Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2000-12-06
2002-12-10
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C244S158700, C244S164000
Reexamination Certificate
active
06491258
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to payload transporting, and more particularly to a process and apparatus for moving materials and personnel from the surface of the earth into space or from one location in space to another location.
2. Description of Related Art
The conquest of space has always been severely limited by the inability to move materials and personnel (payload) from the surface of the earth to space. At first, this limitation was substantially technical, but with the development of chemical rockets and improved guidance systems, technical issues have ceased to be the primary driver. Instead, the primary limitation today is the cost (often measured in dollars per pound) of moving payload from the surface of the earth to orbit, to the moon, or to other planets. Currently, the most modern launch systems achieve launch costs no better than $4,000-$10,000 per pound for moving payloads from the ground to low earth orbit.
Currently, chemical rockets employing liquid and/or solid fuels are the primary methods used for placing objects in orbit and transferring objects from one orbit to another. To achieve orbit, massive quantities of propellant (oxidizer and fuel) are required. For example, for the space Shuttle, 3.8 million pounds of propellant are required. The propellant must be carried with the vehicle as well as the payload as it travels to orbit. The fraction of the total vehicle weight that must be allocated to propellant for the rocket is a function of the required velocity change (&Dgr;V) and the engine specific impulse (I
sp
), and is determined by the following equation:
M
Propellant
M
GLOW
=
1
-
EXP
[
-
Δ
V
g
·
I
SP
]
The engine I
sp
is a measure of engine performance and currently is on the order of 455 seconds for high performance chemical rockets. To go from earth to the lowest stable orbit requires a &Dgr;V change (energy input) of 32,000 ft/s and thus a vehicle exceeding 90% propellant is required.
Achieving such a large propellant fraction is not easy, and meeting this requirement drives the size of the vehicle. If the &Dgr;V requirements (energy required) can be reduced, the size of the vehicle and the amount of propellant required by the vehicle can be reduced. This, in turn, will reduce the cost of placing payloads into orbit.
The problem is further exacerbated by the requirement to move payloads from the lowest stable orbit to higher orbits in the same or different planes. Payloads left in the lowest stable earth orbits are not useful, so some additional energy is always expended; the exact amount varies from launch to launch. To transfer a payload from one orbit to another requires an additional &Dgr;V change above the initial launch energy, approximately 13,000 ft/sec to transfer from low earth orbit to geosynchronous orbit (a common destination). To achieve such an orbit transfer, the transfer vehicle, also known as an “upper stage”, must be approximately 59% propellant (by mass). While a 59% propellant fraction is much easier to achieve for the upper stage alone, propellant is still consumed. Also adding to cost, the upper stage vehicle is typically not reusable. The major cost driver comes from the fact that the upper stage transfer device has already been lifted to low earth orbit as a “payload” on the main stage, and the fractions are thus multiplicative, making the original vehicle on the ground less than 1% useful payload.
While improvements to rocket performance (Isp and thrust-to-weight) increase the useful payload fraction a small amount, and increased reusability and ground handling can reduce costs substantially, the cost of moving payload to low earth orbit using chemical rockets will likely, in the foreseeable future, not fall below $1000/lb. To further reduce launch costs, a substantially different system will be required. It will be necessary to take advantage of natural orbital physics to reduce the required energy to move payloads into orbit. By reducing the energy required, and therefore the fuel fraction, the useful payload can be increased, resulting in a substantial reduction in overall launch costs.
Historically, many methods for adding or subtracting &Dgr;V from orbiting payloads have been conceived. One class of such methods pursuant to the present invention consists of entities utilizing the “tether”, or long single strand of material connecting two points in orbit. Tethers have typically been classified as propulsive, de-orbit, spinning or lifting.
Propulsive tethers can be used in low earth orbits in conjunction with the earth's magnetic field to produce thrust (i.e., adding &Dgr;V). Electrical current is run through a conducting wire oriented vertically to the Earth's surface, producing an electromagnetic field around the tether. The interaction of the tether's electromagnetic field and the earth's magnetic field results in an electrodynamic force parallel to the direction of travel that can be used to propel the tether and its host vehicle. Pursuant to the current invention, many variants of propulsive tethers remain strong candidates as primary re-boost engines for the Space Elevator.
De-orbit tethers can also be used in low earth orbits in conjunction with the earth's magnetic field. The de-orbit tether has current induced into a conducting wire (oriented vertically relative to the earth's surface) from the earth's magnetic field. The current produces power, which is converted into heat through the resistance of the tether's conducting material or some resistance means connected to the circuit. The heat dissipation extracts kinetic energy from the system, thereby reducing &Dgr;V. In the present invention, the re-boost electrodynamic tethers could be reconfigured to function as a de-orbit tether if required to slow the Space Elevator.
Spinning tethers add or subtract &Dgr;V by actively changing the angular velocity of the payload. The payload is attached to the launcher motor by the tether. The motor increases or decreases the angular velocity of the payload and then releases the payload. The present invention does not employ spinning tether motion or attributes, though spinning tethers represent a potential competitive system.
Lifting tethers add or subtract &Dgr;V by transporting the payload to higher or lower orbits while maintaining the angular momentum of the lifting tether system. The payload is translated along the tether to the desired orbit and then released. The structure of the tether is typically a single strand of material oriented vertically to the surface of the planet orbited. Many such designs, including several which are anchored to planetary surfaces are noted in the references. The earth-orbiting tether disclosed in October 1994 in SAE Technical Paper Series #942120 (Aerotech '94, Los Angeles, Calif.) represents the state of the art for lifting tether designs. It consists of an elevator, two crew-inhabitable, variable-location, endpoint stations, and a crew-inhabitable, variable location, midpoint station. The location of the earth orbiting tether's center of mass is controlled by moving the elevators, the endpoint stations, and the midpoint station, and by use of an on-board ion propulsion system. The present invention would be classified in the “lifting” tether category and represents a substantial improvement in the state of the art for movement of payloads in space, as outlined in the detailed description.
Against this background of known technology, the inventor has devised a permanent orbiting upper stage, or Space Elevator, which will allow payload transfer from space vehicles in sub-earth orbits to space vehicles in higher orbits using a substantially smaller amount of energy while also minimizing cost of operation.
OBJECTIVES AND SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a novel method and apparatus for moving payload from sub-earth orbits to higher altitude orbits using
Boyd Robert Raymond
Thomas Dimitri David
Holzen Stephen A
Lockheed Martin Corporation
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