Space Station Parafoil Unfurls Beautifully in Test
A 7,500-square-foot NASA parafoil, the size of half a football field, successfully opened in a drop test Jan. 19, paving the way for its eventual use as an emergency tool for evacuation from the International Space Station.
Personnel from The Aerospace Corporation who provided independendent assessments and helped establish test criteria were elated at the success of the test.
The parafoil, the largest ever to be opened successfully, was dropped from a transport plane over a Yuma test range. The full-scale prototype is designed to carry more than 23,000 pounds and will be used with the crew return vehicle (CRV), a "lifeboat" designed to hold up to seven people for emergency evacuation from the space station.
The parafoil is intended to be used for the lifeboat’s final descent and landing. The lifeboat performs its initial reentry from orbit flying like the shuttle, using its lifting body shape for control.
Once the lifeboat has completed its reentry and is 23,000 feet above the landing site, the recovery sequence begins. A drogue first slows the lifeboat down. The parafoil is then released from a pack smaller than a 5- by 4- by 3-foot box.
Opened in Stages
"You can’t open a parafoil this huge at one time," said Bruce Wendler, a senior engineering specialist in The Aerospace Corporation’s Vehicle Systems Division, who has been working on its development. "It’s falling so fast that it needs to slow down before opening.
"Five release stages slow the descent. They are color coded, beginning with white. As the different colors unfold, you can see how well the staging process is working.
"It was truly an engineering feat that the parafoil was successfully deployed and performed," he continued. "A second feat was the science behind the event, which took a major step forward when the predicted deployment dynamics and handling qualities matched the flight results.
"Prior parafoil development was by trial and error, with the error being unforgiving even when only dummy payloads were involved," said Wendler. "The project had already advanced to a 5,500-square-foot parafoil and used subscale tests to validate analysis and design approaches."
Working with NASA
The Aerospace Corporation began its involvement with the CRV program in October 1998, when a group of Engineering and Technology Group personnel supplemented with NASA experts conducted an independent assessment that was completed in March 1999.
Wendler, with co-chair Steve Cavanaugh from NASA’s Independent Program Assessment Office, briefed the independent analysis results to NASA’s highest council. A key recommendation was a deployment test of the full-scale recovery system to demonstrate that the concept had sufficient maturity to preclude the use of circular chutes as an alternative.
Over the summer Wendler and his team worked with Cavanaugh from NASA’s office in Langley, Va., providing technical assessments during the parafoil’s critical design review. As a result, several action items involving loads, design margins, and material selections were accepted by the project.
Together with Chuck Eldred, a retired NASA project engineer who had been responsible for the parachutes for the Apollo command module, Wendler’s team worked on establishing test success criteria for the full-scale test, including loads, aerodynamics, handing qualities, and landing characteristics.
Standards Raised
Although the process was difficult, it raised the team’s standard of excellence and resulted in higher test readiness and flight readiness reviews before the drop test. The night before the drop, Wendler said the team was just as tense during its crew review as before any major launch activity.
On the morning of the test, several "cold passes" were made in rehearsal for the actual drop. Following the parafoil’s release, both the visual videos and quick-look data indicated that the success criteria were satisfied with no damage to the parafoil.
Subsequent analysis has proven that the parafoil met or exceeded the success criteria. Its success was one of the key events needed for the project to enter its next engineering phase in the fall, which Wendler said involves releasing competitive contracts for aerospace companies to continue developing the crew return vehicle.
The lifeboat is scheduled to be docked on the International Space Station in 2004.
IMAGE CAPTIONS: [http://www.aero.org/news/current/parafoil.html]
[Image 1]
Parafoil half the length of a football field drifts over Yuma test range in successful drop test Jan. 19. (NASA photo)
[Image 2]
Artist’s conceptual drawing shows a "lifeboat" attached to the International Space Station. NASA’s 7,500-square-foot parafoil is designed to help get the lifeboat safely to Earth during an emergency. (NASA illustration)
