Shadow Shaping is patented technology (U.S. Patent No 8,515,595) that can be used to create images on the surface of the Moon that are visible from Earth. Practical uses for these images include advertising and memorials.
The moon is covered with a fine dust that can be compacted to create shadow patterns. An excellent example of this is man’s first step on the moon.
Man’s First Step on the Moon (Top View)
Notice the three components to Shadow Shaping: the background, the shadow and the highlight.
Shadow Shaping Components (Cross Section)
As light hits the shadow pattern at an angle, a shadow is created that is significantly darker than the background. At the end of the shadow, there is a portion of the pattern that receives sunlight at a more direct angle and actually becomes lighter than the background. By making the slope of the highlight steep, the relative highlighted area as seen from above is minimal compared with the larger shadow area. The average of the two areas produces a net result that is still significantly darker than the background.
As demonstrated in both figures above, the pattern need not be very deep to create the desired effect. Spacing between the raised areas of the pattern needs to correspond to the end of the shadow for the darkest result. If the ratio of height to spacing for this pattern is constant the effect will be the same whether the pattern is 1 cm deep or 1 meter deep. Larger ratios will prolong the time that the pattern is visible during the cycle of the moon to a point by minimizing the highlight at more direct sunlight angles. Symmetrical patterns will provide the same effect for waxing and waning lunar cycles. Note that when the moon is full, there will be no image since the sunlight will no longer be hitting the pattern at an angle.
Different images formats can be created such as outline (faster to create), solid (easier to see) or grayscale (more detailed – created by interleaving shadow and background at different intervals).
Image Formats: Outline, Solid and Grayscale
To create these patterns in the moon dust, a remote controlled or autonomous, programmable rough terrain vehicle or robot can be used. Technology to provide autonomy and resistance to extreme temperature has been demonstrated by the Mars rovers that have run reliably for several years. Since the patterns have to cover large areas to be visible from Earth, a combination of higher speed and multiple vehicles may need to be used to create the patterns within reasonable amounts of time.
One possible vehicle could be a combination of the Mars rover (solar panels and extreme temperature resistance), and a three-wheeled, multi-axis rough terrain robot. The pattern is made with the tread of the wheels. If the raised area in the shadow pattern is created by a crosswise void in the tread pattern, then the vehicle will need to travel laterally. If the raised area in the shadow pattern is created by a longwise void in the tread pattern, then the vehicle will need to travel longitudinally. Angled voids could also be created for traction, but whatever the tread pattern, the raised area must be created perpendicular to the angle of the sun during partial phases of the moon. Three wheels allows for full coverage of the travel path, where a four-wheeled design would leave a gap in the middle. If extra weight is needed to provide sufficient dust compression, dust, rocks and soil could be collected in an onboard reservoir.
Longwise Tread Example with Solar Panel (Top View)
Elevation data from can be used to select an ideal area with flatter terrains. Other area selection data may include the dust color (background darkness), visibility factor (reduced visibility due to the angle of the terrain to Earth) and optimal solar angle regions.
Autonomous navigation can be accomplished through optical recognition of the sky (stars, sun, earth) and gyroscopic instrumentation. Occasional reprogramming and calibration can be done with communications from Earth. A combination of sensors, lasers, and optical recognition can be used for collision avoidance. Shock absorbing technologies can be used as well for handling collisions. Optical recognition can be used for path alignment. During the lunar nights, the vehicle would need to stow itself in a hibernation mode since solar power is no longer available and cold temperatures can be extreme.
Due to a lack of atmosphere on the Moon, Shadow Shaping images can last for thousands of years, unless they are redrawn or erased by Shadow Shaping robots. The images are only visible during partial moon phases when the light to the visible surface of the Moon is at an angle, so the full moon will look the same as it always has.
In addition to the images themselves, there is much to be gained by the development of Shadow Shaping technologies such as space exploration and space development techniques. Shadow Shaping on the Moon has been called “Shadow Farming” since the techniques used could be adapted to the terra-formation of other worlds including the planting of extraterrestrial crops. Spatial diversification of our species is the only way that mankind will be able to survive in the long run as threats to our world, such as impact events, pandemics, wars, environmental changes, or the expansion of the Sun, will eventually make the Earth uninhabitable. There are also advantages to moving these technologies out of the government sector and into the commercial sector, freeing up government resources to deal more effectively with humanitarian and social challenges.