[Show abstract][Hide abstract] ABSTRACT: The Pluto system was recently explored by NASA's New Horizons spacecraft,
making closest approach on 14 July 2015. Pluto's surface displays diverse
landforms, terrain ages, albedos, colors, and composition gradients. Evidence
is found for a water-ice crust, geologically young surface units, surface ice
convection, wind streaks, volatile transport, and glacial flow. Pluto's
atmosphere is highly extended, with trace hydrocarbons, a global haze layer,
and a surface pressure near 10 microbars. Pluto's diverse surface geology and
long-term activity raise fundamental questions about how small planets remain
active many billions of years after formation. Pluto's large moon Charon
displays tectonics and evidence for a heterogeneous crustal composition, its
north pole displays puzzling dark terrain. Small satellites Hydra and Nix have
higher albedos than expected.
[Show abstract][Hide abstract] ABSTRACT: The New Horizons mission to Pluto is the first deep space mission to include the capability of supporting regenerative PN ranging. During the current phase of the mission, sequential tone ranging supports the mission navigation requirements but regenerative ranging will expand the conditions (antenna selection, integration time, etc.) over which ranging will be successful during any extended mission following the Pluto fly-by, to objects in the Kuiper belt. Experience with regenerative ranging is being obtained now in preparation for its use in an extended mission. During most of 2012, New Horizons was in a hibernation state. Tracking was conducted between late April and early July. Six regenerative ranging passes were performed to bookend this interval; 2 at the beginning and 4 at the end. During that time, the distance between the spacecraft and Earth was in excess of 22 Astronautical Units (AU) and the Pr/No levels were below 15 dB-Hz. A seventh regenerative ranging pass was performed in May at a higher signal level in order to test the acquisition of the ranging code by the spacecraft during a variety of conditions. The consistency of the regenerative range measurements with the adjacent sequential tone ranging measurements has been demonstrated and serves as a check on the calibration of the regenerative ranging system conditions. The range measurement precision has been shown to follow the predictions that are based on the uplink and downlink signal power. The regenerative ranging system has been shown to acquire the uplink ranging code with and without a commanded reset and regardless of the noise bandwidth setting of the system. This paper will present the data that was obtained during 2012 and will describe the analysis results for the regenerative ranging experience during 2012.
[Show abstract][Hide abstract] ABSTRACT: Deep-space missions traditionally use sequential, turnaround ranging to measure the distance to the spacecraft. The spacecraft demodulates the uplinked ranging signal (composed of sequential frequency tones) and retransmits it (“turnaround”) onto the downlink. Since this operation is bent-pipe, noise on the uplink within the ranging channel bandwidth is also retransmitted. When the received uplink signal-to-noise ratio (SNR) is low, regenerating the ranging signal can increase the retransmitted ranging SNR by 30 dB or more, compared to the bent-pipe method. The Regenerative pseudo-noise (PN) ranging creates this gain by using a PN digital ranging signal on the uplink and detecting that signal in the spacecraft receiver. The PN signal is regenerated digitally, with no uplink noise, and retransmitted to the ground. We report the first deep-space flight demonstration of regenerative ranging on the New Horizons Mission to Pluto. We provide an overview of the technique, including the operational PN ranging capability deployed at NASA's Deep Space Network (DSN). We describe the regenerative ranging implementation on the New Horizons spacecraft. Finally, we report on the operational flight tests, compare their results to the current trajectory (and sequential ranging), and detail how this technique will aid this mission in the future.
[Show abstract][Hide abstract] ABSTRACT: The Johns Hopkins University Applied Physics Laboratory has conducted an upgrade to its 18.3 meter ground station. These upgrades include adding a high-power S-band uplink, dual polarization S- and X-band downlink, multiple parallel downlink channel capability and software-defined telemetry, tracking and command (TT&C) units. The 18-m antenna size provides full-disk lunar coverage in S-band. This coverage, in combination with the parallel downlink capability and APL's coherent transceiver technology, affords the ability to track multiple lunar targets simultaneously. This paper presents the upgraded station architecture, its performance for current lunar missions, and discusses its application for different lunar mission scenarios.
