My Science School

So far space probes have visited every planet in the Solar System except Pluto. Venus was the first planet to be investigated as Mariner 2 flew by in 1962. Mariner 10 orbited Mercury in 1975. Mars is the most visited planet in the Solar System, with over five probes landing on its surface. The Pioneer and Voyager probes, launched between 1979 and 1989, investigated the outer planets Jupiter, Saturn, Uranus and Neptune. The Pluto-Kuiper Express aims to visit Pluto between 2006 and 2008.

NASA launched the Voyager spacecraft in 1977 to take advantage of a rare alignment among the outer four planets (Jupiter, Saturn, Uranus and Neptune) that would not take place for another 175 years. A spacecraft visiting each planet could use a gravitational assist to fly on to the next one, saving on fuel. The original plan called for launching two spacecraft pairs — one pair to visit Jupiter, Saturn and Pluto, and the other to look at Jupiter, Uranus and Neptune. The plan was cut back due to budgetary reasons, resulting in two spacecraft: Voyager 1 and Voyager 2.

The primary five-year mission of the Voyagers included the close-up exploration of Jupiter and Saturn, Saturn's rings and the larger moons of the two planets. The mission was extended after a succession of discoveries. After passing by Saturn in 1980, Voyager 1 made a sharp turn out of the plane of the solar system. Voyager 2's trajectory, however, was planned to take it past Uranus and Neptune. While the initial budget for Voyager 2 didn't guarantee it would last long enough to transmit pictures from those two planets, it thrived and made successful flybys of Uranus in 1986 and Neptune in 1989.

Between them, the two spacecraft have explored all the giant outer planets of our solar system — Jupiter, Saturn, Uranus and Neptune — as well as 49 moons, and the systems of rings and magnetic fields those planets possess. 

The current mission, the Voyager Interstellar Mission, was planned to explore the outermost edge of our solar system and eventually leave our sun's sphere of influence to enter interstellar space — the space between the stars. Since passing the boundary of interstellar space in 2012, Voyager 1 is examining the intensity of cosmic radiation, and also looking at how the sun's charged particles are interacting with particles from other stars, according to Voyager project scientist Ed Stone. Voyager 2 is still traveling within the solar system, but is expected to breach interstellar space in the next few years.

The first space probe to complete its mission was Luna 2. It was launched by the USSR in 1959 and successfully landed on its destination — the Moon. Its predecessor, Luna 1, was launched towards the same target several months earlier but missed by 6000km (3730 miles).

Luna 1 (launched Jan. 2, 1959) was the first spacecraft to escape Earth’s gravity. It failed to impact the Moon as planned and became the first man-made object to go into orbit around the Sun. Luna 2 (launched Sept. 12, 1959) was the first spacecraft to strike the Moon, and Luna 3 (Oct. 4, 1959) made the first circumnavigation of the Moon and returned the first photographs of its far side. Luna 9 (Jan. 31, 1966) made the first successful lunar soft landing. Luna 16 (Sept. 12, 1970) was the first unmanned spacecraft to carry lunar soil samples back to Earth. Luna 17 (Nov. 10, 1970) soft-landed a robot vehicle, Lunokhod 1, for exploration. It also contained television equipment, by means of which it transmitted live pictures of several kilometres of the Moon’s surface. Luna 22 (May 29, 1974) orbited the Moon 2,842 times while conducting space research in its vicinity. Luna 24 (Aug. 9, 1976) returned with lunar soil samples taken from a depth of seven feet (about two metres) below the surface.

Luna 2 was the first object of human origin to make contact with another celestial body. The spacecraft scattered spherical emblems of the Soviet Union on the lunar surface. The spacecraft's sensors found no evidence of a lunar magnetic field or radiation belt.

After an aborted launch on Sept. 9, the Ye-1A probe, also known at the time as the Second Soviet Cosmic Rocket, successfully lifted off on Sept. 12 (Sept. 13 Moscow time). When the spacecraft reached about 97,000 miles (about 156,000 kilometers) from Earth, it released one kilogram of sodium gas on Sept. 12 in a cloud that expanded to about 400 miles (650 kilometers) in diameter and was clearly visible from the ground.

