In support of NASA's Space Communications and Navigation (SCaN) Program Systems Engineering (PSE) Office, the Jet Propulsion Laboratory (JPL) periodically models and analyzes projected future-mission demand on the Deep Space Network (DSN) out to a thirty-year horizon. These efforts culminate in a set of capacity, spectrum, capability, and network loading trends and associated implications that can then be used to inform decisions regarding the DSN's evolution. This chapter, an expanded version of the paper presented at SpaceOps 2023, describes the findings and recommendations emerging from the latest iteration of these studies [1]. These are always presented to SCaN for strategic planning and programmatic decisions. On the whole, three key factors appear to be driving how the DSN will need to evolve in the future: (1) unparalleled growth in the number of robotic spacecraft; (2) the emergence of relatively short but tracking-intensive human lunar exploration missions requiring DSN support in the coming decade, followed by an increasing cadence of robotic and then human exploration missions to Mars; and (3) dramatic data rate and associated data volume increases. The growth in robotic spacecraft numbers is projected to substantially raise the level of "base load" demand on the network. On top of this, the intensive tracking associated with each 2-to-4 week human lunar mission is projected to create periodic peak demand levels well in excess of what the DSN has historically supported. To the extent that these missions and certain types of robotic science missions also require much higher data rates, larger-bandwidth uplink and downlink frequencies (e.g., 22/26 GHz) will be needed. And, the data volumes associated with these higher data rates will likely create data handling and management challenges far greater than what NASA has previously had to contend with for deep space missions. In the human Mars exploration era, these higher data rates, in combination with the extreme range distance when Mars is far from Earth, will necessitate arraying up multiple antennas in order to close the communications links-potentially exacerbating any unresolved antenna-hour demand issues in that timeframe. These findings suggest that, in addition to its planned Lunar Exploration Ground System (LEGS-a subnet of new antennas anticipated to be 18 m-class or slightly larger apertures), NASA should: (1) pursue commercial and international/university partner antenna agreements for backfilling antenna-hour supply shortages during peak demand periods; (2) implement ways to use existing antennas more efficiently (e.g., by improving antenna beam-sharing capabilities and equipping more antennas with expanded frequency band capabilities); (3) mitigate increases in "base load" demand by building two additional antennas per Deep Space Communications Complex beyond what is currently planned; and (4) introduce new technologies and systems that will change and optimize the architecture and operations of deep space communications. Example new technologies and systems include: "trunk link" relays at the Moon and Mars that "funnel" all the data from each of these planetary locations down to a single in-view antenna (or antenna array), Delay Tolerant Networking (DTN), optical communications, and greater reliance on autonomous spacecraft and ground systems. SCaN-funded studies are currently in work to further investigate and refine these suggested measures.

Within a decade, the number of spacecraft requiring support from NASA’s Deep Space Network (DSN) is expected to increase by a factor of 2–3. Key drivers behind this expectation include NASA’s increasing reliance on more affordable, targeted smallsat missions, a more robust science program in general, and the emergence of multi-element human lunar exploration missions. Given that a proportional increase in the number of antennas needed to communicate with all of these missions might prove prohibitively expensive, NASA has been exploring ways to gain increased capacity from its existing antennas.

To expand frontiers and achieve measurable progress, instruments such as hyperspectral imagers are increased in resolution, field of view, and spectral resolution and range, leading to dramatically higher data volumes. Increasingly, data need to be returned from greater distances, ranging from the Sun-earth L1/ L2 points at 1.5 million km, to L4/L5 halo orbits at 1 AU, to several AU in the case of planetary probes. Optical communications can significantly reduce resource competition, requiring significantly fewer passes per day and/or shorter overall passes, and thereby enable far greater, transformative science return from individual missions and the capacity to support multiple such missions within a smaller ground network. Optical communications also provides superior performance and increased ranges for Inter-satellite Links (ISL) from 2,000 to 10,000 km for Swarms and DSMs. Lastly, the only way to guarantee timely space weather warnings (with a target of 15 minutes latency) is through space relays in MEO or GEO orbits, a strategy which also includes optical communications.

