Spacecraft on-orbit servicing consists of exchanging components such as payloads, orbital replacement units (ORUs), and consumables. To accomplish the exchange of consumables, the receiving vehicle must mate to the supplier vehicle. Mating can be accomplished by a variety of docking procedures. However, these docking schemes are mission dependent and can vary from shuttle bay berthing to autonomous rendezvous and docking. Satisfying the many docking conditions will require use of an innovative docking device. The device must provide fluid, electrical, pneumatic and data transfer between vehicles. Also, the proper stiffness must be obtained and sustained between the vehicles. A device to accomplish this, the resupply interface mechanism (RIM), was developed. The RIM is a unique device because it grasps the mating vehicle, draws the two vehicles together, simultaneously mates all connectors, and rigidizes the mating devices. The NASA-Johnson Manipulator Development Facility was used to study how compatible the RIM is to on orbit docking and berthing. The facility contains a shuttle cargo bay mockup with a remote manipulator system (RMS). This RMS is used to prepare crew members for shuttle missions involving spacecraft berthing operations. The MDF proved to be an excellant system for testing the RIM/RMS compatibility. The elements examined during the RIM JSC test were: RIM gross and fine alignment; berthing method sequence; visual cuing aids; utility connections; and RIM overall performance. The results showed that the RIM is a good device for spacecraft berthing operations. Mating was accomplished during every test run and all test operators (crew members) felt that the RIM is an effective device. The purpose of the JSC RIM test and its results are discussed

Gallo, Frank G.

Jackson, Stewart W.