Three days later, Luna 2 achieved escape velocity (the speed and direction required to travel beyond Earth’s gravity). This sixth Soviet attempt at lunar impact was much more accurate than its predecessors, and the spacecraft reached the surface of the Moon at 23:02:23 UT on Sept. 14, 1959, becoming the first object of human origin to make contact with another celestial body.

The probe collided with the moon at approximately 30 degrees north latitude and 0 degrees longitude on the slope of the Autolycus crater, east of Mare Serenitatis.

Luna 2 (as it was renamed in 1963) deposited Soviet emblems on the lunar surface carried in 9 x 15-centimeter metallic spheres. The spacecraft’s magnetometer measured no significant lunar magnetic field as close as 55 kilometers to the lunar surface. The radiation detectors also found no hint of a radiation belt.

Space probes are highly advanced robotic craft, often the size of a large car, launched into space to investigate celestial objects. They use radio transmitters to communicate with mission specialists on Earth. All probes have highly sensitive electronic equipment on board.

The accurate navigation of space probes depends on four factors: First is the measurement system for determining the position and speed of a probe. Second is the location from which the measurements are taken. Third is an accurate model of the solar system, and fourth, models of the motion of a probe.

For all U.S. interplanetary probes, the antennas of the Deep Space Network (DSN) act as the measurement system. These antennas transmit radio signals to a probe, which receives these signals and, with a slight frequency shift, returns them to the ground station. By computing the difference between the transmitted and received signals, a probe's distance and speed along the line from the antenna can be determined with great accuracy, thanks to the high frequency of the signals and a very accurate atomic clock by which to measure the small frequency changes. By combining these elements, navigators can measure a probe's instantaneous line-of-sight velocity and range to an accuracy of 0.05 millimeter-per-second and three meters respectively, relative to the antenna.

Many probes also carry cameras that are used to image the destination, whether it be a moon, planet or other body. During the final approach, these images are used when the distance becomes small. For example, the Cassini spacecraft's camera provides an angular measurement with an accuracy of three microradians (three kilometers) at a distance of one million kilometers. The images complement the radio data and provide a direct tie to the target.

Calculation of the trajectory of a space probe requires the use of an inertial coordinate system as well, wherein a grid is laid over the solar system and fixed relative to the star background. For interplanetary missions, an inertial coordinate system with an origin at the center of mass of the solar system is used. Because the measurements provide information on the position of a probe relative to the antenna, knowledge of the antenna's location relative to this inertial coordinate system is used to convert the measurements into elements in the system. Where the antenna is depends not only on its geographic location on Earth's surface, but on Earth's position relative to the solar system center of mass (known as the Earth ephemeris). Measurements of this ephemeris have an accuracy of about 0.5 kilometer and the location of the antenna is known to an accuracy of better than five centimeters.

Airlocks are vital for protecting the crew of a space-craft. In a submerged submarine, if there was no airlock, the vessel would instantly be flooded with water as soon as the hatch was opened. In the same way, a space station with no airlock would depressurize the instant the door was opened, killing anybody on board who was not wearing a spacesuit. This is because air always tries to remain at a level pressure. If the pressure inside a spacecraft is greater than the pressure outside, as soon as the hull is breached, air will rush out into outer space.

Airlocks, typified by the International Space Station’s (ISS) primary Quest Joint Airlock, are designed to permit safe passage of people and objects between a pressurised vessel and its surrounding environment. Further, they are designed to minimise pressure and air-level changes within the host craft.

The Quest airlock of the ISS is split into two main sections: an equipment chamber and crew lock chamber. The former connects to the ISS and supplies an auxiliary holding bay for any essential equipment, such as Extravehicular Mobility Units (EMUs – or spacesuits), as well as other key gear. It also supplies a staging area where astronauts can prepare for a spacewalk -namely get in and out of their spacesuits.

