Space

Outer Space, or simply Space, is the area that is above the Kármán Line, a line that is drawn at an altitude of 100 km (62 mi). The vast majority of space is empty, as there is on average just 1 atom per cubic meter in space. However, there are some objects, both natural and artificial in space, including planets, moons, stars, space stations and artificial satellites.

History

Starting from the invention of the telescope in 1610, space travel and rocketry had been theorized. The first rocket is launched in 1926 but it did not cross the Kármán Line (one of the commonly accepted boundaries of "space"), and the first rocket to cross the Kármán Line is the V-2 Rocket launched by Germany in 1944. The first animals to be sent into space is some fruit flies launched in 1947 by the US, and the dog Laika was the first animal to be sent into earth orbit launched in 1957 by the Soviet Union.
Driven to prove their superiority during the Cold War, as well as to gain a strategic advantage, the U.S.A. and the Soviet Union began the "Space Race" during the 1960s. In 1961, the first human, Yuri Gagarin, was sent into space by the Soviet Union and after the Americans managed to put some men into space as well, the USSR put Valentina Tereshkova, the first woman, into space in 1963. In 1969, the American Neil Armstrong became the first person on the Moon. Starting from 1971, the Soviet Union launched the Salyut space stations and they were the first space stations ever. Probes began to explore the solar system also around this point. Space seemed very close; at one point, tickets to the moon and to as-yet-nonexistent space stations were being sold.
After the Space Race ended, a new sense of reality set in. The wild dreams of the 1960s and 70s died, and humanity turned its attention earthward again. Space travel beyond Earth's orbit became the exclusive domain of mankind's robotic explorers, and high-profile tragedies both reaching and returning from orbit provided sobering reminders of the risks of space travel. By the end of the 20th century, travel into space was still exclusively the domain of governmental organizations.
However, necessity changed the situation with the dawn of the 21st century, starting with the construction of the International Space Station in 1998. Desperate for funds, the Russian Space Agency began to sell seats on Soyuz launches. Businessman Dennis Tito became the first pay-to-fly space tourist in April 2001, and since then a handful have followed in his footsteps, some of them even on more than one flight.

Environment

Space is an extreme environment. The temperature is about −270 °C (−454 °F), cosmic rays would cause fatigue, nausea, vomiting and damage to the immune system, and body fluids, such as blood, boil in space. So a space suit must be worn when outside of spaceships and space stations.

There are many languages spoken on the International Space Station, including Japanese, Italian, French, German, Russian, English and occasionally Portuguese. Everyone knows how to speak English, and all signs are written in English and Russian. You might need to learn some Russian, as only Russia provide rockets to the ISS.

Although physical fitness remains a concern, the main obstacle to reaching space is the depth of your wallet. In increasing order of both cost and distance from the Earth:

On Earth

Even if you never get to go to space yourself, there are quite a few space-related places on Earth. At these museums and launch sites, you can learn about crewed missions and the robotic probes used as a scientific research tool where cost, distance, lack of sufficiently-advanced technology or extreme conditions make human exploration impractical or impossible. Points which are beyond the reach even of probes are typically only accessible to remote observation from afar, such as by astronomy or radio astronomy.

Museums

Because there are so many space museums around the Earth, it will be impossible to list them all. Below are the most popular:

• Beijing Planetarium

  phone: +86 10 6835 2453
  address: 138 Xizhimenwai St (西直门外大街138号; Xīzhíménwàidàjiē), Beijing, China
  This is the first large-scale planetarium in China, with 2 buildings, one old and one new. The old building have a Foucault's Pendulum, a device used to show the Earth's rotation, and an exhibition which have many facts about Space. The new building have more stuff than the old one, and it have models of all the planets. There's also exhibitions about the Sun and the Big Bang in the new building. 4 theaters with over 10 different movies are located in the buildings, and 2 are 3D theaters and the other 2 are dome-shaped theaters.

