LightSail® is a citizen-funded project of the Planetary Society to test solar sailing technology for CubeSats. Solar sailing uses reflective sails to harness the momentum of sunlight for propulsion. CubeSats are small, standardized satellites that hitch rides to space with larger payloads. 1)
CubeSats have revolutionized the space industry, thanks in part to the continuing trend of technology miniaturization. They use off-the-shelf hardware and can be manufactured rapidly, which makes them an economical alternative to large satellites.
CubeSats can test new technologies that aren't ready full-fledged missions, or fly single science instruments to measure very specific things like Arctic sea ice loss. Educators use CubeSats to give students real-world space experience at a fraction of the cost of large missions. Companies like Planet deploy swarms of CubeSats to blanket the Earth with daily imagery, while SpaceX hopes to use CubeSats to deploy a global broadband Internet constellation.
One disadvantage to CubeSats is that they typically lack propulsion, which limits their range of applications. LightSail will demonstrate the viability of using solar sailing for CubeSats.
The idea of solar sailing dates back to the 1600s, but the story of LightSail begins in the late 1970s, when NASA considered flying a giant solar sail to Halley's comet, and Planetary Society co-founder Carl Sagan promoted the concept during an appearance on The Tonight Show with Johnny Carson. The project was ultimately cancelled.
The Planetary Society was founded in 1980. Scientific collaboration between the Society and Russia led to the creation of Cosmos 1, a solar sail spacecraft launched aboard a repurposed ICBM. Both the partial test (2001) and full flight (2005) of Cosmos 1 failed due to problems with the Russian rocket.
Figure 1: Cosmos 1, The Planetary Society's first solar sail, was lost due to a Russian rocket failure in 2005 (image credit: The Planetary Society)
The first successful solar sail finally took flight in 2010, when Japan's IKAROS spacecraft was deployed from a Venus-bound probe named Akatsuki.
NASA has investigated using solar sails to de-orbit CubeSats with atmospheric drag. The first attempt, Nanosail-D, was lost during a Falcon 1 rocket failure in 2008. A follow-on mission named Nanosail-D2 was successful in 2010.
The Planetary Society's LightSail program, initiated in 2009, aimed to construct a CubeSat similar to Nanosail-D that would demonstrate true solar sailing. LightSail 1 was awarded a slot aboard an Atlas V launch in 2015, but the target orbit was not high enough for solar sailing thrust to overcome atmospheric drag. We accepted the free ride anyway, and flew LightSail-1 as a shakedown cruise to test the spacecraft's sail deployment mechanism. The mission was a success, and we downloaded a selfie of the spacecraft's sails in space.
Figure 2: This image was captured by a camera aboard LightSail 1 on June 8, 2015, shortly after solar sail deployment. It was color-corrected by Dan Slater to remove the camera's artificial purplish tint based on ground test images, and is a closer approximation to what the human eye would see (image credit: The Planetary Society)
LightSail-2 Mission Details
LightSail-2 will be enclosed within Prox-1, a Georgia Tech student-built spacecraft the size of a small washing machine. Both spacecraft will be attached to the upper stage of SpaceX's Falcon Heavy rocket, which is launching a payload for the U.S. Air Force called STP-2 (Space Test Program-2).
Prox-1 will detach from the Falcon Heavy into a circular, 720-kilometer-high orbit, and then deploy LightSail-2.
Figure 3: Prox-1 deploys the LightSail-2 spacecraft in Earth orbit (image credit: Josh Spradling / The Planetary Society)
After a checkout period, LightSail-2 opens its hinged solar arrays and unrolls four, tape measure-like sail booms, which pull the spacecraft's four triangular sails from storage. The sail deployment sequence takes roughly two minutes.
LightSail-2 will then begin swinging its solar sails into and away from the Sun each orbit, giving the spacecraft enough thrust to raise its orbit (technically, the orbit semi-major axis) by several hundred meters per day. This portion of the mission will last one month.
Figure 4: LightSail-2 orbital raising. LightSail-2 makes 90-degree turns to gradually raise the semi-major axis of its orbit by several hundred meters per day (image credit: Josh Spradling / The Planetary Society)
LightSail-2's attitude control system does not have the precision to maintain a circular orbit. Therefore, as one side of the spacecraft's orbit rises, the other side will dip lower, until atmospheric drag overcomes the forces of solar sailing, ending the primary mission. The spacecraft will remain in orbit up to a year before succumbing to destructive reentry.
Though LightSail-2 cannot raise its orbit indefinitely, this would be possible by angling the sail more precisely during each orbit.
