LightSail2 Update – Sails Unfurled

In an earlier post, we told you about the Planetary Society’s project called LightSail2. It’s a crowdfunded project to launch a CubeSat satellite into space and maneuver it using solar sails. Solar sails are large reflective sheets against which photons from the sun bounce. Photons have no mass but they do have momentum. For that reason, when a photon bounces onto and off of the reflective solar sail, it gives the sail an infinitesimal nudge.

The nudge gives the sail, and the small satellite attached to it, a small amount of momentum. Over time, the momentum from each nudge builds up and, with no air resistance in space, the satellite can gradually accelerate to high speeds.

LightSail2 was launched onboard a Space-X Falcon Heavy rocket on June 25. Since then, it has been in orbit while tests took place on its telemetry, computer software and equipment. The testing has taken longer than expected, The mission team uploaded a software patch that improved the operation of the torque rods that keep the CubeSat stable. They team also placed LightSail2’s attitude into solar sailing mode and analyzed its telemetry to test performance.

The mission team also updated the software controlling the onboard sun sensors which track the sun’s position during orbit. These sensors send the data needed to adjust the sails to the best angle to capture the sun’s energy. The main concern during all this testing was to make sure that the attitude control system was optimized for solar sailing, ensuring the longest possible orbital life for the satellite.

The testing was completed on July 24, at which time the mission team deployed the sails. Bill Nye, president of the Planetary Society, declared, with his usual enthusiasm, “yesterday, we successfully set sail on beams of sunlight”. Sailing has always seemed romantic. We seem to be inspired by the idea of traveling without expending effort or fuel, relying on nature to take us where we’re going. Sailing gives us a sense of freedom, and even wonder, at the earth’s forces and how we can harmonize with them.

Over the next month or so, LightSail2 will go through a process called orbit raising. The satellite is in a comparatively low earth orbit. This means that the upper atmosphere still drags on it. The mission team needs to correct for this, otherwise the orbit would decay too soon and the spacecraft would burn up before it could complete its mission.

To compensate for this, LightSail2 needs to raise its orbit. It does this by turning its sails broadside to the sun once per orbit. The photons from the suns’ rays add a bit more momentum each time which will gradually raise LightSail2’s orbit to a more sustainable altitude. This process will take up the next month or so of its mission. This may seem like a glacial pace, but remember that no fuel is needed to do any of this.

Once LightSail2 is in its raised orbit, it will stay in a slow, gradual de-orbit for about a year. Then, its orbit will have decayed to the point where it burns up on re-entry to the Earth’s atmosphere. During this one year orbital period, the mission team will prove the solar sailing concept by putting LightSail2 through its planned maneuvers.

Solar sailing is an important idea for more than merely the romantic, natural freedom it invokes from the Age of Sail. NASA plans to use the solar sailing technique to send a CubeSat called NEA Scout to a near-Earth asteroid. NEA Scout will be carried to the moon onboard the first Space Launch system flight. From lunar orbit, it will unfurl its sails and head for the asteroid. Solar sailing also has potential for traveling into deep space. Awkward and slow as it may seem, it has the potential to carry a payload to a nearby star. The reason is that with solar sailing, the acceleration is continuous and uses no fuel. Over time, enormous velocities could be achieved using this technique, Like the tortoise and the hare, slow and steady wins the space race.

Space exploration has another value. As we talked about last week about the moon landing, it gives us quests we can share as stories. We need our hero’s journeys. Despite its impressive sails, LightSail2 is only the size of a loaf of bread.

Yet, this plucky little explorer may be showing us the way to the stars.

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