• Canada Aviation and Space Museum

  phone: +1 613-991-3044
  address: 11 Aviation Parkway, Ottawa, Ontario, Canada
  Not to be confused with Canada Air and Space Museum, that's a whole different museum. The Canada Aviation and Space Museum have 5 exhibitions, of which 3 is about space and not aviation: Life in Orbit: The International Space Station, Canada in Space, and Health in Space: Daring to Explore. Life in Orbit: The International Space Station is about life in the ISS and how the astronauts handle a micro-gravity environment. There's a model of the ISS that you an climb in! Canada in Space is an overview of Canada's most notable Space achievements, including a full-scale model of the satellite Alouette-1 and the Disorientation Station, which you can climb in and spin and get dizzy. And finally, Health in Space: Daring to Explore is about the effect of outer space on humans, such as micro-gravity and cosmic radiation.

• Johnson Space Center

  phone: +1 281 483-0123
  address: 1601 NASA Parkway, Houston, Texas, USA
  Mission Control for Space Shuttle and International Space Station activities, with an adjacent museum. In the museum, there's the Starship Gallery, which includes the Apollo 17 command module and a touchable moon rock. The International Space Station Gallery has interactive live shows and real ISS artifacts, and the Mission Mars gallery is an interactive exhibit about Mars. Outside, the Independence Plaza has a model of a space shuttle that you're able to go in. There's a Rocket park nearby and it's available for personal tours.

• Mars Desert Research Station

  phone: +1 303 984-9346
  address: 2200 Cow Dung Road, Hanksville, Utah, USA
  Experience how it would be to live on Mars. The campus includes 6 buildings: the 2-storied round habitat with a diameter of 28 ft (8 m), 2 observatories, the GreenHab (a crop farming lab), the Science Dome (a lab and control center for the entire station) and the RAMM (Repair and Maintenance Module).

• Memorial Museum of Cosmonautics

  phone: +7 495 683-79-14
  address: 111 Prospekt Mira, 129223 Moscow
  This is a large space museum with over 98,000 items about Soviet and Russian space exploration, and is located inside the base of the Monument of the Conquerors of Space. There's a Soyuz rocket and a duplicate of the very first artificial satellite inside! Tours are available for booking and can be in English. Not far from the Museum is the Sergey Korolev Memorial House, which is the house where Sergey Korolev, the designer of the first artificial satellite once lived. This house is also a museum, with over 13,000 items about Sergey Korolev's life.

• Musée de l'Air et de l'Espace

  phone: +33 1-49-92-70-00
  This is one of the earliest air and space museums in the world, and it is over 100 years old. There are 12 halls (exhibitions) in the museum, and 1 of them is about space: La conquête spatiale (the space conquest). There are many models of rockets and satellites. Of the 4 activities, the Planetarium and Planète Pilote (Pilot Planet) is space-related. The Planetarium have a large dome-shaped screen with 7039 stars and 20 deep space objects. The Planète Pilote is dedicated to 6 to 12 year olds, but parents and/or educators may enter. It have an Aviation part and a Space part, and it have over 40 interactive activities.

• Smithsonian National Air and Space Museum

  phone: +1 202 633-2214
  address: 600 Independence Avenue SW, Washington, DC, USA
  This museum has exhibitions about both aviation and space exploration, and there's 3 exhibitions about space exploration. The Space Race exhibit, like its name, is about the Space Race and features a model of the Hubble Space Telescope. The Moving Beyond Earth exhibit is about modern space exploration. It includes presentation stages and gigantic drawings of Earth and the ISS on the wall. Finally, the Exploring the Planets exhibit is about the exploration of the Solar System, and it contains models of the Voyager space probes and the Curiosity Mars rover.

