Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
2001-04-06
2002-10-01
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C244S158700
Reexamination Certificate
active
06459205
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a propulsion device particularly for a spacecraft, comprising a plasma chamber in which a plasma is producible in a propellant, and a focussing arrangement for focussing an electromagnetic radiation field into a focussing region in the plasma chamber in order to produce the plasma.
It also relates to a method of forming shock waves, particularly for propelling a spacecraft, by producing a plasma in a propellant, wherein an electromagnetic radiation field is focussed into a focussing region of a plasma chamber to produce plasma in the propellant.
It has been proposed for example in U.S. Pat. No. 3,825,211 to propel a spacecraft by means of a laser beam, the laser being installed on earth or in a satellite. For this purpose the spacecraft has a parabolic cylindrical reflector, and a propellant is fed to a focal axis of that reflector.
Similar arrangements are described in U.S. Pat. Nos. 3,818,700, 4,426,843 and 5,152,135.
The laser beam produces a plasma in the propellant, which expands and thus in turn accelerates the propellant. This is then converted into propelling energy to propel the spacecraft by a suitable device such as a nozzle arrangement.
With the development of pulsed high-powered lasers the high spatial coherence of laser radiation enables the radiation energy to be transmitted into the plasma chamber over distances of the order of magnitude of 100 to 1000 km.
As a laser-assisted propulsion system need not carry its energy generator with it and may even be installed quite far away from the propulsion system, the starting mass of a spacecraft provided with such a propulsion system can be kept low. In addition higher specific momentums can be produced with laser propulsion systems than with conventional propulsion systems based on chemical combustion.
It is the object of the invention to provide a propulsion device and a method of forming shock waves, which is highly efficient and controllable, respectively.
BRIEF SUMMARY OF THE INVENTION
This object is achieved in accordance with the invention, in that there is arranged in the plasma chamber a plasma ignition arrangement for bringing a material (the ignition medium) which lowers the plasma breakdown threshold in the propellant into the focussing region.
In accordance with the invention it is possible to produce a plasma at a pre-defined location in the focussing region, namely substantially where the material which lowers the plasma breakdown threshold is positioned or introduced, the plasma in turn leading to the formation of a pressure wave. Plasma ignition thereby takes place in a controlled manner and particularly at a point-like location, that is to say, the time and place of ignition are guaranteed to be highly reproducible.
As the electromagnetic radiation field and particularly laser radiation is absorbed better by a plasma than by a neutral propellant, the defined plasma production also increases propelling efficiency; the invention greatly improves the coupling in of the energy of the electromagnetic radiation field into the propulsion device. In particular the invention makes it unnecessary to feed an additional absorber medium to the plasma chamber as proposed e.g. in U.S. Pat. Nos. 3,818,700 or 4,036,012.
The fact that the plasma and consequently plasma pulses are produced at a pre-defined location in the plasma chamber, owing to the introduction of the material which lowers the plasma breakdown threshold in the propellant into the focussing region, makes it possible to control the thrust vector of the propulsion device, as the pre-defined location of plasma production in the focussing region is controllable. This can be achieved in a simple way by positioning the threshold-lowering material in the focussing region in a controlled manner. The position of a spacecraft provided with the propulsion device in accordance with the invention can thereby also be controlled.
With the location of plasma formation being controllable it is also possible to inject the electromagnetic radiation field at a transverse angle of incidence to the axis of the plasma chamber and thus to inject it transversely to the axis of a spacecraft, as the thrust vector of the propulsion device can accordingly be appropriately tilted by controlling the pre-defined location of plasma production. It is then unnecessary for the focussing arrangement to be aligned accurately with the incident electromagnetic radiation field. As a result the coupling of the energy of the electromagnetic radiation field into the plasma chamber can be improved, as the coupling field can be correspondingly guided; it may e.g. be advantageous for the radiation field not to be guided through a propellant discharge region of the drive device in order to avoid energy losses through absorption.
Misfiring is largely avoided by use of the material which lowers the plasma breakdown threshold in the propellant. Such misfiring starts in particular at a wall of the plasma chamber and leads to degradation and/or denudation of material in that structure. Moreover use of an ignition medium greatly reduces fluctuations in the magnitude and direction of the thrust vector of the propulsion device, which are observed without such a medium.
It is especially advantageous for the material which lowers the plasma breakdown threshold to be a metal. In particular the material which lowers the plasma breakdown threshold is copper. For example the breakdown threshold in air has been found to be about three orders of magnitude higher than the corresponding value for copper vapour over a copper surface in air. In the case of a CO
2
laser with a wavelength of 10.6 &mgr;m given a pulse duration of 10 &mgr;s the breakdown threshold in air is about 15 kJ/cm
2
and that in copper vapour about 10 J/cm
2
. In this connection see also H M Musal, “Pulsed laser initiation of surface plasma on metal mirrors”, Bennett, H E, Glass, A J, A H Guenther, eds, Damage in laser materials: 1980, Nat. Bur. Stand. (U S) Spec. Publ. 620 (1981), page 227.
It is particularly advantageous for the plasma ignition arrangement to be arranged in the plasma chamber so displaceably that the material which lowers the plasma breakdown threshold can be positioned within the focussing region. In this way a plasma pulse can be produced at a reproducible, pre-defined location in a controlled manner within the plasma chamber, thereby allowing thrust vector control of the drive device. Such thrust vector control enables an angular momentum to be generated, as a means of changing the position e.g. of a missile. The corresponding change in the angular momentum of the missile depends on how the resultant thrust vector is located relative to the centre of gravity of the missile. Rotating movements of the missile about an axis transverse to the direction of flight can then also be obtained by changing the mass distribution in the missile with no change in the resultant thrust vector. Since the thrust vector is controllable according to the invention, i.e. it can in particular also be maintained constant, there is thus a further method of changing the position e.g. of a missile.
In a particularly advantageously designed embodiment the plasma device includes a pin made of a material which lowers the plasma breakdown threshold. This pin then acts as an ignition pin. It can be positioned in the plasma chamber and especially in the focussing region in a simple manner to control the thrust vector of the propulsion device (e.g. in order to adjust the position of a spacecraft). The actual pin material may be used as a fuel when the pin evaporates; the material vapour can then act as an absorber to improve plasma production and also directly help to generate thrust. Plasma is produced in a substantially defined manner on a surface of the pin. Contact between the propagating plasma and an inner wall of the plasma chamber is thereby avoided.
It is beneficial for the pin to be arranged pivotably in the plasma chamber in order to control the thrust vector and thus the position e.g. of a spac
Mayerhofer Wilhelm
Riede Wolfgang
Schall Wolfgang
Zeyfang Eberhard
Deutsches Zentrum fuer Luft-und Raumfahrt e.V.
Lipsitz Barry R.
McAllister Douglas M.
Minh D. A.
Wong Don
LandOfFree
Propulsion device and method of generating shock waves does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Propulsion device and method of generating shock waves, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Propulsion device and method of generating shock waves will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2976933