The Geospace Dynamics Observatory (GDO) mission observes the near-Earth region in space called Geospace with
unprecedented resolution, scale and sensitivity. At a distance of 60 Earth Radii (Re) in a near-polar circular orbit and a
~27-day period, GDO images the earth’s full disk with (1) a three-channel far ultraviolet imager, (2) an extreme
ultraviolet imager of the plasmasphere, and (3) a spectrometer in the near to far ultraviolet range that probes any portion
of the disk and simultaneously observes the limb.
The exceptional capabilities of the GDO mission include (1) unprecedented improvement in signal to noise for globalscale
imaging of Earth’s space environment that enable changes in the Earth’s space environment to be resolved with
orders of magnitude higher in temporal and spatial resolution compared to existing data and other approaches, and (2)
unrivaled capability for resolving the temporal evolution, over many days, in local time or latitude with a continuous
view of Earth’s global-scale evolution while simultaneously capturing the changes at scales smaller than are possible
with other methods.
This combination of new capabilities is a proven path to major scientific advances and discoveries. The GDO mission (1)
has the first full disk imagery of the density and composition variability that exist during disturbed “storm” periods and
the circulation systems of the upper atmosphere, (2) is able to image the ionosphere on a global and long time scale
basis, (3) is able to probe the mechanisms that control the evolution of planetary atmospheres, and (4) is able to test our
understanding of how the Earth is connected to the Sun.
This paper explores the optical and technical aspects of the GDO mission and the implementation strategy. Additionally,
the case will be made that GDO addresses a significant portion of the priority mission science articulated in the recent
Solar and Space Physics Decadal Survey.1
The National Aeronautics and Space Administration (NASA) is launching a bold and ambitious new space initiative.
A significant part of this new initiative includes exploration of new worlds, the development of more innovative
technologies, and expansion our presence in the solar system. A common theme to this initiative is the exploration
of space beyond Low Earth Orbit (LEO). As currently organized, NASA does not have an Agency-level office that
provides coordination of space environment research and development. This has contributed to the formation of a
gap between spaceflight environments knowledge and the application of this knowledge for multi-program use. This
paper outlines a concept to establish a NASA-level Applied Spaceflight Environments (ASE) office that will provide
coordination and funding for sustained multi-program support in three technical areas that have demonstrated these
needs through customer requests. These technical areas are natural environments characterization and modeling,
materials and systems analysis and test, and operational space environments modeling and prediction. This paper
will establish the need for the ASE, discuss a concept for organizational structure and outline the scope in the three
Far ultraviolet (FUV) images of Earth from space have proven invaluable in revealing contextual phenomena associated with space weather in the high latitude auroral regions and in the mid and equatorial regions. Images of this nature can be used to investigate compelling questions associated with the interaction of the ionosphere/mesosphere-magnetosphere-solar wind.
Observations using images that lead to quantitative analyses are required to significantly advance the state of knowledge with regard to the affects of space weather and the interaction between and within these regions of Geospace. Current available image data sets are sufficient for qualitative analysis and morphological investigations, and while quantitative analyses are possible, they are difficult and limited to few events at best1,2. In order to qualitatively access the time, spatial, and causal phenomena on global scales, simultaneous images of various FUV emissions with a combination of better spatial, temporal and spectral resolution and sensitivity than currently available are required.
We present an instrument concept that is being developed to improve the spatial, temporal and spectral resolution and sensitivity needed to perform the quantitative analysis that enable significant advancement in our understanding of the impact of space weather on Geospace. The approach is to use the "self-filtering" concept3 that combines the imaging and filtering functions and thus reduces the size of the 4-mirror off-axis optical system. The optical and filter design will de described.
