There has been a recent surge in interest in hosted and rideshare payloads that would launch aboard commercial
communications satellites. Much of this interest originates with the satellite customers themselves as a way to sell
excess mass and power margins that exist at launch. In 2008, NASA selected GOLD (Global-scale Observations of
the Limb and Disk) as a mission of opportunity to fly as its first hosted payload experiment on a geosynchronous
commercial communications satellite, a STAR-2 bus satellite built by Orbital Sciences. CHIRP (Commercially
Hosted Infrared Payload), a hosted payload to test infrared sensors for the Air Force, is also being developed for a
STAR-2 bus communications satellite.
The mass limitation on a STAR-2 bus hosted payload is roughly 50 - 60 kg and the volume is roughly constrained to
a 25" x 30" x 28" box on the nadir deck. Telescope apertures are therefore limited is size to about 50 cm in diameter.
The diffraction limit for visible (much less IR) imaging missions barely improves upon ground-based image performance,
but UV missions can achieve better than 0.1" resolution. There is at least one family of optical designs
that (a) provide the necessary focal length and (b) are light and compact enough to fit within the STAR-2 bus mass
and volume constraints. These designs also afford opportunities to maintain 0.05" pointing accuracy through a
combination of a fine steering mirror and an orthogonal transfer CCD.
A standardized interface has been developed for the integration and accommodation of secondary payloads on to Orbital
Sciences Corporation's StarBus line of GEO-based commercial communications satellites. This standardized interface
through hardware adaptations and methodology incorporates all the major subsystems of the spacecraft and will allow
for a variety of hosted secondary payloads to be accommodated while not interfering with the "spacecraft product line"
manufacturing scheme common on commercial communications satellites. Indeed the low cost and fast schedules,
typically two years from contract start to launch, for commercial communications satellites relies upon a high level of
design standardization and exacting heritage. The Hosted Payloads interface as developed and exercised on the StarBus
makes the hosted payload components look like the usual communications components that are routinely comprise the
standard bent-pipe type of communications payload architecture - the kind of payload that the host spacecraft is
optimized to carry. Furthermore the hosted payload accommodation methodology has been developed to flow into the
timeline of the host spacecraft while still allowing for a small degree of margin. Being able to reconcile the aggressive
development process of a commercial communications satellites with the more elongated process seen in a remote
sensing payload is one necessary step to secure a viable future of commercially hosted payloads.
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 km<sup>2</sup> on the Earth's surface. The modulation transfer function is above 0.90 at 2.8 line pairs-millimeter<sup>-1</sup> over the field, which corresponds to a line pair separated by 20 km on the Earth. The spatial resolution is approximately 10 × 10 km<sup>2</sup> 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.
The first of five Special Sensor Ultraviolet Limb Imager (SSULI) sensors was launched on the Defense Meteorological Satellite Program (DMSP) F16 spacecraft in October of 2003 into a sun-synchronous 830 km circular orbit at a local time of 0800-2000 UT. During initial sensor turn-on and evaluation, unusually high levels of background events were observed by the detector. The severity of this background is often sufficient to exceed the counting limit of the electronics as well as contribute to a rapid decrease in detector performance. In light of the SSULI performance degradation and concerns that the subsequent sensors may be affected in a similar manner, a "Tiger Team" investigation was launched to determine the source of the anomalous events. The conclusion from the investigation attributes the observed anomalous events to high levels of non-photon noise caused by ambient ions entering the instrument and striking the front microchannel plate. Additionally, the team made recommendations to mitigate the problem on future flights.
The Atmospheric Neutral Density Experiment (ANDE) is a series of four microsatellites that will study the atmosphere of the Earth from low earth orbit. Each microsatellite is based on a common design; however, each differs in the instrument payloads and the associated science and mission requirements. The primary mission objective is to provide total neutral density along the orbit for improved orbit determination of resident space objects. Each ANDE microsatellite has several secondary goals. It is the unique design of the microsatellites that allows this task to be accomplished.
Each microsatellite is a compact, near perfect sphere; this reduces shape and drag errors so that the local density of the atmosphere can be determined by instantaneous tracking variations detected by very high accuracy laser and radar ranging whereby the spacecrafts themselves are the primary sensing instrument. The accuracy of the atmospheric density measurements inferred from the orbital tracking of ANDE microsatellites will be much greater than that achieved by similar experiments in the past or from any currently proposed.
