Basic spacecraft concepts Flashcards
Definition of spacecraft
Vehicle or machines designed to fly in outerspace
Definition of sub-orbital
enters space and then returns to the surface of the Earth - without going into permanent orbit
Definition of orbital
enters closed orbit (permanent) around Earth or other celestial body (moon)
Definition of interplanetary
travel between planets
Definition of interstallar
leave solar system
At what point is it considered spaceflight
Consider L = 0.5pSV^2Cl
as altitude increase, p decreases, therefore speed increases
when this speed = orbital speed the object stays in orbit which is considered spaceflight
What distance from Earth is considered space flight and what is this boundary called
100km above the surface
called the Karman line
Name the key stages of a complete space mission
- Pre-launch phase
- Launch phase
- Orbit transfer
- On-station operations
- Decommisioning
What happens during pre-launch phase
ignition, separation from ground launch facilities
What happens during launch phase
placing spacecraft into an intermediate orbit
What happens during orbit transfer
transferring the spacecraft to its operational orbit
What happens during on-station operations
mission itself, station keeping, attitude control
What happens during decommisiong
place spacecraft into a higher orbit or controlled re-entry
What is a launch window and how long is it
the limited time interval available for a launch.
Typically few minutes each day. However gets much smaller when trying to rendezvous with ISS or reach another planet
What is Low Earth Orbit (LEO)
- Altitude is 160-2000km
- orbit period about 88-127 minutes
- spacecraft moves with respect to Earth’s surface
- simplest and cheapest, high bandwidth and low communication delay
- see Earth’s surface more clearly
- most statellites and ISS are in LEO
What is Geostationary Earth Orbit (GEO)
- Altitude is 35,786km above equator
- Orbital period is 24hrs, therefore at a fixed position with respect to Earth’s surface
- used for communication and weather satellites
- high cost, communication delay of 0.25seconds
How do chemical rockets change momentum
by discharging hot products of combustion at very high velocities
high power but limited energy
How does electrical propulsion work and why is it useful
by electrically heating or charging particals to increase kinetic energy
useful as it is not energy limited and so used for station keeping and interplanetary missions
Rocket equation
ΔV = Vex . ln(Mo/M1)
where: ΔV = change in velocity Vex = exhaust velocity Mo = initial mass of rocket inc. fuel M1 = final mass after fuel burn
Calculating mass of the propellant (fuel)
Mprop = Mo - M1
Mprop = Mo(1 - e^-(ΔV/Vex))
