WO2011045798A1

WO2011045798A1 - Balloon decoy device and method for frustrating an active electromagnetic radiation detection system

Info

Publication number: WO2011045798A1
Application number: PCT/IL2010/000850
Authority: WO
Inventors: Dov Zahavi; Eliyahu Gamzon
Original assignee: Elbit Systems Ltd.
Priority date: 2009-10-18
Filing date: 2010-10-18
Publication date: 2011-04-21
Also published as: IL201606A0

Abstract

A balloon decoy device for frustrating an active electromagnetic radiation detection system is disclosed. The device may include an inflatable balloon that is substantially transparent to electromagnetic radiation emitted by the system. The balloon may enclose a retroreflector for reflecting the electromagnetic radiation toward a source of the radiation.

Description

BALLOON DECOY DEVICE AND METHOD FOR FRUSTRATING AN ACTIVE ELECTROMAGNETIC RADIATION DETECTION SYSTEM

FIELD OF THE INVENTION

[0001] The present invention relates to defense against electromagnetic detection systems. More particularly, the present invention relates to a balloon decoy device and method for frustrating an active electromagnetic radiation detection system.

BACKGROUND OF THE INVENTION

[0002] A missile or missile guidance system may be provided with a homing system. Some homing systems are designed to acquire and home in on a target by actively reflecting electromagnetic radiation, such as radar or laser radiation, off the target. For example, some types of missiles employ active radar guidance to acquire a target and guide the missile to the target. Such a homing system may detect a target by emitting electromagnetic radiation in a given direction of a possible target, and receiving a portion of the emitted radiation that is reflected back toward the missile. The reflected signal may be analyzed to identify the direction and range of the object or surface from which the radiation was reflected. Further analysis may be performed to determine whether properties of the reflected signal reasonably match a signal that is typical of radiation reflected from a particular type of target. A typical example of such a guidance system is an anti-ship radar guided missile.

[0003] A potential target may be provided with appropriate countermeasures for protection against an active electromagnetic homing system. For example, a device may emit a jamming signal or another signal designed to reduce the effectiveness of the electromagnetic homing system in locating the target. Chaff or another screening material may be dispersed in order to mask the target from the homing system, or to otherwise mislead the homing system.

[0004] Another possible countermeasure is to deploy a decoy target. A decoy target may be deployed at a distance from the target to mislead an active electromagnetic homing system so as to identify the decoy as the actual target. Thus, for example, a missile guided by the homing system may be induced to fly toward the decoy and miss the actual target. For example, a decoy target may be designed to reflect electromagnetic radiation emitted by the homing system back toward the source of the radiation. Typically, the decoy is designed and deployed such that a signal reflected by the decoy target is more intense than a signal reflected by the actual target. Thus, the homing system may be induced to lock onto the signal reflected by the decoy rather than a weaker signal reflected by the actual target.

[0005] In order to produce a strong reflected signal for detection by a homing system, a decoy target may be provided with one or more retroreflectors. A retroreflector is shaped so as to reflect radiation emitted by a radiation source back toward the source of the radiation. For example, a typical retroreflector may include one or more corner cube reflectors. A corner cube reflector includes three adjacent mutually perpendicular reflecting walls that are arranged in the form of a corner of a cube. A beam or ray of radiation that is incident on the concave side of the corner cube reflector is directed after two or more reflections back toward the origin of the beam or ray.

[0006] When a radiation signal from a missile homing system is incident on a decoy target that incorporates retroreflectors, a portion of the signal is reflected back toward the homing system. Typically, the signal reflected from a retroreflecting decoy is stronger than the signal that would be reflected by a typical target of similar area having a flat, rounded, or diffusely reflecting surface. Thus, a missile homing system may identify the decoy as the most strongly reflecting object in the vicinity, and thus as the likely target. In some cases, it may be necessary to simulate the shape or reflection properties of a large, extended target. In such a case, several individual decoys may be deployed in an appropriate spatial arrangement. For example, a ship may be simulated by deploying several decoys in the approximate outline of a ship.

[0007] Retroreflecting decoys have been described previously. Doron in EP 1336814 describes a decoy system for deploying decoys from a platform. Decoys are initially stored in a folded or compacted form in a container such as a mortar or artillery shell or a rocket nose cone. The container may be launched by means of a suitable launching device, such as a mortar, gun, or rocket. After the container is launched, the container may release one or more decoys in the air. Upon release, the decoys are opened from their folded form to form corner reflectors. Once opened and deployed, a decoy falls at a rate determined by its weight and by air resistance.

