Planetary Society Declares Success as LightSail 2 Sails on Sunbeams


Rockets are great if you want to get someplace fast, but there’s something whimsical about sailing on a beam of light. The Planetary Society has declared its LightSail 2 mission a success after it did just that. The satellite deployed its solar ail last week, and now it has successfully maneuvered in space without the help of engines. 

The Planetary Society launched its spacecraft aboard a SpaceX Falcon Heavy rocket in late June, which carried numerous other spacecraft into space. It took a decade of development for the organization to get LightSail 2 ready, and individual donations from some 50,000 supporters funded almost all of the $7 million price tag. 

Last week, The Planetary Society announced the craft had successfully deployed its sail. That was a problem for the first version of the spacecraft, which suffered from communication issues when it headed to the edge of space in 2015. It never got its sail deployed before falling back into the atmosphere. However, that mission was never intended to actually use the sail. LightSail 2 was more ambitious from the start. 

A light sail uses a large reflective surface area to harness the thrust from photons hitting the sail. LightSail 2 has a surface area of almost 30 square meters (322 square feet), but the thrust is still tiny. The Planetary Society reports that LightSail 2 enjoys forward propulsion equal to the weight of a paperclip when its mylar sail is facing the sun. Over time, that small speed boost can build up in the vacuum of space. 

A rocket would obviously be able to accelerate much faster, but LightSail 2 doesn’t need to explode out of the starting gate. At the lowest point in its orbit (perigee) the sail points directly at the sun, adding a little more speed to its orbit. That pushes the top of the orbit (apogee) higher. The Planetary Society now confirms the probe has raised its orbit by 1.05 miles (1.7 kilometers) using only sunlight. 

The team will continue raising the probe’s orbit for about a month until the perigee drops into the atmosphere and generates enough drag to outweigh the solar sail thrust. During this time, scientists will work to refine the solar sail, particularly how the craft’s momentum wheel works to keep the sails pointed at the sun. 

The Planetary Society doesn’t have any current plans to build a third solar sail spacecraft. However, it will make its technology available to future exploration missions that may want to use solar sails.

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