Challenges and Design of LightSail-1 Boom Deployment Module

Chris Biddy, Stellar Exploration Inc.chris@stellar-exploration.com

LightSail-1 Overview

• LightSail-1 is made up of a 3U CubeSat– 10 x 10 x 34 cm, <5kg

• LightSail-1 will deploy a 32m^2 aluminized Mylar sail via 4m booms

• LightSail-1 will demonstrate controlled flight by Light

LightSail-1 with deployed sail

Avionics Module

Sail Storage Section

Boom Deployer

Payload Section

LightSail-1 Sail Blades

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 Blades are Z-folded in two directions into a wedge shape for storage • Z-fold provides a path for gases to escape

• Verified with vacuum chamber test

LightSail-1 Booms

• Lightsail-1 will use the AFRL developed TRAC (Triangular Rollable and Collapsible) boom

• Stainless Steel rigid booms can be collapsed and rolled around a spindle providing a compact storage solution

• Booms “self-deploy” due to stored strain energy when wrapped around a spindle – Boom deployment rate control via dc brushless motor coupled with worm drive

gear train

TRAC boom shown in deployed state

LightSail-1 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

Isometric view of deployer

LightSail-1 Boom Deployer

Deployer Mounting Boss

Flexure Clamp

Top Mounting Plate

Flexure Spring

Tensioner

Boom exit guide

Spindle Design

• Boom mounting bolts react boom loads• Spindle flanges constrain and protect booms• Cable clearance through center of spindle (cable pathway from

payload section to avionics section)

Spindle section view

Cable clearance through hole

Spindle Flanges

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

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

Boom Exit

Flexure Clamp

• Flexure Clamp fastened with stainless flat head cap screws• Flexure clamp rotationally constrained by square cutouts in top and bottom

mounting plates • Square recess in top mounting plate also reacts

shear loading under vibration

302 Stainless Steel

Recessed Square pocket constrains Flexure clamp

Tensioner

• Tensioner is fastened with and pivots about Stainless shoulder screws

• Rulon (or Delrin AF) bushings take axial and radial loads – Bushings reduce friction between tensioner and shoulder bolts

• Roller Shaft and Flexure Contact Pin have tapped ends and held in place with socket head cap screws

• Roller Shaft and Flexure Spring Contact pin made from 304 SS

6061-T6 Aluminum Roller

Flexure Contact Pin

Shoulder Screw

Delrin AF bushings

Boom Deployer

• The first engineering model of the boom deployer has been manufactured – Initial testing has confirmed required flexure spring rate

Boom deployer with bottom plate removed

Boom Deployer with partial boom deployment

Deployer Planned Tests

• Boom stowed/deployment test– Verify clearance between stowed booms

and deployer components– Verify boom deployment without

interference or resistance from deployer components

• Boom with Sail Blade deployment test• Full deployment test with deployment

rate control

Questions?

Montgomery, E. 2008, NanoSail-D, CubeSat Developers Workshop, San Luis Obispo, CA, California Polytechnic State University