Nonlinear Vibration of Deployable Booms

Deployable Booms

Deployable booms are an important spacecraft component. The Ulysses spacecraft (launched in 1990) uses specific types of deployable boom for different purposes: Bi-STEM used as a dipole antenna (35m length, 5mm diameter); CTM used as a monopole antenna (8m length, 40mm width); radial boom for dispensing sensors (5.5m length, 50mm diameter). Deployable booms are also used for gravity gradient stabilization and as actuators to deploy and retract other structures, e.g. the solar arrays of the Hubble Space Telescope. The STEM and CTM are formed from thin sheet metal. They are initially stored on a drum and are deployed, once in orbit, to their working configuration by an electric motor housed in a mechanism box.

Ulysses Spacecraft	STEM-type deployable booms	Collapsible Tube Mast (CTM)

Finite-Element Analysis of First and Second Modes

The first two eigenmodes of a cantilevered rib.

First mode (1st Torsional)	Second mode (1st Flexural)

Amplitude-response results for the first mode and second mode show softening spring behaviour; consequently, resonance curves bend to the left of the natural frequency.

First Mode	Second Mode

Experimental Results

Experimental results have verified the softening behaviour exhibited by the first and second mode. In addition, dominant quadratic nonlinearities cause the rib to exhibit superharmonics, subharmonics, combination resonances, and quasiperiodic motion. Chaotic motion has also been observed.

Frequency-response plots for first and second modes.

First mode (1st Torsional)	Second mode (1st Flexural)

Amplitude-response plots for first and second modes.

First Mode	Second Mode

Last updated on the 15th of February, 1998