Lunar Trailblazer

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Overview

Lunar Trailblazer is a planned NASA mission that will provide new insights into the lunar water cycle and geology. The mission is a Class D lunar orbiter mission that was selected by NASA’s Small Innovative Missions for Planetary Exploration (SIMPLEx) programme in 2019, set to join the first generation of planetary science SmallSats. The Principle Investigator (PI) is provided by the California Institute of Technology (CalTech), while the mission is managed by NASA’s Jet Propulsion Laboratory (JPL). Lockheed Martin provided the spacecraft and integrated flight system, and science and mission operations are led by CalTech’s Infrared Processing and Analysis Centre (IPAC). Alongside Lunar Trailblazer’s SIMPLEx selection, NASA selected Pasadena City College as a collaboration opportunity for graduate students and postgraduate scholars to participate in the mission. The initiative seeks to provide real-world experiences in space mission design and operations to the next generation of scientists and engineers. 1) 2) 7) 16)

While the result of the Apollo missions were indicative of a dry Moon, technological advancements in lunar exploration led to the discovery of water within volcanic glass and minerals 11). Alongside this, the Indian Space Research Organisation’s (ISRO) Chandrayaan-1 mission discovered large quantities of water and hydroxyls across the surface. Since these discoveries, the Moon has further become of interest for its science and potential resources. 5)

The mission will map the distributions and abundances of different forms of water on the surface of the Moon. While the existence of water on the lunar surface has been established, little is known about where it is located, how its forms change over time, or how the thermal properties of the surface affect its distribution. 1)

Lunar Trailblazer will investigate the distribution and abundance of molecular water (H2O), water ice, and hydroxyls (OH). Molecular water can exist on the moon in vapour form through a phenomenon called ‘cold trapping’ in which water vapour accumulates in regions shielded from sublimation. Evidence for the presence of water ice was found by NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS), a companion spacecraft to the Lunar Reconnaissance Orbiter (LRO). LCROSS performed a controlled impact into the lunar surface which created a plume of lunar ejecta that revealed information into volatiles and water on the Moon. Hydroxyls are a form of water found bonded to minerals as well as the lunar regolith, which can be produced in the Moon’s mantle by geological processes, by solar wind interactions of Hydrogen ions impacting silicate rocks, or by external deposition from comets, asteroids, and interplanetary dust particles. Lunar Trailblazer’s high spectral resolution instrument suite is designed specifically to distinguish between these types of water. 13)

The mission will conduct observations of both sunlight terrains and permanently shadowed regions (PSRs). PSRs are hypothesised to house water ice that could contain organic matter. Investigating the form, quantity, and purity of water in different geological and topographical contexts is crucial for our understanding of the lunar water cycle and for future resource exploitation. The mission will also assess the dynamics of lunar volatiles (materials that evaporate quickly when exposed to air and other environmental factors), map lunar crust compositions, and perform reconnaissance for future landed missions. 3)

CalTech’s Lunar Trailblazer team created an interactive map that shows the mission’s planned targets on the lunar surface in which water will be searched for. Areas of interest include PSRs around the lunar South Pole and inside craters, as well as sunlight regions and regular latitude surveys.

Lunar Trailblazer will carry two science instruments: the High-resolution Volatiles and Minerals Moon Mapper (HVM3) and the Lunar Thermal Mapper (LTM). Each instrument will acquire a minimum of 1000 images of the Moon covering at least 800 targeted sites, in order to study lithology and water content. At least 50 of these sites will be visited a minimum of three times daily to study the dynamics of volatile material under varying temperatures. At least 150 targets have been selected that lie in PSRs, which will be searched for water ice and volatile content by measuring terrain-scattered light and multiple-latitude coverage. 16)

Spacecraft

The Lunar Trailblazer spacecraft is based on Lockheed Martin’s Curio platform, a low-cost spacecraft designed for deep space SmallSat missions and for mounting onto an ESPA (Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter) ring for a rideshare launch configuration. Featuring two deployable solar arrays, the spacecraft spans 3.5 m when fully deployed. Communications are provided by an X-band Iris radio system, and the mission’s design life is one year. 4) 6) 16)