• U.S. Space and Rocket Center

  phone: +1 800 637-7223
  address: 1 Tranquility Base, Huntsville, Alabama, USA
  Features a Saturn V rocket that was never launched and also includes exhibits on the "Space Race", the programs that led up to the moon visits, and the ISS. There is a planetarium and a National Geographic theater, with 6 different shows available. Outside of the museum are replicas and test units for numerous other space vehicles, including life-size replicas of the space shuttle and a vertical Saturn V. There is also space simulators outside to experience what it would be like if you're in space. The Spark!Lab contains many design challenges for you to work on, and there's a Mars Grill, which is a place to eat.

Launch sites and labs

• Baikonur Cosmodrome

  phone: +7(495)745 72 61
  address: Baikonur, Kazakhstan
  The rocket launch site of Sputnik 1 and Yuri Gagarin in Kazakhstan, and to this day the main Soyuz launch site. Long strictly off-limits, but now open to limited tourism. Several tour companies operate tours to here, including Star City tours and Baikonur Cosmodrome tours. The Baikonur Cosmodrome plus the entire city of Baikonur is off limits unless you get a special permit, which is usually done by getting a tour company to get the permit for you.

• Jet Propulsion Laboratory

  phone: +1 818 354-9314
  address: 4800 Oak Grove Dr, Pasadena, California, USA
  The designers of the Curiosity Mars rover and the Voyager space probes, it gives public lectures monthly. Tours need to be reserved at least 3 weeks ahead, and they are 2-2.5 hours in length. Passport/identification are required to enter the lab.

• Kennedy Space Center Visitor Complex

  phone: +1 855 433-4210
  address: Cape Canaveral, Florida, USA
  This busy tourist attraction offers museums, movies, a rocket garden and bus tours of former shuttle preparation and launch facilities. This is an official federal site — however, the visitor complex is run by contractors for a profit, so prices are comparable to private tourist attractions, not a typical national park. Basic admission (a 1 day pass) includes an excellent bus tour (including the complimentary bus tour of Launch Complex 39 and the Apollo/Saturn V Center), the museums (including the exhibit featuring the Space Shuttle Atlantis), and the IMAX movies. Additional special tours or programs should be booked in advance since they sell out quickly. NOTE: this facility may

*sometimes* be closed on launch days! Cape Canaveral also includes the Air Force Space and Missile Museum.

• Guiana Space Centre

  phone: +594 37 77 77 (museum and tours), +594 33 44 53 (rocket launches)
  address: Kourou, French Guiana
  The European Space Agency's launch site in French Guiana, and there's a Space Museum nearby. The space museum have 2 floors. It has 7 permanent exhibits and a planetarium. The launch site provide tours twice a day, from 8AM to 11:30AM and from 1PM to 4:30PM, and it must be reserved 48 hours in advance. Children under 8 cannot go on the tour. You can watch rocket launches from a distance of 7km, 15km or 20km. Children under 8 cannot watch rocket launches, and children between 8 and 16 are sometimes not allowed to watch rocket launches.

• Mojave Spaceport

  phone: +1 661 824-2433
  address: 1434 Flight Line, Building 58, Mojave, California, USA
  The first FAA-certified Spaceport and the home of Scaled Composites' private spaceflight program. It does not offer tours, but there are Plane Crazy Saturdays which is open to the public, and allows you to see what the spaceport is like.

• Columbus Control Centre

  address: Weßling (outside Munich), Germany
  Is used to control the Columbus research laboratory of the International Space Station, as well as a ground control centre for the Galileo satellite navigation system. Open to the public depending on mission status.

• Star City

  address: Moscow Oblast, Russia
  Cosmonaut training facility northeast of Moscow. This town's location is kept in secret until the 1990s, even though the news often talk about it. There's a statue of Yuri Gagarin in town. About 70% of its population of 6 thousand have jobs about space. There are 2 parts: the residental area and the training facility.

• Yuri Gagarin Training Center

  phone: +7 495 526-26-12
  address: Star City, Moscow Oblast, Russia
  The cosmonaut training facility inside Star City. The world's first and largest centrifuge is located here, and it can produce up to 20 times Earth's gravity. There's also an airport for parabolic "vomit comet" flights (see below). The Hydro Lab uses many advanced technology to simulate a weightless environment, and have a big tank of water. Finally, there are many simulators used to train various skills.

