Astronauts and cosmonauts all agree that floating in space indeed is great fun, after you have adjusted to the new environment of microgravity. And by the way, scientists do not like to call it zero- gravity because unless you are exactly at the center-of-gravity of the spacecraft going around Earth in "free fall", there are always unavoidable forces, from tiny accelerations and tidal effects acting on you even if they are extremely small, on the order of one millionth of Earth's gravity. That's why we use the expression microgravity.

While micro-g generally is fun, specific feelings are different for different people. About 30-40 percent of all individuals experience "space adaptation syndrome" (which is a kind of motion sickness) upon first entering a low-gravity or microgravity condition, for 2-3 days. Others have no problems. Over a period of a week or so the fluids in the body, now without weight of their own, try to reach an equal pressure throughout the body, so the crews find that fluids, which heretofore tended downward toward the legs, collect in the upper torso, among else in their sinuses, resulting in stuffy feelings and difficulty in tasting food as well as on Earth. It's also interesting that the body actually grows slightly in length (by 1-2 inches) as fluid collects in the spinal discs, and the spine expands without the weight it normally has to carry. In microgravity, when all muscles are relaxed, the body assumes a slightly hunched over posture with legs slightly rising forward and arms floating in front, much like being under water. There is no perceived "up" or "down", so the spacecraft interior should preferably be designed to suggest a ceiling and floor to provide orientation. The amazing thing is, you can tell your brain which way is "up", and it immediately switches to that illusion, like "click!". So, what you "think of" becomes all-dominant for your orientation, translation, locomotion, etc. in microgravity, instead of the feelings you were used to rely upon on the ground. It is very easy, though, to move about in space, and crewmembers quickly adapt to moving around and positioning themselves at workstations where they fasten themselves, mostly by means of foot restraints. Locomotion becomes more difficult in a space suit, but only because the suit is bulky, much like wearing a balloon, and vision and feel are restricted.

Nominal duration of excursions in a pressure suit usually runs between 5 and 7 hours. It depends, of course, on the consumables available to the suit, such as oxygen, battery power, cooling water, etc. (spacesuits really being rudimentary spacecraft), but working in a suit is also quite strenuous, and so its use is also limited by the comfort level and endurance of its wearer.

Fortunately, NASA in all of its 120 crewed space missions has never had to deal with a medical emergency more serious than, say, Fred Haise's urinary infection on Apollo 13 or a few flu episodes in the early days. Spacecraft always carry a richly equipped medical kit for immediate needs. As long as such an emergency occurs in Earth orbit, the crew member is returned to Earth as quickly as possible, either on the Shuttle or, on a standby Soyuz capsule on the International Space Station. If a bone is broken, there is always equipment on board to set and immobilize it prior to reentry. When humans start out into deep space, e.g., on expeditions to Mars, their ships will carry elaborate health maintenance stations and one or more of the crewmembers will be medically trained because a quick return to Earth would then not be possible. In all likelihood, there will be a full-fledged doctor on board.

Whatever they individually prefer. They do take their own preference kits along on their missions. Some read or write e-mails home on their laptops, others listen to music or play games. Again others just chat with folks on the ground via ham radio or with other crewmembers. However, for nearly all of them, at least in the early stages of their mission, the most preferred pastime is hanging around the windows, looking out into space and watching Earth roll by underneath.

Any adult man or woman in excellent physical condition who meets the basic qualifications can be selected to enter astronaut training.

For mission specialists and pilot astronauts, the minimum requirements include a bachelor's degree in engineering, science or mathematics from an accredited institution. Three years of related experience must follow the degree, and an advanced degree is desirable. Pilot astronauts must have at least 1,000 hours of experience in jet aircraft, and they need better vision than mission specialists. Competition is extremely keen, with an average of over 4,000 applicants for about 20 openings every 2 years.

Astronaut recruiting occurs periodically. For more information, write to:

Astronaut Selection Office
NASA Johnson Space Center
Houston, TX 77058

Let me try to keep this simple (it's not easy because you really need to go to college to properly understand this complex area).

Basically, you start from knowing that space is three-dimensional, so you make yourself a coordinate system with three axes at right angles to each other. In astronomy, astronomers map space with coordinates like azimuth (direction from North), elevation (angle above the horizon), right ascension (angle from a agreed-upon point in the sky, most often the vernal equinox in the direction of the Ram), distance, and time (measured from another agreed-upon reference point).

