31 Oct 2014 No Comments
This activity asks children to think about what drives a rocket, how hard it is to leave our Earthly home in any grand scale through rocket technology, and also to think about what it might be like to ride one of these ungainly beasts into space.
- Two Seater “Rocket” Cart, see below. Or skateboard, helmet and medicine ball if “Rocket Cart” not available.
- Extract of “When We Left The Earth”; interviews with William Anders, Frank Borman and James Lovell on their Apollo 8 mission to circle the Moon and become the first humans ever to see the dark side of the Moon. Copy can be seen on YouTube here.
- Simple straw or cleaning broom;
- Imaginative and Curious Children (that’s most if not all children, in my experience);
The “Rocket Cart” is a billy cart with (i) very free running, low friction wheels (bicycle wheels are best), (ii) preferably enough room for two children and a washing basket holding between five and ten, 2kg medicine balls.
6 to 16
This activity is best done in a sports hall or somewhere where there is a wide space to move in with a very smooth, polished floor. This activity could be done as a physical education class.
Sit in the rocket cart or stand on the skateboard. Move your arms or other parts of your body. What happens to the cart/skateboard? Can you move in such a way that the cart/skateboard runs continuously in a given direction? Otherwise put: could you move your body so as to get from one end of the sports hall to the other?
Now, do this experiment again, but whilst holding a medicine ball. Throw the medicine ball either directly forwards or backwards (in the direction that the cart/skateboard is pointing). What happens?
If you have the “rocket cart”, take turns at being part of the crew to fly it. See how fast you can get it going as follows. Countdown to “blast off” and then begin throwing the medicine balls, one after the other, either directly forwards or backwards (along the direction that the cart is pointing). This will work best with two “pilots”: one to steer, and one to be the “rocket engine” and throw the medicine balls.
What do you notice?
Below I’ve plotted the speeds you see for a cart of kilograms, two children weighing 10 and 22 kilograms throwing ten, 4 kilogram medicine balls. The child in this case could throw the ball at about 0.9 metres a second. That’s just over three kilometres an hour. You can download a spreadsheet I’ve used to do these calculations by clicking here.
Now I’ve plotted the speed of a “Rocket Cart” that was more like the Apollo 8 Launch Vehicle, that blasted the eighty tonne Apollo spacecraft to the Moon. This “Rocket Cart” weighed eighty tonnes, but it burnt and threw out 20 tonnes of fuel each second, and the force of burning threw this 20 tonnes a second out at a speed of about two and a half kilometres a second. The rocket’s weight on launch was almost all fuel; four thousand tonnes of fuel were needed to get eighty tonnes of spacecraft to the Moon.
In a matter of minutes, the spacecraft was accelerated to a speed of eleven kilometres a second, fast enough to reach the Moon, and then “fall” back to Earth. The rocket engines burned for less than ten minutes in a journey that took ten days. You can download this spreadsheet by clicking here.
You might like to find out about the spacecraft Voyager 1. Where is this spacecraft? How long has it been travelling? What keeps it travelling so long?
Thinking About Leaving Home
Watch the video of the launch of Apollo 8 on YouTube here. Some questions to get you thinking about a trip to the Moon, and also some of the things that were happenning fifty years ago.
Find out how much of the enormous rocket actually got to the Moon. On a photograph of the rocket, colour the part that went all the way to the Moon and back in. With a different colour, mark the part that reached the Moon.
William Anders: “Somebody had the bad taste of telling it was like a two kiloton (two thousand tonnes of dynamite) nuclear explosion if it blew up. So, we just hoped it wouldn’t blow up!”
Do people stay in the launch tower throughout the launch? Why? Bear in mind that the horrible bomb that levelled Hiroshima in 1945 was equivalent to about seven thousand tonnes of dynamite.
Bear in mind that all this happened nearly fifty years ago, when I was but four years old, and technology was very old and primitive. Most astounding in my mind is the thought that even the humblest mobile phone today has far more computing power than the computers that were on the rocket and whereon the astronauts’ lives totally depended. A rocket cannot fly like an aeroplane, which thrusts air downwards so that the air lifts the aeroplanes wings up. Rather, a rocket is lifted up from its hinder end by the force of the engines, and it is rather like lifting a broom balanced upright on the end of your hand.
Try balancing a broom like this; how do you keep it upright?
As the rocket tips and tilts, the computers feel the tilt through special sensors and swivvel the engines to stop the rocket from falling over. A failure of these tiny, primitive computers would have meant almost certain death for the astronauts. Not only this: the computers were responsible for the spacecraft’s navigation. There was no Google Maps, no GPS, no Tom-Tom.
What is the device below? When and where was it mainly used?
taken from “Sextant” Wikipedia Page
The Apollo missions also carried a ship’s sextant, just like the ones used at sea. On one occasion (Apollo 13), the astronauts had to use it to check and correct the computer’s navigation on the way to the Moon.