Launch

Lunar Trailblazer is planned to launch as a secondary payload in a Falcon 9 rideshare mission alongside PRIME-1 (IM-2), the second lunar lander mission of the commercial space exploration company Intuitive Machines. 2) 14)

Orbit

Following the spacecraft’s launch and launcher separation, Lunar Trailblazer will travel to Lagrangian point L1 where it will perform a series of manoeuvres over an approximate six month translunar injection (TLI) period. Upon lunar orbit insertion (LOI) the mission will reduce and circularise its orbit to a nominal 100 ± 30 km polar orbit around the Moon. Due to its small size, the spacecraft cannot perform direct deceleration burns for lunar descent, so the mission makes use of a low-energy transfer trajectory that will take between four and seven months to reach the Moon, but saves a lot of fuel. 3) 4) 14)

The Moon has a heterogenous (non-uniform) gravity field due to an uneven distribution of mass within the celestial body, which will require Lunar Trailblazer to perform orbital maintenance manoeuvres approximately every three months in order to maintain its polar orbit. 1000 observation sites have been targeted, covering between 1 - 2 % of the Moon’s surface. The low altitude polar orbit will place a given target at the spacecraft’s nadir every two months, and the same viewing geometry every six months. 4) 16)

Development Status

• 16th August 2023: Lunar Trailblazer receives its final science instrument, LTM. 18)

• 27th October 2022: Lunar Trailblazer enters its Assembly, Test, and Launch Operations (ATLO) phase at Lockheed Martin. Shortly after in early December 2022, the HVM3 instrument was installed on the spacecraft. 6)

• 2nd December 2020: NASA approves the Lunar Trailblazer mission for its final design and construction, beginning with the spacecraft’s development at Lockheed Martin. 6)

Sensor Complement

Lunar Trailblazer’s 20 kg science payload consists of two instruments: the High Resolution Volatiles and Minerals Moon Mapper (HVM3) and the Lunar Thermal Mapper (LTM). The pair will make observations of the lunar surface simultaneously with co-aligned fields of view. Each instrument will acquire a minimum of 1000 images of the moon alongside calibration data. 16) 4)

Figure 6: highlights the potential of Lunar Trailblazer’s simultaneous observations. The left image is an illustration of both sensors pushbroom scanning over the lunar surface to cover selected targets over PSRs and sunlit regions. The middle image is a multispectral image cube, a type delineation that describes both the spatial and spectral information of a scene within the same image. This particular image cube houses observations from both sensors of the same scene, enabling an in-depth analysis of the lunar surface’s composition across more wavelengths than preceding missions like M3. More on spectral cubes can be read here. 16)

HVM3 (High-resolution Volatiles and Minerals Moon Mapper)

HVM3 is a pushbroom SWIR imaging spectrometer that aims to characterise the different forms of water and produce high-resolution maps of the lunar surface by observing reflected sunlight. The instrument is designed to detect volatiles on the lunar surface for the mapping of hydroxyls, bound molecular water, and water ice. 16)

The instrument is provided by NASA’s Jet Propulsion Laboratory (JPL), and is a modernised version of the M3 imaging spectrometer flown on-board Chandrayaan-1, optimised to identify the forms of water. The device is an Offner-type spectrometer based on NASA’s Ultra-Compact Imaging Spectrometer (UCIS) combined with a three-mirror anastigmat (TMA) telescope similar to the M3 spectrometer. 1) 14) 17)

LTM (Lunar Thermal Mapper)

LTM is a pushbroom multispectral thermal radiometer that will observe temperature properties of the Moon’s surface by measuring thermal emission calibrated against the deep space temperature. The device’s primary function is to investigate the covariance of water content with temperature, as well as to independently measure the Moon’s surface temperature to pair with HVM3’s thermal correction procedure in the 3 μm region. 1) 2) 14)

