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U.S. space station freedom: Orbital assembly and early mission opportunities
Acta Astronautica Vol. 21, No. 4, pp. 255-265, 1990 Printed in Great Britain
0094-5765/90 $3.00+ 0.00 PergamonPress plc
U.S. SPACE STATION FREEDOM: ORBITAL ASSEMBLY A N D EARLY MISSION OPPORTUNITIESt DAVID C. WENSLEY McDonnell Douglas Astronautics Co.--Space Station Division, 5301 Bolsa Avenue, Huntington Beach, CA 92647-2048, U.S.A. (Received 7 March 1989; received for publication 27 November 1989)
Abstract--This paper describes the U.S. Space Station launch and assembly sequence and the mission support capabilities available in man-tended and permanently manned modes. Design and operational constraints affecting launch package configurations and orbital deployment and assembly are defined. The resulting flight configurations and associated payload accommodations are described with emphasis on the early flights through man-tended capability. The initial mission objectives will emphasize engineering data collection (structural, thermal, power, control, propulsion, etc.) to verify design and to calibrate system models and simulation tools. On-board information will be used to characterize the microgravity, electromagnetic, particulate, and other environmental features for the benefit of Space Station users. Early flight configurations will provide accommodation for attached payloads which may include experimentation in materials exposure, solar physics, and Earth and stellar observations. These mission payloads, once installed and initialized by the Shuttle flight crews, will be operated by ground control from their mission specialists. When the pressurized laboratory is added, the mission emphasis will shift to microgravity experimentation including material processing and manufacturing research, life sciences, and supporting technology research and development. These missions will be operated in a man-tended mode. Installation, real-time operation, and servicing will be performed by Shuttle during periodic visits; a combination of ground control and automatic modes will be used between Shuttle flights. As Station build-up continues, resources available for payloads will also increase. With the achievement of the permanently manned capability, continuous crew support will be available for mission activities. This paper summarizes each step of this build-up process and the capabilities available for Station operation and payload activities versus time.
I. INTRODUCTION Construction of the U.S. Space Station Freedom will begin in early 1995. Current planning calls for flights every 60-90 days beginning in March 1995, with assembly completed in July 1999. The orbital assembly sequence for the Station will take place over approx. 4½ years as each modular increment of the Station is transported to orbit, assembled in place, tested, and put into operation. This process will represent the most complex assembly and operational sequence ever accomplished in space. At the assembly complete (AC) phase, the U.S. Space Station will span 155 m (508 ft), provide 75 kW of electrical power and matching thermal control to subsystems and mission equipment, and will house a crew of up to 8 persons. Growth phases of the Station will add more capability to the power and thermal systems, will provide a vertical truss structure for mounting celestial viewing and Earth viewing payloads and for attaching large storage and servicing hangars. ?Based on paper IAF-88-65 presented at the 39th Congress of the International Astronautical Federation, Bangalore, India, 8-15 October 1988. The original paper has been updated to reflect design and assembly sequence revisions as of January 1990.
Selection of this configuration is the result of a lengthy and complex process which considered all influencing engineering and mission requirements and all factors that affect the utility, safety, reliability, and operational efficiency of the permanent, manned Space Station. Figure 1 illustrates some of the key considerations leading to this design selection. 2. ASSEMBLYSEQUENCE Development of the assembly sequence and launch package (Orbiter cargo) configuration for each flight also involves a complex set of interacting requirements and constraints. Table 1 lists the most important ground rules on constraints and design considerations, applicable to this activity, as defined by NASA. Inherent in the assembly sequence selection, and the allocation of Station resources such as crew time, extravehicular activity (EVA) and intravehicular activity (IVA), power and weight (launch capability) vs time, is the objective of supporting the potential users (both scientific and commercial) as soon as practical. This desire for an "early return on investment" must be delicately balanced with the longer term objective of establishing the full Station capability as soon as possible and achieving fully efficient flight operations at the earliest date. The
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DAVID C. WENSLEY
overlay of mission activities during construction will, ideally, have no significant effect on the assembly and orbital verification process or on the total time required to reach AC. The ground rules established by N A S A have been carefully selected as a means of meeting the mission and operational goals, including early mission return, while simultaneously advancing the related technologies and staying within the projected funding requirements. The resulting requirements represent a major system engineering challenge for the Level III N A S A centers and their prime contractor and subcontractors. At the present time, the Work Package teams are preparing their preliminary design review (PDR). In parallel, the teams are continuing to refine the conceptual design and to establish objectives and approaches for early mission activities. The N A S A Level II has recently developed a candidate assembly sequence (Table 2), that is consistent with the assembly requirements and constraints. This sequence, referred to as the "reference" sequence (AC in 20 flights; P M C in 13), begins with first element launch (FEL) in March of 1995; provides "man-tended" capability (MTC) in June 1996 with the launching of the U.S. Laboratory Module;
Table I. Many factors influence assembly Schedule and sequence requirements • FEL--March 1995 • Flight telerobotic servicer available on or before MB-2 • Man-tended capability by MB-7 • Assembly complete with 29 flights • Lab module on orbit before habitation module launched • Design requirements and constraints • Orbiter lift capability • Sufficientorbital life for missed launch • All essential systems are, as a minimum, single failure tolerant during initial assembly; two failure tolerant after PMC • Until next assembly flight, spacecraft able to communicate, operate control, safely sustain itself • 37.5kW power (min) available before habitation module launched • MSC used to support SS assembly • EVA 24 manhours per orbiter flight • No EVA first 72 h in orbit
achieves permanent manned capability (PMC) in July 1997; and reaches AC in July 1999. P M C is attained when a logistics flight (L-I), Flight 13, brings the 4 person crew and consumables to the station. MB-1 is a passive flight. It consists of the electrical power module, the truss outboard of the solar alpha gimbal on the starboard side, the truss assembly work platform and the FTS. MB-2 makes the station active and requires all of the functional capability of an autonomous spacecraft. Power, heat rejection,
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XAxis • Station flight
direction • Y axis
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Orbiter flight
corridor • Z axis • Payload growth - Earth viewing - Stellar viewing - Satellite servicing
hangars
/ Earth Viewing +Z
+X
Fig. 1. Many factors influence Space Station design.
