The Stratospheric Observatory for Infrared Astronomy (SOFIA) tracking camera simulator is a component of the Telescope Assembly Simulator (TASim). TASim is a software simulation of the telescope optics, mounting, and control software. Currently in its fifth major version, TASim is relied upon for telescope operator training, mission planning and rehearsal, and mission control and science instrument software development and testing. TASim has recently been extended for hardware-in-the-loop operation in support of telescope and camera hardware development and control and tracking software improvements. All three SOFIA optical tracking cameras are simulated, including the Focal Plane Imager (FPI), which has recently been upgraded to the status of a science instrument that can be used on its own or in parallel with one of the seven infrared science instruments. The simulation includes tracking camera image simulation of starfields based on the UCAC4 catalog at real-time rates of 4-20 frames per second. For its role in training and planning, it is important for the tracker image simulation to provide images with a realistic appearance and response to changes in operating parameters. For its role in tracker software improvements, it is vital to have realistic signal and noise levels and precise star positions. The design of the software simulation for precise subpixel starfield rendering (including radial distortion), realistic point-spread function as a function of focus, tilt, and collimation, and streaking due to telescope motion will be described. The calibration of the simulation for light sensitivity, dark and bias signal, and noise will also be presented
Emerging standards for video metadata provide the means, in principle, for accurate geopositioning from full motion
video. Georegistration to reference data as part of the workflow adds value by improving the metadata accuracy,
establishing a check against mismodeling in the metadata and the corresponding a priori error covariance, and providing
a mechanism to recover usable geopositioning capability in the event of failure of the system generating or transmitting
the metadata. Georegistration may be done on board the collecting platform, at a ground station, or at any point in the
exploitation process. A system capable of full motion video georegistration to reference data will be described, which
establishes a photogrammetrically rigorous sensor model for each video frame. The sensor model operating parameters
and error covariance are updated based on matches between pairs of frames and between frames and reference data. The
challenge of finding associations between the reference data and the video images taken under very different imaging
conditions is met by using both direct and feature matching approaches. Methodology for the validation of
georegistration will be presented. Test results will be given for an operational real-time video georegistration system.
Sufficient conditions for strictly positive definite correlation functions are developed. These functions are associated
with wide-sense stationary stochastic processes and provide practical models for various errors affecting tracking, fusion,
and general estimation problems. In particular, the expected magnitude and temporal correlation of a stochastic error
process are modeled such that the covariance matrix corresponding to a set of errors sampled (measured) at different
times is positive definite (invertible) - a necessary condition for many applications. The covariance matrix is generated
using the strictly positive definite correlation function and the sample times. As a related benefit, a large covariance
matrix can be naturally compressed for storage and dissemination by a few parameters that define the specific correlation
function and the sample times. Results are extended to wide-sense homogeneous multi-variate (vector-valued) random
fields. Corresponding strictly positive definite correlation functions can statistically model fiducial (control point) errors
including their inter-fiducial spatial correlations. If an estimator does not model correlations, its estimates are not
optimal, its corresponding accuracy estimates (a posteriori error covariance) are unreliable, and it may diverge. Finally,
results are extended to approximate error covariance matrices corresponding to non-homogeneous, multi-variate random
fields (a generalization of non-stationary stochastic processes). Examples of strictly positive definite correlation
functions and corresponding error covariance matrices are provided throughout the paper.
BAE SYSTEMS is developing a "4D Registration" capability for DARPA's Dynamic Tactical Targeting program. This will further advance our automatic image registration capability to use moving objects for image registration, and extend our current capability to include the registration of non-imaging sensors. Moving objects produce signals that are identifiable across multiple sensors such as radar moving target indicators, unattended ground sensors, and imaging sensors. Correspondences of those signals across sensor types make it possible to improve the support data accuracy for each of the sensors involved in the correspondence. The amount of accuracy improvement possible, and the effects of the accuracy improvement on geopositioning with the sensors, is a complex problem. The main factors that contribute to the complexity are the sensor-to-target geometry, the a priori sensor support data accuracy, sensor measurement accuracy, the distribution of identified objects in ground space, and the motion and motion uncertainty of the identified objects. As part of the 4D Registration effort, BAE SYSTEMS is conducting a sensitivity study to investigate the complexities and benefits of multisensor registration with moving objects. The results of the study will be summarized.
Georegistration of an image typically requires either 3-5 control points measured in the target image or 6-10 tie points to at least two georegistered reference images. Often control points are not available, and tie points are difficult to find across sensor types, particularly for automatic processes. This work shows that registration can be achieved by measuring 3-5 lines in a target image and two reference images. The same ultimate registration accuracy can be achieved with tie points alone, lines alone, or a combination of both. Line triangulation enables automatic cross-sensor georegistration since lines can be found reliably across sensor types. Lines are measured by indicating two or more image positions on corresponding lines in each image. There is no need to identify corresponding points between images. There is no need for a priori line information, but such information can be exploited. Initial estimates of the lines can be made from the image measurements and a priori sensor models. The evaluation of image registration accuracy is discussed. Examples of image registration with line triangulation are presented.
