Reusable rockets are launch vehicles that are are able to perform multiple launches with minimal refurbishment. This can be contrasted with current expendable launch vehicles which are used for only one mission.This technology has the potential to greatly reduce the per-kilo cost of putting things into orbit and to allow routine space access, both necessary conditions for space industrialization and expanded exploration efforts. As an illustration, imaging how much more expensive a trans-oceanic ticket would be if a new airliner had to be purchased for each flight; reusable rockets are at base an attempt to approach designing rockets as vehicles rather than as ammunition.
2012-2013 has been an exciting year for this technology, with more activity than in the previous decade. Also notable is that much of this activity is associated with privately-operated companies. Perhaps the single largest development has been the progressive flight testing of SpaceX’s “Grasshopper,” a technology demonstrator for the first stage of a planned multi-stage vertical take-off, vertical landing (VTVL) reusable rocket launching system based on their successful Falcon 9.
SpaceX performed a series of 8 successful test flights of the 32 meter Grasshopper v1.0 before it was retired to work on the larger v1.1 which is designed to explore an expanded flight envelope that includes supersonic speeds. SpaceX plans to fully develop the reusable first stage before working to do the same for other stages. This eminently sensible piecewise plan will allow for incremental reductions in launch costs on the path to full reusability.
Reaction Engines Ltd. is also a source of continuing interest since the successful test of their SABRE engine pre-cooler in 2012. This British company secured mixed commercial/government funding in 2008 to develop their innovative propulsion concept to Tech Readiness Level 4 – 5, the stage immediately prior to the demonstration of a full prototype. This year, the British government and EU pledged an additional £67 million for development work through 2016. It is estimated that a full prototype SABRE engine test rig will cost around £200 million.
The SABRE engine has two modes of operation. In the first, air-breathing mode it combines a powerful pre-cooler with a turbo-compressor. Pre-cooling the air entering the engine allows the maintenance of high pressure ratios (and thus high thrust) even at very high velocities and in the thin upper atmosphere. In the second, closed mode SABRE operates as a rocket burning liquid oxygen and liquid hydrogen in the same combustion chamber. Intended for use on spaceplanes, especially the company’s Skylon design, single-stage to orbit (SSTO) SABRE-propelled spaceplanes would take off from a large runway like an airliner and then simply fly into space. This has the advantage of simplicity, but comes at the cost of much reduced payload capacity. Some other spaceplane concepts thus involve being launched from a conventional jet-powered “mothership” to get a jump on the velocity needed for orbit.
On the whole, it is incredibly encouraging to see varied lines of reusable rocket development by multiple companies that seem to be on a sound financial footing. This is a set of circumstances that has never existed before in the history of spaceflight and, while there are still many difficulties to be overcome, it shows that routine space access is finally making the transition from dream to reality.
For more information on the activities of these two companies, see the SpaceX and Reaction Engines Ltd. websites at: