Summary information on the key parameters of the space stations and platforms introduced in Chapter 1 is provided in Table 1. In this table, 33 parameters are listed, and for each parameter a numerical value or other data point is provided for ISS (at assembly complete), Mir (with the Priroda module attached), the Space Shuttle with a Spacelab module, the Space Shuttle with a Spacehab module, the plans for Space Station Freedom (which was redesigned into ISS starting in 1993), and the capabilities that existed on Skylab. The 33 parameters listed are quantifiable or are other objective factors that, taken together, provide a summary of the overall capabilities of each space vehicle.
Including other parameters in the table to further characterize the space platforms was considered but rejected. In general, parameters were rejected by the committee when: (1) the parameter was one that tends to vary widely throughout a given time period, and including a single value in the table would have been inaccurate but including a wide range of values would have been uninformative (e.g., CO2 or humidity level in cabin atmosphere); (2) the parameter was potentially misleading (e.g., design life); or (3) reliable data were not available for every space platform in the table (e.g., additional data on the microgravity environment). [5]In order to increase the value of the data to the reader, a brief definition explaining each parameter has been placed in the table above the data provided on the space stations and platforms. Because the capabilities of Mir and ISS are more directly relevant to present and future plans for research in space, information in addition to that provided in Table 1 regarding these two space stations is provided in more depth in Chapters 4 and 5, respectively.
The data and information provided in Table 1 are derived in part from published documents that appear in the bibliography, unpublished sources such as NASA, and industry presentations and information releases, as well as from communications with NASA and industry personnel. The data have been assessed through the best technical judgment of the committee and are based on the best information available at the time this report was written.
Parameter Mir International Space Shuttle Space Shuttle Space Station Skylab
(in early 1996, Space Station with Spacelab with single Freedom at (1974)
with all at assembly Module Spacehab Module assembly-complete
modules) complete [double Spacehab (based on 1993
(based on Module] CDR data)
1995 IDR data)
Program Overview
The countries providing significant contributions to the assembly and operation of the space
station. Potential advantages of a large number of national participants include
availability of multiple launch systems, efficient use of national space technology
specialties, increased safety through independent analyses, and cost sharing. Potential
disadvantages include conflicting operational objectives, incompatibility of systems,
political instabilities and wavering commitments, multiple funding approval authorities, and
cost increases due to integration issues. In addition to their association through ESA, some
ESA countries have separate agreements describing additional involvement in the programs
(e.g., France and Germany with Russia regarding Mir, and Italy with the United States
regarding ISS).
Countries Involved
Russia, U.S., U.S., Russia, U.S., ESA U.S., Italy, U.S., ESA U.S.
ESA countries ESA countries, countries, Japan countries,
Japan, Canada Japan Japan, Canada
Projected Availability Date The date at which permanent habitation can be initiated.
through at 1998 habitable while habitable while 1999 not applicable
least late 1997 (to be the Space the Space (to be (last used in
completed in Shuttle remains Shuttle remains completed in 1974, deorbited
2002) in orbit in orbit 2000) in 1979)
Research Emphases The types of research that have been emphasized in the development and planned utilization of
the space station. Normally, these topics will include the five basic orbital scientific
disciplines: life sciences, microgravity sciences, space sciences, Earth observations, and
space technology development. Different modules of the space station may be specially
outfitted to support only one or a few of these disciplines.
astrophysics, life sciences, life sciences, commercial and life sciences, life sciences,
Earth microgravity microgravity technology microgravity solar
observations, sciences, sciences, research, sciences, astronomy,
microgravity technology and commercial and life sciences, technology and Earth
sciences, life commercial technology microgravity commercial observations,
sciences, research research sciences research astrophysics,
technology and microgravity
commercial sciences,
research technology
research
Configuration and Dimensional Parameters
Total Pressurized Volume (m3) The measure of the interior space of the facility in which the crew and most experiments must
fit. The volume of the space station will determine the nominal long-term and maximum
short-term crew sizes and will directly affect the design of the life-support, electrical
power, and thermal control systems. Volume tends to be minimized to reduce the size and cost
of the space station, but larger volumes are conducive to crew productivity and well-being
and permit greater experiment flexibility.
410 1,120 166 104 [135] 680 354
(93 Spacelab (31 [62]
only) Spacehab
modules only)
Total Modules (including nodes and crew-return vehicles) The number of separate air-filled elements brought together in space to form the standard
permanent habitation and working areas. Each module must be equipped with one or more
docking ports, and many support systems (e.g., electricity, propellant, communications)
require module interfaces. Modular assembly permits the construction of larger space
stations than could be outfitted on and then launched from Earth. Modular assembly also
allows replacement of major components, future reconfiguration of the space station, and the
ability to maintain the station in the event of a serious breach or malfunction in one area.