English

NASA Technical Reports Server

N90-22090
THE RESUPPLY INTERFACE MECHANISM
RMS COMPATIBILITY TEST
Stewart W. Jackson,* Frank G. Gallo*
ABSTRACT
Spacecraft on-orbit servicing consists of exchanging components
such as payloads, orbital replacement units (ORUs), and
consumables. To accomplish the exchange of consumables, the
receiving vehicle must mate to the supplier vehicle. Mating can
be accomplished by a variety of docking procedures. However,
these docking schemes are mission dependent and can vary from
shuttle bay berthing to autonomous rendezvous and docking.
Satisfying the many docking conditions will require use of an
innovative docking device. The device must provide fluid,
electrical, pneumatic and data transfer between vehicles. Also,
the proper stiffness must be obtained and sustained between the
vehicles. Fairchild Space Company has developed a device to
accomplish this, the resupply interface mechanism (RIM). The RIM
is a unique device because it grasps the mating vehicle, draws
the two vehicles together, simultaneously mates all connectors,
and rigidizes the mating devices.
Johnson Space Center (JSC) Manipulator Development Facility (MDF)
was used to study how compatible the RIM is to on orbit
docking/berthing. The MDF contains a shuttle cargo bay mockup
with a remote manipulator system (RMS) . This RMS is used to
prepare crew members for shuttle missions involving spacecraft
berthing operations. The MDF proved to be an excellent system
for testing the RIM/RIMS compatibility. The elements examined
during the RIM JSC test were:
0
0
O
O
0
RIM gross and fine alignment
Berthing method sequence
Visual cuing aids
Utility connections
RIM overall performance
The results showed that the RIM is a good device for spacecraft
berthing operation. Mating was accomplished during every test
run and all test operators (crew members) felt that the RIM is an
effective device.
This paper will discuss the purpose of the JSC RIM test and its
results.
* Fairchild Space Company Germantown, Maryland
143
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INTRODUCTION
The recovery of LDEF in late January 1990 has once again
demonstrated that on-orbit retrieval of spacecraft is a routine
operation for the shuttle. Perfecting the process of spacecraft
retrieval would lead to the enhancement of on-orbit spacecraft
servicing. TO facilitate on-orbit servicing a spacecraft must be
designed for maintainability. Maintainable spacecraft provide
easy access for exchange of various components using Extra
Vehicular Activity (EVA) or a robotic manipulator such as the
RIMS. The various components are ORUs, payloads, and consumables.
Consumables maintain the spacecraft functional integrity. These
consumables consist of propellant, coolant, water, waste, etc.
With replenishing capability, the spacecraft operational life can
be extended. Replenishing can be accomplished using two
scenarios. The first would involve rendezvous and docking of a
spacecraft and refueling tanker. The second would require
retrieval of a spacecraft using the RMS, and then berthing it to
a refueling tanker in the shuttle cargo bay. The interface used
to mate the two vehicles has to provide transfer of utilities
across the separation plane. The type of utilities requiring
transfer are electrical, pneumatic, and fluid. Additionally, the
mating interfaces must be brought together to their specified
rigidization. The Fairchild Space Company (FSC) realizes the
important role that the interface must play in spacecraft
servicing. Therefore, FSC initiated an Internal Research and
Development (IR&D) program to define, design, build, and test an
interface system for generalized spacecraft. The RIM illustrated
in figure 1 is the result of this program. The RIM functions
are:
I ,
,
3.
4.
To provide mating guidance during the docking/berthing
process.
To capture and draw the two vehicles together.
To connect simultaneously all utility connectors.
To rigidize the interface.
The unique aspect of the RIM is that it accomplishes the above
docking tasks in a single action.
The RIM was tested at JSC MDF to determine its compatibility to
the RMS.
RIM DESIGN DESCRIPTION
The RIM illustrated in figure 2 consists of two parts: an active
half and a passive half. The cylindrical shape of the RIM is
designed such that the passive half fits internally into the
144
iI-4
I-I
f_
145
GRAPPLE
RECEPTACLE (3)
_ PASSIVE INTERFACE
--___'_""_ CON N ECTOR DECK
" __'_ ..... _. " SYSTEM
-- _ _ TAB(3)
ACTIVE / _ 7"_
INTERFACE .,._' _ j DRIVESYSTEM
MARMON/- "" - - CONNECTOR DECK
Figure 2: RIM, EXPLODED VIEW
active half. The active half is normally mounted to the
refueling tanker. It contains the proprietary
capture/rigidization mechanisms, sensors, a controller system, a
safety system and the female halves of the electrical connectors
and fluid couples. Also, the active half has an opening with a
conical rim. The conical rim accepts gross positioning and
alignment tolerance of ± 2.0 inches and _ i0 °. This opening is
gradually tapered at a 45 ° angle providing for a passive RIM
final alignment of ± .200 inches. Fine alignment and positioning
of the passive half is provided by the active half inner wall and
capture/rigidization system. A radial keyway on the active RIM
inner wall corrects for rotational alignment. This keyway is
designed to accept a passive RIM final positioning alignment
within the connectors' and fluid couplings' mating tolerance.
The proprietary capture/rigidization system (see illustration in
figure 2) consists of three grapples and tab devices. The
grapples and tabs are located two inches below the conical
146
section and 120 ° apart. These grapples are actuated
simultaneously via a chain drive system that is driven by one
motor. The grapples travel radially toward the RIM center. The