Tanegashima Space Center

phone: +81 997-26-2111 (launch site), +81 997-26-9244 (space museum)

address: Tanegashima, Japan

Japan's main launch site. The Space Museum beside have free exhibits, and tours of the launch site are also free. There are crowded public viewpoints for launch days, but you can watch rocket launches from anywhere outside 3 km (1.9 mi) from the launch site. There's a model of Kibo, a Japanese part of the ISS that you can go in and the Rocket Launch Theater in the Space Museum.

Vostochny Cosmodrome

address: near Zilokovskiy, Amur Oblast, Russia

Functional since 2016, the Vostochny Cosmodrome was built to reduce Russian dependency on the Baikonur site in Kazakhastan, since after the Soviet Union dissolved, the Baikonur Cosmodrome was in a different country. 15 km off the Trans-Siberian Railway, launches are certainly within viewing distance to train passengers, provided the train passes in the right moment. It had not opened to tourism just yet.

See astronomy for information on observing space phenomena from the ground.

Zero-G

While not actual space travel, the weightlessness experienced in orbit can be duplicated (for durations of less than a minute at a time) with a calibrated parabolic aircraft flight, which alternates low g-forces at the heights of its arcs with high g-forces at the bottoms. The parabolic flights are notoriously nausea-inducing, leading to the nickname Vomit Comet, but commercial operators claim that their shorter flights (15 parabolas) are considerably gentler than lengthy research flights (40–80).

• Incredible Adventures

  phone: +1 941 346-2603
  address: 1903 Northgate Blvd, Sarasota, Florida, USA
  This company provides zero-g flights either from Moscow or from Florida. You can customize when do you want to fly in the Florida flights. In the Florida flights, your plane will go from Martian gravity (1/3 Earth gravity) to Lunar gravity (1/6 Earth gravity) and finally to zero-g, and the flight will last for 10~12 maneuvers and each maneuver lasts for 10 seconds. In the Moscow flights, the flight will last for 1.5 to 2 hours but you'll only get to float for 5 minutes. The plane will depart from the Chkalovsky Airfield for Moscow and St Pete-Clearwater International Airport for Florida. Children under 18 years old are not allowed to go on either flight.

• Zero Gravity Corporation

  phone: +1 703 894-2188
  address: 4601 N. Fairfax Drive, Suite 1200, Arlington, Virginia, USA
  Offers flights from Las Vegas (Nevada), San Francisco (California), Orlando, Miami and Cape Canaveral (all Florida) on a modified Boeing 727 named "G-FORCE ONE" with a large compartment suitable for weightless tumbling. 15 parabolas will be flown, with several brief simulations of freefall, Lunar gravity (1/6 Terran), and Martian gravity (1/3 Terran). There's about 8 minutes of freefall. After the flight ends, there will be a Regravitation Ceremony and you'll be handed out certificates and pre-flight photos.

• Space Affairs

  phone: +49 421 24 13 311
  address: Bismarckstraße 72, 28203 Bremen, Germany
  Provides 5-day zero-g missions from Moscow. Includes a guided visit to Star City and the Yuri A. Gagarin Museum inside in the second day. The real zero-g flight is on the third day, and there's 10 parabolas with about 25 seconds of freefall each, so that sums up to a little over 6 minutes of freefall. In the fourth day, there's another guided visit to Star City, but this time to the Gagarin Training Center, and a Russian cosmonaut will be joining dinner. In the final day, you'll leave Moscow, maybe stopping at the Red Square.

