Mid-air retrieval

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A helicopter with a long hook can catch a parachuting object in mid-air, as seen here in a practice run for the planned retrieval of Genesis.

Mid-air retrieval is a technique used in atmospheric reentry when the reentering vehicle is incapable of a satisfactory unassisted landing. The vehicle is slowed by means of parachutes, and then a specially-equipped aircraft matches the vehicle's trajectory and catches it in mid-air.

This is a risky technique, and so is only used when other forms of landing are infeasible. Successful mid-air retrieval requires correct operation of the retrieving aircraft, favourable atmospheric conditions, and successful execution of a tricky manoeuvre, in addition to correct operation of the vehicle itself. Complicating matters, helicopters, which are the optimal aircraft for these operations due to their manoeuverability, are particularly prone to mechanical breakdown. These risks can be mitigated somewhat: for example, multiple recovery aircraft can be used. The need for human aviators to perform a manoeuvre which would normally be classed as a stunt may in the future be avoided by advances in unmanned aerial vehicles.

Notable uses of the technique:

• The early-1960s era Corona reconnaissance satellite returned delicate film capsules to Earth that required mid-air retrieval by a C-130 Hercules airlifter.
• The Genesis mission returned a sample of solar wind that was so delicate that it would have been damaged by a parachute landing, so a mid-air retrieval using helicopters flown by Hollywood stunt pilots contracted by NASA was planned. Its parachutes failed to deploy, so mid-air retrieval was impossible and the capsule crashed. The similar Stardust mission was successfully retrieved using the same technique.
• An early design for SpaceShipOne called for a shuttlecock-like shape that would have made it incapable of landing independently, necessitating mid-air retrieval. This was deemed too risky, and the final design made the spacecraft capable of independent horizontal landing while cleverly retaining the desired aerodynamic qualities for the early part of reentry.

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