The rocket engines lift the spacecraft above the earth’s atmosphere and throw it into orbit exactly the same way that you would lift your upright broom up to the ceiling.
Once in orbit, the engines stop whilst checks are made before blasting off again to the Moon; why doesn’t the rocket fall back to Earth?
You might like to expore the idea that if something moves parallel to the Earth’s surface fast enough, the Earth’s curvature is such that the surface of the Earth “falls away” from the object at exactly the same speed that the object falls to Earth. Explore this idea with a ball or globe. So the object “falls around” the Earth; this happens at about twenty five thousand kilometres an hour.
William Anders: “I had decided that there was about a one third chance that the flight would be totally successful. Then I thought that there was a one third chance that we wouldn’t make it back.“
William Anders was saying something like this: I was willing to play a game of dice wherein if I rolled a 5 or a 6, then I would become one of the first people to circle the Moon. But if I rolled a 1 or a 2, I would die.
Would you play such a game? Why do you think someone would be willing to do this?
William Anders: “The sideways shaking was unbelievable, the vibration so intense you could not see the instrument panel. I thought we’d had it during the launch”
How would you feel at the beginning of a flight like this? Do you think fear would be helpful if you were an astronaut?
Listen to James Lovell and (Malcolm) Scott Carpenter (from 9:30 minutes onwards) talk about their fear. James Lovell’s experience seems to be the commoner one, but Scott Carpenter’s is surely the more interesting and seldom.
Scott Carpenter: “There’s nothing wrong with being afraid. It means you will do a better job“.
Frank Borman: “The mission was more important than anybody. It was more important than our lives, our families. That’s what we were there for. We were killed more times in simulation than you can shake a stick at”.
How would you feel if your father or mother were an astronaut and said this?
Watch Neil Armstrong embrace his little daughter after a risky test mission of the X15 experimental aeroplane. How old do you think this little girl is? What do you think she feels on seeing her father come back?
Frank Borman: “It was very, very cold. We sat in there and shivvered and froze.”
Why was it so cold? Think about what was inside the main rocket and why. What is the main difference between a rocket and a jet aeroplane?
As the rocket engines start up, the rocket is held back by big pins until the rocket computers tell the pins, “I am ready, let me go”.
Why must the rocket be held back until the engines start fully up? Why can’t it simply light its engines and be lifted off? (Think back to the broom)
What are all the huge chunks and white powder raining down on the ground just after the launch?
What colour is the fire at launch? Is it cooler or hotter than the Sun’s surface? Why doesn’t the rocket burn up?
Frank Borman says that the rockets yield about seven and a half million pounds of thrust. That’s enough to lift a weight of 3 500 tonnes. If the rocket and its fuel weigh two thousand tonnes, how much could the rocket lift off the Earth’s surface.
How much is this?: find out the weight of an elephant, a car, a fully laden semitrailer lorry, an A380 Airbus fully laden, a fully laden six metre shipping container. How many of each of these things could the rocket lift?
The rockets burnt 20 tonnes (20 000kg) of fuel each second. Let’s find out how much it would take your car to burn this much fuel. If the fuel weighs 1 kilogram for each litre, how many litres of fuel is this? How much fuel do you put in your car to fill its tank from empty? How often do you fill the tank? How long would 20 tonnes of fuel last? A litre is one tenth of a metre times one tenth of a metre times one tenth of a metre. So how many litres are there in a cubic metre? A big backyard swimming pool is four metres wide, two metres deep and five metres long? How many litres is this?
What is the collar of vapour that shows up fleetingly on the rocket and then vanishes about one minute after launch?
What is the colour of the fire when the third stage main engine starts up? Why?
I have myself always thought of sending people to the Moon somewhat silly. But in the 1960s a person on the Moon could do something that a robot couldn’t have then. He or she could find rocks and bring them back to Earth. So here is a question leading to the most astounding finding of those missions:
What did we find out the Moon was made of? Why were the rocks that were brought back special? Why were they NOT special? Find out about the “Genesis Rock”.
Another iconic photograph from the 20th Century was taken on this mission by William Anders. It is shown below and is called “Earthrise”. We see here our home – all that most of us shall ever ken or know – as a tiny globe in the blackness of deep space.
A few years after William Anders took this photograph, the Voyager 1 Spacecraft was launched (1977). In 1990, it took the famous Pale Blue Dot photograph of our Earth from roughly the distance of Pluto (about six thousand million kilometres away) – the biggest known dwarf planet in the Kuiper Belt at the Solar System’s edge. Our Earth is the tiny blue dot at about halfway height in the brown band at the right of the photograph. The bands themselves are swathes of dust orbitting the Sun, leftover from the Solar system’s formation.
Carl Sagan (1994 from his book “Pale Blue Dot: A Vision of the Human Future in Space”) From this distant vantage point, the Earth might not seem of any particular interest. But for us, it’s different. Consider again that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.