Private-sector spaceflight company SpaceX chalked up a partial success on 14 April, launching its supplies-laden Dragon capsule to the International Space Station, but failing to recover the first stage of its Falcon 9 rocket – which crashed on a barge meant to receive it following a powered descent.
The mission – flown as CRS-6 under contract to NASA – marked SpaceX's second attempt to recover a rocket stage. Another Falcon 9 stage suffered a similar fate in January, and rough Atlantic weather made it impossible to deploy the autonomous barge, named Just Read the Instructions, for a subsequent flight in February.
SpaceX has yet to describe the crash in detail. But founder Elon Musk, the Silicon Valley billionaire who made his fortune from PayPal before starting the rocket business and the Tesla electric cars company, said on Twitter of the recovery attempt: “Rocket landed on droneship, but too hard for survival.” He went on to add: “Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post-landing.”
The barge, he said, “is fine. No hull breach and repairs are minor. Impact overpressure is closer to a fast fire than an explosion.”
The Dragon capsule, loaded with nearly 2,000kg (4,400lb) of supplies for the ISS's six astronauts, will take about two days to reach the station. During about five weeks in orbit, it will be unloaded and then packed with about 1,300kg of trash and completed science experiments and released for recovery, following a splashdown in the Pacific Ocean off Southern California. Later versions of Dragon will be capable of carrying crew from later this decade; SpaceX and Boeing will be providing that service for NASA from 2017, launching astronauts from US soil for the first time since the Space Shuttle fleet was retired in 2011.
A successful rocket stage recovery would be a first, and holds out the promise of cutting launch costs, which for a Falcon 9 can be $70 million or more. Musk, whose SpaceX “was founded in 2002 to revolutionise space technology, with the ultimate goal of enabling people to live on other planets”, but today makes its revenue by launching commercial satellites and missions like last week's ISS resupply flight, believes that ambitious plans such as colonising Mars will only be financially possible with reusable spacecraft.
Two near-misses – following a powered "soft splashdown" in 2014 – suggest that SpaceX may be near to success with a first-stage recovery, which is widely regarded in the space industry as feasible and possibly desirable, given the large cost of launcher hardware.
However, reusability depends on more than intact recovery, and other launcher components may remain disposable. Even Musk has said that, to achieve reusability, efficiency will have to be doubled, to push about 4% of launchpad mass to orbit, to make up for the extra launcher mass associated with robust construction, landing gear and, in the case of Falcon 9, a fuel load for descent. In an operation where every scrap of efficiency is clearly needed, that doubling is no easy target.
And, as NASA's Space Shuttle demonstrated, reusability is difficult to achieve in practice. The runway landing orbiter never came close to achieving envisioned turnaround times between flights.
Musk, though, is determined, well resourced and buoyed by a sense of humour. As he tweeted during the CRS-6 mission: “If this works, I'm treating myself to a volcano lair. It's time.”