Note: Descriptions are shown in the official language in which they were submitted.
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SPACECRAFT DOCKING MECHANISM
FIELD OF INVENTION
This invention relates to a spacecraft docking mechanism for docking of
two spacecraft, and more particularly the present invention relates to a
docking
mechanism capable of interacting with apogee boost motors (ABM) or liquid
apogee motors (LAM) on a spacecraft to be serviced.
BACKGROUND OF THE INVENTION
Since 1957, thousands of satellites of various types and for various
purposes have been launched into different earth orbits. As these satellites
near
the end of their projected lives, there are economic incentives to attempt to
extend the life of these satellites. Unfortunately, most satellites were never
specifically designed to be captured midlife in space and so most commercial
satellites have no special docking features. However, many satellites have
either
an Apogee Boost Motor (ABM) or a Liquid Apogee Motor (LAM) which includes a
generally conical-shaped exhaust nozzle with a throat that narrows and widens.
These motors therefore present an opportunity for capture by a servicing
satellite
if somehow the servicing satellite can be coupled to these motors.
United States Patent No. 3,508,723 issued to Warren et al. is directed to a
method and apparatus for securing two spacecraft together which involves the
capturing spacecraft to come up behind the target spacecraft being captured
and
inserting a probe into the rocket engine nozzle of the target spacecraft. The
securing device includes gas driven pistons connected to a spring-loaded
collar
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which slides along a rigid boom with the boom having at one end a
hemispherical
tip which is inserted into the engine nozzle. Locking shoes pivot outwardly
once
the tip is located inside the nozzle which locks the two ships together.
United States Patent No. 4,588,150 issued to Bock et al. is directed to a
docking device for space vehicles and uses a coupling member which is a
telescopic rod. At the end of the rod several latch elements project outwardly
and
backwardly and are spring loaded so that when the end of the rod is inserted
into
the passageway located in the coupling mechanism of the spacecraft being
captured they grip thus preventing withdrawal of the rod.
United States Patent No. 4,664,344 issued to Harwell et al. is directed to
an apparatus for capturing spacecraft predominantly for use either by an
astronaut in a self-propelled thruster unit to which the device is attached or
it may
be attached to a space arm operated from the spacecraft. The apparatus
includes a probe coaxial with the center of a ring which may be padded to form
a
cushion when engaged against a separation ring on the spacecraft being
captured. The probe includes a slide cover which retains grappling fingers
within
the probe until the slide cover is retracted once the end of the probe has
been
inserted into the nozzle throat of the spacecraft ABM. Once the fingers are
released they prevent withdrawal of the probe from the nozzle throat.
United States Patent No. 5,735,488 issued to Schneider is directed to an
apparatus for coupling two spacecraft which includes a long tube with a bumper
at its distal end. A pair of inflatable bladders are located near the bumper
and a
second pair of bladders are spaced down from the first pair of bladders. The
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pairs of bladders are spaced a distance apart such that they match the
surfaces
of the nozzle of the spacecraft being captured. Once the tube is inserted into
the
nozzle the bladders are inflated thereby securing the two craft together.
United States Patent Publication 2002/0063188A1 published May 30,
2002 to Steinsick et al. is directed to an apparatus for recovering a
spacecraft
and includes a mast or tube described as a telescoping tube that has an
adjustable length while being substantially rigid. The distal end of the pipe
which
engages the spacecraft being captured includes three spreader arms which are
connected to the pipe using pivot struts. When the spacecraft is captured the
ends of the arms grip a ring located at the coupling point on the spacecraft.
United States Patent No. 6,299,107 B1 issued to Kong et al. is directed to
a docking apparatus for coupling spacecraft and uses a spike extended from the
capturing craft which is captured by a flexible net located on the craft being
captured.
United States Patent No. 5,005,786 issued to Okamoto et al. is directed to
a docking and damping mechanism for securing a spacecraft to a space
structure. United States Patent No. 5,511,748 issued to Scott is directed to a
method of extending the life of a satellite and includes docking an extension
spacecraft to the satellite with details of the docking system and refers to
the
probe and ring assembly disclosed in U.S. Patent No. 4,664,344 issued to
Harwell et al.
