The present application claims priority from United States Provisional Patent Application No. 62044488, filed on September 2, 2014.

TECHNICAL FIELD

The field of the invention is subterranean vehicles, i.e. vehicles that can travel

underground and burrow through soil or other media.

BACKGROUND ART

There is a widespread and increasing need for inexpensive means to access underground sites, or to reach remote sites by travelling underground, and to perform any of a variety of operations at, or enroute to, such a site. The need may arise, for example, in civilian and military applications such as:

• Rescue missions,

• Geological, hydrological or archaeological research and exploration,

• Mining and underground construction,

• Laying pipes and cables

• Seismic monitoring,

• Intelligence operations,

• Destroying underground spaces and structures,

There is likewise a need for means to access sites within other solid media, such as industrial waste, trash heaps or even organic and biological matter. In the sequel, all references to ground and soil should be understood to possibly also mean such other media.

The means would preferably be a self- propelling vehicle that travels through the ground. According to any particular application, it may carry a payload, such as a sensor, survival means or a bomb; it may also pull behind it a flexible object, such as a tow rope, an electric cable or a communication cable. For some applications there may also be an additional need for the vehicle to return from the site, for carrying back information or specimens gathered there or just to be re-used.

Certain configurations of a vehicle to meet the needs have been suggested, but are deemed inadvantageous or ineffective. In one such configuration, for example, the vehicle comprises a main body, whose outer surface is in contact with the surrounding soil and generally formed so as to glide along the soil while remaining in a fixed attitude; in addition, the vehicle comprises one or two rotatable members, also in contact with the soil and configured to propel the vehicle. A major disadvantage or this configuration is the drag that the soil exerts on the main body, resulting in energy loss, and lack of attitude constancy, due to possible rotational slippage of the body.

DISCLOSURE OF THE INVENTION

It is the objective of the present invention to provide a self- propelling subterranean vehicle that meets the stated needs and is efficient and controllable.

In a minimal configuration of the present invention there is provided a self-propelling subterranean vehicle (STV), consisting of an elongated capsule that comprises two members, arranged in tandem along the capsule and rotatable about its length axis in mutually opposite senses. The outer surface of each member is formed as, or has attached thereto, a helical flighting (formerly referred to as a ridge) - preferably with a diameter that diminishes toward the outer end of the member - so that the member appears generally similar to a wood screw or an auger. The helical flightings of the two members are of mutually opposite senses; that is, the flighting of one member is formed as a right-hand helicoid, while the flighting of the other member is formed as a left-hand helicoid. Preferably the two rotating members are attached to each other by a mutual bearing assembly. Also preferably a motor inside the capsule is configured and operative to simultaneously rotate the two members in mutually opposite senses - possibly through a gear transmission assembly. In operation, when the capsule is in the ground and the two members rotate, by the action of the motor, the helical flightings engage and wind through the surrounding soil, thereby propelling the capsule forward; since both the helicoids and the rotations of the two members are in mutually opposite senses, both members contribute to the forward propulsion. When the motor rotation is reversed, the rotation of both members is reversed as well - thereby similarly propelling the capsule backward. The operation of each member is similar to that of a wood screw or of an earth-drilling auger. However, in contra-distinction to the latter devices, where the driving rotational moment is supplied by an external stationary agent (e.g. a hand with a screwdriver or a driving mechanism), the driving moment for each rotational member of the STV of the invention is provided by the internal motor, counterbalanced by the reactive moment of the other member (which similarly rotates in the opposite sense). Also in contra-distinction to an earth- drilling auger, the STV of the invention is, in general, not pulled out periodically to remove soil (which action would form a hole), but rather is let to advance continuously.

The motor may be powered by a battery, carried inside the capsule, or from an external stationary source through an electric power-carrying cable pulled by the capsule.

Operational control may be effected from a control module within the capsule and/or from a stationary above-ground controller through a communication cable pulled by the capsule. Control preferably includes means to detect whether one of the members rotates unduly fast, indicating disengagement from the surrounding soil, and to effect remedial action.

In variations of the minimal configuration the capsule may comprise more than two rotatable members, similarly connected in tandem, wherein preferably any pair of adjacent members is rotatable in mutually opposite senses.

In general, the STV is configured to carry a payload. The payload may include various devices, to be activated at an underground site or upon exiting the ground, or objects or materials to be deployed and left there; it may also include specimens or devices collected from an underground site, to be carried in a return journey of the STV. Devices to be activated may include instruments, such as, for example, a measuring instrument or a sample collector. Objects to be deployed may include, for example, sensors, signal sources or objects having a military mission. Such payloads are generally carried within the capsule. Another form of a payload may be, for example, a cable that needs to be layed underground (for example, underneath an existing structure); such a payload would usually be pulled by the STV from an entry point to an exit point.

In a group of more advanced configurations an STV capsule comprises also a core, which is a generally non-rotating member (previously referred to as a stationary member), interposed between and/or within a pair of oppositely rotating members, or rotors, such as disclosed hereabove. Preferably, the core has a cylindrical form, at least in its middle section, and each rotor is attached to the core through one or more bearing assemblies. In some configurations the core extends to, or forms, one or both ends of the capsule, the corresponding end or ends of the rotors possibly being truncated and having a matching hole. In variations of this configuration, a capsule may have fewer than two rotors or it may have more than two rotors; in some variations the location of a rotor need not be at the end of the core but may rather be at or near its middle. In certain configurations a core may consist essentially of two parts in tandem, which are normally joined together but may be separated at a site, to enable carrying out specific missions.

The core may contain or carry some of the internal components of the STV, such as the motor, the gear transmssion, the control unit and/or the battery. It may additionally carry one or more navigational sensors. In some of the configurations the core may also carry a payload, such as described above. In the latter case, the outer surface of a middle section of the core is preferably exposed and preferably provided with a window, through which some of the payload objects may be introduced to the surrounding soil and possibly retrieved therefrom.

In certain configurations of a capsule that includes a core, there may be more than one motor to drive the rotors; preferably there is one motor exclusively driving each rotor. Beside simplifying the transmission mechanism, this arrangement is advantageous in some control functions, as described below.

Where the core extends to the rear end of the capsule, forming its tail, it may be configured to have attached thereto any of (a) a steering assembly, (b) a trailer, (c) a payload cable or tow rope and (d) an umbilical cable assembly (all of which are described below). A steering assembly at the tail of a capsule may include tiltable rudder-like elements, movable to, or holdable in, any tilt angle by means of a controllable steering mechanism. Such an assembly is operative to affect pitch- and yaw angles of the capsule through interaction of the rudder-like elements with trailing soil and thus enables steering the STV, that is - controlling the direction of its forward motion.

A trailer may be a module that is attachable to the tail of a capsule , thus following it as it travels forward. It may contain or carry a payload and may be detachable at any chosen site underground, to be left there while the STV continues to travel.

The end of a cable may be attachable to the tail of a capsule, to be pulled from an entry point to an exit point, as described above. Similarly, the end of a tow rope may be attachable to the tail of a capsule, to be pulled from an entry point to an exit point and susequently used to pull, for example, a pipe from the entry point.

