Passive optical proximity fuze

DETAILED DESCRIPTION OF THE INVENTION FIG.
1 shows the geometry of the invention which enables it to be used to determine the slant range of ballistic vehicles to projected impact point 6 on the ground.
Vehicle 2 is falling on ballistic path 4 to impact point 6 on the ground.
Ground path 8 lies vertically below ballistic path 4.
Approach angle .
beta.
is the angle between ballistic path 4 and ground path 8.
Because vehicle 2 is near the end of flight, it may be assumed that path 4 is straight.
Because ballistic vehicle 2 may be rotating at an angular velocity, .
omega.
, sensors 10 may in fact be oriented at any angle .
alpha.
with respect to the vertical depending on the roll altitude of vehicle 2.
Therefore, field of view track 12 may be at any angle to ground path 8 of vehicle 2.
Angle .
phi.
+.
gamma.
, the angle between ballistic path 4 and viewpath 16a of sensor 10 viewing the ground at field of view 16, is chosen to be less than the smallest angle expected (from ballistic tables) for angle of approach .
beta.
of vehicle 2.
In the preferred embodiment of the invention, angle .
phi.
+.
gamma.
is 10.
degree.
.
This assures that, for any angle of roll of vehicle 2, as long as approach angle .
beta.
with respect to the horizontal is more than 10.
degree.
, sensors 10 will be able to view the ground.
The second of two sensors 10 views the ground at 14 along view path 14a.
The displacement angle .
gamma.
of view path 14a from view path 16a is very small, being only 4 milliradians, for example.
Of course, the magnitude of angle .
gamma.
will affect the time differential between the time when first sensor 10a (not separately shown in FIG.
1) views a given landmark on the ground and the time when second sensor 10b views the same landmark.
The angles given here for .
phi.
and angle .
gamma.
have been determined by considerations of the sizes of landmarks that are expected to be viewed and the expected velocity of the ballistic vehicle.
It is, of course, necessary to the operation of the invention to provide assurance that each of two sensors 10 are sequentially viewing the identical landmark, even though an indefinitly large number of landmarks may be viewed in a single flight