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Contact! LightSail Phones Home after 8-Day Silence

Posted by Jason Davis

30-05-2015 23:08 CDT

Topics: mission status, LightSail

The Planetary Society’s LightSail test spacecraft reported for duty this afternoon, heralding the end of an uneasy silence caused by a suspected software glitch. At 5:21 p.m. EDT (21:21 UTC), an automated radio chirp was received and decoded at the spacecraft's Cal Poly San Luis Obispo ground station. Another came in eight minutes later at 5:29 p.m. The real-time clock on board the spacecraft, which does not reset after a software reboot, read 908,125 seconds—approximately ten-and-a-half days since LightSail’s May 20 launch.

You can see LightSail's phone-home packet here

"Based upon the on-board timers contained within the beacon (and comparing them to beacons following deployment), it appears that a reboot occurred within the past day," wrote Georgia Tech professor David Spencer, LightSail’s mission manager. "Due to uncertainty in the orbit state (TLEs), our ability to reliably track the spacecraft is marginal at this point. Cal Poly is coordinating with international colleagues to arrange their support in acquiring beacon telemetry," he said.

LightSail is not out of the woods yet. Its exact position remains fuzzy, complicating two-way communication. Today’s contact marks the first time engineers can compare the spacecraft’s signal with orbital models called two-line element sets, or TLEs. There are ten TLEs associated with the ULTRASat fleet that joined LightSail for a free ride to orbit courtesy of a United Launch Alliance Altas V rocket. Which TLE represents LightSail is unknown, but each radio chirp's doppler shift helps narrow down the possibilities.

The ten ULTRASat spacecraft have drifted into two groups. At the time the first signal was received at Cal Poly, all ten spacecraft appeared to be in range—no help, from a visual standpoint. But when the second signal came in eight minutes later, only the trailing group appeared to be close enough. (This is only a rough estimation; a full simulation by Georgia Tech is pending.)

A first look at the new LightSail data shows the rotation rate has increased from -7, -0.1 and -0.3 degrees per second about the X, Y, and Z axes to 10.8, -7.3 and 2.9 degrees. The cause for the tumbling uptick currently unknown, but with the spacecraft's attitude control system offline, sail deployment is likely to be a wild ride.

The next ground station pass is scheduled for 5:30 a.m. EDT, when the ULTRASat cadre passes within range of Georgia Tech. As of today, the patch intended to fix LightSail's file write vulnerability is still being tested. In order to buy more time, additional reboots could be scheduled. However, having dodged one close call, the team wants to initiate sail deployment as soon as possible. A plan of action is still being assembled, with discussions likely to last into the night.

In the meantime, all of us at The Planetary Society are cheering the good news. Many of you are, too, and we're thankful for the support. We'll keep you updated as more news develops.

See other posts from May 2015


Or read more blog entries about: mission status, LightSail


Starfire: 05/31/2015 05:15 CDT

All that engineering and no watchdog timer, *Facepalm*

Cyrus: 05/31/2015 09:47 CDT


G_Marcus: 05/31/2015 10:14 CDT

Wonder why the ACS is off would think that a reboot would bring up all essential system functionality, particularly attitude control as so much else hinges on it....

CharlesHouston: 05/31/2015 11:32 CDT

The Air Force has some funny rules about releasing some TLEs - for instance the DMSP orbits are "classified" as "For Official Use Only" or FOUO. I suspect that the objects deployed from that launch (since they also do not appear in the JSpOC catalog) are also FOUO. Can you comment? Can you release TLEs for those objects?

cassowary: 05/31/2015 11:34 CDT

If it's bugs they wanted, it's bugs they're getting. This whole thing is going wahooni-shaped. But true to our history, the Planetary Society is not going to give up! It looks like this is going to be a nail-biting scrap from start to finish, but I believe Lightsail has a significant role to play in not just space exploration, but human history. Solar sailing is the key that will unlock the solar system, and possibly even beyond. There is a REASON that people have been fighting to fly this mission for nearly 40 years. I am proud to have played my little part in making it happen, and I am confidentifies that if it IS possible to fly this mission successfully (which I believe it is) that the Lightsail team will make it happen GO Lightsail! GO Planetary Society!

DaveMan50: 05/31/2015 12:28 CDT

Kids these days have no idea what a watch-dog circuit is or for.

Tomas : 05/31/2015 01:23 CDT

Answers to DaveMan50 - Lightsail is equipped with a hardware watchdog timer but it has been wired incorrectly, so it is ineffective (it has been reported)

Jody: 05/31/2015 01:54 CDT

G_Marcus, the ACS problem was documented here, It is a software bug, no number of reboots will help. The fact that this unit was packed for launch already when the bug was found is unfortunate, but it happens.

Tim R: 05/31/2015 02:50 CDT

Incredible great news! Not out of the woods but there is a chance.

Bob Ware: 05/31/2015 06:22 CDT

Back from mapping Martian surface features... What great news to see! Hopefully a full recovery can be made. If the tumble can't be stopped can they sails still be deployed at the current tumble rate?

tom hancock: 05/31/2015 10:46 CDT

A guess would be insufficient systems engineering and IV&V. Experiences like this are how organizations grow. Consider seeking out systems engineering and IV&V experts before your next flight. Bet many would help. Great mission, good news on recontact! Cheers!

Beacon: 06/01/2015 10:53 CDT

Carl Sagan reset the satellite from heaven!

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