Robert J. Cesarone

Mars network for enabling low-cost missions

Abstract Mars is the first planet where significant steps are being taken to establish a “virtual presence throughout the solar system”—one of NASAs strategic goals. Preparations are under way to begin implementation of an evolving Mars Network of satellites to meet the future communications and navigation challenges of the ongoing international Mars exploration campaign. The Mars Network concept is to deploy two classes of satellites. The first class is very low-cost MicroSats, launched piggyback on Ariane 5, for deployment in 800-km circular orbits in a variety of planes for frequent global contacts. From their low orbits, the MicroSats provide highly efficient relay communication links for small, energy constrained landers, and their orbital motion provides strong navigation signatures. The second, larger class of Mars areostationary satellites (MARSats) are deployed in 17,000-km orbits with 1-sol periods, as required, to support very high bandwidth users.

Prospects for a Next-Generation Deep-Space Network

A next-generation deep-space network is currently under consideration by the National Aeronautics and Space Administration. Building upon its many past successes, this network will be required to meet the needs of current and planned missions. These will, no doubt, include the familiar suite of telemetry, command, tracking, and navigation services, with performance levels derived from analysis of the probable future mission set. Additionally, it will be expected to provide enabling capabilities for missions still on the drawing boards. Traditionally, the network serves the robotic deep-space exploration fleet. However, at this time, consideration of the special needs of planned future human lunar missions is appropriate, as well as the evolution to the eventual human exploration of Mars.

Array antennas for JPL/NASA Deep Space Network

Recently, JPL has begun an assessment of the long-term capability of the antennas for the Deep Space Network (DSN). Various alternative plans for upgrading or replacing the present 70-meter antennas have been considered. Several options have been studied which include modifying the present antennas for extended life and reliability, new 70-meter single aperture antennas with offset or symmetric feeds, 100-meter spherical antennas, an array of a few smaller 34-meter antennas, a much larger array (hundreds) of much smaller (5-10 meter) reflector antennas, and finally active planar phased arrays with millions of elements. In this paper we briefly discuss various options but focus on the feasibility of the phased arrays as a viable option for this application. Of particular concern and consideration will be the cost, reliability, and performance compared to the present 70-meter antenna system. Many alternative phased arrays including planar horizontal arrays, hybrid mechanically/electronically steered arrays, phased array of mechanically steered reflectors, multi-faceted planar arrays, phased array-fed lens antennas, and planar reflect-arrays are compared and their viability is assessed.

Strategies for telecommunications and navigation in support of Mars exploration

Abstract The planned exploration of Mars will pose new and unique telecommunications and navigation challenges. The full range of orbital, atmospheric, and surface exploration will drive requirements on data return, energy-efficient communications, connectivity, and positioning. In this paper we will summarize the needs of the currently planned Mars exploration mission set, outline design trades and options for meeting these needs, and quantify the specific telecommunications and navigation capabilities of an evolving infrastructure.

Integrated network architecture for sustained human and robotic exploration

The National Aeronautics and Space Administration (NASA) Exploration Systems Mission Directorate is planning a series of human and robotic missions to the Earths Moon and to Mars. These missions will require telecommunication and navigation services. This paper sets forth presumed requirements for such services and presents strawman lunar and Mars telecommunications network architectures to satisfy the presumed requirements. The paper suggests that a modest ground network would suffice for missions to the near-side of the Moon. A constellation of three Lunar Telecommunications Orbiters connected to a modest ground network could provide continuous redundant links to a polar lunar base and its vicinity. For human and robotic missions to Mars, a pair of areostationary satellites could provide continuous redundant links between a mid-latitude Mars base and Deep Space Network antennas augmented by large arrays of 12-m antennas

Deep-space optical communications

Current key initiatives in deep-space optical communications are treated in terms of historical context, contemporary trends, and prospects for the future. An architectural perspective focusing on high-level drivers, systems, and related operations concepts is provided. Detailed subsystem and component topics are not addressed. A brief overview of past ideas and architectural concepts sets the stage for current developments. Current requirements that might drive a transition from radio frequencies to optical communications are examined. These drivers include mission demand for data rates and/or data volumes; spectrum to accommodate such data rates; and desired power, mass, and cost benefits. As is typical, benefits come with associated challenges. For optical communications, these include atmospheric effects, link availability, pointing, and background light. The paper describes how NASAs Space Communication and Navigation Office will respond to the drivers, achieve the benefits, and mitigate the challenges, as documented in its Optical Communications Roadmap. Some nontraditional architectures and operations concepts are advanced in an effort to realize benefits and mitigate challenges as quickly as possible. Radio frequency communications is considered as both a competitor to and a partner with optical communications. The paper concludes with some suggestions for two affordable first steps that can yet evolve into capable architectures that will fulfill the vision inherent in optical communications.

