Apparatus for releasably connecting first and second objects in predetermined space relationship

Apparatus is disclosed for releasably connecting first and second space objects, such as a spacecraft and a space vehicle, in predetermined spaced relationship. The apparatus comprises at least one probe member (10) mounted on the first object (1), having an elongated shank portion (11), the distal end of which is provided with a tapered nose portion (12). At least one drogue assembly (20) is mounted on the second space object (2) for releasably capturing the probe member 10 upon the first and second objects (1 and 2) being brought into close proximity with each other. The drogue assembly (20) may comprise a housing (21, 28) which carries a cone subassembly (40, 41) having inwardly tapered conical surfaces (42, 43) for receiving the probe member (10). The housing (21, 28) carries a plurality of latch members (70) radially movable between retracted positions in which the latch members (70) do not project inwardly of the tapered conical surfaces (42, 43), and extended positions, in which the latch members (70) project inwardly of the tapered conical surfaces (42, 43) for engagement with the probe member (10). An operator assembly including an actuator arm (90) is carried by the housing (21, 28) and operable, when the probe (10) has been fully received, to lock the latch members (70) in the extended positions engaging the probe members (10) and releasably connecting the probe members (10) and the drogue assembly (20) in a substantially fixed axial relationship.

TECHNICAL FIELD 
The present invention pertains to apparatus for releasably connecting first 
and second objects in predetermined space relationship. Specifically, the 
present invention pertains to docking apparatus suitable for allowing 
remote control of undocking and redocking of a space experiment vehicle to 
a supporting spacecraft. 
BACKGROUND ART 
A number of patents disclose apparatus for docking of spacecraft or 
connecting aircraft in flight. For example, U.S. Pat. No. 3,737,117 
discloses a spacecraft docking structure in which space vehicles are 
joined at a conical receptacle in conical projection. One unique feature 
of this patent is the provision of a pressurized gas compartment for 
absorbing docking energy. 
U.S. Pat. No. 3,443,773 discloses a docking structure for spacecraft in 
which docking elements of the spacecraft are mated with circular openings 
of a space vehicle. Docking energy is absorbed by crushable materials 
strategically placed on the space vehicle. Spring biased latches are also 
utilized in absorbing some of the docking energy. 
U.S. Pat. No. 3,475,001 discloses an aerial refueling probe and drogue 
structure for passing fuel between aircraft. The probe is provided with 
circumferential groove or channel which is locked into operational 
position by a hydraulic actuator pushing a roller into the groove or 
channel. 
U.S. Pat. No. 3,737,181 discloses apparatus for releasing a pair of 
coaxially related tension menbers. The apparatus is fixed to one of the 
tension members and may be attached to a second tension member by way of a 
disconnect shaft. A protuberance on the disconnect shaft is held to the 
apparatus by means of collet lugs or fingers held in place by a circular 
piston. Movement of the circular piston in response to expanding gases in 
a chamber allows movement of the collet lugs to release the protuberance. 
U.S. Pat. No. 3,174,706 discloses a separation device for retention of a 
satellite but for release thereof in response to a signal. A circular cam 
is rotated by disengage clamps which hold the satellite to a space 
vehicle. Such apparatus is strictly for separation and not suitable for 
redocking. 
U.S. Pat. No. 4,065,217 discloses a mechanism for releasably locking a nose 
tip to a vehicle utilizing a pawl and ratchet and pinion arrangement. The 
primary purpose of such mechanism is to allow attachment and detachment of 
radioactive nosetips from vehicles with minimal exposure to personnel. 
Such attachment or detachment is not done in flight. 
Finally, while it is not related to space vehicles, U.S. Pat. No. 2,645,506 
discloses connection apparatus which could be used in space. Specifically, 
it discloses a pipe flange connector in which a circular cam plate is used 
to move dogs or latches into or out of locking arrangement. However, no 
mechanism is disclosed suitable for guiding and capturing an object in 
space. 
DISCLOSURE OF INVENTION 
In accordance with the present invention, apparatus is disclosed for 
releasably connecting first and second space objects in predetermined 
space relationship. The apparatus comprises at least one probe member 
mounted on the first space object, having an elongated shank portion, the 
distal end of which is provided with a tapered nose portion which 
terminates in an enlarged diameter with a reverse conical shoulder 
receding into the aforementioned elongated shank. The reverse conical 
shoulder provides a surface for retention of the probe into a drogue 
assembly. At least one drogue assembly is mounted on the second space 
object for releasably capturing the probe member upon the first and second 
space objects being brought into close proximity with each other. 