• MiGFlug

  phone: +41 44 500 50 10, +44 20 3179 3070
  address: Grüngasse 19, CH-8004 Zurich, Switzerland
  Offering flights with Russian Ilyushin 76MDK (Special training airplane for Cosmonauts) departing from Moscow and also zero-g flights in the U.S. with a Boeing 727-200, or a smaller aircraft leaving from Tampa daily. The Russian flight includes a tour of Star City, and the Gagarin Training Center inside it. American flights includes some parabolas at Lunar gravity.

Edge of space

Flights at altitudes of less than 100 km do not qualify as true space flight, but it is possible to see the curvature of the Earth from altitudes as (comparatively) low as 25 km.

• Space Affairs

  phone: +41 44 500 50 10, +44 20 3179 3070
  address: Bismarckstraße 72, 28203 Bremen, Germany
  Flights on Russian MiG-31 Foxhounds have ended, but flights on balloons named "BLOON" have not started yet, and commercial BLOON flights are expected to start in 2020. However, you can already book a flight as of August 2019. BLOON is a very safe and steady balloon, and can ascend up to 36 km (22.5 mi). On the day before your flight, you will head over to southern Spain, where the BLOON launch site is located. That night, there will be some easy training and stargazing using telescopes. The next day, you must get up early for the flight, and the BLOON will ascend to about 36 km. See the curvature of the Earth! After 2 hours, the BLOON will descend, and you'll soon be back on Earth.

• MiGFlug

  phone: +41 44 500 50 10, +44 20 3179 3070
  address: Grüngasse 19, CH-8004 Zurich, Switzerland
  As of October 2019, this program is unavailible, but you can contact MiGFlug for them to put you on the waiting list. Offering supersonic flights with a Russian MiG-29 Fulcrum jet up to 22 km (13.75 mi), departing from Russia. The MiG-29 Fulcrum is not guaranteed to go that high, but 17 km (10.6 mi) up is guaranteed. The MiG-29 Fulcrum will be climbing up in a ballistic path at nearly Mach 2. The flight package also includes trasportation between your hotel and the airbase, a medical checkup before flight, flight training, flight certificate with max altitude, a visit to the airbase museum and an optional HD video and photo service of you at the edge of space.

Sub-orbital flight

Sub-orbital flight is defined as flight at altitudes higher than 100 km but at speeds insufficient to achieve orbit. While there are no operators offering sub-orbital flight, the privately funded and built SpaceShipOne in 2004 demonstrated that this is a possible market and the race is on to commercialize it.

• Virgin GalacticFounded by who else but Richard Branson, Virgin Galactic is selling tickets for sub-orbital flights on SpaceShipTwo for US$250,000 a seat. Flights will go up to ~50,000 ft (110 km) and reach speeds of Mach 3, but while total flight time is 2.5 hours, weightlessness will only last for about six minutes. The company has placed an order for five second-generation spaceships from Scaled Composites, the builders of SpaceShipOne. Initial flights will take place from Mojave, California (US), but later flights will move to Spaceport America near Truth or Consequences, New Mexico (US) and Kiruna, Sweden. Departures will first be weekly, and eventually climbing to once or twice daily. Three-day training will be available on site. A successful test flight was performed on 5 April 2018.

• BoeingBoeing announced the CST-100, a sub-orbital plane capable of suborbital flight and 7-passengers capacity in "competitive prices".

Orbital flight

All that sub-orbital stuff is pretty nifty, but these days no one's really ready to accept that you were "in space" until you've been in orbit around the Earth. There's no single altitude for this (it depends on your orbital velocity), but due to atmospheric drag it's only practical above 350 km. Commonly known as Low Earth Orbit, it is the exclusive domain of Russian Soyuz vessels, Chinese Shenzhou craft, and the International Space Station. This itinerary is likely the most expensive in the world.