grapples protrude a maximum of one inch beyond the active half
inner wall before driving downward. The grapples are used to
grasp the RIM passive half and drive the two halves together.
The grapples maintained coupler and connector mating during
servicing operations and provided the required rigidization.
The passive half is normally mounted to the servicing vehicle.
The RIM passive half contains the receptacles for the grapple
system and the male half of the electrical connectors and fluid
couplings.
All connectors and fluid couplings are mounted on the RIM
connector decks (illustrated in Figure 2) that are utilized in
each half of the RIM. One deck is located inside of the RIM
active half. The connectors on this deck are mounted on floating
interface plates which provide 6 degrees of freedom for each
connector and coupling. Also, the active RIM connector deck
contains load bearing pads. The loads that are produced from
berthing and rigidization are transferred by the load-bearing
pads, into the RIM structure. The other connector deck forms the
interface surface of the passive half. Each connector on the
passive connector deck is rigidly mounted.
The RIM is also equipped with an emergency release system. This
system consists of three jettison spring assemblies mounted on
the periphery of the active half of the RIM at 120 ° apart. A
marmon clamp (illustrated in Figure 2 ) with explosive bolts is
used to secure the two halves of the active RIM system. Firing
the bolts releases the marmon clamp, enabling the outer portion
of the active half of the mechanism to be jettisoned, demating
the connectors in their normal fashion.
The fluid couplings used in this test were supplied by Fairchild
Control System Company (FCSC), Moog, and Futurecraft. Electrical
connectors have been supplied by both G&H Technologies and AMP.
RIM TWO-PART TESTING
A two-part proof-of-concept RIM test was performed. The first
test was conducted in-house to verify mechanism operation and
berthing alignment range. The second test verified the
compatibility of the RIM mating scenarios with the RMS controls.
The RMS test was performed as part of the JSC satellite resupply
demonstration/test held in the MDF. In addition to the RIM test
JSC also demonstrated the capability of their Magnetic
End-Effector (MEE), Force Torque Sensor (FTS) and Tracking and
Reflecting Alignment Concept (TRAC). The results of testing
these systems will not be presented in this paper.
147
sighting the cuing marks made it necessary to add two vertical
cuing marks on the active RIM. The cuing marks on the active RIM
were collimated with the one vertical cuing mark on the passive
RIM. When viewed from either camera, the cuing marks were
aligned as illustrated in figure 4b. The front of the RIM (the
part facing the orbiter aft deck window) had one cuing mark on
the passive and one on the active RIM, as illustrated in figure
5a. These cuing marks were arranged to be collimated viewed from
the aft flight deck window as illustrated in figure 5b.
To obtain a successful berth, the RIM front and aft cuing marks
must be simultaneously aligned before driving the passive and
active RIM together.
ALIGNMENT_--_.._,_. • I jPASSIVE SIDE
MATCH N _ _ OF RIM
MARKS _ • /
!
a: RIM AFT VISUAL CUEING MARKS
PASSIVE SIDE
ALIGNMENT_. /
MATCH _ _ _ OF RIM
MARKS I "% • I
i i
a: RIM FRONT CUEING MARKS
_CAMERA #1
t
CAMERA #1
II I
CAMERA #2 /
i" iJ
SPLIT SCREEN MONITOR
b: OPERATORS VIEW OF ALIGNMENT MARKS
FIGURE 4: AFT RIM CUEING MARKS
AFT FLIGHT DECK WINDOW
,t
_OPERATOR
b: OPERATORS VIEW OF ALIGNMENT MARKS
FIGURE 5: RIM FRONT CUEING MARKS
150
TESTING PLAN
After completing the test setup procedures, the test plan
required that the manipulator with the MEE attached grasp
spacecraft mock-up. The spacecraft is then maneuvering to a
position approximately five to six feet above the active RIM on
the tanker. From this hovering position the spacecraft was
skewed and placed out of the TRAC camera line of site. This
procedure was performed at the beginning of each test run by a
different manipulator operator than the one performing the test.
The test operator had no prior knowledge of the spacecraft
mock-up position at the berthing sequence initiation. Using the
FTS, TRAC, and various visual aids, the operator aligned the RIMs
and maneuvered them together. When the passive RIM engaged the
active RIM, the capture/rigidization mechanism pulled the RIMs
together and simultaneously mated all connectors and couplings.
For the berthing schemes, we used five different test conditions:
I .
2.
3.
4.
5.
Normal mode with FTS and TRAC
Normal mode with TRAC
Visual mode with cargo bay cameras
Visual mode and FTS
TRAC and FTS mode
The above test conditions were accomplished by reducing the
number of berthing aids available to the operator for each mode.
Varying the berthing modes created testing conditions that
provided data on the RIM functional operation. The five test
conditions are described below.
Normal mode with FTS and TRAC
For the normal mode, the operator had five berthing aids
available to assist in the berthing process. These aids are:
i o
2.
.
o
5.
Visual inspection out of the aft flight deck window.
Camera view of the cuing marks on the RIM from the four
cargo bay cameras.
RMS control coordinate display. This is a digital display
that describes the location of the active RIM center point
by cartesian (X,Y,Z) and attitude control (P,Y,R)
coordinates. This coordinate system is not orbit defined
but it is spacecraft (shuttle) fixed, as illustrated in
figure 6.
FTS
TRAC
These berthing aids were used at the operator's discretion.
Normal mode with TRAC
This mode is the same as the normal mode with FTS and TRAC,
151
Normal mode with TRAC
Normal mode with TRAC did not create any additional challenges
