India’s Chandrayaan-3 Vikram lander has started serving as the first active laser retroreflector on the lunar surface, marking a major milestone in space exploration capabilities. Though the lander crashed in 2019 before reaching its intended landing site, one of its instruments – a laser retroreflector array – survived intact. NASA’s Lunar Reconnaissance Orbiter (LRO) recently beamed lasers down to this array and detected the reflected photons, proving the concept of using active retroreflectors for precision tracking of locations and assets on the Moon.
Background Leading Up to Recent Developments
The Chandrayaan-3 mission is the successor to India’s Chandrayaan-2 mission, which launched an orbiter, lander and rover to explore the lunar south pole in 2019. The Vikram lander experienced problems during its powered descent and crash landed on the near side of the Moon.
Though a disappointment, the crash left an opportunity – the lander’s laser reflector array survived. This 15cm cube features an array of 100 corner cube reflectors that reflect light directly back at its source. Though designed to calculate the lander’s range from the Chandrayaan-2 orbiter, the array can reflect signals from any source, becoming the Moon’s first long-lived active laser retroreflector.
How the Laser Ranging Experiment Was Conducted
On November 18th, 2022, NASA scientists aimed pulsed lasers from the LRO spacecraft down at the array. The team detected laser photons reflected directly back, proving the technology’s usefulness for precisely tracking locations on the Moon.
The Lunar Orbiter Laser Altimeter (LOLA) instrument used for this experiment measures ranges to lunar terrain features by timing reflected laser pulses. Though it was designed to measure topography by aiming at natural terrain features, the corner cube design of the Vikram reflector array provides strong, precise reflections visible from spacecraft orbits.
|Lunar Orbiter Laser Altimeter (LOLA)
|Lunar Reconnaissance Orbiter
|Ranging lasers to map lunar topography
|Laser Retroreflector Array
|Chandrayaan-3 Vikram Lander
|Reflects incoming lasers back to source
This demonstration opens possibilities for using active optical instruments as navigational aids and benchmarks to precisely track locations and guide future lunar landings.
Significance of Developing Precision Lunar Navigation Infrastructure
Precisely tracking locations on the Moon is critical for future lunar exploration, but the Moon presents unique challenges. It lacks GPS satellites for easy positioning, while terrain features can look similar across vast distances. Natural reflectors like Lunokhod retroreflectors provide only faint, broad reflections visible to ground telescopes.
Active retroreflectors offer stronger, more precise reflections detectable from lunar orbit. If expanded into larger arrays or networks, they could enable centimeter-level tracking of landers, rovers, and astronauts on the surface. This could aid future missions with:
Precision Landing: Retroreflector networks can guide landers to precise locations like permanently shadowed craters or sites identified as scientifically interesting. This helps ensure safe, accurate landings.
Localization: Landers and rovers could calculate precise location by ranging to multiple retroreflector beacons, aiding long-traverses or sample return missions.
Navigation: Astronauts could use reflector networks to monitor their real-time location, heading, and altitude – similar to an aircraft instrument landing system. This situational awareness enables safer exploration.
|Enables Capabilities Like
|Landing in shadowed craters, at identified features of interest
|Long rover traverses, sample returns
|Real-time positioning/heading info for astronauts
In essence, reflector infrastructure acts akin to a GPS constellation, enabling game-changing positioning capabilities taken for granted in Earth navigation.
What Comes Next – Expanding Lunar Navigation Infrastructure
The success of this demonstration opens the possibility for expanding laser reflector networks across more lunar landers and dedicated beacons. Upcoming Indian and American lander missions plan to carry reflector payloads to contribute to this emerging infrastructure.
NASA also proposes to fly more precise next-generation arrays tuned to orbital laser altimeters like LOLA. These could strengthen reflections to ease acquisition from space.
If implemented across multiple nations’ landers, a networked array of even 10-20 reflectors could enable centimeter-level precision tracking across lunar near and far side areas of interest.
This collaborative assembly of lunar laser infrastructure promises to greatly aid the coming decade of lunar exploration, research, and development. By removing navigation uncertainties, it allows missions to target more ambitious and sensitive scientific and exploration objectives confidently.
The recent laser ranging experiments with Chandrayaan-3’s reflector mark the humble beginning of what promises to become indispensable infrastructure for positioning, landing and exploring across the lunar surface. By pooling resources and reflector payloads across different nation’s landers and rovers, space agencies can cooperatively advance exploration capabilities faster than any one nation alone. As more assets take shape on the lunar surface, precision navigation networks will move from novelty to necessity for operating in this GPS-deprived environment.
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