To navigate and maneuver in space, our three coordinates are usually given the designation X, Y and Z. Then, everyone involved agrees on a "reference system", i.e., a location and orientation of the coordinate system from which all measurements and determinations are universally made. Generally, this system has its origin at the center of the Earth, with the Z-axis up and the X- and Y-axes in the equatorial plane. Sometimes it is assumed to rotate with Earth, and sometimes it's fixed in space, depending on what one wants to use it for. This reference system is also stored in your onboard computer.

The spacecraft (as any larger airplane today) also has an internal guidance system which senses the motions of the vehicle around its own three axes and continually calculates the changing position of the craft in relation to the agreed-upon reference system. Of course, by looking at the coordinates of the intended target it can also calculate where it has to go. And presto: that way you know where you are and where you are going, and if it looks like you're off your desired path, you can also calculate what changes to make with your engines to correct your flight.

Basic utensils like knives, forks and spoons are the same as on the ground. The crew can eat most any food or beverage that can be restrained in a container. Otherwise, it may float off during the attempt to consume it. Foods such as peas, beans, etc. usually are prepared in a sauce so that they will stick to the eating utensil. However, some things are not currently available to the crew. They have stated that for long term missions they long for fresh vegetables and freshly-perked coffee. Plants are being grown experimentally aboard the Shuttle and the space station. By the way, since crewmembers' sinuses fill with fluid as the body fluids reach equistatic pressure, the senses of taste and smell are reduced. Hence, astronauts on-orbit always prefer food to be more highly seasoned in order to taste acceptable.

Space has LOTS of gravity! But I know you didn't mean it that way. To explain: Gravity is rooted in matter which has "mass". Mass acts on (affects) space in very specific ways (Einstein would say, mass "curves" space), and this action is transmitted by a force which Isaac Newton discovered and which we call gravitation. At least, this is what the theory of gravitation says, and from all our observations it seems to hold true. If it wouldn't, our Apollo missions would not have reached the moon on their trajectories (and we would have been very surprised, I'm sure).

On Earth, the gravity generated by its mass shows itself as a "pressure" on things physically connected to the ground, and we call that "weight". When not connected, as for example in an orbit around Earth, there is no direct contact, thus no weight. But a spacecraft still has mass, and its mass generates its own gravity field (which is pretty close to nothing for small spacecraft, of course). Also, the gravitation going out from a body of mass falls off with the square root of distance from the mass's center. This means that space, with all its heavy mass centers like the Sun, Earth and the other planets, is really chock full of gravitation. Newton also found that a body in vacuum without any accelerations would travel endlessly in a straight line. But a body can be "weightless" even close to a large body of mass pulling it and keeping it in an orbit, as demonstrated by a space station: thus, what makes an orbiting space station "weightless" is NOT the absence of gravity (because it's still there) but just the condition of falling freely, without connection or resistance, around the mass: it is the absence of the EFFECT of gravity. As soon as there is resistance, such as atmospheric drag forces, engine firings, centrifugal acceleration due to rotation, etc., weightlessness is gone.

On the launch pad, astronauts are on their backs, feet up, because of the orientation of their cabin and seats (which, by the way, limits the time they are allowed by the medics to spend waiting prior to a delayed liftoff). After the hatch is closed and all final checks are behind, crewmembers prepare themselves mentally for the launch, once again going in their minds through all the procedures which they trained for during the preceding months and years. For example, are all lockers above them really firmly latched? And what does the cue card in front of your nose have to say about emergency situations? Finally, the countdown reaches T minus 6 seconds, and the three liquid rocket engines of the Orbiter are ignited. The Shuttle sways forward and backwards once, by about 5 feet, and you can feel it clearly, while the Orbiter is shaking and vibrating strongly. But the crew hears nothing of the thunderous noise generated by the engines.

Then the count reaches zero, and the voice in your helmet radio calls "SRB Ignition - Lift-Off!" The two strapped-on solid rocket boosters ignite, and the Shuttle starts to move upward. You don't feel much acceleration at this time, no more than in an airplane during takeoff. The solid boosters do not burn smoothly at all; their thrusting feels rough and bumpy. The crew cabin shakes and rattles through and through like a car driving at top speed over cobblestones.

Once they are lit, those boosters cannot be shut down anymore before burnout. When that point is reached at two minutes after liftoff, their empty casings are separated, things become quiet and smooth, and every crewmember feels tremendous relief. The three liquid propellant main engines continue their burn, quietly humming along, and as propellants are depleted and the Shuttle consequently becomes lighter, the acceleration on the crew keeps rising (because, according to Isaac Newton, acceleration equals thrust divided by mass).

