Planetary / Space Internet

Author : Sajid S Shaikh

Prepared for Dr. Javed Khan

Department of Computer Science, Kent State University

December 2004


Abstract : With the rapid development in space technologies, the exploration of the celestial world has been given an extra boost. As the number of space missions increases the amount of data sent by these missions back to earth is also rapidly increasing. The existing methods being used to do this are not an efficient and scalable enough to support it. Thus the researchers are looking towards the development of  networks in space which could talk to each other as well to the network on earth. In the following survey I give a brief overview about this Planetary / Space Internet.

Table Of Contents
  1. Introduction

  2. Issues

  3. Various Scenarios

  4. Protocols

    1. Transport Protocol

    2. Network Protocol

    3. Data Link Layer Protocol

    4. Physical Layer Protocol

  5. Case Studies

    1. Mars Mission Internet

    2. International Space Station

  6. References


      As the human expertise in space technologies increases there is a growing urge to send more and more deep space scientific missions to other planets, similar to the Mars exploration. At present most of these explorations, have been carried out by robotic space crafts. The robotic missions are a steeping stone for further missions which would involve humans in a more direct way. This current exploration of the Solar System by robotic means and later by missions involving humans are among the primary motivation for the researchers’ interest in an Interplanetary Internet. The vision of future space exploration includes missions to deep space that require communication among planets, moons, satellites, asteroids, robotic spacecrafts, and crewed vehicles. These missions produce significant amount of scientific data to be delivered to the Earth. In addition, these missions require autonomous space data delivery at high data rates, interactivity among the in-space instruments, security of operations, and seamless inter-operability between in-space entities.

      For successful transfer of scientific data and reliable navigational communications, NASA enterprises have outlined significant challenges for development of next-generation space network architectures. The next step in the design and development of deep space networks is expected to be the Internet of the deep space planetary networks and defined as the InterPlaNetary (IPN) Internet

       The InterPlaNetary Internet is envisioned to provide communication services for scientific data delivery and navigation services for the explorer spacecrafts and orbiters of the future deep space missions. The applications of IPN can be described as follows:
• Time-Insensitive Scientific Data Delivery: The main objective of InterPlaNetary Internet is to realize communication between in-space entities allowing large volume of scientific data to be collected from planets and moons.

• Time-Sensitive Scientific Data Delivery: This type of application is required to deliver great volumes of audio and visual information about the local environment to Earth, in-situ controlling robots, or eventually in-situ astronauts.

• Mission Status Telemetry: The status and the health report of the mission, spacecraft, or the landed vehicles can be delivered to the mission center or other nodes. This application requires periodic or event-driven, unreliable transmission services.

• Command and Control: Another important application of the InterPlaNetary Internet is the command and control of in-situ elements. The closed-loop command and control may involve in direct or multi-hop communication of the remote nodes, i.e., Earth station controls the mission rover on planet surface.

The following table gives the values for the various parameters if there is a link between earth and the different celestial bodies. The assumptions that I have made for this table are as follows
1. The link speed is 10 Mbps,
2. Speed of light 3*108 meters/second
3. File transfer size 5 Mb.


Space Body

Distance (m)


Delay * Bandwidth (Mb)

Time to Transmit


384403 * 103

2.56 sec


1.78 sec


55 * 109

366.67 sec


183.835 sec


629 * 109

69.89 min


34.95 min


1.3 * 1012

144.45 min


72.23 min


2.76 * 1012

306.67 min


153.34 min


4.5 * 1012

8.34 hrs


4.17 hrs


5.75 * 1012

10.64 hrs


5.32 hrs

Issues Affecting Space Internet

      We can thus see from the above table  that the implementation of a Planetary/Space Internet has its own unique challenges and characteristics that need to be addressed. These could be listed down as follows:
1. The propagation delays would be extremely long and variable.

2. The link capacities of the forwarding link and the retrieval link could be drastically different.

3. High link error rates for radio-frequency (RF) communication channels.

4. There would be times when there will not be any connection at all i.e. intermittent connection.

5. Since the satellites and structures would be moving, there won't be a fixed infrastructure.

6. The planetary distances, which would differ from planet to planet, would have an effect on the signal strength and the protocol design

7. Power, mass, size, and cost constraints for communication hardware and protocol design backward compatibility requirement due to high cost involved in deployment and launching processes.

