Egg Lander
A few key points before we start to design our own Martian Lander.
Mars has 38% the gravity of Earth. So things weigh less, in other words, if you weigh 100 kg on Earth, your weight on Mars is 38 kg. Just keep in mind that there is a difference between mass and weight. Mass is actually the amount of matter measured in kilograms while the weight is the force that is pushing you down on the scales. So astronauts would have the same mass a here on Earth but have only 38% of their weight on Mars. Its low gravity is due to the fact that Mars is, about, half the size of Earth.
Martian atmosphere is quite different from that of Earth with atmospheric pressure being more than a hundred times lower than on Earth. Martian atmosphere atmosphere is almost entirely composed of carbon dioxide. However, the atmosphere is thick enough to support strong winds and huge dust storms the play havoc with Martian Rovers solar panels.
The Martian conditions make it easier to land and take off. The low atmosphere reduces the forces of drag during take off and the low gravitational force decreases the escape velocity necessary for vehicles to escape the Martian surface. Escape velocity on Mars is 18072 km/h, that being 45% that of Earth's escape velocity. This means we have to use less fuel to escape and therefore less fuel that has to be carried onboard from Earth.
The speed with which an object falls, known as terminal velocity, is also a factor. Terminal velocity of a falling body occurs when the body experiences zero acceleration. This is because of the retarding force known as air resistance or drag. Air resistance (drag) exists because air molecules collide into a falling body creating an upward force opposite to gravity. This upward force and gravity will eventually balance each other and the object will descend at constant speed.
A particular object at free fall reaches a terminal velocity of 53m/s on Earth.
A low air pressure on Mars would cause the terminal velocity of this object to
Explain why.
A lower force of gravity than on Earth would cause the terminal velocity of this object to Explain why.
What factors determine the terminal velocity an object can reach on Earth?
What happens when a skydiver stretches their arms and legs out as shown above?
The graph on the right shows the speed of an object falling on an unknown planet over time.
Does the planet have an atmosphere? How can you tell?
What two forces are acting on the object?
What is the terminal velocity of the object?
How would the speed vs time graph be different for an object twice the size but weighing the same as this object?
The same object on Earth reaches a terminal velocity of 53 m/s in 3 seconds. Compare the atmosphere and size of this planet with the Earth. Explain your reasoning
Lets follow the deployment of Martian Rovers.
Firstly we must escape the Earth's gravity by accelerating our spacecraft to around 40,000km/h. This takes a great deal of energy.
Once out of the Earth's atmosphere the protective shield can be discarded and the landing craft is accelerated towards its destination.
The engine attached to the landing craft is discarded and a second stage engine accelerates the craft to a greater speed.
Once in orbit around Mars the lander separates from the orbiting vehicle and starts its voyage to the surface. A heat shield protects it from the heat created by frictional forces as it hurtles through Mars' thin atmosphere.
Parachutes are deployed to slow the lander to a safe speed, while the heat shield is ejected. Air bags inflate around the lander and it is ready to be dropped onto the surface.
Once the lander is at a safe altitude the connection is severed and the lander hits the surface bouncing for hundreds of metres before it comes to a complete stop.
The lander unfolds and the Martian Rover emerges.
A huge parachute would have been enough to slow the Lander here on Earth but on Mars rockets also need to be used. Why?
Design a lander to deliver a sensitive probe to the surface of a planet which is one tenth the size of the Earth and has no atmosphere. The device must carry a raw egg safely to the ground from a height of at least 5m. The rules include:
- no padding such as styrene, paper or any other shock absorbing material. However inflatable balloons can be used, however, this is not practical as space in a shoe box is limited, unless some mechanism is devised to inflate the balloons after the lander exits the shoe box.
- the lander must fit into a shoe box and when tipped upside down must return to the right way up position before landing.
- it must extend to twice its length as soon as it leaves the shoe box, which simulates the orbiting vehicle.
The lightest lander that delivers a raw egg safely to the ground and meets all the above requirements is the winner.
