>>Validation of the UltraFlex 175 Solar Array

The goal of the ST8 UltraFlex 175 validation experiment is to demonstrate empirically that the technology advance represented by this design is sufficiently mature that it can be included in the design of a space or Earth science mission. When validated, this advanced technology solar array will be capable of providing 7 kW of power with a deployed specific power of 175 W/kg. To this end, the ST8 project will build a 5.5-m diameter UltraFlex solar array and conduct a series of tests in air and in a vacuum chamber that will accomplish three objectives:

1. Model and predict steady-state and transient deployment motion and torques in air and vacuum within 10% of the measured data for UltraFlex arrays up to 5.5-m diameter;

2. Model and predict the first (lower frequency) two dynamic modes of the fully deployed UltraFlex design in air and vacuum within 10% for arrays up to 5.5-m diameter;

3. Verify that the thermal performance of the solar cells, when attached to the Vectran mesh, is acceptable for Earth-orbiting and deep space applications whether the cells are illuminated by the Sun or eclipsed.

To accomplish these objectives a 5.5-m diameter UltraFlex 175 array will be built and instrumented (although the expensive solar cells will be represented by a lower-cost simulator). Accelerometers, optical targets, for measuring displacement remotely, and instrumentation to measure deployment forces and torques will be the principal instrumentation. Deployment tests will be conducted in air and vacuum. For these deployment tests the heavy end panel will be supported by an “off loader” to simulate zero gravity during deployment. The data from these tests will be compared to the steady-state and transient forces and torques predicted by the deployment analytical model and used to validate that model so that the deployment forces and torques expected in a flight application can be predicted and used to establish design margins.

The dynamic response of the deployed UltraFlex 175 array will also be measured in both air and vacuum. Displacement and accelerometer data will be used to measure the two lower frequency modes of the deployed UltraFlex 175. The data from these tests will be compared to the dynamic behavior predicted by the analytical structural model of the array and used to validate that model so that the in-space dynamic behavior of an UltraFlex can be predicted and used in spacecraft system design activities. The dynamic frequency response of the UltraFlex 175 can be straightforwardly tailored by incorporating stiffness-changing modifications to support struts for the spar structure to which the triangular gores are attached. This tailoring is beneficial, for example, in minimizing spacecraft attitude control requirements.

The thermal performance of the solar cells will be measured in separate vacuum tests designed for this purpose. The results of these thermal tests will be used to validate the analytical thermal models, allowing prediction of the in-space thermal behavior of the UltraFlex 175 array.

At the conclusion of the ST8 UltraFlex 175 validation experiments, the critical elements of the UltraFlex solar array’s behavior will have been demonstrated: deployment, dynamic response, and thermal characteristics. In the course of demonstrating the successful execution of these critical functions, data will have been obtained and used to validate analytical models that illuminate the engineering behavior of the array and allow its in-space behavior, and that of similar, smaller designs, to be predicted and used in spacecraft design activities

These tests and validation of the design and analytical models of the design, will reduce the risk of incorporating the UltraFlex solar array into a spacecraft design to an acceptable level, thus making the benefits of 175-W/kg, solar-array performance available to the U. S. spacefaring community.

The UltraFlex 175 solar array is being developed and tested by ATK Space Systems in Goleta, CA. The Principal Investigator is Mr. Steven White.