The Earth’s orbital speed around the sun provides an initial velocity in space when heading to another part of the solar system. The time of the year for launch is chosen depending on which direction the Earth is heading and where you want to go. Discuss the effect of the Earth‘s orbital motion and its rotational motion on the launch of a rocket

‘g forces’ refers to the ratio of apparent weight during launch to normal true weight. It is a convenient indicator of the forces on astronauts body. CAUTION: a ‘6g’ launch may also refer to an acceleration of a = (6 x 9.8), giving an apparent weight of 7g ! (and a g-force of 7) A rocket accelerating upwards at 9.8 m/s 2 causes the astronaut to experience a g-force of 2. A rocket accelerating upwards at 19.6 m/s 2 causes the astronaut to experience a g-force of 3. A stationary or constant velocity rocket causes the astronaut to experience a g-force of 1. A rocket accelerating upwards at 49 m/s 2 causes the astronaut to experience a g-force of 6. Identify why the term ‘g forces’ is used to explain the forces acting on an astronaut during launch Rollercoaster simulation

If we know the initial mass of the rocket, the Rate of expulsion (kg/s) and how long it has burnt for, we can work out the new mass of the rocket. During launch, the momentum of the propellant expelled downwards (per second) produces a thrust force upwards. For a moving (inertial) frame of reference: i.e. total momentum is unchanged If this thrust force exceeds the weight of the rocket system, the rocket begins to accelerate upwards. As the rocket expels more and more propellant, the mass of the rocket system decreases. If the thrust force remains constant, Newton’s Second Law tells us that the acceleration will increase. Conservation of momentum tells us that the change in momentum (= Impulse = Force x time ) down produces an Impulse up. So an upwards force (thrust) is produced. Water Rocket Experiment Analyse the changing acceleration of a rocket during launch in terms of the: – Law of Conservation of Momentum

If we know the initial mass of the rocket, the Rate of expulsion (kg/s) and how long it has burnt for, we can work out the new mass of the rocket. During launch, the momentum of the propellant expelled downwards (per second) produces a thrust force upwards. For a moving (inertial) frame of reference: i.e. total momentum is unchanged Analyse the changing acceleration of a rocket during launch in terms of the: – Law of Conservation of Momentum – forces experienced by astronauts If this thrust force exceeds the weight of the rocket system, the rocket begins to accelerate upwards. As the rocket expels more and more propellant, the mass of the rocket system decreases. If the thrust force remains constant, Newton’s Second Law tells us that the acceleration will increase. Conservation of momentum tells us that the change in momentum (= Impulse = Force x time ) down produces an Impulse up. So an upwards force (thrust) is produced. The astronauts will experience g-forces produced by this net increasing acceleration while the rockets burn propellant. When the burn finishes, the rocket will continue to move at a constant velocity (subject to drag).

(Graphic from HSC Online) The astronauts will experience changing g-forces produced by this net increasing acceleration while the rockets burn propellant. When the burn finishes, the rocket will continue to move at a constant velocity (subject to drag). Analyse the changing acceleration of a rocket during launch in terms of the: – forces experienced by astronauts

He proposed the use of reaction motors that were powered by liquid fuels. He suggested the use of green plants to provide oxygen to space crew and dispose of carbon dioxide Identify data sources, gather, analyse and present information on the contribution of one of the following to the development of space exploration: Tsiolkovsky, Oberth, Goddard, Esnault-Pelterie, O‘Neill or von Braun Tsiolkovsky built the first wind tunnel in Russia which enabled him to observe aerodynamic problems.

Objects which are subject to a centripetal force undergo uniform circular motion. A centripetal force always accelerates the object in the direction perpendicular to the velocity of the object. This causes the object to move in a circle. If a mass attached to a string is twirled in a circle, the centripetal force is the tension in the string. For a car turning in a circle, the centripetal force is the frictional force between the road and the tyres. For a satellite, the centripetal force is the gravitational pull of the planet. tangential to the circle towards the centre of the circle Analyse the forces involved in uniform circular motion for a range of objects, including satellites orbiting the Earth

Solve problems and analyse information to calculate centripetal force acting on a satellite undergoing uniform circular motion about the Earth using F= mv 2 /r A geostationary satellite has a mass of 200 kg and orbits at an altitude of km. Calculate the centripetal force on the satellite. Data: Radius of Earth = 6.38 x 10 6 m For one revolution of the Earth,  t=24hrs=86400s  x10 -5 rads/sec v=(  x10 -5 )x(6.38 x x 10 7 )= m/s F=200( ) 2 /(6.38 x x 10 7 )= 44 N

Compare qualitatively low Earth and geo-stationary orbits Other Advantages: 1. Remote sensing of the Earth’s weather, oceans, pollution, ozone etc. need low orbits to increase resolution and sensitivity. 2.Spy satellites often need to get as close as possible. 3.Geopositioning needs high accuracy and hence low satellite orbit to reduce errors. 4.It costs more to place objects at high altitudes.

