Time to Collect the Corona
|Helicopter capture of Genesis during descent rivals a James Bond stunt for visual spectaculars.
At about 9 o’clock Wednesday morning, a fireball will appear in the sky over the western United States.
The sample capsule from the Genesis spacecraft will be returning to Earth at supersonic speeds. The spacecraft has been gathering atoms streaming off the sun’s corona for the past two years. These solar wind samples, which are contained in collector wafers made of gold, sapphire, silicon and diamond, are stored within the capsule.
If all goes as planned, the capsule will enter the atmosphere above Oregon. In less than two minutes it will zoom across the sky toward its destination in the Utah desert.
"The 450-pound capsule, moving 25,000 miles per hour, carries with it the same kinetic energy as a four-and-a-half-million pound freight train at 80 miles an hour," says Genesis recovery team chief Bob Corwin, of Lockheed Martin Space Systems in Denver. "So you can see the job the atmosphere has to do in slowing this capsule down to the point where we can deploy parachutes."
|Caltech’s Don Burnett, Genesis Principal Investigator.
At an altitude of 108,000 feet, a drogue shoot will deploy and slow the capsule down to subsonic velocities. The main parachute, a parafoil, will deploy six minutes later, at an altitude of 20,000 feet.
Two recovery helicopters will be waiting at 10,000 feet, seven miles away from the predicted intercept point. There will also be a military helicopter present to ensure the safety of the aircraft at the U.S. Air Force’s Utah Test and Training Range, as well as a media helicopter to record the capture attempt.
Ground controllers at Hill Range Radar will be scanning the skies for the capsule, and once they locate it they will send a position advisory to the helicopters. The helicopter crew then will try to spot the capsule as it falls out of the sky.
Although they could potentially spot the capsule as high up as 16,000 feet, the helicopters won’t try to grab the capsule until it descends to 8,500 feet above sea level.
The lead helicopter will use a long line with a large hook at the end to grab onto the capsule’s parafoil. A second helicopter will wait 1,000 feet behind the lead, and if the lead helicopter misses, the second helicopter will swoop in and attempt a capture. The pilots will be able to make these capture attempts until the capsule descends to an altitude of 500 feet.
Cliff Fleming, of South Coast Helicopters in Santa Ana, California, will be piloting the lead helicopter. He estimates the two helicopters will have about eight capture attempts.
|Updated: NASA reported that parachute and parafoil failures led to desert impact on Sept. 8.
If the helicopters miss and the capsule parachutes to the ground, the damage could be extensive. By the time it lands, the capsule will only be traveling forward at about 20 miles per hour. But a calibrated instrument on the capsule could be damaged, and the solar collector wafers could break into fragments. Then, says Genesis payload team leader Don Sevilla, of NASA’s Jet Propulsion Laboratory, "we’d end up with a can full of glass."
But since the pilots have never missed on their first try during each of their practice runs — except for one time when they intentionally missed as part of a simulation — Fleming is confident that they won’t need all eight capture attempts on Wednesday morning.
Once the parafoil is captured, the helicopter will slowly lower it and place it down to Earth. The other helicopter will land and its crew will detach the parafoil, and then the capsule will be flown to the Michael Army Air Field at the U.S. Army Dugway Proving Ground, where a temporary clean room is set up.
|From outside the influence of the Earth’s magnetic field, pristine solar wind was captured on semiconductor-grade wafers.
Principal investigator Don Burnett, of the California Institute of Technology in Pasadena, says they will apply nitrogen to the capsule as soon as they get it opened. This nitrogen will purge the container of any contaminated air that might have entered the capsule during its entry into Earth’s atmosphere.
Less than a week later, the samples will be moved to a special laboratory at NASA’s Johnson Space Center in Houston. From there, says Burnett, the samples will be sent out to laboratories specially set up to study the solar wind particles.
"We have a billion billion atoms that we’ll be studying," says Burnett, "and we will be analyzing one atom at a time."
The Genesis sample will reflect the composition of the solar nebula – the disk of gas and dust that formed the planets in the solar system – because, according to Burnett, "the nebula is frozen for us in the surface layers of the sun." By comparing the nebula materials with the composition of the planets today, scientists hope to determine how the planets have changed over time.
"Most of what has been learned about the early solar system has been gotten from meteorites and cosmic dust," says NASA Genesis program scientist David Lindstrom, of NASA Headquarters in Washington. "We also know these have been modified by later processes in the solar system." The sun’s corona, on the other hand, is considered to be a relatively unaltered representation of the solar nebula.
This will be NASA’s first sample return mission since December 1972, when Apollo 17 returned lunar samples to Earth.
"Sample return is the next big thing with NASA," says Corwin. "Stardust will also be doing a sample return next year, as will future missions."