Modern space system prototyping calls for bold, non-sequential approaches to engineering design. Embracing such an approach poses a new challenge on the design of passive vibration isolation systems: Accommodating large uncertainties in the payloads they support. Isolators are typically tuned and configured to the exact mass properties of the payload and do not perform well outside those assumptions. The number of candidate isolator configurations across which random vibration performance must be assessed also presents a significant challenge. This effort is observed to scale with 10^N, where N is the number of design variables studied. Here, 10^24 practical, unique designs were available. Our work describes the application of robust optimization techniques, global search algorithms, and massively parallelized job execution inside the LLIMAS software environment to overcome such computational challenges and identify isolator configurations that provide acceptable attenuation over a wide range of payload assumptions. Final geometry for the selected point design is presented, and performance comparisons of gradient-based, local, robust, non-robust and genetic algorithms are discussed.
MIT Lincoln Laboratory’s Integrated Modeling and Analysis Software (LLIMAS) enables the development of novel engineering solutions for advanced prototype systems through unique insights into engineering performance and interdisciplinary behavior to meet challenging size, weight, power, environmental, and performance requirements. LLIMAS is a multidisciplinary design optimization tool that wraps numerical optimization algorithms around an integrated framework of structural, thermal, optical, stray light, and computational fluid dynamics analysis capabilities. LLIMAS software is highly extensible and has developed organically across a variety of technologies including laser communications, directed energy, photometric detectors, chemical sensing, laser radar, and imaging systems. The custom software architecture leverages the capabilities of existing industry standard commercial software and supports the incorporation of internally developed tools. Recent advances in LLIMAS’s Structural-Thermal-Optical Performance (STOP), aeromechanical, and aero-optical capabilities as applied to Lincoln prototypes are presented.
For more than two decades, Northrop Grumman Xinetics has been the principal supplier of small deformable
mirrors that enable adaptive optical (AO) systems for the ground-based astronomical telescope community. With
today’s drive toward extremely large aperture systems, and the desire of telescope designers to include adaptive
optics in the main optical path of the telescope, Xinetics has recognized the need for large active mirrors with the
requisite bandwidth and actuator stoke. Presented in this paper is the proposed use of Northrop Grumman Xinetics’
large, ultra-lightweight Silicon Carbide substrates with surface parallel actuation of sufficient spatial density and
bandwidth to meet the requirements of tomorrow’s AO systems, while reducing complexity and cost.
High resolution imaging from space requires very large apertures, such as NASA’s current mission the James Webb Space Telescope (JWST) which uses a deployable 6.5m segmented primary. Future missions requiring even larger apertures (>>10m) will present a great challenge relative to the size, weight and power constraints of launch vehicles as well as the cost and schedule required to fabricate the full aperture. Alternatively, a highly obscured annular primary can be considered. For example, a 93.3% obscured 30m aperture having the same total mirror area (91m2) as a 10.7m unobscured telescope, can achieve ~3X higher limiting resolution performance. Substantial cost and schedule savings can be realized with this approach compared to fully filled apertures of equivalent resolution. A conceptual design for a ring-shaped 30m telescope is presented and the engineering challenges of its various subsystems analyzed. The optical design consists of a 20X annular Mersenne form beam compactor feeding a classical 1.5m TMA telescope. Ray trace analysis indicates the design can achieve near diffraction limited images over a 200μrad FOV. The primary mirror consists of 70 identical rectangular 1.34x1.0m segments with a prescription well within the demonstrated capabilities of the replicated nanolaminate on SiC substrate technology developed by AOA Xinetics. A concept is presented for the deployable structure that supports the primary mirror segments. A wavefront control architecture consisting of an optical metrology subsystem for coarse alignment and an image based fine alignment and phasing subsystem is presented. The metrology subsystem is image based, using the background starfields for distortion and pointing calibration and fiducials on the segments for measurement. The fine wavefront control employs a hill climbing algorithm operating on images from the science camera. The final key technology required is the image restoration algorithm that will compensate for the highly obscured aperture. The results of numerical simulations of this algorithm will be presented and the signal-tonoise requirements for its successful application discussed. It is shown that the fabrication of the 30m telescope and all its supporting subsystems are within the scope of currently demonstrated technologies. It is also shown that the observatory can be brought to geosynchronous orbit, in its entirety, with a standard launch vehicle.
Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are
analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will
measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements
will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary
systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks
made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition,
Zodiac II will observe hot, young exoplanets as targets of opportunity.
The Zodiac II instrument is a 1.1-m diameter SiC telescope and an imaging coronagraph on a gondola carried
by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visiblewavelength
bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images
of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights within
the United States followed by half-global flights in the Southern Hemisphere. These longer flights are required to
fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more
sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope
can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the
near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs,
deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope
for high-contrast exoplanet imaging.
The search for extrasolar habitable planets is one of
three major astrophysics priorities identified for the next decade.
These missions demand very high performance visible-wavelength
optical imaging systems. Such high performance
space telescopes are typically extremely expensive and can be
difficult for government agencies to afford in today's economic
climate, and most lower cost systems offer little benefit because
they fall short on at least one of the following three key
performance parameters: imaging wavelength, total system-level
wavefront error and aperture diameter. Northrop
Grumman Xinetics has developed a simple, lightweight, low-cost
telescope design that will address the near-term science
objectives of this astrophysics theme with the required optical
performance, while reducing the telescope cost by an order of
magnitude. Breakthroughs in SiC mirror manufacturing,
integrated wavefront sensing, and high TRL deformable mirror
technology have finally been combined within the same
organization to offer a complete end-to-end telescope system in
the lower end of the Class D cost range. This paper presents
the latest results of real OAP polishing and metrology data, an
optimized optical design, and finite element derived WFE
High performance optical coatings are an enabling technology for many applications - navigation systems, telecom,
fusion, advanced measurement systems of many types as well as directed energy weapons. The results of recent testing
of superior optical coatings conducted at high flux levels have been presented. Failure of these coatings was rare.
However, induced damage was not expected from simple thermal models relating flux loading to induced temperatures.
Clearly, other mechanisms must play a role in the occurrence of laser damage. Contamination is an obvious
mechanism-both particulate and molecular. Less obvious are structural defects and the role of induced stresses. These
mechanisms are examined through simplified models and finite element analysis. The results of the models are
compared to experiment, for induced temperatures and observed stress levels. The role of each mechanism is described
and limiting performance is determined.