Kepler’s 3rd Law Solve problems and analyse information using: r 3 /T 2 = GM/4  2 Define the term ‘orbital velocity’ and the quantitative and qualitative relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of orbit using Kepler’s Law of Periods

Kepler’s 3rd Law (Law of periods) Define the term ‘orbital velocity’ and the quantitative and qualitative relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of orbit using Kepler’s Law of Periods Orbital velocity is the instantaneous linear velocity of an object in circular motion. It is tangential to the circular motion and can be calculated as the circumference divided by the period. and then subst. to give So, around a central body, mass M, the orbital velocity decreases as radius increases

Solve problems and analyse information using: r 3 /T 2 = GM/4  2 A planet in another solar system has three moons, all of which travel in circular orbits. Some information about these moons is given in the table. MoonRadius of orbit (orbs)Period of revolution (reps) Alpha Beta Gamma2.5 The radius of orbit and period of revolution are measured in orbs and reps respectively, which are not metric units. (a) Use the data to show that Kepler’s third law is obeyed for the moons Alpha and Beta. (b) Calculate the speed of moon Gamma in orbs/rep. We can then find the orbital speed = v=  r=2  r/T =2  x 2.5/7.9 = 2.0 orbs/rep

Account for the orbital decay of satellites in low Earth orbit There may be unpredicted drag due to solar winds producing unexpected heating and expansion of the atmosphere

Discuss issues associated with safe re-entry into the Earth’s atmosphere and landing on the Earth’s surface Retrofire to slow and drop into atmosphere Friction with atmospheric molecules produces extreme heat A blunt surface will produce a shock wave in front to absorb heat MATERIALS : Ablation - Surface vaporises and takes heat away MATERIALS : Insulation - prevents heat entry g-forces: prefer 3g, 8g may cause chest pain, loss of consciousness g-forces: transverse application best, not too much or too little blood to brain g-forces: eyeballs in! g-forces: contoured body support Ionisation blackout: heat causes layer of ionised particles preventing radio contact for some minutes Landing: After re-entry, parachute to water for earlier missions; banked turns and controlled descent to runway for space shuttle

To initiate reentry a retrofire is used to slow the spacecraft and drop into atmosphere Friction with atmospheric molecules produces extreme heat A blunt surface is best on the front of the spacecraft. This will produce a shock wave in front to absorb heat Materials on the outer surface to protect the spacecraft have varied. Early spacecraft such as those used in the Mercury, Gemini and Apollo programs used ablation - where the surface vaporises and takes heat away The space shuttle uses insulating tiles which provide a protective barrier that prevents heat entry Another issue is g-forces: A deceleration of near 3g is preferable, higher g-forces cause discomfort and affect body function - 8g may cause chest pain, loss of consciousness g-forces: a transverse (front to back) application is best, as up or down forces can cause too much or too little blood to the brain g-forces: eyeballs in! g-forces: contoured body support Ionisation blackout: heat causes layer of ionised particles preventing radio contact for some minutes Landing: After re-entry, parachute to water for earlier missions so flotation of capsule and location are important; Shuttle: banked turns and controlled descent to runway Discuss issues associated with safe re-entry into the Earth’s atmosphere and landing on the Earth’s surface

Identify that there is an optimum angle for re- entry into the Earth’s atmosphere and the consequences of failing to achieve this angle Too steep means burning up Too shallow means skipping off atmosphere Need correct time, direction and duration of retroburn Too shallow means skipping off atmosphere For the Apollo spacecraft, the optimum angle was between 5.2 and 7.2 degrees below horizontal

The optimum angle of re-entry is best angle for the spacecraft to approach the level of the atmosphere If the angle is too steep, the spacecraft will collide with too many atmospheric molecules too quickly at high speed, causing the temperature to rise dramatically and causing the spacecraft to burn up. The g-forces would also be too great, causing loss of consciousness or fatality. By ensuring the correct time, direction and duration of the retroburn (forward facing rockets) If the angle is too shallow the spacecraft will not re-enter, but ‘skip’ off the atmosphere For the Apollo spacecraft, the optimum angle was between 5.2 and 7.2 degrees below horizontal What is meant by optimum angle of re-entry? What is an example of an optimum angle of re-entry? How is the correct angle achieved? What are the consequences of failing to achieve this angle?