A solar array paddle (SAP) is a vital primary power bus device that absorbs solar light to generate and supply the power required for satellite operation.

Satellites and other devices operating in space are powered by electricity. Since any satellite will run out of power and be rendered inoperable within 40 to 50 minutes if using an onboard battery alone, they need a constant supply of additional power. SAPs are designed to be folded up and stowed compactly during launch and then deployed once in orbit to provide a stable supply of power generated by the solar cells mounted on the light-receiving surface.

Functionality and performance requirements for solar array paddles

Power generation (several hundred to several kW)

Power generation requirements vary from one satellite to the next. These requirements are calculated using power analysis based on orbital temperatures that take into account seasonal fluctuations, while also factoring in orbital degradation (i.e., degradation caused by radiation, ultraviolet rays, atomic oxygen, and other factors) throughout the satellite’s expected lifetime.

The ability to be stowed for launch and deployed once in orbit

SAPs are designed to be folded up and stowed compactly for launch to withstand the severe conditions (e.g., vibrations, acoustic noise) experienced during a rocket launch. Once in orbit, the holding mechanism is activated, and the solar array paddles are deployed by the spring force of the deployment mechanism before being locked into place.

In addition to thermal vacuum and electrical performance tests, ground tests include vibration and acoustic tests performed while the SAPs are stowed in position. A deployment test unique to SAPs is also conducted in which they are levitated using air pads and suspended from above to cancel out their own weight. This is done to confirm whether they will still be able to operate according to the timing and sequence of operations specified in the design.

Tolerance of a wide range of temperatures

Since SAPs are part of the satellite exposed to the elements, they must be capable of withstanding a wide range of temperatures: -100℃ to +120℃ or higher for near-Earth orbiting satellites, 180℃ or higher for satellites orbiting inner planets, and -200℃ or lower for satellites in deep space.

Since there is a complex causal relationship between high and low temperature resistance when solar cells are mounted on SAPs, confirmation is not only conducted through design analysis but also verification in advance through element testing (coupon testing) using partial prototypes of actual hardware.

Types of SAP

NEC offers several types of SAP that can be used for different purposes.

Small standard SAP

This SAP series is comprised of standardized components, including panels, deployment mechanisms, and holding mechanisms that can be combined to accommodate various satellite requirements. Moreover, up to around 2 kW of power can be generated by changing the number of panels, and both one-dimensional deployment and two-dimensional deployment are possible, depending on the rigidity and field of view requirements following deployment.

Medium and large SAPs

Since SAPs for medium and large satellites use larger panels (approximately 2m x 2m in size), they also have a large structural mass. This means that the deployment impact load will increase, and excessive reinforcement will be required if the paddles are deployed by spring force alone. Therefore, a synchronization mechanism is added to each deployment mechanism, while a rotary damper* is also installed to enable slow, synchronized deployment of the entire SAP.

While most SAPs generate up to 5 kW of power using two wings, with each wing comprised of two to three panels, NEC has successfully combined more than 10 panels per wing in the past.

*Rotary damper: A rotary damper is a component used to slowly close lids and covers by utilizing the viscous resistance of oil.

Thin membrane SAPs

NEC employed a unique method focused on weight reduction to develop its thin membrane SAP, which has achieved the world’s highest level of performance with a power-to-weight ratio (i.e., the ratio of power generated to SAP mass) that is two to three times better than conventional SAPs (150W/kg or higher).

While the cost and time required for delivery are higher than that for ordinary SAPs due to the unique structure and process in which solar cell sheets are mounted on a curved surface rather than the conventional approach of mounting solar cells on a single plate, thin membrane SAPs are ideal for specialized applications where mass is crucial, such as deep space exploration and lunar surface. In fact, plans are slated for NEC’s thin membrane SAPs to be installed on the DESTINY+ deep space probe.

SAPs are the largest moving mechanical component among the equipment onboard a satellite, and various measures are taken for all components to ensure reliable operation while in orbit. In addition to the extensive lineup of products with a proven track record featured here, NEC is developing a new SAP to achieve even greater scalability and versatility in the future.

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