Connected to the equipment compartment is the crew lock, a smaller cylindrical chamber into which astronauts enter prior to any spacewalk. Once inside this section, the interior hatch between the equipment lock and the crew lock is shut. This provides a sealed environment for the suited astronaut and allows depressurisation to proceed. When the crew lock is fully depressurised, an external hatch becomes operational, providing an exit for the astronaut to enter space.

Importantly, before any spacewalk is attempted, astronauts must ‘camp out’ within the equipment chamber of the airlock in a reduced-nitrogen environment in order to purge nitrogen from their blood stream. This ensures that astronauts avoid decompression sickness in the low pressure experienced within the pure-oxygen atmosphere of the spacesuit. Nitrogen and oxygen are supplied and replenished via four externally mounted gas tanks, which ensures that the lock does not need to draw upon the host ISS’s own gas supplies.

Space probes are designed to do different jobs. Some fly by their target at a distance of several thousand kilometres, taking pictures of the planet's surface and surveying its atmosphere. Other probes are designed to enter a planet's orbit, which allows them to survey the planet in more detail. The probes that provide the most information about planets are called landers because they touch down on the planet's surface.

This is a list of space probes that have left Earth orbit (or were launched with that intention but failed), organized by their planned destination. It includes planetary probes, solar probes, and probes to asteroids and comets, but excludes lunar missions, which are listed separately at Lunar proves and Apollo mission. Flybys (such as gravity assists) that were incidental to the main purpose of the mission are also included. Flybys of Earth are listed separately at Earth flybys. Confirmed future probes are included, but missions that are still at the concept stage, or which never progressed beyond the concept stage, are not.

Space probes are made to conduct science experiments. They do not have people on them. Space probes have helped scientists get information about our solar system. Most probes are not designed to return to Earth. Some have landed on other planets! Others have flown past the planets and taken pictures of them for scientists to see. There are even some space probes that go into orbit around other planets and study them for a long time. The information they gather is used to help us understand the weather and other changes which happen on planets other than the Earth. This information is important in helping to plan other space missions such as ones to Mars and to Saturn.

During the summer of 2003, NASA launched twin robotic rovers named Spirit and Opportunity. The rovers were launched approximately 3 weeks apart, but they had the same destination. Spirit and Opportunity were headed to Mars. The rovers landed in January of 2004 on different parts of the planet. They were sent to Mars to look for evidence of water. Each rover carried scientific instruments to help scientists explore the planet from Earth. The Earth-bound scientists tell the rovers where to go and what to examine. As the rovers move across the surface, they examine soil and rocks. This information is sent back to Earth. The rovers were built to last approximately 90 days. Spirit went silent on March 22, 2010. Opportunity is still working as of November 1, 2015! And they have found lots of evidence that water was once all over the surface of Mars!

The Cassini probe to Saturn was launched on October 15, 1997. It is the biggest and most expensive probe to ever visit another planet. The Cassini spacecraft went into orbit around Saturn in July 2004. It has studied the planet, its ring system, and many of its moons for more than ten years!

The New Horizons spacecraft was launched in 2006, and flew past Pluto in the summer of 2015. It was the first spacecraft to visit that dwarf planet, and is now moving farther away from our Sun to explore more distant objects for the first time.

The first human being to leave the confines of a spacecraft and take a “walk” in space was the Soviet cosmonaut Alexei Leonov. He crawled through the airlock of Voskhod 2 in 1965 and was so overwhelmed by the view that he shouted out the first words he could think of: “The Earth is round!” During his twenty minutes in space, Leonov’s spacesuit expanded, due to the lack of pressure, and he was barely able to fit back in the airlock.

Selected alongside Yuri Gagarin among the first 20 Soviet Air Force pilots to train as cosmonauts in 1960, Leonov flew twice into space, logging a total of 7 days and 32 minutes off the planet.

Launched on Voskhod 2, the world's 17th human spaceflight, on March 18, 1965, Leonov made history as the first person to exit his spacecraft for an extravehicular activity (EVA).