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United States Patent Nos. 5,806,802, 5,803,407, 6,330,987 B1, 6,017,000
and 6,484,973 B1 all issued to Scott are all related to Patent No. 5,511,748
discussed above and discloses the same type of coupling mechanism.
It would be very advantageous to provide a spacecraft docking
mechanism that is capable of interfacing with Apogee Boost Motors (ABMs) and
liquid apogee motors (LAMs) to allow a servicing spacecraft to dock with a
satellite that has no special docking features.
SUMMARY OF INVENTION
The present invention provides a docking mechanism that is capable of
interfacing with Apogee Boost Motors (ABM) including Liquid Apogee Motors
(LAM) to allow a servicing spacecraft to dock with a satellite that has no
special
docking features.
The present invention provides a docking mechanism for capturing and
coupling a target spacecraft to a servicing spacecraft, the target spacecraft
having an apogee motor with a thruster, comprising:
a support frame which is attachable to the servicing spacecraft, and at
least one elongate berthing post having first and second ends, the berthing
posts
being attached to the frame at said first ends, the berthing posts including
berthing pads attached to the second ends thereof for contacting the target
spacecraft being docked with the servicing spacecraft;
a berthing mechanism attached to the support frame, the berthing
mechanism including an extendable stage;
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a compliance mechanism mounted on the extendable stage of the
berthing mechanism;
a probe including an elongate flexible shaft having first and second ends,
a probe head assembly attached to the first end of the longitudinal flexible
shaft
and the second end of the longitudinal flexible shaft being attached to an
abutment plate, the abutment plate being attached to the compliance
mechanism, the probe head assembly including fingers extendable laterally
therefrom, the compliance mechanism providing kinetic energy absorption and
damping of the docking mechanism during capture and coupling of the two
spacecraft together for reducing overshooting and undershooting of the probe
with respect to the apogee motor; and
wherein during capture and coupling of the spacecraft together the
servicing spacecraft is positioned behind the thruster of an apogee rocket on
the
target spacecraft with the extendable stage in the fully extended position,
and
wherein the probe head assembly is extended into the thruster by movement of
the servicing spacecraft and once it has been extended past a throat in the
thruster, the fingers are deployed laterally therefrom and the extendable
stage of
the berthing mechanism is retracted until the berthing pads on the ends of
berthing posts contact an interface ring on the target spacecraft.
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BRIEF DESCRIPTION OF DRAWINGS
The following is a description, by way of example only, of the spacecraft
docking mechanism constructed in accordance with the present invention,
reference being had to the accompanying drawings, in which:
Figure 1 is a cross sectional elevation view of a docking mechanism;
Figure 2 is a cross sectional elevation view of the docking mechanism of
Figure 1 approaching a satellite to be captured by the docking mechanism;
Figure 3 is similar to Figure 2 showing the docking mechanism capturing
the satellite;
Figure 4 is a cross sectional view showing the satellite captured by the
docking mechanism and the two spacecraft locked together;
Figure 5 is an isometric view of another embodiment of a docking
mechanism constructed in accordance with the present invention;
Figure 6 shows a side view of the docking mechanism of Figure 5;
Figure 7 shows an exploded view of the docking mechanism of Figure 5;
Figure 8a shows a docking mechanism probe head assembly used in the
docking mechanism of Figures 5, 6 and 7; and
Figure 8b shows a cross sectional view along the line A-A of Figure 8a.
DETAILED DESCRIPTION OF THE INVENTION
As pointed out in the Background, many satellites have either an Apogee
Boost Motor (ABM) or a Liquid Apogee Motor (LAM) and both types of motors
include a generally conical-shaped exhaust nozzle with a throat that narrows
and
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widens. These motors therefore present an opportunity for capture by a
servicing
satellite if somehow the servicing satellite can be coupled to these motors.
The
present invention provides a device for coupling a servicing spacecraft to
both
ABMs and LAMs. Hereinafter in describing the present invention the motor on
the
spacecraft will be referred to as a Liquid Apogee Motor (LAM) but it will be
understood that this term refers to both ABMs and LAMs.
