Wesley P. Millard

The RF telecommunications system for the New Horizons mission to Pluto

This work describes the design and development of the RF telecommunications system for the New Horizons mission, NASAs planned mission to Pluto. The system includes an advanced, low-power digital receiver, and a card-based transceiver implemented within an integrated electronics module. An ultrastable oscillator (USO) provides the precision frequency reference necessary for the uplink radio science experiment. The 2.1 meter high gain antenna is the primary communications antenna, with medium gain and low gain antennas used for wider beamwidths during early operations, cruise-phase and sun-pointing mission phases. The paper will discuss the salient aspects of the system design, including design drivers from mission operations, science, and spacecraft considerations. It will also detail individual subsystems1 performance, operational modes (including beacon mode operation), and navigation technology, including the first deep-space flight implementation of regenerative ranging.

X-band digital receiver for the New Horizons spacecraft

A low-power X-band digital uplink receiver has been developed by the APL for NASAs planned New Horizons mission to Pluto and the Kuiper Belt, which is scheduled to launch in January 2006 with a Pluto encounter as early as 2015. The uplink receiver provides X-band carrier tracking, command detection/demodulation, critical command decoding, ranging tone demodulation, and built-in radiometrics modes. The primary RF carrier tracking, command detection, and ranging requirements are similar to those of predecessor deep space RF systems, including both the small deep space transponder (SDST) and CONTOUR RF transceiver systems. Additional design requirements for radioscience compatibility and reduced power consumption led to a new design approach. The new receiver design makes use of digital processing techniques and revised system architecture to meet these new requirements, while at the same time enhancing performance and flexibility over predecessor systems. A 53% to 68% reduction in secondary power consumption over comparable predecessor systems has been achieved. This paper provides a detailed description of the new low-power digital receiver design.

Flexible coherent digital transceiver for low power space missions

A flexible coherent digital transceiver architecture has been developed by the APL in order to enable mission specific performance tailoring while maintaining modularity and minimizing program-incurred cost and risk. The new transceiver architecture is based on the heritage X-band transceiver system that is currently integrated into the New Horizons spacecraft. Using this new architecture, a low power, coherent, X-band digital transceiver has been made that meets the requirements for two-way Doppler tracking. The new transceiver contributes less than 0.01 mm/s to the Doppler velocity error measured over a 60-second interval in coherent mode. Secondary power consumption is 2.8 W in the uplink-only mode of operation including the reference oscillator. Transceiver designs on the TIMED, CONTOUR, and New Horizons spacecraft were noncoherent, which required downlink telemetry in order to support two-way Doppler tracking (Jensen, 1999). The addition of a coherent capability allows this new architecture to be used on missions where carrier-only Doppler tracking is desired. This paper provides a description of the new transceiver architecture and its demonstrated performance

Optical communications development for spacecraft applications: recent progress at JHU/APL

Free-space optical communication systems for deep space as well as near terrestrial space environments are now under development for deployment aboard spacecraft within the next few years. Ever-increasing requirements for high data-rate communications are driving significant investments by NASA and DoD in critical technology readiness for spaceflight. One of the key NASA requirements is science data retrieval at rates much higher than heretofore possible with RF systems, for missions as far out as interstellar space and as close as geosynchronous Earth orbit (GEO). Recent efforts at Johns Hopkins University Applied Physics Laboratory (JHU/APL) are summarized that are focused on these requirements and challenges. We are developing a spacecraft optical communications terminal architecture initially using commercial off-the-shelf components while accelerating the development of state-of-the-art replacement components, which minimize mass and prime power while maintaining or improving performance. Recent technology development efforts will be summarized that include pulse position (PPM) modulator/demodulator chip development, compact optical beamsteering technology, including micro-electromechanical systems (MEMS), an ultra-lightweight deployable dual-band antenna concept, and a low-mass low-power optical downlink terminal design intended for deployment on a realistic interstellar explorer (RISE) mission

Development of a laser transceiver system for deep-space optical communications

The National Aeronautics and Space Administration (NASA) continues to plan and anticipate the development of high data rate communications for future deep space missions. The Johns Hopkins University Applied Physics Laboratory is responding to this challenge by developing a breadboard laser transceiver package using commercial off-the-shelf components. We plan to demonstrate a breadboard transceiver unit, integrated with a fine pointing and tracking capability by the end of FY-03. A potential mission application is to ultimately demonstrate a live video link from Mars. Our near-term demonstration goals are to achieve a modest 5 Mbps data rate over an equivalent range of 2 AU. To achieve this we are modeling and testing the components for a hybrid analog/digital receiver in conjunctino with semiconductor laser diodes and silicon PIN and avalanche photodiodes. Our efforts leading up to hardware implementation and test have consisted of a trade-of between coherent and direct detection receiver architectures, and a link analysis for deep space applications, which established the laser power requirements for supporting a real-time video link from Mars as well as other missions, where the encoded bit error rate is from 10-6 to 10-9. Current efforts include the development of a direct-detection 4-ary pulse position modulation scheme using a FPGA-based modulator/demodulator as well as a separate quadrant photodiode receiver for tracking. We plan to integrate this transceiver with lightweight diffractive optical elements for beam-forming. The design and initial testing of the transceiver components will be discussed.

Microwave Technologies for the New Horizons Mission to Pluto

An advanced deep space microwave radio communications system has been developed for the New Horizons spacecraft that is currently headed for Pluto and beyond. The system includes two, low-power, X-band digital receivers developed to minimize power consumption. This effort was critical to the mission, as the power saved using the digital receivers was approximately equal to the power consumed by the entire instrument suite. Each receiver is accompanied by an X-band exciter and an ultrastable oscillator to form a complete transceiver, providing command, science, and telemetry links and radionavigation functions. An uplink radioscience capability is built into the receive system to collect data on Plutos tenuous atmosphere by recording phase and amplitude measurements of the uplink signal, as opposed to traditional downlink-only or turnaround experiments. Low power, increased functionality, and flexibility were obtained by leveraging from commercial technologies and techniques. Careful examination and screening were used to mitigate concerns for radiation effects and reliability.

Power remote input output ASIC (PRIO)

The ability to monitor a variety of voltages and currents is a basic need for spacecraft and other complex systems. Although this function can be performed with a handful of components (FPGA, ADC, op-amps, etc), it is at the expense of board area, mass and power. The power remote I/O (PRIO) ASIC is a single chip, multi-channel monitoring device. The PRIO has internal buffers with externally programmable attenuation to allow the PRIO to safely monitor voltages in the range of -40 V to +40 V DC. The current monitoring is accomplished with an external toroid pickup. The ASIC operates from a 5 V supply and communicates with the spacecraft via the I2C bus

Radiation tolerant mixed signal microcontroller for Martian surface applications

We are developing a radiation tolerant, mixed-signal microcontroller for applications exposed to the Martian surface thermal environment. The part can be used for spacecraft/rover engineering data collection, parameter monitoring, and fault detection at the sensor and needs minimal external support circuits. The 8-bit microcontroller includes timer resources, three serial communications ports, a 16-bit programmable digital interface, an 8-level interrupt controller, and I 2C master/slave bus interface. Mixed signal peripherals include a 16-channel, 10-bit successive approximation A/D converter, 10-bit D/A converter, programmable gain amplifier, and voltage reference. All memory interfaces use a 13-bit wide two-bit error detection, single-bit error correction code for each byte. There is an internal 512 times 13 bit scratchpad static random access memory and 2 Ki times 13 bit electrically erasable programmable read only memory