Despinning method and apparatus

In a method for changing the spin of bodies released from an aggregate, the bodies are connected by straps or bars which serve as tension or compression members. Spin of the connected bodies results in either compressive or tensile forces in the connecting member. Those forces in turn provide torque which counters or enhances the spin and converts that spin to or from translational energy. Once the spin of the bodies has been changed a predetermined amount, the connecting member is released.

TECHNICAL FIELD 
This invention relates to a method and apparatus for changing the spin of 
bodies which have been released from a spinning aggregate. It has 
particular application to such bodies which have been dropped together 
from an airplane or separate from a spacecraft. 
BACKGROUND ART 
It is common practice to drop bombs joined together as an aggregate and to 
then release the individual bombs from that aggregate. In order to provide 
translational movement of individual bombs relative to each other, the 
aggregate is set spinning as it is dropped so that when the bombs are 
released they spin off from each other. A disadvantage of such a system is 
that, although translational movement is imparted to the individual bombs, 
each continues to spin at the angular velocity of the aggregate. The 
primary object of this invention is to provide a means for de-spinning 
such bombs once they have been released. 
The bombs noted above may be explosive or incendiary devices, or they may 
carry fire extinguishing material or the like. The invention has further 
application to groups to satellites which may be similarly released. A key 
advantage to the invention is that it provides a passive means for 
de-spinning a number of independently functional bodies without the 
requirement of substantial additional masses such as used in the satellite 
de-spinning systems shown in the U.S. Pat. No. 3,030,049 to Pilkington et 
al. and U.S. Pat. No. 3,229,930 to Fedor et al. Further, although total 
de-spinning of individual bodies is possible, proper design of the passive 
system enables any degree of change to the spin. 
DISCLOSURE OF THE INVENTION 
In accordance with the invention the individual spins of at least two 
bodies released from a spinning aggregate are changed by connecting the 
bodies with a connection means which, once the bodies are released from 
the aggregate, provides torque to each body. The torque results from the 
restriction of the relative spins and/or translational velocities of the 
bodies by the connecting device. Once the spins have been changed, the 
bodies are disconnected. 
In the primary embodiment of the invention, the connecting means is 
elongated and flexible and is wrapped about each of the bodies to oppose 
the spin of the other. More than two bodies may be joined in such a way 
that torque is applied to each. 
The invention has particular applicability to de-spinning of independently 
functional bodies. By varying the connecting details and geometry of the 
bodies it is possible to spin all bodies to zero, to reduce the spin to 
rates other than zero, to increase the spin rate of some or all, or to 
reverse the direction of spin of the bodies, essentially limited only by 
the requirements that energy and momentum be conserved in all cases.