[0008] Billard in US 4,695,841 describes a decoy for deceiving an active electromagnetic detector, such as a detector designed to detect a ship. The decoy is delivered to a deployment location by rocket. At the location, several balloons are filled with gas. each balloon when filled lifts a panel that includes several trihedral retroreflectors.

[0009] It is an object of the present invention to provide a decoy that is deployable without the need for rockets, and that may remain aloft for an extended period of time.

[0010] Other aims and advantages of the present invention will become apparent after reading the present invention and reviewing the accompanying drawings.

SUMMARY OF THE INVENTION

[0011] There is thus provided, in accordance with some embodiments of the present invention, a balloon decoy device for frustrating an active electromagnetic radiation detection system, the device including an inflatable balloon that is substantially transparent to electromagnetic radiation emitted by the system, the balloon enclosing a retroreflector for reflecting the electromagnetic radiation toward a source of the radiation.

[0012] Furthermore, in accordance with some embodiments of the present invention, the retroreflector is initially enclosed in a collapsed state within the balloon and upon inflating of the balloon is deployed.

[0013] Furthermore, in accordance with some embodiments of the present invention, the retroreflector includes a plurality of corner cube reflectors.

[0014] Furthermore, in accordance with some embodiments of the present invention, at least two corner cube reflectors of the plurality of corner cube reflectors are oriented in different directions.

[0015] Furthermore, in accordance with some embodiments of the present invention, the decoy is configured to be buoyant in the atmosphere when the balloon is filled with a gas lighter than air. [0016] Furthermore, in accordance with some embodiments of the present invention, the gas is selected from a group of gasses consisting of heated air, helium, and hydrogen.

[0017] Furthermore, in accordance with some embodiments of the present invention, the assembly includes a reflecting foil in the form of a folded retroreflector.

[0018] Furthermore, in accordance with some embodiments of the present invention, at least two points of the reflecting foil are attached to the inner surface of the balloon.

[0019] Furthermore, in accordance with some embodiments of the present invention, the balloon when inflated is configured to provide an aerodynamic lifting force in the presence of relative motion between the balloon and a surrounding atmosphere.

[0020] Furthermore, in accordance with some embodiments of the present invention, the balloon is provided with one or more openings for filling the balloon with air in the presence of relative motion between the balloon and a surrounding atmosphere.

[0021] There is further provided, in accordance with some embodiments of the present invention, a method for frustrating an active electromagnetic radiation detection system. The method includes providing an inflatable balloon that is substantially transparent to electromagnetic radiation emitted by system, the balloon enclosing a retroreflector for reflecting the electromagnetic radiation toward the source of the radiation. The method further includes inflating the balloon with a gas lighter than air and releasing the balloon.

[0022] Furthermore, in accordance with some embodiments of the present invention, the retroreflector is initially enclosed in a collapsed state within the balloon and upon inflating of the balloon is deployed

[0023] Furthermore, in accordance with some embodiments of the present invention, the retroreflector includes a plurality of corner cube reflectors.

[0024] Furthermore, in accordance with some embodiments of the present invention, at least two corner cube reflectors of the plurality of corner cube reflectors are oriented in different directions. [0025] Furthermore, in accordance with some embodiments of the present invention, the method includes selecting the gas from a group of gasses consisting of heated air, helium, and hydrogen.

[0026] Furthermore, in accordance with some embodiments of the present invention, the assembly includes a reflecting foil in the form of a folded retroreflector.

[0027] Furthermore, in accordance with some embodiments of the present invention, at least two points of the reflecting foil are attached to the inner surface of the balloon.

[0028] Furthermore, in accordance with some embodiments of the present invention, the method includes configuring the balloon when inflated to provide an aerodynamic lifting force in the presence of relative motion between the balloon and a surrounding atmosphere.

[0029] Furthermore, in accordance with some embodiments of the present invention, the method includes inflating the balloon by towing the balloon through a surrounding atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals.

[0031] Fig. 1A shows a balloon decoy with a deflated balloon and open retroreflector, in accordance with some embodiments of the present invention.

[0032] Fig. IB shows a balloon decoy with folded retroreflector prior to deployment, in accordance with embodiments of the present invention.

