TECHNOLOGICAL FIELD

The presently disclosed subject matter relates to methods for dropping a payload from altitude via parachute, in particular in the absence of active guiding or steering.

BACKGROUND

Payloads of many different types can be dropped from various altitudes via different types of parachute. In some such applications, the parachute is steerable and the payload can be configured to operate the parachute to actively guide the path of the payload towards a desired landing site. In other applications the parachute is nonsteerable, and/or the payload is not configured for operating the parachute after opening, and there is no active or real-time control over where the payload will finally land once the parachute has been deployed.

By way of non-limiting example, US6343244 discloses an automatic guidance system guides a flight vehicle having a para foil to a target grounding point. The system opens the para foil of the flight vehicle dropped in a predetermined area above the target grounding point. The system estimates wind velocity and wind direction after the para foil of the flight vehicle is opened. Then, the system determines the landing flight path of the flight vehicle based on the estimated wind velocity and wind direction, guides the flight of the flight vehicle to the determined landing flight path and descends the flight vehicle according to the landing flight path.

Also by way of non-limiting example, US6144899 discloses a recoverable airborne instrument platform that accurately determines its present position and uses this data to execute a predetermined flight plan and ultimately guide its descent to a predetermined landing site. This is accomplished by installing the instrument package payload in the aerodynamic exterior housing of the recoverable airborne instrument platform, which has a plurality of moveable control surfaces thereon to autonomously control the altitude, attitude and flight path of the recoverable airborne instrument platform. A navigation circuit contained within the aerodynamic housing determines the geographic location of the recoverable airborne instrument platform as well as the location of at least one predetermined recovery site. The determined position data is used to dynamically calculate a flight path which allows the guidance control circuit to both execute a predetermined flight plan and controllably descend the recoverable instrument platform to a selected predetermined recovery site. Upon arrival at the selected predetermined recovery site, the recoverable airborne instrument platform descends to a predetermined height over the selected predetermined recover}' site and activates a parachute release mechanism to controllably descend to the selected predetermined recovery site.

Also by way of non-limiting example, KR100673524 discloses a flight control method of a transporting system of a parafoil guide parachute to rapidly and accurately transfer the freight to the destination by measuring the position data and the angle of azimuth in real time and analyzing the effect of the wind. A flight control method of a transporting system of a parafoil guide parachute comprises a step of inputting the destination; a step of judging the free flight starting time; a step of measuring the latitude, the longitude, the height, and the angle of azimuth; a step of calculating the expected flight path and the expected flight time; a step of calculating the upper and lower limit flight angles; a step of analyzing the effect of the wind; a step of deciding the flight control mode; and a step of controlling the servo actuator.

Also by way of non-limiting example, KR20180096847 relates to an algorithm for automatically generating a path for accurately landing a precision guided parafoil system on a target point. When a mission plan goes wrong, a parafoil may be dropped to the ground by all losing the altitude before reaching a target point, or may pass by an arrival point since the altitude remains. According to a flight control method for a precision guided parafoil system applied with an automatic mission planning algorithm of this reference, an automatic mission planning algorithm calculates whether to reach an arrival point in consideration of the gliding performance of a parafoil, descending of the altitude during circling, a wind direction and a wind speed for each altitude. Also, the number of times of circling and the radius thereof in an energy consumption section are automatically adjusted by calculating an altitude margin at the arrival point. In addition, an advantage of generating a path mission for safe landing with crosswind in consideration of a wind direction of a landing point is provided. According to an embodiment of this invention, the flight control method for a precision guided parafoil system applied with an automatic mission planning algorithm, comprises: a step of inputting a target position; a step of inputting a wind direction and a wind speed for each altitude; a step of calculating an airdrop position; a step of generating a basic path from the airdrop position to the dropping to the target position by calculating the wind direction and the wind speed and a gliding ratio of a parafoil; an altitude margin calculating step of calculating an altitude margin of the parafoil, and calculating a number of times of circling in an energy consumption section in accordance with the position of the parafoil; and an altitude margin recalculation step of calculating a circling radius in accordance with the number of times of circling of the parafoil to allow the parafoil to be dropped with an optimized altitude margin value.

Also by way of non-limiting example, US9500454 discloses a new mortar projectile for use to resupply various payloads to distant troops. The mortar projectile has the capability of rapidly and accurately transporting the payloads to forward disposed combatants without interference of terrain or enemy action. The mortar projectile includes a shell body for housing the payload to be delivered, and a GPS-guided parafoil for delivering the payload to the designated remote target location .

Also by way of non-limiting example, discloses inflight location predictions using ascent wind data for high altitude balloons.

Also by way of non-limiting example, http s : //tinyurl . com/ d76xd 7y 4 discloses meteorological conditions forecast and balloon trajectory estimations. GENERAL DESCRIPTION

According to an aspect of the presently disclosed subject matter there is provided a method for operating a parachute-payload system with respect to a predetermined target zone location, comprising

(a) providing the parachute-payload system;

(b) constructing a predicted descent trajectory for the parachute-payload system from a nominal start altitude to the target zone location based on meteorological data;

(c) deploying the parachute-payload system to passively descend along a real descent trajectory, at least nominally corresponding to the predicted descent trajectory, starting at a chosen deployment location on the predicted descent trajectory.

For example, the parachute-payload system comprises a payload coupled to at least a primary parachute arrangement, the primary parachute arrangement comprising at least one primary parachute selectively deployable from a stowed configuration to a deployed configuration when coupled to the payload, the at least one primary parachute being non-steerable in operation of the parachute-payload system at least concurrent with the at least one primary parachute being in deployed configuration.

In at least one example step (b) comprises constructing the predicted descent trajectory for the parachute-payload system from the nominal start altitude to the target zone location by extrapolating backwards starting from the target zone location, utilizing respective said meteorological data corresponding to at least an atmospheric zone defined between the target zone location and the nominal start altitude.

For example, the method comprises:

(d) choosing said deployment location on said predicted descent trajectory as a start location for initiating the descent of the parachute-payload system with the primary parachute arrangement in said deployed configuration;

(e) transporting the parachute-payload system to a release location and releasing the parachute-payload system in a manner such as to enable the parachute-payload system to reach the deployment location; (f) causing the at least one primary parachute to be in the respective deployed configuration at least when the parachute-payload system is located at the deployment location;

(g) allowing the parachute-payload system to passively descend along the real descent trajectory at least nominally corresponding to the predicted descent trajectory.

