The NASA Radiation Belt Storm Probes (RBSP) mission, launching in 2012, features two spacecraft that will measure the dynamics of the radiation belts as they proceed in nearly identical orbits around the Earth. The Radio Frequency (RF) telecommunications subsystem will utilize an S-Band version of the Johns Hopkins University Applied Physics Laboratory's (JHU/APL) Frontier Radio. The Frontier Radio is a low-power, low-mass, modular Software Defined Radio (SDR) platform designed for communications, navigation, radio science, and sensor applications. The RBSP Frontier Radio is the first of this platform with a full software implementation to demonstrate a Technology Readiness Level (TRL) of 6. The Engineering Model (EM), with mature packaging, hardware, firmware, and software implementations has successfully completed environmental and compatibility testing designed to simulate the space environment expected for the RBSP mission. The ground support equipment (GSE) utilized a ground station modem with turbo and convolutional decoding and internal bit and frame error rate (BER/FER) testing capabilities. The modem, JHU/APL-built equipment for emulating the spacecraft interfaces, and the use of EM hardware for other RF subsystem components enabled test-as-you-fly scenarios that were used throughout testing. Several novel packaging and process technologies were also qualified during the development of this radio. These include a high-reliability assembly process for installing Quad Flat Pack No-Lead (QFN) integrated circuits and a 152-pin stacking connector that serves as the main interconnect between the functional blocks of the radio. The RBSP radio is the first Frontier Radio to be qualified for a spaceflight mission. This demonstration of a high reliability, low power, and low mass radio further validates the platform for use in future space missions.

Two NASA deep-space probes, Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) and New Horizons (NH), are moving towards the extremes of our solar system (Mercury and Pluto). The delivery of the science in these extreme environments is a challenge, and the missions require unique approaches. MESSENGER's antenna system utilizes the first electronically scanned high-gain array for a deep-space telecommunication application. The array, which provides the high-data-rate downlink, is scanned in one dimension and is circularly polarized. Although a linearly polarized array would have satisfied the minimum mission science data rate requirements, MESSENGER's circularly po- larized array doubles it. To achieve this, the Johns Hopkins University/Applied Physics Laboratory (JHU/APL) developed an innovative technique to produce circular polarization from a narrow-wall slotted waveguide array. The new technique uses short parasitic monopoles mounted to the exterior of the waveguides. The result is a simple, lightweight, and all- metal circularly polarized array capable of operating at þ300 � C, and a variety of measurement techniques were used to verify phased-array antenna system performance during qualification.

Two NASA deep-space probes, Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) and New Horizons (NH), are moving towards the extremes of our solar system (Mercury and Pluto). The delivery of the science in these extreme environments is a challenge, and the missions require unique approaches. MESSENGER'S antenna system utilizes the first electronically scanned high-gain array for a deep-space telecommunication application. The array, which provides the high-data-rate downlink, is scanned in one dimension and is circularly polarized. Although a linearly polarized array would have satisfied the minimum mission science data rate requirements, MESSENGER'S circularly polarized array doubles it. To achieve this, the Johns Hopkins University/Applied Physics Laboratory (JHU/APL) developed an innovative technique to produce circular polarization from a narrow-wall slotted waveguide array. The new technique uses short parasitic monopoles mounted to the exterior of the waveguides. The result is a simple, lightweight, and all-metal circularly polarized array capable of operating at +300 O C, and a variety of measurement techniques were used to verify phased-array antenna system performance during qualification. The NH antenna system is a stack arrangement of a high-gain antenna (HGA), medium-gain antenna (MGA), and low-gain antenna (LGA). To minimize mission operating costs, the spacecraft is spin stabilized at all times except during encounters to maintain a fixed spacecraft attitude. This approach and application for a narrow beamwidth antenna is unique for a deep-space mission, resulting in new approaches to accurately measure the gain and radio-frequency (RF) boresight direction in a compact range facility. Because of the importance of the HGA function to overall mission success, testing of the HGA system at operational temperatures of -200 O C was also performed. Recent in-flight measurement of the NH HGA pattern verified ground alignments. The RF design of the NH antenna also forms the baseline RF design for a deployable antenna system JHU/APL is developing called the Hybrid Deployable Antenna (HDA). The HDA combines a fixed parabolic dish with a deployable/inflatable reflector annulus that greatly increases antenna area after launch. This concept provides a high-payoff deployable antenna system that is being developed to address the "all or nothing" risk by providing a viable backup capability. This paper discusses some of the challenges to advance this concept for a future deep-space mission.

