James W. Cutler

Reducing recovery time in a small recursively restartable system

We present ideas on how to structure software systems for high availability by considering MTTR/MTTF characteristics of components in addition to the traditional criteria, such as functionality or state sharing. Recursive restartability (RR), a recently proposed technique for achieving high availability, exploits partial restarts at various levels within complex software infrastructures to recover from transient failures and rejuvenate software components. Here we refine the original proposal and apply the RR philosophy to Mercury, a COTS-based satellite ground station that has been in operation for over 2 years. We develop three techniques for transforming component group boundaries such that time-to-recover is reduced, hence increasing system availability. We also further RR by defining the notions of an oracle, restart group and restart policy, while showing how to reason about system properties in terms of restart groups. From our experience with applying RR to Mercury, we draw design guidelines and lessons for the systematic application of recursive restartability to other software systems amenable to RR.

Applying Model Based Systems Engineering (MBSE) to a standard CubeSat

Model Based Systems Engineering (MBSE) is an emerging technology that is providing the next advance in modeling and systems engineering. MBSE uses Systems Modeling Language (SysML) as its modeling language. SysML is a domain-specific modeling language for systems engineering used to specify, analyze, design, optimize, and verify systems. An MBSE Challenge project was established to model a hypothetical FireSat satellite system to evaluate the suitability of SysML for describing space systems. Although much was learned regarding modeling of this system, the fictional nature of the FireSat system precluded anyone from actually building the satellite. Thus, the practical use of the model could not be demonstrated or verified. This paper reports on using MBSE and SysML to model a standard CubeSat and applying that model to an actual CubeSat mission, the Radio Aurora Explorer (RAX) mission, developed by the Michigan Exploration Lab (MXL) and SRI International.

Attitude-Independent Magnetometer Calibration with Time-Varying Bias

We present a method for on-orbit, attitude-independent magnetometer calibration that includes the effect of time-varying bias due to electronics on-board a spacecraft. The calibration estimates magnetometer scale factors, mis-alignments, and constant as well as time-varying bias. Time-varying effects are mitigated by including spacecraft telemetry in the measurement model and estimating constant parameters that map the telemetry data to magnetometer bias. The calibration is demonstrated by application to flight data from the Radio Aurora Explorer satellite and significantly reduces the uncertainty of off-the-shelf magnetometers embedded within the satellite and subject to spacecraftgenerated fields. This method simplifies the satellite design process by reducing the need for booms and strict magnetic cleanliness requirements.

Characteristics of low‐latitude Pc1 pulsations during geomagnetic storms

[1] We use search-coil magnetometer data from a low-latitude station in Parkfield, California (L = 1.77) to study the occurrence of Pc1 pulsations associated with geomagnetic storms. The Pc1 pulsations and storms are identified using automatic algorithms, and the statistical distributions are examined using a superposed epoch analysis technique, as a function of local time, time relative to storm main phase, and storm intensity. Results show that Pc1 pulsations are 2–3 times more likely (than normal) to be observed in the 2–4 d following moderate storms and 4–5 times more likely in the 2–7 d following intense storms. The Pc1 frequencies are higher in moderate storms than theyareinnonstormtimesandbecomeevenhigherandoccupyagreaterrangeoflocaltimes as the strength of the storms increase. These results are consistent with the idea that the source of EMIC waves extends to lower L values as storm intensity increases.

Large-Scale Multidisciplinary Optimization of a Small Satellite’s Design and Operation

The design of satellites and their operation is a complex task that involves a large number of variables and multiple engineering disciplines. Thus, it could benefit from the application of multidisciplinary design optimization, but previous efforts have been hindered by the complexity of the modeling and implementation, discontinuities in the design space, and the wide range of time scales. We address these issues by applying a new mathematical framework for gradient-based multidisciplinary optimization that automatically computes the coupled derivatives of the multidisciplinary system via a generalized form of the adjoint method. The modeled disciplines are orbit dynamics, attitude dynamics, cell illumination, temperature, solar power, energy storage, and communication. Many of these disciplines include functions with discontinuities and nonsmooth regions that are addressed to enable a numerically exact computation of the derivatives for all of the modeled variables. The wide-ranging time scales in the ...

Development of an Off-the-Shelf Bus for Small Satellites

KySat1 is a 1 kilogram picoclass satellite being developed by college students across the state of Kentucky. To the best of our knowledge, the KySat effort is the first by a state to develop a satellite. The consortium assembled to fund and develop KySat includes public, private and educational partners throughout Kentucky. While the primary mission of KySat1 is educational outreach, the goals of the KySat program include (1) Educational experience for secondary and post secondary students (2) Cultivate an aerospace and satellite technology base in Kentucky (3) Develop a reliable reusable satellite bus that will form the basis for future education and commercial KySat missions. The timeline for KySat1 is aggressive and off-the-shelf technology is leveraged whenever possible. This paper overviews the KySat1 design and development.

