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LightSail Falls Silent; Battery Glitch Suspected

Posted by Jason Davis

04-06-2015 17:45 CDT

Topics: LightSail

The LightSail test spacecraft has fallen silent for a second time, less than a day after completing what appeared to be a successful solar panel deployment. Mission managers believe the CubeSat's batteries are in a safe mode-like condition designed to protect the electronics until power levels are safe for operations. 

In an e-mail summary sent this afternoon, mission manager David Spencer said before contact was lost, LightSail’s batteries did not appear to be drawing current from the solar arrays; nor were they properly shunting power to the spacecraft’s subsystems.

"Following solar panel deployment," he wrote, "it was noticed that all of the battery cells were drawing near zero current. This indicated that the batteries were likely in a fault condition stemming from the solar panel deployment event."

On the next ground station overflight, the team regained contact. But the battery situation remained unchanged, and the spacecraft appeared to have rebooted unexpectedly. "The flight team discussed the option of commanding an emergency solar sail deployment, Spencer said. "However, all ground testing of solar sail deployment had been performed under battery power, with all battery cells online and fully charged. It was considered to be doubtful that the sail deployment could be successfully completed without battery power (relying only upon direct input from the solar cells). The flight team decided to address the electrical power subsystem issue and approach solar sail deployment in a known state consistent with ground testing."

LightSail’s last automated telemetry chirps came in Wednesday at 4:40 p.m. EDT (20:40 UTC). The spacecraft then moved out of range for ten-and-a-half hours. When Thursday’s expected contact time arrived, LightSail was silent.

There were 11 ground station overflights today, but LightSail has yet to phone home. Commands were sent "in the blind" to activate the radio system, but there was no status change. The team opted not to command the spacecraft further until the situation is better understood. LightSail’s power system can enter a variety of failsafe conditions based on the behavior of the batteries. Engineers at Ecliptic Enterprises Corporation are working through a complex fault tree to determine the spacecraft's likely state, as well as options for moving forward.

If LightSail is suffering from a chronic undervoltage condition, help could arrive naturally, Spencer said. "The spacecraft orbit is in a geometry where eclipse occurs roughly 2100 seconds each orbit.  This is near the maximum eclipse duration that LightSail-A will experience during the mission. Over the next couple of weeks, the orbit will precess to a full-sun condition, where the entire orbit is sunlit."

When contact with LightSail is reestablished, the sail deployment sequence will likely be triggered as soon as battery levels are heathy enough to proceed.

LightSail spreads its sails

Justin Foley

LightSail spreads its sails
The Planetary Society's LightSail spacecraft sits on its deployment table at Cal Poly San Luis Obispo following a day-in-the-life test on Sept. 23, 2014.
See other posts from June 2015


Or read more blog entries about: LightSail


Tony Fisk: 06/04/2015 10:30 CDT

While it *would* be nice to hear that sails were successfully deployed, picking up on this sort of thing is the real aim of the mission.

sepiae: 06/05/2015 02:05 CDT

Concur with Tony Fisk; I sometimes forget that this is what the mission about - see what's not, or what might not be working properly. No learning without fails. It's early in the morning here in Europe, and I'm trying to twist my mind enough to imagine an orbit that has LightSail be bathed in sunlight without interruption, unless it's buzzarding above a pole... I might get a lil more lucid later on, just in case I won't, could there be a note on this, perhaps a graphic for morning-dummies like me...? This is some thriller... :)

sepiae: 06/05/2015 02:16 CDT

oooohh sepiae... Okay, no graphic necessary, but that's what mornings are like in Europe... Of course, I get it, the orbit, duh :) Anyway, actually the mission is even more successful than it would have been would everything work out perfectly. It's like LightSail's up there determined to demonstrate what *can* happen, paving the way for her sister next year. Thanks for the great updating, btw., it's utterly engaging.

Edgar: 06/05/2015 03:31 CDT

Hm, I still cannot see which way this orbit would ever be fully sunlit!?

pbarnrob: 06/05/2015 03:34 CDT

"If you never do anything, you'll never make a mistake!" --Rudolf Roy Show, AmHist, Tustin CA HS 1961 (as encouragement to go DO something!) G. Harry Stine, that old hairy-eared engineer, always griped at the risk-averse. 1. Build one, test it to destruction. 2. Build another, take it to the limits also. 3. If needed, do yet another with all those lessons-learned. You always learn much more from failures than successes. AND, the only dumb question is the one you DIDN'T ask ('cause you thought it'd sound dumb!)

Edgar: 06/05/2015 03:48 CDT

While this may be true for the engineer who has all material, methods and tools at his/her immediate disposal it is not at all a good advice for a space project. Mostly you only have one chance for a failure and that's it then. Don't tear such 'wisdom' out of its context!

odqstr2: 06/05/2015 05:34 CDT

From the stand point of a programmer, if I didn't want to know there were errors I wouldn't test. I'm always suspicious of projects that implement without any failures, from experience I've learned that it only means I've missed something. Keep testing, get and then learn from those failures, make it better. Best of luck!

Mark: 06/05/2015 05:37 CDT

And the award for most dramatic cubesat goes to...

PaulF: 06/05/2015 11:08 CDT

It is possible the arrays weren't quite tight against the cubesat body, and so one or more of the sails became partially unfolded during the vibrations of launch and wriggled out past the solar array, holding them partially open? That might explain the sun light the camera saw while still stowed. If some sail was then sticking out asymmetrically and causing an unbalanced solar or drag torque, that might also explain the increasing rotation rate after launch. Finally, if one or more sails had unfolded early on, then they might will have expanded outward when the solar arrays were deployed, and are now shading the solar arrays, causing the battery to drain without sufficient recharging.

robnsonm: 06/05/2015 05:32 CDT

I agree with odqstr2. If my program ran without errors the first time, I double checked since something was wrong. Keep up with the tests, you'll get it fixed. I am happy to be a part of something I can really feel close to. Thanks.

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