>> SAILMAST Validation Experiment

The SAILMAST validation experiment will test a 40-meter boom in an ambient laboratory environment. The SAILMAST will be deployed and characterized both statically and dynamically. Overhead and air-bearing supports will be used to offset the effects of gravity during deployment and characterization tests. Static load tests and dynamic tests will be conducted in a horizontal plane to obviate the effects of gravity; the mast will be rotated in 90-degree increments and retested to fully characterize the structure. The data taken during these tests will be used to validate analytical models of the mast’s deployment and its structural behavior. The models will then permit scaling the test results to similarly constructed masts of different lengths and stiffness that are being considered for use on Earth science and space science missions.

The free-state shape (degree to which the mast is less than perfectly straight) of the mast is an initial condition that must be measured to predict the mast’s performance accurately. It will be measured multiple times while the horizontally deployed 40-meter mast is supported by a system of supports to counter the effects of gravity without restraining shape perturbations except for those in the gravity direction. The mast will be rotated in 90-degree increments and the measurements repeated. Multiple measurements over the course of the test effort will discern changes in shape (if any) that are due to loadings and deployments of the mast. These data will address three key questions:

1. What is the local waviness of the longerons?

2. How much does the entire boom structure bend or twist?

3. What is the effect of these imperfections on the overall structure?

The validation experiment will begin by deploying the SAILMAST from the stowage canister by paying out a lanyard with a motor. It is a phenomenon of uncoiling a "spring-loaded" mast that there is an instantaneous "kick-over" as the final few centimeters of its length snap to straightness. The deployment test will be designed to measure the transient forces transmitted to the spacecraft during this final deployment transient. This approach will permit this kick-over to be measured and modeled, and its effect on a spacecraft predicted.

The performance of the mast will be tested in a horizontal plane using the technique of vertical supports to offset gravity. To determine the mast's static and dynamic response, it will be retested after it has been rotated 90 degrees .

The fully deployed horizontal SAILMAST will be tested (still using the technique of vertical supports to offset
gravity and testing in a horizontal plane, repeating tests after rotating the mast in 90-degree increments) to determine its static and dynamic response.

Detail of vertical supports to offset gravity in testing the SAILMAST in a horizontal plane.

Static tests will measure both the load carrying capability of the mast and its buckling performance. Load carrying performance will be characterized by measuring the force necessary to displace the mast’s tip a series of specified amounts horizontally. Its buckling performance is of primary concern when the SAILMAST would be subjected to axial loads for a solar-sail application. Buckling will be measured by reversing the deployment-lanyard motor, pulling on the lanyard and putting a known axial load on the mast. (For the purpose of supporting solar sails, it is in the axial direction that the predominant load forces will act.) The mast will experience some displacement, which will be measured. This process will be repeated at increasing known loads until the mast begins to buckle. The loading process will then be reversed in increments and the displacements measured.

Dynamic response of a horizontally deployed mast will be determined by using a vibration-inducing device applied in a horizontal direction and then measuring the mast’s response.

All the data taken will be used to confirm the analytical models (also developed as part of the ST8 effort) of the SAILMAST’s deployment, static, and dynamic characteristics, as well as associated predictive and design capability regarding overall behavior and performance. These empirically validated models will be able to predict the operating characteristics of masts constructed similarly to SAILMAST but of different size and stiffness. This capability significantly matures the technology advance represented by SAILMAST.

At the conclusion of the ST8 SAILMAST validation experiment, the comprehensive tests of the 40-m test article and the validated models combine to make selection of SAILMAST-like, lightweight structural elements for Earth and space science missions possible. As a result, for applications for which these structural elements are suitable, significant mass savings are possible.

The SAILMAST is being developed and tested by ATK Space Systems located in Goleta, CA. The Principal Investigator is Mr. Michael McEachen.