[Show abstract][Hide abstract] ABSTRACT: Through an agreement between the National Aeronautics and Space Administration (NASA) and the Indian Space Research Organisation (ISRO), use of the Applied Physics Laboratory (APL) Satellite Communications Facility (SCF) has been made available to support the Chandrayaan-1 mission to the Moon, namely its 18.3-m dish antenna resource. The SCF, using the 18.3-m dish, served as the primary Western hemisphere ground station for the mission, principally to support downlink of the spacecraft's science data at X-Band. Recent upgrades to the 18.3-m dish and ground station have been completed in order to meet the requirements of the mission, including an upgrade of the pointing system of the 18.3-m dish antenna. The historically observed accuracy of the dish's pointing capability was sufficient for S-Band operations but not for the newly installed X-Band downlink capability. A number of potential solutions were considered and ultimately a step-track enhancement to program-track was selected as the best option for efficiently improving the pointing accuracy of the dish while requiring minimal funding support. This paper will describe the steps taken to quantify the pointing accuracy of the 18.3-m dish and the implementation of the step-track algorithm in order to achieve the required improvement in pointing performance.
[Show abstract][Hide abstract] ABSTRACT: Spacecraft for deep space come in a variety of sizes as befits their missions, from the large, flagship-class spacecraft such as Cassini or Galileo to smaller craft such as New Horizons (Pluto) or Lunar and Martian landers classified by NASA as Discovery or New Frontiers missions. All missions are constrained in mass, power, or cost, or frequently all three. A communications system that reduces demands on these resources enables, for example, either increased science return (by devoting more resources to the payload) or more such missions to be flown (by helping to meet critical mass or power margins). In this paper, we review the evolution and current capabilities of deep-space transponders and transceivers, noting the differences that lend themselves to particular classes of missions. We report on the development of a flexible, low-power, low-cost, deep-space transceiver architecture for competed mission sets such as Discovery, Mars Scout, and New Frontiers, one that possesses unique communications and radio science capabilities. This state-of-the-art transceiver architecture leverages from high-performance commercial integrated circuit technology and frequency synthesis and digital signal-processing techniques, lending itself to integration, miniaturization, and further power reduction. A transceiver based on this architecture, developed for the space-borne New Horizons spacecraft's primary communications link and uplink radio science experiment, is reviewed in this paper. We conclude discussion of the modern deep-space transceiver architecture with a description of near-term and long-term future functional and performance communications and radio science enhancements to the transceiver.
Proceedings of the IEEE 11/2007; 95(10-95):2009 - 2018. DOI:10.1109/JPROC.2007.905090 · 4.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The New Horizons spacecraft was launched on 19 January 2006. The spacecraft was designed to provide a platform for seven instruments that will collect and return data from Pluto in 2015. 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 needed to reach the Pluto system prior to the year 2020. The spacecraft subsystems were designed to meet tight mass and power allocations, yet provide the necessary control and data handling finesse to support data collection and return when the one-way light time during the Pluto flyby is 4.5 hours. Missions to the outer solar system require a radioisotope thermoelectric generator (RTG) to supply electrical power, and a single RTG is used by New Horizons. To accommodate this constraint, the spacecraft electronics were designed to operate on less than 200 W. The spacecraft system architecture provides sufficient redundancy to provide a probability of mission success of greater than 0.85, even with a mission duration of over 10 years. The spacecraft is now on its way to Pluto, with an arrival date of 14 July 2015. Initial inflight tests have verified that the spacecraft will meet the design requirements. Comment: 33 pages, 13 figures, 4 tables; To appear in a special volume of Space Science Reviews on the New Horizons mission
Space Science Reviews 09/2007; 140(1-4). DOI:10.1007/s11214-008-9374-8 · 6.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 Pluto's 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.
