Chris Jackson

Saratoga: a Delay-Tolerant Networking convergence layer with efficient link utilization

Saratoga is a lightweight transport protocol based on the user datagram protocol (UDP/IP). Saratoga was developed by Surrey Satellite Technology Ltd (SSTL) for file transfers of imaging data recorded onboard the Internet-Protocol-Based Disaster Monitoring Constellation (DMC) satellites, and has been in operational use from low Earth orbit since 2004. Saratoga focuses only on efficient communication to the next hop when link connectivity is available, by filling the link with packets sent at line rate. This ensures that as much data as possible is transferred to the peering node during a twelve-minutes-or-less pass over a satellite ground station. Saratoga uses a minimal bandwidth-efficient negative acknowledgement mechanism to ensure reliable data transfer. We examine how Saratoga can be adapted to serve as an efficient convergence layer for delay-tolerant networking (DTN), by transferring DTN bundles as well as files. This will allow DTN networks to increase efficiency of communication across briefly-available disrupted links -for long-distance deep space links as well as for short-distance terrestrial mobile ad-hoc networks.

Using Internet nodes and routers onboard satellites

An Internet router was integrated into the UK-DMC remote-sensing satellite as a secondary experimental payload. This commercial product has been orbiting in space for over three years. We describe the integration of the router and satellite and the successful on-orbit testing of the router, which took place using the Virtual Mission Operations Center (VMOC) application as part of a larger systems internetworking exercise. Placing this Cisco router in Low Earth Orbit (CLEO) onboard a small satellite is one step towards extending the terrestrial networking model to the near-Earth space environment as part of a merged space-ground architecture.

Large File Transfers from Space Using Multiple Ground Terminals and Delay-Tolerant Networking

Abstract-We use Delay-Tolerant Networking (DTN) to break control loops between space-ground communication links and ground-ground communication links to increase overall file delivery efficiency, as well as to enable large files to be proactively fragmented and received across multiple ground stations. DTN proactive fragmentation and reactive fragmentation were demonstrated from the UK-DMC satellite using two independent ground stations. The files were reassembled at a bundle agent, located at Glenn Research Center in Cleveland Ohio. The first space-based demonstration of this occurred on September 30 and October 1, 2009. This paper details those experiments.

Taking Saratoga from space-based ground sensors to ground-based space sensors

The Saratoga transfer protocol was developed by Surrey Satellite Technology Ltd (SSTL) for its Disaster Monitoring Constellation (DMC) satellites. In over seven years of operation, Saratoga has provided efficient delivery of remote-sensing Earth observation imagery, across private wireless links, from these seven low-orbit satellites to ground stations, using the Internet Protocol (IP). Saratoga is designed to cope with high bandwidth-delay products, constrained acknowledgement channels, and high loss while streaming or delivering extremely large files. An implementation of this protocol has now been developed at the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) for wider use and testing. This is intended to prototype delivery of data across dedicated astronomy radio telescope networks on the ground, where networked sensors in Very Long Baseline Interferometer (VLBI) instruments generate large amounts of data for processing and can send that data across private IP- and Ethernet-based links at very high rates. We describe this new Saratoga implementation, its features and focus on high throughput and link utilization, and lessons learned in developing this protocol for sensor-network applications.12

Virtual Mission Operations of Remote Sensors With Rapid Access To and From Space

This paper describes network-centric operations, where a virtual mission operations center autonomously receives sensor triggers, and schedules space and ground assets using Internet-based technologies and service-oriented architectures. For proof-of-concept purposes, sensor triggers are received from the United States Geological Survey (USGS) to determine targets for space-based sensors. The Surrey Satellite Technology Limited (SSTL) Disaster Monitoring Constellation satellite, the United Kingdom Disaster Monitoring Constellation (UK-DMC), is used as the space-based sensor. The UK-DMC s availability is determined via machine-to-machine communications using SSTL s mission planning system. Access to/from the UK-DMC for tasking and sensor data is via SSTL s and Universal Space Network s (USN) ground assets. The availability and scheduling of USN s assets can also be performed autonomously via machine-to-machine communications. All communication, both on the ground and between ground and space, uses open Internet standards.

Surrey global networking groundstations; gathering data from constellations

Abstract SSTLs low cost nano-, micro- mini-satellites provide an affordable solution for profitable commercial space constellations. SSTL has pioneered the field of low cost small satellite technology for the past 21 years and, based on its skills, experience and resources, is now set to launch a new breed of collaborative satellite constellations which will provide operational Earth Observation. Surreys satellites normally operate autonomously with data downlink to a single ground station of 1–2 hours per day. But with the advent of constellations of satellites, Surrey has begun networking a number of customers ground stations with the Surrey Mission Operations Centre. By extending this across the globe, through the Surrey Space Club, the visibility of each spacecraft can be increased by a factor of three to six. By collaborating in this network all parties benefit from: • • increased data capacity • • timely command access • • regular telemetry acquisition International collaboration in orbit, linked through networked ground stations, creates a system synergy that enables single satellites to contribute to a practical operational Earth Observing constellation, giving significant benefits to the Surrey Space Club partners.