Dennis J. Duven

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.

A Weak-signal GPS Architecture for Lunar Navigation and Communication Systems

As envisioned by a broad series of trade studies, the lunar elements of the NASA Exploration Initiative will require a significant increase in navigation and communication capacity. Exploration combines robotic and human mission elements that should ideally support each other in terms of advancing the ability to discover, operate, and support a sustained human presence in the lunar environment. While a small set of individual sorties may be able to incur the inefficiencies of developing mission-specific navigation and communication capability, or relying on current systems, realizing the fundamental goal a sustained human presence will greatly strain current systems. In conjunction with a small spacecraft-based lunar navigation and communication system solution jointly among JHU/APL, NASA/GSFC, NASA/GRC and JPL, JHU/APL analyzed the incorporation of a Global Positioning System component to an infrastructure of spacecraft designed to provide communication and navigation service to lunar assets. This research is described, included the technology basis for reception of GPS in the lunar environment, the impact on the space, ground, and user segments of a lunar navigation and communication infrastructure, and the benefits and costs of such an architectural implementation. Specific technologies include leveraging JHU/APL weak-signal GPS processing and the use of disciplined ultra-stable oscillators.

Lunar Navigation and Communication System Implementation Concept

The NASA exploration Initiative provides a defining vision for the U.S. space program that will include a series of human and robotic missions to the Moon, thereby enabling ultimate exploration of Mars and other destinations. Exploration combines robotic and human mission elements that should ideally support each other in terms of advancing the ability to discover, operate, and support a sustained human presence in the lunar environment. In support of these missions, NASA has considered the implementation of a system to realize lunar navigation and communication service essential to assets at the moon. This paper describes the results of JHU/APLs efforts within a joint study between JHU/APL and NASA/GSFC, with support from NASA/GRC and JPL that details an implementation of a Lunar Relay System that could represent a floor capability of such an infrastructure by providing basic communication and navigation service to lunar assets. The approach provides a flow from a reasonable, if basic, set of requirements and desired capabilities, and details space system implementation that meets those requirements. This includes a conceptual mission design, space and payload segment, ground segment, and operational performance.

A theoretical analysis of Ka-band turnaround noise in radios used for deep space comm/Nav

Deep-space missions typically use a radio link between the Deep Space Network (DSN) ground stations and the spacecraft to transmit telemetry data and to generate the range and Doppler shift measurements that enable precise navigation. The amount of carrier phase noise present in this radio link is an important metric of performance, and radios are often designed to minimize the impact of this noise. From a communication perspective, more noise causes an increase in the systems frame-error rate, and from a navigation perspective more noise causes larger errors in the range and Doppler shift measurements. A thorough understanding of how carrier phase noise enters the spacecraft radio system and how that noise is modified during the communication process enables the radio designers to build a better system. This paper contributes to the current body of knowledge on turnaround noise for Deep Space communication and Doppler data, and how to mitigate the resulting performance degradation. In particular, this paper focuses on systems with an X-band uplink and a Ka-band downlink, as is planned for the NASA Solar Probe Plus and Europa Missions. The analysis in this paper compares the design equations listed in the DSN Telecommunications Link Design Handbook (810-005) with more rigorous and higher fidelity equations recently proposed by one of the authors. Numerous factors that affect the final noise level are considered: thermal noise at the DSN receiver, turn-around factors, uplink scintillation, uplink thermal noise, radio filtering effects, downlink scintillation, DSN receiver filtering, and implementation loss. The equations that result from this analysis accurately verify and explain data collected from a recent DTF-21 test. The resulting higher fidelity models permit analysts to make refinements to current radio designs to mitigate this interference. Several example mitigation techniques are discussed and evaluated for the previously mentioned missions in terms of noise levels and the resulting frame-error rates.

Global positioning system surface navigation accuracy study

Abstract This report discusses the accuracy to be expected in using the Global Positioning System (GPS) satellites for surface navigation. Several theoretical analyses are given to determine what accuracy in horizontal position may be achieved when range data from various sets of four satellites from the current five‐satellite GPS constellation are used to solve for the position state vector. Results indicate a horizontal position accuracy of 10m to 20m may be expected. In addition, the benefits of using a priori vertical position information are discussed, as well as sensitivity to errors in such a priori estimates. The theoretical basis of each analysis is summarized, and the results of each analysis are expressed in terms of the net horizontal position uncertainty resulting from the technique implemented. Finally, the results of using actual recorded GPS data to navigate a receiver with known coordinates are given to provide verification of the theoretical results.