[Show abstract][Hide abstract] ABSTRACT: 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/APL's 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.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the RF telecommunications system designed for the New Horizons mission, NASA's planned mission to Pluto, with focus on new technologies developed to meet mission requirements. These technologies include an advanced digital receiver—a mission-enabler for its low DC power consumption at 2.6 W secondary power. The receiver is one-half of a card-based transceiver that is incorporated with other spacecraft functions into an integrated electronics module, providing further reductions in mass and power. Other developments include extending APL's long and successful flight history in ultrastable oscillators (USOs) with an updated design for lower DC power. These USOs offer frequency stabilities to 1 part in 1013, stabilities necessary to support New Horizons’ uplink radio science experiment. In antennas, the 2.1 m high-gain antenna makes use of shaped sub- and main reflectors to improve system performance and achieve a gain approaching 44 dBic. New Horizons would also be the first deep-space mission to fly a regenerative ranging system, offering up to a 30 dB performance improvement over sequential ranging, especially at long ranges.The paper will provide an overview of the current system design and development and performance details on the new technologies mentioned above. Other elements of the telecommunications system will also be discussed.Note: New Horizons is NASA's planned mission to Pluto, and has not been approved for launch. All representations made in this paper are contingent on a decision by NASA to go forward with the preparation for and launch of the mission.
[Show abstract][Hide abstract] ABSTRACT: Noncoherent Doppler tracking has been devised as a means to achieve highly accurate, two-way Doppler measurements with a simple, transceiver-based communications system. This technique has been flown as an experiment on the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft, (launched 7 December 2001), as the operational technique for Doppler tracking on CONTOUR, and is baselined on several future deep space missions at JHU/APL. This paper reports on initial results from a series of successful tests of this technique between the TIMED spacecraft and NASA ground stations in the Deep Space Network. It also examines the advantages that noncoherent Doppler tracking and a transceiver-based system may offer to small satellite systems, including reduced cost, mass, and power.
[Show abstract][Hide abstract] ABSTRACT: This work describes the design and development of the RF telecommunications system for the New Horizons mission, NASA's 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.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the development and performance of a highly integrated RF transceiver system. The system is card-based, allowing for ready incorporation into an integrated spacecraft electronics module, and scalable, enabling easy adaptation to meet varying mission requirements. A description of the transceiver architecture is presented, highlighting particular advantages in cost and size savings. The use of commercial off-the-shelf parts and a recently developed, non-coherent, two-way doppler tracking technique is also reported, as are performance results on transceivers built for two NASA missions that will use these cards. (C) 2003 Published by Elsevier Science Ltd.
[Show abstract][Hide abstract] ABSTRACT: This paper provides a detailed description of the radio
communications system developed for the Comet Nucleus Tour (CONTOUR)
Project. The communications system embodies a delicate balance of
minimizing cost while providing the high performance needed to support a
deep-space science mission. CONTOUR employs a transceiver-based X-band
system instead of traditional deep-space transponders. For navigation,
we have a conventional ranging channel and employ a novel Doppler
frequency measurement technique. A reference oscillator with low phase
noise is included to allow narrow bandwidth downlink carrier tracking at
the ground stations. The antenna system is a combination of high- and
low-gain antennas to support high-data-rate science returns and
low-data-rate emergency operations. As CONTOUR is spin stabilized for
most of the mission, including emergency operations, all antennas have
been designed to provide continuous coverage around 360° of
[Show abstract][Hide abstract] ABSTRACT: The long-duration and long light-time delay of NASA's planned New Horizons mission to Pluto, its moon Charon, and the extended mission to one or more Kuiper Belt Objects poses unique chal-lenges to mission operations, especially in this time of limited space exploration budgets. A num-ber of courses of action can be followed to reduce wear on Observatory hardware, reduce opera-tions staffing costs, and reduce Deep Space Network usage and costs without sacrificing the health and safety of the Observatory or risking the successful completion of the primary mission. Major components in this system are an autonomy subsystem that can react quickly enough to safe the Observatory when it is out of contact with the ground station; the use of a beacon to indi-cate the health of the Observatory during the dormant phases of the mission; command loading and verification strategies to accommodate the long light-time delays; and the combining of op-erations personnel to take advantage of similarities of Observatories, supporting ground station setup, and procedures. When planned early in the mission development phase, these compo-nents are easily integrated into the operations concept and Observatory hardware to form a co-hesive plan to mitigate cost and risk. Cost reduction measures for long-duration missions, such as those planned for New Horizons, enable funding for a greater number of equally important space exploration missions from a limited space exploration budget.