Operating in 11 spectral bands between 7 and 10 μm and another four bands between 6 and 100 μm, LTM will simultaneously map temperature, physical properties, and water-bearing area compositions. The instrument is developed by the University of Oxford and supported by the UK Space Agency. 4) 8) 14)

Ground Segment

Lunar Trailblazer’s dataset will consist of the highest spatial and spectral resolution SWIR and MIR maps of the Moon for the determination of volatile distribution and abundances, as well as surface composition and thermophysical properties. Data products will be delivered from the spacecraft to the Planetary Data System (PDS) every three months. During the mission’s primary science phase, the mission team will schedule science observations every two weeks based on target visibility, favourable viewing geometries, and local times of day while managing the spacecraft’s onboard data capacity and downlink capability. 7)

NASA’s open source Advanced Multi-Mission Operations System (AMMOS) will be used for the commanding, housekeeping, and health monitoring of the spacecraft. The spacecraft will communicate with NASA’s Deep Space Network 34 m antennas for uplink and downlink services, and science data will be processed at CalTech’s Bruce Murray Laboratory for Planetary Visualization. 7) 16)

References  

1) https://www.jpl.nasa.gov/missions/lunar-trailblazer

2) https://trailblazer.caltech.edu/index.html

3) “Lunar Trailblazer Science Objectives,” URL: https://trailblazer.caltech.edu/objectives.html

4) https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=L-TRLBLZR

5) https://www.planetary.org/space-missions/lunar-trailblazer

6) https://www.lockheedmartin.com/en-us/products/nasa-s-lunar-trailblazer-the-hunt-for-lunar-water.html

7)https://www.ipac.caltech.edu/project/lunar-trailblazer

8) https://www.ox.ac.uk/news/2023-08-17-oxford-university-built-instrument-ready-map-water-moon

9) https://www.space.com/nasa-lunar-trailblazer-hunt-water-on-moon

10) https://ieeexplore.ieee.org/document/9843663

11) Saal, A., Hauri, E., Cascio, M. et al. Volatile content of lunar volcanic glasses and the presence of water in the Moon’s interior. Nature 454, 192–195 (2008). https://doi.org/10.1038/nature07047

12) https://www.caltech.edu/about/news/nasas-lunar-trailblazer-gets-final-payload-for-moon-water-hunt

13) Belinda Blakley, “What is Lunar Water?,” CalTech Lunar Trailblazer, URL: https://trailblazer.caltech.edu/lunarWater.html

14) “Lunar Trailblazer Instruments,” CalTech Lunar Trailblazer, URL: https://trailblazer.caltech.edu/instruments.html

15) “Lunar Trailblazer's Thermal Mapper Has Arrived at Lockheed Martin,” NASA JPL, April 26, 2023, URL: https://www.jpl.nasa.gov/images/pia25831-lunar-trailblazers-thermal-mapper-has-arrived-at-lockheed-martin

16) Ehlmann BL, Klima RL, Seybold CC, Klesh AT, Au MH, Bender HA, Bennett CL, Blaney DL, Bowles N, Calcutt S, Copley-Woods D. “NASA's Lunar Trailblazer Mission: A Pioneering Small Satellite for Lunar Water and Lunar Geology”, In 2022 IEEE Aerospace Conference (AERO) 2022 Mar 5 (pp. 1-14). IEEE.

17) Bender HA, Smith CD, Ehlmann BL, Thompson DR, Vinckier QP, Mouroulis P. “Optical design and performance of the Lunar Trailblazer High-resolution Volatiles and Minerals Moon Mapper (HVM3)”. In Imaging Spectrometry XXV: Applications, Sensors, and Processing 2022 Sep 30 (Vol. 12235, pp. 11-17). SPIE.

18) “Lunar Trailblazer Spacecraft Nears Completion,” NASA JPL, August 15, 2023, URL: https://www.jpl.nasa.gov/images/pia25837-lunar-trailblazer-spacecraft-nears-completion