An umbilical cable, generally comprising power-transmission wires and/or

communication wires, may be attachable near its end to the tail of a capsule (the actual ends of the constituent wires being electrically connectable to the respective modules inside the capsule), thus serving to carry power to the STV and two-way signals between the STV and a ground station. The cable generally extends from a reel at the launching site and trails the STV as it advances.

In some configurations of a STV according to the present invention, two or more capsules, each configured with a core, are linked end-to-end in tandem, to form a trainlike STV. The linking between each pair of adjacent capsules is preferably by means of joints that are configured so that the angle between the capsules' longitudinal axes is variable, while the roll angles of the cores of the two capsules (about their respective longitudinal axes) remain mutually locked. In some of these configurations each capsule in the train may comprise two or more rotors, as described above, or, in alternative configurations, any two adjacent capsules may have a single rotor, the rotors of the two capsules having helical flightings of mutually opposite sense and being rotatable in mutually opposite sense.

A joint between adjacent capsules in a train-like STV may be configured with a steering mechanism that is controllably operative to force the angle between the longitudinal axes of the capsules to assume any given value (within a range) in any given transverse plane. The effect of such operation is to cause the STV to travel along a circular path, of a commensurate radius, thus changing its direction of travel. It is noted that this steering capability of an STV by means of inter-capsule joint mechanisms presents an alternative solution to that provided by the tail rudders mechanism described above.

A rotor, in any of the configurations described above , may optionally be modified, wherein the continuous helical flighting is replaced by a series of fins, arranged along a similar helicoid surface. Each fin is slidingly or pivotally attached to the body of the rotor so that it may protrude radially to a variable extent; the degree of protrusion is controllably affected through an appropriate mechanism. An alternative arrangement is for the fins to be spring loaded and to be thus pressed against the soil for engagement, wherein softer soil would permit greater pentration by the fins, whereas harder soil would cause them to contract but press against it with greater force. The overall effect of the variably protruding fins is to form a helical flighting of a variable outer diameter - which may be advantageous in properly engaging soil of varying density or fluffyness or where voids are prevalent. When encountering such situations, the extent of fin protrusion is automatically adjusted for optimal engagement of the fins with the surrounding soil, thus avoiding ineffective or uncotrolled rotation of the rotor and achieving orderly axial propulsion of the STV. As an alternative option, a capsule may be equipped, prior to a mission, with any of a variety of rotors, varying in the diameter and/or the pitch of the flighting, to suit the expected soil characteristics. Also extendable fins, such as described above, may be arranged to selectively form flightings of various pitches.

For the case of encountering relatively dense or hard soil, there is optionally provided a soil softening device, such as a drill that is rotatably attached to the front end of a STV capsule and driven by a motor inside the capsule. The drill serves to break up the soil in the path of the STV, making it more amenable to be sliced and engaged by the rotors' flightings and less resistant to their rotation. As a further option, there may be provided a duct lengthwise through the capsule, by which soil crushed by the drill may be tranported to the rear of the STV, thereby clearing a passageway for its forward travel. Other means for loosening or softening the soil ahead of the STV may include, for example, a vibrating hammer or a water jet. In general according to the present invention, operation of the STV, including travel motion, is controlled through an electrical control system, which may include an onboard control module and/or (if a umbilical cable is employed) a control unit at a ground station. The control system generally receive signals from any of a variety of sensors and outputs signals to the main motors (which drive the rotors) and to any other mechanism on board, such as a steering mechanism, payload delivery- or collection mechanism, drill motor and flighting fins actuators. The control system preferably includes one or more stored programs for directing its control operations. Control operations are of three main categories: (1) driving the propulsion mechanism (mainly the rotors), (2) navigation and (3) mission-directed operations (including deployment of the payload).

The rotational speed of each rotor is controlled to effect orderly propagation of the STV in face of varying soil conditions and so as to maintain economic use of power.

Normally, rotation of all the rotors is maintained at the same speed (each in its appropriate sense - clockwise or counterclockwise). Such control is facilitated by the employment of a dedicated motor for each rotor, as described above for some

configurations. The latter also facilitates controlling the roll angle of the core, if any, of the capsule, preferably maintaining it at an essentially upright position - which may be important for navigational operations and for certain mission-directed operations. In configurations that include rotors with fins, the degree of fin protrusion may be controlled so as to maintain proper propulsion at a desired rotor speed in face of varying soil characteristics, thus, for example, avoiding slippage, on the one hand, and overly resistance, on the other hand.

Navigation may be carried out with the aid of dedicated on-board devices, which may sense gravitational direction and the direction of North (e.g. magnetic or gyroscopic compass), from which the current attitude (i.e. pitch- and yaw angles) of an STV capsule may be calculated. Other devices (possibly using sonic or electromagnetic waves or employing gamma-ray sensors) may be instrumental in determining the absolute location of the STV, e.g. its depth below ground level. Optionally, external beacons (i.e. devices emitting, for example, sonic or electromagnetic waves) may be deployed at chosen locations near ground level, to which on-board sensors would be responsive for determining geographic location of the STV. Current location data may also be continuously calculated, by employing an odometer and integrating, or accumulating, attitude data along the path of travel (i.e. so-called dead reckoning). All resulting location- and attitude data are used, in conjunction with stored programs, to calculate control commands to any steering mechanism in the STV so as to direct it in the desired course of travel.

The control system may also include sensors to sense charateristics of surrounding soil and/or to detect impassable obstacles and may be programmed to maneuver the STV according to the outputs of such sensors. Such maneuvers may include, for example, repeated back-and-forth motion of the vehicle, vibrational- or hammer-like effects in the rotors and directing the vehicle in a by-pass course.

The invention also contemplates various means for launching the STV into the ground before it commences self propulsion therein. One class of such launchers are hollow cylindrical devices from which a capsule according to the invention emerges by the action of a pushing member or by enabling the capsule to self propel by engaging a matching helical structure inside the cylindrical device. Another class of launchers are projectiles, each containing a capsule according to the invention, that may be dropped from an aircraft or shot from a mortar or configured as a rocket missile; such a projectile is configured so that its head may open prior to hitting the ground and so that the projectile thereafter becomes anchored to the ground and lets the capsule self propel therein.

Overall operation of the STV, or possibly of a collection of STVs, varies according to the mission and according to the configuration of any one STV. In some missions the STV travels only one way - either to an underground site or to a ground level site remote from the launching site; in some missions it may return by propagating backward, retracing its original path of travel; in yet other missions it may return to the launching site by propagating forward in a looped path. Following are some non-exhaustive examples: 1. To lay a cable underneath a ground obstacle (such as a structure or a river), a STV equipped with a rear attachment device, to which an end of the cable is attached, is launched into the ground horizontally from a suitably deep hole and is programmed to travel horizontally to a point beyond the obstacle, pulling the cable behind it. 2. To carry emergency supplies to trapped miners or avalanche victims, a STV with a suitable payload compartment is launched toward the site, where it may be retrieved by the trapped persons. Optionally it may be relaunched in a return path to carry messages.

