Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2002-03-07
2004-07-06
Dinh, Tien (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
Reexamination Certificate
active
06758443
ABSTRACT:
THE FIELD OF THE INVENTION
The present invention generally relates to satellite orbital propulsion and satellite power generation systems, and more particularly to a method and apparatus of employing a conducting tether to control satellite system state, such as to produce an electrodynamic propulsion force to change the orbit of a satellite through interaction between an electric current in the tether and an external magnetic field, or to generate electric power onboard the satellite.
BACKGROUND OF THE INVENTION
Space tethers have attracted a lot of attention in the past 40 years. Many researchers have contributed to the theory of tether behavior in orbit. The theory has been applied and proved in a number of space flights involving tethers attached to spacecraft.
In 1966, Gemini 11 and 12 manned spacecraft were attached with a tether to a rocket stage and demonstrated libration and rotation modes of tethered motion.
In 1992, TSS-1, the Shuttle-based Tethered Satellite System, including a 550-kg satellite and a 20-km electrically conductive tether, was partially deployed from the Shuttle orbiting at an altitude of 296 km. The measurement of the voltage-current profiles shed new light on electric behavior of conducting tethers in orbit.
In 1993, SEDS-I, the Small Expendable Deployment System, including a 26-kg mini-satellite on a 20-km non-conductive tether, was successfully deployed downward from a Delta rocket second stage. SEDS-I was a flight experiment to test the deployment of a long tether by means of a light and simple deployment mechanism and the deorbit and reentry of the mini-satellite after the release of the tether from the Delta stage. The 20-km non-conductive tether was the longest structure ever deployed in orbit.
Also in 1993, PMG, the Plasma Motor Generator, including a 500-m-long electrodynamic tether, was deployed from the Delta second stage with the primary goal of testing power generation and thrust by means of an electrodynamic tether. This mission was the first example of a propulsion system for space transportation that did not utilize any propellant, but rather achieved propulsion by converting orbital energy into electrical energy (deorbit) and electrical energy into orbital energy (orbit boosting).
In 1994, SEDS-II, the Small Expendable Deployment System (second flight), with the same equipment as SEDS-I, was utilized for a longer and more ambitious mission. SEDS-II was stabilized along the local vertical at the end of deployment and kept attached to the Delta stage to study acceleration environment. During the extended mission phase, the deployed SEDS-II was used to study the survivability of a thin tether to micrometeoroid impacts. During the extended mission phase, SEDS-II also provided important data on the micrometeoroid risk as the tether was cut at the 7-km point three days after the completion of the one-day primary mission.
In 1996, TSS-1R, a reflight of TSS-1 was attempted. The mission was terminated before due time by an electrical arc that severed the tether just before the end of deployment. Nevertheless, it was an important mission for tethered satellites, because it showed that the electrodynamic tethers were more efficient at collecting electrons than most theories and models predicted, providing valuable data on electric performance of electrodynamic tether systems.
In 1996, TiPS, the Tether Physics and Survivability Experiment, including a 4-km-long passive tethered system for the investigation of the long-term survivability of tethers in the space environment, was successfully started. This system proved that a sufficiently fat tether can survive for a very long time the harsh space environment, and also provided valuable data on the long-term passive internal damping of tether librations.
In 1999, the Advanced Tether Experiment (ATEx) began deployment in orbit. About 18 minutes into deployment, at a deployed length of only 22 meters, the tether went slack, bent, and triggered several tether departure angle optical sensors. This led to the tether experiment being automatically ejected, to protect the host vehicle. The slackness occurred just after sunrise and may have resulted from a thermal transient on the thin polyethylene tape tether.
In 2002, ProSEDS, the Propulsive Small Expendable Deployer System, is scheduled to deploy 10 km of Dyneema tether followed by 5 km of uninsulated wire from a Delta-II stage to test the electrodynamic propulsion capabilities of the tether.
“Tethers in Space Handbook,” First Edition, NASA Office of Space Flight, NASA Headquarters, Washington, D.C., 1986, edited by P. A. Penzo and P. W. Ammann, provides summaries of various applications and features of space tethers, including methods to change orbital elements with electrodynamic tether propulsion and methods to control the attitude dynamics of such tethers. The basic concept is to vary the electric current in the tether based on the estimate of the tether state obtained from measurements of certain tether system parameters.
The following patents cover certain details of electrodynamic tether usage.
U.S. Pat. No. 6,116,544, entitled “Electrodynamic Tether and Method of Use,” issued Sep. 12, 2000, to Forward et al., describes electrodynamic tethers for deorbiting out-of-service satellites.
U.S. Pat. No. 6,260,807, entitled “Failure Resistant Multiline Tether,” issued Jul. 17, 2001, to Hoyt et al., discusses various multistrand tethers to improve strength and stability.
U.S. Pat. No. 4,923,151, entitled “Tether Power Generator for Earth Orbiting Satellites,” issued Mar. 1, 1988 to Roberts et al., discloses use of an electrodynamic tether as a power generator for earth orbiting satellites.
U.S. Pat. No. 4,824,051, entitled “Orbital System Including a Tethered Satellite,” issued Jan. 12, 1987 to Engelking, discloses use of an electrodynamic tether attached to a satellite to compensate for the air drag and the orbit degradation.
U.S. Pat. No. 3,868,072, entitled “Orbital Engine,” issued Feb. 25, 1975, to Fogarty, discloses a tether to rotate/revolve one mass about the other and provide energy.
U.S. Pat. No. 3,582,016, entitled “Satellite Attitude Control Mechanism and Method,” issued Jun. 1, 1971, to Sherman, discloses a study about transverse waves and rotational dynamics. The '016 Patent does not disclose electrodynamics or use of magnetic fields.
Most of the early estimates of performance of electrodynamic tethers were based on static stability considerations, where non-stationary processes were ignored. In recent years, however, more attention has been given to dynamic stability considerations, where complex non-stationary dynamic response to real perturbations is taken into account.
V. V. Beletsky and E. M. Levin in “Dynamics of Space Tether Systems,” Advances in the Astronautical Sciences, v. 83, AAS, 1993, described many modes of inherent instabilities of electrodynamic tethers that are observed even in equatorial circular orbits, and even when dynamic models neglect magnetic field variations along the orbit. The Beletsky and Levin reference points out that it would be virtually impossible to operate electrodynamic tether systems anywhere close to the boundaries of static stability, because of a very strong, uncontrollable or hardly controllable dynamic instability in these regions. It has been shown in this study that realistic expectations for safe electric current levels must be typically lowered by an order of magnitude compared to static levels because of dynamic instabilities.
More evidence of rigid dynamic instability constraints was accumulated, as more detailed and realistic simulations were performed.
J. Pelaez, E. C. Lorenzini, O. Lopez-Rebollal, and M. Ruiz in “A new kind of dynamic instability in electrodynamic tethers,” AAS 00-190, AAS/AIAA Space Flight Meeting Jan. 23-26, 2000, pointed out that instability is inherent in any uncontrolled electrodynamic tether motion and simply cannot be avoided.
R. P. Hoyt and R. L. Forward in “The Terminator Tether: Autonomous Deorbit of LEO Spacecraft for Space Debris Mitigation,” AIAA 00-03
Carroll Joseph A.
Levin Eugene M.
Dicke Billig & Czaja, PLLC
Dinh Tien
Tether Applications, Inc.
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