Status of solar sail technology within NASA

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Advances in Space Research 48 (2011) 1687–1694

Review

Status of solar sail technology within NASA

Les Johnson ⇑, Roy Young, Edward Montgomery, Dean Alhorn

NASA George C. Marshall Space Flight Center (MSFC), Mail Code EDO4, Huntsville, AL 35812, USA

Received 23 October 2010; received in revised form 8 December 2010; accepted 10 December 2010Available online 21 December 2010

Abstract

In the early 2000s, NASA made substantial progress in the development of solar sail propulsion systems for use in robotic scienceand exploration of the solar system. Two different 20-m solar sail systems were produced. NASA has successfully completed functionalvacuum testing in their Glenn Research Center’s Space Power Facility at Plum Brook Station, Ohio. The sails were designed and devel-oped by Alliant Techsystems Space Systems and L’Garde, respectively. The sail systems consist of a central structure with four deploy-able booms that support each sail. These sail designs are robust enough for deployment in a one-atmosphere, one-gravity environmentand are scalable to much larger solar sails – perhaps as large as 150 m on a side. Computation modeling and analytical simulationswere performed in order to assess the scalability of the technology to the larger sizes that are required to implement the first generationof missions using solar sails. Furthermore, life and space environmental effects testing of sail and component materials was alsoconducted.

NASA terminated funding for solar sails and other advanced space propulsion technologies shortly after these ground demonstrationswere completed. In order to capitalize on the $30 M investment made in solar sail technology to that point, NASA Marshall Space FlightCenter funded the NanoSail-D, a subscale solar sail system designed for possible small spacecraft applications. The NanoSail-D missionflew on board a Falcon-1 rocket, launched August 2, 2008. As a result of the failure of that rocket, the NanoSail-D was never successfullygiven the opportunity to achieve orbit. The NanoSail-D flight spare was flown in the Fall of 2010. This review paper summarizes NASA’sinvestment in solar sail technology to date and discusses future opportunities.Published by Elsevier Ltd. on behalf of COSPAR.

Keywords: Solar sail; NanoSail-D; In-Space Propulsion

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16882. Large solar sail system-level development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1688

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2.1. 20-m ground demonstration project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16882.2. Integrated software tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16882.3. Optical diagnostic system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16902.4. Advanced computational methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16902.5. Structural analysis and synthesis tools. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16902.6. Lightweight attitude control system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16912.7. Characterization of candidate solar sail materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16912.8. Advanced manufacturing technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16912.9. Smart adaptive structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1691

177/$36.00 Published by Elsevier Ltd. on behalf of COSPAR.

1016/j.asr.2010.12.011

rresponding author.ail address: [email protected] (L. Johnson).

http://dx.doi.org/10.1016/j.asr.2010.12.011

mailto:[email protected]

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1688 L. Johnson et al. / Advances in Space Research 48 (2011) 1687–1694

2.10. Sail charging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16912.11. Long-Term space environmental effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1691

3. Small solar sail system-level development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1692
3.1. NanoSail-D overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16923.2. NanoSail-D design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1692
4. The future of solar sails in NASA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1693Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1693References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1694

1. Introduction

Solar sail propulsion uses sunlight to propel vehiclesthrough space by reflecting solar photons from a large, mir-ror-like sail made of a lightweight, reflective material. Thecontinuous photonic pressure provides propellantlessthrust to hover indefinitely at points in-space, or conductorbital maneuver plane changes more efficiently than con-ventional chemical propulsion. Eventually, it could propela space vehicle to tremendous speeds – theoretically muchfaster than any present-day propulsion system. Since theSun supplies the necessary propulsive energy solar sailsrequire no onboard propellant, the overall mass of the sys-tem may be reduced.

First generation sails will vary in size from 100 to 200 mdepending on mission destination, and will typically be 3-axis stabilized. They will be compacted and stowed forlaunch. Once deployed ultra-lightweight trusses will sup-port the sails. Solar sails are composed of a flat smoothmaterial, covered with a reflective coating, and supportedby lightweight structures that are attached to a centralhub. Near-term sails will likely use aluminized Mylar orCP1e. Both are proven materials previously flown inspace. More robust sails might use a meshwork of inter-locking carbon fibers.

