The Lucy Thermal Emission Spectrometer (L’TES) Instrument
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-12-19 |
| Journal | Space Science Reviews |
| Authors | P. R. Christensen, V. E. Hamilton, G. Mehall, Saadat Anwar, H. Bowles |
| Institutions | Southwest Research Institute, Arizona State University |
| Citations | 22 |
| Analysis | Full AI Review Included |
Technical Documentation: CVD Diamond for Space-Flight Fourier Transform Spectrometers (FTS)
Section titled “Technical Documentation: CVD Diamond for Space-Flight Fourier Transform Spectrometers (FTS)”Executive Summary
Section titled “Executive Summary”The Lucy Thermal Emission Spectrometer (L’TES) instrument relies on Chemical Vapor Deposited (CVD) diamond for its critical beamsplitter and detector lens components, validating diamond’s essential role in high-performance space optics.
- Critical Component: A 38-mm diameter, 1-mm thick CVD diamond beamsplitter is central to the Michelson interferometer, enabling the wide spectral range (5.71-100 µm).
- Material Advantage: Diamond’s low thermal expansion coefficient and high heat conductivity are crucial for maintaining precise interferometer alignment and thermal stability (<0.1 °C per minute) across the extreme operational range (-10 °C to +30 °C).
- Optical Performance: The diamond substrate, enhanced with an Antireflection Microstructure (ARM), significantly increases throughput, demonstrating the need for ultra-high-quality, polish-ready substrates.
- Measurement Accuracy: The instrument achieves an absolute temperature error of <2 K for scene temperatures ≥75 K, directly supported by the stability provided by the diamond optics.
- 6CCVD Capability: 6CCVD specializes in providing custom, optical-grade Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates up to 125 mm, perfectly suited for replicating or advancing this class of space-flight FTS technology.
Technical Specifications
Section titled “Technical Specifications”The following hard data points highlight the stringent requirements met by the CVD diamond components and the overall L’TES instrument performance.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Beamsplitter Material | CVD Diamond | N/A | Chemical Vapor Deposited |
| Beamsplitter Dimensions | 38 x 1 | mm | Diameter x Thickness |
| Detector Lens Diameter | 4.4 | mm | CVD Diamond lens on DLATGS detector |
| Spectral Range | 5.71-100 | µm | 1750-100 cm-1 |
| Spectral Sampling Intervals | 8.64, 17.3, 34.6 | cm-1 | Selectable resolution modes |
| Absolute Temperature Error | <2 | K | Required for scene temperatures ≥75 K |
| Thermal Inertia Accuracy | ±15 | % | Primary science objective requirement |
| Operational Temperature Range | -10 to +30 | °C | In-specification performance |
| Survival Temperature Range | -30 to +55 | °C | Non-operational protoflight survival |
| Metrology Laser Wavelength | 0.851 | µm | Used for precise moving mirror control |
| Thermal Stability Requirement | <0.1 | °C/minute | Required to maintain calibration |
| NESR (300-1350 cm-1) | ≤2.2 x 10-8 | W cm-2 sr-1 /cm-1 | Radiometric precision (single spectrum) |
Key Methodologies
Section titled “Key Methodologies”The successful deployment of the L’TES instrument relied on advanced material processing and rigorous thermal testing, specifically leveraging the properties of CVD diamond.
- CVD Diamond Substrate Fabrication: The beamsplitter and detector lens were fabricated from Chemical Vapor Deposited (CVD) diamond, selected for its high thermal conductivity and low dispersion properties, allowing a single substrate to be used without a compensator.
- Antireflection Microstructure (ARM): An ARM was applied to the diamond beamsplitter surface, increasing raw diamond transmission by ∼25% (7 to >25 µm), resulting in a 50% increase in beamsplitter throughput.
- Precision Mounting: The 38-mm diamond beamsplitter was installed in a radial three-point mount to ensure precise alignment and mechanical integrity across the wide operational temperature range.
- Metrology Interferometer Integration: A single 0.851 µm VCSEL laser diode feeds a fringe counting metrology interferometer that uses the same diamond beamsplitter and mirrors as the IR signal chain, providing precise moving mirror control and IR sampling at 772 Hz.
- Thermal Vacuum (TVAC) Calibration: Radiometric calibration was performed in vacuum at instrument temperatures ranging from -10 °C to 25 °C, viewing NIST-calibrated blackbody targets (85 K to 330 K) to simulate space and scene observations.
- Vibration Mitigation: The moving mirror velocity and IR sampling frequency were increased (from 656 Hz to 772 Hz) to shift spacecraft Inertial Measurement Unit (IMU)-induced microphonic interference out of the L’TES information band, confirming the robustness of the digital servo control system.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the next generation of high-performance diamond optics required for FTS instruments like L’TES, ensuring superior thermal stability and optical throughput.
