NanoSail-D is a small solar sail payload, a nanosatellite, designed and developed at NASA/MSFC in partnership with NASA/ARC (Ames Research Center) and several industry and academic partners. The objective is to demonstrate a successful deployment in space under proper attitude control to be followed with some “sailing” capability by using only the solar radiation pressure onto the sail as a propulsion means. A success of this demonstration would open up a bright future for space exploration. 1) 2) 3)
The goal of the NanoSail-D mission is to deploy a 10 m2 solar sail from a triple-CubeSat bus of ~4 kg mass with passive magnetic stabilization of GeneSat heritage. The NanoSail-D spacecraft consists of a sail subsystem stowed in a 2U volume with a 1U bus (total of 3 units = triple Cube) provided by NASA ARC.
The spacecraft bus is configured with a flight proven computer, power supply, S-band radio and UHF beacon radio. Passive attitude control is provided by permanent bar magnets that are installed in the bus closeout panels. The spacecraft bus occupies the upper 1/3 volume of the 3U-sized CubeSat class spacecraft.
The passive magnets are located on opposite sides of the bus with the North-South axes of the magnets oriented perpendicular to the long axis of the spacecraft. The body will be free to rotate about the magnetic field lines as the permanent magnets align with the Earth’s magnetic field.
Figure 1: View of the triple CubeSat containing the NanoSail-D payload (image credit: NASA)
The solar sail subsystem occupies the lower 2/3 volume of the spacecraft. Sail closeout panels provide protection for the sail and booms during the launch phase of the mission. These panels have spring loaded hinges that will be released on-orbit, under the command of the spacecraft bus. Figure 3 depicts the NanoSail-D on-orbit after closeout panel release, prior to the sail deployment.
Figure 2: Illustration of the NanoSail-D payload in the triple CubeSat (image credit: NASA) 4)
Figure 3: Panel deployed configuration of NanoSail-D (image credit: NASA)
Launch: The NanoSail-D spacecraft was launched as a secondary payload on the Falcon-1 vehicle of SpaceX (Space Exploration Technologies Inc., El Segundo, CA) on Aug. 2 2008 (test flight 003 of Falcon-1 launch vehicle). The launch site was the “Reagan Test Site (RTS)” on Omelek Island in the Kwajalein Atoll, part of the Republic of the Marshall Islands in the Pacific Ocean - a US Military Range run by the Army (location: 9.99º N, 167.6º E).
• PRESat (PharmaSat Risk Evaluation) of NASA/ARC, also a technology mission and a triple Cube with a mass of ~4.5 kg, was the other secondary payload on this flight.
• The primary payload for this mission was the Trailblazer spacecraft, a microsatellite (83.5 kg) of DoD which was assembled on schedule and budget by SpaceDev in less than five months.
Unfortunately, the mission ended in failure about two minutes after launch, when the SpaceX Falcon-1 launch vehicle experienced a problem during stage separation and was unable to achieve an Earth orbit. 5)
Fortunately, the team that built NanoSail-D also built a flightworthy spare spacecraft. The development team is currently exploring possible launch opportunities for that craft. 6)
Orbit: Elliptical orbit of 685 km x 330 km, inclination = 9º.
Payload deployments: 7)
• SPASS (Secondary Payload Adaptor and Separation System): The three separating satellites attach to the Falcon 1 second stage via the SPASS which is owned and developed by ATSB (Astronautic Technology Sdn. Bhd), a government-owned company of Kuala Lumpur, Malaysia that develops and commercializes space technology.
The SPASS design was conceptualized by ATSB as a payload adaptor for Falcon 1 to accommodate small satellites as an affordable access to space. The SPASS was engineered by Space Access Technologies of Ashburn, VA, USA. SPASS remains attached to the second stage, along with a number of other systems and payloads.
• P-POD (Poly Pico-satellite Orbital Deployer): The two NASA nanosatellites (PRESat and NanoSail-D) are housed during launch and deployed using P-POD dispensers from the California Polytechnic Institute (CalPoly) in San Luis Obispo. The dispensers are attached to the exterior of the SPASS adaptor described above.
Figure 4: Photo of the integrated payload stack with SPASS and one P-POD externally attached (bottom) and Trailblazer (top), image credit: NASA 8)
Solar sail experiment:
The main goal of the mission is to demonstrate proper deployment of the solar sail in LEO (an enabling technology). NanoSail-D deploys about 4 minutes after PRESat, then several days later, it will unfurl an ultra-thin solar sail measuring about 3.3 x 3.3 m (~10 m2 sail area). The aluminum coated gossamer sail is affected by solar pressure and aerodynamic drag. By tracking the NanoSail-D from the ground, the mission team will be able to pick up slight changes in its orbit after just a few days into the mission.
A secondary objective is to use the solar sail as a drag sail to demonstrate orbital debris mitigation technology.
Figure 5: Structure of deployed sail configuration (image credit: NASA)
Sail subsystem description: ManTech SRS (MSRS) of Huntsville, Alabama was responsible for the design, development and testing of the sail subsystem for NanoSail-D. Though the sail subsystem was utilized as a drag device for the current mission, all the essential components of the sail subsystem are scalable to > 40 m2 sail missions and were merely truncated due to the aggressive timeline of the current mission - from inception to launch in less than 6 months (Ref. 3).
