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Acta Astronautica

Acta Astronautica 68 (2011) 571–575

0094-57

doi:10.1

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journal homepage: www.elsevier.com/locate/actaastro

NanoSail-D: A solar sail demonstration mission

Les Johnson a,�, Mark Whorton a, Andy Heaton a, Robin Pinson a, Greg Laue b, Charles Adams c

a NASA George C. Marshall Space Flight Center, Marshall Space Flight Center, AL 35812, USAb ManTech SRS Technologies, 500 Discovery Drive, Huntsville, AL 35806, USAc Gray Research, Inc., 655 Discovery Drive, Suite 300, Huntsville, AL 35806, USA

a r t i c l e i n f o

Article history:

Received 22 October 2009

Received in revised form

2 February 2010

Accepted 7 February 2010Available online 6 March 2010

Keywords:

Solar sail

NanoSail-D

Cubesat

65/$ - see front matter Published by Elsevier

016/j.actaastro.2010.02.008

responding author. Tel.: +1 256 544 7824; fax

ail address: c.les.johnson@nasa.gov (L. Johnso

a b s t r a c t

In the early to mid-2000s, NASA made substantial progress in the development of solar

sail propulsion systems. Solar sail propulsion uses the solar radiation pressure exerted

by the momentum transfer of reflected photons to generate a net force on a spacecraft.

To date, solar sail propulsion systems were designed for large robotic spacecraft.

Recently, however, NASA has been investigating the application of solar sails for small

satellite propulsion. The NanoSail-D is a subscale solar sail system designed for possible

small spacecraft applications. The NanoSail-D mission flew on board the ill-fated Falcon

Rocket launched August 2, 2008, and due to the failure of that rocket, never achieved

orbit. The NanoSail-D flight spare is ready for flight and a suitable launch arrangement is

being actively pursued. This paper will present an introduction solar sail propulsion

systems and an overview of the NanoSail-D spacecraft.

Published by Elsevier Ltd.

1. Introduction

Solar sail propulsion utilizes the solar radiationpressure exerted by the momentum transfer of reflectedlight. The integrated effect of a large number of photons isrequired to generate an appreciable momentum transfer;therefore, a large sail area is required. Since acceleration isinversely proportional to mass for a given thrust force, themass of the sailcraft must be kept to a minimum.

Fig. 1 illustrates how the solar radiation pressure isutilized for propulsion. Incident rays of sunlight reflect off thesolar sail at an angle y with respect to the sail normaldirection. Assuming specular reflection from a perfectly flatsail membrane, there will be two components of force—onein the direction of the incident sunlight and the second in adirection normal to the incident rays. When the force vectorsare summed, the components tangent to the sail surfacecancel and the components normal to the surface add toproduce the thrust force in the direction normal to the sail

Ltd.

: +1 256 544 0242.

n).

surface. For a perfect 40-m�40-m square sail at 1 AU fromthe Sun, the solar radiation thrust force is E0.03 N.

2. NanoSail-D objectives

The objectives of the NanoSail-D project are primarilyprogrammatic, with several technology goals to beserendipitously demonstrated:

�

Establish NASA Ames Research Center (ARC)–NASAMarshall Space Flight Center (MSFC) collaborativerelationship for future small satellite initiatives.(Comment: MSFC is known for developing NASA’s‘‘large’’ space missions. A partnership with ARC wouldhelp diversify the MSFC science portfolio.) � Deploy first solar sail leveraging work by MSFC

approved under the Science Mission Directorate In-Space Propulsion Technology Program [1]. (Comment:The hardware from the solar sail ground demonstra-tion program was in storage and NanoSail-D providedan opportunity to use the hardware and the MSFCexpertise developed in the program to fly a relativelylow-cost demonstration.)

L. Johnson et al. / Acta Astronautica 68 (2011) 571–575572

�

Demo orbital debris mitigation technology—drag sail.(Comment: When flown in low-Earth orbit, the aero-dynamic drag experienced by the NanoSail will exceedsolar photon thrust, resulting in a rapid deorbit of thesail spacecraft. If a similar sail were stowed on aspacecraft and deployed at the end of its life, it mightserve as a lightweight deorbit system [2].) � Ground imaging to reduce spacecraft instrumentation.

(Comment: The NanoSail-D is very small and it wasimpossible to place much diagnostic instrumentationon board. With ground imaging, it would be possible toconfirm solar sail deployment, attitude, etc.)

3. Performance

Solar sail performance is typically specified in terms ofcharacteristic acceleration that is defined as the accelera-tion from solar radiation pressure at a distance of 1 AUfrom the Sun. It is both a function of the reflectiveefficiency of the sail as well as the total system mass andreflective area. To date, solar sail propulsion systemdesign concepts have been investigated for large space-craft in the tens to hundreds of kilograms mass range,consequently requiring sail areas in the thousands ofsquare meters or larger range [3]. Recently, however,MSFC has been investigating the application of solar sailsfor small satellite propulsion. If the payload mass can besubstantially reduced, then similar characteristic accel-eration performance can be achieved with substantiallysmaller sails, thus reducing the technical risk and costassociated with the sail propulsion system. Moreover,these propulsive solar sails can be doubly utilized todeorbit a small satellite to meet the end-of-missiondisposal requirements without the need of a dedicatedchemical propulsion system that would otherwise incur

Fig. 1. Solar radiation thrust force.

parasitic mass and volume impacts. At the same time, ARChas been developing small spacecraft missions that couldbenefit from this mass-efficient propulsion and deorbitcapability. Hence, a synergistic collaboration was estab-lished between these two NASA field Centers with theobjective of conducting a flight demonstration of solar sailtechnologies for small satellites.