Direction
of Flight
U.S. Space Station Freedom
257
Table 2. NASA Level II assembly sequence. Reference assembly sequence overall manifest launch schedule Date
Flight
3/31/95
C ) FEL
MB-1
Assembly elements
6/15/95
C)
MB-2
8/30/95
(~
MB-3
11/15/95 1/31/96
(~) C)
MB-4 MB-5
4/I/96
(~)
MB-6
6/15/96 8/30/96 11/15/96 1/31/97 4/1/97 6/15/97 7/30/97 9/15/97 10/31/97 12/15/97 2/I/98 3/15/98 4/30/98 6/15/98 7/30/98 9/15/98 10/31/98 12/15/'98 1/31/99 3/15/99 4/30/99 6/15/99
7 EMTC 8 C) 10 11 @ 13 PMC 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
MB-7 OF-I MB-8 MB-9 OF-2 MB-10 L-1 MB-11 L-2 L-3 MB-12 L-4 L-5 MB-13 L-6 MB-14 L-7 L-8 OF-3 L-9 L-10 OF-4
7/30/99
29
L-11
Starboard inboard integrated equipment assembly (IEA), solar array/beta joint (2), truss (SA2-SAI), starboard utilities (SA2-SA1), alpha joint, assembly work platform/astronaut positioning system, mobile transporter, FTS, FTS SAE Truss (SB8-SBI, SB8LL), utilities (SB8-SB5, SB8LL), starboard antenna pallet (Ku/S-band, avionics), propulsion pallets (2), starboard central TCS pallet, CETA device Starboard and port TCS radiators and condensors, utilities (SB4-SBI), PMAD pallet, module support truss (MST), GNC pallet (4 CMGs), APAE SIA Forward port node, pressurized docking adapter, MRS, cupola Repress tanks (O2/N2), port TCS pallet, utilities (PBI-PB7), propulsion pallet (l), port antenna pallet, ULC berthing mech. (2), truss (PB1-PA6, PBTLL, SA3-SA6) Port inboard integrated equipment assembly (IEA), Solar array/beta joint (2), utilities (PAI-PA2), alpha joint, MT batteries, propulsion pallet (l) U.S. Laboratory Module (6 system racks, I user rack) Pressurized logistics module, lab outfitting (13 system racks, 6 user racks), SPDM/MMD Aft port node, aft starboard node Habitation module 08 system racks) Pressurized logistics module, habitation outfitting (17 racks), repress tanks (O2/N2) Forward starboard node, airlock, EMUs, cupola Crew (4), pressurized logistics module, unpressurized logistics carrier, logistics resupply, cryo O2/N 2 Starboard outboard lEA, solar array/beta joint (2), port outboard IEA, solar array/beta joint (2) Pressurized logistics module, logistics resupply Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier JEM module Pressurized logistics module, logistics, resupply Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier ESA module Pressurized logistics module, logistics resupply, ECLSS upgrade JEM exposed facility 1 and 2, JEM ELM Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier Pressurized logistics module, logistics resupply Pressurized logistics module, module outfitting, FMAD, stinger/resistojet, MT/MSC upgrades Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier Pressurized logistics module, logistics resupply Pressurized logistics module, node and module outfitting and DMS, MS, C&T upgrades, pressurized docking adapter, CMGs (2), crew of 8 Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier
attitude control, propulsion (to maintain altitude), communication and data systems, and the structural/ mechanical framework are all essential on the first flight. On subsequent flights, as the Station is assembled in orbit, the same functional ability must remain as the configuration changes and system capacities are gradually increased. Of all the design and programmatic consideration affecting assembly sequence definition, those listed in Table 3 are the most demanding. Packaging of the desired cargo in the Orbiter bay, especially on MB-I and the other initial flights, poses major difficulties for the design team. Weight and CG limitations are extremely difficult to meet and the EVA time constraint of 24h per mission limits the extent of assembly operations that can be scheduled for each flight. The "29 flights" assembly plan demands that full efficiency be obtained from the weight and volume capabilities of each Orbiter flight. Initial assembly flight altitude is planned at 220 n.mi.; however, assembly altitude strategies are being considered that start at lower altitude for
the initial launch while still providing for 90 days between launches with adequate margin to permit a missed launch. At each step of the assembly, complete system functional capability must be verified, and planning must include the possibility of an unexpected event that would require interruption of the assembly without compromising safety or the ability to continue assembly on subsequent flights. In addition to these construction criteria, the desire to achieve early mission results provides an added element of system engineering complexity.
Table 3. Assembly sequence design requires simultaneous system considerations NSTS (shuttle) Payload CG EVA constraints Number of flights Orbit life End-to-end integration Assembly interruption Mission capability
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DAVIDC. WENSLEY
Fig. 2. Assembly Flight 1 first element launch (FEL). 3. LAUNCH PACKAGINGAND CONSTRUCTION IN ORBIT Figure 2 illustrates a current Level II configuration for MB-1. The task of the design teams, in this case the Johnson Space Flight Center (JSC) and their prime contractor, McDonnell Douglas Space Systems Co.--Space Station Division (MDSSCSSD), is to translate the concept and its functional and performance requirements into a detailed design which can be packaged, launched, and deployed from the Orbiter, while meeting all design and operational constraints. MB-1 is a passive spacecraft it must incorporate all functions necessary to permit subsequent Station build-up. The assembly includes a complete 18.75 kW photovoltaic power system with its own heat rejection system provided by the WP-4 LeRC/Rocketdyne
design team. Oriented to fly in the "gravity/gradient" mode, the assembly is stabilized with several passive dampers. Although launch packaging constraints will probably result in some geometric changes to the configuration, the basic functionality will remain intact. At present, the structural approach remains the 5 m 3 erectable truss concept selected during Phase B. Figure 3 illustrates the Level II concept for packaging MB-1 for orbit launch and subsequent deployment and assembly. Again, the designers' job is to convert this concept to a practical installation, observing the allowable Orbiter sill and keel fitting loads, the vibration, acceleration and thermal loads, deployment sequence preferences, clearance requirements, hazardous cargo access requirements, remote
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Fig. 3. Level II concept for packaging MB-1 for orbit launch.
Flight
I
U.S. Space Station Freedom
259
Fig. 4. Assembly work platform with mobile transporter. manipulator system (RMS) reach limitations, and weight and CG limits. These packaging considerations will require some adjustment to the preferred dimensions and modularity of large items such as the thermal radiators. The McDonnell Douglas concept for orbital construction of the flight segments employs several unique mechanisms. One is the AWP (Fig. 4) that is erected in the cargo bay. This is the key to construction, much like a workman's scaffold is for a building. Several design versions are being considered but each provides a stabilized framework to assist construction of the truss segments and installation of pre-package, "palletized" subsystems and components. A second mechanism is the mobile transporter (MT) which is attached to the AWP and is used to translate and rotate the Space Station segments as the build-up takes place. Astronaut Positioning System (APS) is a third type of mechanism used in the construction process. APS is armed with small platforms at the ends which support the astronauts as they position themselves to perform assembly tasks. Figure 5 illustrates MB-I in the process of construction using these devices, and the Orbiter RMS, to assist the EVA flight crew. The phases of construction for MB-I are as follows:
bay, while supporting assembly of a candidate MB-I configuration. Several versions of the AWP are being considered: erectable, deployable, and fixed. In each case the AWP attaches at the Orbiter sill at one end and provides a mounting frame for the mobile transporter at the other. The APSs allow the astronauts to reach all areas of the truss, internal and external equipment supports, and utility trays. The APS operates as a two-segment, 6 degrees-of-freedom platform. The foot restraints are mounted on a rotary platform so the astronaut can reach internal work locations. Externally mounted equipment is reached by rotating the APS to provide accessibility and clearance. The MT holds each truss segment in position during construction and then translates it so the next one can be built below it. After MB-I is assembled, the AWP, APS and MT remain attached in orbit to support the next orbital assembly step for MB-2. Installation of the power, signal, and fluid utilities presents unique challenges. While truss structure can • Propulsion module
(1) The AWP is erected in the cargo bay. (2) The mobile transporter with APSs is fixed to the sides of the AWP so that the astronauts can more efficiently perform the assembly operations. Containers of truss segments and other assembly components are attached to the AWP for easy access by the crew. (3) As each truss segment is constructed, the mobile transporter translates the segment to clear the way for the next segment's assembly. Pre-assembled pallets for avionics, fluids, thermal systems, and other functions are retrieved from the cargo bay using the SRMS and positioned next to the required truss segment for attachment by the crew. Also shown in Fig. 5 are details of the construction devices as they would appear in the Orbiter cargo
Fig. 5. Flight MB-I mid-construction.