Applicable Materials
Section titled “Applicable Materials”To replicate or extend the performance of the L’TES instrument, 6CCVD recommends the following materials, optimized for optical and thermal performance in space environments:
- Optical Grade Single Crystal Diamond (SCD): Recommended for beamsplitters requiring the highest level of optical homogeneity and lowest absorption across the mid-infrared spectrum (5.71-100 µm). SCD offers superior thermal conductivity compared to PCD, critical for maintaining the required <0.1 °C/minute thermal stability.
- 6CCVD Capability: SCD plates available in thicknesses from 0.1 µm up to 500 µm.
- Optical Grade Polycrystalline Diamond (PCD): Suitable for large-area windows or beamsplitters where cost-effectiveness is balanced with high thermal performance.
- 6CCVD Capability: PCD plates/wafers available up to 125 mm diameter, exceeding the 38 mm requirement of L’TES.
Customization Potential
Section titled “Customization Potential”6CCVD’s in-house fabrication and processing capabilities directly address the specific needs demonstrated by the L’TES design:
| L’TES Requirement | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| Custom Dimensions (38 mm dia., 1 mm thick) | Custom Plate Fabrication: We provide SCD/PCD plates in custom dimensions up to 125 mm diameter (PCD) and 500 µm thickness. | Enables rapid prototyping and production scaling for flight hardware. |
| Ultra-Smooth Surface (Required for ARM) | Precision Polishing: SCD surfaces polished to Ra < 1 nm; Inch-size PCD polished to Ra < 5 nm. | Essential for applying complex Antireflection Microstructures (ARM) or thin-film coatings (e.g., Ge beam-dividing coating) with minimal scatter loss. |
| Gold-Coated Mirrors (Primary/Secondary) | Internal Metalization: We offer custom metalization services including Au, Pt, Ti, Pd, W, and Cu deposition. | Allows for single-source procurement of diamond optics and highly reflective gold-coated mirrors (reflectance >0.99) used throughout the optical path. |
| Small Diamond Lens (4.4 mm detector lens) | Micro-Optics Fabrication: Custom laser cutting and shaping for small, precision diamond components. | Provides high-purity diamond lenses necessary for optimizing detector performance (D*). |
| Global Logistics | Global Shipping: DDU default, DDP available. | Ensures reliable, timely delivery of sensitive flight hardware worldwide. |
Engineering Support
Section titled “Engineering Support”The successful development of L’TES highlights the complexity of integrating diamond optics into thermally sensitive FTS systems. 6CCVD’s in-house PhD engineering team specializes in:
- Material Selection Optimization: Assisting researchers in selecting the optimal diamond grade (SCD vs. PCD) based on required spectral range, thermal load, and optical homogeneity for similar Thermal Emission Spectrometer projects.
- Thermal Modeling Consultation: Providing data and expertise on diamond’s thermal properties to ensure compliance with stringent thermal stability requirements (e.g., L’TES’s <0.1 °C/minute stability).
- Interface Engineering: Consulting on mounting strategies (like the radial three-point mount used in L’TES) to mitigate thermal expansion mismatch and maintain alignment stability in zero-G and TVAC environments.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract The Lucy Thermal Emission Spectrometer (L’TES) will provide remote measurements of the thermophysical properties of the Trojan asteroids studied by the Lucy mission. L’TES is build-to-print hardware copy of the OTES instrument flown on OSIRIS-REx. It is a Fourier Transform spectrometer covering the spectral range 5.71-100 μm (1750-100 cm −1 ) with spectral sampling intervals of 8.64, 17.3, and 34.6 cm −1 and a 7.3-mrad field of view. The L’TES telescope is a 15.2-cm diameter Cassegrain telescope that feeds a flat-plate Michelson moving mirror mounted on a linear voice-coil motor assembly to a single uncooled deuterated l -alanine doped triglycine sulfate (DLATGS) pyroelectric detector. A significant firmware change from OTES is the ability to acquire interferograms of different length and spectral resolution with acquisition times of 0.5, 1, and 2 seconds. A single ∼0.851 μm laser diode is used in a metrology interferometer to provide precise moving mirror control and IR sampling at 772 Hz. The beamsplitter is a 38-mm diameter, 1-mm thick chemical vapor deposited diamond with an antireflection microstructure to minimize surface reflection. An internal calibration cone blackbody target, together with observations of space, provides radiometric calibration. The radiometric precision in a single spectrum is ≤2.2 × 10 −8 W cm −2 sr −1 /cm −1 between 300 and 1350 cm −1 . The absolute temperature error is <2 K for scene temperatures >75 K. The overall L’TES envelope size is 37.6 × 29.0 × 30.4 cm, and the mass is 6.47 kg. The power consumption is 12.6 W average. L’TES was developed by Arizona State University with AZ Space Technologies developing the electronics. L’TES was integrated, tested, and radiometrically calibrated on the Arizona State University campus in Tempe, AZ. Initial data from space have verified the instrument’s radiometric and spatial performance.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 1988 - Theory and practice of radiation thermometry