Characterization and Performance Comparison of Low-Voltage, High-Speed, Push-Pull and traveling-wave Silicon Mach-Zehnder Modulators

The well-known power and memory walls are recognized as the current bottlenecks in computing performance, and with the increasing computational load of commonly run applications, it is necessary to nd ways to alleviate the issues presented by the aforementioned bottlenecks. It is therefore necessary to not focus solely on extracting performance improvement by way of changes to the processing architecture, but rather by holistically improving the computing platform, namely the communications backbone. This work focuses on the characterization and performance comparison of two families of optical data modulators, both fundamentally Mach{Zehnder modulators (MZMs); namely, a modulator with a Push-Pull (PP) modulation scheme, and another modulator with a Traveling-Wave Electrode (TWE) design, prioritizing the effects on high-speed performance. A number of operating conditions temperature, wavelength, bias voltage, and bit rate were varied to determine effects of modulator performance, measured in terms of DC performance characterization, bit error rate, electrical bandwidth, and power-penalty. Custom xtures were designed and fabricated to achieve long-term experimental stability, and software was written to accomplish long term experimentation; the con uence of the two resulted in a wealth of data for use in performance comparison. Despite the use of a push-pull modulation scheme, the devices using a traveling-wave electrode outperformed the push- pull modulators in almost all metrics, even at what was assumed to be a relatively low bit rate of 3 Gbps. This work then accentuates the importance of velocity and impedance matching, even at presumably low data rates, in spite of increased device fabrication complexity

CAPSTONE: Recovery & Operations of a Tumbling Small Satellite in Deep Space

The Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) satellite, deployed in July 2022, experienced a thruster anomaly in September 2022 during its Ballistic Lunar Transfer (BLT) into the Earth-Moon L2 Near Rectilinear Halo Orbit (NRHO). CAPSTONE\u27s primary mission objective to achieve and maintain NRHO serves to validate the cislunar CONOPS contemplated for NASA\u27s Lunar Gateway. Terran Orbital designed and built CAPSTONE, and serves as the operator of the on-orbit spacecraft. Advanced Space owns and operates the CAPSTONE payload and its software on behalf of NASA, as well as performs mission navigation and maneuver design. This 12U+ lunar nanosatellite contains a pump-fed hydrazine propulsion system from Stellar Exploration, enabling all orbital maneuvers and momentum management for the mission. The CAPSTONE mission is funded by the NASA Space Technology Mission Directorate (STMD) through the Small Spacecraft Technology program, and by the Human Exploration and Operations Mission Directorate (HEOMD) through the Advanced Exploration Systems program. This paper will examine the timeline, innovation, and steps taken by the spacecraft team to recover the vehicle from the thruster anomaly and the resulting high-rate tumble. The high-rate tumble was induced by a valve which became stuck open at the conclusion of Trajectory Correction Maneuver 3 (TCM-3). The timeline discussion includes initial autonomous fault recovery, the evolution of the state of the vehicle, and the recovery actions taken by a small, agile engineering team. The off-nominal attitude and thermal state was determined from a limited data set, requiring the largest assets in NASA\u27s Deep Space Network (DSN) to support communications with the vehicle. Once a determination was made that the hydrazine propellant was freezing, an assessment was made on the minimum amount of heat required to thaw propellant without placing the spacecraft in a power-negative state. The integrated spacecraft team performed root cause analysis and incrementally tested the propulsion system to recommission it in the face of an anomalous thruster valve. The recommissioning approach eventually lead to the development of a new propulsive state machine and Guidance Navigation and Control (GNC) thruster controller for detumbling. After recovering 3-axis attitude control, power and thermal stability, and establishing nominal communications, significant development and testing was required to ensure the vehicle could operate in the presence of a continued thruster anomaly. This effort enabled CAPSTONE to execute future propulsive maneuvers with an open thruster valve. The resultant updates were tested on Terran Orbital\u27s Hardware-in-the-Loop (HITL) platform in partnership with Stellar Exploration. A comparison of GNC subsystem requirements will be presented pre-and post-anomaly, based on the resulting capability and restrictions of the propulsion system to meet mission objectives. Ultimately, the spacecraft was successfully recovered from body rates exceeding 120 deg/s, allowing the CAPSTONE spacecraft to continue its mission, including successful insertion into NRHO in November 2022. An examination of the lessons learned for future deep space small satellite missions is also discussed herein

