The IRIDIUMR main mission antenna concept

The design of a novel phased array panel that provides the L-band satellite to ground links for the IRIDIUM global communications system is presented. Key components and aspects of this phased array antenna are discussed, including the beamforming architecture, radiated intermodulation products, the patch radiators, and the T/R module. The strategy for minimizing DC power consumption over a large range of multicarrier rf output power is described. Finally, test results showing compliant array operation are summarized     

Experimental results for Titan aerobot thermo-mechanical subsystem development

This paper describes experimental results from a development program focused on maturing Titan aerobot technology in the areas of mechanical and thermal subsystems. Results from four key activities are described: first, a cryogenic balloon materials development program involving coupon and cylinder tests and culminating in the fabrication and testing of an inflated 4.6 m long prototype blimp at 93 K; second, a combined lab experiment and numerical simulation effort to assess potential problems resulting from radioisotope power source waste heat generation near an inflated blimp; third, an aerial deployment and inflation development program consisting of laboratory and helicopter drop tests on a near full scale (11 m long) prototype blimp; and fourth, a proof of concept experiment demonstrating the viability of using a mechanically steerable high gain antenna on a floating blimp to perform direct to Earth telecommunications from Titan. The paper provides details on all of these successful activities and discusses their impact on the overall effort to produce mature systems technology for future Titan aerobot missions.     

A Nomogram for Look Angles to Geostationary Satellites

TA chart is presented that allows for the rapid determination of the azimuth and elevation to a geostationary satellite, given the satellite longitude and the latitude and longitude of the ground site.     

Observation of Transition Region Fine Structures with Soho/Sumer

We present a preliminary analysis of two quiet Sun transition region areas observed with the SOHO/SUMER spectrometer, using lines from oxygen, nitrogen and silicon. The average quiet Sun physical parameters are studied as a function of line intensity. Systematic variations of line position and width with increasing intensity are found. A large number of small-scale active points have been observed, and preliminary analysis of the physical properties and dynamics of these active features is presented. A jet-like structure, found in an active point, is also investigated and its velocity along the line of sight determined. This revised version was published online in June 2006 with corrections to the Cover Date.     

Atmospheric Distortion of Signals Originating from Space Sources

The phasefront distortion imposed on space signals by fine-grained refractivity variations of the atmosphere is an important consideration in the design of large-aperture antennas, antenna arrays, antenna systems for measuring spacecraft position and position-rate, and radioastronomy systems. The distortion caused by ionospheric and tropospheric refractivity variations imposes fundamental limitations on the capabilities of these antennas and antenna systems, particularly on systems which must operate at low elevation angles. The purpose of this paper is to present numerical estimates of distortion imposed on signals passing through the atmosphere. Atmospheric models based on available literature are selected for this purpose.     

On the Differences in Composition between Solar Energetic Particles and Solar Wind

Although the average composition of solar energetic particles (SEPs) and the bulk solar wind are similar in a number of ways, there are key differences which imply that solar wind is not the principal seed population for SEPs accelerated by coronal mass ejection (CME) driven shocks. This paper reviews these composition differences and considers the composition of other possible seed populations, including coronal material, impulsive flare material, and interplanetary CME material.     

Techniques for transmitting digital data on the spacelab's analogvideo channel

A study was made of various techniques for transmitting digital data over a composite video channel, with data from experiments on the Space Shuttle Orbiter in mind. Broadcast television telecommunications schemes and other techniques described in the literature were reviewed and compared. PSK (phase shift keying) MPSK (M-ary PSK), and or PAM (pulse amplitude modulation), which can be transmitted on visible lines of a frame, unassigned lines of the VBI (vertical blanking interval), or during the HBI (horizontal blanking interval), were all judged attractive under the proper conditions. However, PAM on visible lines or during the VBI should be relatively easy to implement, provide adequate average data rates, and give acceptable BERs (bit error rates)     

Vehicle health management research for legacy and futureoperational environments

The Air Force will require the ability to diagnose and predict component failures in order to more effectively meet the requirements of the fast and agile Aerospace Expeditionary Force (AEF) and future space vehicles. This paper will cover topics relevant to vehicle health management for current and anticipated support environments. It reflects current projects underway at the Air Force Research Laboratory in the air vehicles and human effectiveness directorates. Specifically, the predictive failures and advanced diagnostics (PFAD) for legacy aircraft, passive aircraft status system (PASS), and the space operations vehicle integrated system (SOVIS) projects will be discussed     

Gravity Recovery and Interior Laboratory (GRAIL): Mapping the Lunar Interior from Crust to Core

The Gravity Recovery and Interior Laboratory (GRAIL) is a spacecraft-to-spacecraft tracking mission that was developed to map the structure of the lunar interior by producing a detailed map of the gravity field. The resulting model of the interior will be used to address outstanding questions regarding the Moon’s thermal evolution, and will be applicable more generally to the evolution of all terrestrial planets. Each GRAIL orbiter contains a Lunar Gravity Ranging System instrument that conducts dual-one-way ranging measurements to measure precisely the relative motion between them, which in turn are used to develop the lunar gravity field map. Each orbiter also carries an Education/Public Outreach payload, Moon Knowledge Acquired by Middle-School Students (MoonKAM), in which middle school students target images of the Moon for subsequent classroom analysis. Subsequent to a successful launch on September 10, 2011, the twin GRAIL orbiters embarked on independent trajectories on a 3.5-month-long cruise to the Moon via the EL-1 Lagrange point. The spacecraft were inserted into polar orbits on December 31, 2011 and January 1, 2012. After a succession of 19 maneuvers the two orbiters settled into precision formation to begin science operations in March 1, 2012 with an average altitude of 55 km. The Primary Mission, which consisted of three 27.3-day mapping cycles, was successfully completed in June 2012. The extended mission will permit a second three-month mapping phase at an average altitude of 23 km. This paper provides an overview of the mission: science objectives and measurements, spacecraft and instruments, mission development and design, and data flow and data products.