Many unique design challenges had to be overcome to achieve the necessary science, mission, and operational requirements as well as severe cost constraints. New methods for parts and assembly fabrication were sought out and implemented. These new methods allowed similar parts to function in each of the microsatellites despite the differences between them. In addition, the command and telemetry links used inexpensive COTS Ham radio transceivers while meeting all the International requirements for operations in the Amateur Satellite Service.
The Tiny Ionospheric Photometer (TIP) instrument is a small, space-based, photometer that observes the ionosphere of the earth at 135.6 nanometers. The TIP instrument will primarily observe the airglow emission of the nighttime ionosphere caused by the radiative recombination of atomic oxygen. In addition, the TIP instrument will observe the auroral region boundaries from the emission caused by electron impact excitation. Six TIP instruments will be launched and flown simultaneously as each one is a payload carried aboard the Republic of China Satellite (ROCSAT-3) spacecraft as part of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) program a constellation built and operated by the country of Taiwan. Observations will be made from three orbital planes spaced 60 degrees apart each containing two TIP instruments. The instruments will be able to provide global coverage as well as system and data redundancy in their intended orbital configuration. Raw data from the TIP instruments will be used for the characterization of ionospheric electron density gradients to improve ionospheric modeling. Data from the TIP instruments can also be combined with the data from the other two payloads on board the spacecraft that are a radio beacon and a GPS occultation experiment to result in enhanced ionospheric measurements. The TIP instrument design had to solve several design challenges in order to achieve its intended science and mission requirements. In addition, the design had to address the operational constraints imposed by the spacecraft and the cost constraints of multiple units.
Within the Space Sciences Division at the Naval Research Laboratory (NRL), new facilities have been built and old facilities have been upgraded to provide greater accuracy and precision during the calibration of instruments used for observation of Extreme and Far ultraviolet airglow emission in the upper atmosphere. In addition to the calibration of whole instruments, the facilities necessary for the construction and characterization of the detectors used in the aforementioned spectral region now either exist or are in their final stages of construction. Also in existence at the Naval Research Laboratory are the facilities for the environmental testing of instruments and components for the space environment. The heart of the NRL ultraviolet calibration facilities is an oil-free vacuum chamber, 2-meters in length, with a diameter of 1.67 meters containing an optical test bench 1.2 m wide by 1.5 m long. Some of the various instruments that have already been calibrated in the chamber are the High Resolution Atmosphere and Auroral Spectrographs flown aboard the Air Force Advance Research and Global Observing Satellite and the five Special Sensor Ultraviolet Limb Imagers for the Air Force Defense Meteorological Satellite Program. The chamber's hardware and control software have been upgraded. The software upgrades to the vacuum calibration chamber will allow for autonomous operation with failure and emergency handling procedures to protect the instruments under test from a loss of vacuum environment. The hardware upgrades allow for chamber pressures in the low 10<SUP>-6</SUP> torr range during the operation of windowless gas discharge lamps. In addition, the upgrades provide the capability to stimulate an instrument using two sources of light simultaneously, one through a monochromater the other by direct illumination.
A Mach-Zehnder based variable resolution fringe projection system has been built for 3D video moire machine vision. This system uses the three main advantages of the Mach- Zehnder - 1) There is no optical feedback to the laser source; 2) The interferometer can accept two different laser wavelengths simultaneously; and 3) The interferometer produces two orthogonal output beams. The lack of optical feedback makes the Mach-Zehnder especially attractive for use with high power laser diode sources which are sensitive to optical feedback. When the two input ports are used with two different wavelength laser, the target can be illuminated by simultaneous projection of two different sets of colored fringes with two different spatial frequencies. This can allow more reliable reconstruction of the 3D surface over discontinuous jumps. Finally, the lack of feedback to the source coupled with the dual outputs means that he Mach-Zehnder fringe projector is very efficient in that 100 percent of the laser light is projected onto the prime and reference targets. Setup and alignment of this interferometer will be discussed for both parallel and diverging light. Plots of fringe visibility will be given for both outputs and both inputs.Application to a video moire based real time 3D error map machine vision system will be discussed.