The drogue assembly may comprise a housing which carries a cone device 
having inwardly tapered conical surfaces for receiving the probe member. 
Latch means are carried by the housing and include a plurality of latch 
members radially movable between retracted positions, in which the latch 
members do not project inwardly of the tapered conical surfaces, and 
extended positions, in which the latch members project inwardly of the 
tapered conical surfaces for engagement with the probe member. Operator 
means are carried by the housing and operable, when the probe has been 
fully received by the cone means, to lock the latch members in the 
extended positions engaging the probe member and releasably connecting the 
probe member and the drogue assembly in a substantially fixed axial 
relationship. 
There are several unique features of the apparatus of the present 
invention. The cone means is mounted for limited floating to allow limited 
misalignment of the first and second space objects as they are brought 
into close proximity. Spring mechanisms absorb both radial and axial 
docking loads. The operator means includes uniquely designed cam members 
for operation of the latch means and cooperating link members by which the 
probe member is rigidly confined in the cone means in a substantially 
fixed axial relationship. Many other objects and advantages of the 
invention will be apparent from reading the description which follows in 
conjunction with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring first to FIG. 1, there is shown a portion of a first space object 
1 and a second space object 2 detached therefrom. The first space object 1 
represents a portion of a spacecraft such as the one referred to as the 
"Orbiter" utilized in space transportation system missions. The second 
space object 2 may be a remotely radio-controlled space satellite vehicle 
to be launched aboard and flown from the Orbiter spacecraft 1. The 
satellite vehicle 2 could be used for numerous tasks such as orbiter 
inspection, experiment transfer, joint experiments, satellite surveillance 
and/or recovery of satellites or experiments. For these purposes, the 
space object or vehicle 2 could be equipped with television cameras 3, 
lights 4, radar 5, and other components such as batteries, sun sensors, 
antennas, manipulators, experiment programmers, various electronics, etc. 
(not shown). While the satellite vehicle 2 is carried into space by the 
Orbiter 1, it may be equipped with its own propulsion system including 
propulsion tanks (not shown) and associated thrusters 6 by which the 
vehicle 2 can be positioned in space relative to the spacecraft 1. 
The satellite vehicle 2 would normally be launched mounted in the cargo bay 
of the Orbiter (spacecraft 1) mounted on a flight support station 7 by a 
docking system which is the primary subject of the present application. 
The docking system allows remote control of undocking and redocking of the 
vehicle 2 to the Orbiter flight support station 7 through the use of 
television as means to guide the vehicle 2 to the docking interface. The 
flight support station 7 includes a docking target 8 which is aligned with 
a crosshair 9 on a television screen emanating from the TV camera 3 
carried by the space vehicle 2. Remote control of the vehicle 2 may be 
performed from a command station on board the Orbiter (spacecraft 1). 
Lateral, radial and axial alignment can be perceived by experienced 
operators using this technique. 
The docking system illustrated in FIG. 1 is a three-point system which 
sustains all structural loads for Orbiter launch and landing. Each point 
comprises a probe member 1, fixed at the support station 7 of the 
spacecraft 1, and corresponding drogue assemblies 20 mounted on the second 
space object or vehicle 2. The probes 10 remain fixed at the flight 
support station 7 and are passive. The drogue assemblies 20 are the active 
mechanisms by which the spacecraft 1 and space vehicle 2 are docked and 
undocked. During the docking maneuver, exact alignment cannot be 
maintained; therefore, misalignment capability is designed into the 
docking system. Thus, the following criterion was utilized in designing 
the docking system of the present invention: 
(1) axial velocity of 0.1 to 0.5 ft./sec.; 
(2) radial velocity of 0 to 0.2 ft./sec.; 
(3) angular velocity of 0 to 1.0 deg./sec.; 
(4) angular misalignment .+-.5.degree. pitch and yaw, .+-.2.degree. roll; 
(5) radial misalignment .+-.2 inches. 
The following additional requirements were established: 
(1) active portion of the docking system should be on the vehicle 2; 
(2) automatic capture, three-position latch; 
(a) locked (latch secure for launch/reentry load); 
(b) capture (latches loose for capture with minimal force, each latch 
independent); 
(c) release (latches fully released without imparting loads to the vehicle 
2). 
