Dennis J. Gallagher

Overview of the optical design and performance of the high resolution science imaging experiment (HiRISE)

The High Resolution Imaging Science Experiment (HiRISE) camera will be launched in August 2005 onboard NASAs Mars Reconnaissance Orbiter (MRO) spacecraft. HiRISE supports the MRO Mission objectives through targeted imaging of nadir and off-nadir sites with high resolution and high signal to noise ratio [a]. The camera employs a 50 cm, f/24 all-reflective optical system and a time delay and integration (TDI) detector assembly to map the surface of Mars from an orbital altitude of ~ 300 km. The ground resolution of HiRISE will be < 1 meter with a broadband red channel that can image a 6 x 12 km region of Mars into a 20K x 40K pixel image. HiRISE will image the surface of Mars at three different color bands from 0.4 to 1.0 micrometers. In this paper the HiRISE mission and its camera optical design will be presented. Alignment and assembly techniques and test results will show that the HiRISE telescopes on-orbit wave front requirement of < 0.071 wave RMS (@633nm) will be met . The HiRISE cross track field is 1.14 degrees with IFOV 1.0 μ-radians.

MAXIM interferometer tolerances and tradeoffs

MAXIM consists of thirty-two individual grazing incidence interferometer channels that act, in combination, like a high-resolution imaging telescope. In this paper, we will describe an optical design for Maxim and calculate principal optical tolerances. These tolerances offer advantages that make anticipated engineering challenges more soluble and affordable within the limitations of current technology. We also discuss key design tradeoffs that contribute to a preliminary tolerance budget.

The Constellation-X RGS options: raytrace modeling of the off-plane gratings

The Reflection Grating Spectrometer of the Constellation-X mission has two strong candidate configurations. The first configuration, the in-plane grating (IPG), is a set of reflection gratings similar to those flown on XMM-Newton and has grooves perpendicular to the direction of incident light. In the second configuration, the off-plane grating (OPG), the grooves are closer to being parallel to the incident light, and diffract along a cone. It has advantages of higher packing density, and higher reflectivity. Confinement of these gratings to sub-apertures of the optic allow high spectral resolution. We have developed a raytrace model and analysis technique for the off-plane grating configuration. Initial estimates indicate that first order resolving powers in excess of 1000 (defined with half-energy width) are achievable for sufficiently long wavelengths (λ ≥ 12Å), provided separate accommodation is made for gratings in the subaperture region farther from the zeroth order location.

Monte Carlo model for describing charge transfer in irradiated CCDs

Radiation exposure of CCD devices degrades the charge transfer inefficiency (CTI) by the creation of electron trap sights within the bulk silicon. The presence of electron traps tend to smear the signal of a point-like image. This affects CCDs used in star trackers where sub-pixel centroiding is required for accurate pointing knowledge. To explore the effects of radiation damage in CCD devices, we have developed a Monte-Carlo model for simulating charge transfer in buried channel CCDs. The model is based on the Shockley-Read-Hall generation-recombination theory. The CTI in CCD devices was measured before and after exposure to mono-energetic 61 MeV protons. Our data show that displacement damage in the bulk silicon increases the CTI of the CCD device. CTI was measure don irradiated CCD devices at various temperatures form -10 to -150 C, thus providing estimates of the electron trap energy levels created in the CCD silicon. The dominate post-radiation rap energy level was the silicon E-center found to be at an energy of 0.46 eV, which is in good agreement with other published values. To fit our data over the complete temperature range, we also required electron traps of 0.36 eV and 0.21 eV. Our model also includes the effects of charge cloud growth with signal volume and clocking rates of the CCD device. Determining the types and levels of radiation a CCD device will encounter during its operational life is very important for choosing CCD operating parameters.

The COSMO coronagraph optical design and stray light analysis

The Coronal Solar Magnetism Observatory Large Coronagraph (COSMO-LC) is a 1.5 meter Lyot coronagraph dedicated to measuring magnetic fields and plasma properties in the solar corona. The COSMO-LC will be able to observe coronal emissions lines from 530-1100 nm using a filtergraph instrument. COSMO-LC will have a 1 degree field of view to observe the full solar corona out to 1 solar radius beyond the limb of the sun. This presented challenges due to the large Etendue of the system. The COSMO-LC spatial resolution is 2 arc-seconds per pixel (4k X 4k). The most critical part of the coronagraph is the objective lens that is exposed to direct sunlight that is five orders of magnitude brighter than the corona. Therefore, it is key to the operation of a coronagraph that the objective lens (O1) scatter as little light as possible, on order a few parts per million. The selection of the material and the polish applied to the O1 are critical in reducing scattered light. In this paper we discuss the design of the COSMO-LC and the detailed design of the O1 and other key parts of the COSMO-LC that keep stray light to a minimum. The result is an instrument with stray light below 5 millionths the brightness of the sun 50 arc-seconds from the sun. The COSMO-LC has just had a Preliminary Design Review (PDR) and the PDR design is presented.

