with a top altitude of 744 meters up.
After Grasshopper, SpaceX tested their F9R development vehicle – basically a Falcon 9 first stage with landing legs – in McGregor, Texas, with several successful attempts and a top test altitude of 1,000 meters.
Their first real-mission attempt to land a Falcon 9 first stage was CRS-5 in January of this year. The experiment ended in a “Full RUD (rapid unscheduled disassembly) event,” as Musk described it at the time. The rocket had run out of hydraulic fluid, which was necessary to steer the grid fins that kept the stage pointed upright.
Another attempt was planned for February, with the launch of the DSCOVR orbiter, but due to stormy weather and dangerous waves, the landing attempt was scrubbed and the booster was directed for a “soft landing” in the water instead. The rocket was not expected to survive in that case.
The next opportunity for the company to try to stick the landing will be the CRS-7 mission, which is currently targeted for June of this year. According to Defense News, Gwynne Shotwell, SpaceX president and COO, said on Wednesday that they hope the next landing will take place on land, not at sea, for the added stability of firm ground.
In that discussion, Shotwell also expanded on the reasons for reuse: “Our point in reusability is because we want to take people back and forth, and you don’t get the return trip if you don’t have a vehicle.”
The color-corrected video of Tuesday’s landing attempt was posted on Wednesday evening and can be viewed below.
Video courtesy of SpaceX
Rae Botsford End is a freelance writer and editor whose primary work currently is writing technical white papers, contributing to SFI, and working on a speculative fiction novel that she hopes to have published soon. Rae wanted an opportunity to report on the various space-related events in and around Florida's Space Coast and approached SFI's founder about the possibility. Rae now covers an array of subjects for our growing website.