(3) docking target must be eighteen inches from the vehicle camera lens in 
the docked position (this requirement dictated by camera focal length). 
Referring now to FIG. 2, the structure and relationship of a probe member 
10 and drogue assembly 20 will be explained. The probe member 10 has an 
elongated shank portion 11 at the distal end of which is provided a 
tapered nose portion 12. The shank 11 and tapered nose 12 are connected by 
an annular conical shoulder 13 facing toward the proximal end 14 of the 
shank portion 11 which is attached to the support station 7 of the 
spacecraft 1 (see FIG. 1). 
The drogue assembly 20 includes a number of subassemblies: housing means, 
cone means, latch means and operator means. The housing means includes a 
cylindrical outer housing 21 substantially closed at one end thereof by a 
circular bottom wall 22. Centrally disposed in the bottom wall 22 is a hub 
made up of an outer hub portion 23 and a smaller diameter inner hub 
portion 24 through both of which an aperture 25 of substantially square 
cross-section is provided. It will be noted that the wall thickness of the 
cylindrical outer housing 21 is increased near the bottom wall 22 to 
provide an upwardly facing annular surface 26. At the upper end of the 
housing 21 is provided a circular flange 27. 
Coaxially received within the outer housing 21 is an inner cylindrical 
housing 28, the upper end of which is provided with a circular flange 
portion 29, corresponding with the flange portion 27 of the outer housing 
21. A circular shim 30 may be provided at the interface between the 
flanges 27 and 28 of the outer and inner housing members 21 and 28, 
respectively. This provides a means of adjusting the docking system 
assembly preload in the locked position by positioning the inner 
cylindrical housing 28 along with the latch pins 71 and latches 70 as 
required to lock the probe nose 12 against the inner surface 43 which will 
be more fully understood hereafter. It will be noted that the inner 
housing 21 is provided with an inwardly projecting shoulder or ring 32, 
the purpose of which is to support other elements of the drogue assembly 
as will be more fully understood hereafter. Surmounted on the flanges 27 
and 28 is a ring-like cover 33. Corresponding holes are provided in the 
flanges 27, 29, shim 30 and ring cover 33 for receiving screws 34 and 
cooperating washers and nuts 35 and 36, which hold the housing subassembly 
together. 
Carried by the housing subassembly is a cone subassembly, the primary 
purpose of which is to guide and receive the probe member 10. The cone 
subassembly comprises an inverted frusto-conical portion 40 and an 
inverted apex portion 41 slightly spaced therefrom. The inner surface 42 
of the frusto-conical portion 40 is inwardly tapered and the inner surface 
43 of the apex portion 41 is also inwardly tapered so that the inner 
surfaces 42 and 43 cooperate in providing inwardly tapered conical 
surfaces for receiving the distal end of the probe member 10 upon the 
first and second space objects being brought together. The tapered surface 
43 of the apex portion 41 may be rounded at the apex to correspond with 
the shape of the probe member nose 12. 
The inverted frusto-conical portion 40 of the cone subassembly has a 
correspondingly tapered outer surface 45 which rests against and is 
partially supported by a plurality of plungers 46 projecting at regular 
radial intervals through holes provided therefor in the inner housing 
shoulder 32. These holes are counterbored to receive an insert 47 through 
which an adjusting screw passes for engagement with a coiled spring 
mounted between the plunger 46 and the insert 47. Holes 50 are provided in 
the outer housing 21 for access to the end of the adjusting screw 48. 
Thus, the amount of force exerted by the coil spring 49 against the 
plunger 46 can be adjusted. The inverted frusto-conical cone portion 40 
thus rests on the plungers 46 and if a downward force is applied thereto, 
may move axially or radially by limited amounts. Upper movement is limited 
by engagement of a tapered shoulder 51 provided on the frusto-conical 
portion 40 with a tapered shoulder 52 provided on the ring cover 33. In 
addition, the lower end of the inverted frusto-conical portion 40 of the 
cone subassembly rests on a spirally wound spring 55 which is in turn 
supported on a flange portion 56 of the inverted apex portion 41 of the 
cone subassembly. Thus, the frusto-conical portion 40 floats within the 
housing subassembly for limited axial, radial and even angular movement 
relative to the central axis of the housing. 