MAXIM Pathfinder: a practical configuration

The x-ray band of the spectrum is the natural place to perform super-high resolution imaging of astronomical objects. Because x-ray sources can have very intense surface brightness and interferometers can be made with very short baselines, x-ray interferometry has great potential. We will discuss MAXIM, the Micro-Arcsecond X-ray Imaging Mission and, in particular, MAXIM Pathfinder, a coordinated pair of x-ray astronomy missions designed to exploit the potential of x-ray interferometry. We will show how it is possible to achieve huge gains in resolution using todays technology. The Pathfinder mission will achieve resolution of 100 micro-arcseconds and will image the coronae of the nearby stars. MAXIM, with a design specification of 0.1 micro-arcseconds, has the goal of imaging the event horizons of massive black holes. We will explain the architecture of a possible Pathfinder mission and describe the activities NASA is supporting in the area of x-ray interferometry.

Subarcsecond x-ray telescope for imaging the solar corona in the 0.25- to 1.2-keV band

We have developed an x-ray telescope that uses a new technique for focusing x-rays with grazing incidence optics. The telescope was built with spherical optics for all of its components, utilizing the high quality surfaces obtainable when polishing spherical (as opposed to aspherical) optics. We tested the prototype x-ray telescope in the 300 meter vacuum pipe at White Sands Missile Range, NM. The telescope features 2 degree graze angles with tungsten coatings, yielding a bandpass of 0.25-1.5 keV with a peak effective area of 0.8 cm2 at 0.83 keV. Results from x-ray testing at energies of 0.25 keV and 0.93 keV (C-K and Cu-L) verify 0.5 arcsecond performance at 0.93 keV. Results from modeling the x-ray telescopes response to the SUn show that the current design would be capable of recording 10 half arcsecond images of a solar active region during a 300 second NASA sounding rocket flight.

Systems engineering overview and concept of operations of the COronal Solar Magnetism Observatory (COSMO)

The COronal Solar Magnetism Observatory (COSMO) is a proposed facility with unique capabilities for magnetic field measurements in the solar atmosphere and corona to increase our understanding of solar physics and space weather. The observatory underwent a preliminary design review (PDR) in 2015. This paper summarizes the systems engineering plan for this facility as well as a preliminary overview of the concept of operations. In particular we detail the flow of science requirements to engineering requirements, and discuss an overview of requirements management, documentation management, interface control and overall verification and compliance processes. Operationally, we discuss the categories of operational modes, as well as an overview of a daily operational cycle.

Modeling optical performance of grazing-incidence x-ray interferometers

This paper discusses X-ray interferometer designs with milli-arcsecond resolution. The goal of this work was to derive interferometer designs that can be built and operated within the budget of a NASA mission. The current interferometer mission designs we propose use separate spacecraft for the optics and detector. Applying design techniques that desensitize the optical performance of the interferometer to spacecraft tip-tilt, and de-center errors was the goal of this work. An interferometer design will be presented with milli-arcsecond resolution. The requirements on relative motion between the spacecraft carrying the interferometer optics and the detector are discussed. Optical performance predictions will be shown.

X-ray testing of grazing incidence optics fabricated at the University of Colorado

Most methods of producing grazing incidence optics require expensive metrology equipment to achieve sub arcminute quality in the X-ray. At the University of Colorado we have been developing methods of manufacturing grazing incidence optics by grinding and polishing on aluminum and nickel surfaces that have been machined to within a few arcminutes on a conventional metal working lathe. The mirrors are tested during fabrication by the knife edge and Ronchi test which are simple optical tests requiring only a collimated source of visible light and a 50 line per inch screen, (Gallagher 1990). No metrology of the surface is done. At graze angles of a few degrees fabricating optics by this method is limited by diffraction of the highly obstructed pupil, but at visible wavelengths figuring to 10 or 20 arcseconds is still possible. This method cannot produce arcsecond quality X-ray mirrors by itself, but can be modified to do so when coupled with normal incidence testing of the optical surface by use of a reference test plate or profilometer. In this paper we only discuss the X-ray testing of a 218 mm diameter F/5.73 Wolter Type I telescope manufactured at the University of Colorado. The mirror flew on a NASA sounding rocket in March of 1991. Testing of the inplane and offplane imaging response at energies of .25 - 1.50 KeV and correlation with surface figure are discussed.