"The Earth is round!" he exclaimed, as he caught his first view of the world. "Stars were to my left, right, above and below me. The light of the sun was very intense and I felt its warmth on the part of my face that was not protected by a filter," said Leonov in a 2015 interview with the Fédération Aeronautique Internationale (FAI) on the 50th anniversary of his spacewalk.

After several minutes outside, his spacesuit ballooned, making it very difficult for him to maneuver. His crewmate, Pavel Belayev, unable to do anything to assist, Leonov made the decision to release air from his suit in order to be able to re-enter his capsule. "I decided to drop the pressure inside the suit ... knowing all the while that I would reach the threshold of nitrogen boiling in my blood, but I had no choice," Leonov told the FAI, the world governing body that certifies aviation and space records.

Ultimately, Leonov made it safely back inside after 12 minutes and 9 seconds floating outside his spacecraft. He and Belyayev returned to Earth the next day on March 19, 1965, having shown it was possible for a human to survive working in the vacuum in space.

Because astronauts can be in their spacesuits for up to seven hours, they need water to avoid dehydration. Spacesuits are equipped with the In-suit Drink Bag (IDB), a plastic pouch connected to the inside of the suit’s torso. It can hold nearly 2 litres (32oz) of water that can be accessed via a straw. The helmet also has a slot for rice-paper-covered fruit and a cereal bar, should the astronaut get hungry.

There is a slot in the hard upper torso (HUT) portion of the EMU for a rice paper-covered fruit and cereal bar. The bar is designed so that the astronaut can take a bite and pull the remainder up. The entire bar must be eaten at once to prevent crumbs from floating within the helmet. However, most astronauts prefer to eat prior to the spacewalk and not use this bar.

The space suit has the In-suit Drink Bag (IDB), which is a plastic pouch mounted inside the HUT. The IDB can hold 32 ounces or 1.9 liters of water and has a small tube (straw) that fits up next to the astronaut's mouth. The astronaut can move his/her head within the helmet and suck water through the tube.

Each spacewalking astronaut wears a large, absorbent diaper called a Maximum Absorption Garment (MAG) to collect urine and feces while in the space suit. The astronaut disposes the MAG when the spacewalk is over and he/she gets dressed in regular work clothes.

Astronauts basically do the same thing when they go to space shuttle. Preparation varies with the food type. Some foods can be eaten in their natural forms, such as brownies and fruit. Other foods require adding water, such as macaroni and cheese or spaghetti. Of course, an oven is provided in the space station to heat foods to the proper temperature. There are no refrigerators in space, so space food must be stored and prepared properly to avoid spoilage, especially on longer missions.

Condiments, such as ketchup, mustard and mayonnaise, are provided. Salt and pepper are available but only in a liquid form. This is because astronauts can't sprinkle salt and pepper on their food in space. The salt and pepper would simply float away. There is a danger they could clog air vents, contaminate equipment or get stuck in an astronaut's eyes, mouth or nose.

Astronauts eat three meals a day: breakfast, lunch and dinner. Nutritionists ensure the food astronauts eat provides them with a balanced supply of vitamins and minerals. Calorie requirements differ for astronauts. For instance, a small woman would require only about 1,900 calories a day, while a large man would require about 3,200 calories. An astronaut can choose from many types of foods such as fruits, nuts, peanut butter, chicken, beef, seafood, candy, brownies, etc. Available drinks include coffee, tea, orange juice, fruit punches and lemonade.

Moving around in space is much like trying to move underwater. Wearing a large suit makes movement even more difficult, and when time is short, an astronaut must be able to move quickly. The Manned Maneuvering Unit was specially designed to allow astronauts to move swiftly and safely through space. The MMU is like an armchair with small thrusters attached. It is operated by a hand control similar to those used in computer games.

