Note: Descriptions are shown in the official language in which they were submitted.
Capture device device and capture method for capturing
uncooperative satellites in space
Description
The present invention relates to a capture device, a
spacecraft and a capture method each for the (in particular
robotic) capture of uncooperative satellites in space.
A capture of uncooperative satellites in space, i.e. which
cannot be moved in a targeted manner by means of remote
control, means gripping and holding firm the respective
satellite by means of a suitable device of a spacecraft
(which may itself be a satellite). The satellite to be
captured (which is also referred to as the "target
satellite") is thus coupled to the spacecraft. The latter
is then able for example to carry out repairs and/or
maintenance operations such as in particular re-fuelling
and/or a payload exchange or also to suitably transfer the
captured satellite into a currently more advantageous
orbit.
Many satellites do not have an interface provided
explicitly for such coupling. Instead, specific holding
means can conventionally be introduced into the nozzle of
an apogee engine, or the payload adapter ring (also
referred to as the "launch-adapter-ring") of the satellite
can be held by means of pincer-like grippers, which are
guided by robot arms: A payload adapter produces the stable
mechanical connection between the rocket and the satellite
at the launch. As a rule, it comprises two components, one
on the rocket and one on the satellite, which at the launch
are connected together. After the launch, this connection
is released and the satellite is thus separated from the
rocket. The satellite-side component of the payload adapter
is the payload adapter ring. Techniques for holding the
payload adapter ring by means of grippers are described in
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documents capturable at
http://www.satelliteevolutiongroup.com/articles/orbitalatk.
pdf or http://hq.wvrtc.com/ICRA2015/posters/ratti.pdf.
High-precision positioning of the respective tool and a
correspondingly expensively controlled movement mechanism
are required in each case for this, in particular because
the contact of the tool with the satellite in zero gravity
can have a great effect on the position and orientation of
the satellite and because the respective elements engage at
least partially in an internal region of the satellite, for
example in a radially interior region of the payload
adapter ring, which can lead to damage to the sensitive
material and in particular damage to the proper functioning
of the target satellite.
The problem underlying the present invention is to provide
a technique, with which capture of uncooperative satellites
can be simplified.
The problem is solved by a capture device, a spacecraft and
a capture method as described throughout the description
and claims. Advantageous embodiments are disclosed in the
description and the figures.
A capture device according to the invention is used, when
it is attached to a spacecraft (possibly together with at
least one further capture device according to the
invention), to capture satellites in space (robotically),
i.e., to grip and hold the latter.
The capture device comprises two legs, which each comprise
a first end and a second end; the respective first ends are
connected to one another by a connecting bracket. A
gripping device for gripping a satellite currently to be
captured (for example at an element arranged thereon such
Date Recue/Date Received 2021-05-31
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as in particular a payload adapter ring) is arranged on the
connecting bracket. At the respective second end of each of
the legs, a fastening foot (one in common or one each) is
arranged, by means of which the respective leg is or can be
fastened to a capturing spacecraft. The connections of the
first ends to the connecting bracket and of the second ends
to the fastening foot or the respective fastening feet are
constituted so as to be swivellable about respective axes
which run (in pairs) parallel to one another (i.e. two of
the axes in each case are parallel to one another). In
particular, the mentioned swivellable connections thus form
links; at least one or each of the links preferably has
precisely one degree of freedom. In particular, at least
one or each of the links can preferably be constituted as a
hinge.
In a state fastened to the spacecraft, therefore, the
capture device forms at least a part of a frame, which is
variable on account of the swivelability about axes
parallel to one another; in the case of a plurality of
fastening feet, such a frame can also comprise a section of
the surface of the spacecraft. In particular, sensitive
positioning of the gripping device arranged on the
connecting bracket can easily be brought about with the
frame arrangement, by means of which a subsequent sensitive
change in the position and orientation of the satellite
currently to be captured can be minimised. The effect of
the frame arrangement is also that the respective angles
mutually influence one another. The gripping device can
thus be brought into a desired position with particularly
little drive and control effort. In particular, the capture
device (especially in the fastened state) preferably
comprises at least two degrees of freedom, so that the
gripping device can be moved precisely in a region which
lies in a plane.
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The spacecraft according to the invention comprises at
least one capture device according to the invention
according to one of the embodiments disclosed in this
specification, which is fastened with its fastening foot or
its fastening feet to a further component such as for
example a base plate of the spacecraft. The legs preferably
extend parallel to one another.