A large number of modules can reduce overall space station mass efficiency and can impose new
safety hazards.
9 17 2 2 8 2
Total Mass (kg) The total terrestrial weight of the space station, including modules, deployed structures,
internal equipment, and consumables. The total mass reflects the size, complexity, expense,
and difficulty of assembling and operating a space station in orbit. The cost of spacecraft,
modules, and space hardware are often a function of their mass, and launch costs are
generally a direct function of mass.
140,000 419,000 about 13,700 about 5,000 281,000 90,000
for [9,070] for
equipped equipped
Spacelab Spacehab
(about 110,000 (about 110,000
for the Space for the Space
Shuttle) Shuttle)
Length x Width (m) The overall maximum dimensions of the assembled space station. This parameter often does not
include small appendages (e.g., antennas), but may include the attachment of temporary
logistics vehicles.
33 x 41 109 x 85 6.9 x 4.1 2.8 x 4.1 107 x 74 36.1 x 28
(length x [5.6 x 4.1]
diameter) (length x
diameter)
Maximum Presurrized Diameter (M) The widest internal dimension perpendicular to the long axis of the pressurized module. This
parameter is normally limited by the space launch systems employed for orbiting space station
components.
4.2 4.3 4.1 4.1 4.3 6.6
Number of Docking Sites The number of places where visiting spacecraft can dock with the space station. This number
does not include docking ports that are occupied by permanently attached elements. Docking
sites may not be of a standard or universal design (i.e., the space station may possess
incompatible docking sites for different classes of spacecraft).
4 6 1 1 2 2
Hatch Diamter (m) The internal diameter of the docking port connecting the space station modules and spacecraft
through which crew and materials may safely pass. Although most hatches will conform to a
standard size, special smaller or larger diameter hatches may be available for experimental
work or extra-vehicular activities.
0.8, 1.0 1.39, 1.0 1.0 1.3 1.39 0.7
Launch and Orbital Parameters
Associated Launch Vehicle The space launch systems required to deploy the space station components, to ferry crews to
and from the space station, and to afford all necessary logistics functions. These space
launch systems may be expendable or reusable and manned or unmanned. Multiple launch
systems, including vehicles and launch complexes, for each category will enhance overall
space station support reliability.
Soyuz, Proton, Space Shuttle, Space Shuttle Space Shuttle Space Shuttle Saturn V,
Space Shuttle Soyuz, Proton, Saturn IB
Zenit, Ariane
Projected Number of Launches to Assemble The number of flights necessary to carry the specified components of the space station to
orbit. To permit appropriate comparisons, this parameter does not include logistics flights
that only carry expendable supplies or crew return vehicles to the space station prior to
completion. The numbers below do not include flights wholly dedicated to resupply or
utilization during assembly.
6 44 not applicable not applicable 27 1
(27 U.S.,
15 Russian,
1 European,
1 undetermined)
Maximum Pauload-Up Mass (kg) The standard maximum mass of useful payload that can be delivered to the space station for
each designated support spacecraft/launch system. This parameter includes both the capacity
of heavy-lift launch systems employed to orbit space station modules and the internal
carrying capacity of logistics spacecraft that do not become a permanent part of the space
station. The former will influence the number of missions needed for assembly of the space
station, while the latter will affect the number of annual missions necessary to support
space station operations.
2,700 15,740 (Space 4,600 inside 2,200 [4,100] 17,600 exact data not
(Progress), Shuttle), Spacelab Module inside Spacehab available (~ a
11,600 2,700 Module few
(Proton), (Progress), hundred kg),
15, 740 (Space 11,600 the pay-load
Shuttle) (Proton), was limited to
4,750 the volume
(Progress M2), available for
9,000 (Ariane stowage in the
5) Command Module
Maximum Payload Return Mass (kg) The maximum mass of materials, excluding crew members, that can be returned to Earth from the
space station for each designated support spacecraft. The ability to return materials to
Earth is essential to the completion of many scientific and technological experiments.
Materials no longer required on the space station and that need not be returned to Earth may
be ejected from the space station and allowed to be destroyed during atmospheric reentry.
150 (Raduga), 17,100 4,600 inside 2,200 [4,100] 17,600 300
17,100 (Space Spacelab Module inside Spacehab
(Space Shuttle) Shuttle) Module
Inclination (degrees) The orbital inclination of the space station, defined as the angle between the space
station's orbital plane and the Earth's equator. In practice, the orbital inclination of a
space station cannot be smaller than the latitude of the most-northern launch facility used
to support assembly of or logistics for the space station. For a given launch site, the
amount of useful payload that can be delivered to a space station decreases as the orbital
inclination increases. Maximum launch vehicle capacity is achieved when the orbital
inclination of the space station is the same as the latitude of the launch site.