Orbital debris in low-Earth orbit in the size range from 1 to 10 cm in diameter can be detected but not tracked reliably enough to be avoided by spacecraft. It can cause catastrophic damage even to a shielded spacecraft. With adaptive optics, a ground-based pulsed laser ablating the debris surface can produce enough propulsion in several hundred pulses to cause such debris to reenter the atmosphere. A single laser station could remove all of the 1 - 10 cm debris in three years or less. A technology demonstration of laser space propulsion is proposed which would pave the way for the implementation of such a debris removal system. The cost of the proposed demonstration is comparable with the estimated annual cost of spacecraft operations in the present orbital debris environment. Orbital debris is not the only space junk that is deleterious to the Earth's environment. Collisions with asteroids have caused major havoc to the Earth's biosphere many times in the ancient past. Since the possibility still exists for major impacts of asteroids with the Earth, it shown that it is possible to scale up the systems to prevent these catastrophic collisions providing sufficient early warning is available from new generation space telescopes plus deep space radar tracking.
Orbital debris in low-Earth orbit ranging in size from 1 to 10 cm in diameter can be detected but not tracked reliably enough to be easily avoided by spacecraft. In addition, shielding protection is extremely difficult and costly to accomplish for sizes above 1 - 2 cm. Debris in this size regime traveling at mean velocities on the order of 20000 miles per hour may cause catastrophic damage. Using adaptive optics technologies, a ground-based pulsed laser of sufficient power ablating the debris particle's surface to produce small momentum changes may, in several hundred pulses, lower a target debris particle's perigee sufficiently for atmospheric capture. A single laser facility could remove all of the 1 - 10 cm debris below 1500 km in altitude in approximately three years. A technology demonstration of ground based laser removal is proposed which would pave the way for the implementation of such a debris removal system. The cost of the proposed demonstration is comparable with the estimated annual cost of spacecraft operations in the present orbital debris environment.
Project ULTIMA is an investigation into the feasibility of building ultra-large aperture visible/mid-IR space telescopes. A promising concept found by the study is a freely flying spherical primary mirror, twenty meters or more in diameter, located at the L1 or L2 Earth-Sun libration point. The primary would be passively cooled to 45 K. There would be no metering structure. Instead, using a combination of alignment and steering mirrors, reaction wheels, and microthrusters, the aspherical secondary mirror, active tertiary mirror, and focal plane instruments would be precisely stationed in the correct position above the primary. The primary advanced composition would be either a membrane or ultra-light segmented technology. Preliminary fmdings show that a 20-30 m telescope may be feasible for imaging in the 1-20 µm regime.
Recent advances in adaptive optics support the feasibility of orbital debris removal by laser photoablation impulse, with laser and tracking systems located on the Earth. An in-depth systems analysis shows that individual laser pulses are most effective in lowering perigee and reducing lifetime at a zenith angle of about 40 degrees when the target is approaching the laser. Many pulses are needed to remove debris, and it is important to begin the engagement at the largest zenith angle permitted by tracking and adaptive optics. The 1-10 cm orbital debris hazard will require damage control equipment and procedures as well as on-orbit addition of shielding to the International Space Station. The current risk to satellites in low Earth-orbit is estimated to be $10-100 million per year in replacement costs. These factors suggest an international laser orbital debris removal system could be cost-effective. A demonstration in which radar and optical tracking together with adaptive optics are used to concentrate a laser on a calibrated target in orbit is the next required step in proving the feasibility and cost-effectiveness of such a system.
The Marshall Space Flight Center, Alabama, in a teaming arrangement with the University of Florida, Gainesville, and the Joint Astronomy Center, Hawaii, has completed a comprehensive investigation into the feasibility of a low-cost infrared space astronomy mission. This mission would map the emission of molecular hydrogen in our galaxy at two or three previously inaccessible mid-IR wavelengths, and provide information on the temperatures. The feasibility of the low-cost mission hinged on whether a thermal design could be found which would allow sufficient passive cooling of the telescope to elimiate the need for a large, expensive dewar. An approach has been found which can provide telescope temperatures on the order of 50 K, which makes the mission feasible at low cost in low-Earth orbit.
The Marshall Space Flight Center, Alabama in a teaming arrangement with the Naval Research Laboratory, Maryland has developed the ISIS (impulsive solar imaging spectrometer) mission for viewing the sun and the sky in the EUV, soft, and hard x rays. The soft and hard x ray imaging as well as the gamma-ray spectroscopy will be provided by a three axis pointed Fourier telescope (i.e. a spatial modulation collimator). The EUV imager will be a supporting context instrument. This paper describes the optimized instrument concept and discusses the associated trades made in developing it. For example, the numbers of spatial frequencies measured versus the sensitivity needed for imaging weak sources is discussed in detail. ISIS builds upon the YOHKOH findings in that the telescope is tailored to image compact simple loop sources. Only two spatial frequencies need be measured, allowing substantial gains in sensitivity. In addition, this allows both the real and imaginary Fourier components to be measured, which is a vast improvement over approaches that measure only the real components.