Cellularized Satellites – Initial Experiments and the Path Forward

Small satellites are an exciting technology in the space industry today. For example, over half a dozen private companies have announced plans to build large networks of smallsats to provide remote-sensing imagery data to customers. While smallsats can provide advantages over traditional large satellites, satellites assembled from “building block” cells called satlets add to those advantages. NovaWurks is developing the cellularization of satellite technology as a way to dramatically decrease the cost of new space assets, while also enabling these assets to be incrementally upgradeable and easily repairable. Basically, a small number of nanosat-scale satlets serve as building blocks for assembling a fully functional satellite, analogous to how living organisms are made up of basic cell types. Novawurks has developed satlet technologies in HISats, to be configured and aggregated as reliable, flexible spacecraft for a variety of space purposes. An initial set of HISat-based experimental missions are either underway or planned for the near future. These experimental missions seek to provide on-orbit verification of the satlet concept, the HISat instantiation of that concept, and verification of key payload accommodation features. The spectrum of space access utilized to execute the experimental missions serves to demonstrate the flexibility of the cellularized architecture concept. One mission is scheduled to be assembled in space aboard the International Space Station (ISS) enabling a deployment. A second, the experiment for cellular integration technology (eXCITe), is planned for launch as a pre-launch assembled payload on an Expendable Launch Vehicle (ELV) to be deployed from a SHERPA. The third experimental mission aims to utilize HISats to fly a Payload Orbital Delivery (POD) system after deployment from a host satellite in geosynchronous Transfer orbit (GTO). The path forward for HISat-based missions promises to push the envelope into the capabilities once thought only achievable by much larger traditional buses. This research was developed with funding from the Defense Advanced Research Projects Agency (DARPA). The views, opinions, and/or findings expressed are those of the authors and do not reflect the official policies or positions of the Department of Defense or the U.S. Government. INTRODUCTION TO CELLULARIZED SATELLITES A cellular satellite architecture allows the disaggregation of typical space vehicles into as many or as few cardinal pieces (called satlets) as required to achieve cost savings, flexibility, and reliability while maintaining the required mission performance. The term “satlet” is intended to define either a single cellularized subsystem (e.g., a propulsion satlet) or a single standalone satlet-based system. The extent of cellularization can vary between the following two extremes. Single-function satlets incorporate one individual satellite subsystem function per satlet and multiple units are aggregated together to increase the required performance (e.g., spatially distributed miniature Reaction Wheel Assemblies (RWAs) that together provide total momentum control). Several diverse satlet types are required to complete a space vehicle-equivalent system. System satlets are designed so each satlet constitutes a complete standalone system that contains requisite individual components such as processors, solar 32nd Space Symposium, Technical Track, Colorado Springs, Colorado, United States of America Presented on April 13-14, 2016 Page 2 of 7 cells, batteries, attitude control sensors and actuators, etc., that can be aggregated together to serially increase performance with increased numbers. For this type, identical satlets are aggregated to complete a space vehicleequivalent system. System satlets provide advantages in their flexibility to respond to changing requirements, particularly requirement changes occurring late in a mission’s life cycle and cost savings achieved by single-type production quantities. NovaWurks has been investigating the cellularization of satellite technology and has developed a hyperintegrated satlet, named HISat, that provides complete satellite functionality in a nanosat-scale package. The HISats can be aggregated and share resources such as electrical power, attitude control sensors and actuators, data processing, etc. With their flexible assembly options resulting in multiple possible configurations, HISats provide a building-block bus (called a PAC – Package of Aggregated Cells) that can conform to and accommodate many different payload sizes and shapes. The potential benefits to payload designers are obvious. HISats provide an app-based, open-source approach to core resource-sharing cellular firmware that provides for simple usercreated applications to coordinate the requisite individual HISat hardware. This enables HISats to be aggregated together informationally so that satlet resource exposure and sharing is transparent to the operation of the system. This critical resource-sharing software provides for basic capability that tailors performance by varying the number of HISats interoperating without skipping a beat. This aggregation of information adds reliability to a cellularized design. The HISat software approach allows the payload user/developer hands-on design, development, and operation of an app to create a specific functionality desired on a HISat cell (like a cell phone). The application building provides a common building block paired with an easily accessible operating system. The benefit is lower-cost software life cycles because application development can be instantiated, maintained and updated in the cloud by