Abstract
Space structures encounter various severe environments in space. One of
these environments is severe thermal conditions. When the Engineering Test
Satellite -VIII (ETS-VIII) entered the Earth’s shadow, the temperature
of the large deployable reflector (LDR) mounted on the ETS-VIII decreased
for about 200 ºC. During this eclipse time, the signal level of a radio
wave from the LDR was observed to change. According to previous work, the
midpoint of the LDR was confirmed to deform by approximately 5 mm as the
temperature decreased, which led to a 65 km transition of the footprint
of communication beam on the surface of the earth. This phenomenon was
assumed to be caused by the thermal deformation of the LDR. It was not
a critical issue for the ETS-VIII because the communication beam from the
LDR tended to spread over a wide range. However, it may affect the performance
of such satellites in the future where highly accurate pinpoint communication
beams are expected to be required. From this point of view, we sought a
means to suppress the thermal deformation mechanically by focusing on the
internal force generated by the spring used to deploy the antenna and by
optimizing the coefficient of thermal expansion of the constituent members.
According to the numerical results obtained from finite element analyses,
the thermal deformations at all apices that support the reflectors were
suppressed at a high correction rate by adjusting the coefficients of thermal
expansion in the structural members and by controlling spring forces differently
in four areas depending on the distances from the constraint point.