for the test operators. The fly-in portion of the berthing
process does not require the FTS. In this case, the FTS is only
used during the RIM insertion. However, the crew members had no
adversities in successfully completing a smooth berth without the
FTS. What was interesting was that all the crew members used
sighting out of the aft flight deck window to adjust the flying
spacecraft attitude and translation coordinate. Then
approximately 6 inches above the tanker, they switched to the
TRAC for the fly-in and mate.
Visual mode with cargo bay cameras
The visual mode with cargo bay cameras presented several
challenges for the crew members. It was difficult to determine
the spacecraft depth perception (x position along the shuttle
velocity axis). Also, pitch adjustment within 1.5 degrees was
hard to obtain. The pitch degree of 1.5 was required to ensure a
smooth insertion of the passive RIM into the active RIM during
the second alignment stage. Furthermore, the pitch adjustment
reduces the probability of binding by preventing any sliding wall
act. Some wall sliding is permissible during mating, but, if a
perfect engagement is to be obtained, the walls of the RIMs
should not touch. These difficulties were solved by first
sighting the RIM's visual cuing marks from the aft flight deck
window and aft cargo bay cameras, and then adjusting attitude and
translational coordinates. Using the split screen mode of the
monitor allowed viewing both images of the aft cameras on the
same screen, which facilitated adjustments. Pitch was adjusted
by using the manipulator digital coordinate display. The digital
display was programed to give coordinate location of the passive
RIM during fly-in. After making the adjustments, the operators
had to only fly the spacecraft into the tanker RIM within the
tolerance of the first alignment stage (+/- 2 inches and +/- i0
degrees). The flying RIM was permitted to slide down the RIM
conical section and position itself to be grasped by the
proprietary capture/rigidizing mechanism. Most of the berths
achieved were jerky but doable.
Visual mode and FTS
Without the cargo bay cameras, the aft vertical cuing lines on
the RIM could not be used. It became extremely difficult to
determine depth perception. Several times the operators had to
back the passive RIM out of the active RIM to avoid binding. All
the crew members decided to use the digital display and follow
similar steps as in the visual mode with cargo bay cameras.
Berthing was achieved successfully.
154
TRAC and FTS mode
Although this mode is unrealistic for RMS berthing operation, it
did give us an opportunity to study the RIM compliance to the
TRAC and FTS. The TRAC and FTS case require that the aft flight
deck window be blocked and the operator have no knowledge about
the position of the spacecraft. The crew members' first step was
to locate the spacecraft. This was accomplished by raising the
spacecraft high enough for it to be observed through the TRAC
camera. The spacecraft was then brought close enough (about 4
feet) to the tanker RIM to see the target mirror for attitude
adjustment. Translational adjustments were performed
continuously during the fly-in. All runs in this case were
smoother than the previous mode.
Optional
The optional runs were similar to the test mode, except for one
case. One crew member decided to use visual mode only. This
involved berthing the spacecraft by viewing the RIM cuing marks
from the aft flight deck window. Berthing was successful without
using any other cuing aid.
TEST CONCLUSION
The test successfully validated the RIM design and demonstrated
the compatibility of the hardware with the RMS. The RIM gross
alignment tolerance worked well. The crew members were able to
successfully berth the RIM during visual mode with cargo bay
cameras scenario by sliding the passive RIM down the conical wall
of the active RIM. This action proved that the RIM gross
positioning alignment tolerance was adequate even though some
jerky motion occurred. The jerky motions produced in some runs
can be alleviated by increasing the active RIM inner diameter and
rounding the edge where the conical ring meets the inner RIM
wall. This would provide smooth transition along the surfaces.
Furthermore, adding horizontal hash lines on the passive RIM can
give the arm operator insertion depth information when the TRAC
and FTS are not available. It was shown when using the TRAC that
high mating tolerance accuracy can be accomplished, whereas the
visual mode only permits low tolerance. Therefore, the test
expressed the importance of determining the proper visual cues
for the docking task. We found that the better the visual cues,
the tighter the berthing tolerance could be. The type of visual
cues to use is a function of the docking vehicle geometry,
visibility, lighting, line of sight, viewing equipment, and
operator's experience. This test was conducted with one vehicle
in the cargo bay. If a second spacecraft was present, the cuing
aid scheme would change. It is important to evaluate the
condition in which the berthing is going to be performed. This
scrutiny will lead to choosing the best cuing aid for the
155
berthing configuration.
ACKNOWLEDGEMENT
The authors wish to thank NASA Johnson Space Center for extending
an invitation to Fairchild Space Company to participate in their
satellite resupply demonstration. We would like to give special
thanks to JSC Propulsion and Power Division, the New Initiatives
Office, and the Manipulator Development Facility.
I o
REFERENCES
Gallo, F. G; Jackson, S. W; Pullen, J. L.; and Gorin, B. F.;
"Resupply Interface Mechanism," AIAA-89-2732, July 10-12,
1989.
156


The resupply interface mechanism RMS compatibility test

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