NASA's New Rocket Sports a Supersonic Look
A bow shock forms around the Constellation Program's 327-foot-tall Ares I-X test rocket traveling at supersonic speed during its Oct. 28, 2009 launch from the Kennedy Space Center, Fla. The rocket produces 2.96 million pounds of thrust at liftoff and goes supersonic in 39 seconds.
Credit: NASA, courtesy of Scott Andrews

NASA?s gleaming new Ares I-X rocket grew an odd-looking hood Wednesday as it launched skyward on a suborbital test flight ? a telltale sign of a rocket going supersonic.

The hood was actually a vapor cone, sort of like a man-made cloud, created as the long, slender Ares I-X rocket hit Mach 1 and broke the sound barrier. Photographer Scott Andrews caught the moment 39 seconds after the 327-foot (100-meter) rocket blasted off from NASA?s Kennedy Space Center in Florida. It can also be seen in NASA?s video of the Ares I-X launch.

The phenomenon is not well studied, but has been seen on jet aircraft and spacecraft, like NASA?s space shuttles and the massive Saturn V rocket, as they surpass the sound barrier. The vapor cone is also referred to as a shock egg or shock collar.

Scientists think the phenomenon is caused by something called the Prandtl-Glauert singularity and starts when a layer of water droplets is trapped between two high-pressure surfaces of air. In humid conditions, condensation can gather in the trough between the two crests of sound waves produced by a launching rocket or flying jet. It does not always coincide with breaking the sound barrier.

Photographers caught a vapor cone on the 363-foot (110-meter) Saturn V rocket that launched the Apollo 11, NASA's first manned moon landing mission in 1969. NASA cameras also capture the phenomenon every now and then during space shuttle launches, such as the STS-106 flight of Atlantis in 2000.

NASA?s Ares I-X rocket is a trial version of the new Ares I booster slated to launch the crew-carrying Orion capsules that the agency plans to use once the shuttle fleet retires. The prototype consisted of a four-segment solid rocket booster (recycled from the space shuttle fleet?s inventory) capped with a dummy fifth segment and mock-ups of a second stage, Orion capsule and abort system.

NASA expected the rocket to hit a maximum speed of Mach 4.7 before its first stage separated from a dummy upper section two minutes after launch.

The first stage carried parachutes to slow its return and splashed down in the Atlantic Ocean to be recovered by a retrieval ship. The dummy second stage, however, was discarded after separation. It crashed in the ocean further downrange as planned.

The launch test demonstrated the feasibility of the Ares I rocket design, mission managers said. NASA?s plan of using Ares I and Orion craft to replace the shuttle fleet and return astronauts to the moon by 2020 is currently under review by the White House.

Click here for SPACE.com's full Ares I-X mission coverage.