The Digital Information Facility

The acceptance and implementation of advanced digital avionics and flight control systems is dependent on the successful integration of these systems into the current and future National Airspace System (NAS). This paper describes a digital avionics systems research facility known as the Digital Information Facility (DIF) developed to provide researchers with the ground systems and air-to-ground interfaces needed to conduct and document experiments involving a mix of new technologies within the existing NAS infrastructure. The DIF supports four NAS functions: Controller Pilot Data Link Communications (CPDLC), Flight Information Services (FIS), Differential Global Positioning System (DGPS) navigation, and Automatic Dependent Surveillance-Broadcast (ADS-B). The DIF also includes the capability to record pilot and air traffic management interactions and document research participant observations. The DIF capability includes connectivity to flight test and simulated aircraft in a fully immersive Communications, Navigation, and Surveillance (CNS) environment.     

Minimizing Effects of Reflected Shocks in Ballistic Ranges

Shock waves originating from hypersonic projectiles flown in ballistic ranges and subsequently reflected from the range walls have been found to produce undesirable effects on the measurements of projectile wakes. This paper reports on the mechanisms through which reflected shock waves perturb the wake, the design, and installation of full-scale fiberglas wedge shock attenuation treatments, the design of equipment for minimum shock reflection, and the results of measurements of the performance of the treatment.     

The New Horizons Spacecraft

The New Horizons spacecraft was launched on 19 January 2006. The spacecraft was designed to provide a platform for seven instruments designated by the science team to collect and return data from Pluto in 2015. The design meets the requirements established by the National Aeronautics and Space Administration (NASA) Announcement of Opportunity AO-OSS-01. The design drew on heritage from previous missions developed at The Johns Hopkins University Applied Physics Laboratory (APL) and other missions such as Ulysses. The trajectory design imposed constraints on mass and structural strength to meet the high launch acceleration consistent with meeting the AO requirement of returning data prior to the year 2020. The spacecraft subsystems were designed to meet tight resource allocations (mass and power) yet provide the necessary control and data handling finesse to support data collection and return when the one-way light time during the Pluto fly-by is 4.5 hours. Missions to the outer regions of the solar system (where the solar irradiance is 1/1000 of the level near the Earth) require a radioisotope thermoelectric generator (RTG) to supply electrical power. One RTG was available for use by New Horizons. To accommodate this constraint, the spacecraft electronics were designed to operate on approximately 200 W. The travel time to Pluto put additional demands on system reliability. Only after a flight time of approximately 10 years would the desired data be collected and returned to Earth. This represents the longest flight duration prior to the return of primary science data for any mission by NASA. The spacecraft system architecture provides sufficient redundancy to meet this requirement with a probability of mission success of greater than 0.85. The spacecraft is now on its way to Pluto, with an arrival date of 14 July 2015. Initial in-flight tests have verified that the spacecraft will meet the design requirements.     

Damage to the photoreceptor cells of the rabbit retina from 56Fe ions: effect of age at exposure, 1.

Optic and proximate tissues of New Zealand white (NZW) rabbits at ages (approximately 3.5 years) near the middle of their median lifespan (5-7 years) were given 0.5-3.5 Gy of 465 MeV u-1 56Fe ions in the Bragg plateau region of energy deposition at a linear energy transfer (LET infinity) of 220 +/- 31 keV micrometer-1. Dose-dependent losses of retinal photoreceptor cells (rods) occurred until 1-2 years after irradiation, the period of this interim report. Similar cumulative losses of photoreceptor cells were seen during the period 1-2 years post-irradiation for rabbits given comparable exposures when young (6-9 weeks old). Since losses of photoreceptor cells at early times had not been determined previously, the current experiment, which was designed to simulate the responses of mature astronauts, redressed that deficiency.     

