International Space Station:
Continuing the Journey
[Reprinted from:
http://mgnews.msfc.nasa.gov/spring98/lead.html
Spring 1998.
This year marks the launch of the first segment of what is to be the
International Space Station (ISS), and the excitement about this event, which is
a triumph of both space engineering and international relations, is growing. The
ISS will be a permanent orbiting laboratory that will allow researchers to
conduct long-term experiments under microgravity conditions. The history of the
long-awaited station is a considerable one. Such an immense undertaking could
not take place without building on the talents, skills, and dreams of
innumerable people fascinated by space and space travel -- from those who work
with the program today to those who lived in the distant past.
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A
blueprint for the Habitat Wheel, a space station concept developed by
Herman Potocnik in 1928. The rotating station was modular in design,
just as the ISS will be. |
From Fiction to Reality
Space stations have long been the stuff of
imagination. The idea of humans living and working in space has enthralled
scientists and visionaries for over a century. As far back as 1869, an American
fiction writer named Edward Everett Hale published a story titled "The Brick
Moon" in which he envisioned a manned satellite that served as a navigational
aid for ships at sea (a function filled by unmanned satellites today). In 1903,
Russian schoolteacher Konstantin Tsiolkovsky illustrated another type of space
station vision when he depicted orbiting settlements that led to expeditions to
the Moon, Mars, and asteroids in a book called Beyond the Planet Earth.
This concept of establishing a space station as an "outpost in the wilderness,"
or a jumping-off point for further space exploration, became a very popular one
that would show up again and again in writings about space.
Inspired by such fictional creations, scientists
and engineers began to consider issues related to space outposts. In 1923,
German physicist Hermann Oberth wrote The Rocket Into Planetary Space, in
which he coined the term "space station." This influential work identified a
wide range of problems related to rocketry and space travel and proposed
solutions to them. Five years later, under the pseudonym Hermann Noordung, a
German engineer named Herman Potocnik published a work that took the space
station concepts even closer to reality. In
The Problem of Space Travel,
Potocnik laid out detailed engineering plans -- blueprints -- for an orbiting
space station he called the "Habitat Wheel." These plans included over 100
illustrations of his station design, which consisted of modules constructed on
Earth and carried to space via spaceships -- just as the modern ISS will be
constructed. The modules were connected to each other in the shape of a wheel,
and the entire station constantly rotated to simulate gravity by generating
centrifugal force.
Potocnik was extraordinarily thorough in his
plans, addressing such problems as obtaining power, heat, and light (he devised
plans for a solar power plant attached to the station); providing ventilation to
the station's inhabitants; and fabricating space suits that would allow humans
to work on the exterior of the station safely. Potocnik's complete technical
blueprint was the first to fully develop the notion of a space station, and many
of his ideas, in modified forms, can be seen in modern technologies that will be
used on the ISS.
In the 1950s, the space station concept found a
powerful and creative supporter in rocketry pioneer Wernher von Braun. Having
emigrated from Germany to the United States to build rockets for the U.S. Army
in 1945, von Braun contributed a great deal to the early days of the U.S. space
program, including his own version of a space station. Von Braun built on
Potocnik's ideas, devising a space station that would take the shape of a
rotating wheel, similar to the Habitat Wheel. Like Potocnik, he felt that
inducing artificial gravity could prevent astronauts from suffering ill effects
that could possibly be associated with long-term weightlessness. Von Braun's
wheel, however, would be built of reinforced nylon and inflated in space prior
to human occupation. According to his plans, the station would orbit 1,075 miles
above the Earth and would serve as a navigational aid, a meteorological station,
a military platform, and a way station for expanded space exploration, echoing
and combining purposes proposed for such a station by those who had preceded him
in imagining such a facility.
Put on Hold - A "Station Break"
Plans for the development of a space station have
been a part of NASA's agenda since the agency's inception. Like von Braun, many
of NASA's trailblazers saw a station as a necessary prerequisite to further
human exploration of space. Their reasoning was that a craft that had escaped
Earth's gravity was already halfway to anywhere they wanted it to go. With an
orbiting space station in place, missions to the Moon and Mars could be planned
without having to deal with the difficulties of designing a vehicle that could
both withstand the stress of escaping the Earth's atmosphere and address the
issues inherent in long-term microgravity spaceflight. Instead, astronauts would
fly one type of craft to the space station, and then transfer to another sort of
craft for extended travel, similar to the space travel depicted in the movie
2001: A Space Odyssey.
When the United States embarked on a "space race"
with the Soviet Union in the 1960s, however, the notion of a space station as a
prerequisite to space travel was deferred. President John F. Kennedy's promise
to put a man on the Moon before the end of the decade resulted in the decision
to pursue a different model -- the lunar orbit rendezvous model -- for getting
to the Moon, and plans for building a space station were put on the back burner.
