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, each with a mass of 280 kg), 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.
• BRICSAT-2, a student built 1.5U CubeSat of USNA (US Naval Academy) to demonstrate a µCAT electric propulsion system and carry a ham radio payload.
• OTB-1 (Orbital Test Bed-1) a minisatellite developed by SSTL (based on the SSTL-150 bus, 138 kg) and owned by General Atomics' Electromagnetic Systems Group (GA-EMS) of San Diego. 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)
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.
Status of LightSail-2 mission
• July 31, 2019: Years of computer simulations. Countless ground tests. They've all led up to now. The Planetary Society's crowdfunded LightSail-2 spacecraft is successfully raising its orbit solely on the power of sunlight. 6)
- Since unfurling the spacecraft's silver solar sail last week, mission managers have been optimizing the way the spacecraft orients itself during solar sailing. After a few tweaks, LightSail-2 began raising its orbit around the Earth. In the past 4 days, the spacecraft has raised its orbital high point, or apogee, by about 2 kilometers. The perigee, or low point of its orbit, has dropped by a similar amount, which is consistent with pre-flight expectations for the effects of atmospheric drag on the spacecraft. The mission team has confirmed the apogee increase can only be attributed to solar sailing, meaning LightSail-2 has successfully completed its primary goal of demonstrating flight by light for CubeSats.
- "We're thrilled to announce mission success for LightSail-2," said LightSail program manager and Planetary Society chief scientist Bruce Betts. "Our criteria was to demonstrate controlled solar sailing in a CubeSat by changing the spacecraft's orbit using only the light pressure of the Sun, something that's never been done before. I'm enormously proud of this team. It's been a long road and we did it."
- The milestone makes LightSail-2 the first spacecraft to use solar sailing for propulsion in Earth orbit, the first small spacecraft to demonstrate solar sailing, and just the second-ever solar sail spacecraft to successfully fly, following Japan's IKAROS, which launched in 2010. LightSail-2 is also the first crowdfunded spacecraft to successfully demonstrate a new form of propulsion.
- "For The Planetary Society, this moment has been decades in the making," said Planetary Society CEO Bill Nye. "Carl Sagan talked about solar sailing when I was in his class in 1977. But the idea goes back at least to 1607, when Johannes Kepler noticed that comet tails must be created by energy from the Sun. The LightSail-2 mission is a game-changer for spaceflight and advancing space exploration."
Figure 8: On Monday (29 July), LightSail-2 sent home a new full-resolution image captured by its camera during solar sail deployment. The perspective is opposite to last week's full-resolution image and shows the sail more fully deployed. LightSail-2's aluminized Mylar sail shines against the blackness of space, with the Sun peeking through near a sail boom (image credit: The Planetary Society)
• July 24, 2019: The Planetary Society's LightSail-2 spacecraft has successfully deployed the large, aluminized Mylar sail it will use to raise its orbit solely with sunlight. 7)
- Flight controllers at CalPoly San Luis Obispo in California commanded the spacecraft to deploy its solar sails on 23 July at about 11:47 PDT (18:47 UTC). Images captured during the deployment sequence and downloaded today show the 32 m2 sail, which is about the size of a boxing ring, deploying as the spacecraft flew south of the continental United States.
- Sail deployment marks a major milestone for the LightSail-2 mission, which aims to demonstrate solar sailing as a viable method of propulsion for CubeSats—small, standardized satellites that have lowered the cost of space exploration.
- "Yesterday, we successfully set sail on beams of sunlight," said Bill Nye, CEO of The Planetary Society. "Thanks to our team and our tens of thousands of supporters around the world, the dream started by The Planetary Society's founders more than 4 decades ago has taken flight."
- Bruce Betts, Planetary Society chief scientist and LightSail program manager, added, "We're ecstatic! The mission team has worked for years to get to this moment when we can start solar sailing."
- Following the start of sail deployment on 23 July, telemetry from LightSail-2 showed the spacecraft's small motor was rotating properly, extending four, 4-meter cobalt-alloy booms from their central spindle. The booms unwind like carpenter's tape measures and are attached to 4 triangular sail sections that together form the square solar sail.