[0033] Fig. 1C shows an inflated balloon decoy, in accordance with some embodiments of the present invention.

[0034] Fig. 2A shows a balloon decoy with multiple retroreflectors, in accordance with some embodiments of the present invention.

[0035] Fig. 2B shows a decoy with multiple retroreflector panels, in accordance with some embodiments of the present invention. [0036] Fig. 3 shows an airfoil shaped balloon decoy, in accordance with some embodiments of the present invention.

[0037] Fig. 4 is a schematic illustration of deployment of a balloon decoy, in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0038] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, modules, units and/or circuits have not been described in detail so as not to obscure the invention.

[0039] A decoy in accordance with embodiments of the present invention includes a retroreflector enclosed by a balloon. The decoy balloon may be stored prior to deployment in an inflated state, or may be stored in a deflated state and inflated as part of a deployment procedure. The decoy is configured to act as a countermeasure for frustrating an active detection system based on the emission and reflection of electromagnetic radiation, for example, radar or ladar (laser radar). The balloon is constructed of a material that is substantially transparent to the radiation employed by the detection system. One or more corner cube retroreflectors may be enclosed by the balloon. Each retroreflectors is constructed of a material that reflects electromagnetic radiation such as emitted by a detection system to be frustrated. Typically, a retroreflector are constructed of a metallic sheet or foil, or a non-metallic material coated with a metallic material.

[0040] Prior to deployment of the decoy, the balloon may be in a deflated state. The retroreflector, when enclosed by the deflated balloon, may be either in a fixed form or in a collapsed, or folded, form. The balloon may be inflated by being filled with a gas.

[0041] If the retroreflector is in a folded form prior to inflation of the balloon, the retroreflector may be opened, unfolded, or otherwise deployed to a retroreflecting state during or following inflation of the balloon. For example, the retroreflector may be constructed of a metallic foil. Corners or other points along the edges of the foil retroreflector may be welded, glued, or otherwise attached to the inner surface of the balloon. Attachment of the corners to the inner surface of the balloon may take place during manufacture of the decoy. For the purpose of attachment of the corners of the foil retroreflector to the inner surface of the balloon, the balloon may be temporarily inverted during manufacture. Temporarily inverting the balloon may expose the inner surface of the balloon to enable attachment of the foil retroreflector corners. When such a decoy is deployed and the balloon is inflated, inflation of the balloon may extend the attached corners or edges, thus unfolding the foil retroreflector. The shapes and dimensions of the balloon and foil retroreflector may be adapted to one another to enable proper inflation of the balloon and concurrent unfolding of the foil retroreflector.

[0042] Alternatively, a folded retroreflector may be constructed with resilient elements that extend or unfold components of the retroreflector after the balloon is inflated, or concurrently with the inflation. For example, a restraining band or other restraining element may preserve a folded configuration of a retroreflector with resilient elements. Opening the balloon, or another suitable stimulus or suitably timed remotely transmitted signal, may cause the restraining element to break, loosen, or otherwise enable the resilient elements to unfold the retroreflector. Alternatively, a folded retroreflector may be provided with actuators that extend or unfold components of the retroreflector in response to a suitable stimulus or signal after the balloon is inflated.

[0043] The balloon may be designed to maintain the decoy aloft for an extended period of time. For example, the inflated balloon may be sufficiently buoyant in air so as to hold aloft the balloon and the enclosed retroreflector. For example, the balloon may be inflated with a gas whose density is lower than the density of the surrounding atmosphere. Such gasses may include, for example, heated air, helium, or hydrogen. For example, the balloon may be provided with a heater for heating a gas, such as air, that fills the balloon so as to lower the density of the filling gas. As another example, an inflation device for inflating the balloon may include a canister of a compressed light gas such as helium. As another example, the inflation device may include a generator for generating a light gas such as hydrogen. For example, when the decoy is configured for deployment while floating in a body of water, an inflation device may include a generator for generating hydrogen from water. [0044] Alternatively to a buoyant balloon, a balloon may be shaped so as to provide an aerodynamic lifting force in the presence of relative motion between the balloon and the surrounding atmosphere. For example, part of the inflated balloon may be shaped to act as a wing or airfoil, or any other shape capable of providing aerodynamic lift. An aerodynamic lifting force may be provided then by a prevailing wind, or by towing the decoy at a suitable velocity relative to the atmosphere.

