Short Questions Flashcards
Why does a launch site restrict the departure asymptotes of rockets?
So that the boosters and rocket stages do not fall back onto populated important areas.
How does a scramjet work?
- Collects and compresses the incoming air with a compression surface
- Air slows but never goes subsonic
- Air enters the combustion chamber where the fuel is introduced into the supersonic flow and burns to increase the air’s enthalpy
- The increased energy is then converted to air velocity on the expansion surface acting as a nozzle would in a conventional engine
What are the two main differences between Orlan and EMU spacesuits?
- EMU is to be services on the ground after 3 EVAs, the Orlan is expected to spend 4 years in orbit and be serviced on the space station
- EMU has a separate secondary oxygen pack whereas the Orlan has secondary supplies within the main backpack assembly
Why is the width of a spacecraft re-entry corridor important?
Too shallow - not enough braking before the object is back in space again. If there is lift, the object can bounce back into the atmosphere
Too steep - object reaches dense atmosphere at high velocity which causes heat and load forces that lead to destruction
Corridor must be wide enough for successful re-entry while accounting for the uncertainty of the location, velocity and angle
Why is anthropometry used in space station design?
Anthropometry is the measurement of human individuals. It is useful in space station design because neutral posture in space is different to that on Earth. This means the design of equipment and restraints is different.
What is a circular-restricted three body problem?
- Two bodies m1 and m2 moving under their gravitation around their barycentre
- Consider a non-inertial co-moving frame of reference xyz whose origin lies at the centre of mass G of the two body system, with the x-axis directed towards m2
- Y-axis lies in the orbital plane to which the z axis is perpendicular.
- In this frame of reference, m1 and m2 appear to be at rest
When is a circular-restricted three body problem useful?
- m’s mass is negligible
- 2 massive bodies and a spacecraft
- Orbits of two bodies are approximately perpendicular
- For finding Lagrange points
How does aerobraking affect the design of a spacecraft?
- Energy loss must be dissipated safely as heat, either using an ablative material or with a radiatively-cooled rigid drag brake
- Precise control and navigation system
- Knowledge of orbit and orbital position
- Knowledge of atmosphere density variation
- Less fuel needed
State two ways of supporting design for crewed space vehicles.
Simulators - can be used to recreate environment for mission preparation
Zero-g Flights - can also be used to recreate space environment
List four ways in which water can be supplied on the ISS.
- Water bags (Soyuz supply vessels)
- Recycling air moisture
- Recycling urine
- Fuel cells
Why does solar radiation perturb orbits? How does this vary with distance from Earth?
There is a transfer of momentum from photons to the orbiting body. It varies slowly with distance from Earth and is dependent on the inverse square of the distance from the Sun.
List the types of heat shield and how they work:
Deployable - Inflatable or umbrella-like shield made from a flexible but high temperature withstanding material. The large area lowers the ballistic coefficient so heating and re-entry forces are lower
Ablative - Resin, normally contained in a metal honeycomb for structural strength. Shield is designed to vaporise and produce a cooler protective boundary layer around the body
What is the transmit chain of a typical university satellite ground station?
Command encoder - Terminal Node Controller - Transmitter - Antenna
Decide commands and encode them using a command encoder, use modulation to put the info on a carrier wave in the TNC, transmitter turns the signal into a radio wave and amplifies it, it is then sent out through an antenna.
What does a downconverter do in a ground station?
Converts the frequency from high frequency RF signal (in GHz) to lower frequency (in MHz) in order to interface with the receiver.
Two different frequencies are used on the up-link and down-link to prevent interference.
What is geometric dilution of precision for Global Navigation Satellite Systems?
If satellites close together are chosen, their intersecting circles cross at shallow angles, increasing the error region. If satellites far apart are chosen, the intersecting circles are at almost right angles, resulting in a minimal error region.