260
DAVID C. WENSLEY
•/--~,'~,~,-~-----Truss Propulsion Pallet ]<{ ~-,/" i ~"~lP~ ~ ~, !,'~2,1~ ~" MobileTransporter ~ V!~'!~I~ UpperBase ~,/-1,~3;ii~1 \ /Astronaut
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Fig. 6. Spool deployment test. easily be assembled from short segments, it is preferable that the utility lines have as few connections as possible. For this reason, a deployment spool has been devised, as shown in the full-scale photo of Fig. 6. This will be used starting with MB-2. Utility lines are pre-assembled in trays which provide environmental protection and also allow nesting in coils within the spool. As each truss segment is completed, the spool is unwound and utility lines and trays are fastened in place. This approach allows minimum EVA time with few assembly connections. Extra utility ports are packaged in the "flip-out" utility panels to accommodate early payloads. Initial development tests of the spool concept were conducted by McDonnell Douglas in 1987 including the deployment tests illustrated in Fig. 7. Neutral buoyancy tests are planned by JSC. Figure 8 shows the combination of these construction devices in a computer-drawn illustration. Computer-aided design (CAD) is being used extensively by MDSSC-SSD to examine the many concepts and geometric variations available to the designs. This drawing illustrates the positioning of truss segments in boxes at each side of the AWP for ease of access by the astronauts. Utility trays are shown deployed on each side of the two completed truss bays.
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solar array alpha joint assembly and the adjacent truss bay. Note that the truss boxes are positioned horizontally for this assembly procedure. 4. EXTRAVEHICULAR ACTIVITY
The Space Station assembly requires a combination of EVA and the use of automation and robotics. With EVA time limited to 24 h per Orbiter mission (two EVA excursion for 2 crew members of 6 h each), it is extremely important that required EVA tasks be carefully evaluated to confirm the assembly concept at each step of construction. In the current design phase, both analyses and tests in ground simulations are being used to assess EVA concepts. The flight crews will use these ground simulations to validate the design concepts and also to train for the assembly work they will do in orbit. One-g mock-ups, zero-g flight tests, and air-bearing test beds, are also used to develop solutions to construction tasks. Figure 10 identifies the basic EVA tasks for one design option MB-1 construction. MB-1 construction begins after the AWP, MT, and APS are in place. Each step of the construction activity is carefully
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Fig. 9. Construction of alpha joint assembly and truss bay.
U.S. Space Station Freedom
=_ Complete bay 1 assembly Assemble EPS pallet to bay 1
• Assemble initial sections of Bay 1 • Install port and starboard solar array assemblies
261
a Install radiator panels a Connect utilities at EPS panel interface
• Attach antenna/truss interface adapters (TIA) • Assembly complete bay 4 assembly
• Complete bay 2 assembly • Install alpha joint • Connect utilities
• Attach utilities to antenna and RCS
Fig. 10. Candidate first flight assembly sequence (post A W P assembly).
planned, from removal from the Orbiter cargo bay to final verification of the completed assembly. As illustrated previously in Fig. 9, computer simulations are used to evaluate the geometry and clearances for each of the required movements and procedures, and timelines are developed for each step of each operation, whether automatically or manually performed. Table 4. Candidate crew EVA timeline (flight MB-I) Activity
Clocktime (h) (× 2 for total EVA man-hours)
Start day 3 (EVA No, I) 1. 2. 3. 4.
Exit airlock, retrieve tools Assembly AWP/MT/APS/FTS Assemble bay 1 (partial) Install port and starboard solar arrays 5. Finish bay 1 6. Translate to airloek End day 3 (EVA No. I)
15 min 240 min I 0 min 90 min 10 min 15 min 6 h 18min
Start day 4 (EVA No. 2) 8. 6. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Exit airloek, translate to AWP Connect utilities Assemble bay 2 (partial) Install IEA Finish bay 2 Install alpha joint Connect utilities to bay Attach utilities to alpha Slow structure magazines Stow tools and EVA aids Translate to airlock End day 4 (EVA No. 2)
Total EVA hours (clocktime)
15rain 10 min 10min 45 min 10 rain 45 min 10 min 10 min 60 min 15 rain 15 min 4h llh
Table 4 is an example of a typical timeline of EVA activities needed to assemble a flight segment in orbit. Contingency procedures are also developed for recovery from unforeseen events. Development of these steps is accomplished by working closely with the suppliers of each system and component that must be assembled in orbit. Initial estimates of time intervals for crew procedures are developed from actual experience on prior missions. These estimates are further refined by neutral buoyancy tests that evaluate the accuracy of the time predictions and also assess the adequacy of the tools and planned procedures as well as the overall geometry of each construction arrangement. Where possible, robotic devices are used to perform the necessary tasks and EVA is used only where robotics are not practical or cost-effective. In most cases, EVA back-ups are provided where robotics are used. Recently, a series of tests was performed on a full-scale mock-up of the EVA airlock configuration to evaluate astronaut ingress and egress and internal mobility, access and procedures. Figure 11 shows a suited astronaut leaving the airlock mock-up during the underwater tests being performed at JSC. The perforated mesh surfaces define the configuration geometry. Mesh surfaces are used in underwater testing to reduce the drag effects of the water as movement takes place. Tests of this type are extremely valuable in refining internal geometry, developing
DAVID C. WENSLEY
262
Fig. Il. Airlock functions evaluation mockup WETF test at
NASA JSC. locations for mobility aids, restraints and controls, and for testing routine and contingency procedures. Figure 12 shows some early neutral buoyancy tests run by MDSSC-SSD in their underwater test facility at Huntington Beach, Calif. These tests were performed to verify the concept of installing large subsystem pallets using EVA techniques.
Fig.
12. Subsystem pallet installation evaluation McDonnell Douglas underwater test facility. AND MISSION OPPORTUNITIES
5. OPERATIONAL PHASES
Full Space Station capability is achieved in three distinct phases. The end points of these three phases are marked by four distinct program milestones as illustrated in Fig. 13. The first, beginning with MB-l
MB-1
Fig, 13. Key assembly
at
sequence
milestones.
