Orbit is falling and missing
Being in orbit has almost nothing to do with height and everything to do with sideways speed. Isaac Newton explained it with an imaginary cannon on a very tall mountain: fire the ball gently and it lands nearby, fire it harder and it lands further off, fire it hard enough and the surface of the Earth curves away beneath it exactly as fast as it falls. It never lands. It is in orbit.
That speed is around 28,000 kilometres an hour close to Earth. A ROCKET spends a little of its effort climbing out of the thick air and nearly all of it going sideways fast enough to keep missing the planet. Astronauts float not because gravity has switched off, but because they and their STATION are falling together, all the time.
Most of a rocket is fuel
A ROCKET is essentially a set of tanks with an ENGINE bolted underneath. Around nine tenths of what sits on the LAUNCHPAD is FUEL, and an empty tank is just dead weight to carry, so rockets throw pieces of themselves away as they climb. That is what a BOOSTER separating actually is: the machine shedding the parts it has finished with.
For sixty years that meant destroying something worth tens of millions on every single flight. Rockets that fly their first stage back and set it down upright have changed the sums completely, and individual boosters have now flown and landed more than twenty times each.
Meeting something else up there is its own puzzle. Both craft are already travelling at that enormous speed, so DOCKING is not about catching up but about matching: nudging with a THRUSTER until the gap closes at the pace of a slow walk, then a few centimetres a second at the moment of contact.
Re-entry heat is not friction
Coming home is harder than leaving. A CAPSULE arrives travelling at orbital speed and has to lose nearly all of that energy, which turns into heat. Almost everyone calls it friction, and almost everyone is wrong. The heat comes from compression: the spacecraft hits the air faster than the air can move out of the way, squashing it into a shockwave that reaches thousands of degrees.
That is why a REENTRY vehicle is blunt rather than sharp. A wide, rounded heat shield holds the shockwave out in front of the craft instead of hugging the skin, and many shields are designed to char and flake away, carrying the heat off with the pieces.
Machines that outlive their missions
Space hardware has a habit of lasting far longer than planned. The Mars ROVER Opportunity was built for ninety days and worked for fifteen years, covering more than a marathon's distance across the surface before a planet-wide dust storm finally silenced it in 2018.
The International STATION has had people aboard continuously since November 2000, circling the Earth every ninety minutes, so the crew sees sixteen sunrises a day. And robots keep taking the jobs no ASTRONAUT could: a LANDER on a comet, a PROBE heading past the outer planets, a TELESCOPE parked a million miles out looking back at the earliest galaxies. Nothing has to come home again, which is the only reason those missions are possible at all.