Rockets Need to overcome Earth's gravity Therefore need to obtain escape velocity Accelerate by throwing out mass (fuel) at very rapid speeds Newton's second law Velocity can be increased by losing mass Therefore, multi-staged Heavier payloads need bigger rockets Saturn V – used send people to the moon was the largest ever rocket as it had the heaviest cargo

Spacecraft Rocket payloads are generally either : Satellites - spacecraft that orbit the Earth Space Probes - spacecraft that leave Earth orbit to explore the solar system All spacecraft are designed with a: Communication antennae Power source – either nuclear batteries, or solar panels with chemical batteries Protective outer layers Instrumentation Maybe a propulsion mechanism (generally ejected from Earth orbiting satellites)

Satellites Typically satellites are used for: Communications / GPS – equally spacing three geostationary satellites will allow at least one satellite to be visible in a straight line from anywhere on the globe, and each of the three satellites will have a clear straight line path of communication. Astronomical instrumentation – e.g. Hubble Space Telescope, Chandra X-ray Observatory, Spitzer Space Telescope Earth Observation – spy satellites, climatology satellites

Launching Satellites Launch site on the Earth is carefully chosen depending upon required final orbit. Launching at the equator provides an “Earth assist”. However polar orbiters need to be launcher at higher latitudes.

Observing Satellites

HST

Problems of Manned Spaceflight Energy, fuel costs Radiation Provisions Muscle fatigue Hardware, Time/Training Costs Communications, and Remoteness in hostile environment Psychological impact of long duration missions Interstellar Travel All of the above – but to a greater extent Velocities/Time