Experimental Satellite System (XSS)

The Air Force Research Laboratory (AFRL) is building and demonstrating a new class of low-cost satellites - referred to as "micro-satellites" - weighing less than 100 kilograms. These new satellites are being flown under the Experimental Spacecraft System (XSS) Microsatellite Demonstration Project. In conjunction with the Air Force Space Command, Air Force Space and Missiles Systems Center, the Naval Research Laboratory, and industry, missions are underway to actively evaluate future applications of micro-satellite technologies to include: inspection; rendezvous and docking; repositioning; and techniques for closein proximity maneuvering around on orbit assets.

The Air Force is conducting the Experimental Satellite System (XSS) series to demonstrate increasing levels of microsatellite technology maturity. The XSS-10 is the first microsatellite in the series and was launched on schedule during Fiscal Year 2003. It demonstrated semi-autonomous operations and visual inspection in close proximity of an object in space-in this case a Delta II upper stage. The success of the XSS-10 flight demonstration was the first step in applying micro-satellite technology to military space missions and paved the way for more ambitious experiments on XSS-11 and future programs

XSS-10 view of Delta II rocket: An Air Force Research Laboratory XSS-10 micro-satellite uses its onboard camera system to view the second stage of the Boeing Delta II rocket during mission operations Jan. 30. (Photo courtesy of Boeing.)

The XSS-10, which cost roughly $100 million, is the stepping stone for future micro-satellite technology demonstrations. The Boeing Delta II rocket and Global Positioning lifted off 29 January 2003 from Cape Canaveral Air Station, FL, carrying the Air Force Research Laboratory's XSS-10 micro-satellite. During its 20-hour mission, the 68-pound XSS-10 separated from the second stage of the Delta II to demonstrate its ability to inspect and navigate around the second stage while in orbit 800 kilometers above earth. The team initiated the primary mission pass and ejected the XSS-10 from the second stage of the Delta II rocket. The separation went as planned and the XSS-10 drifted about 200 meters from the second stage. The team then visually acquired the second stage with the integrated camera system.

This mission called for the XSS-10 to acquire and track the second stage, then perform three intervals of inspection maneuvers at varying distances from the Delta II as it circled 800 kilometers above the Earth. Taking directions from its mission control software, the XSS-10 positioned itself at distances ranging from 100 meters to 35 meters from the Delta II. Each pass took about 12 minutes, with about 90 minutes between passes. Ground-based controllers received real-time images relayed from the XSS-10's space-to-ground link system during the mission. Telemetry was briefly lost between the micro-satellite and the ground tracking station at the end of the primary mission sequence, but picked up again through a different ground station within 10 minutes. The team then successfully put the micro-satellite into sleep mode and reactivated it as planned, to test its on-board software. While small in size, the 65-pound satellite had a big mission in space.

Key Technologies

• Lightweight propulsion system
• Guidance, navigation & control (GNC)
• Miniaturized communications system
• Primary lithium polymer batteries
• Integrated camera and star sensor

Milestones

• Successful mission duty cycle test - Sep 1998
• GNC & Digital Signal Processor software delivery - Dec 1998
• Mission operations development - Jul 1999
• Avionics delivery - Oct 2000
• Micro-satellite delivered to Kirtland Air Force Base - Nov 2000
• Environmental testing and space qualification - Jul 2001
• Integration with Delta II launch vehicle - Sep 2001
• Launch at Cape Canaveral Air Force Station - Jan 2003

The micro-satellite demonstrated key technologies that included miniature communication systems, a lightweight propulsion system, advanced lithium polymer batteries, and autonomous operations through specially developed software. AFRL's use of lithium polymer batteries, a first ever in space, is an added demonstration scientists will study to evaluate how well the batteries perform in the vast unknown. Swales Aerospace developed the Sconce Payload Platform for XSS-10 as an interface between the XSS-10 micro-satellite and the Delta-II 2nd Stage, procuring Starsys Qwknuts for use as part of the system. Two Qwknuts were installed on the Sconce to hold the deployment table vertical for flight through the vibration-intense ascent. On-orbit, upon receiving an initiation command from the 2nd stage, the XSS-10 experiment "fired" the Qwknuts (in parallel) and rotated the deployment table outward, where it was released to begin its mission. The Starsys Research Qwknut is a fast acting separation nut for release of loads up to 3,000 lbf. The Qwknut may be reset in under a minute by pushing an integral reset lever, allowing mission engineers to functionally test the same hardware that is to be flown.

The Air Force Research Laboratory/Boeing XSS-10 Team was nationally honored by the American Institute of Aeronautics and Astronautics (AIAA). The team was awarded the Space Systems Technical Team Award for 2003, which is presented to recognize outstanding achievements in the architecture, analysis, design and implementation of space systems. The award was presented in September at the AIAA Space 2003 Convention, Long Beach, Calif. AFRL's Space Vehicles Directorate, Kirtland Air Force Base, N.M., with Air Force Space Command developed the 65-pound XSS-10. The first on-orbit experimental micro-satellite, with a program valued at $100 million, launched aboard a Boeing Delta II rocket Jan. 29, from Cape Canaveral Air Force Station, Fla. During its 20-hour mission, the XSS-10 successfully performed a series of on orbit maneuvers around the second stage of the Delta II. Other key contractor teams members were Boeing Rocketdyne, Octant Technologies, Jackson and Tull, and Swales Aerospace.

The XSS-11 will demonstrate autonomous operations and provide experience with command and control in proximity operations to another space object. The Autonomous Rendezvous in Low-Earth Orbit high-precision autonomous rendezvous system will allow two spacecraft to approach and meet each other in close proximity. This technology could significantly enhance in-space rendezvous for future sample return missions. Scientific Systems Company's contributing partners include the NASA Mars Program at JPL and the Air Force Research Laboratory, Kirtland Air Force Base, NM.

The Air Force's XSS-11 Microsat was scheduled for launch in 2004. The 138-kilogram XSS-11 blasted off on 10 April 2005 from Vandenberg Air Force Base aboard a Minotaur rocket. During its mission, the XSS-11 craft will approach inactive US satellites or old rocket bodies. At each rendezvous, the satellite will burn its engines to move around the object while taking pictures. XSS-11 will take instructions from the ground on where to find a target. An on-board planner will control maneuvers around the target. Ovre the course of the mission, XSS-11 will rendezvous with six to eight objects, the first of which will probably be the upper stage of the Minotaur rocket.