Various Scenarios

      The four main scenarios that the scientists have to consider while developing the Space or Planetary internet are as follows:

  1. Sensor Web for Earth Observation – As more and more countries acquire the technology to send spacecrafts and satellites into earths orbit, their number is steadily increasing. In such a scenario these various satellites can communicate with each other for information sharing and processing. This communication would require some kind of protocol.

  2. Multiple Scientific Missions for Space Science – Understanding an alien planet requires the exploration of different aspects of the planet. This requires the deployment of diverse kind of equipment. These equipments have to work together and communicate with each other in a hostile and alien environment. In this scenario, the information gathered by these entities has to be sent back to earth for human consumption. Thus we require protocols for the inter-entity (on the surface equipment) communication and for the entity and the overhead satellite communication.

  3. Lunar Colony Scenario – Colonizing the moon in order to exploit it for commercial purpose (mining) has been a human dream for a while. In this scenario one has to consider the architecture and the communication technologies we need to deploy. It is assumed that we would require a very high data rate network in order to enable any in-space or on-surface operations.

  4. Formation Flying and Distributed Processing Mission – This scenario uses a formation flying set of spacecraft with large diameter ultra-lightweight radar antennas placed in solar orbit at Jupiter’s distance from the sun. The purpose of the mission is to detect and locate objects in the outer reaches of the solar system. It is assumed that high rate inter-spacecraft communications is necessary to enable in-space distributed processing to greatly reduce the quantity of data sent back to Earth – thus reducing the load on the Deep Space Network.



      A standardized suite of space data communication protocol standards would be beneficial to both the military and civilian space communications user communities. Use of common protocols for data communications will increase interoperability and reduce the cost of space systems, which are often designed and customized for every mission or set of missions.

Transport Protocol

      This Space Communications Protocol Specification (SCPS) has proposed a Transport Protocol called SCPS-TP. Its key features are as follows:

• TCP for Transactions : Reduces the handshaking necessary to start a TCP connection and provides ‘reliable datagram’ operation to handle command-response traffic, for very long delay environments in which it is desirable to begin data transfer without waiting for a connection handshake.

• Window Scaling: Addresses communication environments that may have more than 65k octets of data in transit at one time.

• Round Trip Time Measurement: Addresses environments that have high loss, changing delays, or large amounts of data in transit at one time.

• Protect Against Wrapped Sequence Numbers: Addresses very long delay environments or very high bandwidth missions.

• Selective negative acknowledgment : Addresses high loss environments;

• Record Boundary Indication : The ability to mark and reliably carry end-of-record indications for packet-oriented applications;

       The following table provide a comparison between TCP with SCPS – TP.




Error Prone Links

TCP’s assumption that virtually all loss is caused by congestion results in severe degradation of performance in error-prone environments.

When losses are not caused by congestion, SCPS- TP’s throughput remains high by avoiding the congestion-control response and by providing enhanced information about data loss via the SCPS-TP Selective Negative Acknowledgment (SNACK) option.

Asymmetric Channels

TCP uses a lot of ACK messages to control flow of data.

SCPS-TP relaxes the TCP ACK messages requirements. The SCPS-TP data-receiver delays acknowledgments for a configurable period of time that is related to its estimate of the RTT.

Limited Link Capacity

Substantial bit overhead associated with TCP (20 bytes header). Consumes sizable bandwidth.

SCPS-TP uses two mechanisms to improve performance in bandwidth-constrained environments: SCPS-TP Header Compression and the SCPS-TP Selective Negative Acknowledgment (SNACK) option.

Intermittent Connectivity

Short term link outages pose a problem for TCP

SCPS-TP uses window scaling to overcome link outages.


Network Protocol

      The SCPS Network Protocol (SCPS-NP) uses a technique called ‘capability-driven header construction’ as a means to control bit overhead. Capability-driven header construction simply means that the format of the SCPS-NP header is based (exclusively) on the protocol capabilities required for the communication of the particular datagram in question. That is, a datagram carries those header elements that are required to provide service properly to the datagram, but not the others.

        The following table provide a comparison between IP with SCPS – NP.




