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The Forefront of Space Science

Measuring Plane Profile of Space Structures by Grating-Projection Method
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While the history of satellite development reveals the quest for large-size and multifunctional satellites, there are also trends of downsizing and improved functionality in an attempt to realize short development lead times, better risk distribution and lower costs. If downsizing of satellites and onboard instruments is possible, we should pursue it. Nevertheless, there is still demand for applications requiring large size. Examples are enlargement of antenna onboard satellites in order to downsize the ground antennas such as the ones on mobile phones, aperture of telescopes onboard astronomical observation satellites, and solar panels for greater power generation. From the aspect of payload transportation, however, there are weight and size constraints. Even when using a large-size launcher, naturally there are limits. Since large-size space structures must be loaded on transportation vehicles in a compactly folded state to launch, they must be able to deploy or extend in outer space. Furthermore, since it is thought to reduce costs by using a small launcher or launching multiple payloads at once with a large launcher, the need for light and efficiently stowable space structures is growing. The mechanics of these elements are also shifting from deployable plate structures to lightweight, stowable structures that can be stabilized with membranes and cables (Fig. 1 and 2).

Figure 1
Figure 1. φ1500mm size-reduction model for a ground test of a mesh antenna to be equipped on satellite

Figure 2
Figure 2. Photo of the deployed sail of Small Solar Power Sail Demonstrator IKAROS

After surviving harsh vibration and load at launch, space structures can maintain their shape in space by applying tension to flexible structural elements with low rigidity such as membrane and cable. Structures too flexible for use on the ground are often usable in space, providing considerable freedom in structural configuration (Fig. 2 and 3). However, that difficulty to use on the ground also makes it difficult to conduct testing on the ground in advance. For example, predicting deployment behavior of flexible structures in orbit based on observation of behavior tests on the ground, with gravity and atmosphere present, is still unsatisfactory even if we utilize full engineering knowledge, insight and imagination.

Figure 3
Figure 3. Photo of the deployed Space Free Flyer Unit (SFU) carrying a flexible solar array with solar cells attached to a film folded like a folding screen

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