Thanks to SpaceX, we know exactly how hard it is to reuse a rocket by landing it on a barge. Of course, there's an excellent reason why why SpaceX is investing so much effort in making a reusable launch system: an enormous percentage of the launch cost is the rocket engine, and if you can reuse that, you can slash costs dramatically.
United Launch Alliance, a joint venture between Lockheed Martin and Boeing best known for their Delta and Atlas rockets, has just announced a next-generation rocket called Vulcan. Using Blue Origin's forthcoming BE-4 engines, and with a not entirely crazy airfoil and helicopter mid-air retrieval system, Vulcan is ULA's attempt field a commercial launch system that can compete with SpaceX on both capability and cost.
Since 2006, ULA has been the exclusive launch contractor for the US military, but as of this year, they're likely to be facing competition from SpaceX, which can launch payloads less expensively and without relying on Russian engines that Congress has recently banned. ULA also needs to factor cost into consideration if they hope to enter the rapidly growing commercial launch market, and if SpaceX manages to start reusing its rockets, ULA will need to do the same to be competitive.
ULA's new Vulcan rocket will use BE-4 engines currently being developed by Blue Origin, the private aerospace company of Amazon founder Jeff Bezos. They'll be 20 percent more powerful than the engines currently powering ULA's Atlas, and Vulcan will be able to handle six strap-on boosters for heavy lifting, as opposed to five on the Atlas. The Vulcan replacement for the Atlas should cost under $100 million, $65 million less than an Atlas launch, and competitive with the SpaceX Falcon.
With 65% of the booster costs of the Vulcan wrapped up in the engines, reusability can slash launch costs dramatically. Rather than try to duplicate SpaceX's not-yet-successful vertical landing to reuse the entire rocket, ULA is planning on reusing just the engines themselves, and to do that, they need to come up with a way of getting them back to Earth in a soft, gentle, non-crashy sort of way.
ULA's engine retrieval system is called Sensible Modular Autonomous Return Technology, or SMART. Once the rocket's payload has been delivered to orbit, the engines separate themselves from the booster, and reenter the atmosphere. Instead of a conventional rigid heat shield, ULA plans on using an advanced inflatable hypersonic heat shield, which is probably something like the one that NASA has been working on for a while now:
Once the engines have made it through the worst part of reentry, they'll deploy a steerable airfoil, just like the ones people use for skydiving. And then the fun part happens, as a helicopter with a big hook dangling from it swoops in to snag the airfoil and engines in mid air. This sounds a little nutty, but it's been done ever since the first spy satellites needed a safe way of getting film back to Earth, starting with the Corona Project in the 1960s. More recently, mid-air capture was intended to be used to retrieve the fragile sample capsule of the Genesis mission in 2004. It even looks like ULA itself has been working in mid-air retrieval since the mid-2000s:
ULA will need to use a much larger helicopter, but this is a relatively well understood technique that seems like it could be a fairly efficient way to reuse rocket engines. The earliest that this could be attempted is probably 2024, as the first launch of the Vulcan rocket won't be until 2019.