Having designed the networking protocols that launched the Internet, Vint Cerf now wants to put the same kind of robust communications network in outer space. Currently, astronauts and robotic spacecraft communicate with Earth using point-to-point radio links and communications schemes that are tailored to nearly every new mission. This inhibits interoperability and the repurposing of communications equipment, and as the number and complexity of missions increases, it will only become more problematic.
Cerf, who is Google’s vice president and chief Internet evangelist, is working with a team at NASA’s Jet Propulsion Laboratory (JPL), where he is also a visiting scientist, and at the MITRE Corporation, based in Washington, DC, to design and implement a revolutionary new scheme for space communication. The project, dubbed the Interplanetary Internet, will be tested aboard the International Space Station (ISS) in 2009, and Cerf hopes that by 2010, new space missions will be designed to use the protocols.
Ultimately, the network could interconnect manned and robotic spacecraft, forming the backbone of a communications system that reaches across the solar system.
Technology Review’s Brittany Sauser caught up with Cerf to discuss the details of the project.
Technology Review: What’s the purpose of the Interplanetary Internet?
Vint Cerf:The project started 10 years ago as an attempt to figure out what kind of technical networking standards would be useful to support interplanetary communication. Bear in mind, we have been flying robotic equipment to the inner and outer planets, asteroids, comets, and such since the 1960s. We have been able to communicate with those robotic devices and with manned missions using point-to-point radio communications. In fact, for many of these missions, we used a dedicated communications system called the Deep Space Network (DSN), built by JPL in 1964.
But one problem with space communication has been the limited use of standards. When we launch a spacecraft with a unique set of sensors onboard, we often end up writing special communication and application software that is adapted to that spacecraft’s sensor systems and manipulators. In the Internet world, we use standards called the TCP/IP protocol suite–packet switching and store-and-forward methods–to allow a lot of different devices, billions of things, to interact compatibly with each other. The team set out to develop a suite of protocols that would allow us to have the kind of network flexibility in space that we have on Earth. The Interplanetary Internet project is primarily about developing a set of communication standards and technical specifications to support rich networking in space environments.
TR:What are the challenges of building such a network in space?
VC:We started by working on a set of protocols that could deal with two very important properties of space communication. The first is delay. The distances between the planets are very large. For example, when Earth and Mars are closest together, it still takes 3.5 minutes for a radio signal moving at the speed of light to propagate. If I were on Mars and you were on Earth, it would take seven minutes at best before you heard a response. When Earth and Mars are farthest apart, the round trip takes 40 minutes! The reason we can talk back and forth on Earth so easily is that propagation times are very short by comparison.
The other problem is that the planets and their satellites are in motion, and most are rotating. The rotation of the planets means that if you are talking to something that is on the surface of the planet, it may rotate out of the line of sight so you cannot talk to it anymore, until the device on the surface rotates into view again. The same could be said for some orbiting satellites. You have to develop protocols that will deal with the fact that you cannot always communicate with the other party: the communication is both delayed and potentially disrupted. So that is what we designed: a delay- and disruption-tolerant networking system [DTN]. It will allow us to maintain communications more effectively, getting much more data because we don’t have to be in direct line of sight with the ultimate recipient in order to transfer data. The new protocols will be proposed to serve as a potential international standard for space networking.