452 LightSail-1 Program Requirements  The main requirements and corresponding selected implementation for LightSail-1 are summarized in  Table 1. Many of these requirements were derived from COSMOS-1.  Table 1. LightSail-1 requirements.  Requirement Selected Implementation  Low Cost CubeSat Platform  Greater Performance than COSMOS-1  3U CubeSat (maximum mass = 5 kg) requires 32 m2 sail  Demonstrate Orbit Energy Change 2 On-board 3 axis accelerometers and optical tracking  Demonstrate Thrust Control Requires ADCS with 90 ˚ Slew Maneuver  Image the Sail during/after deployment 2 On-board Aerospace Corporation Cameras 

Based on the customer requirements and associated trades it was decided to build LightSail-1 on a 3U  CubeSat platform with a 32-m2 square solar sail achieving a solar sail characteristic acceleration of   0.050 mm/s2.   LightSail-1 Configuration  The overall spacecraft was divided into three sections that include the avionics section, sail module, and payload section. The avionics section is ~1U and houses the avionics board, the sensor interface board, a transceiver, eight Lithium Polymer batteries and battery control boards, three torque rods, a momentum bias wheel, three single axis MEMS gyros, and a three-axis MEMS accelerometer. The sail module is ~1.5U and includes the sail storage cavity, and boom deployer. The payload section is ~0.5U and contains the deployer spindle drive motor and gear train, a three-axis MEMS accelerometer, a deployable monopole antenna, a deployable panel burn wire mechanism, and a storage compartment for two Aerospace Corporation built cameras mounted to the ends of the deployable panels.   Design Challenges  The following is a list of design challenges to the development of the sail module for LightSail-1.   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  It was determined early in the design phase that controlled deployment of the sail would be achieved by  driving the deployer spindle that the booms are attached to with a brushless DC motor. Because the booms have a large stored strain energy when fully stowed, a method of constraining the booms while the motor was not energized was required to avoid auto-deployment of the booms. It was decided that this could be achieved by implementing a worm drive that could not be back driven in the gear-train. The worm drive provided the required gear reduction from the motor to the spindle as well as eliminated the need for an additional mechanism to constrain the booms during launch. In order to keep the sail material contained in the sail storage structure the deployable solar cell panels closed over the sail storage module constraining the sail material in place.   Detailed Design  The boom chosen for LightSail-1 is the TRAC boom developed by AFRL because of its packaging  efficiency and specific stiffness. These booms were used in NanoSail-D and successfully flown on NanoSail-D2 last year. The TRAC boom consists of two Elgiloy metal strips each formed into a c-shaped curve and laser welded together back-to-back forming an inverted v-shape. The TRAC boom is shown in Figure 2.