Radiofrequency (RF) communications offer reliable but low data rates and energy-inefficient satellite links, while free-space optical (FSO) promises high bandwidth but struggles with disturbances imposed by atmospheric effects. A hybrid RF/FSO architecture aims to achieve optimal reliability along with high data rates for space communications. Accurate prediction of dynamic ground-to-satellite FSO link availability is critical for routing decisions in low-earth orbit constellations. In this paper, we propose a system leveraging ubiquitous RF links to proactively forecast FSO link degradation prior to signal drops below threshold levels. This enables pre-calculation of rerouting to maximally maintain high data rate FSO links throughout the duration of weather effects. We implement a supervised learning model to anticipate FSO attenuation based on the analysis of RF patterns. Through the simulation of a dense lower earth orbit (LEO) satellite constellation, we demonstrate the efficacy of our approach in a simulated satellite network, highlighting the balance between predictive accuracy and prediction duration. An emulated cloud attenuation model is proposed to provide insight into the temporal profiles of RF signals and their correlation to FSO channel dynamics. Our investigation sheds light on the trade-offs between prediction horizon and accuracy arising from RF beacon numbers and proximity.

The NASA Near Earth Network (NEN) project consists of globally distributed tracking stations, including NASA, commercial, and partner ground stations, that are strategically located to maximize the coverage provided to a variety of orbital and suborbital missions, including those in low Earth orbit (LEO), geostationary Earth orbit (GEO), highly elliptical orbit (HEO), lunar orbit and Lagrange point L1/L2 orbits. Analyses involving the NEN have applicability to other ground station networks. Our studies addressed nanosatellite direct-to-ground communication and nanosatellite constellations with a mother-ship direct-to-ground communication.

Free space optical (FSO) communication links increase data rate, reduce size and power, and increase security. These criteria are particularly important in space communication. Increasing mission complexity and crowding of lower frequency bands is driving the need for optical communications. This makes FSO communication technology extremely attractive, and there is significant ongoing work towards the development of FSO transceivers, ground stations, and relays. Notable projects include the Laser Communications Relay Demonstrator (LCRD), Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T), and CubeSat Laser Infrared Crosslink (CLICK) CubeSats. These technologies will eventually operate in unison with existing Radio Frequency (RF) systems, but there is little experimental investigation of such hybrid networks. This paper presents some experimental underpinnings of switching strategies for hybrid RF/FSO systems in various attenuation conditions. A 170 m optical path was constructed in an enclosed test chamber where atmospheric conditions can be tightly controlled. The performance of a 1550 nm infrared FSO link was evaluated in this chamber under varying conditions of turbulence and jitter. The system will eventually be used to investigate switching criteria between the FSO and RF channels. Optimizing the use of RF/FSO communication links will allow data rate, size, power, and security improvements. Therefore, this research will help to mature the network architecture and improve the performance of communication networks to be used for LEO, GEO, Lagrange, Lunar missions and beyond.

The prospect of mankind returning to the Moon has garnered a great amount of attention in recent years. Dozens of lunar missions are planned for the coming decade which will require the development of a sustainable communication infrastructure with high data rates and minimal latency. Space communication systems thus far have relied on Radio Frequency (RF) links alone, but recent developments in laser communications have demonstrated that Free Space Optical (FSO) links can achieve much higher data rates. Upon considering the respective benefits and drawbacks of RF and FSO links, we make a case for the integration of these two technologies into a hybrid RF/FSO lunar communications architecture which leverages small satellites in a Low Earth Orbit (LEO) constellation. We include a case study for this technology designed in Analytical Graphics' Systems Tool Kit (STK) software. Results are presented in terms of chain access duration, propagation delay, transmission loss, Signal-to-Noise Ratio (SNR), and Bit Error Rate (BER). This architecture shows potential to revolutionize extraterrestrial communications and pave the way for highly ambitious future missions in space.

