MINISPEC Moon IN-situ imaging SPECtrometer: an innovative compact IR spectrometer for lunar surface exploration

1. Introduction and scientific objectives
The MINISPEC (Moon IN-situ Imaging SPECtrometer) instrument concept has been conceived with the aim to perform imaging spectroscopy directly from the lunar surface. Operating in the infrared (IR) spectral range from 0.8 to 4 µm, the instrument addresses critical needs for future lunar exploration.
The primary scientific objectives of MINISPEC are: 

• mapping the local geological context near landing sites selected for robotic rovers or human crews; 
• identifying hydrated minerals (H2O/OH) and detecting volatile compounds potentially trapped beneath the surface regolith;
• discriminating between adsorbed water and water ice.

2. Performance requirements
One of the challenges of the design is the optical head layout. Balancing the required optical performance with the compactness of the instrument, available mass and power resources and the harsh lunar environment. 
MINISPEC utilizes a compact hyperspectral architecture based on a Linear Variable Filter (LVF) coupled with a proven space-qualify detector.
Key desired features are:

• A wide field of view angle (target 20°)
• The capability to focus both at infinity and at 1-2 meters.
• A spectral resolution of 30/40 nm across the wavelength range. 

3. Technological challenges
Active illumination
For the MINISPEC instrument an active wide-band illumination concept is considered.
The goal of this subsystem is the capability to perform spectral measurements in low lunar illuminated regions, during the lunar night or in permanently shadowed regions. 
Thermo-mechanical design
The lunar peculiar environment coupled with the IR working spectral range require a thorough study of the thermo-mechanical design for the instrument. The detector needs to be cooled and also the optical head. An active solution is foreseen for the detector and a passive one for the head.
Different thermal architectures are presently being considered and simulated.
Materials and coating development
In the framework of the instrument study experimental facilities are implemented for validation for advanced optical materials. These will allow the characterization of optical components, and possibly lunar analogues measurements, across a wide range from 400 nm to 5 µm to ensure long-term stability and high reflectance/transmittance and prove instrument reliability.

4. Conclusions
The MINISPEC instrument design study aims at realizing a new class of compact planetary spectrometers for the lunar surface.
Different challenges are address by the project team: radiometric modelling, optical layout, illuminator and thermo-mechanical designs.
MINISPEC aims to advance the technological maturity of a compact imaging spectrometer for in-situ characterization of both lunar and planetary surfaces.

Acknowledgements
The MINISPEC project is funded by the Italian Space Agency (ASI) via Contract number 2024-1-U.0.