Abstract:
A display system for a parachutist is provided based on navigation data and calculations of locations where the parachutist should steer the parachute to increase likelihood of reaching a target. A two-dimensional representation of a navigation funnel is displayed. The display may increase situational awareness by use of color to indicate preferred positions in the navigation funnel.

Description:
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. W911QY-06-C-0104 awarded by U.S. Army Soldier Systems Center. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to navigation systems, and specifically to navigation and guidance systems for parachutists. 
     2. Description of Related Art 
     Special Operations soldiers, sailors, marines, and airmen engage in a type of parachuting that requires advanced training, special equipment, and a high degree of operational and situational awareness. These special types of operations include HALO (High Altitude Low Open) and HAHO (High Altitude High Open) jumps. These jumps may be performed at altitudes above 30,000 feet, requiring a long glide time onto a selected target. Poor weather, low or no visibility, and the use of bulky equipment, including insulating clothing, oxygen masks, combat packs, reserve chutes, and weapons are all challenges facing the special operator as he jumps. 
     The use of navigational computers in parachute jumps is known in the art. U.S. Pat. No. 7,302,340 (“the &#39;340 patent”), “High Altitude Parachute Navigation Flight Computer,” discloses a navigational computer having a display with a self centering satellite map, and a second “window” with a navigational “roadmap” providing a two-dimensional look ahead with right and left steering inputs, onto a 2-D graphical “highway” displayed by operation of an algorithm. A third window indicates selected navigational information, which may include waypoint tracking, glide ratio, ETA (estimated time of arrival, presumably on target), heading, and bearing. The display described is two-dimensional, and it is stated that “ . . . the autopilot graphical highway need not be truly three-dimensional but rather two-dimensional, providing look ahead for only right and left required inputs.” 
     What is needed is a display adapted to clearly display information based on three dimensions in a two-dimensional space that provides greater situational awareness to the parachutist than prior displays. 
     SUMMARY OF INVENTION 
     A display is provided that displays three-dimensional navigational information through a two-dimensional display. This display includes icons representing the parachutist and the target. The parachutist is guided onto a target through circles, normally eccentric, that are centered on a 3D line that is calculated based on descent rate and wind velocities. The radii of the circles for different altitudes, displayed for the parachutist, indicate the boundary of a three-dimensional volume (designated herein a “navigation funnel”) within which the parachutist is predicted to reach the selected target. The situational status of the parachutist may be further communicated by the use of colors or symbols in the circles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective 3-D view of a navigation funnel without wind. 
         FIG. 2  is a perspective 3-D view of a navigation funnel calculated for a constant wind velocity at different altitudes. 
         FIG. 3  is a perspective 3-D view of a navigation funnel calculated for varying wind velocities at different altitudes. 
         FIG. 4  is a view of a 2-D display based on the method and apparatus disclosed herein. 
         FIG. 5  is a flow chart illustrating gathering of data, performing calculations of a navigation funnel and outputting to hardware for display. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a perspective view of funnel  11  is illustrated. For this illustration, wind velocity is assumed to be zero at all altitudes. Line  13  is a hypothetical 3D line, which is determined only by the descent rate of the parachute and wind velocities. (A hypothetical 3D line will be defined herein as the center line of a volume or navigation tunnel within which a parachutist is predicted to reach the target.) Since wind velocity is assumed to be zero in this illustration, line  13  is vertical. Beginning at a given altitude, the three-dimensional volume within which the parachutists may reach target  14  is described by surface  11  of the navigation funnel. In this case the funnel is a cone. The circular cross-section of any point in the cone is determined by radius  12  around hypothetical 3D line  13 , where radius  12  is calculated by multiplying L/D (glide ratio) for the parachute by the parachutist&#39;s altitude. Said another way, radius  12  is the distance that a parachutist can travel forward relative to the wind at a given glide ratio (L/D) and at the current altitude. 
       FIG. 2  illustrates the effect of a constant wind velocity at different altitudes on the hypothetical 3D line and the three-dimensional volume within which the parachutists may reach target  24 . Hypothetical 3D line  21  is a straight line at an angle to vertical that is determined by vector addition of the vertical descent rate of the parachute and the velocity of the wind. Descent rate of the parachute is determined by weight supported by the parachute and canopy characteristics. Surface  22 , which again limits the three-dimensional spatial volume within which the parachutists may reach selected target  24 , is determined by the glide ratio (L/D) of the parachute. The radius of a circle around 3D line  21  at any altitude is again calculated by multiplying L/D for the parachute by the parachutist&#39;s altitude. 
     The general case is illustrated in  FIG. 3 , where wind velocities vary at different altitudes. In one embodiment, hypothetical 3D line  31  is calculated by starting at target  34  and calculating coordinates as a function of altitude by vector addition of the vertical descent rate of the parachute and the horizontal velocity of the wind, just as discussed above. This calculation will normally extend up to the altitude where the canopy is deployed. The resulting string of coordinates describes the three-dimensional path the parachute would take with no steering or forward movement relative to the wind. Input parameters to calculate line  31  include parachute descent rate, wind velocities vs altitude and target and canopy deployment and target coordinates. The 3D navigation tunnel is then calculated by calculating the radius from the 3D line a parachutist can be at present altitude and any lower altitude and still reach the target if he were to steer straight towards the 3D line, given the L/D of his parachute, with the limitation that he must reach the line when he reaches the target. Doing this calculation at selected altitudes produces the coordinates of the surface  32  of the navigation funnel. The funnel may twist and turn depending on the variation of the winds at altitude, but the cross-section of the funnel is circular at any altitude. 
