hink of an astronaut and chances are you will
visualise him complete with a bulky spacesuit and a tinted-glass
visor. If the apparel has come to be treated as an integral part of
his macho persona, it is because space journey is just not possible a
space suit.What appears to be an unwieldy quilted dress from outside
is actually a marvel of cutting-edge technology. How sophisticated and
complex this suit is can be gauged from the fact that each costs
upwards of $ 12 million (Rs 60 crore). That is why it is no longer
custom-fitted as per the measurements of the person selected to go on
a space mission. Instead, it is modular in design, with many
interchangeable parts. The upper torso, lower torso, arms and gloves
are manufactured in different sizes and can be assembled to fit men
and women astronauts. This way, the suit can be reused, for nearly
eight years, of course after elaborate cleaning and drying after every
flight use.
If the price tag staggers you, just think of the
environment in which an astronaut has to work. There is no atmospheric
pressure and no oxygen to sustain life out there. The spacesuit is his
only shield against the hostile elements that he encounters. A person
not hiding inside this cocoon in space will have his bodily fluids
"boiling" and then freezing within seconds. That, in other
words, means an almost instantaneous death.
Without the earth’s
atmosphere to filter the sunlight, the side of the suit facing the sun
can simmer at a temperature of 120 degrees C while the other side
exposed to the darkness of deep space could be at minus 100 degrees.
That is far worse than half of you being in the Sahara desert at noon
in the summer and the other half being on Mt Everest at midnight in
winter — simultaneously.
That is talking only about the
temperature extreme. There are several other equally severe extremes
that an astronaut has to encounter. He has to carry his own earth-like
environment with him and it is the spacesuit that provides it by
supplying oxygen and maintaining a pressure around the body to keep
body fluids in liquid state.
Essentially, a spacesuit is an inflated
balloon that is restricted by some rubberised fabric, in this case
Neoprene-coated fibre. The restriction placed on the outside supplies
air pressure on the inside. The standard environment in the suit is
just 0.29 atmosphere of pure oxygen. The pressure is deliberately
reduced for two reasons. One, it considerably improves freedom of
movement for the wearer. And two, it decreases the overall stress on
the suit.
Hundred per cent oxygen (instead of the normal air
comprising 78 per cent nitrogen, 21 per cent oxygen and 1 per cent
other gases) is provided either through a life support system in his
backpack or through umbilical cords running from the spacecraft to the
spacesuit. This life-support system re-circulates the user’s
exhalations, removing carbon dioxide with the help of lithium
hydroxide canisters and adding oxygen as needed.
But due to the
decreased pressure, an astronaut has to spend several hours breathing
pure oxygen before leaving the space shuttle to perform tasks in
space. This procedure is mandatory to remove nitrogen dissolved in
body fluids and thereby to prevent its release as gas bubbles when
pressure is reduced. If this precaution is not taken, the astronauts
can develop, like deep-sea divers, severe cramps called "the
bends".
Suitable communication arrangements are also
incorporated into the space suit. The "snoopy cap", or the
communications carrier assembly, has headphones and microphones for
two-way communications and caution-and-warning notes, plus a
biomedical instrumentation subsystem to monitor the astronaut’s
vital signs such as respiration rate, heart rate, temperature
etc.
Things have changed a lot from the early days of space
exploration when an astronaut had to wear a spacesuit, like a jet
pilot, throughout the duration of his journey.
Astronauts of the
space shuttle era have an elaborate wardrobe and what they wear
depends on the job they are doing. During ascent and entry, each
crewmember wears special equipment consisting of a partial pressure
suit, a parachute harness assembly and a parachute pack. During orbit,
they work in shirtsleeve comfort inside the shuttle. But to work in
the open cargo bay of the shuttle or in space, they wear the
extravehicular mobility unit (EMU) spacesuit, which is more durable
and flexible than previous spacesuits. It comprises the spacesuit
assembly, the primary life support system (PLSS), the display and
control module and several other crew items designed for spacewalks
and emergency life support. In short, EMU is a mini-spaceship in
itself.
