SpaceX has reached a milestone in its bid to develop reusable rockets, with the apparently successful soft splashdown and recovery of the main stage of a Falcon 9 vehicle.
The launcher went on to deliver a Dragon cargo capsule to the International Space Station. In the post-Space Shuttle era, the Dragon capsule is unique in being able to return cargo from the ISS to Earth, and is being readied to demonstrate crew-carrying capabilities from 2015.
The 18 April launch from Cape Canaveral – the third of 12 ISS resupply missions SpaceX is to supply under a $1.6 billion contract with NASA – ended with Dragon, carrying nearly 2,300kg (5,070lb) of cargo, guided by the station’s robotic arm to a successful berthing with the Harmony module. It “looked to be a picture-perfect launch”, according to the company.
But while attention is naturally focused on Dragon, the novel part of the CRS-3 mission came in the third minute of flight. After first stage shut-down and separation, reignition of some of the stage’s nine Merlin 1D engines allowed the vehicle to achieve a soft splashdown. According to SpaceX, flight computers continued transmitting for 8s after reaching the water, and stopped when the booster went horizontal.
Re-usability will ultimately depend on SpaceX being able to return a Falcon 9 main stage to a vertical ground landing on its integral, folding legs.
This feat has been achieved following a flight to several hundred metres with a Merlin 1D-based test vehicle, Grasshopper, at SpaceX’s test site in McGregor, Texas. SpaceX is aiming for 3,300ft, and is understood to be readying take-off and landing tests of a Falcon 9 from Spaceport America in New Mexico, where flight altitude is unrestricted.
SpaceX founder Elon Musk’s objective sees “fully and rapidly reusable” rockets as the key to bringing airline-style economics to spaceflight – and critical to his ultimate goal of establishing and supporting a human colony on Mars.
However, while reusability may prove technically feasible, whether it can actually be cost effective remains to be seen. In a November 2012 address to the Royal Aeronautical Society, Musk laid out the problem as one of essentially doubling the mass-to-orbit efficiency of disposable rockets, in order to buy back the fuel and structural mass penalties related to a reusable design.
A disposable Falcon 9 flight to geostationary orbit is understood to cost about $70 million – half or less, depending on payload, of its heavy lift rivals, Europe’s Ariane 5 or United Launch Alliance’s Delta IV or Atlas V.