What is Space?

Outer space is the vast region beyond Earth’s atmosphere where air ends and the universe begins. On Earth, the atmosphere contains the gases we need to breathe, but as you go higher, the air gets thinner and thinner. About 62 miles above Earth’s surface, the atmosphere becomes so thin that it blends into outer space. This boundary is called the Karman Line and is considered to be the beginning of space.

Click the NASA Logo to learn more about the Karman Line.

Where do Objects Orbit?

The International Space Station (ISS) and most satellites orbit Earth in a region called low Earth orbit (LEO). This is the area between about 100 to 1,200 miles above Earth’s surface. The ISS, for example, orbits at about 250 miles above Earth—roughly the distance from Chicago to Detroit!

Satellites in LEO move incredibly fast, circling Earth in about 90 minutes. This high speed keeps them from falling back to the planet due to gravity. The ISS, for example, travels at around 17,500 mph—fast enough to see 16 sunrises and sunsets every day!

Not all satellites stay in low Earth orbit. Some move higher:

Medium Earth orbit (MEO) (1,200–22,000 miles up) is used for navigation satellites like GPS.
Geostationary orbit (GEO) (about 22,000 miles up) is where satellites stay fixed over one spot on Earth, making them ideal for weather forecasting and TV signals.

So, whether in LEO, MEO, or GEO, satellites and the ISS stay in orbit by balancing speed and gravity—giving us communication, navigation, and even a home in space!

International Space Station (ISS)

Click here to learn more about the problem of Space Debris

The Vacuum of Space

Space is often called a vacuum, but what does that mean? A vacuum is a place where there is little or no matter—no air, no water, and almost nothing else. On Earth, we are surrounded by an atmosphere full of gases like oxygen and nitrogen. But in space, these gases are almost completely absent.

The reason space is a vacuum comes down to gravity and distance. Planets and stars have strong gravity that holds onto gases, creating atmospheres. However, the farther you get from these objects, the weaker their gravity becomes. As a result, there aren’t enough forces pulling gases together, leaving space mostly empty.

Although space isn’t a perfect vacuum—there are tiny particles, dust, and even stray atoms floating around—it is emptier than anything we can experience on Earth. Because of this, astronauts need spacesuits and spacecraft with air supplies to survive. Without air, there’s also no way for sound to travel, which is why space is completely silent!

In short, space is considered a vacuum because it lacks the air and gases that fill our planet. It’s a vast, mostly empty expanse, making it very different from the world we live in!

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Heat Transfer

Since space is a vacuum with no air or other matter to carry heat, you might wonder how the Sun’s warmth reaches Earth. On Earth, heat typically moves in three ways: conduction, convection, and radiation.

Conduction happens when heat moves through direct contact, like when you touch a hot pan.
Convection happens when heat moves through a fluid or gas, like warm air rising.
Radiation is the transfer of heat through electromagnetic waves, like sunlight warming your skin.

In space, there is no air or material to conduct or convect heat. Instead, the Sun’s energy travels as radiation—specifically, infrared and visible light waves. These waves don’t need air or particles to travel; they move freely through the vacuum of space. When they hit an object, like an astronaut or a spacecraft, they transfer heat to it.

Humans in Space

Since space is a vacuum with almost no matter, there’s nothing to retain heat. Without an atmosphere to trap warmth, most of space remains extremely cold. The average temperature of space is about -455°F, which is just a few degrees above absolute zero (-459.67°F), the coldest possible temperature.

If you were floating in space without a spacesuit, the experience would be extreme. The side of your body facing the Sun would heat up quickly, potentially reaching temperatures over 250°F—hot enough to boil water!

Meanwhile, the side facing away from the Sun would lose heat rapidly and could drop to -250°F—colder than Antarctica’s coldest temperatures.

In a proper spacesuit, astronauts are protected by reflective materials that manage heat. The suit prevents dangerous overheating or freezing, allowing astronauts to survive in space’s harsh environment.

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What Would Happen Without a Spacesuit?

If you suddenly found yourself floating in space without a spacesuit, you wouldn’t survive for long—but the way you’d die might not be what you expect.

1. You Wouldn’t Explode

Movies sometimes show people bursting in space, but that wouldn’t happen. However, because space is a vacuum (with no air or pressure), the gases in your body would expand. Your skin and organs would keep you from bursting, but your body would swell up.

2. You Couldn’t Breathe

Since space has no oxygen, you’d pass out in about 15 seconds from lack of air. Holding your breath wouldn’t help—trying to do so could cause your lungs to rupture as the air inside expands.

3. You’d Experience Extreme Temperatures

If you were in direct sunlight, you’d heat up quickly to 250°F (121°C).
If you were in the shade, you’d lose heat and could freeze at -250°F (-157°C). However, you wouldn’t freeze instantly because heat leaves your body slowly in a vacuum.

4. Your Blood Would Start to Boil

With no atmospheric pressure, the boiling point of liquids drops. This means the fluids in your body—like saliva and blood—would start to form gas bubbles, causing swelling and tissue damage.

5. You’d Die in About 1–2 Minutes

Without oxygen, you’d likely be unconscious in seconds and dead within 1 to 2 minutes from suffocation and decompression.

