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Planetary / Space Internet Author : Sajid S Shaikh Prepared for Dr. Javed Khan Department of Computer Science, Kent State University December 2004 |
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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. |
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| Table Of Contents
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| Introduction
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-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
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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: |
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| Various
Scenarios
The four main scenarios that the scientists have to consider while developing the Space or Planetary internet are as follows:
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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. |
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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.
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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.
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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. |
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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. |
| Mars Mission Internet |
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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. |
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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: 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 : http://marsnet.jpl.nasa.gov/ |
| Benefits Of Mars Internet |
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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 |
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| Source : http://marsnet.jpl.nasa.gov/ Source : http://marsnet.jpl.nasa.gov/ |
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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. |
| International Space Station |
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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. |
| Benefits of ISS |
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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:
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The International Space Station Source: http://www.shuttlepresskit.com/ISS_OVR/ |
References
Web Sites
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