The Planetary Society's oft-delayed Cosmos 1 solar sail is finally on the verge of launching on its test mission to validate the practicality of a revolutionary propulsion method that relies on sunlight instead of chemical rocket fuels.

An artist's concept of the solar sail. Credit: Babakin Space Center, The Planetary Society

Launched aboard a converted Volna ballistic missile from a nuclear submarine, the solar sail will reach a circular polar orbit some 800 kilometers high within 20 minutes. The three-stage Volna will place the 220-pound spacecraft on a suborbital trajectory, and an apogee kick motor will fire to circularize the orbit.

Officials reported last week that the launch will have to be delayed from earlier targets in March, but project director Louis Friedman said there is currently nothing standing in the way of a launch some time in April.

"We now project that Cosmos 1 will launch in April. The testing on the flight spacecraft, but some corrections and fixes have been required," Friedman reported in an update on the Planetary Society website.

The submarine will set sail from the naval base at Severmorsk, near the port city of Murmansk in far northern Russia. It will reach the launch point in the Barents Sea about three days later.

Plans call for Cosmos 1 to deploy its eight 15-meter sail blades several days into the mission. Later, controllers will shift the blades to allow sunlight pressure to begin to slowly accelerate the craft so it will climb to a higher orbit. It is expected the blade material and spacecraft systems will begin to degrade within a few months' time, so the mission is only planned to be conducted for a short period.

Ground stations in the United States, Russia, and the Czech Republic will keep tabs on the progress of the mission using imaging cameras to take pictures of the sails, along with a variety of engineering data to determine the health of the systems and to operate the solar sails by orienting them toward the Sun.

The Planetary Society and partner Cosmos Studios kicked off the Cosmos 1 program in 2000, and it has since been plagued by a number of delays and setbacks. A botched suborbital test flight in July 2001 suffered a separation failure that prevented the deployment of two small blades that were designed to test the validity of the mission concept.

Cosmos 1 will be launched from a submarine aboard a Volna rocket. Credit: Michael Carroll, The Planetary Society

The launch was originally scheduled for late 2001, but after the failed suborbital attempt and a series of testing setbacks and delivery delays, the flight was postponed for almost four years until now. Other issues included concerns over the Volna rocket, which launched on a second doomed mission in 2002 that ended much like the solar sail test the year before.

The Volna rocket underwent a series of separation tests in a 60-meter drop tower in Russia in 2003 to certify the booster for flight. However, Cosmos 1 suffered from other issues in its radio and electronic systems, which required much more substantial testing than officials had anticipated. The S-band radio instrument was not delivered until 2004 -- well over a year behind schedule.

Electronic systems were finally deemed to be qualified for flight last August. Final assembly of the satellite then began at the NPO Lavochkin factory in Russia. Officials finally announced a launch date for March in November as final tests were well underway.

"With the spacecraft now built and undergoing its final checkout, we are ready to set out a launch date," said Planetary Society Executive Director Louis Friedman. "The precedent-setting development of the first solar sail has had its ups and downs like a roller coaster ride, but now the real excitement begins."

Last week Friedman announced an additional delay of the mission due to a few unexpected developments late in the assembly and testing process. At this point, the flight spacecraft has been almost fully integrated. The schedule calls for the attachment of the ultra-thin sail blades within the next few weeks when the craft goes into the vacuum chamber for leak checks.

The technology and components of a solar sail have never been tested before, despite the great promise scientists and engineers have their ability to significantly improve travel times across great distances in space. If officials can determine that the satellite's orbit grows larger by any amount due to the operation of the solar sail, the mission will be deemed a success.

Friedman says his two biggest worries about the flight are the interaction between individual systems, as well as the stability of the fragile solar sail blade material as it flies through space. The eight blades are made from a reinforced Mylar one-quarter the thickness of a trash bag.

Funding for Cosmos 1 comes mainly from Cosmos Studios, a new media company emphasizing science and space founded by Ann Druyan, wife of the famous late scientist Carl Sagan. Many private donations from Planetary Society members have also greatly contributed to the mission.