U.S. Space Station Freedom and MB-2 is the unmanned phase which has as its primary objective the on-orbit assembly of initial flight elements necessary to provide full spacecraft capability work. Once the Orbiter and its crew completes assembly, MB-I and MB-2 will function as a free-flyer operated on automatic control, supplemented by ground command. This mode of operation will continue as each subsequent Orbiter mission adds more Station subsystems and elements. In this phase, each Orbiter cargo flight is nearly filled with construction materials and equipment: there is only limited capacity available for payload equipment. Most of the available resources, such as power, thermal, and EVA hours are devoted to achieving the construction tasks and operating the initial Space Station. The second phase begins with the arrival of the U.S. Lab Module on MB-7, when man-tended capability (EMTC) is achieved. Flight crews will support the set-up and initialization of early payloads that will operate between continuing construction flights. Principal Investigators will monitor payload operations from the ground and will issue commands to sequence the necessary test scenarios. As part of this phase our extended duration Orbiter flight will be used to minimize user mission accommodation. The third phase, PMC, is achieved at Flight 13. This completes the outfitting and provisioning required to begin continuously manned operations. From this point forward, the crew can participate actively in the on-board operation and monitoring of payloads. EVA operations can be routinely con-
263
Table 5. Station payload build-up(science, technologyand commerce candidatepayloads) Unmanned(MB flights 1-6) • Distributed measurement sensors (plasma mapping and structural dynamics) Man-tended(MB flights7-10) • Materialsprocessing(crystal growth, containerlessfurnace) • Life scienceand biotechnology • Attached science instruments (cosmic dust collector, solarterrestrialobservatory,diffuseX-rayspectrometer,ASTROMAG, rainfall measurementmission) • Materialsand thermal technology Permanently-manned(MB flights 13-29) • Full productivityon all the above • Additionalcrew-intensivepayloads in all categories
ducted from the Station, rather than from the Orbiter. On the 29th flight, including those used for outfitting and logistics, the Station reaches AC. At this point it provides the full set of capabilities in terms of resources, pointing, crew operations, logistics, etc. needed to support the wide spectrum of user payloads. 6. PAYLOADS
In order to optimize the nation's return on investment in the Space Station, every effort is being made to accommodate experiments as early in the program as is feasible. This requires satisfying the operational and environment requirements of the early payloads without adding significant schedule impacts and costs in the manifesting and assembly of the Station itself. Otherwise these costs could negate the value received from the early scientific and technology returns achieved.
PIM__SS
Cosmic dust collector
• Plasma interactions monitoring system • Contaminates, EMI • 4-6 modules (0.5 m3, 100 kg)
:: Measures velocity vectors Captures particles for analysis on earth (planetary, exobiological orbital debris)
Integration issues
Integration issues
• Premium EVA deployment time • Extra utility ports needed
• Contamination avoidance • 2-3 hr EVA time per harvest (--'90 days)
Astromag
Containerless processing
Direct sampling of galactic material Antimatter, dark matter '• Large, opposing magnets
• Produce hi~lh quality materials without contamination from containers
Integration issues
Integration issues
• Cantilever truss mounting • 12,000 Ibs, 5x5x5 m • Helium venting (5 Itr/dy) Magnetic field impacts
• Micro-g environment • Extreme data processin~ requirement for controlhng specimen position
Fig. 14. Integration issues for early candidate payloads.
264
DAVIDC. WENSLEY
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iio
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U24
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Fig. 15. U.S. laboratory module: trial payload manifest (September 1988) UOF-I (payloads after OF-I). In response to this challenge, NASA is manifesting the U.S. pressurized Laboratory Module in Flight 7 and providing for delivery of externally attached payloads that can operate productively during the assembly phase of the Station. Table 5 traces the build-up of payloads, both in quantity and complexity as a function of the three assembly phases of the Space Station: (1) the initial unmanned flights where only those payloads needed for measuring the environment and which have modest resource requirements will be manifested, through; (2) a man-tended mode which will accommodate payloads needed only periodic attention for deployment, initiating, and servicing during Orbiter revisits, to (3) the fully outfitted permanently-manned Space Station capable of supporting a much wider range of experiments. Table 5 also provides examples of the scientific and applications disciplines involved and candidate payloads that are currently under consideration by NASA. In addition to the deployment issues associated with the early manifesting of payloads, each payload presents its own set of integration issues and requirements that must be accommodated by the Station even under normal operational (non-assembly) conditions. Some candidate early payloads, depicted in Fig. 14, illustrate the wide range of such issues, even for payloads selected for their low crew time and relatively low utility requirements. These issues range from providing power and data management services to regions of the Station for which there are no utility ports planned (as for the PIMS package) to the isolation of the Station from the large magnetic field and venting requirements of ASTROMAG. The pressurized experiments will be housed in the European ESA Columbus Module which will
house a Biotechnology Research Lab, the Japanese Pressurized Module dedicated to material sciences experiments, and the U.S. Laboratory Module which will pursue a balanced program in both material and life sciences. All of these experiments depend upon the micro-g environment provided by the Station. A candidate "floor plan" of the U.S. Laboratory Module, illustrated in Fig. 15, demonstrates the efficiency with which one can utilize available space on orbit. Since there is no preferred direction, there are no "ceilings" or "floors", and all surfaces are equally accessible and useful for astronaut interaction. It also illustrates the modularity of the design in which all experiments and equipments are housed in standardized racks, each of which provides access to all utilities. The Station has been designed to enable early utilization of the emerging Station capabilities as summarized in Table 6. In this manner maximum use will be made of each capability addition to the Station, and also permit building on user integration Table 6. SpaceStationFreedomorbitalassemblyand early missionopportunitiessummary Enables early, graduated utilization Starts with station environmentmeasurements • Minor impact payload precursors • Providesdata of key interest to payloads Initiallybuilds up laboratoryexperimentation • Emphasison payloadswhich can use telerobotics • Gainsearly insightinto largest user group (labs) Then, adds exterior sensinginstruments • Complementaryto spacecraft and platform payloads • Emphasison payloadswhich benefitfrom: --On-sitecrew involvement --Large-scale facility ---CombinedEVA/automatedservicing --Periodic Shuttle logisticsaccess Builds on lessonslearnedfrom Skylab,Spacelab
U.S. Space Station Freedom
26~
• Composed of internationally provided elements (US, Japan, ESA, Canada) • Assembled through an orderly series of orbiter flights • Accomodates a wide variety of micro~ravity and viewing payloads • Provides a resource-rich payload envtronment • 75-kw power • 8 pressurized modules • 8-man crew • 5 orbiter flights per year • Has inherent growth capability
Fig. 16. Space Station Freedom assembly complete. lessons learned from each successive step as well as from previous manned space programs such as Skylab and Spacelab. 7. SUMMARY One goal of the assembly sequence activity is to achieve "assembly complete" as safely and as quickly as possible. Figure 16 illustrates this flight configuration and some of its key features. In the process of reaching this full capability Space Station, beneficial resources and services are provided for all classes of
users. The opportunities for early mission return are thus given full consideration. At each step in the build-up, including the mantended configuration in the computer-drawn illustration of Fig. 17, significant opportunities will exist for high priority payloads that build a sound foundation of scientific, technological, and commercial knowledge for subsequent mission operations on a much grander scale.
Acknowledgements--I am indebted to Bradley Bell, David Homan, Sharon Poi, and David Shores at NASA/JSC for computer modelling illustrations; Scott Wicks of Stellacom Co. for photos of airlock underwater evaluation tests; Dr Joseph N. Barfield, Southwest Research Institute for information and conceptual payload design of PIMS; Dr Susan R. Breon of NASA/GSFC for ASTROMAG data; Dr Fred Horz of NASA/JSC for Cosmic Dust Collector data; and Boeing/Teledyne Brown for the illustration of a typical pressurized equipment rack, and candidate layout of the U.S. Pressurized Laboratory Module. Special thanks to the McDonnell Douglas technical staff including John Hill, George King, Steve LaPonsie, Bill MacVicar, Gideon Marcus, Keith Murch, Frank Ohgi, Dave Riel, Fritz Runge and Harry Wolbers, Ph.D. REFERENCES
Fig. 17. U.S. Space Station Freedom.
1. T. L. Moser, NASA Headquarters, Space Station Freedom---Getting ready to go. Aerospace America, September (1988). 2. R. Snyder. NASA Level II Space Station program briefing to the Associate Administrator. Space Station assembly sequence review, September (1988).