According to a preferred embodiment, a spacecraft according
to the invention comprises two, three or more capture
devices according to the invention, which are arranged
rotationally symmetrical to one another about an axis; the
axis can preferably lie perpendicular to a surface on which
the capture devices are arranged. The gripping device of at
least one of the capture devices with such embodiments can
preferably be swivelled radially with respect to the
mentioned axis (i.e. along a plane containing the axis
optionally towards the axis or away from the axis), in
particular by swivelling the legs of the respective capture
device relative to their respective fastening foot. In this
way, the capture device on a spacecraft can be adapted to
different elements of satellites currently to be captured,
with which the respective satellites can be gripped, for
example to different diameters of given payload adapter
rings.
According to an advantageous embodiment of the present
invention, the spacecraft itself is a satellite. A
satellite to be captured may in each particular case be
uncooperative; it is preferably position-controlled in each
case, i.e. stabilised with regard to its orientation.
The two legs of a capture device according to the invention
preferably have the same leg length; such a leg length is
understood in this specification to mean a respective
distance of a swivelling axis at the first end to a
swivelling axis at the second end of the respective leg. In
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embodiments in which the second ends of the legs are
connected to a common fastening foot, the swivelling axes
at the second ends of the legs also preferably have the
same distance from one another as the swivelling axes at
the first ends from one another; in embodiments in which
the second ends are connected to different fastening feet,
the latter can preferably be fastened correspondingly to a
spacecraft (i.e. so that the distance of the second ends
from one another is equal to that of the first ends from
one another). With such embodiments, the four associated
links then form together the corners of a parallelogram. In
such embodiments, the at least one capture device fastened
to a spacecraft according to the invention is then
preferably fastened in such a state, which is subsequently
referred to as the "parallelogram state" of the respective
capture device.
In such embodiments, swivelling of the legs relative to the
foot or the feet (or swivelling of the capture device as a
whole relative to the spacecraft, in particular on a
surface thereof) only changes the characteristics of the
respective parallelogram, but not the basic fact that the
four links form the corners of a parallelogram. An
(abstract, straight) connection of the links to the first
two ends of the legs to one another thus remains parallel
to an (abstract, straight) connection of the links to the
second two ends of the legs. It thus emerges that an
alignment (i.e. respective angles) of the connecting
bracket with respect to a surface of the spacecraft also
remains (remain) constant with swivelling, which thus also
applies to the gripping device, in particular for a contact
surface that may be present and/or a clamping finger of the
gripping device, which are described below.
In particular, the gripping device does not then have to be
adapted to changed angles when swivelling of the legs takes
place, but rather it retains its orientation with respect
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to the satellite to be captured (or with respect to an
element of the satellite, for example its payload adapter
ring). On the one hand, this facilitates the control of the
capture device, on the other hand it enables a methodical,
cautious approach of the gripping device towards the
satellite (e.g. its payload adapter ring).
The legs of a capture device according to the invention can
for example each have a leg length which lies in the range
from 35 cm to 65 cm, in particular from 40 cm to 60 cm.
With a capture device according to the invention, a
distance of the swivelling axes at the first ends from one
another can lie for example in a range from 20 cm to 50 cm,
in particular from 30 cm to 45 cm.
According to advantageous embodiments of the present
invention with a plurality of fastening feet, the latter
have the same foot height; the latter denotes in this
specification a distance between a contact surface of the
respective fastening foot, which when fastened to a
spacecraft lies adjacent to a surface thereof, and the
respective swivelling axis, about which the respective
fastening foot can be swivelled relative to the connected
leg. Such variants of embodiment are particularly suitable
for fastening to a flat surface of the spacecraft.
The gripping device of a capture device according to the
invention can preferably comprise a contact surface, which
is designed, during capture (preferably with flat contact),
to be placed on a surface of a satellite currently to be
captured, said surface facing the capturing spacecraft.
Such a contact surface is preferably flat.
Embodiments are particularly preferred wherein the legs
have the same leg length and comprise such a contact
surface. The contact surface then preferably runs in a
plane parallel to the plane that is produced through the
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swivelling axes at the first ends of the legs (to the
connecting bracket). In a parallelogram state of the
capture device as mentioned above, the contact surface is
then not tilted during swivelling, but rather retains its
angle with respect to a facing surface of the satellite.
The requirement for compensatory movements can thus be
avoided, movement mechanisms required for this can be
dispensed with and the control can be simplified.
According to an advantageous embodiment, the gripping
device comprises a clamping finger, which is designed to
engage around an element arranged on the satellite
currently to be captured (for example a radially external
projection on a payload adapter ring of the satellite) or
to engage in a groove on the element (for example the
payload adapter ring of the satellite).
In particular, such a clamping finger can be mobile
relative to a contact surface which may also be present.