The LightSail project started in 2009. The spacecraft was built by Stellar Exploration, Inc. The lead contractor for integration and testing is Ecliptic Enterprises Corporation, with testing, storage and ground support provided by Cal Poly San Luis Obispo. Planetary Society Chief Scientist Bruce Betts serves as the LightSail program manager. The project manager and mission manager is Purdue University's David Spencer.
The Planetary Society's LightSail-2 spacecraft is ready to embark on a challenging mission to demonstrate the power of sunlight for propulsion. with a mass of just 5 kg, the 3U CubeSat is scheduled to launch in June 2019 aboard a SpaceX Falcon Heavy rocket from Kennedy Space Center, Florida. Once in space, LightSail-2 will deploy a boxing ring-sized solar sail and attempt to raise its orbit using the gentle push from solar photons. 2)
It's the culmination of a 10-year project with an origin story linked to the 3 scientist-engineers who founded The Planetary Society in 1980.
"Forty years ago, my professor Carl Sagan shared his dream of using solar sail spacecraft to explore the cosmos. The Planetary Society is realizing the dream," said Planetary Society CEO Bill Nye. "Thousands of people from all over the world came together and supported this mission. We couldn't have done it without them. Carl Sagan, and his colleagues Bruce Murray and Louis Friedman, created our organization to empower people everywhere to advance space science and exploration. We are go for launch!"
If successful, LightSail-2 will become the first spacecraft to raise its orbit around the Earth using sunlight. While light has no mass, it has momentum that can be transferred to other objects. A solar sail harnesses this momentum for propulsion. LightSail-2 will demonstrate the application of solar sailing for CubeSats, small, standardized spacecraft that have made spaceflight more affordable for academics, government organizations, and private institutions.
Figure 5: The deployed LightSail-2 spacecraft (image credit: Josh Spradling / The Planetary Society)
The Planetary Society's solar sailing CubeSat has successfully shipped to the Air Force Research Laboratory (AFRL) in Albuquerque, New Mexico, where it was integrated with Prox-1, the Georgia Tech-designed spacecraft that will carry LightSail-2 to orbit aboard a SpaceX Falcon Heavy rocket. The joining of the two spacecraft marked a key mission milestone, as LightSail-2 passed from its Planetary Society-led team's hands for what is expected to be the last time. 3)
Figure 6: LightSail-2 sits inside its P-POD at the Cal Poly San Luis Obispo CubeSat clean room on 6 May 2019 prior to final shipment to the Air Force Research Laboratory (AFRL) in Albuquerque, New Mexico (image credit: Ryan Nugent / Cal Poly SLO / The Planetary Society)
Table 1: LightSal-2 parameters
Launch: LightSail-2 is a secondary payload on the STP-2 rideshare mission of USAF, launched on 25 June 2019 (06:30 UTC) aboard a SpaceX Falcon Heavy launch vehicle from Launch Complex 39A at NASA’s Kennedy Space Center. The STP-2 payload includes six FormoSat-7/COSMIC-2 satellites (primary payload), developed by NOAA and Taiwan’s National Space Organization to collect GPS radio occultation data for weather forecasting. The mission also carries several NASA technology demonstrations. The STP-2 mission is led by the Air Force Space Command’s Space and Missile Systems Center (SMC). The total IPS (Integrated Payload Stack) has a mass of 3700 kg. 4)
The secondary payloads on this flight are:
• DSX (Demonstration and Science Experiments) mission of AFRL
• GPIM (Green Propellant Infusion Mission), a demonstration minisatellite of NASA (~180 kg). 5)
• FalconSat-7, a 3U CubeSat mission developed by the Cadets of the U.S. Air Force Academy (USAFA) at Colorado Springs, CO.
• NPSat-1 (Naval Postgraduate School Satellite-1) of the Naval Postgraduate School, Monterey, CA. A microsatellite of 86 kg.
• OCULUS-ASR (OCULUS-Attitude and Shape Recognition), a microsatellite (70 kg) of MTU (Michigan Technological University), Houghton, MI, USA.
• Prox-1, a microsatellite (71 kg) of SSDL (Space Systems Design Laboratory) at Georgia Tech.
• LightSail-2 of the Planetary Society, a nanosatellite (3U CubeSat, 5 kg) will be deployed from the parent satellite Prox-1.
• ARMADILLO of UTA (University of Texas at Austin), a nanosatellite (3U CubeSat) of ~ 4 kg.
• E-TBEx (Enhanced Tandem Beacon Experiment), a tandem pair (3U CubeSats) of SRI International.