Referring first to Figure 1, a spacecraft docking mechanism shown
generally at 10 is attached to a servicing spacecraft and includes a first
cylindrical housing 12 and a second cylindrical housing 14 of a smaller
diameter
than housing 12 is concentrically mounted within housing 12. A third
cylindrical
housing 16 of a smaller diameter than housing 14 is concentrically mounted
within housing 14. Cylindrical housing 14 is mounted in cylindrical housing 12
so
it can telescope in and out of housing 12 along their respective cylindrical
axis
18. Two guide rails 20 (only one shown in Figure 1 ) are mounted along the
inner
wall of cylindrical housing 12 and brackets 22 mounted to housing 14 slide
along
rail 20 between a retracted position (Figure 4) and an extended position shown
in
Figure 1 of housing 14 with respect to housing 12. A berthing drive mechanism
24 is mounted on the interior of housing 12 for driving housing 14 with
respect to
housing 12 and includes a motor 26, a gearhead, rack and pinion with the rack
27 mounted on the outer surface of housing 14. Berthing mechanism 24 includes
a brake to facilitate smooth movement of housing 14 with respect to housing
12.
The docking mechanism includes a compliant mechanism 60 which
includes an eddy current damper with a rack and pinion assembly mounted in
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housing 16 which is connected to the proximal end of a connecting rod 62. The
distal end of rod 62 is connected to the bottom of housing 16. The role of the
compliant mechanism 60 is to provide kinetic energy absorption and damping of
the docking mechanism during capture and coupling of the two spacecraft and it
is integrated with the berthing drive mechanism 24 which is important for
preventing overshooting causing the probe to push the satellite away.
Three support arms 36 are attached at the proximal end of each arm to
one end of housing 12 and arranged 120° apart around the end of the
housing 12
(only two are shown in Figure 1 ). A berthing plate 38 is mounted at the
distal end
of each support arm 36 and a compliant pad 40 is affixed to the outer planar
face
of each of the berthing plates 38.
A compression spring 50 is mounted on a post 52 which in turn is
mounted along the cylindrical axis 18 inside housing 14. Post 52 is mounted in
a
bearing housing 54 attached to the bottom of housing 14 adjacent to a hole 56
through which one end of post 52 can protrude. The other end of post 52 bears
against the bottom of housing 16 for biasing housing 16 with respect to
housing
14. Docking mechanism 10 includes an alignment assembly 70 which includes a
compliant alignment guide tube 72 aligned in an alignment tube guide 74 along
the cylindrical axis 18. Also mounted in the distal end of the compliant tube
72 is
a probe head assembly 86 which includes three spring-biased retaining fingers
92 and a lanyard 94 is connected at one end to the fingers 92 and connected at
the other end to a probe release mechanism 76 located in housing 16. Lanyard
94 is used to retract the fingers 92 when withdrawing probe head assembly 86
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and tube 72 from the Liquid Apogee Motor when the two spacecraft are
separating. The probe release drive 76 includes a pulley 78, gear head and
motor 80 for retracting the lanyard which closes the fingers 92.
The docking mechanism 10 includes three webbings 82 equidistantly
disposed around alignment tube guide 74. Webbings 82 are flexible so they can
engage the Liquid Apogee Motor (LAM) of the target spacecraft being captured
by the docking mechanism without damaging the rockets. Three light sources 93
are mounted within the webs 82 which are turned on during docking. A boresight
camera 87 is mounted on the distal end of guide tube 72 and three monitoring
cameras 88 are mounted in one of each of the three support arms 36 and a
proximity sensor 90 is mounted on the back surface of each berthing plate 38.
A rigid flange 98 is mounted on the top of housing 16 just below webs 82
and has a hole through its middle through which the tube guide 74 and tube 72
extend. A rigidization drive 100 located inside housing 16 includes a motor,
gear
head, brake and ball screw.