This paper presents the network architecture utilized at NASA's Goddard Space Flight Center (GSFC) to support a mission set of five 6U CubeSats. These five CubeSats employ a multi-waveform Software Defined Radio (SDR) platform developed by Vulcan Wireless for use with NASA's Space Relay (SR) and Direct to Earth (DTE) networks. The performance testing of the SDR is discussed via a comprehensive S-band and communication link analysis. The tested capabilities of the SDR and antenna components are reviewed in terms of the mission requirements for each CubeSat. Size Weight and Power (SWaP), required availability, and access times are discussed. The measured data from experimental compatibility testing is incorporated into detailed simulations of the CubeSat mission set to verify desired performance over the mission lifetime. The model is also used to investigate the impact of potential adverse effects on the communication links such as interference and weather conditions. This paper also reviews potential improvements from future technological advances and commercial partnerships. A collaborative investigation between GSFC and Oklahoma State University is presented in which a qualitative analysis of Hybrid RF/Optical communication strategies is performed. The data rate improvements of optical communication techniques are weighed against attitude control and science mission requirements for CubeSats, and network architectures/switching strategies are discussed. A separate analysis reviews the potential benefits of ground station partnerships, which aligns with NASA's future goal to include commercial partners in its Earth and space network architectures, e.g. LunaNet.

This paper presents the development and testing of the Software Define Radio (SDR) transceiver to meet the emerging needs for SmallSat communication and navigation. Vulcan Wireless and NASA Goddard Space Flight Center (GSFC) collaborated in testing the Vulcan Wireless S-band SDR engineering model. Apart from testing, communication link analysis was performed for a Low Earth Orbit (LEO) 400 km scenario. The results of the compatibility, radiation, environmental testing, and link analysis are presented. Also, this paper reviews a set of SmallSat missions under development at NASA GSFC.

National Aeronautics and Space Administration (NASA) CubeSat/SmallSat missions are expected to grow rapidly in the next decade. As the number of spacecraft on a ground network grows, employing higher data rates could reduce loading by reducing the contact time per day required. CubeSats also need to communicate directly to earth from space from longer distances than low earth orbit (LEO). These challenges motivate the need for bandwidth and power efficient modulation and coding techniques. Today, Digital Video Broadcast, Satellite Second Generation (DVB-S2) is a communications standard for larger satellites. DVB-S2 uses power and bandwidth efficient modulation and coding techniques to deliver performance approaching Radio Frequency (RF) channel theoretical limits. NASA’s Near Earth Network (NEN) conducted a demonstration test at the Wallops Flight Facility in spring of 2019 for CubeSat/SmallSat missions for enhancing data rate performance in NASA’s S-band 5 MHz channel. The goal is to upgrade NEN with DVB-S2 to increase science data return and enable greater numbers of CubeSats. This paper presents the NEN DVB-S2 demonstration testing objectives and performance measurement results. Results of the demonstration testing are compared with evolving SmallSat/CubeSat radios. DVB-S2 S-band transmitter development concepts for SmallSats/CubeSats and use of DVB-S2 by future missions are discussed. INTRODUCTION As of January 2019, there have been over 2100 CubeSats and nanosatellites launched according to nanosats.eu1. Figure 1 shows Planet Labs Flock 1 CubeSats being deployed from the International Space Station (ISS). NASA CubeSats are used for Earth, Heliophysics, Astrophysics, and Planetary science and for space technology advancement. The NASA Goddard Space Flight Center (GSFC) continues to study methods to provide the highest data rate communication from the longest distance from earth with the least size, weight and power (SWaP) for NASA spacecraft to maximize the science and technology advancement return. In spring of 2019, NASA Near Earth Network (NEN) conducted a Digital Video Broadcast, Satellite Second Generation (DVB-S2) demonstration, testing over the NEN 5 MHz channel at Wallops. DVB-S2 is a family of modulations and codes for maximizing data rate and minimizing bandwidth used and SWaP. DVB-S2 uses power and bandwidth efficient modulation and coding techniques to deliver performance approaching theoretical limits of RF channels. This paper describes the demonstration objectives, and performance measurement, test configuration and results. The DVBS2 simulation analysis for the expected maximum data rate performance over the 5 MHz channel and link margin analysis with a typical CubeSat communication system are presented. Comparison of results of the

A team of eight subject matter experts at NASA Goddard Space Flight Center (GSFC) completed a Lean Six Sigma project to identify process improvements for the compatibility test process for small satellites planning to use the NASA Near Earth Network (NEN). Ground station network compatibility testing is designed to reduce the risk to missions by resolving issues between the spacecraft's flight communication and navigation components and the ground systems prior to launch. Compatibility testing, which consists of a series of tests performed over a period of months and documented in reports, is an important step meant to prevent post-launch anomalies that could lead to expensive troubleshooting or mission failure. Compared to traditional missions, small satellite missions typically have a smaller budget and compressed schedules, which can result in small satellite projects' willingness to accept the risk associated with less comprehensive compatibility testing. Optimization and or refinement of the compatibility test process for small satellite missions could alleviate some of the pressures inherent with these factors. The goal of the Lean Six Sigma project was to develop alternative scalable methods of compatibility testing for small satellites. The Lean Six Sigma approach and the results of the project are reviewed in this paper.