As smallsats become increasingly capable, longer-lived, and have more secondary payload launch opportunities to beyond-GEO destinations, they are expected to play an increasing role in deep space science investigations. This expectation is borne out by several relatively recent NASA Science Mission Directorate solicitations regarding smallsat studies and small innovative missions. With the potential for these smallsats to substantially add to the number of spacecraft operating in deep space, we need to be thinking about ways to support communications with all of them without the huge expense of trying to build a commensurate number of deep space antennas. One approach to this challenge might involve making greater use of beam-sharing techniques that allow all the spacecraft within the beamwidth of a single ground antenna to simultaneously downlink to the antenna. One of these techniques, Opportunistic Multiple Spacecraft Per Antenna (OMSPA), may be particularly suited to smallsats. In the concept for this technique, smallsats within the scheduled ground antenna beam of some other spacecraft, make opportunistic use of that spacecraft's beam by transmitting "open-loop" to a recorder associated with the antenna. These transmissions get captured on the recorder and can be later retrieved, demodulated, and decoded so that the smallsats can recover their data - all without them having to schedule the antenna itself and compete with larger missions for antenna time. Widespread use of such a technique could lead to more efficient use of receiver antenna resources and result in a dramatic increase in downlink throughput. An opportunity to demonstrate the technique occurred in May 2018, when the Mars CubeSat One (MarCO) mission, consisting of two nanospacecraft (MarCO-A & B) launched alongside InSight, a NASA Mars lander mission. To demonstrate the capabilities of OMSPA for this launch window opportunity, X-band downlink telemetry was recorded for all three spacecraft (InSight, MarCO-A, and MarCO-B) at both the Deep Space Network (DSN), using its 34-m antennas, and at Morehead State University (MSU) using its 21-m antenna - with all of the involved antennas pointed at InSight. Open-loop recordings were collected at the DSN using wideband very long baseline science receivers and at MSU using Universal Software Radio Peripheral (USRP) devices operated using GNU Radio. All the recordings were then processed at the Jet Propulsion Laboratory, California Institute of Technology (JPL) using an OMSPA Software Receiver, a signal processing/communications tool used to extract telemetry transfer frames from baseband samples. The results of extracting telemetry data from InSight/MarCO recordings collected by the DSN and at MSU are described in this article. In particular, details pertaining to the processing chain used by the OMSPA Software Receiver to demodulate the DSN and MSU recordings are presented, from carrier/symbol synchronization, to frame alignment using attached sync markers (ASMs), followed by error correction code decoding. Validation results with closed-loop data obtained by the DSN are also presented in order to highlight the viability of OMSPA for future multiple spacecraft demodulation opportunities.

We describe a software approach for simultaneous demodulation and decoding of multiple frequency-multiplexed spacecraft across multiple ground stations.The approach involves the use of a single ground antenna with wide enough aperture to receive multiple angularly adjacent spacecraft simultaneously.This technique uses a wide-band RF signal digitizer coupled with easily and cheaply duplicated software-receiver modules to independently process the frequency-channelized downlink signals from the spacecraft.This approach relaxes the need for realizable modems at each antenna, for example in the Deep-Space-Network (DSN), and can also function as a delayed data retrieval method for cubesat missions with routine science data return.Thus, we hope that this solution can enable more efficient utilization of DSN assets.We concentrate on a simulation similar to the proposed Exploration Mission 1 (EM-1) mission from a geometric perspective.To that end, the simulated scenario involves ten secondary cubesats deployed and tracked for a span of four days (the modeled motion over the first four days of the mission does not include any Trajectory Correction Maneuvers (TCMs) that may be necessary as the cubesats approach the moon).Transmissions from the cubesats may be received through a combination of DSN ground sites based on visibility.The cubesats are assumed to utilize typical cubesat transmit powers and a waveform similar to that of the Iris radio.One cubesat is chosen as the "target" and is considered tracked by all ground-stations throughout the simulation (i.e., it is consistently at the center of the main lobe of each ground station antenna when the ground station is in view of the cubesat in terms of elevation angle).The simulation effort involves synthesizing a wideband signal that includes the ten cubesats across a large bandwidth due to each cubesat having its own center-frequency in X-band, near 8.4 GHz.Each signal is characterized by its own Doppler-frequency shift and free-space path-loss computed through the underlying geometry of the simulation as well as the cubesat transmit power.Finally, each cubesat signal experiences a unique antenna gain at each ground station due to the underlying antenna pattern and spacecraft-ground station geometry.We establish two interesting findings: First, the link-budget for the EM-1-like scenario is almost completely limited by the angle between the center of the antenna main beam and the cubesat, which means that the signal-to-noise ratio is wholly adequate for demodulation and decoding at the simulated bitrates unless the cubesat exits the main beam.Secondly, and fortunately due to the use of a software radio architecture, we show that it is possible to successfully receive signals from most cubesats for the entire 4-day simulation.Due to the signal-to-noise ratio being sufficient for demodulation even after the side-lobe's 17dB reduction in SNR, the software radio can still demodulate such cubesats as long as the radio is capable of re-establishing carrier lock as the cubesats leave the main beam and enter the side-lobe.Considering that the target application utilizes offline processing, a loss of lock can be detected and lock can be re-established by iterating over the data.Extensive simulations demonstrate these results.

