LightSail-1™ Solar Sail Design and Qualification

Chris Biddy,

Stellar Exploration Inc.

41st Aerospace Mechanism Symposium

LightSail-1™ Introduction

• Project of The Planetary Society

• Completely privately funded through member donations

Objectives are to:

• Demonstrate viability of Solar Sails – Ability to alter orbit energy in positive direction

– Ability to manage orbital energy

– Ability to control spacecraft under solar sail power

• Develop and demonstrate key technologies – Sail deployment

– Sail material management during flight

– Gossamer structure dynamics

• Demonstrate pathway to deep space with solar sails

Requirements are to:

• Achieve greater sail area/mass than COSMOS-1

ACS Orbit Raising Mode

• Orbit raising will be accomplished by 90 degree pitch

maneuver

• >800 km orbit needed for SRP > Aerodynamic Drag

LightSail-1™ Design Challenges

• How to package the sail and booms in the

allowable volume

• How to manage boom strain energy while

stowed and during deployment

• How to control the sail deployment

• How to constrain sail material and booms prior

to deployment (including during launch)

• How to manage sail material during deployment

LightSail-1™ Configuration

• 3U CubeSat Spacecraft organized into 3

sections

• Avionics Section/Sail Storage (~2U)

– Contains Avionics Board, radio, Sensor

Interface board, Battery Pack, 3- single

axis MEMS Gyros, 3 Torque Rods, 1

Momentum Bias Wheel, a 3 axis

accelerometer, and sail storage cavity

• Deployer Section (~0.5U)

– Houses 4 x 4 meter TRAC booms

• Payload Section (~0.5U)

– Houses boom drive motor and gear train,

storage area for cameras (attached to

deployable arrays), monopole antenna,

deployable array burn wire mechanism

and a 3-axis accelerometer

Boom

• Lightsail-1™ uses the AFRL developed TRAC (Triangular Rollable

and Collapsible) boom

• The TRAC boom can be collapsed and rolled around a spindle

providing a compact storage solution

• Booms “self-deploy” due to stored strain energy however an external

torque is required to deploy the sail

– Booms are driven by a brushless dc motor coupled with worm drive

gear train

Deployed TRAC boom

Boom Deployer

• Key Requirements Store and deploy 4m booms

– Control deployment rate so as to not damage booms or sail blades

• Deployer Functions – Provide normal reaction force against booms at all times (required to keep booms “pinched”)

– Provide for smooth deployment (no interference between booms and deployer components)

– Guide booms at deployer exit

• Deployer Features – Bearing supported spindle

– Rocker arm tensioner with flexure springs

keep booms against spindle

– Delrin AF boom guides at deployer exit

• Deployer Size – Maximum height = 5.5 cm

– Maximum width = 10 cm

Deployer

• Rocker arms deflect flexure springs during boom winding

• Flexures stick out past solar panel plane only at the end of boom

deployment (after solar cell panels are deployed)

• Booms exit at corners (denoted by arrows)

Fully deployed state (flexure springs not deflected) Fully stowed state (flexure springs deflected)

Deployer Lessons Learned

• Significant boom axial force required to deploy sails

• Boom management within deployer critical for reliable

deployment of the sail

– Determined that the flexure spring rate affected required motor

torque to deploy the sail

– Determined that high coefficient of friction is

required between adjacent boom wraps

• Difficult to predict cold performance

– Deployment motor required additional

current as temperature decreased

Flight Deployer and payload section

Sail Folding and Storage

Z-fold sail quadrant from outside edge to

center

Z-fold sail from

center outward

to form

“wedge”

shaped fold

Folded sail

quadrants fit

into wedge

shaped

cavities and

restrained by

deployable

Solar Cell

panels

• Sail quadrants are z-folded in two directions to form a wedge shaped folded

cross-section

• Z-fold provides a path for gases to escape

• Verified with vacuum chamber test

Sail Attachment

• The triangle shaped sail quadrants are attached to the spacecraft at

all three corners

– At the base of the sail storage cavity and the tips of the booms

• Metal grommets and split rings were used to connect the sails to the

booms with extension springs in series to account for thermal

distortions

Sail quadrant to boom attachment Sail base grommet

Sail Management

• The stowed sail is held in place with the deployable arrays

• During deployment the sail is withdrawn from the storage cavities 1

fold at a time due to a slight interference fit between the folded sail

quadrants and the storage cavity

TRAC Boom

Tensioned Sail

Remaining Sail Material

Engineering model deployment testing Stowed Flight unit

Qualification Testing

• Qualification testing included sail deployments before and after

TVAC and random vibe tests

• Off-loading was achieved by building a table to support the booms

during testing

Sail deployment table

LightSail-1 undergoing random

vibration testing at Cal Poly

Onboard camera view of sail deployment

Conclusion

• LightSail-1™ is ready for launch

• Reliable sail deployment has been demonstrated (over a dozen

successful deployments)

• LightSail-1™ achieved ~150g/m^2 with an 80:1 pre to post

deployment ratio

Questions?