Photographing the Universe using a flimsy high-technology plastic sheet

A post on ultralight actively controlled polymer space telescopes.

A space telescope is a glorified bathroom mirror mounted far above your head and made to exacting standards. The curved primary mirror collects light from distant objects, and reflects them backward toward a single point. This single point is the focus, wherein a camera sensor may be placed to collect the light and create an image. Clearly, in order to discern from where the light has come accurately, the shape of the mirror must be highly precise. Further, it must be extremely stable, and is therefore likely made of a fairly thick low-expansion glasses, with significant weight.

However, since reaching orbit is difficult [citation needed], reducing this weight would allow missions with larger mirrors, or to farther destinations. Of particular interest is the Solar Gravitational Focus, where the intense gravitational field of the sun bends the fabric of space time and therefore functions as a lens. A future space telescope could utilize this lens to image an exoplanet in high detail and look for intelligent life in the Universe (no such thing has been detected yet).

An activity was started at the European Space Agency (ESA), and the following post illustrates some of this ongoing work. The idea was to replace the heavy glass mirror by an extremely thin and lightweight spherical shell made of an engineering grade polymer. On it, a thin layer of PVDF-TrFE is deposited. This material serves as a form of articifial muscle, contracting slightly in the presense of an electrical field. Small conductive electrode areas distributed over the reflector can thus control the shape, allowing active improvement of the figure accuracy while the reflector is in space.

Above a CubeSat with a future ultralight deployable space telescope is illustrated. The thin polymer shell is folded into a confined space, and once in orbit deploys to a size larger than the satellite itself. Contrary to segmented designs such as the impressive James Webb Space Telescope, the structure is a single monolithic part with no hinges or other moving parts. The focus of my research is the following:

1. The initial manufacturing of the reflector is critical, how do we accurately measure it and ensure the manufacturing process is up to standard?
2. The space environment is hostile, and can lead to significant temperature deviations because of the lack of atmosphere and intense heating from the sun. Can the reflector be produced with sufficient thermal stability?
3. The stowage of the reflector leads to significant stresses which are partially relaxed because of the viscoelastic nature of the polymer material. We must confirm that the shape of the reflector after deployment remains precise enough to be within the control range of the piezoelectric layer.

To address these questions I have:

1. Constructed metrology setups and software based on the Software Configurable Optical Testing System (SCOTS).
2. Investigated the performance of the space telescope in Finite Element Modelling tools with regard to control performance, thermal aberrations, etc.
3. Investigated the viscoelastic nature of the reflector numerically and experimentally.

Future posts will dive deeper into these issues. I add one more illustration:

The above illustration shows how a 10 degree thermal gradient across the reflector leads to an aberration (left). Control voltages are applied on the reflector in a specific pattern depending on the aberration (middle). The error is corrected and only a small residual remains (center). The residual error depends on the amount of electrodes, with finer electrodes leading to better control.