Z d I The First Mission of the Tethered Satellite System Table of Contents A Line To The Universe 1 The First Tethered Satellite System Mission 2 Major Tethered Satellite System Elements 6 Tether Dynamics 10 TSS-1 Science Background 14 TSS-1 Science Investigations 23 Mission Scenario 28 TSS-1 Crew 30 A Line To The Future 32 Quick Reference To Experiments And Investigators 35 For Further Reading 36 Glossary Of Abbreviations And Acronyms 37 N/ A ORIGINAL PAGE National Aeronautics and PHQTOGRAPH, Space Administration il A Line To The Universe The first Tethered Satellite System (TSS-1) will soon be launched aboard the Space Shuttle. Circling Earth at an altitude of 296 kilometers (kin), the reusable tether system will be well within the tenuous, electrically charged layer of the atmosphere known as the iono- sphere. There, a satellite attached to the orbiter by a thin conducting cord, or tether, will be reeled from the Shuttle payload bay. This will grant scientists experi- mental capabilities never before possible. On this mission, the satellite will be deployed 20 km above the Shuttle. The conducting tether will generate high voltage and electrical currents as it moves through the ionosphere and allow scientists to examine the electrodynamics of a conducting tether system. These studies will not only increase our understanding of physical processes in the near-Earth space environment but will also help provide an explanation for events witnessed elsewhere in the solar system. In addition, the Deployment of the Tethered Satellite System upward mission will explore the mechanical dynamics of teth- from the Shuttle On TSS-I allows scientists to gather ered systems, providing information that will improve data on performance, while providing an excellent future missions and possibly lead to a variety of future platform for a variety of plasma physics and electro@- =..... tether applications. namics investigations. Tethered spacecraft can be deployed toward or away from Earth. Downward deployment (toward Earth) on future missions could place the satellite in regions of MIllilllAL ".... "" the atmosphere that have been difficult to study because they lie above the range of high-altitude balloons and below the minimum altitude of free-flying satellites. A series of Tethered Satellite System flights, exploring in both directions from the Shuttle, could gather data previously impossible to obtain. Each flight would The Tethered Satellite allow scientists and engineers to conduct new experi- System has the potential to be deployed toward the ments, explore phenomena discovered through previous Earth. On such a future missions, and develop new uses for tethers in space mission, large-scale exploration. investigations of previ- ously inaccessible regions of the atmosphere could be performed. The First Tethered Satellite System Mission _%____ Mission Objectives _, _;_._r n The era of space-age tethered operations moves ._, _ $_ _ - _/7..-_._ _---_y toward reality with the launch of TSS-I. The C "_P_"_'_ _ / primary objective of this m_ss,on ts to demon- _ A_:._,_,_ _ i [ strate the technology of long tethered systems e_ efrtevat ._ in space and to demonstrate, through scien- ---_ ._i.i._ _ _,:"! " : tific investigations, that such systems are Science Goals _%_ _ useful for research. Speeding through _ _ the magnetized iono- Engineering Goals spheric plasma at almost 8 km Manipulating a satellite on a tether from the per second, a 20-kin long Launc orbiter is a unique engineering challenge, conducting • " and tether :i_%ii_y:_'_t///, t Because gravity, cenmfugal force, atmo- !_'_'a_/i_l _/ spheric drag vary with altitude, each of the should _ .. _i_: _ , two bodies in a tethered system, one orbiting create __--'____yar_ah/-_ : above the:other:is subject to different influ __: :avari= r -'='_r. __ encesi_Consequently, the primary engineering .....ety ofvery :" " " ' _ ........ goalofrss-i is to demonstrate that a satellite interesting ptasma- ii'.i,_-_i: _ -..: can be deployed, stabilized, and retrieved on a electrodynamic phenomena. These are - long tether in space and that an electrically expected to provide a variety of unique exper- i " conducting system can be operated success- imental capabilities, including the ability to fully. Tether dynamics and control are not collect an electrical charge and drive a large intuitive; while reeling out a satellite on a current system within the ionosphere, to tether is somewhat analogous to flying a kite, generate high voltages [on the order of the analogy breaks down when the environ- 5 kilovolts (kV)] across the tether at full ments in which the systems operate are com- deployment, to control the satellite potential pared. Unlike a kite in the atmosphere, the and the satellite's plasma sheath, and to gener- tethered satellite is in an_electrically charged ate low-frequency electrostatic and electro- environment and is controlled by gravity magnetic waves. It is believed that these gradient rather than aerodynamic forces. TSS-1 capabilities can be used to conduct controlled will improve our understanding of tether experimental studies of phenomena and dynamics and allow scientists and engineers processes that occur naturally in plasmas to develop more sophisticated tether control throughout the solar system, including Earth's models for future tethered missions, magnetosphere. 