Deep Space Research By: Bhavin Gurjar 08MCES53 Gayatri Jain 08MCES54
Topics Highlighted • Introduction • Architecture and how it works • Tools for DSN Technology • Antennas and data delivery System make it possible • IDSN & Chandrayan 1 • STP ( Satellite Transport Protocol) • Types of Packets for Data Transfer • Test Bed • Conclusion
Deep Space Research • Is the research on Deep Space Network (DSN) • International network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. • First DSN • Established NASA
Deep Space Network (DSN) • DSN responsible for providing • communications, • tracking, and • science services to most of the world's non-geostationary spacecraft that travel beyond low Earth orbit
Deep Space Network • Currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world: • at Goldstone, in California's Mojave Desert; • near Madrid, Spain; and • near Canberra, Australia. • This strategic placement permits constant observation of spacecraft as the Earth rotates, and helps to make the DSN the largest and most sensitive scientific telecommunications system in the world.
Tools for DSN Technology • Beam Waveguide Antennas. • Ka-Band Communications. • HEMT amplifiers. • Antenna Arraying • New Receivers • New Error Correcting Codes • Data Compression
Antennas and data delivery systems make it possible to • Acquire telemetry data from spacecraft. • Transmit commands to spacecraft. • Track spacecraft position and velocity. • Perform very-long-baseline interferometer observations. • Measure variations in radio waves for radio science experiments. • Gather science data. • Monitor and control the performance of the network.
Indian Deep Space Network (IDSN) • Consists of a 18-m and a 32-m antenna that are established at the IDSN campus, Byalalu, Bangalore. • Augmented with a couple of stations in the western hemisphere in addition to the 64-m antenna in Bearslake, Russia to improve the visibility duration and to provide support from the antipodal point (diametrically opposite it ). • The DSN, installed at an upfront cost of Rs.1 billion in this 135-acre campus, will be the base station for l lunar missions of Chandrayan-l
CHANDRAYAAN-1: India's first mission to Moon: The Objective • To prepare a three-dimensional atlas (with high spatial and altitude resolution of 5-10 m) of both near and far side of the moon. • To conduct chemical and mineralogical mapping of the entire lunar surface for distribution of mineral and chemical elements such as Magnesium, Aluminum, Silicon, Calcium, Iron and Titanium as well as high atomic number elements such as Radon, Uranium & Thorium with high spatial resolution.
18-m Antenna • Is configured for Chandryaan-1 mission operations and payload data collection. • A fibre optic / satellite link will provide the necessary comm- on link between the IDSN Station and Mission Operations Complex (MOX) / Indian Space Science Data Centre (ISSDC).
32-m Antenna • Antenna is a state-of-the-art system that will support the Chandrayaan-1 mission operations and beyond. • A fiber optics / satellite link will provide the necessary connectivity between the IDSN site and Spacecraft Control Centre / Network Control Centre.
Satellite Transport Protocol • Transport protocol for use over IP-compatible networks specifically designed to overcome the following three problems encountered with TCP over satellite links : • Reverse channel usage • uses less of the reverse channel bandwidth than does TCP • Performance with high BERs • STP operates efficiently by using selective negative acknowledgments and a robust data acknowledgment system • Sensitivity to RTT variations • immune to problems related to highly-varying round trip times
STP has four basic packet types for data transfer • Sequenced Data (SD) • a variable length segment of user data, together with a 24 bit sequence number and a checksum. SD packets which have not yet been acknowledged are stored in a buffer, along with a timestamp indicating the last time that they were sent to the receiver. • POLL • packet contains a timestamp and the sequence number of the next in-sequence SD packet to be sent • STAT(us ) • message reports the entire state of the receiver buffer • USTAT (unsolicited STAT) packet • are data-driven explicit negative acknowledgments, and are used by the receiver to immediately report gaps in the received sequence of packets without waiting for a POLL message to arrive
Analysis of Existing Transfer Protocols • To support better mobility in the network layer, the STP checksum does not cover the IP header. • Periodically, the sender sends a POLL packet to the receiver. The receiver detects the packet loss and notes the sender's retransfer.
TCP-Peach • TCP-Peach is composed of two new algorithms, namely • Sudden Start and • Rapid Recovery. • The new algorithms are based on the novel concept of using dummy packets to probe the availability of network resources without carrying any new information to the sender. • Dummy packets which are marked low-priority do not affect the delivery of actual data traffic.
Space Communications Protocol Standards-Transport Protocol (SCPS-TP). • It adopts some existing options in TCP, such as • window scaling, • to improve bandwidth utilization in the presence of long propagation delays. • It also incorporates other new features, such as • selective negative acknowledgement to increase throughput by accelerating the retransmission of packets received in error, header compression to reduce bandwidth overhead, and "best effort" service to deal with loss or impairment of acknowledgement traffic • allow for optimum packet transmission rates under all conditions of channel noise and network congestion
Conclusions • Two main issues in the current research of the deep space communication protocols • the complicated characteristics of deep space environment and • the lack of systematic research method.
References •  CCSDS, http://www.ccsds.org JPL, http://www.jpl.nasa.gov spec-02.txt, Sep 2004. • http://www.isro.org/Chandrayaan/htmls/ground_segment_spacenetwork.htm •  Zhou Youxi, Li Yunsong, Wu Chengke • National Key Laboratory of ISN, Xidian University, Xi'an 710071, China, Transport Protocols in Deep Space Communication •  http://www.tomh.org/stp/stp_doc.pdf