0094-5765/90 $3.00+ 0.00 PergamonPress plc
U.S. SPACE STATION FREEDOM: ORBITAL ASSEMBLY A N D EARLY MISSION OPPORTUNITIESt DAVID C. WENSLEY McDonnell Douglas Astronautics Co.--Space Station Division, 5301 Bolsa Avenue, Huntington Beach, CA 92647-2048, U.S.A. (Received 7 March 1989; received for publication 27 November 1989)
Abstract--This paper describes the U.S. Space Station launch and assembly sequence and the mission support capabilities available in man-tended and permanently manned modes. Design and operational constraints affecting launch package configurations and orbital deployment and assembly are defined. The resulting flight configurations and associated payload accommodations are described with emphasis on the early flights through man-tended capability. The initial mission objectives will emphasize engineering data collection (structural, thermal, power, control, propulsion, etc.) to verify design and to calibrate system models and simulation tools. On-board information will be used to characterize the microgravity, electromagnetic, particulate, and other environmental features for the benefit of Space Station users. Early flight configurations will provide accommodation for attached payloads which may include experimentation in materials exposure, solar physics, and Earth and stellar observations. These mission payloads, once installed and initialized by the Shuttle flight crews, will be operated by ground control from their mission specialists. When the pressurized laboratory is added, the mission emphasis will shift to microgravity experimentation including material processing and manufacturing research, life sciences, and supporting technology research and development. These missions will be operated in a man-tended mode. Installation, real-time operation, and servicing will be performed by Shuttle during periodic visits; a combination of ground control and automatic modes will be used between Shuttle flights. As Station build-up continues, resources available for payloads will also increase. With the achievement of the permanently manned capability, continuous crew support will be available for mission activities. This paper summarizes each step of this build-up process and the capabilities available for Station operation and payload activities versus time.
I. INTRODUCTION Construction of the U.S. Space Station Freedom will begin in early 1995. Current planning calls for flights every 60-90 days beginning in March 1995, with assembly completed in July 1999. The orbital assembly sequence for the Station will take place over approx. 4½ years as each modular increment of the Station is transported to orbit, assembled in place, tested, and put into operation. This process will represent the most complex assembly and operational sequence ever accomplished in space. At the assembly complete (AC) phase, the U.S. Space Station will span 155 m (508 ft), provide 75 kW of electrical power and matching thermal control to subsystems and mission equipment, and will house a crew of up to 8 persons. Growth phases of the Station will add more capability to the power and thermal systems, will provide a vertical truss structure for mounting celestial viewing and Earth viewing payloads and for attaching large storage and servicing hangars. ?Based on paper IAF-88-65 presented at the 39th Congress of the International Astronautical Federation, Bangalore, India, 8-15 October 1988. The original paper has been updated to reflect design and assembly sequence revisions as of January 1990.
Selection of this configuration is the result of a lengthy and complex process which considered all influencing engineering and mission requirements and all factors that affect the utility, safety, reliability, and operational efficiency of the permanent, manned Space Station. Figure 1 illustrates some of the key considerations leading to this design selection. 2. ASSEMBLYSEQUENCE Development of the assembly sequence and launch package (Orbiter cargo) configuration for each flight also involves a complex set of interacting requirements and constraints. Table 1 lists the most important ground rules on constraints and design considerations, applicable to this activity, as defined by NASA. Inherent in the assembly sequence selection, and the allocation of Station resources such as crew time, extravehicular activity (EVA) and intravehicular activity (IVA), power and weight (launch capability) vs time, is the objective of supporting the potential users (both scientific and commercial) as soon as practical. This desire for an "early return on investment" must be delicately balanced with the longer term objective of establishing the full Station capability as soon as possible and achieving fully efficient flight operations at the earliest date. The
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DAVID C. WENSLEY
overlay of mission activities during construction will, ideally, have no significant effect on the assembly and orbital verification process or on the total time required to reach AC. The ground rules established by N A S A have been carefully selected as a means of meeting the mission and operational goals, including early mission return, while simultaneously advancing the related technologies and staying within the projected funding requirements. The resulting requirements represent a major system engineering challenge for the Level III N A S A centers and their prime contractor and subcontractors. At the present time, the Work Package teams are preparing their preliminary design review (PDR). In parallel, the teams are continuing to refine the conceptual design and to establish objectives and approaches for early mission activities. The N A S A Level II has recently developed a candidate assembly sequence (Table 2), that is consistent with the assembly requirements and constraints. This sequence, referred to as the "reference" sequence (AC in 20 flights; P M C in 13), begins with first element launch (FEL) in March of 1995; provides "man-tended" capability (MTC) in June 1996 with the launching of the U.S. Laboratory Module;
Table I. Many factors influence assembly Schedule and sequence requirements • FEL--March 1995 • Flight telerobotic servicer available on or before MB-2 • Man-tended capability by MB-7 • Assembly complete with 29 flights • Lab module on orbit before habitation module launched • Design requirements and constraints • Orbiter lift capability • Sufficientorbital life for missed launch • All essential systems are, as a minimum, single failure tolerant during initial assembly; two failure tolerant after PMC • Until next assembly flight, spacecraft able to communicate, operate control, safely sustain itself • 37.5kW power (min) available before habitation module launched • MSC used to support SS assembly • EVA 24 manhours per orbiter flight • No EVA first 72 h in orbit
achieves permanent manned capability (PMC) in July 1997; and reaches AC in July 1999. P M C is attained when a logistics flight (L-I), Flight 13, brings the 4 person crew and consumables to the station. MB-1 is a passive flight. It consists of the electrical power module, the truss outboard of the solar alpha gimbal on the starboard side, the truss assembly work platform and the FTS. MB-2 makes the station active and requires all of the functional capability of an autonomous spacecraft. Power, heat rejection,
Stellar/Solar
r•
XAxis • Station flight
direction • Y axis
Power growth
Orbiter flight
corridor • Z axis • Payload growth - Earth viewing - Stellar viewing - Satellite servicing
hangars
/ Earth Viewing +Z
+X
Fig. 1. Many factors influence Space Station design.