4. NanoSail-D system overview

The NanoSail-D mission was launched on board aFalcon 1 launch vehicle in August 2008. The NanoSail-D, aCubeSat-class satellite, consisted of a sail subsystemstowed in a CubeSat 2 U volume integrated with a CubeSat1 U volume bus provided by ARC. Shortly afterdeployment of the NanoSail-D from a Poly PicosatelliteOrbital Deployer (P-POD) ejection system, the solarsail was to have deployed and mission operationscommence. Unfortunately, the launch vehicle failedduring ascent and the NanoSail-D never had the oppor-tunity to deploy.

Given a near-term opportunity for launch, the projectwas met with the challenge of delivering the flighthardware in E6 mo, which required a significant con-straint on flight system functionality. As a consequence,the baseline spacecraft functionality is limited to passiveattitude control with no ground command capability andonly minimal health and status telemetry sent to theground. No onboard camera or instrumentation are to beutilized to image the deployed sail or measure theattitude dynamics since these functions require consider-able software and avionics infrastructure that was beyondthe scope of the project budget and schedule.

The stowed configuration of the NanoSail-D spacecraftis illustrated in Fig. 2. The spacecraft bus, provided byARC, is configured with a flight-proven computer, powersupply, S-band radio, and ultra-high-frequency (UHF)beacon radio. Passive attitude control is provided bypermanent bar magnets that are installed in the buscloseout panels. The spacecraft bus occupies the upperone-third volume of the 3 U-sized CubeSat-classspacecraft.

The solar sail subsystem occupies the lower two-thirdsvolume of the spacecraft. Sail closeout panels provideprotection for the sail and booms during the launch phaseof the mission. These panels have spring-loaded hingesthat will be released onorbit, under the command of thespacecraft bus. Fig. 3 shows the fully deployed NanoSail-Din a ground test.

ManTech SRS, Huntsville, Alabama, was responsible fordesign, development, and testing of the sail subsystem forNanoSail-D. Though the sail subsystem was to be utilizedas a drag device for the current mission, all the essentialcomponents of the sail subsystem are scalable to 440 m2

sail missions and were merely truncated due to theaggressive timeline of the current mission.

Due to the aggressive time constraints of the mission(from inception to launch in o6 mo), the sail subsystemwas purposely designed to be as modular as possiblewith the sail subsystem divided into two primary

Fig. 2. On-orbit stowed configuration.

Fig. 3. NanoSail-D ground deployment test.

Fig. 4. The coiled trac boom.

L. Johnson et al. / Acta Astronautica 68 (2011) 571–575 573

components—the sail assembly and the boom mechanicalassembly. Dividing the subassembly allowed for: (1)separate relevant functional testing of the sail mechanicalassembly and the boom mechanical assembly during thedevelopment of the system and (2) complete testing of theentire sail subassembly (deployment functionality) priorto integration with the NanoSail-D bus and releaseelectronics. This basic approach allowed for quick in-corporation of lessons learned and design modificationsduring the development at the subsystem and subassem-bly level without affecting the activities/design of anyother components. Once assembled, the sail subassemblyconsisted of a standalone unit that bolted to the bus andconnected to the release electronics. Launch operationsconsists of a simple, timed, two-actuation system. Theinitiating event consists of a burn-wire release of the doorpanels. The door panels protect the sail material and helpto constrain it for the launch environment and ascentventing.

The sail membrane is a piece of the 400-m2 solar sailtested by NASA in 2005 [1]. The sail is 2mm CP1 with1000 A of aluminum on the front, and bare CP1 on theback. CP1 is a clear polyimide developed by NASA andlicensed to ManTech SRS Technologies. The exact chemi-cal formulation is proprietary. CP1 has a wide variety ofoperating temperatures (from cryogenic to 250 1C) and isresistant to ultraviolet radiation.

The trac booms, developed by the Air Force ResearchLaboratory (AFRL), are also rolled onto a boom spool. Thestored strain energy of the rolled booms provides thedriving force to simultaneously deploy both the boomsand the sail quadrants. Figs. 4 and 5 show the trac boomsin coiled and uncoiled configurations.

