# Lunar Trailblazer

Lunar Trailblazer was a small (class D) lunar orbiter, part of NASA's SIMPLEx program, with a mission to detect and map water on the lunar surface to determine how its form, abundance, and location relate to geology. Its mission is to aid in the understanding of lunar water and the Moon's water cycle. Lunar Trailblazer was launched on 27 February 2025, as a secondary payload on the IM-2 mission. The Principal Investigator (PI) of the mission is Bethany Ehlmann, a professor at Caltech. Soon after launch, NASA lost contact with the spacecraft.

## Mission

Lunar Trailblazer was selected to be part of NASA's Small Innovative Missions for Planetary Exploration (SIMPLEx) program in 2019. The goal of the planned mission is to use a small satellite to map water on the Moon.
The mission has four scientific objectives:
* measure and map the amount, location and form (hydroxyl, H$_2$O, or ice) of lunar water and determine any correlation to latitude and surface makeup
* study the time-variability of lunar water in sunlit portions of the Moon
* determine the form, amount, and location of lunar water in permanently shadowed parts of the Moon
* study how changes in surface temperature affect concentrations of water and ice
In addition, the spacecraft will search for good locations for future lunar landings.

### Launch and mission outcome

Like other SIMPLEx missions, Lunar Trailblazer was launched as a "rideshare" with another NASA or commercial mission. It was launched as a secondary payload on the IM-2 mission in February 2025 with a number of other payloads. Originally it was going to launch with IMAP in 2025, but NASA found a different rideshare opportunity since the spacecraft was scheduled to be completed in 2022.
Soon after launch, NASA lost contact with the spacecraft.

### Orbit

Lunar Trailblazer was to orbit the Moon in a 100 kilometres (62 mi) polar orbit to study water on the Moon using its two scientific instruments.

## Scientific background

Unshielded from the vacuum of space, lunar landscapes are exposed to full illumination from the Sun for about two weeks, and total darkness for another two weeks. The Moon's day—one full rotation—is equivalent to about twenty eight Earth days. Adding to the harshness of this surface environment, the Moon has almost no atmosphere and no magnetosphere to protect it from the Sun's radiation. So, the lunar surface undergoes extreme temperature swings every day and night. During the day, temperatures near the equator are well above boiling, up to 400 K, or 260 °F. At night, these latitudes reach temperatures far below freezing (around 170 K/-150 °F at most). Any water that reaches the surface during the night would be expected to boil away during the day, or quickly sublime away in the low pressure.
On the Moon, there is no rainfall, but there are other ways that water can be delivered to the surface: micrometeorite impacts can carry water from space or excavate water from below the surface, and potentially, water could be created directly on surface minerals by implantation of hydrogen from the solar wind. Still, until very recently, scientists did not expect water to be present on most of the surface of the Moon.
In 1998, Feldman et al. showed that water ice might be present in permanently shadowed craters at the poles of the Moon. They detected the presence of hydrogen in the upper half-meter (1.5 feet) of the lunar surface, which was most likely evidence of water ice. This discovery was debated in the scientific community as missions to study the lunar surface waned and further data was unavailable—until, in 2009, LCROSS (Lunar Crater Observation and Sensing Satellite) jettisoned one of its empty propellant tanks in a controlled collision to impact an area of the Moon that lay in permanent shadow to test for the presence of ice. When the tank hit, it created a plume that was observed by both the LRO (Lunar Reconnaissance Orbiter) and the LCROSS spacecraft as well as telescopes on Earth. Tremendous amounts of data were captured from the observed plume, including signatures of water ice and other volatiles.
Also in 2009, researchers reviewing data from three separate spacecraft—Chandrayaan-1, Deep Impact, and Cassini—extracted a hydration signature throughout the whole lunar surface. This was a surprise to the lunar science community, particularly because this meant that water may be present on boiling-hot sunlit portions of the Moon. However, the instruments gathering the spectral data weren't designed to look for water, and did not have enough resolution in the 3-micron band of infrared light for researchers to distinguish between the absorption features of hydroxyl (OH), H$_2$O, and water ice. Lunar Trailblazer's instruments are specifically designed to detect and distinguish between these three forms of water.

## Spacecraft

The Lunar Trailblazer spacecraft was built and tested by Lockheed Martin. It uses two deployable solar arrays, which provide 280 watts of power, and a chemical propulsion system. With its solar panels fully extended it was 3.5 meters (11 ft) long. The spacecraft weighed 200 kilograms (440 lb). It carried two science instruments, High Resolution Volatiles and Minerals Moon Mapper (HVM$^3$), and the Lunar Thermal Mapper (LTM). HVM$^3$ was provided by JPL and the LTM was provided by the University of Oxford.

## Science payload

There are two scientific instruments on the Lunar Trailblazer satellite, totaling 20 kg. The High Resolution Volatiles and Minerals Moon Mapper (HVM$^3$) will gather and map shortwave infrared spectral data of the lunar surface. Simultaneously, Lunar Thermal Mapper (LTM) will acquire midwave infrared data. Together, the two instruments will create a simultaneous map of the surface mineral composition, temperature, and forms of lunar water, each measuring at least one thousand targets on the lunar surface over the course of the satellite's one-year primary mission.

### High Resolution Volatiles and Minerals Moon Mapper (HVM$^3$)

The HVM$^3$ instrument was developed by the Maturation of Instruments for Solar System Exploration (MatISSE) program, and was manufactured by the Jet Propulsion Laboratory. It is a pushbroom short-wave infrared imaging spectrometer based on the design of the M$^3$ instrument, which was one of the instruments to first find evidence of hydration in sunlit regions of the Moon. HVM$^3$ has a spectral range from 0.6 to 3.6 microns—it is designed to work with high sensitivity (10 nm resolution) right at the center of water's key wavelength region in infrared light (from 2.5 to 3.5 microns) with high enough spectral resolution to differentiate between forms of water. Each pixel in an image from HVM$^3$ will cover 50–90 meters of the lunar surface.

### Lunar Thermal Mapper (LTM)

The LTM instrument was designed and built by the University of Oxford. With eleven narrow channels between seven and ten microns and resolution smaller than 0.5 microns, it acquires multispectral images to characterize the Si-O stretch in silicates to derive mineralogical composition. At the same time, using the four broadband channels from 6 up to 100 microns, it derives surface temperature with a precision of 5 K (9 °F/5 °C) in the range of 110–400 K (-262 to 260 °F/-163 to 126 °C). The pixel size of LTM is 40–70 meters.