Additionally or alternatively, for example, step (b) comprises:

(bl) modelling the atmospheric zone as a series of contiguous control volumes, each said control volume comprising a respective altitude portion between a respective lower control volume altitude and a respective upper control volume altitude;

(b2) starting at the target zone location, constructing a first portion of the predicted descent trajectory through a first said control volume, wherein the respective lower control volume altitude corresponds to the target zone location, utilizing respective meteorological data corresponding to the said first control volume, said respective meteorological data including at least respective air density, respective wind velocity and respective wind direction, and extrapolating the first portion of the predicted descent trajectory within the first control volume to the respective upper control volume altitude by determining respective descent velocity and respective wind-induced displacement corresponding to the respective meteorological data corresponding to said first control volume;

(b3) constructing a next portion of the predicted descent trajectory through a next contiguous said control volume, wherein the respective lower control volume altitude of the said next control volume corresponds to the respective upper control volume altitude of the previous said control volume, utilizing respective meteorological data corresponding to the said next control volume, said respective meteorological data including at least respective air density, respective wind velocity and respective wind direction, and extrapolating the next portion of the predicted descent trajectory within the said next control volume to the respective upper control volume altitude of the said next control volume by determining respective descent velocity and respective wind-induced displacement corresponding to the respective meteorological data corresponding to the said next control volume; (b4) repeating step (b3) until the respective upper control volume altitude of the respective said next control volume corresponds to the nominal start altitude.

For example, for each said control volume, the respective descent velocity is determined by the relationship: wherein:

V - descent velocity p - air density corresponding to the respective control volume

S - plan area of the at least one primary parachute

CD - drag coefficient of the at least one primary parachute

W - weight of the parachute-payload system

Additionally or alternatively, for example, for each said control volume, the respective descent velocity provides a respective residence time within the respective said control volume.

For example, for each control volume, the respective wind-induced displacement corresponds to a respective three-dimension displacement within the respective control volume, between the respective lower control volume altitude and the respective upper control volume altitude, along a vector corresponding to the respective said wind direction, the magnitude of the respective three-dimension displacement being derived from the respective wind velocity and the respective said residence time.

Additionally or alternatively, for example, said predetermined target zone location comprises a target zone geographical location, and a target zone altitude relative to sea level.

Additionally or alternatively, for example, for each said control volume, the respective portion of the predicted descent trajectory defines altitude portion, and further defines a respective upper control volume latitude and longitude. For example, a respective said upper control volume latitude and longitude of one control volume corresponds to a respective lower control volume latitude and longitude of an upwardly adjacent contiguous said control volume. In at least another example, step (b) comprises constructing the predicted descent trajectory for the parachute-payload system from the nominal start altitude to the target zone location by extrapolating forwards starting from the nominal start altitude, utilizing respective said meteorological data corresponding to at least an atmospheric zone defined between the target zone location and the nominal start altitude.

Additionally or alternatively, for example, said nominal start altitude is an altitude above at least one of the following altitudes above sea level: 10km, 15km, 20km, 25km, 30km, 35km, 39km.

Additionally or alternatively, for example, said nominal start altitude is in the range between about 10km and about 40km above sea level.

Additionally or alternatively, for example, said nominal start altitude is chosen at a respective altitude above sea level not exceeding at least one of: 60km, 50km, 40km.

Additionally or alternatively, for example, said deployment location is chosen having a respective geographical location within a predetermined radius from the predetermined target zone geographical location.

Additionally or alternatively, for example, said deployment location is chosen having a respective altitude above at least one of the following altitudes above sea level: 10km, 15km, 20km, 25km, 30km, 35km, 39km.

Additionally or alternatively, for example, said deployment location is chosen at a respective altitude in the range between about 10km and about 40km above sea level.

Additionally or alternatively, for example, said deployment location is chosen having a respective altitude above sea level not exceeding at least one of: 60km, 50km, 40km.

Additionally or alternatively, for example, in step (e) the parachute-payload system is transported to the release location via a carrier vehicle, wherein the carrier vehicle is configured for releasing the parachute-payload system at the release location. For example, the carrier vehicle operates exclusively within the atmosphere. Additionally or alternatively, for example, the carrier vehicle remains within altitude not exceeding at least one of 85km, 100km during operation thereof. Additionally or alternatively, for example, operation of the carrier vehicle at least in step (e) excludes operation in space.

Additionally or alternatively, for example, the parachute-payload system is released at the release location, and wherein the primary parachute arrangement is in the respective stowed configuration until the parachute-payload system reaches the deployment location. For example, the release location is chosen such as to enable the parachute-payload system to reach the deployment location in free-fall.

Additionally or alternatively, for example, said carrier vehicle is a rocket.

For example, the rocket is launched from a suitable launch site at launch conditions such as to reach the release location is an unguided manner. For example, wherein said launch conditions for the rocket are set such as to cause the rocket to nominally follow a predicted rocket trajectory that intersects the release location. For example, said launch conditions include launch azimuth and elevation. Additionally or alternatively, for example, said predicted rocket trajectory in constructed based on meteorological data between the launch site and the release location.

Additionally or alternatively, for example, the target zone and the launch site are geographically spaced within a spacing, wherein the spacing is not greater than at least one of the following: 30km, 25km, 20km, 15km, 10km, 5km, 3km, 2km, 1km, 0.5km.

In at least some other examples, said carrier vehicle is any one of a missile or aircraft.

Additionally or alternatively, for example, the parachute-payload system is configured for deploying the at least one primary parachute at the deployment location.

Additionally or alternatively, for example, said at least one primary parachute is in the form of a non-steerable canopy parachute.

Additionally or alternatively, for example, said predetermined target zone location comprises a geographical area of any one of up to: 1 square kilometer; 2 square kilometers; 5 square kilometers; 10 square kilometers; 20 square kilometers; 50 square kilometers; 100 square kilometers. Additionally or alternatively, for example, the predetermined target zone location is an Earth surface zone.

Additionally or alternatively, for example, the predetermined target zone is a ground surface landing zone or sea surface landing zone.

Additionally or alternatively, for example, the predetermined target zone is located at a predetermined final approach altitude above a ground surface landing zone or sea surface landing zone.

For example, the method further comprises: decoupling the primary parachute arrangement from the payload at the predetermined primary target zone location; causing the parachute-payload system to execute a landing maneuver enabling the parachute-payload system to reach the target zone.

For example, the step of executing the landing maneuver comprises allowing the parachute-payload system to free-fall for at least a portion of the predetermined final approach altitude towards the ground surface landing zone or sea surface landing zone.

Additionally or alternatively, for example, the parachute-payload system comprises a secondary parachute arrangement, the secondary parachute arrangement comprising at least one steerable secondary parachute, secondary parachute arrangement configured for being steering via the payload, and wherein executing the landing maneuver comprises steering the parachute-payload system via the for at least a portion of the predetermined final approach altitude towards the ground landing zone for at least a portion of the predetermined final approach altitude towards the ground landing zone.

Additionally or alternatively, for example, a passive descent time of the parachutepayload system between the deployment location and the target zone via the real descent trajectory is in the range of between about 20minutes and about 60minutes.