Finally, at 7-1/2 minutes into the flight, when the huge external tank is 90 percent empty, the Shuttle, which had weighed 2000 tons at launch, now weighs less than 200 tons, and the force pressing you down has grown to 3g - three times Earth gravity. The engines throttle down to stay at 3g's. At that acceleration, breathing has become hard enough for you to choose consciously between going without breathing (and suffocating) or forcing yourself to inhale and each time lift your chest with the heavy suit on top. I think everyone knows which option the astronauts prefer.

And finally, there's "MECO" (main engines cut-off). Within seconds, the thrust from the engines drops off to zero; just as suddenly the pressure disappears from your chest, and you become weightless. You are in space!

There are many reasons behind this nation's decision to build a permanent platform in Earth orbit, and to enter into partnerships with other countries in order to avail ourselves of the benefits of international cooperation and collaboration.

The Space Station provides access to a totally new way of going about improving life on Earth. As everybody should know by now, in Earth orbit, space offers a number of highly useful attributes which you do not find on Earth, such as: weightlessness, high vacuum, wide temperature extremes for heating and cooling, unfiltered solar energy, and unique vantage points for overviewing Earth and its environment and also for looking into the Universe unobstructed by the atmosphere with its haziness due to air molecules, clouds and pollutants. These features enable innovative research in many scientific areas of importance to human, animal and plant life on Earth. They also lead to new medical breakthroughs, to technological developments, new industrial products, new medicines and pharmaceuticals, and many other new challenges which will help us retain our prominent place among the world's nations. Of course, they will keep our economy, our industries and their trade and commerce highly competitive, and they generate jobs, knowledge and wealth.

The Space Station, by its very permanence, allows these many uses of space, which need more time than the 14 days a Shuttle mission could provide at most, to be conducted over extended periods of time. The space station also provides more electric power, more volume, a greater range of instruments and other equipment, more varied astronaut skills, and other advantages, just like a large research facility, product development center, and technology demonstration site on the ground. In the longer run, too, the Space Station is necessary as a "spaceport" for more advanced space missions by humans out into deep space, a staging point, springboard and launch platform moving at a speed (23,000 feet per second) which is already close to what it takes to embark on interplanetary flights (37,000 ft/sec).

A spacesuit is really a small spacecraft, with all the features that are required to keep its occupant healthy and productive over many hours of extravehicular activity (EVA). Since there is no atmospheric pressure in space and no oxygen to sustain life, human beings must take their environment with them. And just like inside the Shuttle cabin, the atmosphere inside the suit can be controlled and regulated.

Thus, spacesuits must primarily supply oxygen (O₂) for breathing while maintaining a pressure around the body to keep body fluids in the liquid state; in vacuum or at very low air pressures body fluids would boil just like warm water on top of a high mountain. Spacesuits for the Space Shuttle era are pressurized at 4.3 pounds per square inch (psi), which is only approximately a third of normal atmospheric pressure (14.7 psi, equal to one atmosphere). But because the gas in the suit is 100 percent oxygen instead of containing only 20 percent O₂ as we are used to in the Earth's atmosphere, the suited person actually has more oxygen to breathe than is available at an altitude of 10,000 feet or even at sea level without the spacesuit. Before leaving the space shuttle to perform tasks in space, an astronaut has to spend several hours breathing pure oxygen before proceeding into space. This procedure is necessary to remove nitrogen dissolved in body fluids and thereby to prevent its release as gas bubbles when pressure is reduced, a condition commonly called decompression sickness or "the bends." On the other hand, if pure O₂ is breathed at normal atmospheric pressure for an extended time, it becomes toxic for the human body. Since the pre-breathing requirement, with its lengthy, unproductive and boring waiting periods for the crewmembers, is a real nuisance, we are lowering it for the Space Station era by going to spacesuits designed for an internal pressure of 8.3 psi which require shorter prebreathing times.

Spacesuits must also shield the astronaut from deadly hazards. Besides providing protection from bombardment by micrometeoroids, the suit insulates the wearer from the temperature extremes of space. Without the Earth's atmosphere to filter the sunlight, the side of the suit facing the Sun may be heated to a temperature as high as 250 degrees Fahrenheit; the other side, exposed to darkness of deep space, may get as cold as -250 degrees Fahrenheit.