Mission data are to be comprised by radar cross-sectional area data, optical images, and orbital elements.Radar cross-sectional area data and optical images are tobe obtained by the US Army’s Reagan Test Site. These datamay enable estimation of a lower bound on the deployed

L. Johnson et al. / Acta Astronautica 68 (2011) 571–575574

sail area (lower bound only because the sail plane waslikely not normal to the line of sight during dataacquisition, hence, the projected area normal to the lineof sight was to be measured). Estimation of the deployedarea will be difficult during initial phases of the missionwhen the sail is to be ‘‘tumbling’’ about the Earth’smagnetic field lines during part of the orbit and passivelystabilized in the maximum drag orientation near perigee.Hence, the estimation of the deployed area from orbit datawill depend on the latter phases of the mission when theorbit circularizes and the sail passively stabilizes due toaerodynamic torque in a relatively constant local vertical/local horizontal attitude. In the event that the sail doesnot stabilize prior to reentry, orbital analysis will allow anestimation of an average ballistic coefficient that may becorrelated to an average area.

Fig. 5. The uncoiled trac boom.

Table 1NanoSail-D on-orbit operations sequence.

Event Hours Minutes

Falcon-1 launch 0 Launch m

NanoSail-D ejection from P-POD; beacon on 0 0

Beacon operating 6 0

Beacon off period 66 0

Panels open 72 0

Booms/sails deploy 72 0

Optical confirmation of deployment 73 44

S-Band on; listen at 30 s and 30 s off 75 0

Deorbit 120 10

5. NanoSail-D flight demonstration mission operations

Seventy-two hours after deployment of the NanoSail-Dfrom the P-POD ejection system, the solar sail will deployand mission operations will commence as described inTable 1.

Passive attitude stabilization will be achieved usingpermanent magnets in the sailcraft bus to initiallydetumble and orient the body with the magnetic fieldlines. The magnets are located on opposite sides of the buswith the north–south axes of the magnets orientedperpendicular to the long axis of the spacecraft. The bodywill be free to rotate about the magnetic field lines as thepermanent magnets align with the Earth’s magnetic field.Since the orbit plane inclination was to be o101, themagnetic field lines will be approximately normal to theorbit plane and gravity gradient torques and aerodynamictorques will tend to passively stabilize the sailcraft in anessentially maximum drag attitude (where the sail planenormal vector is approximately pointed in the velocityvector direction).

Since the orbit is elliptical with a 685-km apogee, a330-km perigee, and 91 inclination, the sailcraft willinitially tend to rotate about the magnetic field lines inthe proximity of apogee while the higher atmosphericdrag at the lower altitudes of perigee will tend toconstrain the attitude to the maximum drag orientation.Because rotation rates are a function of tipoff rates, it is

Seconds Comments

inus 45 0

0 Assume launch plus 45 min

0

0

0

15

0 Assumed time (one orbit after

sail deployment; orbit period 1:34)

0

0 Assumed 4 days after deployment

Fig. 6. Orbit decay as a function of sail area.

Fig. 7. Mission duration as a function of sail size.

L. Johnson et al. / Acta Astronautica 68 (2011) 571–575 575

not possible to precisely predict the transition from thelow-drag, one-axis ‘‘tumble’’ to drag equilibrium state;hence, only upper and lower bounds on mission durationmay be estimated. However, the drag force at perigee willtend to circularize the orbit, lowering the apogee, andhence increasing the amount of time in the maximumdrag orientation, and ultimately passively stabilizing theattitude in the maximum drag orientation for the durationof the orbit as the orbit tends to become more circular.It is through the means of correlating this anticipatedorbital motion with orbital simulations that the deployedarea of the sail can be estimated and the functionality fordeorbiting can be demonstrated.

Fig. 6 shows the type of mission analysis that will beused to estimate the deployed sail area from the orbit

decay. Beginning with the initial state vector for thedeployed sail, the orbit decay over 24 h was determinedby propagating the orbit. The change in semimajor axis isa linear function of the deployed sail area, suggesting thatthe change in orbit energy can be correlated to thedeployed sail area and can therefore be used to validatethat the sail actually deployed.

Fig. 7 shows an estimate of the mission elapsed timeuntil the sail reenters the atmosphere, assuming a dragcoefficient of 2 with a constant projected frontal area(assuming passive stabilized equilibrium). The sail areavaried from 10 m2 (fully deployed sail) to 0.0378 m2 (nosail deployed).

6. Conclusions

The NanoSail-D would have been the first on-orbitsolar sail deployment demonstration. Unfortunately, dueto the launch vehicle failure, it never had the opportunityto deploy. MSFC is now working to obtain a launch for theflight spare, which is identical to the original spacecraftused in the August 2008 launch attempt.

References

[1] L. Johnson, R.M. Young, E.E. Montgomery, Recent advances in solarsail propulsion systems at NASA, Acta Astro 61 (2007) 376–382.

[2] P.C.E. Roberts, P.G. Harkness, Drag sail for end-of-life disposal fromlow Earth orbit, J. Spacecr. Rockets 44 (6) (2007) 1195–1203.

[3] V. Lappas, M. Leipold, A. Lyngvi, et al., Interstellar heliopause probe:system design of a solar sail mission to 200 AU, AIAA Guidance,Navigation, and Control Conference and Exhibit, San Francisco,California, August 15–18, 2005.