51.6 51.6 varies with varies with 28.8 50
mission mission
Mean Orbital Altitude (km) The average altitude of the space station as it completes one revolution about the Earth.
The mean altitude may vary during normal and logistics operations or during fluctuations in
the Earth's atmospheric density, primarily caused by solar activity. Normally, the space
station is maintained in nearly circular orbit (i.e., the difference between the closest
[perigee] and farthest [apogee] approaches to the Earth during each orbit is small).
400 400 varies with varies with 435 430
mission mission
Assured Crew Return Vehicle The spacecraft attached to the space station for the express purpose of returning the crew
members to Earth at any time. The crew return vehicle may or may not be part of normal
logistics operations. The vehicle or vehicles at a minimum must be capable of immediately
supporting all of the crew members in emergency situations (major space station system
failure or medical emergency) and of returning them to Earth in a timely manner. Multiple
crew return vehicles permit the emergency return of crew members with medical problems
without completely abandoning the space station.
Soyuz Soyuz not applicable not applicable Soyuz or new Apollo Command
(Space Shuttle (Space Shuttle) (Space Shuttle) U.S. vehicle Module
and Soyuz for
routine
return)
Crew Parameters
Permanent Crew Capability The ability to keep a space station inhabited for an indefinite period of time. For a space
station to be able to support crews for extended durations, the facility and its
infrastructure must be able to furnish expendables (food, air, water, propellants,
short-lived equipment, etc.) at a rate exceeding consumption.
yes yes no no yes no
Typical Crew Size (persons) The number of people who normally inhabit the space station and conduct scientific and
technological experiments or perform space station control and maintenance functions. The
crew size will normally vary for short periods during crew rotations (handovers) and
logistical missions. The typical crew size is directly limited by the capacity of the
life-support and electrical systems, the resupply network, and the size of the space station
itself.
3 6 up to 7 up to 7 4 3
Crew Duration The number of continuous days a crew will spend on board the space station. The crew duration
may vary due to mission requirements and logistical capacity. Individual crew members may
conduct extended stays on board the space station for biomedical and psychological purposes.
4-6 months 3 months up to 15-20 up to 15-20 3 months 28, 59, and 84
typical (but up standard days days standard days
to 14 proven)
Primary Constraint to Longer Missions For space stations that are not permanently inhabited, the reason why crews cannot stay on
orbit longer. The principal technical constraints are normally the supply of electrical
energy and other consumables.
none technical none technical energy energy none technical not designed
(dependent on (dependent on for resupply
the Space the Space
Shuttle) Shuttle)
Crew Time for Research Use (person-hrs/day) The total person-hours each day that the crew can devote to research-oriented work. Other
activities which limit crew time for users are space station maintenance activities, meals,
hygiene chores, personal time, sleep, and mandatory exercise periods.
about 7.5 about 23 about 30-40 about 30-40 about 18 about 18
Power and Operations Parameters
Total Power (kW) The maximum electrical power capable of being generated and utilized by the space station
under normal power conditions. This is the power available for all uses, including essential
housekeeping requirements and non-essential activities, e.g., experiments. Space stations are
primarily dependent upon the conversion of solar energy into electrical energy to meet daily
power requirements. Various storage devices are used to maintain minimum power levels during
periods of transit through the Earth's shadow or of low angles between the sun and the
orbital plane of the space station. Electrical power is one of the major limitations to
space station utilization efficiency.
<25 110 7.7 3.15 71 18
User Power (kw) The amount of electrical power normally available to the crew for non-essential uses such as
powering laboratory equipment. This power level will, in part, determine the number and the
combination of experiments that can be performed simultaneously.
4.5 ~50 3.5 to 7.7 3.15 30 3
Voltage (V-dc) The electrical potential at which the power is supplied to systems and outlets. Spacecraft
voltage is usually provided as direct current (e.g., 28 Volts dc) by the main electrical bus,
but alternating current can be generated via electrical converters at the subsystem or
experiment level. High voltage levels can increase the complexity and the safety
requirements of the electrical distribution system.
28.5 120 and 28 28 28 120 28
Solar Array Area (m2) The amount of active surface area on all solar arrays capable of converting solar energy
directly into electrical energy. The area of the solar arrays is thus directly proportional
to the amount of power that can be used for housekeeping and experimental purposes. The type
of solar cell material (e.g., silicon or gallium arsenide) will determine the power density
of the array (i.e., the amount of power generated per square meter).