• Space Adventures

  address: 8000 Towers Crescent Drive, Suite 1000, Vienna, Virginia, USA
  Space Adventures has organized orbital flights to the International Space Station (ISS), the only fully functioning space station in orbit. Around US$35 million per person will buy you basic training and a launch on a Soyuz vessel from the Russian Cosmodrome at Baikonur to the ISS. Participants must also fulfill certain physical fitness requirements to ensure their and the mission's safety. The ISS was launched in 1998 and has a Russian half and an American half. It orbits the Earth once every 90 minutes, and 16 sunrises and sunsets can be seen from it every 24 hours. The ISS consists of 14 main modules including 4 labs, a utility hub, an airlock and a life support module.

• Private firms SpaceX and Boeing plan to begin transporting astronauts to the International Space Station. Russia's Soyuz spacecraft had exclusively filled this gap since the 2011 end of the US space shuttle program. NASA plans to allow tourists to stay on the ISS starting in 2020, charging $35,000 per night. The charge for transportation to and from the ISS by Boeing or SpaceX is estimated at $60 million per flight, though as of 2019 these flights have not yet started.

China is testing out the technology for space stations and is planning to launch a complete modular space station (like the ISS) by 2022.

Trans-orbital flight

Human travel beyond Low Earth Orbit has not been done since the cancellation of the U.S. Apollo program by President Nixon in 1972. The only programs actively working to re-establish this capability are governmental in nature. Whilst there have a been a a few speculative commercial proposals for trans orbital tourist flights, nothing has yet been reliably offered to the potential traveller.
SpaceX is planning a pilot tourist flight around the Moon for Japanese billionaire Yusaku Maezawa, who wants to invite a group of artists to come with him. The trip is planned for 2023, but the company has a history of making ambitious plans and then delaying or canceling them, so it remains to be seen whether they'll stick to the schedule.
Unmanned space craft have traveled around and outside the solar system, like the Voyager probes, but no human has yet travelled to a planet other than Earth. For years there has been talk of sending someone to Mars, but the barriers are formidable – travel time could be anywhere from several months to a couple of years, the environment is cold and inhospitable, the voyager would be subject to an extended period of weightlessness and exposure to radiation, the entire mission must be self-contained and the question of how to bring the astronauts back to Earth at the end of the journey remains unanswered. In the meantime, the robots bring back valuable scientific data which may not yet be obtainable by any other means.

• The sight of the Earth from Space is reputed to be incomparable.
• At altitudes above the thick atmosphere, the stars cease to "twinkle" and eventually disappear from view completely.
• Sunrise and sunset lose much of their multicolored glory, but take on greater intensity and speed at orbital and even suborbital velocities.
• The Northern and Southern Lights can be seen from space.

• Freefall (often inaccurately called "zero gravity") is a phenomenon which, while not unique to Space travel, occurs only momentarily on Earth, such as in thrill rides or high-speed elevators. If you experience freefall and don't do some aerobatics and float around the craft, you've wasted a great deal of money.
• Take pictures – what else are you going to do all day? Don't forget the extra memory cards.
• Tourists traveling on otherwise scientific missions may be expected to contribute to them, participating in medical observations at the least.
• Extravehicular activity (EVA). Perhaps better known as spacewalking, this involves exiting the spacecraft to float around in space. This is now available as an option at Space Adventures, but there have been no takers yet: this costs US$20 million extra, requires an extra month of training and has additional fitness qualifications.

• Space diveOrbital Outfitters is designing Sub-orbital Space Suit One, a suit to be worn by crew on sub-orbital flights and potentially suitable for "space diving" from 120,000 ft.

• Space campNASA runs space camps at various locations in the U.S. for children and teenagers with an interest in astronomy.

Although space food has come a long way in terms of taste and variety in recent decades, the quality and taste is still not up to standards of most connoisseurs of fine cuisine. Your transportation provider may offer some choice in the foods available, but you will be limited by their willingness to indulge you.
The freeze-dried "astronaut ice cream" sometimes sold on Earth as a novelty item is a misnomer; it has never actually been served on any manned space mission (in a zero-gravity environment, the floating crumbs would likely have interfered with the onboard equipment). However, real ice cream has been eaten in space by astronauts aboard Skylab, the Space Shuttle, and the International Space Station.