Direction
of Flight
U.S. Space Station Freedom
257
Table 2. NASA Level II assembly sequence. Reference assembly sequence overall manifest launch schedule Date
Flight
3/31/95
C ) FEL
MB-1
Assembly elements
6/15/95
C)
MB-2
8/30/95
(~
MB-3
11/15/95 1/31/96
(~) C)
MB-4 MB-5
4/I/96
(~)
MB-6
6/15/96 8/30/96 11/15/96 1/31/97 4/1/97 6/15/97 7/30/97 9/15/97 10/31/97 12/15/97 2/I/98 3/15/98 4/30/98 6/15/98 7/30/98 9/15/98 10/31/98 12/15/'98 1/31/99 3/15/99 4/30/99 6/15/99
7 EMTC 8 C) 10 11 @ 13 PMC 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
MB-7 OF-I MB-8 MB-9 OF-2 MB-10 L-1 MB-11 L-2 L-3 MB-12 L-4 L-5 MB-13 L-6 MB-14 L-7 L-8 OF-3 L-9 L-10 OF-4
7/30/99
29
L-11
Starboard inboard integrated equipment assembly (IEA), solar array/beta joint (2), truss (SA2-SAI), starboard utilities (SA2-SA1), alpha joint, assembly work platform/astronaut positioning system, mobile transporter, FTS, FTS SAE Truss (SB8-SBI, SB8LL), utilities (SB8-SB5, SB8LL), starboard antenna pallet (Ku/S-band, avionics), propulsion pallets (2), starboard central TCS pallet, CETA device Starboard and port TCS radiators and condensors, utilities (SB4-SBI), PMAD pallet, module support truss (MST), GNC pallet (4 CMGs), APAE SIA Forward port node, pressurized docking adapter, MRS, cupola Repress tanks (O2/N2), port TCS pallet, utilities (PBI-PB7), propulsion pallet (l), port antenna pallet, ULC berthing mech. (2), truss (PB1-PA6, PBTLL, SA3-SA6) Port inboard integrated equipment assembly (IEA), Solar array/beta joint (2), utilities (PAI-PA2), alpha joint, MT batteries, propulsion pallet (l) U.S. Laboratory Module (6 system racks, I user rack) Pressurized logistics module, lab outfitting (13 system racks, 6 user racks), SPDM/MMD Aft port node, aft starboard node Habitation module 08 system racks) Pressurized logistics module, habitation outfitting (17 racks), repress tanks (O2/N2) Forward starboard node, airlock, EMUs, cupola Crew (4), pressurized logistics module, unpressurized logistics carrier, logistics resupply, cryo O2/N 2 Starboard outboard lEA, solar array/beta joint (2), port outboard IEA, solar array/beta joint (2) Pressurized logistics module, logistics resupply Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier JEM module Pressurized logistics module, logistics, resupply Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier ESA module Pressurized logistics module, logistics resupply, ECLSS upgrade JEM exposed facility 1 and 2, JEM ELM Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier Pressurized logistics module, logistics resupply Pressurized logistics module, module outfitting, FMAD, stinger/resistojet, MT/MSC upgrades Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier Pressurized logistics module, logistics resupply Pressurized logistics module, node and module outfitting and DMS, MS, C&T upgrades, pressurized docking adapter, CMGs (2), crew of 8 Hydrazine resupply tanks (2), unpressurized logistics carrier, cryo sub carrier
attitude control, propulsion (to maintain altitude), communication and data systems, and the structural/ mechanical framework are all essential on the first flight. On subsequent flights, as the Station is assembled in orbit, the same functional ability must remain as the configuration changes and system capacities are gradually increased. Of all the design and programmatic consideration affecting assembly sequence definition, those listed in Table 3 are the most demanding. Packaging of the desired cargo in the Orbiter bay, especially on MB-I and the other initial flights, poses major difficulties for the design team. Weight and CG limitations are extremely difficult to meet and the EVA time constraint of 24h per mission limits the extent of assembly operations that can be scheduled for each flight. The "29 flights" assembly plan demands that full efficiency be obtained from the weight and volume capabilities of each Orbiter flight. Initial assembly flight altitude is planned at 220 n.mi.; however, assembly altitude strategies are being considered that start at lower altitude for
the initial launch while still providing for 90 days between launches with adequate margin to permit a missed launch. At each step of the assembly, complete system functional capability must be verified, and planning must include the possibility of an unexpected event that would require interruption of the assembly without compromising safety or the ability to continue assembly on subsequent flights. In addition to these construction criteria, the desire to achieve early mission results provides an added element of system engineering complexity.
Table 3. Assembly sequence design requires simultaneous system considerations NSTS (shuttle) Payload CG EVA constraints Number of flights Orbit life End-to-end integration Assembly interruption Mission capability
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DAVIDC. WENSLEY
Fig. 2. Assembly Flight 1 first element launch (FEL). 3. LAUNCH PACKAGINGAND CONSTRUCTION IN ORBIT Figure 2 illustrates a current Level II configuration for MB-1. The task of the design teams, in this case the Johnson Space Flight Center (JSC) and their prime contractor, McDonnell Douglas Space Systems Co.--Space Station Division (MDSSCSSD), is to translate the concept and its functional and performance requirements into a detailed design which can be packaged, launched, and deployed from the Orbiter, while meeting all design and operational constraints. MB-1 is a passive spacecraft it must incorporate all functions necessary to permit subsequent Station build-up. The assembly includes a complete 18.75 kW photovoltaic power system with its own heat rejection system provided by the WP-4 LeRC/Rocketdyne
design team. Oriented to fly in the "gravity/gradient" mode, the assembly is stabilized with several passive dampers. Although launch packaging constraints will probably result in some geometric changes to the configuration, the basic functionality will remain intact. At present, the structural approach remains the 5 m 3 erectable truss concept selected during Phase B. Figure 3 illustrates the Level II concept for packaging MB-1 for orbit launch and subsequent deployment and assembly. Again, the designers' job is to convert this concept to a practical installation, observing the allowable Orbiter sill and keel fitting loads, the vibration, acceleration and thermal loads, deployment sequence preferences, clearance requirements, hazardous cargo access requirements, remote
MB-I Volume~ CG Allocation
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Fig. 3. Level II concept for packaging MB-1 for orbit launch.
Flight
I
U.S. Space Station Freedom
259
Fig. 4. Assembly work platform with mobile transporter. manipulator system (RMS) reach limitations, and weight and CG limits. These packaging considerations will require some adjustment to the preferred dimensions and modularity of large items such as the thermal radiators. The McDonnell Douglas concept for orbital construction of the flight segments employs several unique mechanisms. One is the AWP (Fig. 4) that is erected in the cargo bay. This is the key to construction, much like a workman's scaffold is for a building. Several design versions are being considered but each provides a stabilized framework to assist construction of the truss segments and installation of pre-package, "palletized" subsystems and components. A second mechanism is the mobile transporter (MT) which is attached to the AWP and is used to translate and rotate the Space Station segments as the build-up takes place. Astronaut Positioning System (APS) is a third type of mechanism used in the construction process. APS is armed with small platforms at the ends which support the astronauts as they position themselves to perform assembly tasks. Figure 5 illustrates MB-I in the process of construction using these devices, and the Orbiter RMS, to assist the EVA flight crew. The phases of construction for MB-I are as follows:
bay, while supporting assembly of a candidate MB-I configuration. Several versions of the AWP are being considered: erectable, deployable, and fixed. In each case the AWP attaches at the Orbiter sill at one end and provides a mounting frame for the mobile transporter at the other. The APSs allow the astronauts to reach all areas of the truss, internal and external equipment supports, and utility trays. The APS operates as a two-segment, 6 degrees-of-freedom platform. The foot restraints are mounted on a rotary platform so the astronaut can reach internal work locations. Externally mounted equipment is reached by rotating the APS to provide accessibility and clearance. The MT holds each truss segment in position during construction and then translates it so the next one can be built below it. After MB-I is assembled, the AWP, APS and MT remain attached in orbit to support the next orbital assembly step for MB-2. Installation of the power, signal, and fluid utilities presents unique challenges. While truss structure can • Propulsion module
(1) The AWP is erected in the cargo bay. (2) The mobile transporter with APSs is fixed to the sides of the AWP so that the astronauts can more efficiently perform the assembly operations. Containers of truss segments and other assembly components are attached to the AWP for easy access by the crew. (3) As each truss segment is constructed, the mobile transporter translates the segment to clear the way for the next segment's assembly. Pre-assembled pallets for avionics, fluids, thermal systems, and other functions are retrieved from the cargo bay using the SRMS and positioned next to the required truss segment for attachment by the crew. Also shown in Fig. 5 are details of the construction devices as they would appear in the Orbiter cargo
Fig. 5. Flight MB-I mid-construction.
