With NASA looking to bring a crewed mission back to the Moon by 2026, and potentially stay there, how the lunar surface is illuminated and navigated is becoming an increasingly important conversation, as Australian lighting designer Claude Zhu explains.
As humanity explores beyond our planet, the Moon has emerged as a stepping stone for further space voyage.
Lunar missions present unique challenges, including the need for artificial illumination to facilitate navigation, research, and construction on the Moon itself. This article intends to delve into the design considerations and requirements of outdoor luminaires for these activities.
LUNAR AMBIENT LIGHTING
Considering lunar day and night first, the Moon is synchronous in relation to the Earth because of gravitational pull. It takes an equal period of about 27.3 days to orbit the Earth, and to rotate around its own axis.
The same lunar hemisphere always faces the Earth, which is known as the nearside, while the far side always faces away. Lunar day and night are each about two weeks long.
Unlike Earth, the Moon of course does not have an atmosphere. During the two-week lunar day, unfiltered sunlight is available full time, without diminution by solar angle, at 128,770 lux.
The experience of the Apollo programme lunar landings suggests that extravehicular activities (EVAs) conducted during the lunar noon may be difficult because of the lack of surface definition caused by elimination of shadows.
SHADOW
The absence of atmospheric scattering results in sharper and darker shadows on the Moon. The floors of some deep craters (permanently shadowed regions) can never receive sunlight, because of the Moon’s nearly perpendicular geometry (axis of rotation) to the sunlight direction.
At the Moon’s poles, the Sun is always near the horizon and the shadows are extremely long.
‘EARTHSHINE’
Light reaches shadowed areas from multiple natural sources which is known as ‘Earthshine’ and starlight, including diffuse inter-reflection of the lunar surface,.
The Earthshine level will be solely a function of Earth phase angle. Full Earthshine illumination on the Moon is about 76 times as bright as a full Moon on Earth.
Investigations indicate that, for most nearside locations, illumination will be adequate throughout most of the lunar night for EVAs, with only minor artificial illumination required.
In contrast, there is no illumination from Earthshine during the lunar night at the lunar far side. Thus, here, artificial lighting will be required on all night EVAs.
LIGHTING STRATEGY
Additional light might be needed during lunar day to bring out details in shades. One proposed option, Heliostat, is a system of reflective mirrors that adapt to the Sun’s arrays using a computer with programmed altitudes, longitudes, and latitudes.
This would be a low-mass, low-energy, and portable way to shine light into caves, crevasses, and other dark or deeply shaded areas. Large vehicles can utilise reflective white materials with artificial lighting to create a diffuse lighting work environment nearby.
During lunar night, rovers would require headlights, adjustable spotlights, running lights, and instruments lights.
When it comes to temperature, temperatures fluctuate dramatically near the Moon’s equator, ranging between scorching hot during the day, at 121°C, and frigidly cold during the night, at -133°C. Outdoor luminaires must therefore be engineered to endure these extremes.
High-temperature resistant materials, such as fused silica and sapphire, are ideal for luminaire optics and lenses in this context.
Metals such as aluminium and titanium are excellent choices for the structural components because they are lightweight, strong, and resistant to temperature extremes.
Effective thermal design is crucial to maintain the luminaire’s functionality. Insulation materials, such as vacuum-sealed layers or aerogels, can keep the luminaire’s internal components at a stable temperature.
SOLAR RADIATION
The vacuum lunar environment means that intense and unfiltered solar radiation can degrade materials at a much faster rate during the lunar day, compared with the Earth environment.
Luminaires can be coated with UV-resistant materials, such as titanium dioxide, or specialised paints designed for space applications to prevent degradation.
DUST
The lunar surface is covered in fine dust, also known as ‘regolith’. These particles can infiltrate equipment and reduce efficiency, light output and luminaire life.
Dust-resistant design is crucial to ensure long-term functionality. Silicone gaskets and o-rings, combined with robust enclosure designs, can keep lunar dust at bay.
CONCLUSIONS
Artificial illumination invariably plays a vital role in lunar scientific research and habitats, and will do so in future celestial exploration.
This may be augmented utilising reflective or light-coloured devices. Material selection is a critical factor in designing luminaires for the lunar environment.
The lunar surface’s extreme conditions, including temperature, solar radiation and lunar dust, necessitate materials like heat-resistant optics, specialised insulation, robust metals, UV-resistant coatings and dust-proof sealing.
All these, combined, will be needed to create luminaires that meet the unique demands of lunar missions.
THE ARTEMIS PROGRAMME
In February, news that the US had successfully landed the first private spaceship on the Moon – albeit on its side – brought home to many just how serious NASA and others are about going back to the Moon, with a crewed mission the ultimate goal, writes Nic Paton.
As Claude Zhu has made clear in his article, the key to this is NASA’s Artemis missions. These, as the Royal Museums Greenwich has explained in an extensive commentary, are aiming to ‘land the first woman and first person of colour on the Moon’, explore the lunar surface, and lay the groundwork for sending astronauts to Mars.
What’s more, the plan is not simply to repeat the feats of the Apollo missions and just land on the surface, but to stay there. This is one reason why how whatever infrastructure eventually is established on the lunar surface is illuminated is becoming a more important conversation.
One Artemis mission, Artemis 1, was completed in late 2022 and was an uncrewed test flight that orbited and flew beyond the Moon. The next missions in preparation are:
- Artemis 2. This will be a crewed flight beyond the Moon, further than any human has been before in space.
- Artemis 3. This will be the first crewed Moon landing mission since Apollo 17 in 1972. The intention is for the astronauts to spend a week on the Moon’s surface performing scientific experiments before returning to Earth.
- Artemis 4. This will bring the first part of a new lunar space station, called Gateway, into orbit around the Moon plus lead to a second crewed landing.
- Artemis 5. This will bring a further Gateway module, followed by a third crewed landing.
The intention is for Artemis 2 to launch no earlier than September 2025, albeit it was originally intended to take off later this year and so that is not guaranteed. Artemis 3 will then be no earlier than September 2026, and Artemis 4 and 5 in 2027 and 2029 respectively.
For any classicists, the reason the missions are being called Artemis is because Artemis is the mythological Greek goddess of the Moon, twin sister of Apollo. The name is therefore intended to link this programme with the Apollo missions that first landed humans on the Moon more than 50 years ago.
NASA ‘LIGHTING EXPERT’
As a final aside, in an illustration of the growing importance of lighting in space, last year NASA appointed lighting designer Haniyeh Mirdamadi as the agency’s new ‘lighting subject matter expert’, based at its Jonson Space Center in Houston, Texas.
Her remit will be to work on interior, exterior and mission lighting designs as well as the engineering of spacecraft, landers, rovers, habitat and suits for Artemis and other missions.
As part of her master’s studies, Haniyeh extensively researched the role of light on human psychological health and the effects of deprivation from earthly light through long-duration space expeditions and human colonisation of planets beyond Earth.