The manned maneuvering unit (MMU) is a self-contained backpack with all the necessary systems to enable the extravehicular activity (EVA) astronaut to fly free in space and reach work areas remote from the supporting spacecraft. An experimental MMU tested onboard the NASA Skylab Program orbital workshop established key piloting characteristics and capability base for future MMU systems. An operational MMU now exists for the Space Shuttle Program. This versatile mobility system has been flown on nine sorties and accumulated 10 hr and 22 min of flying time during three Space Shuttle missions. These Space Shuttle flights have demonstrated a capability for free space traverses up to 98 m (320 ft.), cargo transfer, and tracking, docking, stabilizing, and orienting large satellites. These and additional MMU capabilities will benefit the Space Station and its onboard payloads. First and foremost is the capability to rescue an EVA crewmember that might inadvertently separate from the Space Station. There will also be tasks at worksites inaccessible by other Space Station equipment and tasks where EVA time is critical. Many Space Station and payload assembly and inspection tasks will need MMU support. Significant Space Station mission flexibility is added by the MMU for backup and contingency roles. These Space Station roles will require a major upgrade to the Space Shuttle MMU design.

Movement in space is very difficult because if you push on something, you will move in the opposite direction. Astronauts on the Gemini missions complained that when they tried to use a spanner in space they spun in the opposite direction. Microgravity means that an astronaut is in danger of floating away mid-job, or losing a vital tool into outer space. To aid astronauts to move around outside, spacecraft are equipped with handles and special footholders into which feet can be locked.

When on a spacewalk, astronauts use safety tethers to stay close to their spacecraft. Tethers are like ropes. One end is hooked to the spacewalker. The other end is connected to the vehicle. The safety tethers keep astronauts from floating away into space. Astronauts also use tethers to keep tools from floating away. They tether their tools to their spacesuits.

Another way astronauts stay safe during spacewalks is by wearing a SAFER. SAFER stands for simplified Aid for EVA Rescue. SAFER is worn like a backpack. It uses small jet thrusters to let an astronaut move around in space. If an astronaut were to become untethered and float away, SAFER would help him or her fly back to the spacecraft. Astronauts control SAFER with a small joystick, like on a video game.

When astronauts go on spacewalks, they wear spacesuits to keep themselves safe. Inside spacesuits, astronauts have the oxygen they need to breathe. They have the water they need to drink. Astronauts put on their spacesuits several hours before a spacewalk. The suits are pressurized. This means that the suits are filled with oxygen.

Once in their suits, astronauts breathe pure oxygen for a few hours. Breathing only oxygen gets rid of all the nitrogen in an astronaut's body. If they didn't get rid of the nitrogen, the astronauts might get gas bubbles in their body when they walked in space. These gas bubbles can cause astronauts to feel pain in their shoulders, elbows, wrists and knees. This pain is called getting "the bends" because it affects the places where the body bends. Scuba divers can also get "the bends."

Astronauts are now ready to get out of their spacecraft. They leave the spacecraft through a special door called an airlock. The airlock has two doors. When astronauts are inside the spacecraft, the airlock is airtight so no air can get out. When astronauts get ready to go on a spacewalk, they go through the first door and lock it tight behind them. They can then open the second door without any air getting out of the spacecraft. After a spacewalk, astronauts go back inside through the airlock.

Astronauts have to perform many different duties that involve leaving their spacecraft. The International Space Station, which is currently under construction, requires many adjustments that can only be done by trained personnel. Robotic equipment is used to put the components of the space station together, but much of the construction can only be done by hand. Astronauts also have to make repairs to complicated items such as the Hubble Space Telescope and damaged satellites.

Astronauts perform many tasks as they orbit Earth. The space station is designed to be a permanent orbiting research facility. Its major purpose is to perform world-class science and research that only a microgravity environment can provide. The station crew spends their day working on science experiments that require their input, as well as monitoring those that are controlled from the ground. They also take part in medical experiments to determine how well their bodies are adjusting to living in microgravity for long periods of time.

Working on the space station also means ensuring the maintenance and health of the orbiting platform. Crew members are constantly checking support systems and cleaning filters, updating computer equipment: doing many of the things homeowners must do to ensure their largest investment stays in good shape. Similarly, the Mission Control Center constantly monitors the space station and sends messages each day through voice or email with new instructions or plans to assist the crew members in their daily routines.

