One of the most ambitious development projects in spaceflight took a giant leap last month when SpaceX achieved a 29s flight to a height of 40m - and safely back to the launch pad - with its Grasshopper rocket, a bid to develop a fully reusable vertical take-off and vertical landing launch vehicle.
Grasshopper - 10 storeys tall and consisting of a Falcon 9 first stage, Merlin 1D engine, four steel legs with hydraulic dampers and a steel support structure - had "flown" for a few seconds to as high as 5.4m, with a brief hover before landing. A series of successively more sophisticated tests will be carried out at SpaceX's development facility in McGregor, Texas, during the next few months.
SpaceX chief Elon Musk says Grasshopper is only the first in a series of projects that he hopes will result in 100% reusability for SpaceX vehicles. Speaking at the Royal Aeronautical Society in London in November - where he showed a video of one of the first Grasshopper test flights, to just a metre or so - Musk said he hoped to be bringing back the first stage from SpaceX flights "in the next year or two", and promised "soon" to unveil a new version of his Dragon cargo or crew capsule capable of landing vertically, on legs. In October 2012 SpaceX began a series of contracted International Space Station resupply flights, and brought material back from the ISS in a splash-landing Dragon capsule.
Musk added that his full-reusability timetable was "five to six years", though he confessed that "could be famous last words". Moreover, he said to the RAeS gathering, he expected that as Grasshopper testing continues "there will be a few craters along the way".
He said the challenge went far beyond merely controlling the thrust of a rocket stage to bring it safely back to a vertical landing. Today, just 2-3% of a rocket's mass reaches orbit, and to add the mass needed to make the craft reusable - in structural robustness and in hardware such as landing gear - will mean adding another 2-3%, employing every weight-saving "trick in the book" to achieve a "rocket that's so mass-efficient that it gets 4-5% to orbit".
Musk is convinced that total reusability and frequent flight must be achieved if the promise of space travel is ever to be fully exploited: "It would open up opportunities that today are hard to envision."
One of his hard-to-envisage objectives is to establish a self-sustaining human colony on Mars. Musk sees reusability, and thus airline-style operating frequency, as the difference between a Mars adventure costing "half a percent of GDP versus all of GDP".
Whether a Mars colony or even a human visit is feasible, Musk's dream of total reusability promises much when it comes to transforming the economics of ordinary Earth orbit spaceflight. As Musk told the RAeS, the cost of a rocket today is only about 0.3% propellant, with the rest thrown away; in the case of a $60 million Falcon 9 launch, that's less than $200,000 for gas and a lot of money ending up in the sea.