2 Anecessary first step toward these studies --and the primary science goal of TSS-1 -- is to characterize the electrodynamic behav- ior of the satellite-tether-orbiter system. Of particular interest is the interaction of the system with the charged particles and electric and magnetic fields in the ionosphere, includ- ing the nature of the external current loop within the ionosphere and the processes by which current closure occurs at the satellite .Liiiiiiiiiz and the orbiter. This will be investigated by a series of experiments conducted with electron accelerators and tether current-control hardware, along with a set of interdependent diagnostic instruments provided by the of the Tethered Satel!i!e System mission. thrusters will spin the satellite so that it rotates TSS- 1 investigators. Flight and science operations are controlled a quarter turn each minute, allowing data to from Johnson Space Center, while Kennedy be collected as the satellite sensors rotate Organization Space Center is responsible for integrating through different electric and magnetic fields. The Tethered Satellite System is a joint payloads into the orbiter and launching Approximately 6 hours later, the satellite venture of the United States' National the Shuttle. is fully deployed 20 km from the Shuttle. Ten Aeronautics and Space Administration An Investigator Working Group, com- hours of on-station operations begin with the (NASA) and Italy's Agenzia Spaziale Italiana posed of TSS-I Principal Investigators and satellite's spin being stopped for an orbit as (ASI, the Italian Space Agency). Based on Associate Investigators, advises NASA and data on tether system dynamics are collected. a 1984 Memorandum of Understanding ASI in the design, development, and opera- After this orbit, thrusters will spin the satellite between NASA and ASI, the Italian agency tion of TSS-1. This group develops and so that it rotates at slightly less than one full has responsibility for developing the reusable reviews all science requirements for the turn each minute. As the Tethered Satellite satellite, while NASA has responsibility mission, recommends mission profiles and System stimulates and interacts with the for developing the deployer system and the experiment sequence_; and specifies how data ionosphere, instruments in the satellite and the tether, integrating the payload, and providing should be acquired, processed, handled, and Shuttle's payload bay measure the response, transportation into space. In addition, the distributed. The Investigator Working Group determine how the Tethered Satellite System U.S. Air Force Phillips Laboratory, by agree- also oversees science activities during collects an electrical current from the iono- ment with NASA, is participating in the the flight. sphere, study the power generation properties program by providing an experiment that of the entire tether system, and characterize supports the TSS-I mission as well as Air Mission Profile the surrounding environment. Force research interests. The deployer system The Shuttle will carry TSS-1 in its payload Retrieval operations begin with the reel and the tether were developed by the Martin bay to a circular orbit where the satellite will assembly winding in the tether. The satellite Marietta Astronautics Group in Denver, be deployed spaceward on a conducting approaches to within 2.4 km of the orbiter, Colorado, and the satellite by the Alenia tether. Thus begins an adventure that could where it stops for 5 hours to gather additional Space Systems Group in Turin, Italy. revolutionize the architecture of space struc- data and stabilize the system for final Both NASA and ASI are sponsoring tures and expand the PoSsibilities for space retrieval. Retrieval resumes and crewmembers experiments to address the goals of the TSS-I investigations. take manual control for final approach mission. Research guidelines specify that The deployed mission begins when a and docking. experiments study Tethered Satellite System crew member unlatche_s the satellite and the electrodynamics and plasma interactions. deployer boom extends. Then the satellite's The experiments selected are compatible with tether-aligned