As a result, although the United States was the first nation to send a human
being to the Moon, the Soviet Union ended up being the first nation to have an
inhabited space station in orbit.
A diagram of a Soyuz capsule docking with
the first Soviet space station, Salyut 1. |
The first Soviet space station, Salyut 1, was
launched, unoccupied, on April 19, 1971. The Salyut program sent a series of
short-term stations to orbit, some designed for civilian purposes, and some for
military purposes. Consisting of only a single, cylindrical module, the first
generation of Salyut space stations had only one docking port, so they could not
be resupplied or refueled while a crew was onboard. Soviet cosmonaut crews used
a Soyuz spacecraft to travel to and from the space station; each crew had three
members. Unfortunately, the early Salyut program met with a string of failures.
The first crew sent to Salyut 1 was unable to enter the station due to
difficulties with the docking mechanism, and they were forced to return home.
The second crew was successful in entering the station and lived aboard it for
22 days -- an extraordinary length of time -- but all three crewmembers were
killed upon their return to Earth when their Soyuz capsule depressurized during
descent. The next three Salyut stations that the Soviets attempted to place in
orbit either failed to reach orbit or broke up in orbit before crews could be
sent to them. The program quickly recovered, however, and Salyut 3, 4,
and 5 supported a total of five crews from 1974 to 1977.
Skylab's
Day(s) in the Sun
In the meantime, NASA was working on its own space
station program. Despite a somewhat unsupportive political environment under the
administration of President Richard Nixon, NASA embarked on a plan that would
use some of the technologies developed under the Apollo program to launch an
unoccupied station called Skylab to orbit. Skylab
was designed to be a precursor to a long-term space station, and one of its
purposes was to prove that humans could live and work in space for extended
periods of time. The station, launched on May 14, 1973, got off to a rocky
start; during launch, its meteorite shield/sunshade was torn loose and one of
the solar arrays (mechanisms by which the station collected power from the Sun)
was destroyed. The subsequent launch of Skylab's
first crew, which was supposed to have been immediate, was delayed for 10 days
while NASA teams worked to figure out how to fix the crippled station.
A solution was found, and the Skylab-2
crew (the Skylab-1
designation was used for the launch of the station itself) was sent to
rendezvous with the station. The first task of their 28-day stay aboard the
station was to create a "parasol" out of foil to replace the damaged sunshade.
The makeshift shade worked, lowering the temperature inside the station from a
sweltering 126 degrees Fahrenheit to 75 degrees. The crew also performed
spacewalks to repair the damaged solar array, supplying the station with power.
For the rest of their stay, the astronauts conducted experiments aboard the
station, with an emphasis on medical experiments designed to assess the effects
of long-duration microgravity on the human body.
The Skylab station provided NASA
with its first platform for conducting long-duration experiments in
microgravity. |
Over the course of its lifetime, Skylab
played host to two more crews of three astronauts each. The Skylab-3 crew
lived onboard the station for 59 days, doubling the previous endurance record in
space.
Skylab-4 crewmembers set another impressive record with a stay of 84 days
(November 16, 1973-February 8, 1974) -- an American record that stood until
astronaut Norm Thagard broke it with a 115-day stay aboard the Russian space
station, Mir, in 1995. After the last crew left
Skylab, the station remained in space until its orbit deteriorated,
causing it to fall harmlessly to Earth in 1979.
Advances in Soviet Stations
The Soviets continued to refine the Salyut program
in the late 1970s, and a second generation of Salyut space stations was begun in
1977. With the launch of Salyut 6, the Soviet program progressed from
short-duration stays in space to long-duration stays -- the first crew beat the
American space endurance record, set on Skylab in 1974, with a stay of 96
days. The new type of station had two docking ports, one on each end of the
cylindrical module, which meant that crews could remain at the station for a
long period of time, with fuel and new supplies arriving at the second docking
port via Progress ships. The second port also allowed Salyut crews to receive
visitors aboard the station; cosmonaut researchers would arrive at the station
to conduct research for a short period of time and then return to Earth, often
trading in their Soyuz capsule for the one already docked at the station (the
Soyuz ships had a limited lifetime in orbit). Salyut 6 played host to six
long-duration cosmonaut crews, with the longest time in orbit being 185 days. In
1982, Salyut 7 (almost identical to Salyut 6) was placed in orbit;
from 1982 to 1986, the station hosted six more long-duration crews, one of which
was in orbit for 237 days. Salyut 7 was abandoned in 1986, and it
re-entered Earth's atmosphere in 1991.