The MESSENGER spacecraft, designed to orbit the planet Mercury, uses the first electronically scanned phased-array antenna for a deep-space telecommunication application. Two lightweight phased arrays, mounted on opposite sides of the spacecraft, provide the high-gain downlink coverage. Medium-gain antennas are used for uplink and downlink during cruise phase. The invention of a method for achieving circular polarization in a high-temperature (+300degC) environment has doubled the science return of the mission relative to the inherent linear polarization from a slotted waveguide array. Monolithic microwave integrated circuits and discrete heterostructure field effect transistors are integrated to provide the high-efficiency X-band solid-state power amplifier.

The Sentinels mission is a key component of NASA's Living With a Star (LWS) program. The Sentinels Science and Technology Definition Team (STDT) has completed a study to define the science objectives, measurement requirements and observational strategies, and mission design for the Sentinels mission. The Inner Heliospheric Sentinels (IHS) are one of the three flight elements (the others are the Near Earth Sentinel and Far Side Sentinel) that make up the Sentinels mission. The four spin-stabilized IHS spacecraft are in elliptical heliocentric orbit with perihelia at ~0.25 AU and aphelia at ~0.75 AU. This orbit presents unique spacecraft thermal control and power challenges. This study has demonstrated mission feasibility by developing a spacecraft design concept using conventional technologies that satisfy the science and mission requirements defined by the Sentinels STDT. Numerous trade studies were performed to optimize the spacecraft design. The trade studies and their results are discussed.

This article describes the design and performance of the medium-gain antenna developed for the MESSENGER spacecraft. The electrical design and performance will be presented, as well as the mechanical design that was necessary to endure the harsh mission environment.

Six electronic technologies under development for the Mars Technology Program are discussed. The scope of this set ranges from electronic packaging to microprocessors to power supply to communication technologies. An overview (motivation, objective, approach) of these six projects is presented, along with a comparison to the state-of-art. The overarching goal is to develop and mature these technologies to a point where the Mars Exploration Program can consider their use in a specific flight mission.

The MESSENGER spacecraft, the first mission to the planet Mercury since 1975, will achieve Mercury orbit in 2011. The spacecraft uses two opposite-facing mission-enabling X-band (8.4 GHz) phased-array antennas to achieve high-rate downlink communications. The spacecraft orientation is constrained such that a preferred direction faces the Sun; rotation about the Sun-line is allowable. The main beam of each antenna is steerable in one dimension. These two degrees of freedom allow the main beam of the phased array to be pointed in any direction about the spacecraft. A novel system-level design requires many different subsystems of the spacecraft to interact together to achieve accurate beam-pointing, and thus, high-rate downlink data from Mercury to Earth

The MESSENGER spacecraft uses an X-band (8.4-GHz) phased array for high-rate downlink communications to meet mission data requirements yet still survive the extreme environment at the planet Mercury. To survive the solar intensity at the planet, the MESSENGER spacecraft uses a sunshade that must remain Sun-pointed; this restricts pointing of the spacecraft. The use of two phased-array antennas alleviates the need for a gimbaled high-gain dish. The RF signal is routed through on-board solid-state power amplifiers that control the phases of the signals fed to the phased arrays, thereby pointing without the need for any moving parts while maintaining a Sun-pointed attitude. Each phased array is composed of eight slotted waveguide sticks. This paper describes a method for a real-time, fast verification of the steering of the phased array during any phase of spacecraft-level testing (including thermal-vacuum) without the need to free radiate, which is specifically critical to a spacecraft during integration and test. This newly developed and implemented approach does not require near-field probing, in-line couplers, or extra flight mates and de-mates. Once the antennas are integrated onto the spacecraft, schedule constraints force the need for very quick verification methods. The technique described herein quickly samples the phase of the signal at each array element and, in conjunction with subsystem-level measurements, mathematically calculates the radiated antenna pattern. The phases within each array element are measured using innovative loop couplers that may simply be removed once testing is complete. These phases are combined using specifically designed software to calculate the far-field radiated pattern to verify pointing.

Current ultra-stable oscillator (USO) technology relies on highly precise quartz resonators that are selected based on the desired output frequency and stability. These constraints on the crystal specifications significantly increase the lead time and expense of each USO. Recent research and development efforts in USOs by The Johns Hopkins University Applied Physics Laboratory (JHU/APL) have focused on a frequency synthesized USO based on a standardized, fixed-frequency resonator. The result of these efforts is a synthesized USO that will provide a frequency reference for transponders and other on-board users on future space missions. The frequency reference is stable enough for radio-science and navigation applications (Allan deviation <1.5 /spl times/ 10/sup -13/ at /spl tau/ = 10 s), and is electronically adjustable to cover the entire deep-space communications band. This frequency agility allows in flight re-assignment of the transponder frequencies. The synthesized USO offers low mass and DC power consumption yet maintains world-class noise performance and frequency stability performance.