2. Large solar sail system-level development

2.1. 20-m ground demonstration project

NASA’s In-Space Propulsion Technology Projectfunded the development of two prototype solar sail systemsfor ground testing to validate design concepts for sail man-ufacturing, packaging, and launch to space and deploy-ment, attitude control subsystem function, and tocharacterize the structural mechanics and dynamics of thedeployed sail in a simulated space environment. A squaresail configuration consisting of a reflective sail membrane,a deployable sail support structure, an attitude control sub-system, and all hardware needed to stow the sail for launchwere developed. Additionally, these systems were requiredto meet the characteristics given in Table 1. A subL1 solarmonitoring mission concept was provided as a referencemission for guidance in design and scalability issues.

NASA awarded two ground demonstration contracts.ATK Space Systems’ approach incorporated their rigid

coilable boom, which is an articulating boom attitude con-trol system (ACS) subsystem and partner SRS0 CP1e sailmembrane (Murphy, 2005). L’Garde Inc. used their inflat-able and cold-temperature rigidizable boom, a controlvane-based ACS and Mylar for the sail membrane (Lichod-ziejewski et al., 2006). The parallel testing and developmentof these two system-level demonstrations that have variedtechnologies in the three major components removed therisk to this technology development if one providerencountered an unrecoverable failure. The system-levelground demonstration work was divided into three phases.A 6-month concept refinement phase was completed inMay 2003. During this phase, the two teams provided anal-ysis of their system’s performance when scaled to theDesign Reference Mission and a preliminary test plan forthe following two 12-month phases. The 12-month hard-ware development phase began in June 2003. In this phase,both teams built and tested components and subsystems,with ATK concentrating on a single 10-m quadrant andL’Garde developing a 10-m square sail. The most compre-hensive of these tests occurred in mid-2004 when therespective teams deployed their integrated subsystem inthe NASA Langley Research Center (LaRC) 14 m vacuumfacility (ATK), and the 30 m vacuum chamber at GRC’sPlum Brook Space Power Facility (L’Garde). Following asuccessful second phase, the teams culminated their workin a 12 month system verification phase. In this phase bothteams built and tested fully integrated 20-m sail systemsthat included a launch packaging container and opera-tional ACS subsystems. In mid-2005, the respective teamstested their system in the Plum Brook Facility under a highvacuum and appropriate thermal environment, as well assubjecting their systems to launch vibration and ascent venttests. Fig. 1 shows the 20-m deployed systems at the PlumBrook Facility. Since the sails represent the largest systemsthat will be tested in a vacuum chamber on the ground, asignificant effort was made to collect static and dynamicdata on the sails and booms with �400 Gb of data col-lected, primarily raw photogrammetric data.

2.2. Integrated software tools

NASA developed a set of integrated simulation tools topredict the trajectory, maneuvers, and propulsive perfor-mance of a solar sail during a representative flight profile(Ellis et al., 2004). The tools were designed to be integrated

Fig. 1. Two 20-m solar sail prototypes are shown – The ATK sail (left) used CP-1 sail material and a three-point quadrant support with a shear compliantborder to insure a flat sail; the L’Garde sail (right) used aluminized Mylar and a stripped net configuration to maintain its overall shape and flatness.

Table 1System-level solar sail ground demonstration reporting metrics.

Metric RFP ATK L’Garde

Dimensions 20 m � 20 m orgreater

� 20-m system with flightlike central structure

� 19.5 m due toPlumbrook

� 4 sails scaled from 80 m � 1 subscaleTVCAD vane

� Truncated 80-m masts � No flight centralstructure scaledfor 100-m system

� Central structure scaledfrom 40 m

� Sails and masttruncated 100-msystem

Sail Subsystem Areal Density <20 g/m2

(scalability to12 g/m2 for104 m2)

� 112 g/m2 – includesspacecraft bus structure,ACS, power, instrumentboom

� 30 g/m2 –includes ACS (4vanes calculated),central structuredropped

� Scaled to 11.3 g/m2 for100-m design and nopayload

� Scaled to 14.1 g/m2with 50-kgpayload and 41.4-kg bus

Stowed volume <0.5 m3

(scalability to1.5 m3 for104 m2)

� 0.9 m3 scaled to1.5 m3

for 100-m design� 2.14 m3 scaled to1.04 m3 for 100-mdesign

Thrust vector turning rate About roll axis >1.5�/h � >35� maneuver in 2 h � 63�/h (.0175�/s)

Effective sail reflectance >0.75 � 92% over solarspectrum

� 85.9

Anti-sunward emissivity >0.30 � 0.30 for 3-l film � 0.40

Membrane characteristics Space-durable,tear-resistant,designed for1 yr in the near-GEOenvironment

