Inflatable Rigidized Heliostat

Last crawled date: 1 year, 11 months ago

Footprint when stowed: ~ 1 meter long, 1.2 meter wide, 0.5 meter in height
Reflective area: ~ 11 m2
Solar area: ~ 1,2 m2
Mass: Inflatable heliostat ~ 5 kg, supportive structure + solar, 10 kg, movement mechanism 20 kg for a total of 35 kg.
Low CoM (Centre of Mass) allows for more flexibility in rover design, without compromising stability in steep slopes and extreme angles.

For further detail please see below:

Please excuse the low quality CAD, severe software issues meant I was unable to do what I wanted in time, I hope it is adequate for the concept to be understood.

In order to minimize mass, failure modes and complexity an inflatable rigidized structure is proposed. The inflatable heliostat would be constructed in a similar way to what was proposed in the QUASAT program [QUASAT program: The ESA reflectorm G.G Reibaldi, M.C Bernasconi] just as tested and suggested in that study the structure would include resin filled ribs that would harden (by heat or UV) and rigidize the structure after deployment, thus the system would not be sensitive to degradation of the mylar film causing a leak. A typical issue with this type of system is keeping a high accuracy shape [Deployable Tensegrity Structures for Space Applications, Gunnar Tibert], for the application of a heliostat this should not be an issue, since the shape stability requirements are substantially lower in comparison to an antenna. This type of structure has the advantages of high deployment reliability, low mass and ability to be tested on earth, using a helium mixture to simulate moon-gravity. Themass per area can be estimated to be 0.421 kg/m2 (including a 10% contingency) according to the QUASAT study. This would suggest a mass of approximately 4.8 kg for the 2 m diameter inflatable proposed. The viability of the suggested mounting position is demonstrated by the deployment sequence presented in Fig.1, this further gives the judges a good demonstration of how such a structure might look in reality. Electrically activated chemical deposition or a pyrotechnic charge would be used to generate the gas needed for inflation.

The inflatable heliostat would however have a different layout in comparison to the demonstrated inflatable antenna in Fig.1 and would have on one side a transparent membrane, on the other a mirror membrane as demonstrated in [Construction and Optical Testing of Inflatable Membrane Mirror Using Structured Light Technique, Felipe Patiño-Jimenez, et.al].


Figure 1: Deployment sequence of an inflatable antenna [Chemically Rigidized Expandable Structures, M.C. Bernasconi]

To minimize the torque and power requirements of the drive motors, the heliostat is limited in its rotation around the horizontal axis, physical stop prevents it tipping forwards more than 45 degrees and a set of springs that assist in the initial deployment prevents it from tipping backwards more than 45 degrees (not depicted). The selection of these limits have been set based on a rough estimate on what might be reasonable considering the application of lumination in dark craters, heating of equipment, shading and the heliostats relative distance to the target.

For power and sun-sensing it is suggested that the plate that carries the inflatable structure (see curved surface in the stowed state, suggested material of choice is a glass fiber sandwich panel), would also hold the solar cells and sun sensors (if using power distribution of individual solar cells is not accurate enough). With this design the solar cell efficiency is maximized (although with some losses due to the transparent film in the way) and the CoM kept low.

To orientate the inflatable structure a bevel gear design would be used around the vertical axis and a simple pinion gear design for the horizontal axis, which would be covered by MLI attached to the back of the moving solar/ inflatable support structure and the rover, completely isolating all moving parts from lunar dust, with the consequence of the heliostat not being able to rotate 360 degrees (since that would tear the MLI).

The rover design is merely a representation of a possible movable platform and the focus of the design lies in the heliostat itself. Rover wheel model is by Daniel Loera.