CAPSTONE: A CubeSat Pathfinder for the Lunar Gateway Ecosystem

The cislunar environment is about to get much busier and with this increase in traffic comes an increase in the demand for limited resources such as Earth based tracking of and communications with assets operating in and around the Moon. With the number of NASA, commercial, and international missions to the Moon growing rapidly in the next few years, the need to make these future endeavors as efficient as possible is a challenge that is being solved now. Advanced Space is aiming to mitigate these resource limitations by enabling the numerous spacecraft in the cislunar environment to navigate autonomously and reduce the need for oversubscribed ground assets for navigation and maneuver planning. Scheduled to launch on a Rocket Lab Electron in October 2021, the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) mission will leverage a 12U CubeSat to demonstrate both the core software for the Cislunar Autonomous Positioning System (CAPS) as well as a validation of the mission design and operations of the Near Rectilinear Halo Orbit (NRHO) that NASA has baselined for the Artemis Lunar Gateway architecture. Currently being developed in a Phase III of NASA’s SBIR program, our CAPS software will allow missions to manage themselves and enable more critical communications to be prioritized between Earth and future cislunar missions without putting these missions at increased risk. CAPSTONE is the pathfinder mission for NASA’s Artemis program. The overall mission will include collaboration with the Lunar Reconnaissance Orbiter (LRO) operations team at NASA Goddard Space Flight Center to demonstrate inter-spacecraft ranging between the CAPSTONE spacecraft and LRO and with the NASA Gateway Operations team at NASA Johnson Space Center to inform the requirements and autonomous mission operations approach for the eventual Gateway systems. Critical success criteria for CAPSTONE in this demonstration are a transfer to and arrival into an NRHO, semi-autonomous operations and orbital maintenance of a spacecraft in an NRHO, collection of inter-spacecraft ranging data, and execution of the CAPS navigation software system on-board the CAPSTONE spacecraft. Advanced Space along with our partners at NASA’s Space Technology Mission Directorate, Advanced Exploration Systems, Launch Services Program, NASA Ames Small Spacecraft Office, Tyvak Nano-Satellite Systems and Rocket Lab, envision the CAPSTONE mission as a key enabler of both NASA’s Gateway operations involving multiple spacecraft and eventually the ever-expanding commercial cislunar economy. This low cost, high value mission will demonstrate an efficient low energy orbital transfer to the lunar vicinity and an insertion and operations approach to the NRHO that ultimately will demonstrate a risk reducing validation of key exploration operations and technologies required for the ultimate success of NASA’s lunar exploration plans, including the planned human return to the lunar surface. This presentation will include the current mission status (which would include the launch and early mission operations), the operations plan for the NRHO, and lessons learned to date in order to inform future CubeSat pathfinders in support of national exploration and scientific objectives

CAPSTONE: A Summary of Flight Operations to Date in the Cislunar Environment

The cislunar environment is about to get much busier and with this increase in traffic comes an increase in the demand for limited resources such as Earth based tracking of and communications with assets operating in and around the Moon. With the number of NASA, commercial, and international missions to the Moon growing rapidly, the need to make these future endeavors as efficient as possible is a challenge that is being solved now. Advanced Space is aiming to mitigate these resource limitations by enabling spacecraft in the cislunar environment to navigate autonomously and reduce the need for oversubscribed ground assets for navigation and maneuver planning. Launched in June 2022, the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) mission utilizes a 12U CubeSat to demonstrate both the core software for the Cislunar Autonomous Positioning System (CAPS) as well as a validation of the mission design and operations of the Near Rectilinear Halo Orbit (NRHO) that NASA has baselined for the Artemis Lunar Gateway architecture. The CAPS software enables cislunar missions to manage their navigation functions themselves and reduces the reliance on Earth based tracking requirements without putting these missions at increased risk. Upon arrival in the NRHO, the CAPSTONE spacecraft will soon initiate its navigation demonstration mission in collaboration with the Lunar Reconnaissance Orbiter (LRO) operations team at NASA’s Goddard Space Flight Center to demonstrate autonomous inter-spacecraft ranging and autonomous navigation between the CAPSTONE spacecraft and LRO. Critical success criteria for CAPSTONE in this demonstration are 1) semi-autonomous operations and orbital maintenance of a spacecraft in an NRHO, 2) collection of inter-spacecraft ranging data, and 3) execution of the CAPS navigation software system in autonomous mode on-board the CAPSTONE spacecraft. Additionally, CAPSTONE continues to demonstrate an innovative one-way ranging navigation approach utilizing a Chip Scale Atomic Clock (CSAC), unique firmware installed on the Iris radio, and onboard autonomous navigation algorithms developed JPL an implemented by Advanced Space. Advanced Space, along with our partners at NASA’s Space Technology Mission Directorate, (STMD), Advanced Exploration Systems (AES), Launch Services Program (LSP), NASA Ames’ Small Spacecraft Office, the Jet Propulsion Lab (JPL), Terran Orbital and Rocket Lab, envision the CAPSTONE mission as a key enabler of both NASA’s upcoming Gateway operations involving multiple spacecraft and eventually the ever-expanding commercial cislunar economy. Over the next 21 months, CAPSTONE will demonstrate an efficient low energy orbital transfer to the lunar vicinity, an insertion into the NRHO, and a risk reducing validation of key exploration operations and technologies required for the ultimate success of NASA’s lunar exploration plans. This paper includes an overview of the mission, the current mission operational status, lessons learned from the launch, lunar transfer, and insertion into the NRHO, an overview of operations plan for the NRHO, and other lessons learned to date in order to inform future missions in support of national exploration and scientific objectives