STAR Array Analysis Assumptions

Joints are Al 6061 or equivalent.

Struts and waveguides are XN70 graphite composite, 60% fiber volume.

Waveguide wall thickness 0.025"

Strut wall thickness 0.058"

Spacecraft assumed as 30" cube for shading purposes (will be modified to cylinder with 40" diameter, 60" length).

Solar panels ignored

XN70 properties used from NASA CR-4708, constant with temperature

All strut ODs currently 1.0".

Electronic boxes controlled to 10°C and isolated from mounting struts.

Backplate for mounting to spacecraft is aluminum beam structure.

Beam connecting three closest waveguides is XN70.

Optical properties: a/e = 0.1 / 0.1 -- unpolished aluminum

MLI (e_eff = 0.1) used on sun-facing side of first waveguide only.

Two orbit extremes of beta 60° and beta 90° evaluated for sun-synchronous orbit with 420 km altitude, year 2000 launch, 6 am crossing time.

Contact resistances between parts neglected (should be small for these thermal ranges).

Shading of waveguide, truss and joint parts for orbital fluxes and views to space considered.

Radiation exchange between array parts neglected (should be small for relatively small temperature differences and small viewfactors between parts).

In beta 90° orbit, 16 time points used for orbital fluxes; in beta 60° orbit, 48 time points used (larger changes).

Fluxes and viewfactors to space averaged over length of each waveguide side, and over length and circumference of each strut. May be modified for spacecraft shading case (highly shaded half of array).

Spacecraft assumed at constant temperature, but isolated thermally.

Worst-case hot and cold points in beta 60 orbit used for deflection prediction.

No ground screen assumed.

Parametrics to be run

Eventually, all of the following alternatives should be evaluated by analysis:

Change all struts (except long diagonals and sliders) to 0.75", and other sizes as required.
Evaluate both halves of array (differ by spacecraft shading direction).
Evaluate any changes due to joint design selected (John vs. Vaughn latch).
Evaluate other joint materials such as Ti-6Al-4V and XN70.
Possibly use properties for XN70 that vary with temperature (both thermal and structural properties).

Analysis Plan

Run all cases necessary through thermal analysis and produce predicted thermal distributions.

Run structural model with all joints assumed to be stiff, for the following set of results:

Predicted deflection in single-point case [change in going from initial alignment temperature (on Earth -- 20°C) to any given on-orbit case]

Predicted single-orbit transient deflection [change between one b-60 time point to another]

Predicted annual transient deflection [change between b-90 thermal distribution to any b-60 Time point distribution]

First natural mode

Joint loads in the above deflection cases

Run structural model with true stiffness and degrees of freedom in rotation at each joint, for the same set listed above. If possible, determine joint loads during deployment.

Make design recommendations based on results above.

Change structural model to aluminum single-bay structure (as built).

Perform stiffness, modal, etc. testing on the aluminum single-bay structure.

Correlate single-bay model to testing results.

Incorporate any changes due to correlation in full flight array model.

Re-run flight analyses.

(Optional thermal correlation)

Change thermal model to aluminum single-bay structure.
Run thermal test described above on aluminum single-bay structure.
Correlate single-bay model to testing results.
Incorporate any changes due to correlation in full flight array model.
Re-run flight analyses.

Return to STAR main page

Content Last Updated: May 27, 1998

By: r.m.amundsen@larc.nasa.gov

Site last reviewed: April 20, 2009.
Responsible NASA Official: Ruth M. Amundsen, Structural and Thermal Systems Branch, Systems Engineering Directorate, Ruth.M.Amundsen@nasa.gov, (757) 864-7044
Site Curator: Ruth M. Amundsen, Structural and Thermal Systems Branch, Systems Engineering Directorate, Ruth.M.Amundsen@nasa.gov, (757) 864-7044
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