Space-station tests network by driving Lego robot on Earth
Late last month in Germany, a robot made its first moves on Earth under commands from an orbiting spacecraft.
Though that may sound ominous, it doesn't represent an impending threat to humankind. The robot was made of Legos, and it only traversed a European Space Agency test facility. The commands were sent by Sunita Williams, commander of the 33rd expedition of the International Space Station. The ESA-led experiment may have helped lay the groundwork for future expeditions to the Moon, Mars and beyond.
ESA and NASA carried out the exercise to test Disruption Tolerant Networking, a set of protocols designed for communication across the void of space. Researchers created DTN to overcome problems that prevent space missions from using Internet Protocol, the system that runs the Internet and most other networks on Earth. In the process, they may create a technology that helps soldiers keep in touch across war zones and consumers use smartphones as they move in and out of cell coverage.
The Internet doesn't work in space because it takes too long to send data packets across the enormous distances. Even at the speed of light, a one-way transmission from Earth to the Moon has a built-in delay of 1.7 seconds, and one from Earth to Mars would face an eight-minute delay. Space networks also suffer from higher error rates than the terrestrial Internet does because of interference from solar radiation, and their transmissions can be blocked temporarily as celestial bodies move through space.
"As NASA extends its reach to the Moon and beyond, a networked architecture such as DTN will be required to successfully complete these missions," the agency wrote on its Web page about the project. NASA envisions DTN being used between assets on the surface of planets and sister spacecraft orbiting above, or between craft in deep space and command centers on Earth.
While IP expects a continuous, end-to-end data path between two devices using it, DTN sends data on its journey one "hop" at a time. At its heart is the Bundle Protocol, which stores bundles of data at each hop until the next link becomes available and then forwards them.
Spacecraft and all forms of surface vehicles have been communicating by radio ever since the dawn of the Space Age, but the technologies they use are specialized and custom-built. NASA and ESA hope to make DTN into the equivalent of IP for space, a standards-based, publicly available protocol. That would reduce labor costs for setting up communications for each mission, NASA said.
Having a standardized communication protocol will become more important if space exploration escalates to setting up bases on the Moon or other planets, said Adrian Hooke, NASA's space DTN project development manager.
"Just as you can communicate on Earth without the Internet, you could build such a space base without DTN, but its communications systems would be very expensive and unreliable, since there would be lots of custom and manual capabilities required that are already fully standardized by DTN," Hooke wrote in an email interview.
NASA has been working on DTN "in earnest" since 2000, according to Hooke. A key proponent of the technology is Vint Cerf, one of the founders of the current Internet. It has used the system successfully to transmit data through space. In the latest experiment, ISS commander Williams controlled the Earthbound robot in Darmstadt, Germany, for about 90 minutes and exchanged data with it. The network connection between the robot and the ISS, more than 200 miles above Earth, delivered 50 kilobytes per second down and 82 bytes per second up. Data took seven seconds to make the round trip.
The agency expects to be able to use DTN on missions that will launch around 2015. But the technology may also have more down-to-Earth applications. Because it's designed to handle intermittent link connectivity, or communication without a constant connection, it could be useful for military networks or for using any type of battery-powered mobile communications device that goes in and out of range of a network, NASA says.
Next stop: Galaxy
There is no limit to how far DTN could go. "There are no limits—DTN could run into interstellar space," Hooke wrote. "It's more a question of how long the user can wait for a response."
However, the hop-by-hop nature of DTN would require some nodes along the way. These could be supplied by spacecraft purpose-built as relays or by older craft that had already fulfilled their original purposes, according to Hooke.
The "Interplanetary Internet" that NASA envisions might be a network of networks all built on DTN, but with two sets of standard protocols.
"DTN can run over the terrestrial Internet protocols in small areas of space where the communications environment is a lot like that on Earth. However, the performance of the Internet protocols rapidly breaks down in long-delay or disrupted environments, so DTN will be the end-to-end protocol, traversing local "islands of IP" along the path," he wrote.