Fourier theory of jumps applied to converter harmonic analysis

The Fourier theory of jumps (FTJ) is demonstrated as an aid in deriving closed-form analytical equations for converter switching harmonics. The switching waveforms analyzed are the input current and output voltage and current of a three-phase, ac-dc, step-down, dead-band pulsewidth modulated (PWM), unity power factor converter. The input current closed-form harmonic equation is derived for two parallel-connected, interleaved-PWM converters supplying the same load and sharing a common input filter. The equations are compared with PSpice^TM simulations and practical results     

Effects of 40Ar and 56Fe ions on retinal photoreceptor cells of the rabbit: implications for manned missions to Mars.

Losses of photoreceptor cells (rods) from the retinas of New Zealand white (NZW) rabbits were detectable within 2 years after localized acute irradiation of optic and proximal tissues with > or = 7 Gy of 530 MeV u-1 40Ar ions or > or = 2 Gy of 465 MeV u-1 56Fe ions in the Bragg plateau region of energy deposition. Those limits were determined only from an analysis of variance of dose groups because the shapes of the dose response curves at early post-irradiation times are not known, a concern being addressed by experiments in progress. Losses of photoreceptor cells for the period 0.5-2.5 years post-irradiation, determined by provisional linear regression analysis, were approximately 1.7% Gy-1 and 2.5% Gy-1 for 40Ar and 56Fe ions, respectively.     

The Scientific Measurement System of the Gravity Recovery and Interior Laboratory (GRAIL) Mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon utilized an integrated scientific measurement system comprised of flight, ground, mission, and data system elements in order to meet the end-to-end performance required to achieve its scientific objectives. Modeling and simulation efforts were carried out early in the mission that influenced and optimized the design, implementation, and testing of these elements. Because the two prime scientific observables, range between the two spacecraft and range rates between each spacecraft and ground stations, can be affected by the performance of any element of the mission, we treated every element as part of an extended science instrument, a science system. All simulations and modeling took into account the design and configuration of each element to compute the expected performance and error budgets. In the process, scientific requirements were converted to engineering specifications that became the primary drivers for development and testing. Extensive simulations demonstrated that the scientific objectives could in most cases be met with significant margin. Errors are grouped into dynamic or kinematic sources and the largest source of non-gravitational error comes from spacecraft thermal radiation. With all error models included, the baseline solution shows that estimation of the lunar gravity field is robust against both dynamic and kinematic errors and a nominal field of degree 300 or better could be achieved according to the scaled Kaula rule for the Moon. The core signature is more sensitive to modeling errors and can be recovered with a small margin.     

Looking for planetary moons in the spectra of distant Jupiters

More than 100 nearby stars are known to have at least one Jupiter-sized planet. Whether any of these giant gaseous planets has moons is unknown, but here we suggest a possible way of detecting Earth-sized moons with future technology. The planned Terrestrial Planet Finder observatory, for example, will be able to detect objects comparable in size to Earth. Such Earth-sized objects might orbit their stars either as isolated planets or as moons to giant planets. Moons of Jovian-sized planets near the habitable zones of main-sequence stars should be noticeably brighter than their host planets in the near-infrared (1-4 microm) if their atmospheres contain methane, water, and water vapor, because of efficient absorption of starlight by these atmospheric components. By taking advantage of this spectral contrast, future space observatories will be able to discern which extrasolar giant planets have Earth-like moons capable of supporting life.     

The Mercury Dual Imaging System on the MESSENGER Spacecraft

The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin and evolution. MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC). The NAC is a 1.5° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 10.5° FOV and 12-color filter wheel. The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled device detector. Only one camera operates at a time, allowing them to share a common set of control electronics. The NAC and the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments. Onboard data compression provides capabilities for pixel binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression. MDIS will acquire four main data sets at Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor images at low incidence angles, and targeted high-resolution images of key surface features. These data will be used to construct a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips. Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement history of volcanic materials, and the thickness distribution and compositional variations of crustal materials. This paper summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated from MDIS data.