� �2-l CP1e with1,000 A of aluminum onfront, bare CP1e onback of sail. All materialshave space flight heritage

� 2-l Mylar� with1,000 A ofaluminum onfront and 200 Ablackenedchromium onback

System flatness Effective forpropulsion

� 3-point quadrantsupport with shearcompliant border toinsure a flat sail, with aproper stress level toobtain local flatness

� Stripped net loss�2%

ACS 3-axis, minimizepropellantusage

� Sliding trim controlmass on truss and tipbars to pinwheelquadrants for roll. MicroPPT backup

� Totallypropellant lessusing four tipvanes

L. Johnson et al. / Advances in Space Research 48 (2011) 1687–1694 1689


into an optimal guidance and navigational control (GNC)subsystem on a future flight mission. The tools incorpo-rated the following analytical models:

� Solar radiation pressure acting on the sail as a functionof sail orientation and distance from the Sun� Disturbance forces acting on the sail such as gravita-

tional torques and thermal deformation of the supportstructure� Orbital mechanics� Sail structural dynamics� Attitude control system dynamics� Navigational sensors

2.3. Optical diagnostic system

The overall objective for this task was to develop anOptical Diagnostic System (ODS) to Technology Readi-ness Level (TRL) 6 for a solar sail. Possible requirementsfor the ODS included observation of the sail deployment,and monitoring of the health and integrity of the sail dur-ing and after deployment. After solar sail deployment theODS would be available to provide shape and vibrationmeasurements adequate enough to infer the stress state ofthe solar sail by aid of computational structural models,which could then feed real time into a closed loop space-craft GNC system. The initial 6-month base periodincluded concept development, preceded by definition ofthe goals, priorities, and requirements for the ODS.

It was determined that continuous real-time integrationwith the guidance system was not necessary due to thequasisteady-state nature of solar sail operations. Further-more, studies showed the relative insensitivity of the thrustvector magnitude and direction to sail billow (Ewing,2005). The conceptual design process identified a numberof significant challenges to on orbit photogrammetryincluding significant weight, power, and data requirementsfor instruments, support structures for camera clusters,achieving sufficient image contrast, integrating targets intothe sail membrane, and considerable software developmentneeds. The concept development activities were conductedin parallel with the development of the ground test capabil-ity for the solar sail demonstrator hardware. A develop-mental test of an L’Garde inflatable boom in a thermalvacuum chamber at NASA Goddard Space Flight Center,as well as tests on smaller sail quadrants, provided anopportunity to familiarize researchers with cameras, ana-lytical tools, and test operations (Pappa et al., 2004). Build-ing on this experience and adding capabilities for dynamicexcitation and laser vibrometry, imaging, and a “truth”

instrument, the ATK 10 m demonstrator testing was per-formed at LaRC. These activities formed the foundationfor the test methods and instrumentation employed in thefinal 20-m demonstrations tests. An exceptional team ofphotogrammetric experts from LaRC, working in conjunc-tion with the contractor test teams, was successful in

acquiring both static and dynamic deflection data in anumber of various thermal and vacuum conditions and sys-tem configurations, despite tremendous difficulties thatarose. For example, condensate “rain” fell on the test arti-cle as the huge Plum Brook chamber was pumped down,causing boom tip positions to change so much that com-plex, remotely operated, adjustable instrument platformshad to be devised. A tremendous volume of data wasrequired to provide high-resolution measurements over400 m2 of area, and data collection was made difficult bythe clean aluminum walls and floor of the chamber thatprovided little natural contrast to the aluminized sails.Finally, the cost of operations in such a large chamber isnot inconsiderable. The teams were constantly under thegun to debug problems, acquire data, and assess data qual-ity quickly with limited hands on the equipment and only afew pumpdowns allowed. The difficulty of photogramme-try was not insurmountable, but it did indicate that thechallenges identified in the conceptual design phase werereal. Combined with a better understanding of the lack ofa need for on-orbit photogrammetry, the further develop-ment of a flight system was not pursued.