[0045] The aerodynamic shape of a towed balloon may be designed so as to minimize aerodynamic drag. Minimizing aerodynamic drag may enable increasing the sized of the towed balloon, and of a retroreflector deployed within the balloon. For example, a maximum dimension of such a minimum drag balloon may range from about half a meter to a meter. (A typical maximum dimension of balloon with typical aerodynamic drag may be about 20 centimeters.)

[0046] A towed balloon may be designed to dynamically fill with air as it is towed. For example, the leading side of the balloon may be provided with an air intake slit, vent, or opening. Towing the balloon through the surrounding atmosphere may force air into the balloon at an air pressure greater than the ambient pressure of the surrounding atmosphere. The pressurized air may thus inflate the balloon and maintain the balloon in an inflated state. The trailing side of a dynamically filled balloon may be provided with an air outlet opening. The air outlet opening is typically smaller than the air intake opening. For example, the air outlet opening may be provided to improve the aerodynamic or mechanical performance of the balloon as it is towed. For example, the air outlet opening may reduced air turbulence that may affect the motion of the towed balloon.

[0047] A decoy may be tethered to a launching platform, to a weight or anchor, or may be free floating. A tether may also include electric or optical cables for controlling various functions of the decoy, such as, for example, an inflation or heating device. A tether may also include tubing or conduit for delivering an inflating gas to the balloon of the decoy.

[0048] Several decoys may be tethered, or otherwise maintained at a substantially constant spatial arrangement with respect to one another, so as to simulate an extended object. For example, a plurality of such decoys may be maintained in a spatial arrangement that simulates the outline of a ship. Tethers holding decoys together may be provided with stiff elements to maintain a desired distance between the decoys.

[0049] A decoy in accordance with embodiments of the present invention may be deployed from a platform. For example, a decoy may be launched from a ground based, marine, or a raised or airborne platform by inflating the decoy balloon and releasing it aloft. In this manner, the decoy may rise to a deployment point above or near the platform. In the case of an airborne platform, the decoy balloon may be jettisoned so that it remains hovering in the air. Alternatively, a container containing one or more decoys, possibly also containing one or more tethers and objects designed to serve as anchors, may be launched or delivered to a delivery point at a desired distance from the platform. At the delivery point, the container may release the decoy. Concurrent with release, a triggering device or signal may cause the decoy to deploy at a deployment point above or near the delivery point.

[0050] Reference is now made to the accompanying Figures.

[0051] A balloon decoy in accordance with embodiments of the present invention may be stored with an inflated or deflated balloon prior to deployment. In the event that the balloon is inflated prior to deployment, the retroreflector is enclosed by the deflated balloon prior to inflation. When enclosed by the deflated balloon, the retroreflector may be either folded or open. Inflation device 20 is attached to balloon nozzle 18.

[0052] Fig. 1A shows a balloon decoy with a deflated balloon and open retroreflector, in accordance with some embodiments of the present invention. Decoy 10 includes deflated balloon 12' enclosing open retroreflector 14. Sections of deflated balloon 12' may be draped over sections of retroreflector 14. Deflated balloon 12' may be filled with gas through nozzle 18. Nozzle 18 may attach to inflation device 20. Inflation device 20 may include, for example, a pump for pumping atmospheric air into deflated balloon 12', a canister of compressed gas, a gas generating device, or any other device known in the art for inflating a balloon. Inflation of deflated balloon 12' causes sections of deflated balloon 12' to expand outward away from retroreflector 14. Alternatively, decoy 10 may be stored while filled with gas. In such a case, deploying decoy 10 may require simply releasing decoy 10 to the air, releasing a ballast weight, or heating a gas in the balloon to enable the balloon to float in the air. [0053] .Fig. IB shows a balloon decoy with folded retroreflector prior to deployment, in accordance with embodiments of the present invention. Decoy 10 includes deflated balloon 12' enclosing folded retroreflector 14'. For example, folded retroreflector 14' may include a shaped foil of radiation reflecting material. At least two corners 16 of folded retroreflector 14' are welded or otherwise attached to the inner surface of deflated balloon 12'. Inflation device 20 may inflate deflated balloon 12' with gas through nozzle 18. Inflating deflated balloon 12' may unfold folded retroreflector 14', or may trigger, or be followed by, activity to unfold folded retroreflector 14'.