The clamping finger can thus be designed to press the
element against the contact surface and thus fix it to the
gripping device. In such embodiments, the clamping finger
preferably comprises a clamping surface facing the contact
surface, the distance whereof from the contact surface
being variable; a maximum distance can amount for example
to at most 16 cm or at most 14 cm. A capture device
according to the invention of such an embodiment preferably
comprises an electric motor for moving the clamping finger
relative to the contact surface.
In an advantageous embodiment of a spacecraft according to
the invention, which comprises (as mentioned above) a
plurality of capture devices according to the invention
arranged rotationally symmetrical about an axis, at least
one of the capture devices preferably comprises a clamping
finger as described above. The clamping finger is
preferably facing the axis, i.e. points towards the axis.
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In particular, all the capture devices fastened to the
spacecraft can be designed in this way.
A payload adapter ring of the satellite, for example, can
thus be gripped radially from the exterior. It is thus
possible in each case to prevent internal structures such
as for example a multilayer insulation material
(multilayer-insulation-material, MLI) from being damaged by
the capture.
The design makes it possible in particular for the
satellite (e.g. at its payload adapter ring) firstly to be
mutually prefixed by means of the respective clamping
fingers and only then to be clamped between the respective
fingers and the respective contact surfaces. Such a so-
called "capture before contact" means an especially
cautious and at the same time secure gripping, with which
damage to the satellite, disruption of its functionality
and/or a change in its position relative to the orbit can
be avoided.
The capture device according to the invention preferably
comprises at least one control device, with which
respective swivelling of the legs relative to the
respective fastening feet and/or a respective gripping
action of the gripping device can be adjusted in an
automated manner. The legs and the connecting bracket
together then thus form with the control device a robot
arm, which is designed to guide and/or to operate the
gripping device in an automated manner.
A capture device according to the invention can comprise at
least one sensor device, which is configured to detect a
respective distance of the gripping device from the
respective satellite to be captured. Such a sensor device
can comprise a laser device and/or a camera. In particular,
the at least one sensor device can be configured, in
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corresponding embodiments with a contact surface and
clamping fingers, to detect whether an element arranged on
the satellite is made contact with in a predefined manner
both by a contact surface and by the clamping finger.
In embodiments with both at least one sensor device and at
least one control device as mentioned above, the latter can
preferably be designed to control swivelling of the legs
relative to the fastening foot or to the respective
fastening feet and/or a gripping state of the gripping
device on the basis of sensor data detected by the sensor
device.
According to advantageous variants of embodiment of a
capture device according to the invention, a connection of
one of the legs to the fastening foot (one in common or one
each) is constituted as a link, which comprises a motor for
swivelling the leg and the fastening foot relative to one
another. Alternatively or in addition, a connection of one
(other) of the legs can be constituted as a purely passive
link, i.e. does not have its own swivelling drive. Such a
passive link in the fastened state thus follows suit, for
example on account of swivelling of the other leg. Finally,
a respective connection of one or both legs to the
connecting bracket can be constituted in each case as a
purely passive link.
In particular, swivelling of a capture device according to
the invention or an approach of the gripping device towards
a satellite to be captured or towards an element thereof
(e.g. towards a payload adapter ring of the satellite) can
thus take place, whereby only one suitable motor is
operated and controlled, whereas the other swivellable
connections adopt the corresponding swivelling. This means
little control effort and - on account of avoiding further
motors - a low mass of the capture device.
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According to advantageous embodiments, a capture device
according to the invention is designed, in a state fastened
to the surface of the capturing spacecraft, optionally to
be placed on the surface (for example such that the legs
run parallel to the surface) or to be erected so as to
project away from a surface. The legs can thus each be
swivelled correspondingly far. This enables advantageous
transport or an advantageous launch or flight phase of the
spacecraft with a folded-down capture device on the one
hand and a suitable use in the erected state of the capture
device on the other hand.
The capture method according to the invention is used to
capture a satellite in space by means of a spacecraft
according to the invention according to one of the
embodiments disclosed in this specification. The capture
method comprises an approach of the spacecraft towards the
satellite to be captured and swivelling of the legs of the
at least one capture device or at least one of the capture
devices, which is/are fastened to the spacecraft, into a
gripping position in which the gripping device and a
predetermined structure of the satellite to be captured
(e.g. a payload adapter ring of the satellite) lie opposite
one another (in a predetermined manner). The structure can
for example comprise an edge of a projection or a groove in
an element of the satellite (e.g. a payload adapter ring),
which in the gripping position can lie opposite a clamping
finger of the gripping device in corresponding embodiments,
so that the clamping finger can engage around the
projection or be introduced into the groove. Alternatively
or additionally, the structure can comprise a surface of
the satellite (which is preferably flat and/or facing away
from the satellite). In corresponding embodiments, a
contact surface of the gripping device can then lie
opposite such a surface in the gripping position.
