NASA's First Quest for a Reusable Rocket
In the name of creating cost effective launch systems, a lot of private spaceflight companies are focusing on developing reusable rocket stages. It’s pretty clear how this would help — refurbishing and reusing hardware is much cheaper than building new hardware for every launch.
A few weeks ago, SpaceX took the first step towards its reusable launch vehicle with a demonstration flight of its Grasshopper. The Grasshopper is the first stage of a Falcon 9 rocket with spindly legs — hence the insect-inspired name — that can launch, hover, and land vertically on its own. The first demonstration test saw the Grasshopper lift a few feet off the ground, but later tests will see it hover a few hundred feet before it eventually lands vertically and autonomously after a launch. Blue Origin has been working toward the same goal with its New Shepard launch system.
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The quest to reuse rockets isn’t a new one. In the 1960s, NASA considered a few ways to recover and reuse the first stage of its Saturn rocket — the S-IC stage — though none went beyond scale testing.
The first and most obvious way to recover and reuse a rocket stage was to have it land by parachute in the ocean. A salvage ship could recover the stage and its contractor could refurbish and ready it for another flight.
This is basically what happened with the shuttle’s solid rocket boosters (SRBs). Jettisoned two minutes after launch, they parachuted to an ocean landing where they were recovered for refurbishment and another launch. But we need to emphasize the scope of the refurbishment operation. After the flight and exposure to corrosive salt water, only five of the SRBs ten sections were reused; the rest were new. Over the course of the shuttle program about 270 SRBs were built.
The problems of corrosion on rocket stage hardware wasn’t unknown in the 1960s, prompting NASA to look into ways of landing the S-IC stage on land instead of in the water. The solution was to use a Rogallo paraglider wing, the same system that was going to land the Gemini spacecraft on land (for the same corrosion-based reasons among others) before it was removed from the program.
The Rogallo paraglider wing is a triangular two-lobe sail design. Stored in flight, it would release during the descent and inflate generating enough lift to turn any payload into a glider. This was the plan for the S-IC stage.
Folded flat against the rocket stage, the Rogallo wing would be in a position where it wouldn’t affect the Saturn’s aerodynamics in flight during launch. Once the stage’s fuel was expended and it fell away, a drogue parachute would automatically deploy. It would stabilize the booster’s fall and, at subsonic speeds, pull the paraglider from its stored position and out to its full extension. With both drogue and paraglider deployed, the booster would stabilize on its side and start to glide thanks for the paraglider’s lift.
The selling point of the Rogallo wing, for both booster recovery and Gemini landing, was its controllability. By shifting the S-IC’s center of gravity relative to the wing — for example, side to side to gain lateral control — it could be remotely guided to smooth runway landing.
But even after contractor studies and small scale tests, there were enough flaws with this plan that it was (as we know) never used. For one, it would take a huge paraglider to slow the S-IC to a survivable runway landing. The weight of such a large paraglider was similarly enormous. A 1:12 scale S-IC was 71.8 feet long, 21.5 feet in diameter, and weighed 120,000 pounds. The paraglider at this scale weighed 24,000 pounds. That translated to a significant increase in the rocket’s overall weight and similarly the overall thrust it would have to develop at launch.
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At the time, there were also too few Saturn-series launches planned that it wasn’t necessarily worthwhile to recover and reuse the stage. Had the rocket been planned for over a hundred flights, it would have been a worthwhile investment. Another problem is the obvious difficulty of a rocket stage making a controlled, autonomous, unpowered landing on runway with a paraglider wing.
It’s highly likely, especially since SpaceX has demonstrated it’s hardware with the Grasshopper already, that these rocket powered vertical landing rocket stages will be the first to make autonomous landings on land. It’s also likely to work better than the paraglider, though a self-controlled runway landing rocket stage would have been an awesome sight.
Image: The two solid rocket boosters (SRB) still glow following their jettisoning from the space shuttle Columbia on its first mission — STS-1 on April 12, 1981. The SRBs were only partially reusable after being dropped by parachute into the Atlantic Ocean. Credit: NASA