Contrary to popular belief, Tang was not invented for the US space programme, although NASA did carry it aboard the Apollo missions.
Water tends to be scarce (as it is heavy and must be brought from Earth), so International Space Station machinery recycles water aggressively. Everything from fuel cell water to humidity and waste water is efficiently recovered. According to some reports on the "fluffy newspiece" pages of the internet, astronauts actually prefer the recycled water. Your mileage might vary, but be assured, that chemically and biologically speaking, the recycled water is 100% safe for human consumption.

• Bigelow AerospaceThey built the first successful prototype of an inflatable space hotel in 2006-2007. In 2016, a prototype was delivered to the ISS on a SpaceX rocket to undergoing testing, but otherwise it will remain unoccupied. A 10–60 day "live and work visit", once available, is expected to cost between $26–37 million.

While more mature technology has made it safer than it was in the 1960s, Space remains an inherently dangerous environment to put yourself in. Cosmic radiation, extreme temperatures, micrometeorites, engineering mistakes, high speeds, explosive fuels, space debris, the distance to terra firma, and the lack of atmosphere make any unplanned situation potentially life threatening. Spacecraft launch testing is extremely expensive, so spacecraft don't and can't have thousands of flight hours. By the standards of aviation, every space flight is a test flight.
Both start (unless they invent the space elevator any time soon, you are basically sitting on a huge bomb of fuel and hope it doesn't explode) and reentry (if you hit it in the wrong angle you burn up in or bounce off the atmosphere) have thus far proven to be the biggest danger during a mission. So far only three humans have died in space (as opposed to start and landing), but there have been several close calls such as Apollo 13 or the very first spacewalk. Some of the technological problems and close calls only became known to the public decades after they happened, so there may still be dangers you won't even know you are facing.
Voyagers should be wary of purchasing space flights on projects that haven't yet begun. Many ventures are highly speculative; PanAm's “First Moon Flights” Club issued over 93,000 waiting list spots between 1968-1971 and predicted launch dates for many subsequent commercial expeditions have slipped just as dramatically. If there are complications with the project or the company goes under, you might lose your money and your plans. Just look at the bold predictions of some private space companies that have already proven to be less permanent than a shooting star.

Astronaut training is physically demanding, so good physical fitness is a good starting point. Similar physical and mental stresses are present in particularly demanding types of military service, piloting fighter aircraft, mountain climbing, Antarctic expeditions and advanced scuba diving such as cave diving. National astronaut programs often require athlete-like physical fitness and experience from these or comparable tasks. There are no hospitals in space and rescue is difficult or impossible, so people with conditions that might require immediate medical treatment are not qualified for space travel.
You need to exercise to stay healthy in zero gravity. Even so, you'll still lose both bone and muscle mass. While exercise helps diminish the problem somewhat a long stay will still see you weakened and several cosmonauts and astronauts had difficulty getting out of their capsule and onto their own feet upon landing.
Another concern is cosmic radiation. While you are exposed to a certain level of background radiation at all times, it gets higher in certain areas on earth and once you leave the protective layers of the atmosphere. This is already notable on a commercial transatlantic flight at 10,000 m and only gets worse if you go up to the International Space Station (ISS) at 200 to 300 km above the earth's surface. While the ISS still enjoys some limited protection against radiation, once you go well beyond that height, or even to the moon, there are short term and long term risks associated with radiation that only get worse the longer you stay. Particularly dangerous are solar storms that may give you a year's worth of radiation in just a couple of hours. Shielding against radiation is also one of the major problems in ever sending humans to Mars, as all known solutions involve huge amounts of extra weight for the space craft or too high a risk to the crew.

What goes up must come down—at least for now.
Once you've exhausted the Moon, there are countless opportunities for exploration and discovery down on the surface, in places such as Africa, Asia, Europe, North America, South America, Australia, Antarctica, and countless islands in between.