In the early days, the job description of an astronaut was basically that of being an observer - someone who would view and document what was happening. It didn't take long for NASA to understand that human interaction would be required. These astronauts work with pilots to conduct experiments, launch satellites, and maintain spacecraft and equipment. Their background can be in engineering, science, or medicine. They can also work as astronaut educators, inspiring students to consider joining the US space program.

These astronauts serve as space shuttle and international space station pilots and commanders. They are responsible for the crew, the mission, the mission success and the safety of the flight. The Johnson Space Center provides a number of simulators and facilities to prepare the astronauts for their work in space, such as a neutral buoyancy simulator, which simulates weightlessness on earth, and a 200' long and 40' deep pool where astronauts train for spacewalks underwater.

When in orbit, most of the time is spent in the craft or space station. At times, a spacewalk is required to make repairs, or to deploy a satellite, and the astronaut must wear a space suit, or an EMU (extravehicular mobility unit) for protection. Most missions last two to three weeks, but long duration missions may run as long as half a year. Training for long duration missions is very arduous and takes approximately two to three years.

Every astronaut who leaves a spacecraft has to wear a specially designed spacesuit. It is called an Extra-Vehicular Activity (EVA) suit and acts like a miniature spaceship. Layers of material protect the astronaut from the Sun’s rays, as well as tiny particles of space dust that travel at hundreds of thousands of kilometres per hour. The suit provides everything that an astronaut needs to survive in space for short periods of time, including oxygen to breathe and water to drink. It also provides heating and cooling, communication devices and toilet facilities.

Astronauts must wear spacesuits whenever they leave a spacecraft and are exposed to the environment of space. In space, there is no air to breath and no air pressure. Space is extremely cold and filled with dangerous radiation. Without protection, an astronaut would quickly die in space. Spacesuits are specially designed to protect astronauts from the cold, radiation and low pressure in space. They also provide air to breathe. Wearing a spacesuit allows an astronaut to survive and work in space.

Spacesuits help astronauts in several ways. Spacewalking astronauts face a wide variety of temperatures. In Earth orbit, conditions can be as cold as minus 250 degrees Fahrenheit. In the sunlight, they can be as hot as 250 degrees. A spacesuit protects astronauts from those extreme temperatures.

Spacesuits supply astronauts with oxygen to breathe while they are in the vacuum of space. The suits contain water to drink during spacewalks. They protect astronauts from being injured from impacts of small bits of space dust. Space dust may not sound very dangerous, but when even a tiny object is moving many times faster than a bullet, it can cause injury. Spacesuits also protect astronauts from radiation in space. The suits even have visors to protect astronauts' eyes from the bright sunlight.

A spacesuit is much more than a set of clothes astronauts wear on spacewalks. A fully equipped spacesuit is really a one-person spacecraft. The formal name for the spacesuit used on the space shuttle and International Space Station is the Extravehicular Mobility Unit, or EMU. "Extravehicular" means outside of the vehicle or spacecraft. "Mobility" means that the astronaut can move around in the suit. The spacesuit protects the astronaut from the dangers of being outside in space.

Nuclear reactions are the result of the strong nuclear force, which binds together the particles that form atoms. During a nuclear explosion, this powerful force is released, expelling vast amounts of energy.

A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, though to date all fusion-based weapons have used a fission device to initiate fusion, and a pure fusion weapon remains a hypothetical device.

Atmospheric nuclear explosions are associated with mushroom clouds, although mushroom clouds can occur with large chemical explosions. It is possible to have an air-burst nuclear explosion without those clouds. Nuclear explosions produce radiation and radioactive debris.

The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere.