• TEPCE (Tether Electrodynamics Propulsion CubeSat Experiment), a 3U CubeSat (3 kg) of NPS (Naval Postgraduate School).
• CP-9 , a joint CP-9/StangSat experiment, which is a collaboration between PolySat at Cal Poly and the Merritt Island High School, and is sponsored by the NASA LSP (Launch Services Program). CP-9 is a 2U CubeSat while StangSat is a 1U CubeSat.
• PSat-2 (ParkinsonSAT), a student built 1.5U CubeSat of USNA (US Naval Academy) with a mass of 2 kg.
• OTB-1 (Orbital Test Bed-1) a minisatellite of SSTL (based on the SSTL-150 bus, 138 kg). One of the hosted payloads is NASA's DSAC (Deep Space Atomic Clock), a technology demonstration mission with the goal to validate a miniaturized, ultra-precise mercury-ion atomic clock that is 100 times more stable than today’s best navigation clocks.
Figure 7: SpaceX's Falcon Heavy rocket, carrying LightSail-2 and 23 other spacecraft for the U.S. Air Force's STP-2 mission, lifts off from Kennedy Space Center on 25 June 2019 at 06:30 UTC (image credit: NASA)
During its ride to orbit, LightSail-2 was tucked safely inside its Prox-1 carrier 3U CubeSat. The Falcon Heavy upper stage's payload stack released Prox-1 about an hour and 20 minutes after liftoff, at an altitude of roughly 720 km. Prox-1 will house LightSail-2 for 1 week, allowing time for other vehicles released into the same orbit to drift apart so each can be identified individually. LightSail-2 deployment is set for 2 July. 6)
The STP-2 mission will be among the most challenging launches in SpaceX history with four separate upper-stage engine burns, three separate deployment orbits, a final propulsive passivation maneuver and a total mission duration of over six hours. It will demonstrate the capabilities of the Falcon Heavy launch vehicle and provide critical data supporting certification for future National Security Space Launch (NSSL) missions. In addition, [the USAF] will use this mission as a pathfinder for the [military’s systematic utilization of flight-proven] launch vehicle boosters.
The three orbits of the STP-2 mission for spacecraft deployment are:
1) The small secondary CubeSat satellites will be deployed into an elliptical orbit of ~300 x 860 km, inclination of ~28º. These are: OCULUS-ASR, TEPCE, E-TBEx, FalconSat-7, ARMADILLO, PSAT-2, BRICSAT, and CP-9/StangSat.
2) The second deployment batch of the STP-2 mission will occur at a circular altitude of 720 km and an inclination of 24º.
- Deployment of LightSail-2, Prox-1, and NPSat-1
- Deployment of OTB-1 with NASA's DSAC and GPIM
- The six FormoSat-7/COSMIC-2 satellites will be deployed into the initial circular parking orbit of 720 km. Eventually, they will be positioned in a low inclination orbit at a nominal altitude of ~520-550 km with an inclination of 24º (using their propulsion system). Through constellation deployment, they will be placed into 6 orbital planes with 60º separation.
3) The third and final deployment will be the Air Force Research Lab's DSX spacecraft as well as the ballast, which will be delivered to an elliptical MEO (Medium Earth Orbit) with a perigee of 6000 km and an apogee of 12000 km, inclination of 43º.
1) ”LightSail - Flight by light for CubeSats,” The Planetary Society, 2019, URL: http://www.planetary.org/explore/projects/lightsail-solar-sailing/
2) Jason Davis, ”LightSail-2 set to launch next month aboard SpaceX Falcon Heavy rocket,” The Planatary Society, 13 May 2019, URL: http://www.planetary.org/blogs/jason-davis/lightsail-2-set-to-launch.html
3) Jason Davis, ”LightSail-2 Integrated with Prox-1 Carrier Spacecraft,” The Planetary Society, 9 May 2019, URL: http://www.planetary.org/blogs/jason-davis/lightsail-2-integrated-prox-1.html
Stephen Clark, ”Falcon Heavy launches on military-led rideshare
mission, boat catches fairing,” Spaceflight Now, 25 June 2019,
5) “GPIM Spacecraft to Validate Use of 'Green' Propellant,” NASA, Aug. 19, 2014, URL: http://www.nasa.gov/content/gpim-spacecraft-to-validate-use-of-green-propellant/
6) Jason Davis, ”LightSail 2 Has Launched!,” The Planetary Society, 25 June 2019, URL: http://www.planetary.org/blogs/jason-davis/lightsail-2-has-launched.html?
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).