Maybe you've got a cardboard box, scissors, and some glue to get started... and hopefully

billions of dollars.

But where do you actually start?

Well, let's look at some of the space stations that have orbited the Earth and had astronauts

or cosmonauts inside.

The first was in 1971, when the Soviet Union designed the Salyut-1, which was basically

a two-room satellite with a docking compartment so cosmonauts could enter.

Over the next decade, the Soviet Union launched more versions of the Salyut, all the way up

to Salyut-7.

Most of them had crews for just a couple months at most, before the empty space stations were

sent back into Earth's atmosphere to safely burn up over the oceans.

But a big breakthrough came in the 1980s, when the Soviet Union built a brand new space

station called the Mir.

The Mir was occupied by cosmonauts for over 12 of the 15 years it spent in space, and

it was unique because it was a modular space station.

Basically, every component of the space station was made separately on Earth, and everything

was put together in space.

This means you can add in new parts, depending on the mission.

Kind of like playing with Legos.

But the tricky part is connecting these pieces together.

There are different ways to do a space rendezvous, but one of the key techniques is called a

Hohmann transfer.

To start out, you want to launch your module into orbit, but closer to Earth than the rest

of the space station.

Then, you ignite the module's engines with two carefully-timed pulses -- the Hohmann

transfer -- to push the module into a higher circular orbit, closer to the station.

When the moment is just right, the module performs another Hohmann transfer to get right

in front of the space station.

Then, the module does a 180 degree U-turn and is steered into a docking platform, where

robotic arms or astronauts can help make the final connections if needed.

Pull it off, and you've built a modular space station like the Mir -- the biggest

man-made object ever to be in space, before its mission ended and it had a controlled

re-entry into Earth's atmosphere in 2001.

But in 1998, the International Space Station program was launched and quickly broke that

record.

The ISS is currently the size of a US football field, weighs over 300,000 kilograms, and

has been occupied by astronauts for over 15 years now!

It's also a modular space station, made up of 16 pressurized modules.

And 16 countries helped with the work, including Canada, the US, Russia, Japan, Brazil, and

some in the European Space Agency.

All of these modules have their own role, but we'll start with the basics: Zarya,

Unity, and Zvezda -- the first three modules of the ISS.

Zarya was the very first module and responsible for the main propulsion, some communication

with Earth, and had two solar arrays to provide electrical power.

But now that we have new modules, Zarya is mainly just used for storage.

Unity is a big connector piece that has over 50,000 cables, pipes, and mechanical parts

-- which connect electronic systems and transport fluids to create a stable, livable environment.

Zvezda is responsible for some of the main controls, and has life support systems, with

enough room for two astronauts to live.

These starting modules were built in Russia and the US, and didn't meet until they were

orbiting around the Earth... at over 20,000 kilometers per hour.

They all pulled off the proper maneuvers in space, including the Hohmann transfer, and

formed the humble beginnings of the ISS!

Then, more modules were added, such as science laboratories like Destiny, Columbus, and Kibo.

Or more connectors, like Tranquility and Harmony.

The ISS also added the Integrated Truss Structure, which is designed to connect external equipment

to the modules -- like big solar arrays.

They've even got a big robotic arm that can do work outside the space station, like

moving supplies, maintaining the station, and even attaching more modules.

And right now, the ISS is experimenting with a new expandable module called BEAM.

It was compressed into a small capsule when it was launched in April 2016, was expanded,

and is currently being tested for its living and working capabilities.

As of today, there are only two space stations in orbit -- the ISS, and China's Tiangong-1,

which is much smaller and part of a CNSA program to create their own large modular space station

by 2023.

Right now, only trained astronauts are living on these space stations.

But some companies hope that inflatable modules like BEAM could eventually host tourists.

And if that's true, maybe someday you can go up yourself and get a real feeling for

how these space stations are built.

Thanks for watching this episode of SciShow Space, and thanks especially to our patrons

on Patreon like Amy Cohen and Samuel E Joseph who help make this show possible.

Thanks Amy and Sam for supporting SciShow and sending us your great, thought-provoking

questions.

If you want to help us keep making episodes like this, just go to patreon.com/scishow

to learn more.

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