In this article we describe the analysis and simulation effort of the end-to-end traffic flow for the Deep Space Network (DSN) in the Human Exploration Era, when DSN will provide communication and navigation services for human missions to distant celestial objects like the Moon, asteroids, and Mars.Using the network traffic derived for the 30-day period within July/August 2039 from the Space Communications Mission Model (SCMM), we simulate the bandwidths of the ground links and the buffer profiles of the network nodes.We also use a 2-state Markov scheme that models the store-and-forward mechanism that regulates the ground network traffic.The network traffic modeling and simulation generates ground bandwidth and buffer statistics, which in turn are used to formulate the future DSN ground network bandwidth and storage requirements. I. IntroductionHE Deep Space Network (DSN) consists of 3 sites with 13 operational antennas.Five additional 34-m beamwave-guide (BWG) antennas are planned between now and 2025 to address the growing communications and tracking needs for current and future deep space missions.The current DSN architecture and evolution plan is depicted in Figure 1 7 .Deep space missions are traditionally robotic missions.Except for the spacecraft uplink command and health and safety telemetry, the bulk of the deep space robotic mission data consists of data types that can tolerate reasonably high latency 8 .This allows the terrestial network to implement a data-buffering scheme that "smooths" the instantaneous bandwidth of the ground links, thus reducing the bandwidth requirements and thus the cost of the terrestial network.The network tracking data -Doppler, ranging, and Delta Differential One-Way Ranging (DDOR) data -are deep space signal measurements at the DSN antenna for generating navigation solutions for spacecraft, and are typically mission time-critical.Circa 2035, in addition to deep space robotic missions, it is envisioned that the DSN will provide communication and navigation services for human exploration missions to distant celestial objects like the Moon, asteroids, and Mars.Data delivery, and data latency requirements of human missions can be very different compared to the robotic deep space missions.This in turn drives the bandwidth requirements of the next-generation DSN terrestrial network to meet future mission needs.In this paper, we describe a top-down and latency requirement-driven analysis and simulation approach to size the bandwidth and storage requirements of a store-and-forward 9 terrestrial network for the DSN, mission traffic scenario, and set of data types with different latency requirements.The focus of this paper is on downlink traffic only, as this is the key driver of the ground bandwidth and storage requirements.

The low costs of development and launch, coupled with new propulsive technologies, have made cubesats increasingly popular for use in science investigations beyond geosynchronous orbit. As this deep space cubesat fleet grows in size, the challenge of trying to provide affordable communications for it grows commensurately. The mass, power, and volume constraints inherent to cubesats limit the antenna size and transmit power that they can use to close the deep space link. As a consequence, cubesats need to rely more heavily on ground antennas that are characterized by large aperture, low noise temperatures, and relatively high-power transmitters. Such antennas are not in great abundance, nor are they inexpensive to build. For this reason, NASA’s Deep Space Network has been advocating a three-pronged approach to meeting anticipated cubesat demand: development of simultaneous, shared-beam multi-spacecraft communications capabilities, development of large-antenna cross-support arrangements with other agencies and universities, and development of less uplink-intensive navigation techniques. This paper focuses on the pursuit of simultaneous, shared-beam multi-spacecraft communications capabilities. While the Multiple Spacecraft per Antenna (MSPA) technique has existed for over a decade, it has generally been limited to supporting downlink for just two in-beam spacecraft at a time. This limitation has largely been a function of the number and cost of available receivers. A relatively new technique that potentially overcomes this limitation is Opportunistic MSPA (OMSPA). Instead of relying on additional receivers, OMSPA makes use of a digital recorder at each ground station that is capable of capturing the intermediate frequency (IF) signals from every spacecraft in the antenna beam within the frequency bands of interest. When cubesat projects see one or more opportunities for their cubesat(s) to intercept the traditionally scheduled antenna beam of a “host” spacecraft, they can arrange for the cubesat(s) to transmit open loop during those opportunities. Via a secure Internet site, the cubesat mission operators can then retrieve the timeand frequency-relevant portions of the digital recording for subsequent demodulation and decoding, or subscribe to a service that does it for them. This “opportunistic” use of a host spacecraft’s ground antenna beam potentially enables cubesat projects to make use of large ground antennas for downlink without having to compete with bigger, better-funded missions for antenna time in the formal scheduling process. In so doing, it also potentially enables cubesat projects to avoid the aperture fees associated with formally scheduled downlink time – fees that factor into the “bottom-line” of competitivelybid NASA missions and that actually get charged to non-NASA missions. Taking advantage of these potential OMSPA benefits, however, will require cubesat projects to pursue mission designs that ensure at least periodic in-beam operations relative to a “host” spacecraft. In the case of a constellation of cubesats with inter-spacecraft distances that do not extend outside of the beam-width of the desired ground antenna at the given range, one cubesat can serve as the “host” and have a formally scheduled downlink while the rest of the cubesats can downlink essentially for “free” via OMSPA. Deep space cubesats, of course, will need uplink in addition to downlink. Beyond commanding, this need is driven by the use of two-way ranging and Doppler for navigation. While OMSPA may not directly facilitate uplink, it does have the potential to free up antennas for those spacecraft that periodically require formally scheduled links for commanding and two-way radio metrics. NASA is also exploring the physical feasibility of an in-beam, simultaneous multi-spacecraft uplink technique. As with OMSPA, if successful, it will require little new equipment, further enabling affordable deep space cubesat communications.