2.4. Advanced computational methods

To address the concern that conventional finite elementmodels might be inadequate to evaluate solar sails, aphased approach to address the structural design issuewas pursued. First, they relied on the prime contractorsto apply standard practices. As part of the Ground SystemDemonstrations, LaRC, ATK, and L’Garde performedFinite Element Analysis (FEA) of the 10-m systems usingboth commercial off-the-shelf and custom software. Thesemodels did not always converge and were computationallyintensive, but no more so than is experienced in typicalspacecraft design. The purpose of this task was to createmethods/algorithms/techniques that improved the conven-tional FEA of the membranes, booms, and other subsys-tems. Several methods were identified, but the optionphases to complete and validate them were not funded,due to the success of the prime contractors in modelingthe 20-m systems with conventional techniques, thus lower-ing the priority of this task below the level of the availablefunding.

2.5. Structural analysis and synthesis tools

This task also addressed the structural analysis issue bydeveloping from the ground-up new and unconventionalmodeling techniques. Techniques considered includedDirect Transfer Function Modeling (DTFM) and Parame-ter Variation Processing (PVP). The overall objectives forthis task were completion of DTFM modeling/analysismethods for long booms, completion of capability to eval-uate effects of imperfections, completion of PVP methodfor analyzing wrinkled membranes, and completion oftest/analysis correlation by using existing test data. As in


the above task, this effort was terminated prior to comple-tion due to success using conventional modeling methodswith the 20-m systems and a lack of funding.

2.6. Lightweight attitude control system

The objectives of this task were: (1) to design, integrate,and test a sail attitude control system employing a two-axisgimbaled control boom and (2) to develop a high-fidelity,multiflexible body model of ATK’s solar sail for the pur-pose of validating a thrust vector control (TVC) conceptemploying a two-axis gimbaled control boom. One of themajor findings from this study was that the two-axis gim-baled control boom was not a mass efficient method of con-trolling a sail. A more efficient method was derived basedon an offset mass moved along the booms by a clothes-line-like apparatus to control pitch and yaw, and rotatingstabilizer bars at the sail tips to pinwheel the sail quadrantsfor roll control. This finding led to a major redesign of theATK 20-m hardware to accommodate the new TVC con-cept. An attitude determination and control block diagramwere derived to present the application/integration of theinertial stellar compass with a range of ACS options fromcp/cm offset to pulsed plasma micro thrusters (Thomaset al., 2005).

2.7. Characterization of candidate solar sail materials

The purpose of this task was to conduct laboratorycharacterization of several candidate solar sail materials.The space radiation and micrometeoroid environmentsfor 1.0 and 0.5 astronomical units missions were definedand candidate materials were tested against these radiationand meteoroid environments. Through a series of learningtests, the sample hold-down design was optimized and aflexure test developed. Several samples of the SRS andL’Garde membrane materials were tested by subjectingthem to gigarad levels of radiation in simulations of long-duration solar wind mission type (Edwards et al., 2004).While some of the samples showed significant levels of deg-radation in mechanical strength, solar sail loading is so lowthat very little strength is needed.

2.8. Advanced manufacturing technologies

The purpose of this task was to investigate and developan integrated approach to ultrathin film solar sail manufac-turing. The focus was on improving coating processes andtechnologies; developing sail seaming technologies for largemonolithic sails; providing an integrated approach tomembrane coating; acceptance, assembly and integration,and integrating future improvements into the process suchas electrospun nanofibers for ripstop enhancement withoutadded mass; and the addition of carbon black nanotubes tothe sail backside to increase emissivity. The final results ofthis 2-year effort are the development of a scroll coatingsystem, the development of coating capabilities of less than

2.5 l, and the development of a membrane seaming systemable to form monolithic sails with coatings as thin as 2.5 l.

2.9. Smart adaptive structures

In order to mature the TRL of solar sail propulsion,advancements must be made in the pointing and dynamicalcontrol of these large space structures. The goal of this taskwas to understand how to model and scale the subsystem andmulti-body system dynamics of a solar sailcraft with theobjective of designing sailcraft attitude control systems.Key aspects of this effort included modeling and testing ofa 30-m deployable boom, modeling of the multi-body systemdynamics of a gossamer sailcraft, and an investigation ofcontrol-structures interaction for gossamer sailcraft bysemi-active control methods using unobtrusive sensors andeffectors. The research concluded that solar sail models thatare validated by ground testing are almost certainly not suf-ficient for full-scale control system design due to controlstructure interactions. It was also found that dynamic mod-els of solar sailcrafts must include multi-body coupling andstructural dynamics of their flexible structural components.For these large structures with stringent control require-ments, the inherent structural dynamics uncertainty repre-sents a significant challenge for existing control approaches.

