← Back to NASA Technology Projects
Completed TRL 3 (started at 3, targeting 4)
The Science Mission Directorate Astrophysics Division is studying four potential missions for input into the National Academy of Science’s 2020 Decadal Review to be recommended as NASA’s next large astrophysics mission: Habitable Exoplanet Observatory (HabEx), Large UV-Optical-Infrared Observatory (LUVOIR), Origins Space Telescope (OST) and LYNX. This proposed Technology Investment Program project supports OST by cryo-testing a 1.2-meter lightweighted bulk aluminum substrate mirror to quantify its thermal stability and cryo-deformation. Additionally, the ability to cryo-null figure the aluminum mirror will be demonstrated. Results will be communicated to the OST Study Scientists for potential inclusion in their final report. Benefit to OST is a mirror system technology that is lower cost and safer to manufacture than beryllium. The business goal for MSFC is to secure a role on OST (similar to MSFC’s role on JWST, i.e. cryo-testing of the OST mirrors) if OST is selected by the Decadal Study. An additional managerial goal is to retain cryo-test capability knowledge by training recently hired optical metrology engineers.
Similar to JWST, which is designed to operate below 50K, the Origins Space Telescope (OST) needs to operate at 4K. Thus, because of thermal conductivity required to achieve cryogenic temperature, it needs a metal mirror. The OST mission is studying two segmented mirror concepts. Concept 1 has a 9.1-meter segmented aperture aluminum mirror – because of aluminum’s low cost and suitable material properties. Aluminum is a common material for large ground based sub-mm wavelength antennas and was used on the small aperture WISE and WIRE space telescopes. Concept 2 has a 5.9-m segmented aperture beryllium mirror. Beryllium is the same material used for JWST. Beryllium is typically used when total mass is constrained, such as when launching with an EELV, but is also very expensive – JWST’s primary mirror cost $6M/meter2. If aluminum mirrors can achieve acceptable performance at the same areal density, they will replace beryllium – because of aluminum’s lower cost. But, to achieve that performance, it may be necessary to cryo-null figure the aluminum mirrors. The OST telescope is specified to be diffraction limited at 30 micrometers. Extrapolating from JWST’s 2 micrometer specification, the individual OST primary mirror segments need to have a surface figure of < 300 nm rms (JWST individual segment surface specification was < 20 nm rms). Because beryllium has a Coefficient of Thermal Expansion (CTE) of ~6.7 ppm/C, the JWST mirror segments had cryo-deformations on the order of 50 to 100 nm rms (causing them to not meet their surface specificaiton). Thus, to meet their specifications, these cryo-deformations had to be removed via cryo-null figured. Given that aluminum alloy 6061 has a CTE of ~24 ppm/C, it is likely to have cryo-deformation on the order 150 to 350 nm rms. If an individual mirror segment has a cryo-deformation at the upper end of this range, it will need cryo-null figuring to remove that deformation.
Additionally, metal mirrors have cryo-instability, i.e. they change shape every time they are cryo- or thermal-cycled. For OST, it is necessary to quantify this instability. For example, on JWST it was necessary to cryo-cycle each beryllium mirror three times before measuring their cryo-deformation. It should be noted that the JWST mirrors did not stabilize after three cycles; rather, their instability dropped to a small enough level that it was acceptable. In their 2001 paper, Vukobratovich and Schafer found that ten thermal cycles between -50 and +71C were required to stabilize a 0.6-meter mirror for ambient temperature operation. (Vukobratovich and Schafer, “Large Stable Aluminum Optics for Aerospace Applications”, SPIE Proceedings 8125, doi: 10.1117/12.902039) .
Given that aluminum is a TRL-9 material with a proven ability to be polished but its thermal stability has only been reported at a subscale of 0.6-m, we are assessing aluminum mirror segments for a potential OST missions to be TRL-4. This study seeks to mature an aluminum mirror segment to TRL-5 by characterizing a full-scale 1.2-m lightweighted bulk-aluminum 6061 alloy mirror in a relevant thermal environment. To do this, MSFC will use the exact same methods it used to characterize the thermal stability and cryo-deformation of JWST’s 1.4m lightweighted bulk-substrate beryllium alloy O-30 mirrors. We expect that three cycles will be sufficient to quantify the mirror’s exponential cryo-stability curve, but are prepared to do more if necessary. The results of this study will help define a cryo-stabilization process for aluminum 6061 mirrors, and demonstrate the ability of 6061 aluminum mirrors to be cryo-null figured. These results will be communicated to the OST Study. Additionally, this study will produce a performance baseline (for bulk-substrate aluminum 6061 mirrors) which can be used to evaluate the relative performance of a 0.75-m additively-manufactured ultra-lightweight 6061 aluminum mirror being manufactured via a current MSFC SBIR Phase 2 contract.
Please note that this study is not procuring the aluminum mirror. Rather, the mirror is being procured by MSFC’s Predictive Thermal Control (PTC) directed work package. The PTC baseline study plan is to use the 1.5m ULE® mirror manufactured under AMTD-2. But, because of the ULE®’s ultra-low CTE, PTC has decided to manufacture a 1.2m lightweighted bulk aluminum substrate mirror to use as a path-finding test article. Aluminum’s higher CTE should produce an easy to measure and quantify response signature. But, once the pathfinding exercise is over, PTC has no further use for the 1.2m aluminum mirror.
Characterizing this mirror for the potential OST Decadal mission provides a high level of utility to NASA for a small incremental cost. And, potentially positions MSFC’s for a role on OST helping to develop and mature its mirror system technology and cryo-testing its flight mirror systems. A best case scenario would be if MSFC were actually assigned responsibility for procurement insight/oversight of the OST telescope.
Listed on TechPort itself — the most direct way to ask about this specific project.
This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.
None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.