3. To deploy geological or intelligence-gathering devices, a suitably equipped STV is launched from ground and programmed to stop at a number of specified sites, at each site inserting a sensor into the surrounding soil. Alternatively, one or more trailers, each carrying one or more devices, are attached in tandem to a STV capsule; the latter is programmed to detach one trailer at each site.

4. To collect soil samples, a suitably equipped STV is launched from ground and programmed to stop at a number of specified sites, at each site employing a sample- gathering tool, and to return with the collected samples to the launching site.

5. To destroy an underground target, a STV loaded with an explosive charge, is launched by means of a mortar shell and is programmed to proceed a certain distance in a certain direction and then to detonate the charge.

Clearly many more different operations and missions are possible for a subterranean vehicle according to the invention, in any of the configurations described or combinations thereof or any other configurations.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described, by way of examples, in terms of specific

embodiments of various configurations, with reference to representative non-exhaustive illustrations, of which -

Figures 1A and IB are external views of a basic configuration of a subterranean vehicle (STV) according to the invention - indicating, respectively, two directions of

propagation.

Figure 2 A is a longitudinal sectional view of the STV of Fig. 1 and Figure 2B is an enlarged trimetric view of a portion thedreof.

Figures 3A and 3B are an external view and a longitudinal section, respectively, of a variation of the configuration of Fig. 1; Figure 3C is an enlarged trimetric view of a portion thedreof. Figure 4A is a trimetric view of another configuration of the STV and figure 4B is an external view thereof, accompanied by two enlarged sectional views.

Figure 5A is a trimetric view of a variation of the configuration of Figs.4; Figures 5B and 5C are, respectively, an exploded view and a longitudinal sectional view thereof.

Figures 6A-6D illustrate steering apparatus for the configurations of Figs 4 and 5, wherein Fig. 6 A is a trimetric view of the rear part of the STV, Fig. 6B is a partial cutaway view thereof and Figs. 6C and 6D are, respectively, vertical and horizontal longitudinal sections thereof.

Figures 7A-7C illustrate optional apparatus, enabling towing of external objects, wherein Fig. 7A is an overall trimetric view and Figs. 7B-C are trimetric views showing details of the coupling mechanism.

Figures 8A and 8B illustrate optional capability for the configurations of Figs 4 and 5 of obtaining power from, and communicating with, a ground station, wherein Fig. 8A is a schematic view of the overall system and Fig. 8B shows a longitudinal section of the STV with the added capability.

Figure 9A is a trimetric view of another configuration of an STV according to the invention, based on a plurality of capsules, each configured as in Figs. 4 or 5; Figure 9B shows a detail of the coupling between the capsules.

Figure 10A shows a variation of the configuration of Figs. 9 and Figure 10B shows another variation thereof;

Figures 11A-11C show, by way of example, additional apparatus for stowing, deploying and retrieving tools and objects within a STV; Fig. 11 A is a trimetric external view, while Figs. 1 IB and 11C illustrate, in cutaway detail view, stowage state and

deployment state, respectively, of a representative tool.

Figure 12A is a trimetric external view of a further variation of the lead capsule of the configuration of Fig. 10B, suitable for stowing and deploying some large objects;

Figures 12B and 12C are a trimetric view and an exploded sectional view, respectively, of the module - separated into two parts; Figure 12D illustrates schematically, as an example, a mode for utilizing the configuration of Figs. 12A-12C in an exemplary military mission. Figure 13A illustrates, in trimetric view, a rotor with a variable-diameter flighting, suitable for various configurations of a STV according to the invention; Figures 13B and 13C are cross sectional views of the rotor of Fig. 13 A, showing the flighting in a state of large diameter and small diameter, respectively; Figure 13D is a sectional view of the rotor, showing detail of the diameter-changing drive mechanism.

Figures 14A and 14B illustrate, in an external view and an enlarged sectional view, respectively, a front drill, serving as a soil crusher and adaptable to various

configurations of an STV according to the invention.

Figures 15A and 15B illustrate schematically apparatus and mode for launching a STV according to the invention into the ground.

Figures 16A and 16B illustrate schematically another apparatus and mode for launching a STV according to the invention into the ground.

BEST MODE FOR CARRYING OUT THE INVENTION

Turning first to Figures 1 and 2, there is shown schematically - in an overall view and in a longitudinal section view , respectively - an embodiment of a first configuration of a self propelling vehicle (STV) according to the present invention. It is seen to comprise basically a hollow oblong cylindrical capsule 10, generally similar in overall shape to a torpedo, that is divided lengthwise into two essentially similar members 20 and 30, mutually joined through a bearing or a set of bearings 40 so that the two members are mutually rotatable, the rotation being essentially about the central longitudinal axis of the capsule. The two rotating members will be rererred to in the sequel also as rotors. The bearings 40 may be seen in greater detail in the enlarged view of Figure 2B. The member on the left, which may be thought of as the fore member 20, serves generally as a container for payload, while the member on the right, which may be thought of as the aft member 30, serves generally as a service module.

Attached to each member 20 and 30 and wound around it is a helicoidal flighting 28 and 38 respectively, the combination looking generally similar to an auger. The flighting is formed so as to penetrate the soil surrounding the capsule and to continuously cut and follow a conforming path therein when the corresponding member rotates, thus propelling that member in an axial direction. The helicoids of the two members have mutually opposite senses and therefore rotating them in mutually opposite senses, as indicated by the vertical arrows in Fig. 1 A, will cause the two members to be axially propelled in the same direction (indicated by the horizontal arrows), as they indeed must, since they are coupled together. That mode of rotation is automatically achieved, whenever the flightings of both members are engaged by the surrounding soil, by the action of a differential rotational mechanism described below. It is noted that, since the pitches of the two helixes in the illustrated embodiment are equal, the rotational speeds of the two members with respect to the ground, during operation, are necessarily equal (though in opposite senses). It is further noted that if the pitches of the two helixes were different from each other, the ratio between their rotational speeds would be

commensurately different from one. Also of note is that, since the driving motor in the present embodiment is of the direct-current type, the absolute speed of rotation of the two members (and hence - the speed of travel of the STV) may vary as a function of resistance exerted by the soil (as well as of the voltage applied to the motor).

Looking at Fig, IB, it is pointed out that when the voltage applied to the DC motor is reversed, the sense of the differential rotation between the two parts is also reversed (as indicated by the vertical arrows) and, as a result, the propulsion will be in the opposite axial direction, as indicated by the horizontal arrows. This ability may be utilized for various purposes: For example, the STV may be directed to thus return to its launch site. As another example, the STV may be commanded to perform back-and-forth

maneuvering in order to overcome a hard site in the soil. Yet another possibility is for the voltage to be applied to the motor in bursts - causing a hammer-like propulsion effect.

The outer diameter of the spiral flightings and their respective pitches are generally design choices and depend on the characteristics of the soil to be traversed and on the type of mission. The diameter of the flighting is preferably tapered toward one or both ends of the capsule.