researchers and mission clients alike. Exhibit 1: System satellite example – HISat (Hyper-Integrated Satlet) 32nd Space Symposium, Technical Track, Colorado Springs, Colorado, United States of America Presented on April 13-14, 2016 Page 3 of 7 Exhibit 2: Payload Testbed-2 – A PAC of twelve aggregated HISats shown with two deployed solar arrays Cellular space systems, like HISats, are an approach, already in space today, for truly low-cost space operations. One proven method of achieving real cost reductions is by mass production, which could reduce costs by two or more orders of magnitude and allow custom tooling and automation to be exploited while their costs are dissipated among units. The satlet cellular approach is a means to reach the promise of increased production to lower costs in the space vehicle business. Satlet production runs of as few as 50 units are predicted to significantly lower cost per satlet. Low production costs, combined with low-cost access to space through flexibility, would enable many space-based services to be competitively offered relative to today’s market. FINDINGS IN DESIGN, ASSEMBLY, AND TEST As noted above, cost savings are expected to be realized in a cellular architecture due to mass-production efficiencies. What is not as immediately apparent is the savings that could be realized in the design and testing phases. This section discusses initial findings in all three product phases. Design One imagines the design process as an unalterable, logical, sequence of iterative steps that can be found with some small variations in any systems engineering handbook. A typical sequence of the fundamental systems engineering activities for a space system are: definition of mission goals and concepts, the identification and allocation of required functions, definition of key requirements to achieve the required functionality (and performance), development and execution of design trade studies, iteration of the trade studies and associated operational concepts until one or more system design solutions are found, and then selection of an optimal system. Once this point is reached, the next level of functionality, requirements, and design trade spaces are addressed. Sufficient depth must be reached to support product baselining and cost estimation. Cellular space system design, while requiring the same basic inputs as a traditional space system, mission goals and concepts, is a very repeatable and flexible process. The functional analysis is minimized as each system satlet provides a broad set of indentical functions as resources for the PAC to use. In fact, there is considerable temporal flexibility as to which satlet, or satlets, would provide a particular resource to satisfy a required function. A list of key requirements is still needed, but satisfying those requirements, in many cases, is a matter of sizing the number of satlets required rather than allocating, sizing, and chosing hardware for each subsystem. The trade space for cellular systems becomes focused on the physical configuration of the satlets that comply with the requirements. Mass and power budgets are simplified since each satlet brings a standard unit of mass and power storage and 32nd Space Symposium, Technical Track, Colorado Springs, Colorado, United States of America Presented on April 13-14, 2016 Page 4 of 7 internal usage-based consumption. For a cellular system, there is no need to repeat the design process at successively lower levels (e.g., from system to subsystem to assembly, etc.) as the satlet is the lowest reducible unit. NovaWurks has exercised the design cycle for its HISat and PACs over 80 times during the last three years. Initial baselines are produced by a small team of two or three engineers in two or three days for a new concept and frequently changes can be accommodated in a single day. Changes are relatively easy to implement, even after the design phase, as occasionally happens due to launch vehicle volume, first fundamental frequency, or center-of-mass requirement updates, and large payload power demands. Assembly NovaWurks has gained considerable experience in the assembly area having assembled over 100 HISats to date. Immediately realizable and apparent are the savings achieved in utilizing selected commercial off-the-shelf (COTS) parts and standard materials. In many uses, satlet reliability is not impacted and in cases where it is, the inherent redundancy of a cellular system where many satlets are available to perform multiple functions mitigates the impact to space system reliability. Satlet assembly is a repeatable process of assembling essentially identical units over and over again. Parts kitting prior to assembly is standardized as well. Lessons are learned on early units, captured in procedures, and applied to subsequent assemblies in an iterative process. While robotics are envisioned to play a role in future satlet assembly lines, NovaWurks is presently using a skilled workforce to perform the assembly tasks. The assembly teams become more efficient in their techniques and task flows due to our human capability to learn and make things better and easier to do. Experience is gained in common failure modes and points, and early intermediate testing can many times be implemented to detect those failures before additional assembly resources and time are wasted. Assembly quality control efforts are focused on the technically difficult areas, resulting in the reduction of satlet acceptance failure rates. Admittedly, NovaWurks HISat production is still in its infancy where a high learning curve is to be expected, but the results are encouraging in that an estimated 5x reduction in assembly time has been achieved for the HISat