430 ~3,000 0 0 ~1,800 165
Data Rate (down rate in Mbps) A measure of the capacity of the space station's communications system to send data to the
Earth. In general, the higher the data rate, the larger the required transmitter power and
antenna size. Data rates can also be limited by the route which is selected (e.g., direct to
ground to a main receiving station or to an auxiliary receiving station or via intersatellite
relays). Data rate requirements can be reduced in some cases by onboard data processing.
7 50 45 16 50 <1
Steady State Acceleration Near Center of Mass (in g x10-6) The degree of microgravity normally existing near the center of the space station.
Microgravity levels for low altitude, unmanned Earth satellites may experience one-millionth
of the force of gravity at the surface of the Earth. Crew activities (e.g., normal movements
and exercising), spacecraft dockings, equipment operations, and orbital maneuvers will reduce
the quality of the space station's microgravity environment. The levels shown below may be
considerably higher (e.g., up to 100 times higher for the Space Shuttle) during especially
energetic on-orbit maneuvers and is also higher at high frequencies. Low microgravity
environments are especially desirable for many microgravity science experiments.
50-250 1 1-10 1-10 1 unavailable
(requirement) (requirement) (not recorded
onboard)
Video Up (yes/no) and The ability of the space station to receive or to transmit video communications. This Video Down (yes/no) capability is useful not only for scientific research (e.g., space science and Earth
observation, but also for daily communications with the space station crew).
yes & yes yes & yes no & yes no & yes no & yes no & yes
Water Recycled (yes/no) The ability of the space station to extract water from its environment (human waste,
atmosphere, experiments, etc.) and to recycle it in a useful (potable or nonpotable) manner.
Recycled water can also be used to maintain the space station's atmosphere and to perform
attitude and altitude control. Normally, different systems are designed to recycle water
from the various sources. The greater the efficiency of the space station's water recycling
systems, the lower the logistical requirements for supplying additional water.
yes yes no no yes no
Atmospheric Pressure (atmospheres) The nominal maintained pressure of the space station's environmental control system. Most
space stations operate with a pressure equivalent to sea level on Earth (1 atmosphere). This
standard facilitates the support of both man and machine on the space station.
.67 - 1.34 1 1 1 1 .34
Nitrogen/Oxygen (percent) 2 Percent of nitrogen and oxygen in the space station atmosphere. When the atmospheric
pressure is maintained near one standard Earth atmosphere, the nitrogen and oxygen
composition of the atmosphere is also approximately that found on Earth. If the atmospheric
pressure is reduced, the relative percent of oxygen must be increased.
79-60/21-40 78/22 78/22 78/22 78/22 26/74
Cabin Temperature (o Celsius) Permissible range of temperature maintained within the space station. The actual temperature
will fluctuate depending upon the atmospheric humidity and pressure. Some areas of the space
station may have elevated or reduced temperatures depending upon experiment requirements or
by-products.
5-40 18-27 18-27 18-27 18-27 13-32
2 Trace gases are discussed in the NRC (1994) report, Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Volume 1.
[5]The following examples are representative of additional parameters considered by the committee.
Design life was not included because it is not as useful in describing a real space station as one might think. This is partially due to the fact that, unlike most planetary or Earth-orbiting spacecraft, a space station regularly visited by astronauts or cosmonauts can be upgraded and repaired during its time in space. The Mir Space Station was designed for seven years on orbit, but it has been used for over nine years and is expected to be used for two more. On the other extreme, NASA planned to use Space Station Freedom (SSF) for 30 years, but current plans call for using its successor, the ISS, for only 10 years. One consequence of the change from 30 to 10 years is that the projected lifetime cost of the program has been greatly reduced, but it is likely that ISS will be used for more than 10 years if it is still functional and there continue to be good reasons to continue to use it after 2012. In general, including design life as a parameter would have lead to misconceptions that the SSF would have been usable exactly three times as long as ISS will be, or that Mir would have been usable only until 1993 (if stated in 1986).
Definitive data regarding microgravity levels and volumes within certain microgravity levels was sought but was not obtainable (e.g., for ISS projections are available, but they are ellipsoids based on computer models that are not readily converted to a conclusive description of useful volumes for research payloads).
The committee considered using the International Standard Payload Rack (ISPR) as a parameter to describe the volume and facilities available for research but found that it was not possible to do so as the parameter was only completely applicable to Space Station Freedom. The racks in a Spacelab are different from the lockers in a Spacehab, and both are different from ISPR racks. ISS will have ISPRs in the U.S., European, and Japanese modules, but the Russian modules will have a different configuration to accommodate pressurized payloads and are not likely to be able to be fitted with payloads designed for ISPRs. Furthermore, because the ISPR provides more than just volume (e.g., standard power, data, and mechanical interfaces) the committee decided that inventing a new payload volume parameter such as an "ISPR equivalent" would be more misleading than illuminating.