Fulfilling Another Presidential
Mandate
In 1984, the United States began with its plans for
what has ultimately become the International Space Station. As part of his State
of the Union address that year, President Ronald Reagan directed NASA to develop
plans for a permanently manned space station "within a decade." Stated Reagan,
"A space station will permit quantum leaps in our research in science,
communications, in metals, and in lifesaving medicines which could be
manufactured only in space." The mandate was reminiscent of Kennedy's call for
putting a man on the Moon, and NASA immediately began to put their plans in
motion. At that time, the space shuttle program had been in place for over three
years, and the rewards of conducting experimental research in the microgravity
environment of orbit were becoming more and more clear. No longer was a space
station seen only as a jumping-off point for further human exploration of space;
instead, a primary benefit of a space station was identified as the ability to
provide a permanent laboratory in which researchers could conduct long-term
microgravity experiments.
In his address, Reagan also called for the
station, which was subsequently named Space Station Freedom, to be an
international effort: "We want our friends to help us meet these challenges and
share in their benefits. NASA will invite other countries to participate so we
can strengthen peace, build prosperity, and expand freedom for all who share our
goals." By forging relationships with nations that had already established space
programs, the space station program would be strengthened and given more
legitimacy. Thirteen countries (Japan, Canada, and those countries that made up
the European Space Agency [ESA]) originally signed agreements in the spring of
1985 to partner in the endeavor, which would be of epic proportions. The station
was to consist of multiple modules, and each partner took on responsibility for
different components of the station.
Freedom's design was complex and
ambitious. Attempting to scale back the project, NASA redesigned the station
several times, trying to reduce costs, stick to a reasonable schedule, and still
satisfy the demands placed on the station by its diverse supporters. This task
proved next to impossible, and many of the station's previous supporters felt
that the compromises being made regarding the station had adversely affected its
potential. Things came to a head in 1993, when President Bill Clinton, newly in
office, issued a directive to NASA instructing the agency to restructure the
space station program to reduce costs and maximize scientific use. NASA went
back to the drawing board. The outcome of NASA's re-evaluation of the program
was the development of three alternative designs for the space station of
varying cost and usefulness in the summer of 1993. The decision was made to
proceed with the "Alpha" design, which incorporated many of the features of
Space Station Freedom and which was moderately priced and useful to
scientists and researchers. The Space Station Alpha design has evolved
into what is now called the International Space Station. Around the same time,
NASA negotiatedwith Russia in an effort to bring them into the international
association of space station partners. The inclusion of Russia in space station
planning was seen as beneficial both to Russia and to the international
coalition, especially since Russia had a great deal of experience in assembling
and maintaining a long-duration modular space station in Earth orbit.
The Russian space station, Mir
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Space Station Mir had been launched and
maintained by the Soviet Union, and subsequently by Russia, since 1986. The
design of Mir
had advanced beyond the days of Salyut; the station was constructed of several
modules that were each launched separately and then assembled while in orbit.
This multimodular construction was similar to what was planned for Space Station
Alpha.
At the time of the U.S.-Russian agreement
involving Russia in the construction of the ISS, Mir had been in orbit
for seven years and had been continuously occupied for four years. The Soviets
(and subsequently, the Russians) had made great strides in the areas of
engineering docking mechanisms and developing resupply and refueling techniques,
and their expertise was seen as a benefit to the ISS program. After Russia
became an ISS partner, NASA embarked on several jointly funded research projects
with Russia aboard Mir
in preparation for conducting research on the ISS. In addition to these
projects, some of which are still under way, seven U.S. astronauts have spent a
total of more than 22 months living and working aboard Mir
to date, including Shannon Lucid, who holds the American record for the longest
time in space -- 188 days. Of course, this record comes nowhere near Russian
cosmonaut Valeri Poyakov's record of more than 438 days in space. The NASA-Mir
program has been referred to as Phase I of the ISS program, and the lessons
learned from the program are numerous.
Realizing Our Common Dream
NASA and its partners currently stand on the brink
of finally making the dream of an international station a concrete reality. The
coalition of international partners has expanded to number 16 countries in all:
Belgium, Brazil, Canada, Denmark, France, Germany, Italy, Japan, the
Netherlands, Norway, Russia, Spain, Sweden, Switzerland, the United Kingdom, and
the United States. In January 1998, all of the space station partners, except
Brazil, signed new intergovernmental agreements establishing the framework for
the assembly of the ISS over the next five years. The launch of the first module
this year will begin the assembly process of piecing together more than 100
space station components. When completed, the ISS will be a platform for
research and international cooperation well into the next century. The journey
from the imaginations of science fiction writers to the physical reality of an
international space station has been a long one -- but in many ways, the journey
is just beginning.
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