According to an aspect of the presently disclosed subject matter there is provided a method for operating a parachute-payload system with respect to a predetermined target zone location, comprising (A) providing the parachute-payload system, the parachute-payload system comprising a payload coupled to at least a primary parachute arrangement, the primary parachute arrangement comprising at least one primary parachute selectively deployable from a stowed configuration to a deployed configuration when coupled to the payload, the at least one primary parachute being non-steerable in operation of the parachutepayload system at least concurrent with the at least one primary parachute being in deployed configuration;

(B) constructing a predicted descent trajectory for the parachute-payload system from a nominal start altitude to the target zone location by extrapolating backwards starting from the target zone location, utilizing meteorological data corresponding to at least an atmospheric zone defined between the target zone location and the nominal start altitude;

(C) choosing a deployment location on said predicted descent trajectory as a start location for initiating the descent of the parachute-payload system with the primary parachute arrangement in said deployed configuration;

(D) transporting the parachute-payload system to a release location and releasing the parachute-payload system in a manner such as to enable the parachute-payload system to reach the deployment location;

(E) causing the at least one primary parachute to be in the respective deployed configuration at least when the parachute-payload system is located at the deployment location;

(F) allowing the parachute-payload system to passively descend along a real descent trajectory at least nominally corresponding to the predicted descent trajectory.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 schematically illustrates a method for operating a parachute-payload system with respect to a predetermined target zone location according to a first example of the presently disclosed subject matter.

Fig. 2(a) schematically illustrates an example of a parachute-payload system according to the presently disclosed subject matter, in which the respective primary parachute system is in the deployed configuration; Fig. 2(b) schematically illustrates the example of Fig. 2(a) in stowed configuration.

Fig. 3 schematically illustrates a predicted descent trajectory according to an example of the presently disclosed subject matter.

Fig. 4 schematically illustrates construction of a predicted descent trajectory according to an example of the presently disclosed subject matter.

Fig. 5 schematically compares a real descent trajectory with a predicted descent trajectory according to an example of the presently disclosed subject matter.

Fig. 6 schematically illustrates transportation of a parachute-payload system to a release location via a carrier aircraft or carrier missile, and compares a real descent trajectory with a predicted descent trajectory according to an example of the presently disclosed subject matter.

Fig. 7 schematically illustrates transportation of a parachute-payload system to a release location via a carrier rocket and compares a real descent traj ectory with a predicted descent trajectory according to an example of the presently disclosed subject matter.

Fig. 8 schematically illustrates method steps relating to evaluation of deviation between real descent trajectory with a predicted descent trajectory, including option of applying a final approach landing maneuver in the operation of a parachute-payload system according to an example of the presently disclosed subject matter.

Fig. 9 schematically illustrates an example of an option of applying a final approach landing maneuver in the operation of a parachute-payload system, including a free-fall trajectory step, according to an example of the presently disclosed subject matter.

Fig. 10(a) schematically illustrates an example of a parachute-payload system according to the presently disclosed subject matter, in which the respective secondary parachute system is in the stowed configuration; Fig. 10(b) schematically illustrates the example of Fig. 10(a) in deployed configuration.

Fig. 11 schematically illustrates an option of applying a final approach landing maneuver in the operation of a parachute-payload system, including a guided trajectory step, according to an example of the presently disclosed subject matter.

Fig. 12 schematically illustrates an option of applying a final approach landing maneuver in the operation of a parachute-payload system, including a guided trajectory step and a free-fall step, according to an example of the presently disclosed subject matter.

Fig. 13 schematically illustrates an option of applying a final approach landing maneuver in the operation of a parachute-payload system, including a guided trajectory step and a free-fall step, according to another example of the presently disclosed subject matter.

Fig. 14 schematically illustrates an option of applying a final approach landing maneuver in the operation of a parachute-payload system, including a guided trajectory step and a free-fall step, according to another example of the presently disclosed subject matter.

DETAILED DESCRIPTION

Referring to Fig. 1, a method for operating a parachute-payload system with respect to a predetermined target zone location according to a first example of the presently disclosed subject matter, generally designated 1000, comprises the steps:

1200 ~ providing the parachute-payload system;

2000 ~ constructing a predicted descent trajectory for the parachute-payload system from a nominal start altitude to the target zone location based on meteorological data;

3000 ~ deploying the parachute-payload system to passively descend along a real descent trajectory, at least nominally corresponding to the predicted descent trajectory, starting at a chosen deployment location on the predicted descent trajectory. Referring to Fig. 2(a) and Fig. 2(b), in at least one example, the parachute-payload system (also interchangeably referred to herein as a payload-parachute system), generally designated with reference numeral 100, comprises a payload 120 coupled to at least a primary parachute arrangement 200.

For example, such a payload 120 can include an instrument platform comprising a plurality of instruments, for example including imaging sensors, radar, lidar and/or other sensors, capable of providing data relating to objects in the atmosphere and/or in space and/or on the ground, that are within the respective field of view and/or line of sight of each such instrument. Additionally or alternatively, the instrument platform can include sensors for measuring or monitoring atmospheric parameters, for example air density, air temperature, air pollutants, and so on. Additionally or alternatively, the instrument platform can include communication equipment for enabling or facilitating communication between a number of entities, each of which can be ground based, seaborne, or airborne, or spacebome, for example.

In at least this example, the primary parachute arrangement 200 comprises one primary parachute 220, selectively deployable from a respective stowed configuration SC (Fig. 2(b)) to a respective deployed configuration DC (Fig. 2(a)) when coupled to the payload 120. The primary parachute is non-steerable in operation of the parachute-payload system 100 at least concurrent with the respective primary parachute being in the respective deployed configuration. While in this example the primary parachute arrangement 200 comprises one primary parachute 220, in alternative variations of this example, the primary parachute arrangement 200 can comprises more than one primary parachute.

For example, such a primary parachute 220 can be in the form of a drag parachute, for example a canopy parachute.

In at least this example, such a primary parachute 220 is coupled to the payload 120 in a non-steerable manner. For example, the payload 120 is devoid of any actuators operatively coupled to the primary parachute 220 in a manner that would allow the primary parachute 220 to be actively steered in the deployed configuration DC. Alternatively, the payload 120 can have actuators operatively coupled to the primary parachute 220, but are not used for steering the primary parachute 220, at least during part or all of step 3000. According to an aspect of the presently disclosed subject matter, the one or more primary parachutes 220 are configured for drifting with the local wind, such as to minimize or eliminate any relative lateral velocity between the parachute-payload system 100 with the primary parachute arrangement 200 deployed in the deployed configuration DC, and the immediately surrounding atmosphere, which is itself moving relative to the Earth at a speed and direction corresponding to the wind speed and wind direction at the respective altitude. It is of course understood that at the same time, the parachute-payload system 100 with the primary parachute arrangement 200 deployed in the deployed configuration DC, is descending at a respective descent velocity with respect to the aforesaid immediately surrounding atmosphere around the parachute-payload system 100.

Referring also to Fig. 3, in at least this example, step 2000 comprises constructing the predicted descent trajectory PDT for the parachute-payload system 100 from a nominal start altitude SA to the target zone location TZ by extrapolating backwards starting from the target zone location TZ, utilizing meteorological data MD corresponding to at least an atmospheric zone AZ defined between the target zone location TZ and the nominal start altitude SA.