260
DAVID C. WENSLEY
•/--~,'~,~,-~-----Truss Propulsion Pallet ]<{ ~-,/" i ~"~lP~ ~ ~, !,'~2,1~ ~" MobileTransporter ~ V!~'!~I~ UpperBase ~,/-1,~3;ii~1 \ /Astronaut
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Fig. 6. Spool deployment test. easily be assembled from short segments, it is preferable that the utility lines have as few connections as possible. For this reason, a deployment spool has been devised, as shown in the full-scale photo of Fig. 6. This will be used starting with MB-2. Utility lines are pre-assembled in trays which provide environmental protection and also allow nesting in coils within the spool. As each truss segment is completed, the spool is unwound and utility lines and trays are fastened in place. This approach allows minimum EVA time with few assembly connections. Extra utility ports are packaged in the "flip-out" utility panels to accommodate early payloads. Initial development tests of the spool concept were conducted by McDonnell Douglas in 1987 including the deployment tests illustrated in Fig. 7. Neutral buoyancy tests are planned by JSC. Figure 8 shows the combination of these construction devices in a computer-drawn illustration. Computer-aided design (CAD) is being used extensively by MDSSC-SSD to examine the many concepts and geometric variations available to the designs. This drawing illustrates the positioning of truss segments in boxes at each side of the AWP for ease of access by the astronauts. Utility trays are shown deployed on each side of the two completed truss bays.
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solar array alpha joint assembly and the adjacent truss bay. Note that the truss boxes are positioned horizontally for this assembly procedure. 4. EXTRAVEHICULAR ACTIVITY
The Space Station assembly requires a combination of EVA and the use of automation and robotics. With EVA time limited to 24 h per Orbiter mission (two EVA excursion for 2 crew members of 6 h each), it is extremely important that required EVA tasks be carefully evaluated to confirm the assembly concept at each step of construction. In the current design phase, both analyses and tests in ground simulations are being used to assess EVA concepts. The flight crews will use these ground simulations to validate the design concepts and also to train for the assembly work they will do in orbit. One-g mock-ups, zero-g flight tests, and air-bearing test beds, are also used to develop solutions to construction tasks. Figure 10 identifies the basic EVA tasks for one design option MB-1 construction. MB-1 construction begins after the AWP, MT, and APS are in place. Each step of the construction activity is carefully
...........
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Fig. 7. Utility tray assembly.
.......
Fig. 9. Construction of alpha joint assembly and truss bay.
U.S. Space Station Freedom
=_ Complete bay 1 assembly Assemble EPS pallet to bay 1
• Assemble initial sections of Bay 1 • Install port and starboard solar array assemblies
261
a Install radiator panels a Connect utilities at EPS panel interface
• Attach antenna/truss interface adapters (TIA) • Assembly complete bay 4 assembly
• Complete bay 2 assembly • Install alpha joint • Connect utilities
• Attach utilities to antenna and RCS
Fig. 10. Candidate first flight assembly sequence (post A W P assembly).
planned, from removal from the Orbiter cargo bay to final verification of the completed assembly. As illustrated previously in Fig. 9, computer simulations are used to evaluate the geometry and clearances for each of the required movements and procedures, and timelines are developed for each step of each operation, whether automatically or manually performed. Table 4. Candidate crew EVA timeline (flight MB-I) Activity
Clocktime (h) (× 2 for total EVA man-hours)
Start day 3 (EVA No, I) 1. 2. 3. 4.
Exit airlock, retrieve tools Assembly AWP/MT/APS/FTS Assemble bay 1 (partial) Install port and starboard solar arrays 5. Finish bay 1 6. Translate to airloek End day 3 (EVA No. I)
15 min 240 min I 0 min 90 min 10 min 15 min 6 h 18min
Start day 4 (EVA No. 2) 8. 6. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Exit airloek, translate to AWP Connect utilities Assemble bay 2 (partial) Install IEA Finish bay 2 Install alpha joint Connect utilities to bay Attach utilities to alpha Slow structure magazines Stow tools and EVA aids Translate to airlock End day 4 (EVA No. 2)
Total EVA hours (clocktime)
15rain 10 min 10min 45 min 10 rain 45 min 10 min 10 min 60 min 15 rain 15 min 4h llh
Table 4 is an example of a typical timeline of EVA activities needed to assemble a flight segment in orbit. Contingency procedures are also developed for recovery from unforeseen events. Development of these steps is accomplished by working closely with the suppliers of each system and component that must be assembled in orbit. Initial estimates of time intervals for crew procedures are developed from actual experience on prior missions. These estimates are further refined by neutral buoyancy tests that evaluate the accuracy of the time predictions and also assess the adequacy of the tools and planned procedures as well as the overall geometry of each construction arrangement. Where possible, robotic devices are used to perform the necessary tasks and EVA is used only where robotics are not practical or cost-effective. In most cases, EVA back-ups are provided where robotics are used. Recently, a series of tests was performed on a full-scale mock-up of the EVA airlock configuration to evaluate astronaut ingress and egress and internal mobility, access and procedures. Figure 11 shows a suited astronaut leaving the airlock mock-up during the underwater tests being performed at JSC. The perforated mesh surfaces define the configuration geometry. Mesh surfaces are used in underwater testing to reduce the drag effects of the water as movement takes place. Tests of this type are extremely valuable in refining internal geometry, developing
DAVID C. WENSLEY
262
Fig. Il. Airlock functions evaluation mockup WETF test at
NASA JSC. locations for mobility aids, restraints and controls, and for testing routine and contingency procedures. Figure 12 shows some early neutral buoyancy tests run by MDSSC-SSD in their underwater test facility at Huntington Beach, Calif. These tests were performed to verify the concept of installing large subsystem pallets using EVA techniques.
Fig.
12. Subsystem pallet installation evaluation McDonnell Douglas underwater test facility. AND MISSION OPPORTUNITIES
5. OPERATIONAL PHASES
Full Space Station capability is achieved in three distinct phases. The end points of these three phases are marked by four distinct program milestones as illustrated in Fig. 13. The first, beginning with MB-l
MB-1
Fig, 13. Key assembly
at
sequence
milestones.
