Lightweight Mirrors for Microsatellites and Small Satellites

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Space Technology

OBJECTIVE: Develop innovative manufacturing methods to produce high-quality lightweight optical mirrors for use in space on microsatellites (microsats) and small satellites (smallsats), particularly at ultraviolet (UV) and extreme ultraviolet (EUV) wavelengths.

DESCRIPTION: The Navy seeks improvements in the manufacturing of lightweight optical mirrors to meet size and weight demands of compact optical systems designed for operation in space on the next generation of microsats being designed to study the ionosphere [Refs 1, 2] and other Navy applications. Availability of high-quality lightweight optics will allow for future mission growth. The Navy seeks to foster the development of affordable optical components and systems that could have broad application to space systems. Current mirror technology involves either fragile glass optics or metal or composite mirrors that have lower optical quality. Innovative substrate materials are sought with the ruggedness, mass, and material properties necessary to produce light weight high-quality optical elements. Innovative techniques are sought to polish and figure these substrates to yield the high optical quality reflective surfaces needed for the new class of remote sensing instruments.

Typical cube satellite (CubeSat) mirrors used in smallsats have been fabricated from special aluminum alloys that are hard enough to be polished with moderate difficulty. Their density is 2.7 g/cm3, leading to significant mass penalties. The example sizes range from a fixed flat mirror (3” x 3.5” by 0.080” thick) to a scanning mirror (2” X 3.5” by 0.375” thick). Improvements are sought in the density, stiffness, polishability, roughness, figure accuracy, and moment of inertia in the scanning case. Goals are figure accuracies of λ/4 at the working wavelength, scratch/dig of 60-40, rms roughness of < 1nm, Coefficient of Thermal Expansion (CTE) compatible with typical spacecraft materials (< 4ppm/K), low outgassing (CVC < 0.1% and TML < 1%), survival at temperatures of -50 – +60°C, and the ability to survive a NASA GEVS3 vibration specification and thermal test environment, all typical of the requirements imposed for flight on small spacecraft.

Technologies proposed should not contain hazardous or high outgassing materials and should be capable of being integrated into typical optical systems. It is desired that they be moderately (> 10-5 O-1/m) electrically and thermally conductive (> 10W/mK) to avoid developing static charge and thermal gradients in space. They should be durable and able to withstand normal optical component handling procedures. They should be delivered in an optically clean state and be robust enough to withstand precision cleaning and vacuum baking as part of normal spacecraft processing.

PHASE I: Demonstrate the feasibility of a concept for an innovative lightweight mirror technology meeting Navy needs for microsat optical systems in the ultraviolet/vacuum ultraviolet (UV/VUV). Demonstrate performance advantages over current technology by producing small (25mm or larger) flat sample mirrors that can be tested to Navy requirements. While exact mirror dimensions are not specified for Phase I, the awardee will establish that the concept can be scaled to sizes of 100 mm diameter or larger. Phase I technology is expected to focus on the small flat mirrors that are needed to fold optical systems into compact smallsat envelopes. The path to using this technology to produce curved mirrors should be defined.

Proposed mirror concepts should meet the following thresholds:

PHASE II: Develop a Phase II prototype mirror of the 100 mm size class for evaluation. The prototype will be evaluated to determine its capability in meeting the performance goals defined in Phase II Statement of Work (SoW) and the Navy’s need for lightweight flight mirrors. The prototype design should provide reflective areas no less than 90mm by 40mm (objective), and should show applicability to be utilized with various mirror geometries and spacecraft architectures. Deliver a minimum of five of these prototypes to the Navy for evaluation. Perform detailed analysis to ensure materials are rugged and appropriate for Navy application. Environmental, shock, and vibration analysis will be performed. Optical checks will include flatness, roughness, and reflectivity. Prototype concave mirrors of 25mm diameter and ~100mm Radius of Curvature (ROC) will be produced and evaluated.

PHASE III DUAL USE APPLICATIONS: Apply the knowledge gained in Phase II to build an advanced mirror, suitably configured for a smallsat application, including flight spares, and characterize its performance in the UV/VUV as defined by Navy requirements. Working with the Navy and applicable Industry partners, demonstrate application to a NAVY Space Test program (STP) flight test. Support the Navy for test and validation to certify and qualify the system for Navy use. Explore the potential to transfer the light weight mirror system to other military and commercial systems (NASA, University, Optics Industry).

Market research and analysis shall identify the most promising technology areas. Develop manufacturing plans to facilitate a smooth transition to the Navy.

REFERENCES:

1. Budzien, Scott; Fritz, Bruce; Stephan, Andrew; Marquis, Peter; Powell, Steven; O'Hanlon, Brady; Nicholas, Andrew; Dymond, Kenneth and Brown, Charles. “Comparison of second and third generation 135.6 nm ionospheric photometers using on-orbit and laboratory results.”, SPIE Proceedings, Volume 11131, CubeSats and SmallSats for Remote Sensing III; 1113102 (2019). https://doi.org/10.1117/12.2528791
2. Attrill, G.D.R.et al. “Coordinated Ionospheric Reconstruction CubeSat Experiment (CIRCE), In situ and Remote Ionospheric Sensing (IRIS) suite.” Journal of Space Weather and Space Climate, (2020) . J. Space Weather Clim. 11, 16, (2021). doi.org/10.1051/swsc/2020066.
3. “NASA General Environmental Verification Standards (GEVS), Rev. A, GSFC-STD-7000 (2013).” https://standards.nasa.gov/standard/gsfc-std-7000

KEYWORDS: Lightweight space qualified mirrors, mirror technology, optical fabrication, spaceflight optics, spaceflight structures; microsatellites; small satellites; cube satellites