An artist's concept of the descent capsule returning to Earth. Credit: NASA

Stardust is scheduled to use its thrusters to fine-tune its flight path three times as it makes its final return to Earth on January 15, 2006. These maneuvers are scheduled 13 days, one day and 12 hours before Earth entry, respectively.

Soon after the final trajectory maneuver at an altitude of 110,728 kilometers (68,805 miles), Stardust will release its sample return capsule. A spring mechanism will impart a spin to the capsule as it is pushed away from the spacecraft in order to stabilize it. After the capsule has been released, the main spacecraft will perform a maneuver to divert itself to avoid entering Earth's atmosphere. The spacecraft will remain in orbit around the Sun.

The capsule will enter Earth's atmosphere at a velocity of approximately 12.8 kilometers per second (28,600 miles per hour). The capsule's aerodynamic shape and center of gravity are designed like a badminton shuttlecock so that the capsule will automatically orient itself with its nose down as it enters the atmosphere.

As the capsule descends, its speed will be reduced by friction on its heat shield, a 60- degree half-angle blunt cone made of a graphite-epoxy composite covered with a new, lightweight thermal protection system.

The capsule will slow to a speed about 1.4 times the speed of sound at an altitude of about 30 kilometers (100,000 feet), at which time a small pyrotechnic charge will be fired, releasing a drogue parachute. After descending to about 3 kilometers (10,000 feet), a line holding the drogue chute will be cut, allowing the drogue to pull out a larger parachute that will carry the capsule to its soft landing. At touchdown, the capsule will be traveling at approximately 4.5 meters per second (14.8 feet per second), or about 16 kilometers per hour (10 miles per hour). In all, about 10 minutes will elapse between the beginning of the entry into Earth's atmosphere until the parachute is deployed.

An artist's concept of the capsule awaiting recovery in Utah. Credit: NASA

The landing site at the Utah Test and Training Range near Salt Lake City was chosen because the area is a vast, desolate and unoccupied salt flat controlled by the U.S. Air Force in conjunction with the U.S. Army. The landing footprint for the sample return capsule will be about 30 by 84 kilometers (18 by 52 miles), an ample space to allow for aerodynamic uncertainties and winds that might affect the direction the capsule travels in the atmosphere. To land within the footprint, the capsule's trajectory must achieve an entry accuracy of 0.08 degree. The sample return capsule will approach the landing zone on a heading of approximately 122 degrees on a northwest to southeast trajectory. Landing time will take place at about 3 a.m. Mountain Standard Time on January 15, 2006.

The actual landing footprint will be predicted by tracking the spacecraft just before the capsule's release. Roughly six hours before entry, an updated footprint will be provided to the capsule recovery team.

Ground recovery
A UHF radio beacon on the capsule will transmit a signal as the capsule descends to Earth, while the parachute and capsule will be tracked by radar. A helicopter will be used to fly the retrieval crew to the landing site. Given the small size and mass of the capsule, mission planners do not expect that its recovery and transportation will require extraordinary handling measures or hardware other than a specialized handling fixture to cradle the capsule during transport.