The NASA Near Earth Network (NEN) consists of globally distributed tracking stations, including NASA, commercial, and partner ground stations, that are strategically located to maximize the coverage provided to a variety of orbital and suborbital missions, including those in LEO, GEO, HEO, lunar and L1/L2 orbits. The NENs future mission set includes and will continue to include CubeSat missions. The majority of the CubeSat missions destined to fly on EM-1, launching in late 2018, many in a lunar orbit, will communicate with ground based stations via X-band and will utilize the NASA Jet Propulsion Laboratory (JPL) developed IRIS radio. The NEN recognizes the important role CubeSats are beginning to play in carrying out NASAs mission and is therefore investigating the modifications needed to provide IRIS radio compatibility. With modification, the NEN could potentially expand support to the EM-1 lunar CubeSats.The NEN could begin providing significant coverage to lunar CubeSat missions utilizing three to four of the NENs mid-latitude sites. This coverage would supplement coverage provided by the JPL Deep Space Network (DSN). The NEN, with smaller apertures than DSN, provides the benefit of a larger beamwidth that could be beneficial in the event of uncertain ephemeris data. In order to realize these benefits the NEN would need to upgrade stations targeted based on coverage ability and current configuration/ease of upgrade, to ensure compatibility with the IRIS radio. In addition, the NEN is working with CubeSat radio developers to ensure NEN compatibility with alternative CubeSat radios for Lunar and L1/L2 CubeSats. The NEN has provided NEN compatibility requirements to several radio developers who are developing radios that offer lower cost and, in some cases, more capabilities with fewer constraints. The NEN is ready to begin supporting CubeSat missions. The NEN is considering network upgrades to broaden the types of CubeSat missions that can be supported and is supporting both the CubeSat community and radio developers to ensure future CubeSat missions have multiple options when choosing a network for their communications support.

There has been a historical trend to increase capability and drive down the Size, Weight and Power (SWAP) of satellites and that trend continues today. NASA scientists and engineers across many of NASAs Mission Directorates and Centers are developing exciting CubeSat concepts and welcome potential partnerships for CubeSat endeavors. From a Telemetry, Tracking and Command (TTC) Systems and Flight Operations for Small Satellites point of view, small satellites including CubeSats are a challenge to coordinate because of existing small spacecraft constraints, such as limited SWAP and attitude control, and the potential for high numbers of operational spacecraft. The NASA Space Communications and Navigation (SCaN) Programs Near Earth Network (NEN) and Space Network (SN) are customer driven organizations that provide comprehensive communications services for space assets including data transport between a missions orbiting satellite and its Mission Operations Center (MOC). This paper presents how well the SCaN networks, SN and NEN, are currently positioned to support the emerging small small satellite and CubeSat market as well as planned enhancements for future support.

