INERTIAL ROLL RATE DECAY MEASUREMENT

Space Electronics has developed a simulator that rotates a payload on a frictionless gas bearing and measures the decay in spin rate resulting from the mechanical losses. Losses corresponding to retarding torques as small as 0.001 lb-inch can be measured.

This device can also be instrumented to measure the net moment of inertia of the payload as well as the gross moment of inertia of the whole rotating assembly.

The frictionless gas bearing is a very sensitive device that allows static balancing through a logical cause and effect method. This device can also be instrumented to measure moment of inertia and product of inertia of the rotating assembly.

Since windage losses would obscure the data, a helium chamber can be built onto the machine. The chamber used with this gas bearing system uses a novel fabric membrane concept that allows the air to be thoroughly expelled before the helium is introduced.

Main Application:

Determining changes in structure inside an assembly - When the inside structure of a payload changes, its roll decay rate changes. By comparing decay curves of a master test object, it is possible to determine very small differences in the payload. This is particularly useful to find out if any internal component is lose or if a fluid filled chamber is leaking. This process can be used as a non-invasive way to verify proper assembly of a payload or to determine if a payload needs service because of internal changes.

Other Applications:

Determining Satellite Rotational Losses - When a satellite rotates in space, the gravitational attraction of the earth causes the structure to flex. This results in a small hysteresis loss, which causes a gradual decrease in the rotation rate over a long period of time. This loss is dramatically increased if relative motion occurs between parts in the assembly. Such motion may occur from slip at bolted joints or sloshing of fluids present in the body.

Determining Windage Losses of Airfoil Shapes - This machine is an extremely sensitive device for determining the windage losses for various airfoil shapes. A baseline windage loss is first established using a smooth cylinder spinning in a helium atmosphere. Various airfoils can then be attached to the cylinder and the decay rate measured in both air and helium at different speeds. The machine reliably measures the drag due to projections as small as the head of a 1/4-inch socket head cap screw located at a radius of 4 inches rotating at speeds below two revolutions per second.