The Space Shuttle and SpaceX have both flown to space with reusable boosters. But that’s not the only way to reduce costs to orbit.
Episode Summary:
Since the early 1960s, the high cost of throwing away expensive boosters was a limiting factor in the development of commercial spaceflight. NASA investigated flyback booster concepts during the Saturn program, and the space shuttle was designed primarily around reusability. Today, SpaceX routinely flies first-stage boosters back to their Cape Canaveral landing pad or to ships at sea. However, there are other approaches. Which one is best?
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Transcript of this week’s show:
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We’ve all seen those remarkable videos of SpaceX first-stage boosters flying themselves down to a soft landing on barges or the landing pad at Cape Canaveral. It is a remarkable achievement to fly something as large as a rocket stage back to a soft landing, a little like balancing a pencil on its end.
The SpaceX effort represents the current state-of-the-art in reusability of spacecraft, and it does what the rockets before it couldn’t do: actually reduce costs.
The Space Shuttle program was designed specifically to reduce the high cost of heavy lift orbit, originally with an entirely reusable design. The tight budgets of the 1970s forced a redesign into the form that we are all familiar with: solid rocket boosters parachuting into the sea to be towed ashore and refurbished after every flight.
The concept worked, but what it did not do was reduce the cost of launching satellites into orbit, and it never replaced expendable systems for satellite launch. But with SpaceX now dropping the price of lift to orbit, new competitors in the orbital launch race are looking to reusability as a necessity to achieve competitive costs.
Space Shuttle solid rocket boosters proved to be 100 percent reusable, but as an overall system, the Shuttle surprisingly delivered no cost advantages in pounds to low earth orbit compared to expendable boosters. The SpaceX flyback system is proven and has reduced costs, but it’s not the only route to reusability.
Rocket Lab, a small satellite launcher that has captured a notable portion of the launch market with its Electron vehicle, has designed a novel first stage that, after burnout, will deploy a parachute and be captured midair by helicopter for flyback and refurbishment. Midair recovery of space vehicles is not new, with spy satellite payloads hooked out of midair by cargo aircraft 60 years ago, but rocket stages are large and heavy, so it will be a noteworthy achievement if Rocket Lab pulls it off.
The other major company in the heavy-lift market is United Launch Alliance, makers of the large Vulcan system. Vulcan will use complex, Blue Origin-designed first-stage engines, and ULA is looking at a novel form of reusability: the severing of main engines from the airframe, and midair parachute recovery of the engine and avionics package. While this idea sounds difficult and complex, involving explosive separation of engine mounts, fuel and electrical lines, there are sound economic rationales for using this approach.
Engines represent over 50 percent of the cost of a Vulcan first stage, but account for only one-quarter of the mass, making the engines the highest value per unit mass for recovery and reuse. It may also be possible to package much of the booster’s avionics into the engines, as well, for further savings. And for midair recovery, capturing a mass that is one-quarter of the launch weight of the stage, looks attractive too.
The SpaceX, ULA and Rocket Lab reusability systems are all different, but all face a similar challenge: the cost of refurbishment versus new build. SpaceX will likely have the lowest cost, since they require minimal recovery infrastructure to soft-land their stages. But they pay a serious performance penalty for doing so, reserving a significant proportion of propellant weight at launch for flyback, and carrying the extra weight of the landing gear and associated hardware. For high-performance launches, SpaceX omits the reusability capability.
Rocket Lab can use most of its first-stage fuel, but still carries a weight penalty in the parachute systems, and it is not known if midair helicopter recovery of something as large as a rocket stage can be done routinely. The ULA approach is especially interesting, because they simply blow off the expensive bits, which should make them easier to capture. To make it work as a system, however, will require low-cost mass production of airframes and tankage to minimize the losses in discarding three quarters of the boosters’ weight into the ocean.
Are any of these systems ideal? Probably not. But the ideal system would be expensive, and would likely look something like the original Space Shuttle booster concept: a rocket-powered glider that would fly itself back to a runway, much like the Orbiter did itself. That idea, however, proved cost-prohibitive in the early 70s, and it would be just as expensive today.
But right now, I’m watching Rocket Lab. They are small, and launch small satellites, but they have a healthy order book, and their system promises to offer the reusability of SpaceX with none of the weight and performance disadvantages of flyback systems.
They’ll be testing it soon, and good luck to them.
