As we near launch, let’s run through the Cosmos 1 sail mission again. The vehicle is privately funded (by Ann Druyan’s Cosmos Studios and The Planetary Society), and will be launched aboard a converted Russian ICBM. Once in orbit, the spacecraft will deploy eight mylar sails. The principle is straightforward: Photons have no mass but they do carry momentum. As solar photons strike the sail blades, Cosmos 1’s orbit should change, providing a test of solar sailing that can be measured from the ground. A later microwave beaming experiment may be able to measure the effect beamed propulsion has on the spacecraft, though the primary mission goal remains to test the principles of solar sailing by photons alone.

Launch is now scheduled for June 21 from a submerged Russian submarine in the Barents Sea. The mission will be controlled from the Lavochkin Association in Moscow and assisted by a project operations center at The Planetary Society’s headquarters in Pasadena. Everyone will be keeping a watchful eye on the Volna rocket — four years ago, a suborbital test flight meant to deploy two solar sail blades failed when the spacecraft was unable to separate from the booster.

Meanwhile, launch rehearsals have been in full gear, as reported by The Planetary Society’s Emily Lakdawalla on a mission weblog. You may remember Lakdawalla’s reporting from Darmstadt during the Huygens descent and landing. She should be equally readable here, well connected to the mission and with a fine ability to talk straight about technical subjects. Here she’s describing the mission sequence; she’s just been asked how long it will be before solar sailing is truly demonstrated:

When will you know if you have demonstrated the principle of solar sailing? I had to put the phone down and do some math on that one. If everything goes well with the commissioning of the spacecraft and the deployment of the blades on the 26th, they are going to start to use the sails to control the flight of the spacecraft on the 105th orbit, which happens on the 28th of June. By looking at data from the spacecraft’s accelerometer, Global Positioning System instrument, and from Doppler tracking of the spacecraft by Strategic Command, we hope to see the sailing effect within 1 to 10 days later. Sorry I can’t be more specific. Look at it this way: if we knew exactly how this mission was going to work, it wouldn’t be worth doing.

Which is how science is supposed to work. Name a mission in the last few years that hasn’t produced a surprise! Information on observing Cosmos 1 from the ground, assuming all goes well, is available here.