NASA fires-up experimental space Internet for robot control

NASA and European Space Agency control robot on ground from International Space Station

NASA said today it had teamed with the European Space Agency to successfully test an experimental version of an "interplanetary Internet" to control a robot on the ground in Germany from a laptop onboard the International Space Station.

Specifically the test employed NASA's Disruption Tolerant Networking (DTN) protocol to transmit messages between the ISS and the robot.  DTN technology is designed to allow Internet-like communications between space vehicles and habitats or infrastructure on another planets NASA said.

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From NASA: "The core of the DTN suite is the Bundle Protocol (BP), which is roughly equivalent to the Internet Protocol (IP) that serves as the core of the Internet on Earth. While IP assumes a continuous end-to-end data path exists between the user and a remote space system, DTN accounts for disconnections and errors. In DTN, data move through the network "hop-by-hop." While waiting for the next link to become connected, bundles are temporarily stored and then forwarded to the next node when the link becomes available.  

Low latency, coupled with low bit error rates (BER), allows TCP to reliably transmit and receive acknowledgements for messages traversing the terrestrial Internet. One of the best examples of high latency, high BER links, with intermittent connectivity is that of space communications. One-way trip times, at the speed of light, from the Earth to the moon incurs a delay of 1.7 seconds; while one-way trip times to Mars incur a minimum delay of 8 minutes. The problem of latency for interplanetary links is exasperated with increased BER due to solar radiation. In addition, the celestial bodies are in constant motion, which can block the required line-of-sight between transmit and receive antennas, resulting in links that at best are only intermittently connected. Intermittent link connectivity is commonplace terrestrially as well. "

NASA says DTN operates in two environments: low-propagation delay and high-propagation delay. "In a low-propagation environment such as may occur in near-planetary or planetary surface environments, DTN bundle agents can utilize underlying Internet protocols that negotiate connectivity in real-time. In high-propagation delay environments such as deep space, DTN bundle agents must use other methods, such as some form of scheduling, to enable connectivity between the two agents.  The convergence layer protocols provide the standard methods for transferring the bundles over various communications paths. The bundle agent discovery protocols are the equivalent to dynamic routing protocols in IP networks. To date the location of bundle agents, DTN agents, has been managed, analogous to static routing in IP networks.

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 NASA says DTNs are likely to be deployed in organizationally heterogeneous environments where one does not control the entire network infrastructure. DTNs may very likely be deployed in environments where a portion of the network might become compromised, posing the usual security challenges related to confidentiality, integrity and availability.

DTN is currently being studied in research environments for a number of applications including: sensor networks, mobile devices, use of data mules, military communications which involve stressed disconnected and disrupted networks, along with space-based store-and-forward networks.  There is current work ongoing to extend the DTN architecture to smart mobile phone-based mobile ad-hoc networks, NASA says.

According to NASA, DTN technology is still under active development. In addition to network security, research goals for the DTN activity will focus on testing and evolving important network services including naming and addressing, time synchronization, routing, network management and class of service.

In the ISS experiment, Expedition 33 commander Sunita Williams used a NASA-developed laptop to remotely drive a small LEGO robot at the European Space Operations Centre in Darmstadt, Germany. The European-led experiment used NASA's DTN to simulate a scenario in which an astronaut in a vehicle orbiting a planetary body controls a robotic rover on the planet's surface.  Such an experiment  may one day be used by humans on a spacecraft in orbit around Mars to operate robots on the surface, or from Earth using orbiting satellites as relay stations, NASA said. 

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