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.

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.

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.