The sail subsystem was designed to be as modular as possible with the sail subsystem divided into two primary components; the sail assembly and the boom mechanical assembly. Dividing the subassembly allowed for:
• separate relevant functional testing of the sail mechanical assembly and the boom mechanical assembly during the development of the system
• complete testing of the entire sail subassembly (deployment functionality) prior to integration with the NanoSail-D bus and release electronics.
This basic approach allowed for quick incorporation of lessons learned and design modifications during the development at the subsystem and subassembly level without affecting the activities/design of any other components. Once assembled the sail subassembly consisted of a stand alone unit that bolted to the bus and connected to the release electronics.
The sail membranes, fabricated from aluminum coated CP-1 material, are z-folded and rolled onto a sail spool. The Trac booms, developed by AFRL, are also rolled onto a boom spool. The stored strain energy of the rolled booms provides the driving force to simultaneously deploy both the booms and the sail quadrants. The fully deployed on-orbit configuration of the NanoSail-D spacecraft is illustrated in Figure 7.
Figure 6: The NanoSail-D team with the fully deployed solar sail (image credit: NASA)
Figure 7: Artist's view of the deployed NanoSail-D configuration (image credit: NASA)
Solar sail fundamentals:
Solar sail propulsion utilizes the solar radiation pressure exerted by the momentum transfer of reflected photons1. The integrated effect of a large number of photons is required to generate an appreciable momentum transfer which implies a large sail area. And since acceleration is inversely proportional to mass for a given thrust force, the mass of the sailcraft must be kept to a minimum (Ref. 3).
Figure 8 shows how the solar radiation pressure is utilized for propulsion. Incident rays of sunlight reflect off the solar sail at an angle s" with respect to the sail normal direction. Assuming specular reflection from a perfectly flat sail membrane, there will be two components of force. One will be in the direction of the incident sunlight and the second in a direction normal to the incident rays. When the force vectors are summed, the components tangent to the sail surface cancel and the components normal to the surface add to produce the thrust force in the direction normal to the sail surface. For a perfect 40 m x 40 m square sail at 1 AU from the sun, the solar radiation thrust force is approximately 0.03 N (newton).
Figure 8: Illustration of solar radiation thrust force (image credit: NASA/JPL)
Solar radiation pressure can be used in different ways to change the orbit elements. If the sail is oriented such that the thrust force is opposite the direction of motion, as in Figure 8 for a heliocentric orbit, the orbit spirals inward. Conversely, if the thrust is in the direction of motion, the sailcraft orbit spirals outward. Orbit inclination changes result when a component of the thrust force is oriented perpendicular to the orbit plane.
Thrust vector pointing is typically accomplished via either three-axis control or spin stabilization. Stringent constraints on mass coupled with the large moments of inertia resulting from the large deployed membranes makes three-axis control difficult, especially in low earth orbit (LEO) where momentum from gravity gradient and aerodynamic disturbance torques must be mitigated by the attitude control system. Alternatively, conventional spin stabilization is ineffective for circular orbits where the net integrated thrust effects cancel.
Solar sail performance is typically specified in terms of characteristic acceleration which is defined as the acceleration from solar radiation pressure at a distance of one astronomical unit from the sun. It is both a function of the reflective efficiency of the sail as well as the total system mass and reflective area. To date, solar sail propulsion system design concepts have been investigated for large spacecraft in the tens to hundreds of kilograms mass range, consequently requiring sail areas in the thousands of square meters or larger range.
The NanoSail-D spacecraft of NASA/MSFC is a small implementation of solar sail area as well as of overall spacecraft mass. If a proper deployment can be achieved, then similar characteristic acceleration performance can be achieved with substantially smaller sails, thus reducing the technical risk and cost associated with the sail propulsion system. Moreover, these propulsive solar sails can be doubly utilized to de-orbit a small satellite to meet the end-of-mission disposal requirements without the need of a dedicated chemical propulsion system that would otherwise incur parasitic mass and volume impacts.
1) “NASA to Attempt Historic Solar Sail Deployment,” June 26, 2008, URL: http://science.nasa.gov/headlines/y2008/26jun_nanosaild.htm
3) Mark Whorton, Andy Heaton, Robin Pinson, Greg Laue, Charles Adams, “NanoSail-D: The Fir st Flight Demonstration of Solar Sails for Nanosatellites,” Proceedings of the 22nd Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 11-14, 2008, SSC08-X-1
4) E. E. Montgomery, C. L. Adams, “NanoSail-D,” CubeSat Developers' Workshop, San Luis Obispo, CA, USA, April 9-11, 2008, URL: http://atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2008/session6/4-NanoSailD-Sandy_Montgomery.pdf
6) Edward D. Flinn, “Solar sails may propel spacecraft,” Engineering Notebook, Aerospace America, October 2008, URL: http://www.aiaa.org/Aerospace/images/articleimages/pdf/Engineering%20Notebook1.pdf
8) “NASA ARC /MSFC NanoSail-D and NASA ARC PRESat (PharmaSat Prototype),” URL: http://microsatellitefreeflyer.arc.nasa.gov/docs/PRESAT_and_NanoSail_Overview.pdf
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.