In at least one example, and referring to Fig. 4, the predicted descent trajectory PDT is constructed by first modelling the atmospheric zone AZ as a series of contiguous control volumes CV. Each control volume CV comprising a respective altitude portion ACV between a respective lower control volume altitude LCVA and a respective upper control volume altitude UCVA.

As will become clearer herein, the control volumes CV are in serially adjacent to one another such that for any pair of vertically adjacent contiguous control volumes CV, the upper control volume altitude UCVA of the relatively lower control volume CV is coincident with the lower control volume altitude LCVA of the relatively upper control volume CV.

The magnitude of each altitude portion ACV can be chosen in a variety of ways; furthermore, the magnitude of the altitude portions ACV can be uniform along the atmospheric zone AZ, or can vary between the control volumes CV within the atmosphere zone AZ. For example, the magnitude of each altitude portion ACV can be chosen according to the characteristics of the meteorological data MD. For example, the magnitude of each altitude portion ACV can correspond to a contiguous altitude portion of the atmospheric zone AZ wherein the respective wind velocity Vw and/or the respective wind direction Dw remain within a predetermined range, wherein each one of these parameters can be considered to be essentially constant.

For example, the magnitude of each altitude portion ACV can correspond to a contiguous altitude portion of the atmospheric zone AZ wherein the respective wind velocity Vw remains within ±10km/h of an average wind velocity within the altitude portion ACV, and thus within the respective control volume CV. Alternatively, the magnitude of each altitude portion ACV can correspond to a contiguous altitude portion of the atmospheric zone AZ wherein the respective wind direction Dw remains within ±5° in azimuth and/or within ±10° in elevation, of an average wind direction within the altitude portion ACV, and thus the respective control volume CV.

For the purpose of the construction of the predicted descent trajectory PDT, it can be assumed that during descent of the parachute-payload system 100 with the one or more primary parachutes 220 of the primary parachute system 200 in deployed configuration DC, the parachute-payload system 100 is passively carried by atmospheric winds at velocity and direction corresponding to the local velocity and direction of the local wind vector. Furthermore, and referring also to Fig. 2(a) and 2(b), the parachute-payload system 100 is considered to be concurrently descending passively within each respective control volume CV, at a descent velocity VA given by the following relationship: wherein:

VA - is the descent velocity; p - is the air density corresponding to the respective control volume CV;

S - is the combined plan area of the one or more primary parachutes 220; CD - is the drag coefficient of the one or more primary parachutes 220;

W - weight of the parachute-payload system. The aforesaid meteorological data MD provides, for each said altitude portion ACV, and thus for the respective control volume CV, at least the respective values for air density p, the respective wind velocity Vw and the respective wind direction Dw

Starting with the control volume CV and the altitude portion ACV corresponding to the target zone location TZ, the respective altitude H, longitude X, and latitude Y of the target zone location TZ are known, since this is where it is desired for the parachute-payload system 100 to reach. As will become clearer herein, a corresponding first portion PTi of the predicted descent trajectory PDT is calculated by essentially extrapolating the theoretical path taken by the parachute-payload system 100 within the corresponding first control volume, also designated herein as CVi, such as to arrive at the target zone location TZ from the respective upper control volume altitude UCVA. As will become clearer herein, in at least this example this is done by determining respective descent velocity VAI and the respective wind-induced displacement WDi corresponding to the respective meteorological data corresponding to the first control volume CVi. The step of extrapolating the aforesaid theoretical path can consist of predicting the starting point location LCui , for example the corresponding latitude and longitude of the starting point location LCui at the altitude corresponding to the respective upper control volume altitude UCVA of the first control volume CVi, such that would cause the parachute-payload system 100 to passively drift to the target zone location TZ under the influence of the respective wind velocity Vw and the respective wind direction Dw within the first control volume CVi (thereby providing the respective wind-induced displacement WDi) and while descending at the corre4spdong descent velocity VAI relative to the air within the first control volume CVi.

The respective descent velocity VAI provides a respective nominal residence time Ti within the respective first control volume CVi. If the respective wind direction and wind speed have corresponding components in the vertical direction, then the nominal residence time Ti can be adjusted accordingly. A downward wing velocity component (for example a down draught) will correspondingly shorten the residence time Ti, while an upward wing velocity component (for example a thermal) will correspondingly lengthen the residence time Ti.

The respective wind-induced displacement WDi for the first control volume CVi corresponds to a respective three-dimension displacement within the respective control volume CVi, between the respective lower control volume altitude LCVA and the respective upper control volume altitude UCVA, along a vector corresponding to the respective wind direction Dw Where there is no significant vertical component to the wind direction Dw or wind velocity Vw, the wind-induced displacement WDi relates to a change in the longitude and/or latitude as compared with the longitude X and/or latitude Y corresponding to the target zone location TZ. Where there is a significant vertical component to the wind direction Dw or wind velocity Vw, the wind-induced displacement WDi, this factor can be accounted for by correspondingly adjusting the residence time Ti in the control volume CVi, for example.

In at least this example, the magnitude of the respective three-dimension wind- induced displacement WDi can be being derived from the magnitude of the respective wind velocity Vw and the respective residence time Ti, for example by applying the relationship:

WDi = Vw*Ti

In at least this example, the direction of the respective three-dimension wind-induced displacement WDi can be being derived from the respective wind direction Dwi, and is in general parallel to said wind direction Dwi.

Thus, the components of the wind-induced displacement WDi parallel to the longitude and latitude can be added to the longitude and latitude of the target zone location TZ, thereby providing the longitude and latitude of the predicted descent trajectory PDT at the upper control volume altitude UCVA of the first control volume CVi.

Since the lower control volume altitude LCVA of the next contiguous control volume CV coincides with the upper control volume altitude UCVA of the first control volume CVi, the respective portion of the predicted descent trajectory PDT within this next control volume CV, and thus the longitude and latitude of the predicted descent trajectory PDT at the respective upper control volume altitude UCVA of this next control volume CV can be predicted in a similar manner to that of the first control volume CVi, mutatis mutandis, the main different being that the starting location of the predicted descent trajectory PDT at the respective lower control volume altitude LCVA will be the longitude and latitude of the predicted descent trajectory PDT at the upper control volume altitude UCVA of the first control volume CVi, rather than the longitude and latitude of the target zone location TZ.

Thus, for each next control volume CVi, the respective starting location of the predicted descent trajectory PDT at the respective lower control volume altitude LCVAi will be the longitude and latitude of the predicted descent trajectory PDT at the respective upper control volume altitude UCVAi-i of the previous control volume CVi-i, and the respective location of the predicted descent trajectory PDT at the respective upper control volume altitude UCVAi will be at a longitude and latitude calculated in a similar manner to that discussed above, mutatis mutandis, for example as follows. The previous control volume CVi-i refers to the control volume immediately adjacent and vertically below the "next" control volume CVi.