Low cost deep space hybrid optical/RF communications architecture

This paper reports on a study of hybrid optical/Radio Frequency (RF) architectures for deep space missions. Previous proposed optical deep space communication architectures were generally designed to achieve 90% or better availability 24/7. This study, instead, considered alternative metrics and architectures. It focuses on a strategy to use RF links and existing RF infrastructure for navigation and for communications requiring high availability, and optical communication links only for high volume downlink data. The optical link can then be designed to maximize data volume rather than availability. Utilizing Automatic Repeat Request (ARQ) with this strategy, a high level of completeness is possible even with low link availability - though with an increase in latency and spacecraft memory requirements. This strategy is suitable for deep space missions whose high volume links are dominated by science data that can tolerate long delays. The study found that with this optical downlink strategy, a single ground telescope can provide the principal expected benefit of optical communications (high data volume) at much lower cost than optical infrastructures designed to provide 90% availability 24/7. The study found also that data volume can, in some cases, be maximized by arraying all ground telescopes at a single site so that they have identical weather statistics. This low cost architecture, here named Single Optical Site (SOS), can eventually be augmented with multiple sites to provide high optical availability.

Uplink array system of antennas for the Deep Space Network

Recently, arraying of large or small and distributed reflector antennas for uplink applications has attracted attention for a capability upgrade to the Deep Space Network (DSN). This interest is driven by the desire to maximize the usefulness of existing DSN large apertures in case of spacecraft emergency and to develop the necessary knowledge of how the array of small and distributed reflector antennas can meet other future uplink throughput needs. The primary challenge for uplink arraying of distributed reflector antennas for deep space applications is the lack of feedback from deep space within a reasonably short period. Furthermore, the individual reflectors (and their transmitter subsystems) are thousands of wavelengths apart, which make the phase coherence of individual transmitted signals an extremely challenging task. Because of the return light time constraints, all closed-loop calibrations and relative phase adjustments for any coherent combination of signals from individual antennas be conducted no farther than near-Earth orbits. This paper discusses the large array background, scope, and evolution, and some of the lessons learned from preliminary studies of the uplink array.

Analysis of telescope site selection for optical deep space network

The successful design of an optical deep space network (ODSN) greatly depends on the selection of optimal telescope sites. At the highest system level, there are two main factors to consider in the design of a global optical communications network for deep space applications: telescope size (i.e., aperture size) and the distance between stations. The size of the individual telescope aperture needs to be selected based on mission needs (e.g., maximization of received photons per bit). At the same time, because of weather effects and Earth rotation, a number of telescopes have to be placed within certain distances around the Earth in order to achieve global coverage. The distance between the adjacent telescopes is driven by other secondary factors, which are basically derived requirements from: 1) outage tolerance; 2) continuity in data stream; 3) operational cost; and 4) minimal requirements on the spacecraft payload design. To perform properly, ground stations must be placed on high-altitude peaks (for better visibility and high atmospheric transmission) around the Earth. However, the scarcity of peaks, along with geopolitical issues, may cause difficulties in the selection of the telescope sites in a global network. In an optical deep space link, the characterization of the atmospheric channel requires great attention. In fact, cloud opacity is the first evident impairment to the successful closure of a space-to-ground (and vice versa) optical link. Likewise, aerosol distribution in the atmosphere can significantly increase the optical thickness of the atmosphere with a detrimental attenuation of the laser signal. Moreover, an optical communication/tracking network must operate during daytime, and in this case, an increase of background sky radiance can dramatically affect the receiver performance by increasing system noise. Therefore, we present an analysis of site selection for an optical deep space network as performed by the ODSN study team at JPL. Given a set of mission requirements, we illustrate how the high-level requirements, along with the properties of the atmospheric channel, can be used to determine the site selection and the architecture of an ODSN. Moreover, we characterize candidate sites for a global optical network and their possible suitability for global architectures such as the linear dispersed optical subnet (LDOS) and cluster optical subnet network (COS).

Prospect for tracking spacecrafts within 2 million Km of earth with phased array antennas

Recent advances in space technology for Earth observations, global communications, and positioning systems have created heavy traffic at a variety of orbits. These include smart sensors in low Earth orbits (LEO), Internet satellites in LEO and GEO orbits, Earth observing satellites in high Earth orbits (HEO), observatory class satellites at Lagrangian libration points, and those heading for deep space. In such an integrated operations environment, future ground tracking antenna networks, such as JPL/NASAs deep space network (DSN) may be required to provide highly agile beams, flexible scheduling, and the capability for simultaneous tracking of multiple spacecrafts at various orbits. In this paper the possibility of cost-effectively replacing the DSNs 26-m antennas with a network of phased array antennas capable of tracking various types of spacecrafts that are within 2 million km of Earth is examined.