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LightSail Test Mission Ends with Fiery Reentry

Posted By Jason Davis

15-06-2015 14:09 CDT

Topics: pretty pictures, LightSail

The LightSail test mission is officially over. Following a 25-day stay in low-Earth orbit, the spacecraft tumbled back into Earth’s atmosphere Sunday afternoon. Orbital models show reentry likely occurred around 1:23 p.m. EDT (17:23 UTC), give or take 10 minutes, near the South Atlantic Ocean. 

LightSail’s last week in space was a microcosm of its six-year history, bookended by exasperation and triumph. A complete image of the spacecraft’s solar sails was downloaded on June 9, confirming the mission’s primary objective of sail deployment had been met. But before engineers could get a picture from the opposite-side cameras, LightSail’s radio began transmitting a continuous, nonsensical signal, and the spacecraft stopped responding to commands.

LightSail 1 with solar sails deployed

The Planetary Society

LightSail 1 with solar sails deployed
LightSail 1 captured this image of its deployed solar sails in Earth orbit on June 8, 2015.

The last time LightSail checked in was Wednesday, June 10 at 11:29 p.m. EDT. The corresponding beacon packet, which turned out to be the mission's last, displayed a real-time clock value of 1,837,416 seconds—21 days since launch on May 20. The gyroscopes, which were able to capture snapshots of the spacecraft’s tumble rate after every reboot, showed LightSail tumbling at 6.7, 2.4, and 0.3 degrees per second about its X, Y and Z axes. The Z-axis runs lengthwise through the oblong CubeSat; if LightSail were a gigantic top with its sails parallel to the floor, it was hardly spinning at all.

The day after sail deployment on June 8, LightSail’s rotational rate was a leisurely 116 seconds, according to observers using a wide-field survey telescope in Russia. That changed as the spacecraft dipped deeper into the atmosphere. By June 11, the rate had sped up to 36 seconds. On the day before reentry, it was 21 seconds.

On Sunday, Cal Poly’s Justin Foley heard from LightSail on its final ground station pass of the day, which began at 12:52 p.m. EDT. It was overflight number 223, and it would be the last time the spacecraft would phone home—even though it wasn't much of a conversation, with LightSail continuing to speak in gibberish. The signals in Justin’s waterfall spectrum shift left to right like a wailing ambulance changing its pitch as it speeds by stopped traffic.

And then there was nothing to do but wait. LightSail’s orbit only brought it within range of its U.S. ground stations early in the day. Ted Molczan of SatObs made the first end-of-mission pronouncement Sunday afternoon, calling time of death at 1:23 p.m. EDT (17:23 UTC), give or take 10 minutes in either direction. His prediction was bolstered by Justin’s observation that LightSail was running 45 seconds early. Further evidence in favor of Ted's numbers came Monday when the Joint Space Operations Center issued a new set of orbital elements. Of the reentry, Ted wrote: 

"Allowing the GMAT propagation to continue to decay revealed that it would have reached the altitude at which decaying objects typically become self-luminous (96 km) on Jun 14 near 17:22 UTC, and would have passed through the typical altitude of "main-break-up" (78 km) near 17:23 UTC. Given its low mass, I doubt it could have survived much longer. If this is correct, then it survived less than half an hour after the Cal Poly pass."

Self-luminous! LightSail was no longer just a reflective object in Earth orbit; it was now glowing on its own amidst a ball of superheated plasma that formed when air molecules in the solar sail’s path couldn’t get out of the way fast enough.

So it was over. Or was it? Late Sunday night from Germany, radio observer Mike Rupprecht posted a screenshot showing what could have been those solid double lines from LightSail’s anomalous radio system, barely visible above the background noise. 

If you plug the spacecraft’s final orbital elements into modeling software, you get an altitude of -53.6 kilometers at 01:39 UTC. In other words, the spacecraft should no longer have been a spacecraft. But it’s fun to imagine a scenario in which LightSail’s solar sails snapped cleanly away as the CubeSat reentered, allowing the avionics and radio systems to skirt around the Earth for a few more orbits. One final act of defiance, so to speak.

Whatever actually happened, LightSail—the test unit, anyway—is no more. The vast list of lessons learned must now be applied to the second mission, a full-fledged solar sailing demonstration slated for late 2016. There will be more stories to tell as engineers prepare the spacecraft for launch. We'll also start focusing on the tale of Prox-1, LightSail’s student-built partner vehicle. And perhaps most importantly, there's the matter of LightSail's ride to orbit: SpaceX's yet-to-be-built Falcon Heavy rocket.

The quest for flight by light continues.

SpaceX launch pad 39A

Jason Davis / The Planetary Society

SpaceX launch pad 39A
SpaceX is overhauling Kennedy Space Center's pad 39A, which was formerly used to launch the Saturn V and space shuttle, for the Falcon Heavy rocket system. The company's integration hangar is on the left at the bottom of the pad ramp. The Falcon Heavy's second flight, currently scheduled for 2016, will carry the Prox-1 and LightSail spacecraft as secondary payloads.

The high-resolution panorama of pad 39A is available here.

See other posts from June 2015


Read more blog entries about: pretty pictures, LightSail


Chris: 06/15/2015 03:23 CDT

What a fantastic mission, really looking forward to the real deal. I understand it wasn't quite possible this time, but it seems like tensioning the sails would have been a valuable test, as there is the possibility of tearing or something. Will that level of deployment (90%? 95%?) be acceptable for LightSail B?

fizzer: 06/16/2015 03:37 CDT

I speculate the sails are attached and the booms are flexible and as the craft hits the atmosphere it spins off the excess speed like a leaf in the wind and will just bounce around until it flutters down on some unsuspecting bystander. I'd like to think it is totally recoverable like that. If it were to stow its tray table it may very well burn up. Can we use the brass motor boom drive gears (once used) as a basic gyro??

sepiae: 06/16/2015 04:21 CDT

So LightSail kept it Hichcockian until the very last moment... Spectacular till the end. Every time a communication reading is called gibberish, the sensational part of me wonders..., perhaps another wow-signal...? :) But everything about this, even without such funny-notions, was spectacular enough :)

Bob Ware: 06/17/2015 04:05 CDT

This was a major success. This test bed did it's job. Flight Test 2 will be the next great step based upon what we learned from this test bed mission.

Planetguy_Bln: 06/18/2015 02:12 CDT

I think it was a nice job done by the LightSail mission. However what slightly bugs me is that no one mentioned that JAXA already has performed the successful IKAROS mission ( That was a interplanetary solar sail flying to Venus and showed for example techniques to steer a solar sail. It was mainly done by students and built on a very low budget. It doesn't diminish the success of LightSail to acknowledge what has been done before and went far beyond Earth orbit.

dougforworldsexplr: 06/22/2015 11:54 CDT

I am glad Lightsail1 turned out quite well and many people in the Planetary Society and everyone else involved deserves congratulations. However there is one other mission that The Planetary Society has tried once or twice but without success that in my opinion would be just as inspiring when it works. This is to use a microphone on a spacecraft to get sounds from Mars or maybe some other body where there is an atmosphere. Is it possible The Planetary Society will try this again in one of the upcoming American, European or other Mars landers or rovers so we can not only see how it looks but also hear how it sounds on Mars or possibly other worlds?

steve: 06/25/2015 08:25 CDT

speaking of past missions that should be tried again; what about the Mars Balloon project? I thought that was quiet innovative and would return a lot of science.

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