Header Size

IPv4 has a fixed 20 byte header

SCPS-NP has variable header 4-20 bytes


Options can be given only after fixed header

Options can be given throughout the header

Routing Protocols

Automated routing protocols

It requires the routing protocols to be configured.

Operating System

It’s built into all the operating systems

It is not supported by the operating system vendors


It cannot drop any features. It’s format is fixed

It can drop features depending upon the environment to reduce overhead.


Data Link Layer Protocol

     The TM Space Data Link Protocol provides the users with several services for transferring data over the space links. To facilitate simple, reliable, and robust synchronization procedures, fixed-length protocol data units are used to transfer data through the weak-signal, noisy space links: their length is established for a particular Physical Channel (a single stream of bits transferred over a space link in a single direction) during a particular Mission Phase by management. A key feature of the TM Space Data Link Protocol is the concept of .Virtual Channels. (VC). The Virtual Channel facility allows one Physical Channel to be shared among multiple higher-layer data streams, each of which may have different service requirements.


Physical Layer Protocol

     Proximity-1 is a bi-directional Space Link layer protocol to be used by space missions. It consists of a Physical Layer , a Coding and Synchronization (C&S) sublayer and a Data Link Layer. This protocol has been designed to meet the requirements of space missions for efficient transfer of space data over various types and characteristics of Proximity space links. On the send side, the Data Link layer is responsible for providing data to be transmitted by the Coding and Synchronization sublayer and Physical layer. The operation of the transmitter is state-driven. On the receive side, the Data Link layer accepts the serial data output from the receiver (Physical Layer) and verified by the Coding and Synchronization sublayer and processes the protocol data units received. It accepts directives both from the local vehicle controller and across the Proximity link to control its operations. Once the receiver is turned on, its operation is modeless. It accepts and processes all valid local and remote directives and received serviced data units.


Case Studies

Mars Mission Internet

     The driving force behind the development of the Mars internet is to support Mars global reconnaissance, surface exploration, sample return missions, robotic outposts, and eventually exploration by humans. We humans would like to have a network which has a substantially high data rates and connectivity between Earth and Mars. This network would also help in coordinating the precise landing of future robots on Mars. By developing a high data rate, high connectivity network there would be a greater information flow from Mars to explorers on Earth. In essence, the Mars network would work as a gateway for accessing the data and information which is being generated by the rovers and pathfinders on Mars surface.


     One of the architecture being considered consists of constellation of microsatellites, or Microsats, and one or more relatively large Mars Areostationary Relay Satellites, or MARSats. The two main objectives of the Microsats:
1. To provide communication between the entities present on the surface viz. landers, rovers, balloons, airplane, space crafts etc. and the Earth.

2. To be a navigational aid for the various spacecraft or other exploration elements.

     The MARSats on the other hand are very high bandwidth geostationary satellites that would orbit Mars. These satellites rotate with the same speed as that of Earth hence they would always be over the same area. The MARSats and the Microsats would together form a network which would receive the data sent from Earth. They would use some protocol similar to the one used by the Earth’s internet.

                  Source :
Benefits Of Mars Internet

     NASA’s aim is to have a virtual presence throughout the solar system. The Mars internet would be the first step in achieving that goal. One way in which the earth station could receive data from the surface robotic entities is if they process the data and transmit it. This would require them to have significant power, antenna size and associated mass. Instead of this a better way is for them to give the data to the overhead satellites which could collect the data from the different entities and when they have sufficient data , send it to earth in a single burst. This would also ensure efficient usage of the space link. The Mars internet could be used as a data processing center for data being sent by satellites probing other planets. Thus it would result in only relevant data being transmitted to earth

                                 Source :                                                                              Source :

     Mars Networks Microsats can provide for navigation. Until now the scientist at NASA use a method called Deep Space Network (DSN) tracking which involves coordinating the landing of the rovers from earth station. Due to which there is lot of discrepancy between where the rover should land and where it actually lands. As the presence of rovers and landers increases on the Mars surface such discrepancies are not acceptable.
     On the other hand, using combined 2-way ranging, three Mars Network Microsats (or 2 Microsats and a properly equipped surface element) would be able to reduce this uncertainty to a large extent.. On the surface, they would be able to reduce position uncertainty to within 10 to 100 meters! With rovers, sample return canisters, balloons, and other mobile exploration elements able to accurately determine their position, Mars Network would enable a whole new level of autonomous robotic and, eventually, safe piloted exploration.