Thus, the "next" control volume CVi has a corresponding altitude portion ACVi, respective lower control volume altitude LCVAi and a respective upper control volume altitude UCVAi. The respective altitude, longitude, and latitude of the predicted descent trajectory PDT at the respective lower control volume altitude LCVAi will be identical to the longitude and latitude of the predicted descent trajectory PDT at the respective upper control volume altitude UCVAi-i of the previous control volume CVi-i, which is already known, having been previously calculated in a similar manner, going back to the original first control volume CVi in which the respective altitude, longitude, and latitude of the predicted descent trajectory PDT at the respective lower control volume altitude LCVAi of course corresponds to the target zone location TZ.

As will become clearer herein, a corresponding next portion PTi of the predicted descent trajectory PDT is calculated for this "next" control volume CVi by essentially extrapolating the theoretical path taken by the parachute-payload system 100 within the corresponding "next" control volume CVi, such as to arrive at the respective lower control volume altitude LCVAi from the respective upper control volume altitude UCVAi. As will become clearer herein, in at least this example this is done by determining respective descent velocity VAI and the respective wind-induced displacement WDi corresponding to the respective meteorological data corresponding to the aforesaid "next" control volume CVi. The step of extrapolating the aforesaid theoretical path can consist of predicting the starting point location LCui, for example the corresponding latitude and longitude of the starting point location LCui at the altitude corresponding to the respective upper control volume altitude UCVAi of the aforesaid "next" control volume CVi, such that would cause the parachute-payload system 100 to passively drift to the respective altitude, longitude, and latitude of the predicted descent trajectory PDT at the respective lower control volume altitude LCVAi, under the influence of the respective wind velocity Vwi and the respective wind direction Dwi within the aforesaid "next" control volume CVi and while descending at the corresponding descent velocity VAI relative to the air within the aforesaid "next" control volume CVi.

The respective descent velocity VAI provides a respective nominal residence time Ti within the respective aforesaid "next" control volume CVi. If the respective wind direction and wind speed have corresponding components in the vertical direction, then the nominal residence time Ti can be adjusted accordingly. A downward wing velocity component (for example a down draught) will correspondingly shorten the respective residence time Ti, while an upward wing velocity component (for example a thermal) will correspondingly lengthen the respective residence time Ti.

The respective wind-induced displacement WDi for the aforesaid "next" control volume CVi corresponds to a respective three-dimension displacement within the respective control volume CVi, between the respective lower control volume altitude LCVAi and the respective upper control volume altitude UCVAi, along a vector corresponding to the respective wind direction Dwi. Where there is no significant vertical component to the wind direction Dwi or wind velocity Vwi, the wind-induced displacement WDi relates to a change in the geographical location (i.e., latitude and/or longitude) as compared with the the geographical location (i.e., latitude and/or longitude) corresponding to the respective geographical location (i.e., altitude, longitude, and latitude) of the predicted descent trajectory PDT at the respective lower control volume altitude LCVAi. Where there is a significant vertical component to the wind direction Dwi or wind velocity Vwi, the wind- induced displacement WDi, this factor can be accounted for by correspondingly adjusting the residence time Ti in the control volume CVi, for example.

In at least this example, the magnitude of the respective three-dimension wind- induced displacement WDi can be being derived from the magnitude of the respective wind velocity Vwi and the respective residence time Ti, for example by applying the relationship: WDi= Vwi*Ti

In at least this example, the direction of the respective three-dimension wind-induced displacement WDi can be being derived from the respective wind direction Dwi and is in general parallel to said respective wind direction Dwi.

Thus, the components of the wind-induced displacement WDi parallel to the longitude and latitude directions are added to the values of the respective longitude and respective latitude of the predicted descent trajectory PDT at the respective lower control volume altitude LCVAi, thereby providing the respective longitude and respective latitude of the predicted descent trajectory PDTi at the respective upper control volume altitude UCVAi of the aforesaid "next" control volume CVi.

It is to be noted that meteorological data relating to each control volume CV can be at least in some cases extrapolated from available meteorological data in other control volumes CV, for example from available meteorological data in control volumes CV directly above and below the respective control volumes CV. For example, where the available meteorological data does not include values for any one of air density and/or wing velocity and/or wind direction, in a particular control volume CV, the respective values for air density and/or wing velocity and/or wind direction in that control volume CV can be estimated by extrapolating the known values for these parameters in the adjacent control volume(s) CV.

In this manner, the predicted descent trajectory PDT can be extrapolated backwards from the predetermined target zone TZ to any desired altitude, for example up to a desired nominal start altitude SA, thereby enabling providing longitude and latitude coordinates associated with any altitude between the altitude corresponding to the predetermined target zone TZ and the nominal start altitude SA.

It is to be noted that in alternative variations of this example, the predicted descent trajectory PDT can instead be constructed by first modelling the atmospheric zone AZ as a series of contiguous control volumes CV, in which each control volume CV is defined by a predetermined residence time therein. In such examples, the respective altitude portion ACV between a respective lower control volume altitude LCVA and a respective upper control volume altitude UCVA can be determined from the respective chosen residence time, and the respective descent velocity.

It is to be noted that in at least some other examples, step 2000 comprises constructing the predicted descent trajectory PDT for the parachute-payload system 100 from a nominal start altitude SA to the target zone location TZ by extrapolating forwards starting from the nominal start altitude SA, utilizing meteorological data MD corresponding to at least an atmospheric zone AZ defined between the target zone location TZ and nominal start altitude SA. In such examples, a particular geographical location can be associated with the nominal start altitude SA, and a first iteration can be conducted to extrapolate a first predicted descent trajectory PDT to arrive at a landing geographical location at the same altitude as that of the target zone TZ. The deviation between the landing geographical location and the geographical location of the target zone TZ can be determined, and if greater than a predetermined threshold value, the geographical location of the nominal start altitude SA can be modified, and a new predicted descent traj ectory PDT can be constructed to arrive at a landing geographical location at the same altitude as that of the target zone TZ. This step can be repeated until the aforesaid deviation between the landing geographical location and the geographical location of the target zone TZ is within the predetermined threshold value. Such an iteration process can be based on gradient descent techniques, for example. In any case, for example, the predicted descent trajectory PDT can be constructed in each iteration cycle using meteorological data, for example air density, wind velocity and wind direction, in a series of control volumes, for example in a similar but inverted manner to that of the example of Fig. 4, mutatis mutandis.

Without being bound to theory, the present inventor considers that, at least theoretically, the parachute-payload system 100 deployed at any point along the predicted descent trajectory PDT with the respective primary parachute arrangement in deployed configuration DP would follow the predicted descent trajectory PDT to the target zone location TZ under the influence of the considered meteorological data.

