Solar Sail Surprise

This was a write of a few of daysago as the sail had failed to deploy at all. Suddenly it sprang free and did deploy and that allowed the sailsthemselves to be deployed a couple of days back.  The satellite is now fully operational andback on program.

The first planned application forthese sails is to begin sweeping for debris. This should work well enough since the craft can use solar pressure onthe sails to match orbits with detected debris.

Thus sending a bundle of thesedevices into orbit makes sense and allows a number of objects to be pursued andsnagged before been brought down into the atmosphere.  It is certainly a practical way to getheavier items out of near Earth orbit

Solar Sail Stunner

January 24, 2011 : Call it a stunner.

In an unexpected reversal of fortune, NASA's NanoSail-D spacecraft hasunfurled a gleaming sheet of space-age fabric 650 km above Earth, becoming thefirst-ever solar sail to circle our planet.

"We're solar sailing!" says NanoSail-D principal investigatorDean Alhorn of the Marshall Space FlightCenter in Huntsville, AL. "This is a momentousachievement."

NanoSail-D spent the previous month and a half stuck inside itsmothership, the Fast, Affordable, Science and Technology SATellite (FASTSAT).FASTSAT was launched in November 2010 with NanoSail-D and five otherexperiments onboard. High above Earth, a spring was supposed to push thebreadbox-sized probe into an orbit of its own with room to unfurl a sail. Butwhen the big moment arrived, NanoSail-D got stuck.

"We couldn't get out of FASTSAT," says Alhorn. "It washeart-wrenching—yet another failure in the long and troubled history of solarsails."

Team members began to give up hope as weeks went by and NanoSail-Dremained stubbornly and inexplicably onboard. The mission seemed to be overbefore it even began.

And then came Jan. 17th. For reasons engineers still don't fullyunderstand, NanoSail-D spontaneously ejected itself. When Alhorn walked intothe control room and saw the telemetry on the screen, he says "I couldn'tbelieve my eyes. Our spacecraft was flying free!"

The team quickly enlisted amateur radio enthusiasts Alan Sieg and StanSims at the Marshal Space Flight Center to try to pick upNanoSail-D's radio beacon.

"The timing could not have been better," says Sieg."NanoSail-D was going to track right over Huntsville, and the chance to bethe first ones to hear and decode the signal was irresistible."

Right before 5pm CST, they heard a faint signal. As the spacecraftsoared overhead, the signal grew stronger and the operators were able to decodethe first packet. NanoSail-D was alive and well.

"You could have scraped Dean off the ceiling. He was bouncingaround like a new father," says Sieg.

The biggest moment, however, was still to come. NanoSail-D had toactually unfurl its sail. This happened on Jan. 20th at 9 pm CST.

Activated by an onboard timer, a wire burner cut the 50lb fishing lineholding the spacecraft's panels closed; a second wire burner released thebooms. Within seconds they unrolled, spreading a thin polymer sheet ofreflective material into a 10 meter-square sail.

Only one spacecraft has done anything like this before: Japan'sIKAROS probe deployed a solar sail in interplanetary space and used it to flyby Venus in 2010. IKAROS is using the pressure of sunlight as its primary meansof propulsion—a landmark achievement, which has encouraged JAXA to plan afollow-up solar sail mission to Jupiter later this decade.

NanoSail-D will remain closer to home. "Our mission is to circleEarth and investigate the possibility of using solar sails as a tool tode-orbit old satellites and space junk," explains Alhorn. "As thesail orbits our planet, it skims the top of our atmosphere and experiencesaerodynamic drag. Eventually, this brings it down."

Indeed, mission planners expect NanoSail-D to return to Earth,meteor-style, in 70 to 120 days.

If this works (and there is little doubt that it will), NanoSail-Dcould pave the way for a future clean-up of low-Earth orbit. Drag sails mightbecome standard issue on future satellites. When a satellite's mission ends, itwould deploy the sail and return to Earth via aerodynamic drag, harmlesslydisintegrating in the atmosphere before it reaches the ground. Experts agreethat something like this is required to prevent an exponential buildup of spacejunk around Earth.

Alhorn and colleagues will be monitoring NanoSail-D in the months aheadto see how its orbit decays. They'd also like to measure the pressure ofsunlight on the sail, although atmospheric drag could overwhelm that effect.

No matter what happens next, NanoSail-D has already made history: Ithas demonstrated an elegant and inexpensive method for deploying sails andbecome the first sail to orbit Earth. Eventually, the team will diagnose thesail’s reluctance to leave FASTSAT—"and then we'll be batting athousand," says Alhorn.

A follow-up story on Science@NASA will explain how sky watchers cantrack and photograph NanoSail-D before it returns to Earth. Stay tuned for"Solar Sail Flares."

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