- Though the motor activity itself was a good indicator of success, confirmation that the sails deployed successfully was only possible via imagery from LightSail-2's dual cameras. The cameras have 185º fields of view, and together can image the entire sail from the main LightSail bus, which is about the size of a loaf of bread.
- "The successful deployment of the solar sail and the onset of sail control completes our critical post-launch phase," said LightSail-2 project manager David Spencer. "Now we are prepared for the solar sail's mission, to track how the orbit changes and evaluate solar sailing performance."
Figure 9: This image was taken during the LightSail-2 sail deployment sequence on 23 July 2019 at 11:48 PDT (18:48 UTC). Baja California and Mexico are visible in the background. LightSail-2's dual 185º fisheye camera lenses can each capture more than half of the sail. This image has been de-distorted and color corrected (image credit: The Planetary Society)
Figure 10: Cheer along with Bill Nye and the flight controllers as The Planetary Society's LightSail-2 spacecraft successfully deploys its solar sail in space (video credit: The Planetary Society, Published on Jul 26, 2019)
- The deployment milestone comes 4 weeks after LightSail-2 launched from Kennedy Space Center, Florida aboard a SpaceX Falcon Heavy rocket, and 3 weeks after the Georgia Tech student-built Prox-1 spacecraft deployed LightSail-2 into orbit. The mission team spent a week checking out the spacecraft's systems before rescheduling sail deployment to allow extra time for testing and tuning the attitude control system.
Figure 11: LightSail-2 orbit raising. This animation shows how LightSail-2 raises its orbit by making two 90º turns each orbit. As the spacecraft approaches the Sun, it turns the sail edge-on to avoid getting pushed by solar photons. As it moves away from the Sun, it turns perpendicular to incoming sunlight, giving it a push that gradually raises its orbit (image credit: The Planetary Society, Josh Spradling)
- Preliminary data shows LightSail-2 is already turning its solar sail broadside to the Sun once per orbit, giving the spacecraft a gentle push no stronger than the weight of a paperclip. Solar photons have no mass, but they have momentum, and as they reflect off the solar sail, some of that momentum is transferred and creates thrust. While this thrust is slight, it is continuous and over time will raise LightSail-2's orbit.
- The orbit-raising portion of the mission will last about 1 month. LightSail-2 does not have the capability to circularize its orbit—as one side of the spacecraft's orbit raises due to solar sailing, the other side will dip lower into Earth's atmosphere, until atmospheric drag overcomes the slight force from solar sailing. LightSail-2 is expected to reenter the atmosphere in roughly 1 year.
• July 3, 2019: The Planetary Society's LightSail-2 spacecraft is healthy in orbit, as its mission team at Cal Poly San Luis Obispo in California works through procedures to prepare the spacecraft for sail deployment. 8)
- Following a successful first contact with the spacecraft yesterday, the team established two-way communications and started working through a 73-step checklist to check out the spacecraft's systems and perform various tests. That checklist is roughly one-third complete; a target time for sail deployment will be announced in the next few days.
- Telemetry from LightSail-2 shows the spacecraft's major systems are operating normally. The spacecraft's tumble rate is near zero, indicating it successfully used its electromagnetic torque rods to stabilize itself after ejection from Prox-1.
- The mission team adjusted LightSail's internal clock and uplinked data to help the CubeSat determine where it is around the Earth, which is required for solar sailing. Mission ground stations at Cal Poly San Luis Obispo, Georgia Tech, and Purdue University have all received LightSail-2 data. Additionally, the SatNOGS (Satellite Networked Open Ground Station) worldwide ground station network has been tracking the spacecraft and capturing additional telemetry.
- The mission's next steps include capturing test images to verify the cameras are working properly, exercising the momentum wheel to prepare for solar sailing, and deploying the dual-sided solar panels.