The Ionospheric Mapping and Geocoronal Experiment (IMAGER) is a space-based, multispectral, imaging payload, designed at the U.S. Naval Research Laboratory. The IMAGER's primary science mission is to find, track, and measure ionospheric irregularities as they move across the surface of the Earth and vary with time. IMAGER will observe the ionosphere of the Earth in narrow extreme- and far-ultraviolet passbands centered at 83.4, 130.4, 135.6, and 143.0 nm. These emissions are produced by naturally occurring airglow emission from the nighttime and daytime ionosphere and thermosphere. The IMAGER consists of an imaging telescope with a filter wheel assembly and a pair of microchannel plate-based imaging detectors with cross delay line readouts. The telescope of the instrument consists of a 160 mm diameter, F/4.0 off-axis very fast aplanatic Gregorian telescope. The focal length is 640 mm and the field of view is 1.6° × 1.6° which will cover approximately 1000 × 1000 km2 on the Earth's surface. The modulation transfer function is above 0.90 at 2.8 line pairs-millimeter-1 over the field, which corresponds to a line pair separated by 20 km on the Earth. The spatial resolution is approximately 10 × 10 km2 and is oversampled by a factor of 9 (3 × 3 pixels per resolution element). A system of reflective filters is used to select different wavelengths of interest. The telescope will be gimbaled to provide a field-of-regard encompassing the entire disk and limb of the Earth. The gimbal will also allow the telescope to track the ionospheric irregularities as they move. This paper describes the design of the optical and mechanical systems and their intended performance and includes an overview of the mission and science requirements that defined the aforementioned systems.
New advances in VUV thin film filter technology have been made using filter designs with multilayers of materials such as Al2O3, BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2. Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 X 9 RE orbit will expose the instrument to approximately 275 krads of radiation. In view of the fact that no previous studies have been made on potential radiation damage of these materials on the thin film format, we report on such an assessment here.
Imaging of the earth's auroral regions in the ultraviolet provides information on a global scale on the energy flux and characteristics of precipitating particles and on the composition of the atmosphere in which the energy is deposited. We report the design of an imager with 0.6-mrad angular resolution over an 8-deg field of view sampled with 39,500 pixels, yielding global auroral coherent imaging from above 6 RE(Earth radii). High-performance filters provide spectrally pure measurements of four key far-UV (FUV) features, with 5 x 10-5 out-of-band rejection. Together with a solar blind intensified CCD detector, a net rejection of 10-9 of all out-of-band emissions is achieved. The optical design comprises a three-mirror f/3 system that yields a noise equivalent sensitivity of 10 rayleighs (R) for a 37-s frame rate. The intrascene and interscene dynamic ranges are 1000 and 105, respectively. The optical surface microroughness is less than 2 nm, providing exceptionally low light scattering characteristics, allowing simultaneous observations of very weak and bright emissions. The imager should provide about two orders of magnitude improvement in performance over previous designs.
The far-ultraviolet (FUV) imager for the International Solar Terrestrial Physics (ISTP) Mission is designed to image four features of the aurora: O I lines at 130.4 and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 and 160 nm (LBH long) and 160 and 180 nm (LBH long). We report the design and fabrication of narrowband and broadband filters for the ISTP FUV imager. Narrowband filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 23.9 and 38.3% at 130.4 and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance close to 60%. Blocking of out-of-band wavelengths for all filters is better than 5 x 10-3% with the transmittance at 121.6 nm of less than 10-6%.
The far ultraviolet (FUV) imager for the International Solar-Terrestrial Physics (ISTP) mission is designed to image four features of the aurora: 0 1 lines at 130.4 nm and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 nm -160 nm (LBH long) and 160 nm 180 nm (LBH long). We report the design and fabrication of narrow-band and broadband filters for the ISTP FUV imager. Narrow-band filters designed and fabricated for the 0 I lines have a bandwidth of less than 5 nm and a peak transmittance of 22.3% and 29.6% at 130.4 nm and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance greater than 40% for LBH short and close to 60% for LBH long. Blocking of outof-band wavelengths for all filters is better than 0.001% with the transmittance at 121.6 nm of less than 10-6%.