     In other embodiments, other methods of calculating the hypothetical 3D line at the center of a navigation funnel may be used. For example, a stochastic method based on probabilities of wind velocities at different altitudes may be used. For purposes of the display method disclosed herein, any method of calculating the 3D line may be used. In each case, the radius of a circle around the 3D line is calculated using the L/D of the parachute as explained above. 
     Referring to  FIG. 4 , boundary  40  of a 2D display is illustrated as it may be presented to the parachutist. The hardware for the display may be comprised of any collection of components adapted for displaying graphical information. Preferably, the display device is capable of displaying information in more than one color. Suitable display devices include liquid crystal displays, cathode ray tubes, and projected images such as “heads up displays.” The display device may be chest mounted or a tablet or helmet-mounted. Night Vision Goggles (NVGs) may be used for the display device. The display disclosed herein may also displayed on wirelessly connected devices, such as an iPhone, where the display is created in a browser. 
     Circles of different radii that correspond to the surface at different altitudes of the navigation tunnel are shown on the display. Outer circle  43  has the radius of the tunnel at the current altitude of the parachutist. Icon  41  represents the present location and orientation of the parachutist, which may be determined by GPS data. Icon  42  represents the target of the parachutist. Eccentric circles within outer circle  43 , such as circle  44 , indicate the spatial extent within which the parachutist has the ability to reach the given target at lower altitudes. Each circle represents the surface of the navigation funnel, such as shown in  FIGS. 2 and 3 , at a selected altitude. These circles may be dotted or have other symbols. Circles may be displayed using a Night Vision Goggle (NVG) device, with the circles represented with various combinations of colors, blinking, dashed lines, line width or other symbols. Circles may be flashed onto the display or iteratively added then redrawn. The relative location of the centers of lower eccentric circles provides an indication of the wind direction and speed at current and lower altitudes. Steering the parachute to stay near the center of the circle at each altitude provides the highest probability of the parachutist attaining the target. 
     Preferably, the direction of the screen is always oriented with the direction of motion of the parachutist up and with the parachutist icon centered on the screen, as shown in  FIG. 4 . If the parachutist performs a turn, the target and funnel intersections will preferably rotate about the parachutist icon. The circles indicating the spatial range where it is possible to reach a given target may be continuously updated based on GPS measurements and other input data. The screen provides a visual description of the parachutist&#39;s situation. Relative bearing to target is provided and the displacements of the circles provide the parachutist with an indication of the wind velocity at different altitudes. The circles also clearly provide an indication of the ability to reach the target. The colors of the largest circle or any combination of circles or icons may change from green, meaning well with the ability to reach the target, to yellow, meaning possible to reach the target but on the very edge of possibility, to red, meaning that it is predicted that it is not possible to reach the target. 
     Wind velocities are generally obtained prior to the jump via meteorological forecasts from, for example, the National Weather Service and provided by local airports or alternately from the Joint Precision Airdrop System (JPADS). Wind velocities may also be updated via drop sondes and recalculated and transmitted from aircraft JPADS units. Navigation inputs, including speed, direction of travel, location and altitude are received from a GPS mounted on or within the navigation computer. 
     For examples: the red zone may be designated as when the parachutist is outside the calculated circle at current altitude; the yellow zone may be when the jumper is within the outer 20% of the radius; and the green zone may be designated as when the jumper is within the inner 80% of the circle. 
     Referring to  FIG. 5 , input data  50  are entered into mission computer  52 . Input data include parachute performance characteristics: glide ratio (L/D) and descent rate for various pressure and temperature conditions and weight of the parachutist and equipment. Data for wind velocities vs. altitude are input. Other input data may be coordinates of the High Altitude Release Point and of the target and the canopy deployment altitude. Mission computer  52  calculates the coordinates of the 3D line that will be the center of the navigation funnel at various altitudes from the target to the canopy deployment altitude. The radii of the circles around the 3D line are then calculated. Results of these calculations go into a mission file, which is provided to display computer  54 . Display computer  54  preferably is continuously receiving navigation data  58 , including location, speed over ground, altitude and heading of the parachutist, which may be sent to display  58 . Display computer  54  controls display  58  for the parachutist. Screen display  58  may also include target/HARP coordinates, wind velocities, funnel centers at various altitudes and other information. 
     Alternatively, an airdrop planning system based on other techniques, such as discussed by Hattis et al, “An In-Flight Precision Airdrop Planning System,” presented at the 23 rd  Army Science Conference, Dec. 2-5, 2002, Orlando, Fla., may be used to generate a mission file that is output to the display computer. The radius of circles around the center line will be calculated as described above. 
     The software to perform the functions described was designed to run on Windows computers and was tested extensively on Windows XP. The current platform of choice is a General Dynamics MR1. Additional text may also be provided on a display to show expected ground speed, actual ground speed, altitude corresponding to each circle in the display, and other information that may be important to a parachutist. This information may include input from other team members. Such information is discussed in the &#39;340 patent, cited above, for example, which is hereby incorporated by reference in its entirety. 
     Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.