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Finally, the capture method comprises gripping of the
element with the gripping device of the at least one
capture device. The gripping can for example (in
corresponding embodiments) comprise a movement of a
clamping finger towards an axis, around which a plurality
of capture devices can be arranged in a rotationally
symmetrical manner (so that the clamping finger is for
example introduced into a groove and/or placed around a
projection), and/or the movement of a/the clamping finger
towards a contact surface (the satellite then preferably
being drawn along).
The gripping preferably does not take place until at least
two or three capture devices are each in a respective
gripping position. The aforementioned "capture before
contact" can thus be implemented.
According to advantageous embodiments of a capture method
according to the invention, at least one of the capture
devices as described above can be designed optionally to be
folded down or erected projecting away from the surface.
The capture method can then comprise erecting the legs in a
direction projecting away from a surface of the spacecraft
and/or folding down the legs (possibly of the same or
another of the capture devices) to the surface (for example
so that the legs run parallel to the surface).
Preferred examples of embodiment of the invention are
explained in detail below with the aid of drawings. It goes
without saying that individual elements and components can
also be combined in different ways than those represented.
Reference numbers for elements corresponding to one another
are used to include all the figures, and may not be
described again for each figure.
In the figures, diagrammatically:
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Figure 1: shows an exemplary embodiment of a capture device
according to the invention in a perspective view;
Figure 2: shows the capture device according to figure 1 in
another perspective and in another state of the
gripping device;
Figure 3: shows the capture device according to figure 1 in
a state folded down on the surface of a
spacecraft;
Figure 4: shows a part of a spacecraft according to the
invention; and
Figure 5: shows a detail view of an exemplary capture
device according to the invention when holding a
captured satellite.
Figure 1 represents, in a perspective view, an example of
embodiment of a capture device 10 according to the
invention for capturing satellites in space. The capture
device comprises two legs 11, 12. A respective first end
lla, 12a of the legs is connected to a connecting bracket
13 so as to be swivellable about a respective axis AI, A2,
said connecting bracket thus connecting first ends 11a, 12a
of the two legs 11, 12 to one another. The respective
connection of the legs to the connecting bracket is in each
case constituted as a hinge (in particular with precisely
one degree of freedom).
A gripping device 14 for gripping a satellite currently to
be captured is arranged on connecting bracket 13, which
gripping device is described below in detail with respect
to figure 2. A sensor device 17 also arranged on connecting
bracket 13 is configured to control a gripping procedure
carried out by gripping device 14 in each case, which for
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example can comprise determining a respective distance of
gripping device 14 from the satellite to be captured.
In the example of embodiment shown, a fastening foot 15, 16
is arranged in each case on respective second end 11h, 12h,
by means of which fastening foot capture device 10 is or
can be fastened to a surface of a spacecraft (not
represented in figure 1). A respective connection of second
ends 11b, 12b of the legs to the respective fastening foot
is also constituted as a hinge, so that legs 11, 12 can
each be swivelled about an axis A3 and respectively A4
relative to the fastening feet. In alternative (not
represented) variants of embodiment, both second ends can
be connected to a common fastening foot in each case in a
swivellable manner (in particular by means of a respective
hinge).
Axes Au A2, A3 and A4 are parallel to one another (in
pairs). As shown in figures 2 and 3 (from a different
perspective from that in figure 1), capture device 10, in a
state fastened to a surface 20 of a spacecraft, forms
together with a section of the surface a frame, which is
variable, i.e. swivellable as a whole, on account of the
parallelism of axes Au A2, A3 and A4. The gripping device
can thus easily be guided into an advantageous position.
As also represented in figure 2, gripping device 14 in
particular comprises a contact surface 14a and a clamping
finger 14b, the distance whereof from contact surface 14a -
as denoted by a corresponding double arrow - is variable.
In the example shown, contact surface 14a extends parallel
to surface 20, and it is designed or provided to be placed
during capture on a surface of a satellite currently to be
captured that is facing the capturing spacecraft. Clamping
finger 14b is designed to engage around a projection (for
example a shoulder) on a surface of the satellite currently
to be captured and/or to engage in a groove in the surface
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of the satellite. By a movement towards the contact
surface, the clamping finger can then guide the satellite
towards the contact surface and/or press it against the
contact surface.
