Tubular Extendible Lock-Out Composite Boom (STELOC)

Mass and volume efficient solar arrays are sought by NASA, DoD and commercial space to enable high power missions from 20-50 kW in the near term and eventually up to 350 kW. Currently, the maximum power available from conventional solar arrays, for a given spacecraft, is limited by either the weight or stowage volume of the honeycomb panel substrates. Flexible substrate arrays can enable higher power spacecraft by improving specific power (W/kg) and specific volume (kW/m3) as well as improving the deployed natural frequency. Typical designs for flexible substrate array require a stiff boom mechanism to deploy the array and provide the deployed structure. Heritage flexible substrate arrays have used metallic slit-tube or coilable longeron booms. To be feasible, large, next-generation flexible substrate solar arrays require deployable booms that are more thermally stable than metallic slit-tubes (STEMs), and less expensive and lighter than coilable longeron booms (i.e. AstroMast). To address this need, CTD has developed the Stable Tubular Extendible Lock-Out Composite Boom (STELOC Boom). The STELOC Boom can provide stiffness equivalent to coilable longeron booms with a significantly reduced volume, mass and cost. The Phase I program demonstrated feasibility of the STELOC boom as the deployment actuator and primary structural component of a 15 kW solar array wing. The proposed Phase II program will advance the STELOC Boom to TRL 5 through the design, fabrication and testing of a flight-like Engineering Development Unit.

Advancement of high power and high specific power arrays and large robust arrays are both listed as critical requirements in NASA's technology roadmap. Advanced arrays are required to enable scaling up to 350 kW systems for interplanetary missions using solar electric power (SEP). While increased efficiencies of PV cells and power distribution will contribute to a portion of this power increase, very large arrays with very stiff support structures will be necessary to reach powers in the hundreds of kilowatts. In addition, large arrays which are structurally and dynamically durable under deployed conditions will require stiff, stable deployable structures to carry the deployed load and provide deployment forces. The stiff, lightweight STELOC booms provide the efficient structural performance necessary to achieve both very large arrays and robust deployed arrays. Therefore, successful achievement of the objectives defined for this program can provide a significant capability to NASA and NASA contractors to aid in the development of a SEP spacecraft tug or SEP for deep space missions. And in the near term, the 10cm twin-boom STELOC mast will enable robust 30 kW array systems for an SEP demonstrator or other high power missions.

Power systems compromise nearly 30% of a spacecraft's mass on average, thus improvements in specific power (W/kg) will enable either a reduction in spacecraft mass or an increase in capabilities. Near term Air Force satellite missions require more capable solar arrays with more total power on the same or smaller platforms. This includes enabling the GPS III Dual Launch variant which can leverage significant cost savings, and overcoming power challenges for Advanced EHF and classified missions. More powerful arrays must also have better specific power, decreased stowage volume and increased deployed stiffness in order to maintain other performance parameters of the spacecraft. Flexible blanket solar arrays can provide all these improvements by eliminating the heavy, bulky honeycomb panels used for conventional arrays. The STELOC boom will enable flexible arrays with all these qualities that could save $50 million per satellite and more than $1.5 Billion for a notional 30 satellite constellation of the GPS III Dual Launch Variant. The next-generation solar arrays being designed by Lockheed Martin are also intended for use on commercial geostationary satellites. Larger arrays will enable more transponders per spacecraft. Solar electric propulsion variants with high power, very stiff arrays can arrive on orbit more quickly and provide longer lifetimes. All these benefits translate to higher total revenues per spacecraft.

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