LightSail-1 is a nanosatellite (a triple CubeSat configuration) project of the Planetary Society of Pasadena, CA, USA. The objective is to demonstrate solar sail technology in a spaceborne mission (test of sail deployment and controlled flight).
LightSail-1 will have four triangular sails, arranged in a diamond shape resembling a giant kite. Constructed of 32 m2 of mylar, LightSail-1 will be placed into an orbital altitude of over 800 km, high enough to escape the drag of Earth’s uppermost atmosphere. At that altitude the spacecraft will be subject only to the force of gravity keeping it in orbit and the pressure of sunlight on its sails increasing the orbital energy. The mission will give us a good, clean trial of sunlight as a means of propulsion. 1)
Figure 1: Artist's rendition of the deployed LightSail-1 mission (image credit: Planetary Society)
Background: On June 21, 2005, the Planetary Society tried to send its first solar sail, Cosmos 1, into orbit but failed because the Volna rocket it was riding didn't reach the needed orbital altitude. Later on, the Planetary Society took over NASA's small project called NanoSail-D, which they renamed to LightSail-1. The NanoSail-D mission had also failed to attain orbit due to the failure of its Falcon 1 launch vehicle in August 2008. The LightSail-1 project was announced by the Planetary Society in November 2009. The project is privately financed. 2)
LightSail-1 is technically more ambitious mission than the NanoSail-D mission of NASA, both because of its lower mass/area ratio (140 versus 300 gram/m2), and because it has attitude control equipment that will allow it to maintain a commanded orientation relative to the sun, and hence will be able to produce a deliberately-directed solar sailing thrust force.
In June 2010, the LightSail-1 nanosatellite project passed its CDR (Critical Design Review). 3)
The LightSail-1 spacecraft is a 3U CubeSat (or triple CubeSat) with a mass of ~ 4.5 kg and a size of 340 mm x 100 mm x 100 mm; it is being built in San Luis Obispo, CA, by Stellar Exploration Inc. The CubeSat platform is provided by CalPoly. One unit of the CubeSat is being used for the central electronics and the control module, while the other 2 units of the CubeSat will contain the payload, i.e. the solar sail module. Cameras, additional sensors, and a control system will be added to the basic CubeSat electronics bus. The function of the cameras is to verify the deployment of the solar sail. 4)
Figure 2: Schematic view of the LightSail-1 nanosatellite (image credit: Planetary Society)
The LightSail-1 spacecraft features (Ref. 3):
- 10 solar panels -- four deployable arrays with panels on each side plus one panel on the top and one on the bottom of the spacecraft
- Two 2 Mpixel cameras mounted at the end of two of the solar panels (only one camera is visible in Figure 3)
- Four sun sensors mounted at the end of four of the solar panels
- Six tiny ultra-sensitive accelerometers that will provide a direct measure of the light-force
- A momentum wheel for attitude control (colored red in Figure 3)
- Three single axis gyros (yellow)
- Three torque rods (gray) also part of the attitude control system
- A battery (salmon-colored, looking like a laptop computer battery).
Figure 3: Alternate view of the LighSail1-1 nanosatellite (image credit: Planetary Society)
Below the empty space in Figure 3, where the solar sail is stowed for launch, there are four new deployer mechanisms, invented by the project team, around which the TRAC (Triangular Rollable and Collapsible) booms are wound. The sails themselves consist of mylar film with 4.5 µm in thickness, aluminized and seamed for rip-stop protection: the thinnest sail so far made for spaceflight. When deployed, it provides a total area of 32 m2 (size of 5.6 m x 5.6 m). The TRAC booms were developed at AFRL (Air Force Research Laboratory).
The avionics assembly is located at the top of the nanosatellite bus in Figure 3, consisting of the command, control and data handling circuit board, the payload interface board, the radio transceiver, and the power regulator.
A whip antenna is mounted at the bottom of of the nanosatellite bus in Figure 3, providing UHF communications to the ground segment (435 MHz in uplink and downlink).
ADCS (Attitude Determination and Control Subsystem) modes:
• B-dot detumble (only sensors used are the magnetometers)
• Momentum wheel turn-on
• Orbit raising (thrust on/thrust off).
The momentum wheel is a reaction wheel assembly provided by Sinclair Interplanetary of Toronto, Canada (heritage of the CanX-2 mission of UTIAS/SFL). The nominal momentum is 0.060 Nms; an angular velocity of 2.5º/s is provided.
Figure 4: Photo of the reaction wheel assembly (image credit: Sinclair Interplanetary)
Launch: A launch of LightSail-1 is planned for mid-2011 (launch arrangements are in progress).
The LightSail nanosatellite is being launched and deployed in P-POD (Poly-Picosatellite Orbital Deployer) system of CalPoly.
Orbit: Sun-synchronous orbit, altitude ~ 820 km (minimum).
Figure 5: Schematic view of the deployment sequence (image credit: Stellar Exploration)
The mission operations team is located at Georgia Tech (Georgia Institute of Technology) in Atlanta, GA. Primary mission control will be at CalPoly with backup at Georgia Tech.
Table 1: LightSail program overview of the Planetary Society
2) John Antczak, “After letdown, solar-sail project rises again,” Nov. 9, 2009, URL: http://rss.msnbc.msn.com/id/33812469/ns/technology_and_science-space/
3) The Planetary Society, June 25, 2010, URL: http://www.planetary.org/programs/projects/solar_sailing/20100625.html
4) Chris Biddy, Matt Nehrenz, “LightSail - The Solar Sail Project of The Planetary Society,” Proceedings of the CalPoly 2010 CubeSat Developer's Workshop, San Luis Obispo, CA, USA, April 21-23, 2010. URL: http://cubesat.calpoly.edu/images/cubesat/presentations/DevelopersWorkshop2010/1...
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.