U.S. Space Station Freedom and MB-2 is the unmanned phase which has as its primary objective the on-orbit assembly of initial flight elements necessary to provide full spacecraft capability work. Once the Orbiter and its crew completes assembly, MB-I and MB-2 will function as a free-flyer operated on automatic control, supplemented by ground command. This mode of operation will continue as each subsequent Orbiter mission adds more Station subsystems and elements. In this phase, each Orbiter cargo flight is nearly filled with construction materials and equipment: there is only limited capacity available for payload equipment. Most of the available resources, such as power, thermal, and EVA hours are devoted to achieving the construction tasks and operating the initial Space Station. The second phase begins with the arrival of the U.S. Lab Module on MB-7, when man-tended capability (EMTC) is achieved. Flight crews will support the set-up and initialization of early payloads that will operate between continuing construction flights. Principal Investigators will monitor payload operations from the ground and will issue commands to sequence the necessary test scenarios. As part of this phase our extended duration Orbiter flight will be used to minimize user mission accommodation. The third phase, PMC, is achieved at Flight 13. This completes the outfitting and provisioning required to begin continuously manned operations. From this point forward, the crew can participate actively in the on-board operation and monitoring of payloads. EVA operations can be routinely con-
263
Table 5. Station payload build-up(science, technologyand commerce candidatepayloads) Unmanned(MB flights 1-6) • Distributed measurement sensors (plasma mapping and structural dynamics) Man-tended(MB flights7-10) • Materialsprocessing(crystal growth, containerlessfurnace) • Life scienceand biotechnology • Attached science instruments (cosmic dust collector, solarterrestrialobservatory,diffuseX-rayspectrometer,ASTROMAG, rainfall measurementmission) • Materialsand thermal technology Permanently-manned(MB flights 13-29) • Full productivityon all the above • Additionalcrew-intensivepayloads in all categories
ducted from the Station, rather than from the Orbiter. On the 29th flight, including those used for outfitting and logistics, the Station reaches AC. At this point it provides the full set of capabilities in terms of resources, pointing, crew operations, logistics, etc. needed to support the wide spectrum of user payloads. 6. PAYLOADS
In order to optimize the nation's return on investment in the Space Station, every effort is being made to accommodate experiments as early in the program as is feasible. This requires satisfying the operational and environment requirements of the early payloads without adding significant schedule impacts and costs in the manifesting and assembly of the Station itself. Otherwise these costs could negate the value received from the early scientific and technology returns achieved.
PIM__SS
Cosmic dust collector
• Plasma interactions monitoring system • Contaminates, EMI • 4-6 modules (0.5 m3, 100 kg)
:: Measures velocity vectors Captures particles for analysis on earth (planetary, exobiological orbital debris)
Integration issues
Integration issues
• Premium EVA deployment time • Extra utility ports needed
• Contamination avoidance • 2-3 hr EVA time per harvest (--'90 days)
Astromag
Containerless processing
Direct sampling of galactic material Antimatter, dark matter '• Large, opposing magnets
• Produce hi~lh quality materials without contamination from containers
Integration issues
Integration issues
• Cantilever truss mounting • 12,000 Ibs, 5x5x5 m • Helium venting (5 Itr/dy) Magnetic field impacts
• Micro-g environment • Extreme data processin~ requirement for controlhng specimen position
Fig. 14. Integration issues for early candidate payloads.
264
DAVIDC. WENSLEY
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Fig. 15. U.S. laboratory module: trial payload manifest (September 1988) UOF-I (payloads after OF-I). In response to this challenge, NASA is manifesting the U.S. pressurized Laboratory Module in Flight 7 and providing for delivery of externally attached payloads that can operate productively during the assembly phase of the Station. Table 5 traces the build-up of payloads, both in quantity and complexity as a function of the three assembly phases of the Space Station: (1) the initial unmanned flights where only those payloads needed for measuring the environment and which have modest resource requirements will be manifested, through; (2) a man-tended mode which will accommodate payloads needed only periodic attention for deployment, initiating, and servicing during Orbiter revisits, to (3) the fully outfitted permanently-manned Space Station capable of supporting a much wider range of experiments. Table 5 also provides examples of the scientific and applications disciplines involved and candidate payloads that are currently under consideration by NASA. In addition to the deployment issues associated with the early manifesting of payloads, each payload presents its own set of integration issues and requirements that must be accommodated by the Station even under normal operational (non-assembly) conditions. Some candidate early payloads, depicted in Fig. 14, illustrate the wide range of such issues, even for payloads selected for their low crew time and relatively low utility requirements. These issues range from providing power and data management services to regions of the Station for which there are no utility ports planned (as for the PIMS package) to the isolation of the Station from the large magnetic field and venting requirements of ASTROMAG. The pressurized experiments will be housed in the European ESA Columbus Module which will
house a Biotechnology Research Lab, the Japanese Pressurized Module dedicated to material sciences experiments, and the U.S. Laboratory Module which will pursue a balanced program in both material and life sciences. All of these experiments depend upon the micro-g environment provided by the Station. A candidate "floor plan" of the U.S. Laboratory Module, illustrated in Fig. 15, demonstrates the efficiency with which one can utilize available space on orbit. Since there is no preferred direction, there are no "ceilings" or "floors", and all surfaces are equally accessible and useful for astronaut interaction. It also illustrates the modularity of the design in which all experiments and equipments are housed in standardized racks, each of which provides access to all utilities. The Station has been designed to enable early utilization of the emerging Station capabilities as summarized in Table 6. In this manner maximum use will be made of each capability addition to the Station, and also permit building on user integration Table 6. SpaceStationFreedomorbitalassemblyand early missionopportunitiessummary Enables early, graduated utilization Starts with station environmentmeasurements • Minor impact payload precursors • Providesdata of key interest to payloads Initiallybuilds up laboratoryexperimentation • Emphasison payloadswhich can use telerobotics • Gainsearly insightinto largest user group (labs) Then, adds exterior sensinginstruments • Complementaryto spacecraft and platform payloads • Emphasison payloadswhich benefitfrom: --On-sitecrew involvement --Large-scale facility ---CombinedEVA/automatedservicing --Periodic Shuttle logisticsaccess Builds on lessonslearnedfrom Skylab,Spacelab
U.S. Space Station Freedom
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• Composed of internationally provided elements (US, Japan, ESA, Canada) • Assembled through an orderly series of orbiter flights • Accomodates a wide variety of micro~ravity and viewing payloads • Provides a resource-rich payload envtronment • 75-kw power • 8 pressurized modules • 8-man crew • 5 orbiter flights per year • Has inherent growth capability
Fig. 16. Space Station Freedom assembly complete. lessons learned from each successive step as well as from previous manned space programs such as Skylab and Spacelab. 7. SUMMARY One goal of the assembly sequence activity is to achieve "assembly complete" as safely and as quickly as possible. Figure 16 illustrates this flight configuration and some of its key features. In the process of reaching this full capability Space Station, beneficial resources and services are provided for all classes of
users. The opportunities for early mission return are thus given full consideration. At each step in the build-up, including the mantended configuration in the computer-drawn illustration of Fig. 17, significant opportunities will exist for high priority payloads that build a sound foundation of scientific, technological, and commercial knowledge for subsequent mission operations on a much grander scale.
Acknowledgements--I am indebted to Bradley Bell, David Homan, Sharon Poi, and David Shores at NASA/JSC for computer modelling illustrations; Scott Wicks of Stellacom Co. for photos of airlock underwater evaluation tests; Dr Joseph N. Barfield, Southwest Research Institute for information and conceptual payload design of PIMS; Dr Susan R. Breon of NASA/GSFC for ASTROMAG data; Dr Fred Horz of NASA/JSC for Cosmic Dust Collector data; and Boeing/Teledyne Brown for the illustration of a typical pressurized equipment rack, and candidate layout of the U.S. Pressurized Laboratory Module. Special thanks to the McDonnell Douglas technical staff including John Hill, George King, Steve LaPonsie, Bill MacVicar, Gideon Marcus, Keith Murch, Frank Ohgi, Dave Riel, Fritz Runge and Harry Wolbers, Ph.D. REFERENCES
Fig. 17. U.S. Space Station Freedom.
1. T. L. Moser, NASA Headquarters, Space Station Freedom---Getting ready to go. Aerospace America, September (1988). 2. R. Snyder. NASA Level II Space Station program briefing to the Associate Administrator. Space Station assembly sequence review, September (1988).