The Internet of Satellites: a C&DH Software Framework for Small Satellites Built on Open Internet Standards and Software

Methods for satellite command & data handling (C&DH) system abound; flight software frameworks, both open and closed source, are available to pick up and build on (e.g. NASA\u27s cFS) and mission developers often choose to build custom systems for their missions from the ground up. Existing flight software packages can offer the advantage of rapid development, which is nothing to shrug off, and custom solutions may eke out performance gains where it is critical. Both approaches, however, fail to addresses a much larger challenge, which is to enable frictionless communication between satellite nodes of various designs, ground stations, ground based sensors, and any resource available on the Internet. Such a standardized approach to communication interfaces, if widely adopted, would not only reduce barriers to flight software development, but would open up a huge array of networked application possibilities that were not possible on traditional siloed satellite systems. There are two steps necessary to enable this. The first is to treat satellites as fully as possible as you would nodes on the Web: that is, as changing collections of data in universally standard formats that can be accessed and acted upon, rather than as specialized machines to be controlled. The second is to adhere to published international Internet standards and use only open source software for all communication and data handling operations. The Internet Engineering Task Force (IETF) has a published standard for Constrained Access Protocol (CoAP), a transfer protocol that closely mirrors the functionality of the HTTP protocol but addresses the needs of resource constrained nodes such as satellites and autonomous sensors. These constraints include reduced bandwidth, unreliable connections, and limited power and memory. CoAP\u27s \u27ReSTful\u27 API and use of familiar URI path conventions make interfacing with the wider Web straightforward. Along with standards for data formatting (e.g. JSON) it can completely describe the control and data interface of a small satellite in a manner that can be replicated across satellite nodes. A CoAP server can be installed on a flight computer running Linux, SQLite, and Python to create an \u27LCSP\u27 stack, analogous to the well-known \u27LAMP\u27 stack that powers much of the Web. We examine the process and results of implementing a \u27LCSP\u27 stack on a nanosat and look at the implications that Internet standard interfaces could have on satellite operations and capabilities