Space Exploration

Season 05

Episode 02

Duration 23:19

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Space is only about 300 kilometres above your head, but it takes an enormous machine to get there. In this episode of Bill Nye the Science Guy, Bill shows why rockets are so big, how gravity keeps spacecraft in orbit and why the vacuum of space means astronauts have to take their whole environment with them.

In this episode you will discover:

Why gravity pulls a spacecraft down even when it is in orbit
How going fast enough sideways lets a ship “fall around” the Earth
Why rockets need a fuel tank many times bigger than the spacecraft
What the vacuum of space would do to an unprotected human body
How spacesuits pressurise, cool and supply oxygen for one person
How the Hubble Space Telescope opened up a clearer view of the universe

Falling around the Earth

Bill uses a car on a string swung around a model to show how orbit works. Sideways motion tries to send the spacecraft off in a straight line, while gravity keeps pulling it back towards Earth, so the two together curve its path into a circle. The spacecraft is still falling; it just keeps missing the ground. To reach that speed at all takes a huge push, which is why almost the whole of a rocket like the Saturn V is a fuel tank.

Key concept
Orbit
A curved path where a spacecraft keeps falling towards Earth while moving sideways fast enough to keep missing the ground.

Key concept
Rocket
A machine that carries almost all of its own fuel because gravity is trying to hold it on Earth from launch to orbit.

Key concept
Spacesuit
A pressurised, airtight, self cooling suit that supplies its own oxygen, working like a tiny spacecraft for one person.

Bill Nye’s demonstrations

Bill swings the hot rod on a string of science to show how a sideways force and a pull toward the centre combine into an orbit. He visits the Clark refractor at Lowell Observatory in Flagstaff, tours the Kennedy Space Center gantry tower and white room where astronauts wait to board the shuttle, and dresses in the water cooled undergarment and pressurised space suit at Johnson Space Center. He also puts cherry soda in a vacuum chamber so the gas boils out, to show what would happen to an unprotected astronaut’s blood in the vacuum of space.

Try this at home

The orbit on a string. Tie a small ball or eraser to a piece of string. Whirl it in a horizontal circle above your head. Your hand pulling in on the string is gravity; the ball’s forward motion is orbital velocity. Slow the ball down and it spirals in; let go of the string and it flies off in a straight line. That is how a spacecraft in orbit keeps falling towards Earth without ever landing. Do this in an open space away from windows.

The vacuum in a marshmallow. Put a fresh marshmallow inside a syringe with the tip sealed, then pull the plunger back to lower the pressure inside. The tiny air pockets inside the marshmallow puff up because there is less air pressing on the outside. Push the plunger in and the marshmallow shrinks. This is why the human body needs a pressurised suit outside a spacecraft.

Cool facts

Space begins about 100 kilometres above the ground at the Karman line, and the space shuttle orbited at around 220 kilometres.
The Saturn V rocket that carried astronauts to the Moon stood over 110 metres tall and was almost entirely fuel.
Space shuttle heat shield tiles were so good at dissipating heat you could hold one by the edges seconds after taking it out of the oven at over 1200 degrees Celsius.
Astronauts rehearse spacewalks in a huge pool because floating in water is the closest thing on Earth to floating in orbit.

Science update: since this episode aired

The Hubble Space Telescope that Bill mentions now has a successor. The James Webb Space Telescope, launched on an Ariane 5 from French Guiana in December 2021, has a mirror almost six times bigger than Hubble’s and collects infrared light from galaxies formed after the Big Bang. European Space Agency, Webb factsheet
In August 2023 India’s Chandrayaan-3 mission set the Vikram lander down softly near the Moon’s south pole, making India the fourth country to soft land on the Moon and the first to reach that unexplored polar region, which is thought to hold water ice. Nature India, 2023
China now runs its own permanently crewed space station, Tiangong, whose three modules Tianhe, Wentian and Mengtian were assembled in low Earth orbit between 2021 and 2022 with launches from Wenchang. Global Times, Beijing

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Curriculum focus

Built on NGSS MS-ESS1-2 (the role of gravity in the motions of orbiting objects) and MS-ESS1-3 (analysing data on scale properties of objects in the solar system). Complementing that, it is pitched at KS3 physics (space physics and gravity) and works as an introduction or revision aid for GCSE and IGCSE physics on gravity, orbits and the solar system, across boards such as AQA, Edexcel, OCR and Cambridge IGCSE. The worksheet and critical thinking questions take these ideas further than the episode alone.

NGSS MS-ESS1
KS3 physics
GCSE revision
IGCSE revision
Gravity
Orbits