Communication with spacecraft, both crewed and robotic, and both in Earth orbit and in deep space, should become a bit easier in the near future. The world’s national space agencies have converged on standards for building a “Solar System Internetwork” (SSI) that is aimed at simplifying communication among engineers, scientists, and robots in space flight missions in much the same way that the Internet simplifies communication among people and businesses on Earth.
By automating flight mission communications, SSI should improve efficiency in communication over space links, simplify “cross support” among missions, and eliminate some chores performed by human operators. Taken together, these improvements should increase the volume of data returned from science investigations, reduce risk in mission operations, and reduce mission costs.
The architecture of the SSI should be fairly familiar to Internet users, but there are some differences. Network traffic is forwarded via internationally standardized protocols, including security protocols; security measures were designed into the SSI’s protocols from the very beginning. Instruments, spacecraft, habitats, ground stations, mission operations centers, investigators’ workstations (and more) all may be “nodes” of a single unified, end-to-end network. But all nodes are peers; departing from the distinction often drawn in the Internet between “hosts” and “routers”, each SSI node may function as an end system, a forwarder, or both.
Because the network needs to operate over radio links spanning interplanetary space, where nodes may be millions of miles apart or may periodically be out of contact as planetary rotations take them out of mutual visibility, the network inherently tolerates long signal propagation delays and recurring extended lapses in connectivity. For this reason, data forwarding may often need to be performed on a store-and-forward basis: when outbound links are unavailable, data must be retained in local storage pending establishment of a link that can carry the data.
The protocols on which the Internet is built don’t operate this way, but the SSI is intended to encompass both Internet-friendly environments and these more exotic interplanetary links. So two different network protocols are integrated into the SSI’s network infrastructure – the familiar Internet Protocol (IP), used in the Internet, and the Bundle Protocol (BP) on which “Delay-Tolerant Networking” (DTN) technology is based. Any SSI node may be equipped with an IP stack, a DTN stack, or both. IP communications may be conducted in parallel with DTN communications. In addition, DTN communications may overlay IP communications in segments of DTN end-to-end paths where the Internet protocols work well.
This concept is very different from the way space flight mission communications have been managed in the past, and of course change is always disruptive; since all nodes of the network will be assets that are individually owned and operated by national space agencies and – potentially – commercial space operators, the SSI won’t work very well if those authorities are reluctant to participate. But they should find the network comfortable to work with.
On the one hand, the SSI is intended to be global in scope, in some very helpful ways: all participation in the network is based on voluntary agreements and governed by internationally adopted protocols. At the same time, all participants retain complete local control of their flight and ground communication resources; only explicitly offered resources are made available through the SSI. Moreover, congestion forecasting and rate control will prevent over-utilization, and authentication, integrity protection, and confidentiality mechanisms will be in place to defend against cyber-attack.
SSI technology was first demonstrated by NASA’s Jet Propulsion Laboratory (California Institute of Technology) in an experiment on the EPOXI spacecraft, 15 million miles from Earth, in 2008. The first fully operational subnet of the SSI is under development now, connecting the International Space Station (ISS) with NASA’s Huntsville Operations Support Center. Initial science network operations on-board ISS began in 2009, connecting instruments to a control center in Boulder, Colorado, and recently an ISS “change request” was approved that authorizes permanent deployment of two DTN nodes on the Joint Station LAN, for use by machines throughout the space station.
You can’t send an email to Mars yet, but the day is coming.