2.10. Sail charging

Due to two extreme characteristics of future solar sailmissions, the large surface area of the sail, and the longduration of potential missions, typical spacecraft chargingissues will be exacerbated. The purpose of this task wasto characterize charged particle and extreme ultravioletenvironments for analyzing solar sail charging in the solarwind and at geostationary orbit and to model surface andinternal electric fields and potentials for solar sails usingexisting spacecraft charging models. Solar sail materialswere tested in simulated charging environments to deter-mine permeability and charge retention properties. A sig-nificant finding was that there will be little charging ofthe sail surfaces, �10 V as a worst case in sunlight. Thestudy found that problems arise if the sail material backingis nonconductive or electrically decoupled from the frontsurface. In that case, the shadowed back surface can reachpotentials of �30 to �40 V relative to the space plasma inthe solar wind on the order of arcing onset potentials. Thesolution is to make sure the sail material is conductivefront-to-back and end-to-end if the sail is to be in geosyn-chronous orbit or in the auroral zone.

2.11. Long-Term space environmental effects

Critical to the development of solar sails is an investiga-tion of space environmental effects on these large thin filmmaterials and the edge support technologies. This task wasrelated to the “Characterization Solar Sail Materials” taskabove. The above task used accelerated dose levels over a


shorter period of time to simulate the total dose of radia-tion received by a material for many years. The purposeof this task is to provide critical thermal, optical, mechan-ical, and surface data on large sails taking into accountedge stresses and edge support technologies that can onlybe characterized using large size sails but not at acceleratedlevels. These resulting test data could be used to validatethe accelerated dose test methodology regarding the dura-bility of candidate sail material (embrittlement, optical,mechanical, surface, and thermal properties). It was foundthat CP-1 should perform very well for long-term solar sailmissions, showing little or no degradation neither in itsoptical performance nor in its structural integrity after test-ing. While the Mylar-based sail retained its optical proper-ties, it mechanical stability was severely adversely affected.

3. Small solar sail system-level development

3.1. NanoSail-D overview

NASA MSFC has recently been investigating the appli-cation of solar sails for small satellite propulsion. Likewise,the NASA Ames Research Center (ARC) has been devel-oping small spacecraft missions that have a need for amass-efficient means of satisfying deorbit requirements.Hence a synergistic collaboration was established betweenthese two NASA field centers with the objective of con-ducting a flight demonstration of solar sail technologiesfor small satellites in a project called “NanoSailDeorbit”or “NanoSailD.”

The original NanoSailD mission flew onboard a Falcon-1 rocket, launched August 2, 2008, and due to the failure ofthat rocket, never achieved orbit. The NanoSailD flightspare will be flown in the Fall of 2010. Both the originalsailcraft and the flight spare are hereafter referred to as

Fig. 2. On-orbit view of the spac

“NanoSailD.” The sailcraft consists of a sail subsystemstowed in a 3-element CubeSat. Shortly after deploymentof the NanoSailD, the solar sail will deploy and missionoperations will commence. This demonstration flight hastwo primary technical objectives: (1) to successfully stowand deploy the sail and (2) to demonstrate deorbit func-tionality (Peter et al., 2007). Passive attitude stabilizationof the spacecraft will be achieved using permanent magnetsto detumble and orient the body with the magnetic fieldlines and then rely on atmospheric drag to passively stabi-lize the sailcraft in an essentially maximum drag attitude.

3.2. NanoSail-D design

The stowed configuration of the NanoSailD spacecraftis illustrated in Fig. 2. The spacecraft bus, provided byARC, is configured with a flight-proven computer, powersupply, Sband radio, and UHF beacon radio. Permanentbar magnets that are installed in the bus closeout panelsprovided passive attitude control prior to sail deployment.There is no active attitude control system included for useafter the sail is deployed. The spacecraft bus occupies theupper 1/3 volume of the 3U-sized “CubeSat” classspacecraft.

The solar sail subsystem occupies the lower 2/3 volumeof the spacecraft. Sail closeout panels provide protectionfor the sail and booms during the launch phase of the mis-sion. These panels have spring-loaded hinges that will bereleased on orbit, under the command of the spacecraftbus. Fig. 3 shows the fully deployed NanoSail-D in aground test.

ManTech SRS, in Huntsville, AL was responsible fordesign, development, and testing of the Sail Subsystemfor Nanosail-D. The sail subsystem, purposely designedto be as modular as possible, was divided into two primary

ecraft before sail deployment.