Depending on the design of the weapon and the location in which it is detonated, the energy distributed to any one of these categories may be significantly higher or lower. The blast effect is created by the coupling of immense amounts of energy, spanning the electromagnetic spectrum, with the surroundings. The environment of the explosion (e.g. submarine, ground burst, air burst or exo-atmospheric) determines how much energy is distributed to the blast and how much to radiation. In general, surrounding a bomb with denser media, such as water, absorbs more energy and creates more powerful shockwaves while at the same time limiting the area of its effect. When a nuclear weapon is surrounded only by air, lethal blast and thermal effects proportionally scale much more rapidly than lethal radiation effects as explosive yield increases. The physical-damage mechanisms of a nuclear weapon (blast and thermal radiation) are identical to those of conventional explosives, but the energy produced by a nuclear explosion is usually millions of times more powerful per unit mass and temperatures may briefly reach the tens of millions of degrees.

Energy from a nuclear explosion is initially released in several forms of penetrating radiation. When there is a surrounding material such as air, rock, or water, this radiation interacts with and rapidly heats the material to an equilibrium temperature (i.e. so that the matter is at the same temperature as the fuel powering the explosion). This causes vaporization of the surrounding material, resulting in its rapid expansion. Kinetic energy created by this expansion contributes to the formation of a shockwaves. When a nuclear detonation occurs in air near sea level, much of the released energy interacts with the atmosphere and creates a shockwave which expands spherically from the center. Intense thermal radiation at the hypocenter forms a nuclear fireball which, if the burst is low enough, is often associated with a mushroom cloud. In a high-altitude burst, where the density of the atmosphere is low, more energy is released as ionizing gamma radiation and X-rays than as an atmosphere-displacing shockwave.

From Earth, space can seem calm and quiet, but in actual fact it is deadly. If humans ventured into space without the protection of a spacesuit they would die almost instantly. The lack of oxygen would mean suffocation. But before this, the lack of pressure would cause gases in the blood to separate as if it were boiling. With no protection from the Sun’s harmful ultraviolet radiation, the astronaut would be burned to death.

What happens to your body in space? NASA’s Human Research Program has been unfolding answers for over a decade. Space is a dangerous, unfriendly place. Isolated from family and friends, exposed to radiation that could increase your lifetime risk for cancer, a diet high in freeze-dried food, required daily exercise to keep your muscles and bones from deteriorating, a carefully scripted high-tempo work schedule, and confinement with three co-workers picked to travel with you by your boss.

But what, exactly, happens to your body in space, and what are the risks? Are risks the same for six months on the space station versus three years on a Mars mission? No. There are several risks NASA is researching for a Mars mission. The risks are grouped into five categories related to the stresses they place on the space traveler: Gravity fields, isolation/confinement, hostile/closed environments, space radiation, and distance from Earth.

Scott Kelly was the first American to spend nearly one year in space aboard the International space Station, twice the normal time. Science takes time, and researchers are eagerly analyzing results of the mission to see how much more the body changes after a year in space. One year is a stepping stone to a three-year journey to Mars, and Scott’s data will help researchers determine whether the solutions they’ve been developing will be suitable for such long, onerous journeys.

Together, the four forces can explain everything that happens in the Universe. Many scientists are now working to prove that they are all separate parts of the same universal force that once existed at the birth of the Universe.

A theory of everything (TOE or ToE), final theory, ultimate theory, or master theory is a hypothetical single, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe. Finding a TOE is one of the major unsolved problems in physics. Over the past few centuries, two theoretical frameworks have been developed that, together, most closely resemble a TOE. These two theories upon which all modern physics rests are general relativity (GR) and quantum field theory (QFT). GR is a theoretical framework that only focuses on gravity for understanding the universe in regions of both large scale and high mass: stars, galaxies, clusters of galaxies, etc. On the other hand, QFT is a theoretical framework that only focuses on three non-gravitational forces for understanding the universe in regions of both small scale and low mass: sub-atomic particles, atoms, molecules, etc. QFT successfully implemented the Standard Model that describes the three non-gravitational forces – strong nuclear, weak nuclear, and electromagnetic force -- as well as all observed elementary particles.