A technology demonstration of free space optical communication at interplanetary distances is planned via one or more future NASA deep-space missions. Such demonstrations will "pave the way" for operational use of optical communications on future robotic/potential Human missions. Hence, the Deep Space Network architecture will need to evolve. Preliminary attempts to model the anticipated future mission set and simulate how well it loads onto assumed architectures with combinations of RF and optical apertures have been evaluated. This paper discusses the results of preliminary loading simulations for hybrid RF-optical network architectures and highlights key mission and ground infrastructure considerations that emerge.

The research described in this publication was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. © 2012 California Institute of Technology. U.S. Government sponsorship acknowledged. abstract. — In this article, we describe the analysis and simulation effort of the end-to-end traffic flow for the Integrated Space Communications and Navigation (SCaN) Network. Using the network traffic derived for the 30-day period of July 2018 from the Space Communications Mission Model (SCMM), we generate the wide-area network (WAN) bandwidths of the ground links for different architecture options of the Integrated SCaN Network. We also develop a new analytical scheme to model the traffic flow and buffering mechanism of a store-and-forward network. It is found that the WAN bandwidth of the Integrated SCaN Network is an important differentiator of different architecture options, as the recurring circuit costs of certain architecture options can be prohibitively high.

The ability to communicate with spacecraft during emergencies is a vital service that NASA's Deep Space Network (DSN) provides to all deep space missions. Emergency communications is characterized by low data rates (typically ∼10 bps) with the spacecraft using either a low-gain antenna (LGA, including omnidirectional antennas) or, in some cases, a medium-gain antenna (MGA). Because of the use of LGAs/MGAs for emergency communications, the transmitted power requirements both on the spacecraft and on the ground are substantially greater than those required for normal operations on the high-gain antenna (HGA) despite the lower data rates. In this paper, we look at current and future emergency communications capabilities available to NASA's deep-space missions and discuss their limitations in the context of emergency mode operations requirements. These discussions include the use of the DSN 70-m diameter antennas, the use of the 34-m diameter antennas either alone or arrayed both for the uplink (Earth-to-spacecraft) and the downlink (spacecraft-to-Earth), upgrades to the ground transmitters, and spacecraft power requirements both with unity gain (0 dB) LGAs and with antennas with directivity ( 0 dB gain, either LGA or MGA, depending on the gain). Also discussed are the requirements for forward-error-correcting codes for both the uplink and the downlink. In additional, we introduce a methodology for proper selection of a directional LGA/MGA for emergency communications

NASA's future scientific missions will place new demands on its deep space network (DSN). Depending on which missions fly and their particular design, NASA's communications ground assets (antennas) may require upgrade or enhancement. The purpose of the mission set analysis tool is to help forecast future demand by (1) cataloguing the characteristics of potential future DSN-user missions consistent with NASA's space communications mission model, (2) calculating the demands that these missions will place on the DSN, and (3) generating mission requirements for other DSN architectural analysis tools. This tool takes the information associated with the Space Communications Mission Model (SCMM) to the next level - using an Microsoft EXCEL reg -based database to catalog and process some 300 mission parameters. These parameters fall into one of five broad categories: mission identity and affiliation, operational schedule, communication system capabilities, data rates and ground tracking schedules. Because NASA's mission forecast changes frequently, analysis templates are used to select sets of missions from the database for analysis. Communication link budgets are calculated for particular dates during mission operation based on mission parameters and automated ephemeris algorithms. The result is expressed in terms of the receiving area on the ground required to close each particular communication link. Plots of this receiving area as a function of time and frequency band reveal future demand for different mission sets. The most demanding individual communication links are automatically identified. Radio-frequency (RF) uplinks (Earth to mission) and downlinks (mission to Earth) are treated separately. The Mission Set Analysis Tool also creates mission requirements used by other analysis tools to assess the cost, operability (link performance), and load capacity of proposed DSN architectures.

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.

A flexible method of parametric, full life-cycle cost analysis has been combined with data on NASA's future communication needs to estimate the required number and operational dates of new antennas for the Deep Space Network (DSN). The requirements were derived from a subset of missions in the Integrated Mission Set database of NASA's Space Communications Architecture Working Group. Assuming that no new antennas are "constructed", the simulation shows that the DSN is unlikely to meet more than 20% of mission requirements by 2030. Minimum full life-cycle costs result when antennas in the diameter range, 18m-34m, are constructed. Architectures using a mixture of antenna diameters produce a slightly lower full life-cycle cost. 123