As may be seen in the sectional view of Fig. 2A, and in greater detail in the enlarged trimetric sectional view of Fig. IB, there are disposed within the service module 30 a DC motor 33, a controller 32 and a battery 31. The battery supplies 24 volt power to the controller, which in turn applies a variable voltage to the motor 33. Also disposed in the service module 30 is reduction gear transmission mechanism 34, whose input shaft is coupled to the rotor shaft of the motor 33. The output shaft of the transmission mechanism 34 is coupled to a drive shaft 37 that extends to the fore member 20 and is fixedly attached thereto be means of clamp 27. Rotation of the motor 33 thus causes mutual rotation between the two members 20 and 30. As noted above, if the the flightings of the two rotors have equal helicoid pitches and if both of them are fully engaged by the surrounding soil, then the rotational speeds of the two members (i.e. rotors) 20 and 30 would be equal, though in opposite senses (opposite rotational directions). The magnitude of the resulting differential rotational speed will generally be proportional to the voltage applied to the DC motor and inversely proportional to the friction between the flighting and the soil and to the effective resistance encountered by the soil to propagation of the vehicle.

In some types of soil there is a possibility of encountering small voids or regions of considerable reduction in soil density. In such locations it may happen that the condition of both flightings being engaged by the soil, mentioned above, may not be entirely met. If, for example, the fore member encounters a void, thus preventing its flighting from being engaged by the soil, it would then freely turn, at the full speed allowed by the motor, while the aft member remains stuck; no propulsion is then effected. To overcome such situations, several alternative configurations are contemplated, to be described herebelow. One way of decreasing the likelihood of such a situation, in the case that the voids are relatively small, is to simply increase the length of the capsule and its members so that each member is longer than the expected length of the void.

In a preferable alternative configuration, illustrated in Figures 3, the capsule may again be of increased length; however it is divided lengthwise into more than two members - five in the illustrated example - which, moreover, need not have identical lengths. The sequential members 41-45 are made to be rotatable alternatingly in the two opposite senses, as indicated by the vertical arrows in Fig. 3A. The rotational drive is similar to that depicted in Fig. 2, but all members rotatable in one or the other sense are rotationally locked together. As a result, the void may be larger than half the length of the capsule; it is sufficient that only a pair of oppositely rotating members be engaged by the soil for them to rotate at equal speed (as explained above for the two-member configuration) and to effect axial propulsion. It is noted that the multi-member configuration, especially where the number of members is odd, has the additional advantage of preventing precession.

A rotational mechanism for a five-member capsule is schematically shown in Figure 3B and, in greater detail, in Figure 3C (which shows, as an example, member 44 and its connections with member 43 and 45). The five members 41-45 are rotationally joined, in sequence, through bearing assemblies 40. In addition, members 41, 43 and 45 are mutually joined by rods 46 and clamps 47. A motor 33 is fixedly attached inside the central member 43. An output shaft 37, rotationally coupled to the motor 33 through a reduction gear assembly, protrudes from both sides of the motor into members 42 and 44. Within each of these two members, the shaft is attached to a small gear 34, which engages a ring gear 35 in a planetary transmission assembly,the ring gear 35 being fixedly and concentrically attached to the body of member 42 or 44 . A similar mechanism may be deployed for capsule configurations with any number of members.

Turning now to Figure 4, there is shown - in trimetric view in Fig. 4A and in a side view in Fig. 4B - another configuration of the STV. The STV comprises a capsule 100, which includes three major parts - a core member (or briefly "core") 110 and two rotatable members (to be referred to as "rotors'), 120 on the left and 130 on the right; the rotors include each a helical flighting 128 and 138 respectively - wound in mutually opposite senses. As before, we consider in this instant the STV to propagate normally to the left abd thus its left end to be the vehicle's front end, or fore , and its right end to be the vehicle's rear end, or aft; other members of the STV will be similarly qualified as needed. The body of each rotor has an essentially conical shape, but may also vary from that; the diameter of each flighting is preferably tapered accordingly. It is noted that in variations of this configuration (some to be discribed below), one or both of the rotors may be truncated at the end.

In an enlarged longitudinal section D-D (below the side view) the core 110 is seen to essentially form the middle part of the capsule 100, but some of its members, such as cylinders 112 and 113, extend almost the full length of the capsule - within the rotors 120 and 130. It is noted that in variations of this configuration (some to be discribed below) in which a rotor is truncated, a corresponding core member may extend to the end of the rotor or beyond. The rotors 120 and 130 are rotationally attached to the core 110 by means of ring bearings sets 124 and 134 respectively. A DC motor 140, fixedly disposed within core 110, receives driving electric current from a battery 150 through a controller unit 152. It is noted that in some derived configurations (such as to be described below), electric current may also be supplied from a ground station through a umbilical cable. The motor may rotate rotor 120 through a reduction gear assembly 141, a shaft 143 and planetary gear assemblyl45; similarly it may concurrently rotate rotor 130 through a reduction gear assembly 142, a shaft 144 and planetary gear assemblyl46. The reduction gear assemblies 141 and 142 cause identical reduction ratios but differ from each other in that they cause shafts 143 and 144 to rotate in mutually opposite senses, which causes also the rotors 120 and 130 to rotate in mutually opposite senses. An enlarged cross sectional view B-B of the front rotor 120 (to the right of the side view) shows the planetary gear assembly 145, the small gear being attached to shaft 143. Also seen in this view is the front cylindrical member 112, the bearing 124 and the flighting 128.

Attention is drawn also to Fig. 5B (to be discussed below), in which similar planetary gears are shown in trimetric view.

Operation of the STV of Fig. 4 is similar to that of the previous configurations, in that rotation of the motor causes the rotors to rotate in mutually opposite senses, thus propelling the STV forward or backward, depending on the sense of rotation of the motor. Operation of the STV of Fig. 4 differs, however, from that of the previous configurations, in that the additional major part - the core - does not necessarily rotate, but generally remains in an essentially steady roll attitude with respect to the ground. The advantages of this arrangement are:

(1) Various sensors may be deployed within, or attached to, the core that sense its position and/or attitude with respect to the world; signal sources for external detection may similarly be deployed. Any of these may be used for gathering navigation

information.

(2) In some derivative configurations, to be described below, a port may be included, through which payload instruments and objects may be deployed outside the vehicle.

(3) In some derivative configurations, to be described below, various objects, such as a trailer vehicle, a umbilical cable and tow line, may be attached to the rear end of the STV.

(4) In some derivative configurations, to be described below, a plurality of similar capsules may be flexibly attached to each other.

(5) In some derivative configurations, to be described below, steering mechanisms may be added, to steer the STV along a desired course or to avoid obstacles.

(6) In a derivative configuration to be described below, the STV may be configured to launch a missile.

