The MUlti-slit Solar Explorer (MUSE) is a NASA medium-class explorer mission that is currently in phase B and scheduled for launch no earlier than 2027. The MUSE science investigation aims to use high-resolution and high-cadence spectroscopic and imaging EUV observations of the solar atmosphere to understand the multi-scale physical processes that heat the multi-million-degree solar corona, drive the source of the solar wind, and cause solar activity (flares and coronal mass ejections) that lead to space weather that impacts Earth. MUSE will consist of an EUV context imager and an EUV spectrograph, both requiring normal incidence mirrors with a very high level of polishing and figuring, in order to allow high-resolution imaging and spectroscopy. The mission is led by Lockheed Martin Solar and Astrophysics Laboratory (LMSAL). The payload is being developed by LMSAL and the Center for Astrophysics (CfA) at the Harvard Smithsonian Astrophysical Observatory, while INAF-OAB will produce the focusing mirrors with the financial support of the Italian Space Agency (ASI). In this paper, we describe the first steps that are being taken in the procurement of the focusing mirrors in Zerodur, the work plan with the ion beam figuring and the pitch tool aimed at bringing the surface defects within the specification. Additionally, we describe the metrology system that we are setting up to detect the residual deviation to the final shape.
The Polstar Mission uses time domain FUV and NUV spectropolarimetric observations to provide insight into how our galaxy became able to support a solar system like ours. Polstar will study the evolution of massive stars, including the inter-stellar dust and gas that they interact with and the dynamics of protoplanetary disks and lower resolution near UV (180nm – 320 nm) to study interstellar reddening mechanism. Polstar will simultaneously measure at high spectral resolving power all four Stokes parameters (I, Q, U, V)T to high accuracy (0.001) with a precision better than 0.0001 using an instrument comprising a modulator with rotating MgF2 retarders and a fixed MgF2 Wollaston prism analyzer that concurrently measures the two orthogonal polarizations of the retarder modulated signal at six optimized rotational angles on a common detector. The output of the Wollaston prism either directly enters an echelle spectrograph, which provides spectral resolution of ~30K with a wavelength range from 122 nm to 200 nm, or is reflected to a prism spectrograph, which provides spectral resolution ranging from 140– 4000 with a wavelength range from 180 nm to 320 nm. In this paper we outline the instrument calibration approach to obtain the Mueller matrices over the full wavelength range that permit us to determine the Stokes parameters, and to spectrally calibrate the instrument. We also describe the ground support equipment for calibration.
The Polstar Mission seeks to study the evolution of massive stars including their effect on the interstellar medium and their behavior in binary systems using a 60 cm telescope with a UV Spectropolarimeter within MIDEX mission constraints on cost cap, throughput, coating requirements, and system-level dimensional stability. The mission is in a high-earth orbit and must ensure precise and repeatable polarimetric observations. Design-to-cost paradigms are exercised throughout all design phases and heritage approaches to structure and mirrors are evoked. In terms of classical error budgets, designing for diffraction-limited performance at 1.2 μm is sufficient, however, there are special design concerns at these wavelengths which require maximizing throughput of photons. Special coatings and minimum reflections are mandatory with meticulous attention to cleanliness throughout the entire mission life cycle. Decontamination heaters must be employed shortly after launch, prior to opening the door, and periodically throughout the mission lifetime. Additionally, spectropolarimetry requirements impose constraints on symmetry and control of phase and amplitude. The secondary mirror must have adjustment capability in three degrees of freedom (tip, tilt, and focus) to address drifts from thermal perturbations, aging, and possibly even spacecraft jitter. We present in-process design approach and analyses to meet the challenges of ultraviolet wavelengths and polarization stability..
Embedding solid-state ceramic actuators in a bending style deformable mirror presents unique athermalization
challenges when operated at cryogenic temperatures. Approaches to athermally embed actuators in a substrate are
presented in this study. Each approach is rated according to established design criteria: unmatched displacement, range,
compliance ratio, bondline stress, design, and manufacturability. We show the results of our design that allows a large
thermal range of operation for the actuators.
A novel tip-tilt mechanism has been designed which is capable of aligning a small 1-inch optic with one arc second resolution. This mechanism performs this function without the aid of a piezoelectric device or other electronic technology. The optic is bonded to a three bipod mount in series with a spring-loaded flexure. Three manually adjustable differential screws drive the flexure. The bipod/flexure arrangement allows highly accurate and stable adjustment. This paper will give an overview of the design, and present laboratory data and analysis quantifying the adjustment resolution of the mechanism. Material and surface coating selection is also presented.
Mark Sullivan, Matthew Bye, Paul Ehrensberger, Enrique Romero, Howard Demroff, Scott Fletcher, Daniel DeBra, John Goebel, Paul Limtiaco, Donald Davidson, Lynn Huff, Ada Jefferson, Ali Kashani, Dale Gill, Kenneth Triebes, Jeff Grant
A proposed baseline design for the Space Infrared Telescope Facility includes a Tertiary Mirror Assembly (TMA)
which selectively redirects the telescope's converging science beam to each of several instruments. The TMA's mirror
rotates on an axis coincident with the beam's axis,'and is held steady during observation by a kinematic mount. A
bearing has been designed whose compliance causes minimal interference with the precision of the kinematic mount, and
which is well suited to the particular requirements of a cryogenic sateffite such as SIRTF. The bearing suspends its rotor
by taking advantage of the repulsion between a superconductor and a magnet. It potentially eliminates problems
associated with mechanical bearings that arise in similar applications, such as lubricant loss or failure, bearing wear, and
sensitivity to particulates, and does so without imposing the thermal load of a bearing heater or active magnetic bearing.
The bearing shows promise of offering an alternative to ball bearings in cryogenic applications where some compliance
is acceptable or advantageous.
This paper describes the design and testing of an indexing system for optical-beam steering. The cryogenic beam-steering mechanism is a 360-degree rotation device capable of discrete, high-precision alignment positions. It uses low-precision components for its rough alignment and kinematic design to meet its stringent repeatability and stability requirements (of about 5 arcsec). The principal advantages of this design include a decoupling of the low-precision, large angular motion from the high-precision alignment, and a power-off alignment position that potentially extends the life or hold time of cryogenic systems. An alternate design, which takes advantage of these attributes while reducing overall motion, is also presented. Preliminary test results show the kinematic mount capable of sub-arc second repeatability.
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