TKK | Tietoverkkolaboratorio | Opetus
This network is thought of as a collection of small networks between devices in space that communicate with ground stations or satellites in orbit. These networks would communicate in a similar fashion as today's web servers: by constantly sending and receiving packets of data. However, in space, the task of communicating is much more difficult than on earth. The man problems are due to the immense distance between the planets. Even at the speed of light, the "lag" that occurs when sending data on round trip to the moon and back will take as much as 3 seconds. From the earth to mars they may take up to 24 minutes, and these transfer time varies constantly, depending on the relative position that earth and Mars have towards each other. Sending packets to Pluto will take around 17 hours. The TCP / IP protocol is quite robust, but it is not at all capable of dealing with these kinds of delays.
Another problem is posed by the fact that communication is at some times completely impossible, because there is not always a clear line of sight between sender and receiver. This happens for instance when spacecraft disappear behind the planet or the moon that they are orbiting. Also, there is the problem of interference. Outside the Earth's atmosphere there is a lot of interference from cosmic rays and natural radio emissions from stars and planets. Empty spe1ce seems to be a pretty noisy place, causing unpredictable distortions in spacecraft transmissions.  This high amount of noise and attenuation is going to make the signal to noise ratio very low, which means that very aggressive error control schemes will be needed for interplanetary communication.
Figure 3: The concept of Interplanetary Internet Gateways 
A likely candidate for the protocol that will be used for these long-haul interplanetary communications is the SCPS protocol, underdevelopment by NASA's JPL . SCPS stands for Space Communications Protocol Standards, in is really a superset of the TCP/IP protocols. SCPS includes protocols for file handling protocols, retransmission control protocols, a data protection mechanism and a networking protocol. This protocol will also likely be given a function in navigating the spacecraft.
There are several projects going on at the same time for this "interplanetary internet". Vint Cerf, one of the people who were responsible for developing the TCP/IP standard 20 years ago, is working on an extensible naming scheme for planets, moons, orbits, asteroids and ships in transit. NASA intends to place one InterPlaNet gateway in an orbit around Mars as a part of their ongoing Mars exploration missions. Also, a test link between the earth and the Moon is planned as part of a mission that would be carried out in 2001.
 Howards, T. , The Interplanetary Internet, Personal Computer World Magazine, November 1998.
 Cerf, V. , Presentation, Cerfs UP, August 1999 URL: http://www.wcom.com/about_the_company/cerfs_up/presentations
 Jet Propulsion Laboratory, SCPS, Extending the Internet into Space, July 1999, URL: http://bongo.jpl.nasa.gov/scps
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