Turning now to Figure 5, there is shown - in trimetric view in Fig. 5A, in an enlarged exploded cutaway trimetric view in Fig. 5B and in an enlarged longitudinal sectional view in Fig. 5C - a variation of the configuration of Fig. 4. The illustrated configuration differs basically from the former in that (1) the rear rotor 130 is truncated and the rear cylindrical member 113 of the core 110 reaches the vehicle's rear end and (2) there are two motors, rather than one, each driving a corresponding rotor. It is noted that other configurations may adopt only one or the other of these different features.

The capsule 100 in the configuration of Fig. 5 is identical in construction to that of Fig. 4 except for the two enumerated features as follows:

(1) Rear rotor 130 is truncated and has a hole 136 at its end. It is noted that in some configurations also the front rotor and the front end of the core may be similarly modified.

(2) A set of two motors, 140a and 140b, rather than a single motor 140 (Fig. 4), is configured to independently rotate rotors 120 and 130 respectively - through similar respective reduction gear assemblies 141 and 142, shafts 143 and 144 and planetary gear assemblies 145 and 146. Both motors receive electric current through the controller 152.

The above first enumerated feature enables the attachment of various external objects to the rear end of the STV, or the attachment of several capsules end-to-end, as will be described below - conveniently enabling advantages 3-5 listed above with reference to Fig. 4. The above second enumerated feature enables conveniently keeping the core in upright (or any other desired) roll attitute, let alone keeping it from continuously rotating - thus maintaining advantages 1, 3 and 5 listed above with reference to Fig. 4. This may be carried out, for example as follows: A gravitational sensor (not shown) is fixedly deployed within the core 110 to continuously sense the vertical direction; any deviation from verticality is transmitted to the controller, which accordingly varies the difference between the voltages applied to the two motors, causing a comensurate difference between their speeds, which in turn causes the core to rotate until reaching an upright attitude (at which point the deviation sensed by the sensor becomes null); such a correction may be generated as a corrective transient or constantly to counteract any bias in the rotational mechanisms (which may be caused by internal inaccuracies or by varying soil conditions).

Turning now to Figure 6, there is shown - in partly cutaway trimetric views in Figs. 6A and 6B and in side- and top sectional views in Figs. 6C and 6D respectively - a rear portion of a capsule according to the configuration of Fig. 5, to which a steering mechanism has been added as follows. As before, rotor 130 is rotatable by motor 140b through planetary gear assembly 146. Rear cylindrical member 113 of core 110 is hollow, and contains a shaft 160, running through its entire length and possibly protruding through hole 136 in the rotor. The shaft 160 is rotationally attached to the cylindrical member 113 through a set of ring bearings 162.

A steerable tail assembly 200, which includes a rudder 202, is pivotally attached to shaft 160 through a swing joint assembly 204. Shaft 160 is hollow (i.e. is formed as a pipe) and may be rotated - typically through a range of about 90 degrees - by means of a motor assembly 210 (including a reduction gear assembly) and a belt- and- gears assembly 212, which results in commensurate rotation of the joint assembly 204 and the tail assembly 200 about the length axis of the capsule. In the views of Figs. 6C and 6D, the tail assembly 200 and the joint assembly 204 are shown in a rotational position such that the rudder 202 and the pivot axis of the joint assembly 204 are in a vertical plane, but a 90 degrees rotation of the shaft 160 may bring them to a horizontal plane.

An axle 223 in the joint assembly 204 is rigidly connected to the tail assembly 200; it is moreover formed with a concentric gear 224. Within the core 110 there is disposed a motor assembly (with a reduction gear assembly) 220, whose vertical output shaft ends with a gear 221. Alternatively, the motor assembly 220 and the the gear 221 may jointly be attached to shaft 160 and thus rotatable therewith. The gears 221 and 224 are rotationally coupled with each other by means of a belt 222. Thus any rotation of the motor in assembly 220 causes commensurate rotation of the axle 223 and consequently - a pivoting tilt of the tail assembly 200. The motors in assemblies 210 and 220 receive appropriate electric current from controller 152.

In operation, while the capsule 100 propagates through the soil, the tail assembly 200 is normally held in an untilted position, i.e. its length axis is collinear with that of the capsule; consequently the capsule tends to propagate along a straight line (unless forced to deviate by inhomogeneity in the soil). When it is desired to steer the capsule into a new direction of travel - say, to the right - a command is sent to the controller 152 to cause the motor in 220 to turn so that the tail 200 tilts (about the pivot axis in joint assembly 204) by a few degrees to the right (into the paper in Fig. 6C, upward in Fig. 6D). Thereupon the rudder 202 interacts with the surrounding soil so as to be pushed to the left, thereby pushing also the aft of the capsule to the left. As a result the capsule tends to gradually turn to the right. When it reaches the desired new direction, the controller causes the motor to turn in reverse until the tail returns to its normal position, whereupon the capsule continues propagating along the new direction.

If the desired change of direction is in a vertical plane (rather than a horizontal plane as in the previous example) - say upward - the cotroller 152 first causes motor assembly 210 to turn the shaft 160 - and with it also the joint assembly 204 and the tail assembly 200 - by 90 degrees. This causes the pivot axle 223 and the rudder 202 to be in a horizontal plane (i.e. parallel to the paper in Fig.6C). The controller then causes motor assembly 220 to turn as described above, which in this instance causes the rudder to tilt upward and thus be pushed by the soil downward, thereby pushing the capsule's aft downward and causing the capsule to turn upward. Clearly a change of direction in any other plane can be similarly effected by first turning the shaft 160 by the appropriate angle and similarly tilting the tail assembly.

Figure 7 illustrates optional means for enabling a STV capsule, such as described above, to tow an external object - in this instance, a trailing container 300 ("trailer" for short). The capsule is preferably of the configuration described above with reference to Fig. 5. As seen in Fig. 7A, one end of a tow cable 302 is attached to the rear end of the cylindrical member 113 (not shown) of core 110. The other end of tow cable 302 is attached to a coupling device 310, which in turn is attached to the trailer 300. The coupling device 310 has preferably a decoupling capability and as such is depicted in enlarged detail views in Figs. 7B and 7C. It is seen to consist of a buckle 312, attached to the trailer 300, and a motorized lock 314, attached to the second end of tow cable 302. Fig. 7B shows the coupling device in locked, or coupled, state, while Fig. 7C shows it in an unlocked, or decoupled, state. Lock 314 has two pins 316 protruding therefrom, which are configured to be slidingly accomodated by matching bores (not shown) in the buckle 312. In addition, there is a central threaded nut 313 rigidly attached to buckle 312 and there is a threaded bolt 315 centrally protruding from lock 314, which bolt is configured to engage the nut 313. Bolt 315 is coupled to the shaft of a motor (not shown) inside the lock 314. The motor is electrically connected, through wires in the tow cable 302, to the controller 152 inside the core - similarly to the connection of the umbilical cable to be described below (Fig. 8B).