Docking mechanism 10 is capable of interfacing with Liquid Apogee
Motors to allow a servicing spacecraft to dock with a satellite that has no
special
docking features. The servicer spacecraft to which docking mechanism 10 is
deployed from approaches the spacecraft which is being serviced and compliant
or flexible tube 72 with the spring-loaded fingers 92 at its tip is inserted
into the
LAM by the approach motion of the servicer spacecraft. When the probe head
assembly 86 has passed beyond the throat of the LAM nozzle the fingers 92
extend to trap the LAM on tube 72 thus achieving capture.
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The rigidization stage of docking using mechanism 10 is achieved by
retracting the probe 72 to pull the two spacecraft together with fingers 92
extended. The three berthing or abutment pads 38 interface with the launcher
interface ring of the target spacecraft. With the preload applied by the probe
72
retraction mechanism reacted through these pads 38 the docking mechanism 10
can maintain a rigid docked interface under loads induced by thrusting
maneuvers of the combined spacecraft. Figures 2, 3 and 4 show the approach
and capture of satellite 200.
Figures 5, 6, 7 and 8 illustrate another embodiment of a docking
mechanism 300 constructed in accordance with the present invention. Docking
mechanism 300 includes a flexible, compliant longitudinal probe 302, a
compliance mechanism 304 and a berthing mechanism 306. A probe head
assembly 310 is located at the end of compliant probe 302. With particular
reference to Figures 5, 6 and 7, the probe consists of a probe head assembly
310 attached to one end of compliant probe shaft 302 which in turn is attached
at
the other end thereof to an abutment plate 314. The abutment plate 314 is
mounted to compliance mechanism 304 which includes a linear guide 316 having
a bracket 318 to which abutment plate 314 is secured. Linear guide 316
includes
a slide bracket 320 on which bracket 318 is mounted with bracket 320 being
slidably mounted on a bracket 322. A spring 324 is attached at one end thereof
to one end of bracket 322 and at the other end thereof to the end of a bracket
328. Compliance mechanism 304 is mounted to berthing mechanism 306 which
consists of a ball-screw actuated sliding stage 330. Bracket 322 in compliance
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mechanism 31 fi is fastened to top plate 332 which forms part of ball-screw
actuated sliding stage 330. Three berthing posts 340 are rigidly attached to a
frame 342 and each has an end portion 344 designed to engage an interface ring
on an exterior surface of the target spacecraft being captured and serviced.
It will
be appreciated that only one (or two) berthing posts may be used instead of
the
three posts shown. The berthing mechanism 306 is driven using a motor 336 and
an associated motor controller and software and its function is to provide
relative
movement between probe 302 and the rest of docking mechanism 300. Frame
342 is attached to the servicing spacecraft.
During capture of the spacecraft, the berthing mechanism 306 is first fully
extended and then fixed in the extended position and the motion of the
servicing
spacecraft inserts the probe 302/probe head 310 into the thruster nozzle of
the
LAM on the spacecraft being captured. Once the fingers 356 on probe head 310
are deployed, the berthing mechanism 306 is retracted thereby retracting the
probe 302 to lock the two spacecraft together.
Referring now to Figures 8a and 8b, head assembly 310 includes a
housing 350 having a longitudinal axis 352 with an axle 354 mounted across the
housing perpendicular to the longitudinal axis. A pair of fingers 356 are
mounted
on the axle 354 and are normally biased open in the deployed position, using a
torsion spring 358 located befinreen the two fingers 356 on the axle 354, as
best
seen in Figure 8b. As with docking mechanism 10 in Figure 1, docking
mechanism 300 may include proximity sensors mounted on the berthing posts
340 for sensing the distance between the posts and the interface ring of the
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target spacecraft during capture and coupling of the spacecraft. The berthing
posts 340 may each include a camera mounted thereon for capturing images
during capturing and coupling of the target spacecraft. The probe head
assembly may also include a camera mounted thereon for capturing images of
the probe head assembly during capturing and coupling of the target spacecraft
and one or more lights may be mounted on the support frame for illuminating
the
apogee motor and target spacecraft. The docking mechanism may include a
laser rangefinder mounted on the support frame or any of the berthing posts or
alternatively it could be mounted on the servicing spacecraft itself. A
flexible web
similar to web 82 in docking mechanism 10 of Figure 1 may be used on docking
mechanism 300 in Figure 5.