The inverted apex portion 41 is provided with a downwardly depending 
substantially square hub portion 57 which is centrally received for 
limited axial movement within the aperture 25 of the outer housing hub 23. 
Since the hub portion 57 and aperture 25 are square, rotation of the apex 
portion 41 is prevented. A central aperture 58 passes through the hub 
portion 57 and through the remainder of the inverted apex portion 41 for 
receiving an actuator 60 attached to a limit switch 61, the purpose of 
which will be more fully understood hereafter. In fact, the end of the 
actuator 60 actually engages the nose portion 12 of the probe member 10 
when the probe member 10 is fully received by the drogue assembly 20. The 
actuator 60 and limit switch 61 are supported on the hub of the outer 
housing member 21 by a bracket member 62 attached to the hub by screws 63. 
Also mounted in the housing of the drogue assembly 20 is a latch 
subassembly comprising a plurality (three in the present case) of latch 
members 70 pivotally attached, as best seen in FIGS. 2 and 8, to the 
mounting shoulder 32 of the inner housing 28 by pins 71 one end of which 
is threaded at 72 for threaded engagement with threaded holes 73 
tangentially disposed about the shoulder 32 at regularly spaced intervals. 
The ends of the pins are slotted 74 for engagement with a screwdriver 
through counterbored tangential holes 75 provided in the shoulder 32. The 
latch members 70 are substantially triangular in shape and are capable of 
radial movement, about the axis of pin 71, relative to the axis of the 
drogue assembly between retracted positions, in which the latch members 70 
do not project inwardly of the tapered conical surfaces 42 and extended 
positions (as shown in FIG. 2) in which at least a portion of the latch 
members 70 project inwardly of the tapered conical surfaces 42 through 
slots 76 provided in the inverted frusto-conical member 40. (See also FIG. 
3) A torsion spring 77 wound around the pivot pin 71, one end 78 which 
bears against the inner housing 28 and the other end 79 which bears 
against the latch member 70 in a slot 80 provided therefor, biases the 
latch member 70 toward the extended position shown in FIG. 2. The base of 
the latch members 70 are provided with a tapered surface 81 which, in the 
extended position shown in FIG. 2, is capable of engaging the tapered 
annular shoulder 13 of the probe member 10. The triangular shape of the 
latch member 70 also provides a slanted edge 82, the purpose of which will 
be more fully understood hereafter. Attached to the base of the 
triangularly shaped latch member 70 is a ball-like cam member 83 the 
purpose of which is to aid in moving the latch members 70 between 
retracted and extended radial positions, as will be more fully understood 
hereafter. 
Carried in the lower part of the housing 21 is a linear actuator arm 90 one 
end of which engages a linear motor (not shown) carried by the space 
object or vehicle 2 in which the droge assembly 20 is mounted. The 
actuator arm 90, as best seen in FIG. 4, is confined by guide brackets 91, 
92 and 93 for linear motion, as indicated by the arrow 94, in a path 
perpendicular to a radial line extending from the axis of the drogue 
assembly 20. Screws or bolts 95, 96 and 97 engaging corresponding holes in 
the lower wall 22 of the housing member 21 hold the guides 91, 92 and 93 
in place. The actuator arm 90 makes up a portion of the operating 
subassembly of the drogue assembly 20. 
The operating subassembly also includes a circular cam member 100 best seen 
in FIGS. 1 and 5. The cam member 100 is circular in shape and the outer 
peripheries thereof are axially retained between the annular shoulders 26 
and 31 of the housing subassembly. However, enough clearance is allowed 
between the cam member 100 and the shoulders 26 and 31 to allow the cam 
member 100 to rotate about a central axis which corresponds with the 
central axis of the drogue assembly 20. The cam member 100 includes a 
central aperture 101 in which the inverted apex member 41 of the cone 
subassembly is disposed. The cam member 100 may be provided with relieved 
pockets 102 to lighten the weight thereof. At radially spaced intervals 
around the upper surface of the cam member 100 are cam slots 103 each of 
which comprises an outer circumferential portion 104 and an inner 
circumferential portion 105 connected by a wider intermediate transition 
portion 106. The ball cam followers 83 attached to the latch members 70 
are disposed somewhere within the cam slots 103. 