Thus, and referring to Fig. 5 for example, according to step 3000 the parachutepayload system 100 is deployed to passively descend along a real descent trajectory RDT, at least nominally corresponding to the predicted descent trajectory PDT, starting at any chosen deployment location DL on the predicted descent trajectory PDT. In at least this example, step 3000 comprises first choosing a desired deployment location DL on predicted descent trajectory PDT as a start location for initiating the descent of the parachute-payload system 100 with the primary parachute arrangement 200 in the deployed configuration DC.

Then, the parachute-payload system 100 is transported to a release location RL, whereupon the parachute-payload system 100 is released in a manner such as to enable the parachute-payload system 100 to reach the deployment location DL.

Any suitable transport system can be used for transporting the parachute-payload system 100 to the release location RL.

It is to be noted that according to an aspect of the presently disclosed subject matter, such a transport system, for example in the form of a carrier vehicle, is configured for operating exclusively within the atmosphere, at least in the capacity of transporting the parachute-payload system 100 to the release location RL, and thus cannot operate in space. In particular, the step of transporting the parachute-payload system 100 to the release location RL excludes any passage through or operation in space.

For example, and referring to Fig. 6, in one such example, such a transport system can include a guidable platform, for example in the form of a guide missile or an air vehicle 400 for carrying the parachute-payload system 100 to the release location RL, for example in a payload bay or in an external pod or stores. The release location RL can be chosen in close proximity to the deployment location DL such that, taking into account freefall characteristics of the parachute-payload system 100 with the primary parachute arrangement 200 in stowed configuration SC, the velocity of the carrier air vehicle at release, and the meteorological data corresponding to the release altitude, it can be expected for the parachute-payload system 100 to reach the deployment location DL with a small margin of error.

In another example, and referring to Fig. 7, such a transport system can include a generally non-guidable platform, for example in the form of a carrier rocket 500 for launching the parachute-payload system 100, from an Earth-bound location EL. Such an Earth-bound location EL can include, for example, a land-based platform, or a fixed sea platform, or alternatively from a mobile platform, for example from a sea-based platform, or from an airborne platform, or a land mobile platform. The carrier rocket 500 is configured to rapidly carry the parachute-payload system 100 to the respective release location RL along a respective launch trajectory LT. In such a case, the release location RL can be chosen in relation to the deployment location DL such that, taking into account deceleration and/or ballistic and/or freefall characteristics of the parachute-payload system 100 with the primary parachute arrangement 200 in stowed configuration SC after release from the carrier rocket 500, the velocity of the carrier rocket 500 at release, and the meteorological data corresponding to the release altitude, it can be expected for the parachute-payload system 100 to reach the deployment location DL with a small margin of error.

For example, the carrier rocket 500 can be launched from a suitable launch site corresponding to the Earth-bound location EL, at launch conditions such as to reach the release location RL in a generally unguided manner. Such conditions can be set such as to cause the carrier rocket 500 to nominally follow the launch trajectory LT (also referred to herein interchangeably as the predicted rocket trajectory) that intersects the release location RL

For example, such launch conditions can include launch azimuth and elevation for the carrier rocket 500 at the Earth-bound location EL. Furthermore, the launch trajectory LT is constructed based on meteorological data between the launch site at the Earth-bound location EL and the release location RL - in other words, the effect of air density, wind speed and wind direction on the carrier rocket 500 at an altitude range between Earth-bound location EL and the release location RL can be calculated using the meteorological data. The launch azimuth and elevation for the carrier rocket 500 at the Earth-bound location EL can then be chosen such that the launch trajectory LT, as affected by the meteorological conditions between the Earth-bound location EL and the release location RL, will deliver the carrier rocket 500 to the release location RL.

In at least some examples, the target zone TZ and the launch site (i.e., the Earth- bound location EL) are geographically spaced within a spacing, wherein the spacing is not greater than any one of the following: 30km, 25km, 20km, 15km, 10km, 5km, 3km, 2km, 1km, 0.5km.

In any case, once the parachute-payload system 100 reaches the desired deployment location DL on the predicted descent trajectory PDT, in at least this example step 3000 continues by ensuring that the at least one primary parachute 220 is in the respective deployed configuration DC at least when the parachute-payload system 100 is located at the deployment location DL. Typically, the parachute-payload system 100 reaches the desired deployment location DL with the primary parachute arrangement 200 in stowed configuration SC, and at the deployment location DL the parachute-payload system 100 operates to deploy the one or more primary parachutes 220 to the respective deployed configuration. For example, the primary parachute arrangement 200 can be configured for deploying to the deployed configuration DC at a predetermined altitude, corresponding to the altitude at the deployment location DL, and this can be preset on the parachute-payload system 100 prior to transporting the parachute-payload system 100 to the release location RL. Alternatively, the parachute-payload system 100 can comprise a communication module and a controller, and is configured for receiving a deployment command from a command center via the communication module, to thereby initiate deployment of the one or more primary parachutes 220 to the respective deployed configuration DC when desired.

Once the parachute-payload system 100 is at the deployment location DL with the one or more primary parachutes 220 in the respective deployed configuration DC, the parachute-payload system 100 is allowed to passively descend along a real descent traj ectory RDT at least nominally corresponding to the predicted descent trajectory PDT.

As discussed above, the descent velocity VA given by the relationship: and thus in applications of the presently disclosed subject matter in which it can be advantageous to maximize the time for descent from the deployment location DL to the target location, the plan area S of the primary parachute system 100 can be maximized, and/or the altitude corresponding to the deployment location DL can be maximized.

It is also to be noted that for the decent velocity VA will in general also decelerate at lower altitudes as compared with higher altitudes, due to the increasing value of the air density p in a descending direction through the atmosphere.

Without being bound to theory, the present inventor considers that, in at least some implementations of the presently disclosed subj ect matter, the parachute-payload system 100 follows a respective real descent trajectory RDT rather than the predicted descent trajectory PDT towards an actual target location ATZ rather than to the target zone location TZ. Also without being bound to theory, and referring for example to Fig. 5, the present inventor considers that, in at least some such implementations of the presently disclosed subject matter, the deviation DV between the respective real descent trajectory RDT and the predicted descent traj ectory PDT can increase in magnitude the closer the parachute-payload system 100 is to the target zone TZ.

For example, such deviations DV can be defined as being in directions orthogonal to the altitude, for example in directions parallel to the longitude and/or latitude.

Optionally, the parachute-payload system 100 can comprise a sensor system, for example a GPS or other sensors that can determine geographical location, as well as sensors for determining the altitude of the parachute-payload system 100, for example altimeters. Additionally or alternatively, the parachute-payload system 100 can include an inertial platform including a system of accelerometers, which can be configured for determining three-dimensional location of the parachute-payload system 100 after reaching the deployment location LC. Optionally, a suitable communication module can be included in the parachute-payload system 100 to enable transmission of the current location of the parachute-payload system 100 along the real descent trajectory RDT. For example, such communication can be via satellite.

Additionally or alternatively, an external source can track the location of the parachute-payload system 100 along the real descent trajectory RDT, for example via radar.

