NASA spacecraft moves one step closer to fall launch

Photo: In this artist's conception, the DART flight demonstrator, top left, rendezvous with the MUBLCOM satellite, bottom right, in orbit. (Orbital Sciences Corporation)

NASA is planning to launch the Demonstration of Autonomous Rendezvous Technology (DART) flight demonstrator no earlier than Oct. 26, 2004, from Vandenberg Air Force Base, Calif. The mission is an in-space demonstration of an autonomous rendezvous prototype system.

NASA successfully ground tested technologies that will enable unmanned spacecraft to rendezvous autonomously, something that has never been done in the history of U.S. spaceflight. The ground tests were performed at the Flight Robotics Laboratory at NASA's Marshall Space Flight Center, Huntsville, Ala.

The tests demonstrated the capability of hardware and software to communicate with each other and to drive the spacecraft autonomously to achieve a safe, assured rendezvous and close approach to a target.

Video guidance sensor and autonomous rendezvous guidance technologies have performed flawlessly, according to NASA managers. The tests verified critical autonomous rendezvous technologies, including the ability of the Advanced Video Guidance Sensor to combine with other technologies, such as the Global Positioning System and Automated Rendezvous and Proximity Operations calculations.

The video guidance sensor sees and determines a spacecraft's exact location, then feeds the information to Automated Rendezvous and Proximity Operations calculations, or algorithms, that function as a brain. The brain commands the spacecraft to turn, throttle, or brake, allowing it to rendezvous with another craft.

The tests were performed using mock-ups of the DART spacecraft and target satellite, demonstrating successful proximity operations with video guidance sensors for target location. DART navigation guidance transitioned successfully from the Global Positioning System to direct use of the video guidance information. The DART spacecraft then moved progressively closer to the target satellite under direct video guidance.

A number of maneuvers were demonstrated in the simulated ground tests, including a collision avoidance maneuver, horizontal approaches toward the target satellite, transition to docking guidance, and docking-hold maneuvers to within five meters of the target.

"The successful automation of these types of maneuvers, demonstrated by DART technologies, will benefit future space systems development requiring in-space assembly, services or other autonomous rendezvous operations," said Jim Snoddy, DART project manager. "This milestone moves us one step closer to a DART launch, where technologies proven on the ground will be demonstrated in space," he added.

DART will be carried into space aboard a Pegasus rocket. The Pegasus rocket will be launched from a Stargazer L-1011 aircraft at approximately 40,000 feet over the Pacific Ocean. The Pegasus will boost DART into an approximately 471-by-479-mile polar orbit.

DART will travel around the Earth to rendezvous with its target, the Multiple Paths, Beyond-Line-of-Site Communications experimental satellite. The target satellite was designed for use with a video guidance system like the Advanced Video Guidance Sensor on DART.

While on orbit, DART will perform several close proximity operations, such as moving toward and away from the target satellite using navigation data provided by onboard sensors. DART will also test additional algorithms by calculating and executing collision avoidance maneuvers and will travel around the target. To conclude the mission, DART will fly away from the satellite. The entire 24-hour mission will be accomplished without human intervention.

DART and the Pegasus vehicle were developed by Orbital Sciences Corp., Dulles, Va. NASA's Exploration Systems Mission Directorate, Washington, funds the DART project.

Source: NASA