As previously mentioned, the cam member 100 is rotatable. To transmit 
linear movement of the actuator arm 90 to rotational movement of the cam 
member 100, the actuator arm 90 is provided with a cam follower 99 which, 
as shown in FIG. 7, engages a recess 110 on the lower side of the cam 
member 100. Thus, upon linear movement of the actuator arm 90, the cam 
follower 99 engaging the recess 110 of the cam follower, causes the cam 
member 100 to rotate in response to linear movement of the actuator arm 
90. For example, with the actuator arm 90 and the cam member 100 in the 
position shown in FIG. 5, the cam followers 83 attached to the base of the 
latch members 70 will be engaging the inner circumferential portions 105 
of the cam slots 103. Upon movement of the actuator arm 90 in the 
direction of the arrow 111, the cam member 100 will be rotated clockwise, 
as indicated by the arrow 112 in FIG. 5, causing the latch member cam 
follower 83 to follow the cam slot first to the transition area 106 and 
finally to the outer circumferential area 104. When the cam follower 83 is 
in the inner circumferential portion 105 of the cam slot 103, the latch 
member 70 will be in the extended position of FIG. 2. When the cam 
followers 83 are in the transition area 106 of the slots 103, the latch 
members 70 will normally be in the extended position of FIG. 2, due to the 
biasing of spring 77. However, if sufficient force is directed against the 
edge surface 82 of the latch member 70, the biasing of spring 77 can be 
overcome forcing the latch member 70 to the retracted position. When the 
cam followers 83 are in the outer circumferential portions 104 of the cam 
slots 103, the latch members 70 are forced and maintained in the retracted 
position. 
In addition to the actuator arm 90 and the cam member 100, the operator 
subassembly comprises a pinion member 120 best seen in FIGS. 2 and 4 which 
is mounted for rotation about the inner hub portion 24 of the outer 
housing 21. Thus, the pinion member 120 rotates about a common axis with 
the central axis of the drogue assembly. The pinion member 120 is provided 
with a gear slot 121 which is engaged by a gear tooth 122 attached to the 
actuator arm 90. Thus, it is clear that upon linear movement of the 
actuator arm 90, the pinion member 120 will be rotated by virtue of the 
engagement of the tooth 122 with the tooth slot 121. As best seen in FIG. 
6, the periphery of the pinion member 120 is also provided with a recess 
123 in which is disposed a stop member 124 attached to the housing end 
wall 22 by a nut 125. The stop is eccentric to the threaded end to provide 
adjustment of the stopped position of the pinion. The engagement of the 
stop member 124 with the ends of the recess 123 limit rotation of the 
pinion member 120. A spring 126, one end of which is attached at 127 to 
housing wall 22 and the opposite end of which is attached at 128 to the 
periphery of the pinion member 120, biases the pinion member 120 in a 
clockwise direction, as viewed in FIG. 4. 
Interspersed between the pinion member 120 and the flange portion 56 of the 
inverted apex member 41 is a plurality of cylindrical link members 130 the 
ends of which are spherically rounded. The pinion member 120 and inverted 
apex member 41 are provided with corresponding recessed holes 131 and 132 
at radially disposed intervals thereabout. One end of each link member 130 
is disposed in corresponding recessed holes 131 of the pinion member and 
the other end of each link member 130 is disposed in corresponding 
recessed holes 132 of the inverted apex member 41. The recessed holes 131 
of the pinion member and 132 of the inverted apex member 41 are angularly 
displaced relative to each other so that the link members 130 are inclined 
relative to the central axis of the drogue assembly. Thus, since the 
pinion member 120 is essentially fixed in the axial direction and since 
the apex member 41 is prevented from rotating, rotation of the pinion 
member 120 will bring recesses 131 and 132 toward angular alignment 
causing the pin members 130 to be less inclined and forcing the inverted 
apex portion 41 toward the inverted frusto-conical portion 40. As will be 
more fully understood hereafter, this will aid in connecting the probe 
member 10 and drogue assembly 20 in a substantially fixed axial 
relationship. 
Referring now to all the drawings, operation of the connecting apparatus of 
the present invention will be summarized. With the spacecraft 1 and the 
vehicle 2 in the undocked positions of FIG. 1, the vehicle 2 is guided 
toward spacecraft 1 and remotely positioned until the drogue assembly 20 
is substantially aligned with the probe members 10. The centerpoints of 
the target 8 and crosshair 9 are aligned by the television camera 3 and 
the vehicle 2 brought toward the spacecraft 1 in close proximity with each 
other. This is done with the latch member 70 in the capture mode. In the 
capture mode, the cam followers 83 of the latch members 70 are disposed in 
the intermediate transition area 106 of the cam member 100 cam slots 103. 