Once the actual three-dimensional position of the parachute-payload system 100 is known in real time, the position can be compared with the corresponding position at the same altitude as predicted in the predicted descent trajectory PDT, and thus the corresponding deviation DV at the altitude can be determined.

Such determination can be made by the parachute-payload system 100 itself, for example via a controller (not shown) included in the payload 120 in which case the controller includes the predicted descent trajectory PDT, for example in electronic form in a memory of the controller. Additionally or alternatively, such determination can be made by via a ground station (not shown), which either tracks the position of the parachute-payload system 100 directly, or receives positional data relating to the parachute-payload system 100 from a suitable external tracking source or from the parachute-payload system 100 itself.

In such alternative variations of the above example illustrated in Fig. 1, and referring also to Fig. 8, step 3000 can be followed by an evaluation step 3200, in which the deviation DV between the real descent trajectory RDT and the predicted descent trajectory PDT is tracked as the parachute-payload system 100 descends from the deployment location DL. According to this evaluation step, so long as the deviation DV remains within a predetermined threshold, the parachute-payload system 100 is allowed to continue to passively descend along the real descent trajectory RDT with the primary parachute system 200 coupled to the payload 120 and in the deployed configuration DC. It is to be noted that such deviation DV can be uniform along the atmospheric zone AZ, or can vary with the actual altitude within the atmospheric zone AZ, for example.

On the other hand, when the deviation DV exceeds a threshold value (which can occur at a corresponding deviation altitude DA), the method further includes the step 3400 of causing the parachute-payload system 100 to execute a final approach landing maneuver FALM. Under such conditions, the predicted descent trajectory PDT is abandoned in favor of the final approach landing maneuver FALM, in an attempt to enable arriving at an actual target zone ATZ that is closer to the desired target zone TZ than would be the case if simply attempting to passively follow the predicted descent trajectory PDT via the deployed primary parachute system 200.

Step 3400 comprises first causing the parachute-payload system 100 to decouple and discard the primary parachute system 200, so that the payload 120 is no longer physically connected to the primary parachute system 200.

Step 3400 further comprises subsequently causing the parachute-payload system 100 to execute a free-fall descent step 3420 and/or a guided landing descent step 3440.

In the free-fall descent step 3420, and referring also to Fig. 9, the parachute-payload system 100, now devoid of the primary parachute system 200, is allowed to follow a freefall trajectory FF through a first desired altitude range ARI towards the ground, with minimal respective free-fall wind-induced displacement WDFF as compared with the respective wind-induced displacement WD that would be expected to occur if the primary parachute system 200 were still coupled to the payload 120 and in the deployed configuration DC. In many cases, such free-fall wind-induced displacement WDFF can be close to zero, such that the modified parachute-payload system 100 (i.e., absent the primary parachute system 200) falls nominally vertically through the desired first altitude range ARI towards the ground.

In at least examples in which it is desired to execute the guided landing descent step 3440, and referring also to Fig. 10(a) and Fig. 10(b), the parachute-payload system 100 further comprises a secondary parachute system 300 configured for enabling the parachutepayload system 100 to be actively steered or guided through a second desired altitude range AR2 while descending towards the ground.

In at least this example, the secondary parachute arrangement 300 comprises one secondary parachute 320, selectively deployable from a respective stowed configuration SC2 (Fig. 10(a)) to a respective deployed configuration DC2 (Fig. 10(b)) when coupled to the payload 120. The secondary parachute 320 is steerable in operation of the parachutepayload system 100 at least concurrent with the respective secondary parachute 320 being in the respective deployed configuration DC2. While in this example the secondary parachute arrangement 300 comprises one secondary parachute 320, in alternative variations of this example, the secondary parachute arrangement 300 can comprises more than one primary parachute.

For example, such a secondary parachute 320 can be in the form of a descending parachute or an ascending parachute, for example a ram-air type parachute.

In at least this example, such a secondary parachute 320 is coupled to the payload 120 in a steerable manner via lines 325. For example, the payload 120 comprises a controllable actuator system 330 operatively coupled to the secondary parachute 320 in a manner that would allow the secondary parachute 320 to be actively steered in the deployed configuration DC2.

In the guided landing descent step 3440, and referring also to Fig. 11, the parachutepayload system 100, now devoid of the primary parachute system 200, but having the secondary parachute system 300 in the deployed configuration DC2, is actively steered to follow a guided trajectory GT through a second desired altitude range AR2 towards the ground, to attempt to correct the deviation DV. In many cases, if the second desired altitude range AR2 is large enough and the meteorological conditions within the second desired altitude range AR2 are conducive for steering, such a guided trajectory GT can enable the modified parachute-payload system 100 (i.e., absent the primary parachute system 200) to approach the longitude and latitude of the target zone TZ closer than as compared with the respective the deviation DV that would be expected to occur if the primary parachute system 200 were still coupled to the payload 120 and in the deployed configuration DC and in the absence of the secondary parachute arrangement 300 in the respective deployed configuration DC2. Such steering of the secondary parachute system 300 can include any suitable maneuver, for example one or more of steering to the left, steering to the right, executing a spiral maneuver, executing a helical maneuver, and so on.

It is to be noted that the relative magnitudes of the first desired altitude range ARI and the second desired altitude range AR2, and the sequence in which the-fall descent step 3420 and the guided landing descent step 3440 are executed, and the choice of executing one or both of free-fall descent step 3420 and the guided landing descent step 3440, can depend on a number of factors. Such factors can include, for example, the magnitude of the deviation DV at the deviation altitude DA, whether the real descent trajectory RDT has overshot the geographical location of the desired target zone TZ, whether significant changes in wind velocity and/or wind direction are occurring and unaccounted for in the predicted descent trajectory PDT, and so on.

In one such example, and referring again to Fig. 9, the Step 3400 comprises only causing the parachute-payload system 100 to execute a free-fall descent step 3420, and does not include the guided landing descent step 3440. In such a case, the first desired altitude range ARI essentially extends from the deviation altitude DA to the altitude of the target zone TZ, which can be on the ground for example.

In another such example, and referring again to Fig. 11, the Step 3400 comprises only causing the parachute-payload system 100 to execute a guided landing descent step 3440, and does not include the free-fall descent step 3420. In such a case, the second desired altitude range AR2 essentially extends from the deviation altitude DA to the altitude of the target zone TZ, which can be on the ground for example. In yet another example, and referring to Fig. 12 the Step 3400 comprises causing the parachute-payload system 100 to execute first a guided landing descent step 3440 during descent through the second desired altitude range AR2, followed by a free-fall descent step 3420 through the first desired altitude range ARI. For example, at the deviation altitude DA the respective real descent trajectory can be projected (annotated at RDT' in Fig. 12) to undershoot the parachute-payload system 100 by a large margin from the desired target zone TZ. The guided landing descent step 3440 enables the parachute-payload system 100 to be brought geographically closer to the target zone TZ via a suitable guided trajectory GT, for example to almost above the target zone TZ but at an altitude therefrom. Thereafter, the secondary parachute system 300 can be decoupled from the payload 120 and discarded, and in the respective free-fall descent step 3420, the payload descends along free-fall trajectory FF rapidly, almost vertically to the vicinity of the target zone TZ, depending on the wind velocities at these low altitudes.

