chapter 3.5; motions of satellites and spacecraft & 3.6; gravity with more than two bodies

satellite

• once an artificial satellite is in orbit, its behaviour is not different from that of a natural satellite, such as the Moon

• if a satellite is high enough to be free of atmospheric friction, it will remain in orbit forever

• at orbital speed of 87km/s, satellites orbit the Earth in around 90 minutes

circular satellite velocity

speed required to launch an object into space so that the object falls around Earth in a complete circle

• 8km/s

escape speed

the speed needed to move away from Earth forever

• approx. 11 km/s

• after an object (e.g. spacecraft) leaves Earth, they are subject only to minor trajectory adjustments provided by small thruster rockets on board

interplanetary spacecraft

• after an object (e.g. spacecraft) leaves Earth, they are subject only to minor trajectory adjustments provided by small thruster rockets on board

• in interplanetary flight, these spacecraft follow orbits around the Sun that are modified only when they pass near one of the planets

• as it comes close to target, a spacecraft is deflected by the planet’s gravitational force inot a modified orbit, either losing or gaining energy in the process

• If we wish to orbit a planet, we must slow the spacecraft with a rocket when the spacecraft is near its destination, allowing it to be captured into an elliptical orbit

• Additional rocket thrust is required to bring a vehicle down from orbit for a landing on the surface

• if a return trip to Earth is planned, the landed payload must include enough propulsive power to repeat the entire process in reverse

perturbations

disturbances