Could You Survive?

If you were quickly rescued (within about 30 seconds), you might survive with some injuries, like swelling and internal damage. But without protection, space is one of the most dangerous places for the human body!

The History of Human Space Exploration

The Space Race (1950s–1970s)

During the Cold War, the United States and the Soviet Union (USSR) competed to be the first to explore space. This became known as the Space Race.

1957 – The Soviet Union launched Sputnik 1, the first artificial satellite.
1961 – Yuri Gagarin (USSR) became the first human in space, orbiting Earth in Vostok 1.
1961 – Alan Shepard became the 1st United States astronaut to fly into space aboard Freedom 7 as part of the Mercury Program.
1969 – NASA’s Apollo 11 landed the first humans on the Moon. Neil Armstrong and Buzz Aldrin walked on the Moon while Michael Collins stayed in orbit. Click here to learn more about the first moon landing.

Click Here to Learn More about NASA's Space Programs:

Project Mercury

Project Gemini

The Apollo Program

How Many People Have Walked on the Moon?

A total of 12 astronauts have walked on the Moon, all of them part of NASA’s Apollo program between 1969 and 1972.

There were six successful Moon landings out of the Apollo missions:

Apollo 11 (1969) – Neil Armstrong & Buzz Aldrin (First Moon landing)
Apollo 12 (1969) – Charles Conrad & Alan Bean
Apollo 14 (1971) – Alan Shepard & Edgar Mitchell
Apollo 15 (1971) – David Scott & James Irwin (First use of the lunar rover)
Apollo 16 (1972) – John Young & Charles Duke
Apollo 17 (1972) – Eugene Cernan & Harrison Schmitt (Last humans on the Moon)

Apollo 13 was supposed to land on the Moon, but an oxygen tank explosion forced the crew to abort the mission. Instead of landing, they used the Moon’s gravity to slingshot back to Earth. This took them farther from Earth than any other astronauts in history. Click here to learn more about Apollo 13.

Astronaut Buzz Aldrin - Apollo 11 - 1969

The Space Shuttle Era (1981–2011)

After the Moon landings, space agencies focused on building reusable spacecraft. NASA developed the Space Shuttle, which carried astronauts and equipment to space.

1981 – The first Space Shuttle, Columbia, launched.
1998 – The International Space Station (ISS) began construction, allowing astronauts from multiple countries to live in space.
2003 – The Columbia disaster led to the retirement of the Space Shuttle in 2011. Click here to learn more about the Columbia disaster.

Space Shuttle Discovery

Modern Space Exploration (2010s - Today)

With the Space Shuttle retired, NASA partnered with private companies like SpaceX and Boeing for space travel.

2011–2020 – NASA relied on Russia’s Soyuz spacecraft to send astronauts to space.
2020 – SpaceX Crew Dragon became the first private spacecraft to send astronauts to the ISS.
2022 – NASA launched Artemis I, the first step toward sending humans back to the Moon. Click Here to Learn More About The Artemis Program
Present – Countries like China and India are expanding their space programs, with plans for Moon and Mars missions.

SpaceX Crew Dragon

NASA Artemis I

SpaceX and Mars

SpaceX, founded by Elon Musk in 2002, has revolutionized space travel with reusable rockets and ambitious plans to make humans a multiplanetary species. Its biggest goal? Colonizing Mars.

Elon Musk believes humanity needs a backup planet in case of disasters on Earth. Mars is the best option because:

It has an atmosphere (although thin).
It has water ice, which can be turned into drinking water and fuel.
It’s the most Earth-like planet in our solar system.

But getting to Mars is extremely difficult. That’s why SpaceX is developing Starship—the most powerful rocket ever built.

SpaceX's Elon Musk

Mars

SpaceX Plans to Get to Mars

1. Starship: The Mars Rocket

100% reusable spacecraft designed for deep-space travel.
Height: 394 feet (120 m) – taller than Saturn V, the rocket that took astronauts to the Moon.
Launches on Super Heavy booster (which returns to Earth for reuse).
Can carry over 100 people and cargo to Mars.

2. Fueling Up in Space

Since carrying all the fuel from Earth would be too heavy, SpaceX plans orbital refueling:

Starship launches into Earth’s orbit.
A tanker Starship brings extra fuel and refuels the Mars-bound ship.
Fully fueled Starship heads to Mars.

3. Surviving on Mars

Once people land, they will need:

Life support systems to produce oxygen.
Mars habitats (pressurized shelters for living).
Food production (hydroponic farming).
Fuel production (using Mars’ atmosphere to make rocket fuel for return trips).

SpaceX plans to use local resources so that astronauts won’t need to bring everything from Earth.

SpaceX's Starship

SpaceX Mars Timeline

2026–2030: Unmanned Starship test flights to Mars.
Early 2030s: First humans land on Mars.
Mid-2030s and beyond: Building the first Mars colony.

Musk envisions a self-sustaining city on Mars within the next 50–100 years, making humans a true spacefaring civilization.

While challenges remain, SpaceX’s Starship, reusable rockets, and ambitious vision could make Mars exploration a reality sooner than we think! Click here to learn more about SpaceX's Mars Mission.