During the mission to couple the two spacecraft, early in the rendezvous
portion of the mission, the range may be determined by the servicing
spacecraft
using a ranging signal from the target satellite. Differential radio
interferometry
and orbital debris tracking information may also be used to plan minimum fuel
approaches. The servicer spacecraft may employ a directional receiver array
that provides bearing to the target spacecraft to provide for contingency
operations. When the servicer spacecraft is within about 100 metres of the
target
spacecraft, a camera and a co-located laser range finder may be used to plot
the
final approach. The radio transponder data will continue to provide range
information in the event that the video is interrupted by off-nominal lighting
events
or data dropouts. This maneuver will bring the servicer spacecraft to within
about
nine metres of the target spacecraft.
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Docking, and undocking, may be accomplished with a suitably configured
video camera (or cameras) and the laser range finder. The final portion of the
docking maneuver is completed with the assistance of a boresight camera
mounted in the tip of the docking mechanism. Accuracies of the optical docking
system are on the order of 1 cm, 1 deg, 1 cm/sec, and 1 deg/sec. During
docking, the docking probe head assembly 310 and part of elongate probe 312 is
inserted into the Liquid Apogee Motor (LAM) of the target spacecraft with the
berthing mechanism 306 fully extended so that compliant probe 302 with probe
head assembly 310 is inserted into the throat of the LAM. The spring-loaded
fingers 356 in the probe head 310 retract to clear the throat of the LAM then
spring open once assembly 310 has passed through the throat of the LAM. The
abutment plate 314 prevents the probe 302 from being inserted too far into the
LAM. This provides capture retention of the target spacecraft. During the
capture
operation, natural damping is provided by the spring 324 and the friction in
the
linear guide 316 in compliance mechanism 304.
Once captured, the berthing mechanism 306 is commanded to retract until
the docking mechanism berthing pads 344 on the ends of berthing posts 340
contact the launch vehicle interface ring on the target spacecraft. The
berthing
mechanism 306 continues to drive until the desired preload is achieved at the
interface.
The present docking mechanism is very advantageous in that it uses
optimized compliance and damping (including lateral compliance of the flexible
probe tube) to control the contact forces such that tip off or sticking of the
probe-
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apogee boost motors is avoided during alignment/insertion. The docking
mechanisms disclosed herein use axial and lateral compliance to increase the
duration for which the probe tip remains inside the LAM combustion chamber
after insertion to give the capture fingers time to extend. The use of the
lanyard
to disengage the fingers for release permits the use of a compliant probe
small
enough to pass through the narrow throat and fit into the small combustion
chamber of the LAM. The docking mechanism is also advantageous in its use of
the launcher docking ring for final alignment and rigidization while
exploiting the
more benign capture characteristics of the LAM.
The docking mechanism disclosed herein is capable of interfacing with the
LAM to allow a servicing spacecraft to dock with a satellite that has no
special
docking features. The docking mechanism disclosed herein may be used in
many space applications including satellite rescue for capturing satellites
stranded in the wrong orbits, satellite repositioning including orbital
adjustments
for satellites nearing the end of their life in order to save their propellant
for
attitude control and thus extend the useful life of the satellite, one example
being
inclination correction for GEO communications satellites. The docking
mechanism is also useful for satellite servicing, repair, replenishment and/or
upgrade of satellites in orbit.
As used herein, the terms "comprises", "comprising", "including" and
"includes" are to be construed as being inclusive and open ended, and not
exclusive. Specifically, when used in this specification including claims, the
terms "comprises", "comprising", "including" and "includes" and variations
thereof
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mean the specified features, steps or components are included. These terms are
not to be interpreted to exclude the presence of other features, steps or
components.
The foregoing description of the preferred embodiments of the invention
has been presented to illustrate the principles of the invention and not to
limit the
invention to the particular embodiment illustrated. It is intended that the
scope of
the invention be defined by all of the embodiments encompassed within the
following claims and their equivalents.
