Musk: I want to retrieve rockets with big Falcon party balloons

NASA: Been there, done that

While waiting for TESS to get off the launchpad on Monday, chief exec Elon Musk joked on Twitter about how SpaceX might set about recovering the second stage of the booster.

SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon

— Elon Musk (@elonmusk) April 15, 2018

The idea is not as outlandish as it seems.

NASA's Low Density Supersonic Decelerator (LDSD), tested off the coast of Hawaii as recently as 2015, takes the form of very large, durable, balloon-like vessels that inflate around the vehicle to slow it from supersonic speeds.

NASA is considering the technology as a part of landing profiles for Mars.

To get from hypersonic to supersonic speeds, NASA developed the Hypersonic Inflatable Aerodynamic Decelerator (PDF) (snappily shortened to HIAD), a set of doughnut-shaped balloons that inflate to form a heat shield for atmospheric re-entry.

Earlier still, NASA worked with ballutes (a combination of BALLoon and parachUTE), using the technology to stabilise the ejection seats of astronauts flung from an exploding Gemini spacecraft in the 1960s before considering them for use on planetary missions.

Thankfully, no Gemini astronaut ever had to pull the D-ring of doom, although Wally Schirra came close during the aborted launch of Gemini 6A in 1965.

Whether an inflatable ballute would have been much use is debatable, since the cabin of the spacecraft was filled with 100 per cent oxygen at 16 psi and firing rockets to fling the crew clear would have resulted in "two Roman candles", as crew member Tom Stafford memorably put it.

As Musk noted: "We are only here because we stand on the shoulders of giants," making use of hypersonic and supersonic balloon and ballute research to return a Falcon 9 second stage is certainly within the realms of possibility should the economics of reuse make sense.

As far as the closing part of Musk's tweet is concerned – "And then land on a bouncy house" – there is no record of NASA using such tech so SpaceX may be on their own there.

The Register would be delighted to have a go on such a device because, after all, everyone loves a bouncy castle. ®