The suit protects him from lethal solar ultraviolet and
infrared radiations and also the constant bombardment of
micrometeoroids. That is why it comprises 13 layers of material,
including an inner cooling garment (two layers), pressure garment two
layers), thermal micrometeoroid garment (eight layers) and outer white
cover to reflect sunlight (one layer). All these layers are cemented
together.
Despite all these preparations, the spacesuit does not
offer much protection from a solar flare. That is why spacewalks are
planned during periods of low solar activity.
Being padded so
heavily, the astronaut’s body generates a lot of heat during active
work periods. It has to be properly dissipated if he has to function
with some degree of comfort. For that the spacesuit has a liquid
cooling and ventilation garment, a one-piece mesh suit made of
spandex, which has water-cooling tubes running through it. Cool water
circulating through this network of spaghetti-like tubes transfers
metabolic heat from the body to the backpack and from there to
space.
Above all, the astronaut has to be able to move over and bend
adequately. That is easier said that done in such a clumsy apparel.
Just try holding something while wearing a heavily padded pair of
gloves and you will get a fair idea of the rigors of adjusting
sensitive instruments up there. The spacesuits are equipped with
special joints or tapers in the fabric to help the wearers bend their
hands, arms, legs, knees and ankles.
A spacewalk can last as many as
seven hours. Since it is not feasible for an astronaut to be brought
back into the space station whenever he has to relieve himself, the
spacesuit also has to double up as a portable toilet. He wears special
types of diapers to collect urine and faeces which are changed only
when he completes his mission.
Similarly, the spacesuit has an
in-suit drinking bag, which is a plastic pouch containing 1.9 litres
of water, and has a small tube, a straw, that is positioned next to
the astronaut’s mouth. There is also a slot in the helmet for a
rice-paper covered fruit and cereal bar that the astronaut can eat if
he or she gets hungry during the spacewalk.
The bar is designed in
such a way that the astronaut can take a bite and pull the remainder
up. The whole bar must be eaten at once lest crumbs start floating
within the helmet. It is another matter that most astronauts prefer to
eat prior to the spacewalk and not use this bar.
The shoes of an
astronaut are also equally complex. The boot inner layers are made
from Teflon-coated glass-fibre cloth followed by 25 alternating layers
of Kapton film and glass-fibre cloth to form an efficient, lightweight
thermal insulation.
If astronauts have to deploy, service, repair or
retrieve satellite payloads, they latch on a manned manoeuvering unit
(MMU), a one-man, nitrogen-propelled backpack, to their EMU. The
maximum total weight of the largest size spacesuit assembly, including
the liquid cooling and ventilation garment, urine collection device,
helmet and visor assembly, communications carrier assembly, in-suit
drink bag and biomedical instrumentation subsystem, is about 140 kg.
Thank God it does not have to be worn on earth. In space it weighs
only a fraction.
There is a complicated drill involved in wearing
the suit. This includes a detailed check list which has more than 25
items.
The EMUs are built under the supervision of prime contractor
Hamilton Sundstrand with contributions from 52 other companies. Cut
and sewn to a tolerance of one-sixteenth of an inch, one needle hole
in the wrong place means back to the start of any one of the
layers.
Many changes have come about in spacesuits over the decades.
The initial suits were adopted from the pressurized flight suits worn
by high altitude jet pilots. The first space suit was designed and
developed during 1959 for Project Mercury and was a compromise between
flexibility and adaptability. It had the design of the early
pressurised flight suits, but had added layers of aluminised Mylar
over the neoprene rubber. Living and moving in this aluminum-coated
nylon and rubber garment was like trying to adapt to life within a car
tyre.
Improvements have been made since then constantly. For future
space missions to Mars, NASA is developing "hard suits" that
are more flexible, more durable, lighter-weight and easier to don than
the current spacesuits.