• July 2, 2019: The Planetary Society's LightSail-2 spacecraft sprang loose from its Prox-1 carrier vehicle as planned today, and sent its first signals back to mission control at Cal Poly San Luis Obispo in California. 9)
- The CubeSat was scheduled to leave Prox-1 precisely 7 days after both spacecraft successfully flew to orbit aboard a SpaceX Falcon Heavy rocket. Following deployment from its spring-loaded enclosure known as a P-POD, LightSail-2 deployed its radio antenna and began transmitting health and status data, as well as a Morse code beacon indicating its call sign. The mission team received LightSail-2's first signals on 2 July at 01:34 PDT (08:34 UTC), as the spacecraft passed over Cal Poly.
Figure 12: LightSail-2 Morse code selfie. Members of the LightSail-2 mission team can be seen in a reflection above a display showing the spacecraft's Morse code beacon after it was first detected on 2 July 2019 at Cal Poly San Luis Obispo in California (image credit: Dave Spencer, The Planetary Society)
Figure 13: LightSail-2's Morse code beacon as it was received on 2 July 2019. The beacon translates to the spacecraft's call sign, WM9XPA (image credit: The Planetary Society)
- "The Georgia Tech Prox-1 spacecraft did its job perfectly, delivering LightSail-2 to the desired orbit for solar sailing," said LightSail-2 project manager Dave Spencer. "Receiving the initial radio signal from LightSail-2 is an important milestone, and the flight team is excited to begin mission operations."
- "We're all very happy—after years of preparation, we are flying an operational spacecraft!" added Bruce Betts, LightSail program manager and Planetary Society chief scientist.
Figure 14: LightSail-2 team members watch as the first signals from the spacecraft are received at Cal Poly San Luis Obispo in California on 2 July 2019 (image credit: Bruce Betts / The Planetary Society)
- More data collected during additional ground station passes today will be used to evaluate the health and status of the spacecraft. The next available opportunity for contact is 3 July at roughly 00:30 UTC (2 July at 20:30 EDT), when LightSail-2 flies over Georgia Tech.
- The team will spend about a week checking out LightSail-2's systems, exercising the spacecraft's momentum wheel, and taking camera test images before and after deployment of the CubeSat's dual-sided solar panels. Following the successful completion of these tests, the team will deploy the 32 m2 solar sail, about the size of a boxing ring. A time for the solar sail deployment attempt will be announced later.
- Once LightSail-2 deploys its solar sail, it will begin turning the sail into and away from the Sun's rays each orbit, giving the spacecraft a gentle push. The goal is to raise the spacecraft's orbit by a measurable amount over the course of a month. After that, the perigee, or low point, of LightSail-2's orbit is expected to drop too far into Earth's atmosphere for the thrust from solar sailing to overcome atmospheric drag. The spacecraft will remain in orbit about a year before entering the atmosphere and burning up.
Figure 15: This video shows brief highlights from The Planetary Society's LightSail-2 mission (video credit: The Planetary Society)
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
4) Stephen Clark, "Falcon Heavy launches on military-led rideshare mission, boat catches fairing," Spaceflight Now, 25 June 2019, URL: https://spaceflightnow.com/2019/06/25/falcon-heavy-launches-on-military-led-rideshare-mission-boat-catches-fairing/
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 Spacecraft Successfully Demonstrates Flight by Light," The Planetary Society, 31 July 2019, URL: http://www.planetary.org/blogs/jason-davis/lightsail-2-successful-flight-by-light.html
7) Jason Davis, "LightSail 2 Successfully Deploys Solar Sail," The Planetary Society, 24 July 2019, URL: http://www.planetary.org/blogs/jason-davis/ls2-deploys-sail.html
8) Jason Davis, "LightSail 2 Healthy as Mission Team Continues Spacecraft Checkouts," The Planetary Society, 3 July 2019, URL: http://www.planetary.org/blogs/jason-davis/lightsail-2-healthy-checkouts.html
9) Jason Davis, "First Contact! LightSail 2 Phones Home to Mission Control," The Planetary Society, 2 July 2019, URL: http://www.planetary.org/blogs/jason-davis/first-contact-lightsail-2.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 (firstname.lastname@example.org).