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17 Facts About Space Travel That Will Make You Go "Huh"

Robots have basically taken over the solar system, and it's great.

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1. Satellites aren't floating in space. They're falling, forever.

Lookang / CC / Via commons.wikimedia.org

Gravity is almost as strong in low Earth orbit (LEO) – where the International Space Station and lots of other satellites are – as it is on Earth's surface. But the satellites are moving so fast that they fall along the curve of the Earth. If they were travelling a bit slower, they'd spiral in and crash; if they were travelling faster, they'd spiral out and head into space.

2. Almost all of the weight of a rocket on the launchpad is just fuel.

NASA / Via en.wikipedia.org

There are some really stark equations involved in getting to space. If you want to take stuff into orbit, you need to get it travelling at about 8 kilometres a second – faster, if you want to leave orbit. To do that, you need a lot of fuel. But to carry that fuel up with you, you'll need more fuel. And to carry that fuel… The numbers get very large very quickly. About 85% of the 2,900-tonne mass of the Saturn V rockets used in the Moon launches were just rocket fuel.

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3. When a spacecraft uses a planet to speed itself up, the planet slows down a bit.

ESA / Via i.imgur.com

Spacecraft often boost their speed by flying close to a planet, falling towards it, and stealing a bit of its speed – it's a little like bouncing a ball off the front of a car as it moves towards you. But it steals a little bit of the planet's energy as it does so. When the Voyager 1 probe flew past Jupiter, it sped up by about 16,000 metres per second (m/s), while Jupiter slowed down by about 0.00000000000000000001m/s.

4. If the Earth was the size of a football, then no humans would have gone more than about 2cm from its surface since we last went to the moon, 44 years ago.

Pumbaa80 / mattbuck / BuzzFeed / CC / Via commons.wikimedia.org

Almost every manned space flight has been in low Earth orbit, aka LEO, which means no more than about 1,000km above the ground. The only humans who have ever left LEO were the 24 men on the Apollo lunar missions, which ended in 1972.

5. By the way, if Earth were the size of a football, the sun would be about 25 metres across. The sun is quite big.

lmspascale / CC / BuzzFeed / Via en.wikipedia.org

It would also be about 2,500 metres away. The nearest star, Proxima Centauri, would be more than 70,000km away, about a third of the distance to the (real-life) moon. Space is quite big.

6. But we're in a golden age for space robots. There are two rovers crawling around on the surface of Mars right now.

NASA / JPL / Via en.wikipedia.org

This is a selfie taken by Curiosity, the most recent robot to have landed on Mars. It's found extraordinary things, including evidence of flowing water. The other active one is Opportunity, which has been trundling around for 12 years.

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9. And there's another one which has entered the orbit of Jupiter just last week.

After 5 years traveling to #Jupiter, @NASAJuno arrives today! This video shows a peek of its final approach: https://t.co/ysOKuGUWaQ

There was also the probe we landed on a comet, and the one that's flying around Mercury, and one around Venus, and – look, there are quite a lot of robots whizzing around the solar system, basically.

10. New Horizons, which flew past Pluto last year, is so far away that it takes 4 hours, 25 minutes for its radio messages to reach Earth.

NASA / Via pluto.jhuapl.edu

It's transmitting photos at a data rate of about 2kb/s – roughly equivalent to a dial-up modem in the mid-1980s. It'll take it until the end of this year to send all the images from the Pluto flyby back to mission control.

11. Then there are the Voyagers. Voyager 1 is travelling at 17,000m/s, or 38,000 miles per hour. That means it would travel from New York to London in five minutes.

NASA / JPL / Via en.wikipedia.org

The Voyager missions launched in 1979, heading towards the outer solar system.

12. Getting Voyager 1 to reach Neptune accurately was the equivalent of sinking a 3,630km (2,260 mile) golf putt.

YouTube / Lookit / Via youtube.com

That is "assuming that the golfer can make a few illegal fine adjustments while the ball is rolling across this incredibly long green", says NASA.

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13. Even though it's going so fast, for part of the year, Voyager is actually getting closer to Earth.

Tau'olunga / CC / Via en.wikipedia.org

That's because the Earth itself is moving even faster – about 30,000km/s, or 67,000 miles per hour. Feel the wind in your hair! (You can't, obviously, because the Earth's atmosphere is moving at the same speed. If it wasn't it would kill you pretty much immediately.)

14. And after 37 years, Voyager 1 has still only just made it out of the solar system.

NASA / Via nasa.gov

It's more than 20 billion kilometres, about 12 billion miles, from Earth, but it's only just reaching interstellar space. If you're wondering how the boundary between "the solar system" and "interstellar space" is defined, there's more info here.

17. …and learn more about them by the day.

NASA / Via nasa.gov

Twenty years ago, we didn't know there were any planets outside our own solar system. Now we know about more than 3,000, most of which were discovered by the space telescope Kepler – which once announced 715 new planets on a single day in 2014.

CORRECTION

If the Earth was the size of a football, the sun would be about 2,700 metres away; the mass of the Saturn V is 2,900 tonnes; and the velocity needed to reach orbit is a little less than 8km/s. An earlier version of this piece misstated these numbers.

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