In typical operation, The lock 314 and the buckle 312 are initially coupled together, wherein pins 316 engage the matching bores in the buckle and bolt 315 engages nut 313. When the STV reaches a designated site, the controller causes the motor to turn the bolt until it is disengaged from the nut, thereby releasing the trailer and leaving it at the site while the STV may continue to propagate. The trailer may contain a mission- specific payload and it may be configured to activate the payload upon sensing the decoupling action or at some delay thereafter. For example, the payload may include scientific instruments or intelligence gathering devices or an explosive charge to be detonated.

In a variation of this arrangement, a plurality of trailers may be similarly connected to a STV in tandem, each pair of consecutive trailers being inter-coupled by a similar lock and buckle mechanism. In typical operation, each trailer is released at a different site - last trailer first.

There may be other tasks in which a STV may be called on to tow an object. For example, it may need to pull a cable through the ground from one point to another underneath a structure that prevents digging a ditch for laying such a cable (as would be done normally). Alternatively, the STV may be similarly utilized to pull a tow line (e.g. a rope) through the ground, which is subsequently used to pull a cable or a pipe. For such tasks, a lock and buckle arrangement such as described above may be employed, though the lock need not necessarily be motorized, the decoupling action being preferably done manually (after the STV emerges from the ground).

Figures 8 illustrate an optional capability for the configuration of Fig 5 (applicable also to other configurations) of obtaining power from, and communicating with, a ground station. Fig. 8A depicts schematically the overall system, wherein the horizontal line represents ground level. A STV capsule 100, which propagates underground, has attached to it a first end of a cable 400, the second end of which is wound on a reel 452 at the ground station and is electrically connected to an electric ground module 450. As the STV propagates forward, it pulls the cable behind it while the latter unwinds from the reel. Optionally, the reel 452 may be configured and operative to the pull cable 400 back and rewind it when the STV propagates backward - possibly to the point of retrieving the STV at the ground station. The cable 400, which is also referred to as a umbilical cable, includes a plurality of electrically conducting wires, some of which may carry power from module 450 to the STV, while others may carry signals both ways between them. The power carried by the cable may be in addition to that obtained from the battery inside the STV or as an alternatie thereto. The signals may be any signals involved in the operation of the STV and/or in the operation of its payload and may include, inter alia, output signals of sensors and command signals. They may, for example, be instrumental in an operational mode by which some or all of the control is carried out within the electric module 450 at the ground station, or by which such control is shared between the module 450 and the controller 152 in the STV.

Fig. 8B shows a longitudinal section of the capsule 100 and the manner by which the cable 400 is attached thereto. A short cable segment 420, similar to cable 400, runs through the rear end hole 136 of rotor 130 and along the inside of cylindrical member 113 of core 110. to which it is tightly and fixedly attached by one or more clamps, such as clamp 422. The wires at one end of the segment 420 are electrically connected to appropriate points in controller 152, while the other end of the segment is mechanically and electrically connected to one member of a connector 410. The other member of connector 410 is mechanically and electrically connected to the first end of cable 400. Connector 410 may generally be any suitable product available commercially. Figure 9A depicts, in trimetric view, another configuration of a STV according to the invention. Two capsules, 100 and 100a, are linked to each other through a joint assembly 504. Each capsule is preferably configured similarly to those described above with reference to figs. 4 or 5, wherein, associated with its end that is connected to the joint assembly, it has a truncated rotor and a cylindrical core member that extends to that end. The joint assembly 504 may be rigid but is preferably configured to allow some pivotal swing between the two capsules. More preferably, the joint 504 allows a steering action - alternatively to that provided by the configuration of Figs. 6. The steering action may, for example, involve a mechanism similar to that described above with reference to Figs. 6, wherein the driving motors are, for example, in capsule 100a. Figure 9B is an enlarged detail of region A of Fig. 9A and shows, within joint assembly 504, a portion of a belt 522 that is similar to belt 222 in Figs. 6. The belt 522 engages a gear that is fixedly coupled to the member of joint assembly 504 that is connected to the right hand capsule 100, while, inside the left-hand capsule 100a, it engages a gear of a mechanism similar to that depicted in Figs, 6B-6D. In operation, the steering action may differ somewhat from that of the configuration of Figs. 6, in that any change in the pivot angle at the joint assembly must be effected more slowly and more gently.

A multi-capsule configuration such as that of Figs. 9 may have several advantages, such as:

(a) generally, a greater overall grip in the soil, in the face of voids or varying soil conditions (in common with the configuration of Figs. 3);

(b) generally, more stowage space for payload (again in common with the configuration of Figs. 3

(c) in conjunction with a steering capability, described above - an alternative to the steering apparatus of Fig. 6, advantageously allowing also backward propagation and moreover avoiding the drag that a tail assembly may cause;

(d) with the leading capsule 100a having a reduced diameter (as depicted in the instance illustrated in Fig. 9A), the STV may be able to propagate forward in a dense soil more efficiently, inasmuch as the trailing capsule 100 would meet less soil resistance in the wake of the smaller leading capsule 100a.

Obviously, a STV may include more than two capsules, similarly connected in tandem. Figure 10A shows yet another configuration of a STV. It is similar to the configuration of Figs. 9 in that it also includes two capsules, 600a and 600b that are inetrlinked through a joint 604. However, in this configuration each capsule has a single rotor, the two rotors being disposed at opposite ends of their respective cores and their flightings having mutually opposite helical senses. Each capsule has a single motor, which serves to drive the respective rotor through a transmission assembly, similarly to peviously described configurations. The two motors, which preferably are fed from a single controller (not shown, but disposed in one of the capsules) normally operate to rotate the rotors in mutually opposite senses. The end of each of the two cores 610a and 610b that has no rotor has a generally truncated conical shape. The joint 604 is similar to the joint 504 in the configuration of Fig. 9 and may similarly be associated with a steering mechanism.

It is noted that, while the ends of the rotors are shown in this instance as being pointed, the rotor of the rear capsule 600b may as well be of the truncated type, wherein the core 610b would extend to the corresponding end of the capsule (as, for example at the rear end of capsule 100 in Fig. 9A). In this case, trailing objects, as well as a umbilical cable, may be attached - similarly to previously described configurations. It is also possible to similarly link to it additional capsules in tandem - e.g. additional similar pairs of single- rotor capsules. In a variation (not shown) of the configuration of Fig. 10A, the rotor of the rear capsule 600b is disposed at the front end of the respective core (rather than at its rear end).

Another variation of the configuration of Fig. 10A is shown in Figure 10B. Here the front capsule 600a has a single rotor 620a, similarly to that in Fig. 10A. However the rear capsule 600 has two rotors, 620 and 630, similarly to the configurations of Figs. 4 and 5. The flightings of the two fore rotors 620a and 620 are wound in the same helical sense, whereas the single aft rotor 630 has a flighting wound in the opposite sense. This configuration may be advantageous for applications in which a long exposed core is required for large payloads or in which the STV needs to emerge from the ground on its own. A particular application of the latter category, using a modified version of the configuration of Fig. 10B, is described below with reference to Figs. 12.