Some of the major features of a spacesuit, besides its multi-layered structure including boots and gloves, are: the primary life support system (PLSS) worn on the back, a display and control module on the chest, and a number of crew items designed for spacewalks and emergency life support, particularly a backup oxygen supply. These elements are combined in an aggregate called an EMU (extravehicular mobility unit) which accommodates a variety of interchangeable subsystems that interconnect easily and securely in single-handed operation for either normal or emergency use. They also include, typically: a urine-collection device that receives and stores urine for transfer later to the Shuttle or Space Station waste management system; the liquid cooling and ventilation garment which is a one-piece mesh suit made of spandex, zippered for front entry, and weighing about 6.5 pounds dry. This undergarment, which resembles long johns, has water-cooling tubes running through it to keep the wearer comfortable during active work periods because the suit's pure oxygen atmosphere cannot provide sufficient cooling like normal air could. There is also an in-suit drink bag containing 21 ounces of potable water, the "Snoopy Cap" or communications carrier assembly, with headphones and microphones for two-way communications and caution-and-warning tones, and a biomedical instrumentation subsystem.

For moving around in space, a suited astronaut straps into a manned maneuvering unit (MMU) weighing about 310 pounds on the ground, a one-person, nitrogen-jet-propelled backpack that latches to the spacesuit's PLSS. Using rotational and translational hand controllers, the crew member can fly with precision in or around the Orbiter cargo bay or to free-flying payloads or structures in the vicinity of the Shuttle or Station, and can reach many otherwise inaccessible external areas. Astronauts wearing MMU's, which some folks have called "space bikes", have deployed, serviced, repaired, and retrieved satellite payloads with great success.

Our current spacesuits/EMUs are a sandwich of 12 layers, each one for a specialized purpose. From the inside out, the first two layers are the liquid cooled undergarment, made from Spandex fabric with plastic tubing sewn in. Next comes the pressure bladder layer, of urethane-coated nylon, surrounded by a fabric layer of pressure-restraining Dacron. The next seven layers are for thermal and micrometeoid protection, consisting of aluminized Mylar, laminated with Dacron scrim. This seven-layer garment is topped by an outer single layer of fabric combining Gortex, Kevlar and Nomex (Kevlar being the material of bullet-proof vests).

The first US guy to fly into orbit twice was Gordon Cooper. First flight: Mercury/Atlas MA 9 on May 15-16, 1963, for 1 day, 10 hours, 20 minutes. Second flight: on Gemini/Titan 5, June 3-7, 1965, for 7 days, 22 hours, 55 min., with Pete Conrad.

However, Gus Grissom was the first US astronaut to fly twice on a rocket into space. But his first flight, on a Mercury/Redstone (MR4) "Liberty Bell" was only suborbital, taking him on a parabola to 190 km altitude on a 15 minute trip, with about 5 minutes of weightlessness on July 21, 1961. He then flew a second time, this time into orbit, on Gemini/Titan 3, on March 23, 1965, for three orbits, with John Young. Incidentally, this flight carried the first computer into space: 74 lbs of miniaturized equipment capable of 7000 calculations a second. With it Grissom was able to compute the thrust needed for orbit changes. From that time, astronauts had gained a genuine ability to "fly" in space, instead of being carried helplessly around the world on a fixed orbital path.

No, you cannot. The crew cannot hear the sonic booms (there are two of them) when the Orbiter passes through Mach 1 and becomes subsonic over Cape Canaveral. The booms are the interpretation of the human ear on the ground when hit by the expanding shock waves at the nose and at the tail of the Shuttle Orbiter. These shocks happen when pressure of the air stream around the Shuttle changes too abruptly to be able to dissipate (i.e. spread out) in accordance with the (slower) natural ability of the air to handle it - its local "speed of sound". These shocks would appear as a cone each, with the object generating it at its point, and spreading out behind it while being dragged along by it. There's a shock generated by the nose and another by the tailing edge of the tail fin. When the bottom portions of these conically spreading wakes hit the ground, the ear drum perceives the sudden pressure change as a boom (it's more like a crack, really - thus: CRACK -- CRACK always announces the Shuttle a few minutes before it lands). If you measure the pressure jumps, their signature look like the letter "N", and that's why aerodynamicists call the phenomenon the "N wave".

Coming back to the question: Since the crew is inside the cabin and not subjected to the expanding shock wave, it cannot hear the booms (other than maybe by having the sound relayed up to it via microphone and radio - which we aren't doing, of course).