Fig. 3. The NanoSail-D development team is shown with the flight system following a successful ground, non-vacuum deployment test.


components – the sail assembly and the boom mechanicalassembly. Dividing the subassembly allowed for (1) sepa-rate 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 incorpo-ration of lessons learned and design modifications duringthe development at the subsystem, and subassembly levelwithout affecting the activities/design of any other compo-nents. Once assembled the sail subassembly consisted of astandalone unit that bolted to the bus and connected tothe release electronics. Launch operations consist of asimple, timed two-actuation system. The initiating eventconsists of a burn-wire release of the door panels. The doorpanels protect the sail material and help to constrain it forthe launch environment and ascent venting. The sail mem-branes that are fabricated from aluminum-coated CP1e

material used originally in the Large Solar Sail GroundDemonstration Project described above, are z-folded androlled onto a sail spool. The Trac booms, developed bythe U.S. Air Force Research Laboratory, are also rolledonto a boom spool. The stored strain energy of the rolledbooms provides the driving force to simultaneously deployboth the booms and the sail quadrants.

Mission data is to be comprised by radar cross-sectionalarea data, optical images, and orbital elements. Radarcross-sectional area data and optical images are to beobtained by the U.S. Army’s Reagan Test Site. This datamay enable estimation of a lower bound on deployed sailarea (lower bound only because the sail plane was likely

abnormal in reference to the line of sight during data acqui-sition, hence the projected area normal to the line of sightwas to be measured). Estimation of the deployed area willbe difficult during initial phases of the mission when the sailis to be “tumbling” about the Earth’s magnetic field linesduring part of the orbit and passively stabilized in the max-imum drag orientation near perigee. Hence the estimationof deployed area from orbit data will depend on the latterphases of the mission when the orbit circularizes and thesail passively stabilizes due to aerodynamic torque in a rel-atively constant local vertical/local horizontal attitude. Inthe event that the sail does not stabilize prior to reentry,orbital analysis would have allowed an estimation of anaverage ballistic coefficient that could have been correlatedto an average area. The NanoSail-D flight spare waslaunched in November 2010.

4. The future of solar sails in NASA

NASA is not currently funding solar sail technology.However, NASA is now preparing for a dramatic changein focus toward the development of advanced space tech-nology that will enable new human and robotic explorationof the solar system. Solar sails are a technology that cansupport this aim, and it is likely that within the next fewyears NASA will again be aggressively advancing the tech-nology toward mission implementation.

Acknowledgments

The large solar sail technology described in this paperwas funded in whole or in part by the In-Space Propulsion


Technology Program, which is managed by NASA’s Sci-ence Mission Directorate in Washington, D.C., and imple-mented by the In-Space Propulsion Technology Project.The NanoSail-D was funded by NASA MSFC and ARC.

References

Edwards, D., Hovater, M., Hubbs, W., et al. Characterization ofCandidate solar sail material exposed to space environmental effects,in: 42nd AIAA Aerospace Sciences Meeting and Exhibit, AIAA2004-1085, Jan. 2004.

Ellis, J., Lisano, M., Wolff, P., et al. A solar sail integrated simulationtoolkit, in: Proc. AAS/AISS Spaceflight Mechanics, Maui, HI, AAS04-283, Feb., 2004.

Ewing, A. Solar sail propulsion sensitivity to membrane shape and opticalproperties using the solar vectoring evaluation tool (SVET), in: 53rdJANNAF Propulsion Meeting, December 2005.

Lichodziejewski, D., Derbes, B., Sleight, D., Mann, T. Vacuum deploy-ment and testing of a 20 m solar sail system, in: 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and MaterialsConference, May 2006.

Murphy, D. Validation of a scalable solar sailcraft, in: 53rd JANNAFPropulsion Meeting, December 2005.

Pappa, R., Blandino, J., Caldwell, D., et al. Optical diagnostic system forsolar sails: Phase 1 Final Report, NASA/TM-2004—213511, Dec.2004.

Peter, C., Roberts, E., Harkness, P.G. Drag sail for end-of-life disposalfrom low earth orbit. J. Spacecraft Rock. 44 (6), 2007.

Thomas, S., Paluszek, M., Wie, B., Murphy, D. AOCS Performance andStability Validation for a 160-m Solar Sail with Control-StructureInteractions, in: 41st AIAA Joint Propulsion Conference, AIAA 2005-3926, July 2005.

Documents

Status of solar sail technology within NASA