Aeronautics and astronautics – Spacecraft – With fuel system details
Reexamination Certificate
2000-09-08
2002-05-14
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Spacecraft
With fuel system details
C244S158700
Reexamination Certificate
active
06386484
ABSTRACT:
TECHNICAL FIELD
The present invention is a tether having the special technical feature of multiple primary load-bearing lines and normally slack secondary lines. These primary and secondary lines are connected together with knotless, slipless interconnections so the tether maintains high strength and some of the lines can be cut without failure of the tether. This type of failure resistant tether may be safely operated near the ultimate failure load of the material from which it is constructed. Such high strength, fail-safe tethers have industrial utility both on Earth and in harsh environments, such as outer space, where a single-line tether experiences a substantial risk of being cut by debris impact.
These tethers' structures, methods of making, deploying and using them; including the specific industrial applications of an electrodynamic tether system to deorbit satellites and a low Earth orbit to lunar surface tether transport system are all part of the general innovative concept of the invention.
RESERVATION OF RIGHTS
This application is subject to an assignment of certain rights to Gary Pansey as defined by an agreement between Gary Pansey and Tethers Unlimited dated Jul. 4, 1996. This application may also be subject to certain rights of the U.S. government as a result of contracts between the U.S. government and the inventors.
BACKGROUND ART
The background art includes tether structures, knotless, slipless connections between lines, tether fabrication and deployment, and space systems using tethers.
Tethers
A tether was originally a rope or chain used to fasten an animal so that it grazed only within certain limits. However, there are many specialized tether uses including bungie jumping and weather balloons. Short tethers have been used for decades in space to attach astronauts to their spacecraft.
In 1974 Professor Guiseppe Colombo, holder of the Galileo chair of astronomy at the University of Padua in Italy, proposed using a long tether to support a satellite from an orbiting platform. U.S. Pat. No. 4,097,010, which issued to Professor Colombo and Mario Grossi on Jun. 27, 1978, teaches a satellite connected by means of a long tether to a powered spacecraft. Colombo actively pursued the design of a tethered satellite system.
Several NASA experiments, such as the two Small Expendable Deployer System (SEDS 1 & 2)) and the Plasma Motor Generator (PMG) used tethers in space. SEDS used a nonconducting tether. The PMG used a 500-meter conducting tether. The Tethered Satellite System flights in 1992 and 1996 (TSS-1 & 1R) used a 22,000-meter conducting tether.
On the TSS-1 mission the tether deployed only 260 meters (853 feet) before the deployer failed. On the TSS-1R the tether was deployed 17,000 meters. In the SEDS-2 flight, a 0.8-mm diameter, 20,000-meter long braided single-line tether was deployed to study tether dynamics and lifetime. Orbital debris or a meteoroid severed this tether in less than four days.
Electric potential is generated across a conductive tether in motion across the Earth's magnetic field lines. Electromagnetic forces acting on a conductive tether in orbit can make the tether system behave like an electric motor or generator, to exert useful force to alter the state vector of any mass attached to the tether.
In the TSS-1R flight, the conducting single-line tether was severed after five hours of deployment. This failure was caused by an electric arc produced by the 3,500 volts of electric potential generated by the conductive tether's movement through the Earth's magnetic field.
The Tether Physics and Survivability (TiPS) satellite consists of two end masses connected by a 4,000-meter long non-conducting tether. This satellite was deployed on Jun. 20, 1996 at an altitude of 1,022 kilometers (552 nautical miles). Its tether is an outer layer of spectra 1000 braid over a core of acrylic yarn. The yam will “puff” its outer braid to two millimeters to “give it a larger cross section to improve its resistance to debris and small micrometeoroids”, according to the National Reconnaissance Office (NRO), which is a sponsor of the TiPS mission. As of Jan. 13, 1997 the TiPS tether had survived 207 days.
These experiments, all using single line tethers, illustrate the problem that long-duration and high-value tether missions require a tether capable of surviving single-point failures due to space impactors, electric arcing, or localized material defects.
In 1991, one of the present inventors, Robert Hoyt, invented a lightweight net-like structure that provides many redundant load-bearing paths. A number of primary load bearing lines running the length of the structure are connected periodically by diagonal secondary lines. Where the secondary lines intersect the primary lines, they are firmly connected by knots. The secondary lines are connected only to the primary lines. At either end of the structure, a support ring enforces the cylindrical spacing between the primary lines. The secondary lines are designed with a small amount of slack. These secondary lines are only put under load if a primary line fails. This invention was disclosed in 1992 (Forward, R. L., “Failsafe Multistrand Tether Structures for Space Propulsion”, AIAA paper 92-3214, 28
th
Joint Propulsion Conference, Nashville, Tenn., 1992 (hereinafter “1992 AIAA Document”). This structure was named a “Hoytether”. The term “Hoytether” is used throughout the remainder of this disclosure for this type of structure.
The 1992 Hoytether design teaches that the normally slack secondary lines have half the cross-section (0.707 the diameter) of the primary lines. There are twice as many secondary lines as primary lines, thus the mass of the secondary lines is equal to the mass of the primary lines. In an undamaged Hoytether, the primary lines carry the entire load, while none of the secondary lines are under load.
While the survival probability of a single-line tether decreases exponentially with time, the Hoytether can maintain a high, i.e. greater than 99 percent, survival probability for periods of months or years (Forward and Hoyt, Paper AIAA 95-2890, 31
st
Joint Propulsion Conference, July 1995).
Slipless High Strength Line Connections
The Hoytethers and apparatus that use Hoytethers taught by the present invention require that the primary lines be firmly connected to the secondary lines, without slipping, at their crossover )unctions. The original Hoytether design did not teach the use of slipless connections. It used knots to connect the primary lines to the secondary lines. Knots cause stress concentrations, which limit the ultimate strength of the overall tether structure. It is essential that the interconnections between the primary and secondary lines be slipless to ensure proper redistribution of the loads when a segment of a primary line fails. The secondary lines in the original Hoytether design were not connected to each other.
Manufacturing companies that make fishing nets use three different knotless, slipless methods of interconnecting two lines. One is used for braided lines; one for twisted lines and one for crocheted lines. Hoytether uses lines braided of three or more smaller lines. These braids must be interwoven where they cross each other to form knotless, slipless interconnections. Alternatively the Hoytether lines may be knitted together. There is a lack of references in the field of braiding. Most of them are instruction books for hand braiding. Appendix B of the Final Report of NASA Contract NAS8-40545 (hereinafter ‘NASA Report-1995’, which is incorporated by reference), written by the present inventors, provides a summary of braiding fundamentals at pages B-1 to B-5. The information in NASA Report-1995 is proprietary in accordance with FAR 52.227-20 until Jun. 14, 1999. No prior art known to the inventors teaches a method of slipless knotless interconnection between a larger diameter primary line and two smaller diameter secondary lines.
Tether Fabrication
The Hoytether is essentially a tri-axial net structure, with ‘primary’ lines running along the length o
Forward Robert L.
Hoyt Robert P.
Dinh Tien
Dula Arthur M.
Jordan Charles T.
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