Model based systems engineering (MBSE) applied to Radio Aurora Explorer (RAX) CubeSat mission operational scenarios

Small satellites are more highly resource-constrained by mass, power, volume, delivery timelines, and financial cost relative to their larger counterparts. Small satellites are operationally challenging because subsystem functions are coupled and constrained by the limited available commodities (e.g. data, energy, and access times to ground resources). Furthermore, additional operational complexities arise because small satellite components are physically integrated, which may yield thermal or radio frequency interference. In this paper, we extend our initial Model Based Systems Engineering (MBSE) framework developed for a small satellite mission by demonstrating the ability to model different behaviors and scenarios. We integrate several simulation tools to execute SysML-based behavior models, including subsystem functions and internal states of the spacecraft. We demonstrate utility of this approach to drive the system analysis and design process. We demonstrate applicability of the simulation environment to capture realistic satellite operational scenarios, which include energy collection, the data acquisition, and downloading to ground stations. The integrated modeling environment enables users to extract feasibility, performance, and robustness metrics. This enables visualization of both the physical states (e.g. position, attitude) and functional states (e.g. operating points of various subsystems) of the satellite for representative mission scenarios. The modeling approach presented in this paper offers satellite designers and operators the opportunity to assess the feasibility of vehicle and network parameters, as well as the feasibility of operational schedules. This will enable future missions to benefit from using these models throughout the full design, test, and fly cycle. In particular, vehicle and network parameters and schedules can be verified prior to being implemented, during mission operations, and can also be updated in near real-time with operational performance feedback.

INSPIRE: Interplanetary NanoSpacecraft Pathfinder in Relevant Environment

The INSPIRE project would demonstrate the revolutionary capability of deep space CubeSats by placing two nanospacecraft in Earth-escape orbit. Prior to any inclusion on larger planetary missions, CubeSats must demonstrate that they can operate, communicate, and be navigated far from Earth – these are the primary objectives of INSPIRE. Spacecraft components, such as a JPL X-band radio and a robust watchdog system, would provide the basis for future high-capability, lower-cost-risk missions beyond Earth. These components should enable future supplemental science and educational opportunities at many destinations. The nominal INSPIRE mission would last for three months and achieve an expected Earth-probe distance of 1.5x10 km (dependent upon escape velocity as neither spacecraft will have propulsion capability). The project would monitor onboard telemetry; operate, communicate, and navigate with both spacecraft; demonstrate cross-link communications; and demonstrate science utility with an onboard magnetometer and imager. Lessons learned from this pathfinder mission should help to inform future interplanetary NanoSpacecraft and larger missions that might use NanoSpacecraft components.

Optimization-based scheduling for the single-satellite, multi-ground station communication problem

In this paper, we develop models and algorithms for solving the single-satellite, multi-ground station communication scheduling problem, with the objective of maximizing the total amount of data downloaded from space. With the growing number of small satellites gathering large quantities of data in space and seeking to download this data to a capacity-constrained ground station network, effective scheduling is critical to mission success. Our goal in this research is to develop tools that yield high-quality schedules in a timely fashion while accurately modeling on-board satellite energy and data dynamics as well as realistic constraints of the space environment and ground network. We formulate an under-constrained mixed integer program (MIP) to model the problem. We then introduce an iterative algorithm that progressively tightens the constraints of this model to obtain a feasible and thus optimal solution. Computational experiments are conducted on diverse real-world data sets to demonstrate tractability and solution quality. Additional experiments on a broad test bed of contrived problem instances are used to test the boundaries of tractability for applying this approach to other problem domains. Our computational results suggest that our approach is viable for real-world instances, as well as providing a strong foundation for more complex problems with multiple satellites and stochastic conditions.

Cyber-Physical Challenges for Space Systems

Modern space systems necessarily have a tight coupling between onboard cyber (processing, communication) and physical (sensing, actuation) elements to survive the harsh extraterrestrial environment and successfully complete ambitious missions. This article first summarizes space exploration missions and existing platforms that to-date have been developed by ad hoc, one-of-a-kind cyber-physical integration efforts. The primary goal of this paper is to present a series of cyber-physical systems (CPS) challenges that, if addressed in the emerging science of CPS, will greatly facilitate complex space systems development in the future. Areas of focus include spacecraft communications, driven by relative orbiting network node positions as well as bandwidth and power considerations, attitude control and orbit determination, and space robotics and science payload systems. A strong CPS challenge problem is introduced: scheduling the instructions executed on a small spacecraft processor such that the magnetic field introduced by this processor induces torques favorable for spacecraft pointing.