This paper introduces the Agile Mission Development Facility (AMDF), a concept for a new mission development platform at NASAWallops that will develop a specific kind of Earth observing missions based on networks of small assets (CubeSats, UAVs and balloons) in a timeframe of weeks to months.To achieve this reduced development time, the AMDF will use a new catalog-based and platform-based approach to mission design that emphasizes commonality at the subsystem or assembly level and the use of COTS components when possible. This will necessarily constrain the range of performance achievable by these missions, since only a few alternatives will be available for each subsystem. Only missions whose objectives can be achieved through a combination of the available modules will be considered.In addition to providing a high-level description of the AMDF architecture, this paper describes the process by which this platform consisting of a few standard modules will be optimally designed to maximize the range of attainable performance while keeping short development times. Particular emphasis is put on the communications module that will enable cross-links between nanosatellites, UAVs, balloons, and ground assets.Importantly, the AMDF focuses on a different customer segment than other similar NASA facilities such as the IDC at GSFC or Team X at JPL. AMDF Missions are not meant to compete with larger NASA missions in terms of performance, operational risk or mission assurance, but rather they intend to be complementary. In particular, the very short development time and multi-asset character of these systems will enable a completely new class of missions that can effectively respond to a rapidly changing phenomenon of opportunity, such as a hurricane, a volcano or a geopolitical event of interest for which a larger mission would be inappropriate. Additionally, they can be used to accelerate technology infusion for future larger missions, as long as the new technology satisfies a certain set of interface requirements.The AMDF will maximize reuse of existing design, integration and testing software and hardware infrastructure at NASA Wallops as well as other NASA centers. All potentially relevant stakeholders, such as NASA Goddard, Headquarters, JPL, Ames, the Aerospace Corp., Applied Physics Lab, and universities with nanosatellite programs will be involved and considered in the AMDF development process.This paper focuses on the description of the design aspects of the AMDF, as this is where most of the novelty lies. Integration, testing, launching and operations are only briefly discussed. A description of the system architecture of the AMDF is given using model-based systems engineering tools (SysML). An example application mission to measure ecological changes in the Jefferson and Washington National Forests is also discussed to illustrate the new kinds of missions that this facility could enable.

Wideband antennas may be designed to have an impulse response that is direction dependent. This property can be used for angle-of-arrival estimation using a single fixed antenna, without the need for an array or antenna rotation. The method is demonstrated using a simple candelabra-shaped monopole operating in the 1-3 GHz range. A known transmitted pulse and high signal-to-noise ratio are needed, and the method is not as accurate or robust as conventional methods. However, it can add direction finding capability to a wideband communication system without additional hardware requirements.

[1] Z. Wu, et. al., MEMS (2013), Taipei, Taiwan, pp. 122-125. [2] R. Tabrizian and F. Ayazi, APL, 106 263504 (2015) [3] E. Ng, et. al., JMEMS, (24) 3, Jun. 2015, pp. 730-741 [4] Z. Wu and M. Rais-Zadeh, JMEMS (24) 6, Dec. 2015, pp. 1747-1758 Miniaturized Phonon Trap Timing Units for PNT of Cubesats Mina Rais-Zadeh1, Adam Peczalski1, Serhat Altunc2, Yun Zheng2, Obadiah Kegege2, Harry Shaw2, Greg Heckler2 1Department of Electrical Engineering and Computer Science, University of Michigan – Ann Arbor 48105 2NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771

The Chip Scale Ultra-Stable Clocks (CSUSC) project aims to provide a superior alternative to current solutions for low size, weight, and power timing devices. Currently available quartz-based clocks have problems adjusting to the high temperature and extreme acceleration found in space applications, especially when scaled down to match small spacecraft size, weight, and power requirements. The CSUSC project aims to utilize dual-mode resonators on an ovenized platform to achieve the exceptional temperature stability required for these systems. The dual-mode architecture utilizes a temperature sensitive and temperature stable mode simultaneously driven on the same device volume to eliminate ovenization error while maintaining extremely high performance. Using this technology it is possible to achieve parts-per-billion (ppb) levels of temperature stability with multiple orders of magnitude smaller size, weight, and power.

This paper presents an integrating of highly transparent X band reflectarray on the cover glass of solar panels. Two types of element geometries are studied, and optimal unit cell element, effect of the solar cell on the antenna, feed consideration, and final design data are presented. The overall transparency and aperture efficiency of the design are more than 90% and 40% respectively, making it a promising solution as a high gain conformal satellite antenna.

A study was performed that evaluated the feasibility of Ka-band communication system to provide CubeSat/SmallSat high rate science data downlink with ground antennas ranging from the small portable 1.2m/2.4m to apertures 5.4M, 7.3M, 11M, and 18M, for Low Earth Orbit (LEO) to Lunar CubeSat missions. This study included link analysis to determine the data rate requirement, based on the current TRL of Ka-band flight hardware and ground support infrastructure. Recent advances in Ka-band transceivers and antennas, options of portable ground stations, and various coverage distances were included in the analysis. The link/coverage analysis results show that Cubesat/Smallsat missions communication requirements including frequencies and data rates can be met by utilizing Near Earth Network (NEN) Ka-band support with 2 W and high gain (>6 dBi) antennas.