Turning now to Figure 11, there is shown, by way of example, an optional addition to any of the configurations of Figs. 4-10, namely arrangement and apparatus for stowing tools and objects, deploying them outside the STV and retrieving them. Fig. 11A is a trimetric view of a capsule 100, such as in the configurations of Figs. 4 and 5. The wall of core 110 includes a window 115, while the inside of the core (not shown) is adapted to stow particular instruments and objects. Figs. 11B and 11C are enlarged views of the window 115, while open, showing by way of example a particular instrument, namely a shovel for collecting soil samples. The window 115 is normally closed by a shutter 116, which may be slidingly opened by means of a suitable electrically operatable mechanism (not shown). In Fig. 1 IB the shovel 118 is seen in a collapsed stowing state, while in Fig. l lC the shovel 118 is seen in an extended deployment state.

In operation, when the STV reaches a designated site it would be commanded to stop, then to open the shutter 116, extend the shovel and cause it to scoop a sample of soil, then to collapse the shovel and possibly deposit the sample in a bin and finally to close the shutter. Subsequently the STV may be commanded to proceed to a different site and repeat the operation or it may be commanded to return to the launching station - either by circling back in a forward motion or by moving backward, retracing its path.

Another possible mode of payload stowage, amenable to a forward delivery of the payload (rather than through a side window as in Fig, 11), is possible with a suitably modified version of the double-capsule configuration of Fig. 10B. In such a modified version the rear capsule 600 remains as shown, but the fore capsule 600a is modified into a configuration to be described now with reference to Figures 12. As may be seen in Fig. 12A, the core of the fore capsule 700 consists essentially of two parts 710 and 715, arranged in tandem, and a single rotor 720, rotationally attached to the fore part 710. The two core parts, 710 and 715 are normally locked together, by means of releasable locks, but can be separated by releasing the locks, as may be seen in Fig, 12B.

As may be seen in the trimetric sectional view of Fig. 12C, in which the two parts are again shown separated, the rear core part 715 is essentially formed as a container, including a compartment 716. in which the payload can be stowed. The front of the compartment 716 is largely open, so that when the core parts are separated, the payload may be removed or phshed out. The front core part 710 is rotationally coupled to rotor 720 through bearings 724. It contains the entire driving mechanism, namely a motor 740, a transmission assembly 745, which is coupled to the rotor 720, and a controller 752. The controller 752 may be electrically connected to the controller of rear capsule 600 (not shown). The two core parts are attached to each other by means of electrically releasable locks 760, each consisting of two interlocked members 760a and 760b. First member 760a, disposed at the front end of rear core part 715, includes a fixed threaded nut; second member 760b, disposed at matching position at the rear of the fore core part 710, includes a motor 761, coupled to a threaded bolt which engages the nut in the first member. The motor 761 is electrically connected to the controller 752 and, upon a command, may operate to turn the bolt so as to disengage it from the nut.

In operation an object is generally stowed in the compartment 716 and, after the STV reaches a designated site, the locks 760 are unlocked and the two parts separate so as to expose the compartment, from which the object is then launched forward. In a particular military application, for example, illustrated schematically in Fig. 12D, the stowed object may be a missile and the site may be a point of emergence from the ground (which is here shown as sloping). The STV consists of a fore capsule 700 and a rear double-rotor capsule 600, as described above. When the front end of the fore capsule 700 emerges from the ground (whereby its rotor is disengaged from it and becomes ineffective, leaving the final propagation action to the rear capsule), front part 710 is separated from the rear part 715 and presumably falls to the ground. The stowed missile 760 is then launched toward a designated target.

Turning now to Figures 13, there is shown an improved flighting, having a variable diameter, which is adaptable to various configurations of the STV. It is aimed at dealing with long and relatively wide voids in the soil and with very loose soil of varying density along the path of the STV - with which a fixed-diameter flighting may find it difficult to be engaged, thus spoiling its propulsion capability. Various means may be employed to in effect achieve diameter variability of the flighting; one practical example is described in what follows.

As shown schematically in Fig. 13A and, in greater detail, in the cross-sectional views of Figs. 13B and 13C, a plurality of fins 50 are pivotally connected to at the body of a rotor - say member 20 in Fig. 1 - along a helical path. All fins 50 are interconnected, in sequence, by links 55 so that pivoting any one of them would pivot also all the rest. In Fig. 13B the fins are depicted in a relatively extended (large diameter) state, while in Fig. 13C they are depicted in a relatively closed (small diameter) state One fin, lead fin 51, is driven into any pivoting state by a mechanism, seen in all the drawings, but in greater detail in the enlarged sectional view of Fig. 13D. Lead fin 51 is connected to a threaded slider 52 that is slidingly attached to a lead screw 53. The latter protrudes radially from inside the rotor body 20, whre it is coupled, preferably through a right-angle gear transmission 56, to a DC motor 57, which obtains a drive voltage from a battery through a controller (both not shown). It is noted that the entire assembly, including motor 57, is attached to the rotor body 20 and rotates therewith. A centrifugal tachometer (not shown) measures the rotational velocity of the rotor and applies it to the controller. The latter compares the received value with a threshold value that corresponds to member rotation when not, or little, engaged with soil and if approaching such value (which would occur when a void or loose soil is encountered), causes the motor 57 to turn the lead screw 53 so as to raise the slider 52 and with it - lead fin 51 and hence also all other fins 50. This operation continues until the fins are engaged by the soil; at that point the rotation slows down and the controller, sensing that, stops the motor. If and when the differential rotational speed becomes abnormally low (as would occur when the STV encounters an end of the void or denser soil), the controller would sense that (by comparing the speed with a corresponding threshold value) and would direct the motor 57 to turn the lead screw in the opposite sense, so as to lower the slider and the fins; this would continue until a normal operating speed is reached, whereupon the motor would be stopped.

Turning now to Figures 14, there is shown, by way of example, an optional addition to any of the configurations of Figs. 1-10, namely apparatus for loosening soil ahead of the STV in cases that the density or hardness of the soil is relatively high so that the STV may otherwise not have enough power to advance through it. The term "loosening" is used to represent also any other type of soil treatment aimed at easing the passage of the STV, as for example, softening, grinding or crushing. The exemplary apparatus illustrated schematically in Fig. 14A and in a sectional view in Fig. 13B, is based on the configuration of Fig. 1, but can be readily adapted to any other configuration. It comprises a rotatable drill 61 attached to the front end of the fore member 20 of capsule 10 through a sealed bearing 62. A motor 63, to which a voltage is applied through the capsule's controller (not shown), serves to rotate the drill 61 at an appropriate speed - generally much higher than that of the rotor. The action of the rotating drill is to loosen or crush the soil in front of the capsule and possibly also in the path of its rotors, so as to decrease the soil resistance to the advance of the capsule and possibly also to the rotation of the rotors. Optionally, the operation of the drill may be intermittent or at variable speed - depending on sensed resistance of the soil. Also optionally, a duct may be provided along the capsule to transport some or all of the soil loosened by the drill to behind the capsule. In the case of a capsule having a configuration as in Figs 4 or 5, the drill and the motor would preferably be attached to a member of the core.