International Space Station

     The International Space Station (ISS) is the largest and most complex international scientific project in history. And when it is complete, the station will represent a huge network in space. This effort has been led by the United States, with active cooperation from 16 other nations including Canada, Japan, Russia, 11 nations of the European Space Agency and Brazil. Once fully operational the ISS will be more than four times as large as the Russian Mir space station. It will have a mass of about 1,040,000 pounds. It will measure 356 feet across and 290 feet long. An acre of solar panels provide electrical power to six state-of-the-art laboratories on the ISS.
      The station will be in an orbit with an altitude of 250 statute miles with an inclination of 51.6 degrees. This orbit allows the station to be reached by the launch vehicles of all the international partners to provide a robust capability for the delivery of crews and supplies. The orbit also provides excellent Earth observations with coverage of 85 percent of the globe and over flight of 95 percent of the population. By the end of this year, about 500,000 pounds of station components will be have been built at factories around the world.
      The ISS would be an important cog in the Sensor Web for Earth Observation. It could be used as a Network Access Point for the various networks present around earth. The ISS will the biggest entity in that network having plenty of storage space. The ISS could lease some of its space to these networks. The ISS could thus be used as a huge data bank. The satellites could use the tremendous processing power available on the ISS.

Benefits of ISS

         The other benefits of permanent human presence in space aboard the ISS have immense practical benefits for mankind. A few of these have been enumerated below:

  •  85 percent of human energy consumption is based on combustion. This posse a lot of environment problems such as atmospheric change and global warming, unwanted fires and explosions, and the incineration of hazardous wastes. The testing of combustion aboard the International Space Station will help humans deal better with these problems.

  • Aboard the International Space Station the field of fundamental physics has a grand opportunity. Not only will the laws of quantum theory as they pertain to mapping of the relic of quantum gravity --gravitational waves generated from the Big Bang -- be tested. But the areas of high powered physics will be able to develop new, more precise atomic clocks with the combination of a new laser cooling technology and microgravity.

  •  The National Institute Of Health has predicted that the protein crystal growth would be the prominent research tool in the next century. These crystals when grown in normal gravity environments results in impurities. But the ISS would provide an idle environment for the growth of these crystals. This will allow the development of more pure pharmaceutical drugs, foods and an assortment of other crystalline-based products including insulin for diabetes patients.

  •  The ability to understand the Earth and its environmental response to natural and human-induced variations such as air quality, climate, land use, food production as well as ocean and fresh water health are some of the benefits expected from Earth science research aboard the International Space Station.

  • In the fundamental field of biology, the scientists of the International Space Station will assist in answering some very basic scientific questions in a different environment.

  • Many of the new engineering technologies being developed on the International Space Station will lead to improved commercial space communication systems for personal phone, computer and video use.

  • The space station research will bring knowledge and insight about the far reaches of space down to Earth. For instance, studies of the Sun's effects on Earth will improve forecasts of events ranging from the temporary disruption of telecommunications to the long-term alterations in climate. The practical applications here on Earth gained from space science on the International Space Station will be invaluable.

The International Space Station


  1. Space Communications Protocol Specification (SCPS)—Transport Protocol (SCPS-TP). Blue Book. Issue 1. May 1999.

  2. Space Communications Protocol Specification (SCPS)—Network Protocol (SCPS-NP). Blue Book. Issue 1. May 1999.

  3. TM Space Data Link Protocol. Blue Book. Issue 1. September 2003.

  4. Proximity-1 Space Link Protocol—Physical Layer. Blue Book. Issue 2. May 2004.

  5. Improving TCP Performance over Long Delay Satellite Links Jing Peng, Peter Andreadis, Claude Bélisle Michel Barbeau

  6. TP-Planet: A Reliable Transport Protocol for InterPlaNetary Internet Ozg¨ur B. Akan, Student Member, IEEE, Jian Fang, and Ian F. Akyildiz, Fellow, IEEE

  7. TCP Extensions for Space Communications Robert C. Durst†, Gregory J. Miller‡, and Eric J. Travis*

  8. Next-Generation Space Internet: Prototype Implementation James Noles Keith Scott, Mary Jo Zukoski Howard Weiss

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