In yet another example, and referring to Fig. 13, the Step 3400 comprises causing the parachute-payload system 100 to execute first a guided landing descent step 3440 during descent through the second desired altitude range AR2, followed by a free-fall descent step 3420 through the first desired altitude range ARI. For example, at the deviation altitude DA the respective real descent trajectory RDT is already overshooting, or can be projected to overshoot, the parachute-payload system 100 with respect to the desired target zone TZ. For example, the respective wind direction WD at and/or below the deviation altitude DA can be expected to be such as to continue the overshoot. In at least some such examples, the respective guided landing descent step 3440 can enable the parachute-payload system 100 to be brought back towards, and geographically closer to, the target zone TZ via a suitable guided trajectory GT, for example to almost above the target zone TZ but at an altitude therefrom. Thereafter, the secondary parachute system 300 can be decoupled from the payload 120 and discarded, and in the respective free-fall descent step 3420, the payload descends along free-fall trajectory FF rapidly, almost vertically to the vicinity of the target zone TZ, depending on the wind velocities at these low altitudes.

In yet another example, and referring to Fig. 14, the Step 3400 comprises causing the parachute-payload system 100 to execute first a free-fall descent step 3420 through the first desired altitude range ARI, followed by a guided landing descent step 3440 during descent through the second desired altitude range AR2. For example, at the deviation altitude DA the respective real descent trajectory can be projected (annotated at RDT' in Fig. 14) to overshoot the parachute-payload system 100 with respect to the desired target zone TZ. For example, the respective wind direction WD at and/or below the deviation altitude DA can be expected to be such as to continue the overshoot. With the secondary parachute system 300 still in the respective stowed configuration SC2, in the respective free-fall descent step 3420, the parachute-payload system 100 descends along free-fall trajectory FF rapidly, almost vertically to the vicinity of the target zone TZ but at an altitude therefrom, depending on the wind velocities at these low altitudes, through the first altitude range ARI. Thereafter, the respective guided landing descent step 3440 can enable the parachute-payload system 100 to be brought back towards, and geographically closer to, the target zone TZ via a suitable guided trajectory GT, for example to the target zone TZ.

It is to be noted that in alternative variations of the above examples, step 3400 can instead comprise more than one free-fall descent steps 3420 and/or more than one guided landing descent steps 3440, in which the respective free-fall descent steps 3420 and the respective guided landing descent steps 3440 are intercalated. In such examples, the secondary parachute system 300 can include a respective plurality of secondary parachutes 320, wherein at the start of each respective guided landing descent step 3440 one such secondary parachute 320 is deployed to the respective deployed configuration DC2, and at the end of the respective guided landing descent step 3440 the deployed secondary parachute 320 is decoupled and discarded. The parachute-payload system 100 then proceeds with the next free-fall descent step 3420 through the respective first desired altitude range ARI, after which starts a subsequent respective guided landing descent step 3440 in which another such secondary parachute 320 is deployed to the respective deployed configuration DC2. At the end of this respective guided landing descent step 3440 the deployed secondary parachute 320 is also decoupled and discarded, and enables another free-fall descent step 3420 to be executed. In this manner, any number of intercalated free-fall descent steps 3420 and guided landing descent steps 3440 can be applied to the parachute-payload system 100 to further control the descent of the parachute-payload system 100 past the deviation altitude DV and towards the target zone TZ, depending on the magnitude of the deviation altitude DV, meteorological conditions, and other factors.

In at least one or more of the above examples, the nominal start altitude SA can be at an altitude of between about 10km and about 40km above sea level. For example, the nominal start altitude SA can be above at least one of the following altitudes above sea level: 10km, 15km, 20km, 25km, 30km, 35km, 39km. For example, the nominal start altitude SA is chosen at a respective altitude above sea level not exceeding at least one of: 60km, 50km, 40km.

In at least one or more of the above examples, the deployment location DL can be at an altitude of between about 10km and about 40km. For example, the deployment location DL can be above at least one of the following altitudes above sea level: 10km, 15km, 20km, 25km, 30km, 35km, 39km. For example, the deployment location DL is chosen at a respective altitude above sea level not exceeding at least one of: 60km, 50km, 40km.

In at least one or more of the above examples, the target zone TZ can comprise a geographical area of any one of up to: 1 square kilometer; 2 square kilometers; 5 square kilometers; 10 square kilometers; 20 square kilometers; 50 square kilometers; 100 square kilometers.

In at least one or more of the above examples, the deployment location DL is chosen having a respective geographical location within a predetermined radius from the geographical location of the predetermined target zone TZ. For example, such a radius can be between 50km and 200km, or between 10km and 300km.

In at least some examples, target zone TZ is an Earth surface zone, for example a ground surface landing zone or sea surface landing zone.

In at least some other examples, the target zone TZ is located at a predetermined final approach altitude above a ground surface landing zone or sea surface landing zone. Such a final approach altitude can correspond to a respective deviation altitude DA.

In at least one application of one or more of the above examples of the method according to the presently disclosed subject matter, the respective payload 120 comprises one or more sensors for detecting and/or tracking, optically and/or via radar, oncoming objects generally downwind of the deployment location DL. For example, such objects may be considered potential or actual threats, and thus hostile, and/or follow a ballistic path towards friendly or home territory. The parachute-payload system 100 can be launched in a relatively rapid manner to reach the deployment location DL whenever there is such an actual or suspected threat to provide detection and/or tracking data so long as the parachute- payload system 100 is at a sufficient altitude such that the line of sight of the sensors can still be directed to the incoming objects. When the deployment altitude is in the range 10km to 40km, the passive descent time of the parachute-payload system 100, i.e., the time taken for the parachute-payload system 100 to passively descend between the deployment location DL and the target zone TZ (or at least to passively descend between the deployment location DL and the deviation altitude DA) via the real descent trajectory RDT is in the range of between about 20minutes and about 60minutes, for example.

A feature of at least some examples of the method according to the presently disclosed subject matter is that the parachute-payload system 100 is returned to the target zone TZ, which is typically in friendly territory and optionally close to a launching point for reuse, and minimize the risk of the payload 120 drifting to land at an undesired location.

In the method claims that follow, alphanumeric characters and Roman numerals used to designate claim steps are provided for convenience only and do not imply any particular order of performing the steps.

Finally, it should be noted that the word “comprising” as used throughout the appended claims is to be interpreted to mean “including but not limited to”.

While there has been shown and disclosed examples in accordance with the presently disclosed subject matter, it will be appreciated that many changes may be made therein without departing from the scope of the presently disclosed subject matter as set out in the claims.