Alternative or complementary embodiments of soil-loosening apparatus according to the invention may vary from the above and may include, for example, a vibrating hammer or an array of water jets; the latter may use water (or other fluids) supplied from the ground station through a hose that is pulled by the STV (in a manner similar to that illustrated in Fig. 8 A with respect to a umbilical cable).

Attention is now drawn to the system aspects of the STV, that is - to external

components that cooperatively enable or support operation of a STV of the present invention. It is noted in this context that the apparatus for mechanically and electrically feeding a umbilical cable, as discussed above with reference to Fig. 8A, constitutes part of a support system.

Figures 15 illustrate schematically an example of apparatus and method for launching a STV into the ground at a station. The apparatus basically comprises a tubular barrel 80, pivotally attached to a base 82 or a carriage so that it may be pointed diagonally downward along the desired launch path. The barrel is configured to hold a STV - e.g. capsule 10 - and equipped with means for ejecting it into the ground. Fig. 15A illustrates a moment of emergence of the capsule from the barrel, while Fig. 15B illustrates the beginning of self propulsion of the capsule into the ground.

Two exemplary means for holding the STV in the barrel and ejecting it therefrom are:

(1) The barrel is lined inside with a layer of soft material to frictionally hold the STV and a piston is deployed at the top of the barrel and is operative to push the STV down and out of the barrel.

(2) The barrel is lined inside with a series of isoled protrusions (formed as fins or pins), arranged so that they simultaneously form two virtual helical grooves of mutually opposite senses that match the helicoid flightings of the STV's rotors. The STV is held inside the barrel with its rotors' flightings engaged by the protrusions; for ejection it is commaned to simply propel itself down the barrel and into the ground.

Figures 16 illustrate schematically an example of apparatus and method for launching a STV into the ground remotely. As is shown in Fig. 16A, There is provided a missile 90, configured to be launched from a remote site or from an aircraft and driven, for example by a rocket engine. The missile 90 is further configured internally to carry the STV and has a detachable nose cap 92. As is shown in Fig. 16B, it is operative, at proximity to the ground, to detach the nose cap 92; consequently, upon impact with the ground, the capsule 90 is stopped but the STV 10 continues the motion by momentum, penetrates the ground and proceeds to propel itself.

A system can in general include various means that may be employed above ground to aid and support various functions, such as navigation, communication and control. While these functions may be carried out autonomously within the STV, some applications may require external means for greater accuracy or effectiveness. Of course, communication and control functions may be facilitated by a umbilical cable (as described above with reference to Fig. 8) wherever practical, but must otherwise be provided by wireless means, as must navigation functions. To this end various devices, such as beacons, sensors and transceivers, are deployed at suitable locations above ground and are operative to cummunicated with matching devices on board the STV. They are preferably also in communication with a central control unit, such as the control module at the ground station (Fig. 8). No particular device types are specified here, as any available and suitable technology may be applied.

It should be understood that other configurations of the STV are possible according to the present invention, some of which may include, or combine, features of configurations described hereabove.

Operation of a STV according to the invention generally proceeds as follows. First the STV is launched into the ground, in an appropriate initial direction, either manually or using a launching means such as described above with reference to Figs. 15 and 16. The STV then proceeds to travel through the ground by its own propulsion, that is by the interaction between the rotors, rotating in their respective senses, and the surrounding soil. Control of the rotation and of the travel (e.g. speed) may be provided by the internal controller, which may be preloaded with a suitable program, and or by an external (on ground) control unit communicating with the STV via a umbilical cable or through wireless channels, if such means are provided. If the STV has a capsule of a

configuration with a core and with a verticality sensor, the controller may control the differential rotation speed of the rotors so as to keep the core upright. If the STV is provided with steering means, such as those described with reference to Figs. 6 and 9, the controller may operate them to change the direction of travel. The latter action may be effected according to a stored course, aided by navigation data obtained from internal and/or external navigational aids, if such have been deployed.

For overcoming hindrances due to soil characteristics, additional apparatus, such as described above with reference to Figs. 13 and 14, may be employed, if provided.

Hindrances and obstacles may also be circumvented by steering the STV into an appropriately modified course. Depending on the configuration of the STV and on the particular application or mission, the STV may tow behind it an object, such as a trailer or a cable (as in Fig. 7), and leave it at a defined site. In general, the STV would stop, according to a stored program or a command, at one or more sites in order to carry out its mission. Such a mission may include, for example, (1) deploying one or more objects at the site, (2) measuring some variables in the surrounding soil or space (including obtaing an image in any modality) and (3) obtaining one or more samples from the surrounding soil. In case '2' the measured data would be transmitted to a ground station, if

communication means have been oprovided, or would be stored internally and later retrieved upon return of the STV to above ground. In case '3' a return of the STV to above ground is imperative.

After carrying out its mission at the last site, the STV may, depending on the nature of the mission, be abandoned or may be directed to return to its launch site, where it would be retrieved; for certain missions, where the last site is at or near ground level (such as pulling a cable underground), the STV may be retrieved there. According to the configuration, return to the launch site may be effected in a forward motion - along a back looping course - or in a backward motion (the rotors rotating in the opposite sense than during the forward travel). In the latter case, if the configuration includes a umbilical cable, the cable would be simultaneous taken up by its reel at the launch site.

Possible applications for an STV have been indicated above, in the background section, as well as in conjunction with certain configurations. Indeed the STV of the present invention, in one configuration or another, is applicable to any of these, as well as to many others. It is noted that in the above descriptions of embodiments no dimensions have been given - either for the STV or for any of its parts - since these depend very much on the application; the size and proportions may greatly vary accordingly.

Furthermore, whereas operation of a STV (as well as its very name) has been described in terms of travelling through the ground, with surrounding soil, similar apparatus may possibly be used for travel through other solid media, such as trash, industrial materials or even biological tissue; dimensions and configurations would then be modified accordingly.

Subterranean applications themselves may vary widely and can be broadly (but not exhaustively) grouped into scientific, civilian and military applications. Among scientific applications for the STV one can mention, for example -

- sensing underground radiation or other physical parameters,

- geological assays,

- biological (micro-organisms) surveys and

- preliminary archaeological surveys.

Among civilian applications one can count -

- testing soil prior to construction or prior to mining,

- exploration for oil and other minerals,

- laying infrastructure items such as cable and pipes under obstacles and

- supply- or rescue missions to trapped miners or to avalanche victims.

Military applications may include -

- intelligence gathering,

- detection of underground structures,

- demolition missions and

- stealth missile launching (such as described with ref. to Fig. 12D). It is noted that some of the applications require mainly horizontal travel, others - mainly vertical travel (possibly into great depths); yet other applications may involve complex routes, which may moreover be determined interactively - in response to detected objects or sensed environmental parameters. All such applications, and others, are addressable with an STV essentially as described above and as defined by the claims to follow.

INDUSTRIAL APPLICABILITY

A subterranean vehicle as described above can be designed in detail by engineering practitioners and can be manufactured by known industrial processes and/or with readily available components.