[0054] Fig. 1 C shows a balloon decoy with inflated balloon and open retroreflector, in accordance with some embodiments of the present invention. Balloon 12 has been inflated, for example, by inflation of a deflated balloon. Retroreflector 14 is open. For example, a balloon of a balloon decoy such as shown in Fig. IB may be inflated to form inflated balloon 12, and a folded retroreflector opened to form open retroreflector 14. For example, inflation of balloon 12 may cause corners 16 to separate from one another. Separation of corners 16 from one another may unfold and open retroreflector 14. Typically, inflation of balloon 12 may cause decoy 10 to be buoyant relative to the surrounding atmosphere. For example, the inflating gas may substantially consist of a low density, lighter than air, gas such as hydrogen or helium. Alternatively, the inflating gas may consist of air or another gas that is heated so as to reduce the density of the gas. For example, inflation device 20 may include a heating device for heating a gas that fills balloon 12, or that is filling balloon 12.

[0055] A free floating decoy may drift with the wind, and eventually move so far away from a platform to be protected so as to cease to provide protection. Drift in the position of deployed decoy 10 may be limited by tethering decoy 10 to one or more anchor points with tether 22. Anchor points may include, for example, a structure attached to a deploying platform or a platform to be protected, a weight or float separate from the platform, or another decoy. When one or more decoys are tethered to one another, at least one of the tethered decoys is typically tethered to an external object or point. A tether 22 may include electrical, fiber optic, or other power supply or communications cables. For example, operation of inflation device 20 may be controlled through an electrical cable included in tether 22. Alternatively, operation of inflation device 20 may be controlled via a wireless signal may be transmitted directly to a receiver incorporated in, or associated with, inflation device 20. Alternatively, operation of inflation device 20 may be controlled by a timer, manually, or by sensors or other devices that sense or detect environmental or other conditions. For example, a hydrogen gas generator may be activated upon detection of contact with water. Alternatively, tether 22 may incorporate a tube through which a separate inflation device may deliver an inflating gas to balloon 12.

[0056] A single retroreflector may need to be maintained in a particular orientation in order to function properly as a decoy. Alternatively, a decoy may be provided with several retroreflectors, each facing a different direction. Fig. 2A shows a balloon decoy with multiple retroreflectors, in accordance with some embodiments of the present invention. Multiple retroreflector decoy 24 includes multiple retroreflector assembly 26. Multiple retroreflector assembly 26 includes individual retroreflectors 26a, each oriented in a different direction. In this manner, rotation of multiple retroreflector decoy 24 may not affect its function.

[0057] Alternatively, the multiple retroreflector assembly may include one or more panels, each panel including an arrangement of individual retroreflectors. Fig. 2B shows a decoy with multiple retroreflector panels, in accordance with some embodiments of the present invention. Panel retroreflector decoy 28 includes retroreflector panel assembly 34. Retroreflector panel assembly 34 includes retroreflector panels 36, each oriented in a different direction. Each retroreflector panel 36 includes an arrangement of individual retroreflectors 36a.

[0058] As an alternative to a buoyant balloon decoy, a balloon decoy may be heavier than air but shaped so as to provide lift in the presence of wind or other relative motion between the decoy and the surrounding atmosphere. For example, a balloon decoy may be provided with wings, airfoils, or other lifting shapes, or may itself be shaped in the form of an airfoil or wing. Fig. 3 shows an airfoil shaped balloon decoy, in accordance with some embodiments of the present invention. Airfoil decoy 30 includes airfoil shaped balloon 32. Airfoil shaped balloon 32 encloses a retroreflector 14, or, typically, an alternative multiple retroreflector assembly. Branched tether 38 may include lateral tether extensions 38a. Multiple tether extensions 38a may enable maintaining a desired orientation of airfoil decoy 30, for example, with respect to the wind or to direction of motion of a towing platform. In order that airfoil shaped balloon 32 provide lift, airfoil decoy 30 may be deployed, for example, in a windy region with predictable winds. Alternatively, airfoil decoy 30 may be towed behind a moving platform or vehicle so as to maintain a desired relative motion between airfoil decoy 30 and the surrounding atmosphere. Relative motion between airfoil decoy 30 and the surrounding atmosphere may provide a lifting force to maintain airfoil decoy 30 at a desired altitude.