BEST MODE OF CARRYING OUT THE INVENTION 
In FIG. 1, four canisters 22, 24, 26 and 28 are held by a holding means 30 
and an aggregate 32. As noted above, the canisters may be bombs, 
satellites or the like. The holding means 30 is shown as a much larger 
canister which may be separated into sections 30A and 30B by an explosive 
charge or the like. The holding means 30 might also be a strap or any 
other suitable structure for releasably holding the several canisters 
together during the initial spinning. 
In the embodiment of FIG. 1, the canisters are grouped in pairs with 
canisters 22 and 24 joined by a strap 34 and canisters 26 and 28 joined by 
a strap 36. 
With the aggregate spinning at an angular velocity .omega..sub.o it can be 
seen that each individual canister has the same angular velocity 
.omega..sub.o about its own center as well as an instantaneous 
translational velocity tangential to the aggregate. At the instant that 
the holding means 30 is released, each pair of canisters can be looked at 
separately as in FIG. 2. Together, the canisters 22 and 24 have a 
horizontal translational velocity of 
EQU V.sub.cm =r.omega..sub.o 
where r is the radius from the center of the aggregate to the center of the 
canister pair. The pair is also spinning at the angular velocity of 
.omega..sub.o, and that spinning results in translational components for 
the individual bodies, relative to the center of mass, as indicated in the 
figure. Finally, each individual body has an angular velocity relative to 
its own center of .omega..sub.o. 
Without a connecting strap 34, the four bodies would spin off in orthogonal 
directions when the holding means 30 is released. However, as shown in 
FIG. 3, as the bodies being to separate the spinning action of each works 
against that of the other through the strap. For example, the spinning of 
bodies 22 and 24 are in opposition through strap 34 so that each body 
applies a torque to the other through the strap. Torque is also applied as 
a result of the opposite translational movement of the bodies. The torque 
applied to each body is opposite to its spin. The spin in the bodies is 
thus converted to translational movement due to the conservation of energy 
and momentum. The change in the translational velocity components is 
indicated through FIG. 4. 
With the strap pulling against the two bodies, the angular velocity of each 
is quickly pulled to zero. At that point, if the bodies remained 
connected, a reverse spin would be applied to each body. But if the bodies 
are disconnected at the instant that the angular velocity is zero, the 
individual bodies continue on their separate paths as shown in FIG. 5, all 
spin kinetic energy having been converted to translational kinetic energy. 
In the case shown in FIG. 5, the bodies are disconnected by disconnecting 
the strap from each canister, but the strap could be disconnected at a 
single point any where along its length. 
The final spin of the bodies, once they have been disconnected, is 
dependent on many variables. Those variables include the initial spin of 
the bodies, the effective length of the connecting strap at the release 
point, the angle between the strap and the body at the time of release, 
the effective radius at which the strap acts on each body, and the mass 
properties of each body. By taking some of the parameters as given and 
others as desired results, still others can be calculated to give the 
desired results. For example, for two identical canisters, a length of 
strap can be determined to provide zero spin with tangential release as 
shown in FIG. 4. That length is equal to 
EQU L=(l+k).sup.1/2 r 
where k is a constant for the particular canisters defined by 
EQU k=I/mr.sup.2 
where I is the moment of inertia of the object, m is its mass, and r is its 
effective radius. 
The two bodies will usually have the same order of mass and inertia. Where 
the moment of inertia of one is less than about 10% of the other, its 
inertia may not be sufficient to provide the necessary torque to the 
other. Thus, the spin of the smaller body would quickly go to zero, and 
even reverse, with little effect on the spin of the other. Even with the 
same order of mass and inertia, if the ratios are different, then one body 
may despin to zero, or even reverse, before the spin of the other body is 
stopped. The final spin rate of a pair of bodies will be equal if the 
ratio of the inertia and the radius of action are the same for each body; 
i.e. if 
##EQU1## 
where r.sub.1 and r.sub.2 are the radii at which the strap acts on bodies 
1 and 2 respectively. 
One embodiment of the feature of variable inertias is the case where 
several canisters or devices are attached to a larger central device as in 
FIG. 17. The energy in the central device 122 would be imparted to the 
smaller devices 124 as they separate from the central device and despin. 
The despinning method here described has particular application to the 
release of two or more independently functional bodies. By merely 
connecting those bodies, despinning can be provided. No other masses for 
changing the moment of inertia of the system are required. 
Other canister arrangements in the aggregate are shown in FIGS. 6 thru 9. 
In FIG. 6, two canisters 38 and 40, joined by a connecting strap 41, are 
retained by holding means 42. In FIG. 7, three canisters, 44, 46, and 48, 
are joined by three straps 45, 47, and 49, which are joined at a center 
connector 50. All three canisters are held in the aggregate by a holding 
means 52. In FIG. 8, four canisters 54, 56, 58, and 60, are joined by 
straps 62 and 64 which pass through a center axis 66. The straps may or 
may not be joined along the axis 66. All canisters are retained in the 
aggregate by holding means 68. In FIG. 9, five canisters 70, 72, 74, 76, 
and 78, are joined by straps 80, all of which are joined at a center 
connector 82. All canisters are held together by a holding means 84 as 
before. Thus it can be seen any number of canisters can be held in the 
aggregate and be connected in such a way that, once released, the spin and 
translational movement of each applies torque to the others through the 
straps. In all cases the straps may be connected to a central structure as 
in FIG. 17 having finite inertia, in width case the structure may 
contribute to despinning and deployment of the canisters. 
There are several ways to releasably connect the strap to each of the 
canisters. For example, in FIG. 10, a rigid link 86 is held against hooked 
pins 88 by a strap 90. When the strap passes an angle .theta. from the 
tangential line, it pulls the link loose from the hook and is 
automatically released. 
In FIG. 11 another release mechanism is shown. In that device the strap 92 
extends into a groove 94 in the canister. It pulls on a pin 96 which 
extends across the slot 98. When the strap is positioned beyond an angle 
.theta. the pin slides out of the slot 98 to release the strap. 
FIG. 12 shows an embodiment for radial release of the strap. A ring 102 at 
the end of the strap 100 is held by a hook 104. When the strap extends 
radially from the canister, it is able to slip off the hook 104. 
Thus far, an elongated flexible connecting member has been described. It 
should be recognized that one or more straps may be used. Further, as 
shown in FIGS. 13 thru 16, a rigid member may be used to apply the torque 
from each spinning body to the other. In FIG. 13, a rigid link 106 joins 
two canisters 108 and 110. The connecting link 106 is joined to the 
canisters by pins 116 and 118. As before, the canisters are held together 
by a holding means 120. 
The aggregate of the two canisters spins at an initial angular velocity 
.omega..sub.o, shown in the counterclockwise direction. Once the canisters 
are released, as shown in FIG. 14, they begin to move vertically in 
opposite directions. Also their spins are in opposition through the link 
106. With the link thus in tension it holds back on the spin of each 
canister and adds a horizontal component to their translational movement 
as shown in FIG. 14. Thus as before, the spin of each canister can be 
reduced to zero or some other desired spin rate. As before, canisters of 
different sizes will provide different results, as will differences in the 
release mechanism and differences in the length of the connecting link. 
The system of FIG. 15 is identical to that of FIG. 13 except that the 
initial spin is in the opposite direction. As a result, when the canisters 
are released from the aggregate as shown in FIG. 16, the connecting link 
106 is placed in compression by the opposing spins of the canisters. The 
link thus presses outwardly on the canisters against their spin to convert 
the spin to translational movement. As before, some passive device may be 
arranged to release the connecting link from both canisters to thus 
provide for proper de-spinning of the canisters. 
FIGS. 18 and 19 show two configurations in which the angular velocity of at 
least one of the bodies may be increased. In FIG. 18 the strap 126 is 
connected such that the spins of the two bodies 128 and 130 are not in 
opposition. However, as the two bodies separate with opposite 
translational movement, torque is applied to each through the strap 126. 
That torque increases the spin rate of body 128, but decreases the spin 
rate of body 130. 
In FIG. 19, the strap is attached so that as the bodies separate, their 
translational movement imparts a torque to each body to increase the spin 
rate of each at a loss of translational velocity. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that various changes in form and details may be made 
therein without departing from the spirit and scope of the invention as 
defined by the appended claims.