Jason Davis • October 27, 2017

Here's how engineers closed out LightSail 2 for flight

Last month, engineers reconfigured The Planetary Society's LightSail 2 spacecraft into its flight-ready state for what is likely to be the last time. It's a big milestone for the program; after years of effort dating back to 2009, work on the CubeSat is finally finished.

The procedure to button up LightSail is called closeout. The team sets the spacecraft's software to start the mission on the next boot, and physically secures all deployable structures including the antenna and solar panels.

LightSail 2 spent 2017 in a hurry-up-and-wait mode while launch dates remained fuzzy for SpaceX's Falcon Heavy rocket. The uncertainty provided an opportunity to perform more tests and tweaks, with the knowledge that the order to ship the spacecraft could come at any time.

Launch is currently scheduled for no earlier than April 30, 2018. But that could always change, based on the timing of one or possibly two Falcon Heavy flights ahead of the STP-2 mission for the U.S. Air Force, which will carry LightSail 2 and its partner spacecraft, Prox-1, as secondary payloads.

Josh Spradling / The Planetary Society

LightSail 2 and Prox-1

Prox-1 deploys the LightSail 2 spacecraft in Earth orbit.

LightSail's final path to launch starts at Cal Poly San Luis Obispo, with integration into a spring-loaded deployer called a P-POD. Once LightSail 2 is inside the P-POD, its battery can't be charged, so the team is currently storing the spacecraft at Ecliptic Enterprises Corporation in Pasadena, where its power levels can be monitored and occasionally topped off. After P-POD integration, LightSail 2 ships to the Air Force Research Laboratory in Albuquerque, New Mexico, for installation aboard Prox-1.

In the meantime, engineers formally closed out the spacecraft. Roughly speaking, closeout is the last time you fiddle with a spacecraft before launch. It's sort of like walking through your house one last time before vacation; you might set the thermostat for your absence, turn on the alarm and lock the doors. At that point, you aren't expecting to go back inside.

Closeouts must be done carefully, and not just because they determine whether things will go well on launch day. Case in point: NASA's TDRS-M satellite recently had a nasty run-in with a crane during closeout, delaying the mission.

At just 33 steps long, the LightSail 2 closeout was far from dramatic, but each procedure was carefully documented by Ecliptic engineer Stephanie Wong. Here's a condensed version of the closeout procedure, with explanations and photos showing how LightSail 2 was buttoned up for flight.

Verify LS2 has been flashed before antenna is stowed.

"Flashing" the software clears all files on the flight computer, such as old telemetry logs and pictures taken during testing. It's like reinstalling the operating system on your computer, giving it a clean, out-of-the-box appearance. There's even a screenshot taken to verify the correct software version was installed.

LightSail 2 software verification

Rotate LS2 with the -Y panel facing up. Remove all internal blue film. Inspect external -Y panel. Inspect internal -Y panel. Restrain panel.

These steps are repeated for all four deployable solar panels, which comprise the X and Y axes of the spacecraft. The blue film protects the solar panels from damage the way new smartphones come wrapped in clear stickers and plastic. At this point, everything on LightSail 2 has been tested as working, so the closeout's main purpose is physically documenting how the spacecraft looked before flight, while making sure nothing is obviously awry.