Physicists have experimentally confirmed virtually every prediction made by GR and QFT when in their appropriate domains of applicability. Nevertheless, GR and QFT are mutually incompatible – they cannot both be right. Since the usual domains of applicability of GR and QFT are so different, most situations require that only one of the two theories be used. As it turns out, this incompatibility between GR and QFT is only an issue in regions of extremely small scale - the Planck scale - such as those that exist within a black hole or during the beginning stages of the universe (i.e., the moment immediately following the Big Bang). To resolve the incompatibility, a theoretical framework revealing a deeper underlying reality, unifying gravity with the other three interactions, must be discovered to harmoniously integrate the realms of GR and QFT into a seamless whole: the TOE is a single theory that, in principle, is capable of describing all phenomena in the universe.

In pursuit of this goal, quantum gravity has become one area of active research. One example is string theory, which evolved into a candidate for the TOE, but not without drawbacks (most notably, its lack of currently testable predictions) and controversy. String theory posits that at the beginning of the universe (up to 10?43 seconds after the Big Bang), the four fundamental forces were once a single fundamental force. According to string theory, every particle in the universe, at its most microscopic level (Planck length), consists of varying combinations of vibrating strings (or strands) with preferred patterns of vibration. String theory further claims that it is through these specific oscillatory patterns of strings that a particle of unique mass and force charge is created (that is to say, the electron is a type of string that vibrates one way, while the up quark is a type of string vibrating another way, and so forth).

Gravity is one of only four forces that govern every event in the entire Universe. Gravity binds together the Universe, while electromagnetic force is responsible for light and electricity. A strong nuclear force holds together basic particles, and a weak nuclear force causes the decay of unstable atoms. These four forces may have been united during the Big Bang, emitted as one superforce bound by extremely high temperatures. As temperatures began to cool, the superforce was gradually broken down into four separate forces. All four forces are linked with special particles that act in the same way as couriers, transferring the force from one place to another. Electromagnetism and gravitation can work over large distances, but the two nuclear forces only operate on an atomic level.

In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four fundamental interactions known to exist: the gravitational and electromagnetic interactions, which produce significant long-range forces whose effects can be seen directly in everyday life and the strong and weak interactions, which produce forces at minuscule, subatomic distances and govern nuclear interactions. Some scientists hypothesize that a fifth force might exist, but these hypotheses remain speculative.

Each of the known fundamental interactions can be described mathematically as a field. The gravitational force is attributed to the curvature of space-time, described by Einstein’s general theory of relativity. The other three are discrete quantum fields, and their interactions are mediated by elementary particles described by the Standard Model of particle physics.

Within the Standard Model, the strong interaction is carried by a particle called the gluon, and is responsible for quarks binding together to form hadrons, such as protons and neutrons. As a residual effect, it creates the nuclear force that binds the latter particles to form atomic nuclei. The weak interaction is carried by particles called W and Z bosons, and also acts on the nucleus of atoms, mediating radioactive decay. The electromagnetic force, carried by the photon, creates electric and magnetic fields, which are responsible for the attraction between orbital electrons and atomic nuclei which holds atoms together, as well as chemical bonding and electromagnetic waves, including visible light, and forms the basis for electrical technology. Although the electromagnetic force is far stronger than gravity, it tends to cancel itself out within large objects, so over large distances (on the scale of planets and galaxies), gravity tends to be the dominant force.

Many theoretical physicists believe these fundamental forces to be related and to become unified into a single force at very high energies on a minuscule scale, the Planck scale, but particle accelerators cannot produce the enormous energies required to experimentally probe this. Devising a common theoretical framework that would explain the relation between the forces in a single theory is perhaps the greatest goal of today's theoretical physicists. The weak and electromagnetic forces have already been unified with the electroweak theory of Sheldon Glashow, Abdus Salam, and Steven Weinberg for which they received the 1979 Nobel Prize in physics. Progress is currently being made in uniting the electroweak and strong fields within what is called a Grand Unified Theory (GUT). A bigger challenge is to find a way to quantize the gravitational field, resulting in a theory of quantum gravity (QG) which would unite gravity in a common theoretical framework with the other three forces. Some theories, notably string theory, seek both QG and GUT within one framework, unifying all four fundamental interactions along with mass generation within a theory of everything.