As shown in figure 2, leg length Li of a first leg 11 given
by the distance of axes Ai and A3 from one another is equal
to leg length L2 of second leg 12 given by the distance of
axes A2 and A4 from one another. Capture device 10 could,
in a parallelogram state in which links Gl, G2, G3, and G4
represent the corners of a parallelogram, thus be fastened
to surface 20 of the spacecraft, as is shown in figure 2.
Like leg lengths Li and length L2, distances G3-G4 and Gi-G2
are identical. As a consequence, when swivelling of capture
device 10 takes place, the alignment (determined by
respective angles) of swivelling bracket 13 and gripping
device 14 arranged thereon remains constant relative to
surface 20. In particular, the parallelism of contact
surface 14a with respect to surface 20 is also retained
with each swivelling action of device 10. The capture
device can thus be controlled in a particularly
straightforward manner, because compensation for a movement
(i.e. swivelling) of the capture device, with which
gripping device 14 is guided towards a satellite, is not
required.
In the represented example of embodiment, links Gl, G2 and
G4 are constituted as passive hinges, which carry out
swivelling only as a reaction to swivelling of the link
which is also constituted as a hinge, is driven by a motor
18 and is therefore active. The use of passive links and
therefore the avoidance of additional motors means both a
saving on mass and also a simplification of the control.
Figure 2 shows capture device 10 in an erected state
projecting away from surface 20, in which gripping device
14 can advantageously be used for capturing satellites.
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In contrast, the capture device in figure 3 is shown in a
state folded down to surface 20, in which it can
advantageously be held for example in a transport
procedure, in particular during transport of the spacecraft
from the earth into space.
Figure 4 represents a part of a spacecraft 1 according to
the invention, to surface 20 whereof three capture devices
according to the invention are fastened, only two of which,
i.e. capture devices 10 and 10', can be seen in the figure
for reasons of clarity. The capture devices are
rotationally symmetrical with an angle of 120 about an
axis X, which is orthogonal to surface 20 (the rotational
symmetry can be seen only partially in the figure on
account of the absence of the third capture device and the
perspective with the viewing direction parallel to surface
20). The capture devices are fastened in each case to
surface 20 in such a way that they can be swivelled
radially with respect to axis X (i.e. along a plane
containing axis X). A distance of the gripping devices of
the capture devices from axis X can thus be changed by
swivelling of the capture device. The arrangement can in
particular thus be adapted to different diameters of
payload adapter rings of satellites currently to be
captured.
Clamping fingers 14b, 14b' of capture devices 10, 10' are
each facing the axis x, i.e. pointing towards it. The
arrangement thus allows capture devices to engage with a
satellite to be captured, in particular its payload adapter
ring, without having to engage into the interior of the
ring. Damage in the sensitive internal region can thus be
avoided.
Figure 5 represents a region of an exemplary capture
device. Its gripping device 14 comprises a contact surface
14a and a clamping finger 14b, between which, in the state
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represented, a shoulder 30a of the payload adapter ring 30
of a captured satellite is clamped. The satellite is thus
firmly held by gripping device 14. Shoulder 30a is
preferably arranged radially outwards relative to a central
axis of payload adapter ring 30. In particular, gripping
device 14 thus grips the payload adapter ring radially from
the exterior.
A capture device 10, 10' for capturing satellites in space
is disclosed. The capture device comprises two legs 11, 12
each with a first end 11a, 12a and a second end 11b, 12b. A
connecting bracket 13 connects the respective first ends of
the two legs to one another. A gripping device 14 is
arranged on the connecting bracket for gripping a satellite
currently to be captured. By means of a common fastening
foot or a fastening foot in each case 15, 16 on the
respective second end of each of the legs, the respective
leg can be or becomes fastened to a capturing spacecraft 1.
The legs are connected to the connecting bracket and to the
fastening foot or fastening feet in each case so as to be
swivellable, wherein the respective (swivelling) axes Au
A2, A3, A4 are all parallel to one another
A spacecraft 1 with at least one, preferably three capture
devices 10, 10' and a capture method for capturing a
satellite in space are also disclosed.
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Reference numbers
1 spacecraft
10. 10' capture device
11, 12 leg
ha, 12a first end of a leg
11b, 12b second end of a leg
13 connecting bracket
14 gripping device
14a contact surface
14b, 14b' clamping finger
15, 16 fastening foot
17 sensor device
18 motor
20 surface of spacecraft 1
30 payload adapter ring
30a shoulder on payload adapter ring
A1, A2, A3, A4 (swivelling) axes
LI, L2 leg lengths
X axis orthogonal to surface 20, about which
capture devices are arranged
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