[0059] Airfoil shaped balloon 32 may be provided with one or more air intake openings 37. When airfoil decoy 30 is towed such that air intake openings 37 are on the leading edge of towed airfoil decoy 30, air may be forced into airfoil shaped balloon 32. Forcing air into airfoil shaped balloon 32 may inflate, and maintain the inflated state of, airfoil shaped balloon 32. Airfoil shaped balloon 32 may be further provided with one or more air outlet openings 39.

[0060] Fig. 4 is a schematic illustration of deployment of a balloon decoy, in accordance with some embodiments of the present invention. For example, one or more balloon decoys may be deployed from a land based or sea based platform, for example, a ship such as platform 40. For example, a balloon decoy 10a may be stored in a canister 42, or similar confining container, prior to deployment. Balloon decoy 10a may be stored in either an inflated or a deflated state. Prior to deployment, balloon decoy 10a is inflated and canister 42 is opened, releasing balloon decoy 10a. After release, balloon decoy 10a may be deployed above or near platform 40, for example, by buoyant or aerodynamic lifting forces. As another example, inflation device 20 may be activated to inflate balloon decoy 10b, causing balloon decoy 10b to deploy above or near platform 40.

[0061] As another example, a balloon decoy may be released from an airborne platform 46. A balloon decoy 10c may be released, or jettisoned, from an appropriate decoy container 48 carried by airborne platform 46. Balloon decoy 10c may be released, for example, with its balloon inflated. Alternatively, balloon decoy 10c may be released with its balloon deflated, the balloon inflating, for example, as the balloon falls to a desired deployment altitude. [0062] It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope.

[0063] It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the present invention.

Claims

1. A balloon decoy device for frustrating an active electromagnetic radiation detection system, the device comprising an inflatable balloon that is substantially transparent to electromagnetic radiation emitted by the system, the balloon enclosing a retroreflector for reflecting the electromagnetic radiation toward a source of the radiation.

2. A device as claimed in claim 1, wherein the retroreflector is initially enclosed in a collapsed state within the balloon and upon inflating of the balloon is deployed.

3. A device as claimed in claim 1, wherein the retroreflector comprises a plurality of corner cube reflectors.

4. A device as claimed in claim 3, wherein at least two corner cube reflectors of said plurality of corner cube reflectors are oriented in different directions.

5. A device as claimed in claim 1, wherein the decoy is configured to be buoyant in the atmosphere when the balloon is filled with a gas lighter than air.

6. A device as claimed in claim 5, wherein the gas is selected from a group of gasses consisting of heated air, helium, and hydrogen.

7. A device as claimed in claim 1, wherein the assembly comprises a reflecting foil in the form of a folded retroreflector.

8. A device as claimed in claim 7, wherein at least two points of the reflecting foil are attached to the inner surface of the balloon.

9. A device as claimed in claim 1, wherein the balloon when inflated is configured to provide an aerodynamic lifting force in the presence of relative motion between the balloon and a surrounding atmosphere.

10. A device as claimed in claim 9, wherein the balloon is provided with one or more openings for filling the balloon with air in the presence of relative motion between the balloon and a surrounding atmosphere.

11. A method for frustrating an active electromagnetic radiation detection system, the method comprising:

providing an inflatable balloon that is substantially transparent to electromagnetic radiation emitted by system, the balloon enclosing a retroreflector for reflecting the electromagnetic radiation toward the source of the radiation;

inflating the balloon with a gas lighter than air and releasing the balloon.

12. A method as claimed in claim 11, wherein the retroreflector is initially enclosed in a collapsed state within the balloon and upon inflating of the balloon is deployed

13. A method as claimed in claim 11, wherein the retroreflector comprises a plurality of corner cube reflectors.

14. A method as claimed in claim 13, wherein at least two corner cube reflectors of said plurality of corner cube reflectors are oriented in different directions.

15. A method as claimed in claim 11, comprising selecting the gas from a group of gasses consisting of heated air, helium, and hydrogen.

16. A method as claimed in claim 1 1, wherein the assembly comprises a reflecting foil in the form of a folded retroreflector.

17. A method as claimed in claim 16, wherein at least two points of the reflecting foil are attached to the inner surface of the balloon.

18. A method as claimed in claim 11, comprising configuring the balloon when inflated to provide an aerodynamic lifting force in the presence of relative motion between the balloon and a surrounding atmosphere.

19. A method as claimed in claim 1 1, comprising inflating the balloon by towing the balloon through a surrounding atmosphere.