Thus, the latch members 70 are in the extended position but are 
susceptible to being independently forced to the retracted position with 
minimal force. 
Upon initial contact between the probe member 10 and the drogue assemblies 
20, the nose portion 12 of the probe member 10 will normally engage a 
tapered surface 42 of the inverted frusto-conical member 40. The initial 
shock of such engagement is cushioned by the spring-loaded plungers 46 and 
the spirally wound spring 55 which allows the frusto-conical portion 40 to 
"float". Upon further engagement, the probe member 10 contacts the slanted 
edge surfaces 82 of the latch members 70 forcing the latch members 70 to 
retracted positions until the nose 12 passes the latch members 70, 
allowing the latch members 70 to spring back, under the influence of 
biasing springs 77, to the extended positions shown in FIG. 2. In such 
position, the tapered surface 81 of latch members 70 engage the tapered 
shoulder 13 of probe 10 and the probe member 10 is essentially cpatured by 
the drogue assembly 20 but not yet ridigly fixed thereto. 
As soon as the nose portion 12 of the probe member 10 engages the inverted 
apex portion 41 it also engages the switch actuator 60 causing the switch 
61 to be energized and activating the linear motor (not shown) attached to 
the actuator arm 90. Either automatically or upon a signal given thereto, 
the linear actuator then causes the actuator arm 90 to move outward 
rotating the cam member 100 counterclockwise until the ball followers 83 
of the latch members 70 engage the inner circumferential portions 105 of 
the cam slots 103. This then essentially locks the latch members 70 in the 
extended positions of FIG. 2. 
Simultaneously with the rotation of cam member 100, the pinion member 120 
is rotated by the actuator arm 90. Rotation of the pinion member 120 
causes the pin members 130 between the pinion member 120 and inverted apex 
member 41 to be less inclined, forcing the inverted apex portion 41 
against the nose 12 of probe 10 and firmly fixing the probe member 10 and 
the drogue assembly 20 in a substantially fixed axial relationship. The 
rounded or spherical ended links 130 provide large contact surface area 
throughout this camming operation. This keeps bearing loads within 
allowable limits up to the on-center locked position. 
The probe members 10 and drogue assemblies 20 are then in a locked position 
firmly holding the vehicle 2 to the spacecraft 1. This is the position 
assumed for launch or reentry. 
To release the vehicle 2 from the spacecraft 1 the actuator arm 90 is moved 
in the opposite direction, causing the pinion member 120 and cam member 
100 to rotate and relieving force against the nose 12 of the probe member 
10. When the retraction of the inverted apex portion 41 is complete, 
pinion member 120 reaches the end of its travel as limited by stop 124 in 
slot 123. At this point in the rotation of pinion member 120, gear tooth 
122 disengages from pinion member 120, gear teeth 121 and actuator arm 90 
is free to continue driving cam member 100. As the cam member 100 
continues to rotate in the opposite direction, the ball followers 83 first 
pass through the transition areas 106 of the cam slots 103 and then 
finally engage the outer circumferential portions 104 of the cam member 
slots 106. As the cam followers 83 engage this portion of the cam slots 
103, the latch members 70 are forced to a retracted position, completely 
releasing the probe member 10 and thus the vehicle 2 from the spacecraft 
1. When this occurs, all internal loads have been relieved and no reaction 
is imparted to vehicle 2 due to the release action. 
Thus, the apparatus of the present invention provides a means for 
releasably connecting first and second space objects in a predetermined 
space relationship by connecting probe members attached to one of the 
space objects to drogue assemblies attached to the other space object in 
substantially fixed axial relationship. The unique design permits limited 
angular misalignment in pitch, yaw and roll. It also absorbs substantial 
docking energy from axial, radial and angular velocities at impact. Its 
operation is relatively simple and easy whether space vehicles are being 
docked or undocked. 
While a single embodiment of the invention has been described herein, many 
variations thereof can be made without departing from the spirit of the 
invention. Therefore, it is intended that the scope of the invention be 
limited only by the claims which follow.