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September 30, 2011

Why Spacex Abandoned Parachuting into Water for Reusable Rockets

New Scientist - SpaceX's original concept for first-stage recovery and reuse didn't work and apparently is being abandoned.

The original concept seemed simple: the spent first stage would parachute down to a splashdown offshore, where it would be recovered by boat and hauled back to shore for refurbishment and reuse. There were some obvious questions about how well a rocket stage would survive being soaked in seawater, which is quite corrosive; perhaps only selected components would be reusable, not the whole stage. (Yes, NASA recovered the shuttle SRBs the same way, but their refurbishment process was so labour-intensive that it's not clear it ever really saved them any money.)

Overall, the idea seemed like a clumsy makeshift, and some doubted that there would be much real benefit, but it didn't seem ridiculous – just challenging.

The only problem was, it didn't work. At the Space Access conference in April, Gwynne Shotwell, SpaceX's president, admitted: "We have recovered pieces of the first stages." The first stages weren't even getting as far as deploying their parachutes – they were breaking up during atmospheric re-entry.




The new plan actually seems much more promising. After the upper stages separate from it, the nearly-empty first stage will reignite some of its engines to turn around and come back to its launch site, and will then land vertically on rocket power, like the experimental DC-X and the private rockets competing in NASA's Lunar Lander Challenge. In due time, SpaceX aims to have the second stage also re-enter behind a heat shield on its nose, and do the same vertical rocket landing.

This method might seem more complicated than the old one, but parachutes and splashdowns are not as simple as they might look, and this way the landing will be gentler and much more controlled... and on dry land, too. There will be some challenges along the way, but the final result should be much more satisfactory.

The biggest near-term advantage won't even be the reuse of the expensive hardware, but something less obvious: the ability to flight-test it. No matter how carefully SpaceX builds its rockets today, each one is always flying for the very first time. This isn't nearly as good as being able to test each and every one repeatedly, to find and fix any problems before a rocket is entrusted with an expensive payload. Development of the new system should also be easier, because each new stage can start with short "bunny hop" tests and gradually work up to higher and faster flights, rather than having to do the full flight the first time.


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