Unit 5 Flashcards
Methods of propulsion
Chemical
Ion
Solar
More fanciful:
Warp Drive
Quantum Drive
Newtons Laws
First: Inertia
Second: F = ma
Third: Law of opposite
LEO
Low Earth Orbit:
- Majority of satellites
- Less than 2,000 km above the surface of the earth
- Orbital period of less than 128min
- Satellites will fall out of orbit and re-enter on relatively short time frames
- Mostly communication satellites since low latency
The Kessler Syndrome
The Kessler effect
The increase in density of objects in LEO, due to space position is high enough that collision between objects could cause a cascade (cause further collisions)
MEO
Medium Earth Orbit:
- Higher than LEO
- Above 2,000 km to 35,786km from the surface of the earth
- Orbital period between ~2 hours and exactly 23h 56m and 4s
- contains Van Allen radiation belts
Van Allen Radiation Belts
Collection of charged particles emanating from the sun and carried by the solar wind
Communications and GPS satellites use this region as it encompasses an orbital period of 12 hours
GSO
Geosynchronous Orbit:
- A Earth centererd orbit with an orbital period that matches Earth’s rotation of 23h 56m and 4s
- Satellites in this orbit return to the same location each day seen from the surface of the earth
- East-west drift associated with elliptical orbit
- North-South motion from inclination
GEO
Clarke Orbit or Geostationary Earth Orbit:
- A special case of GSO when the satellite is orbiting the Equatorial plane
- Satellites seen appear stationary
- Used widely by telecommunication satellites
HEO
High Earth Orbit:
- Satellites are rare
- Orbital period greater than 24 hours
- From Earth appears to move westward
- Will never re-enter Earth’s atmosphere
Periods of Orbit
The orbital periods depend upon the major axis of the orbital ellipse and the mass
P^2 = 4pi^2 a^3 / G M2
Escape Velocity
For a satellite to escape from the gravitational fields of the Earth must reach escape velocity
Vsec = root (2GM/R)
Chemical Rocket Fuel
Combustion
- A chemical process that releases energy, often in the form of heat
An oxidizer is important since there is no air in space
Liquid fuel can be stopped and started potentially many times
Solid rocket fuel can not be stopped when ignited
- Also it also interacts minimally with their environment (more stable)
Chemical fuel parts
Liquid Oxidizer is always liquid oxygen
Liquid fuel can be hydrogen (commonly) or Kerosene (RP - 1)
Ion Propulsion
Chemical rocket propulsion is essential for lifting a rocket
Ion engines produce low thrust and thus low acceleration
Same for chemical rocket propulsion
How does Ion propulsion work
Step 1: Electrons are remitted by the discharge hollow cathode, traverse the disc charge chamber, and are collected by the anode walls
step 2:propellant is injected from the plenum and travels towards the discharge cathode
Step 3: Electrons impact the propellant atoms to create ions
Step 4: Ions are pulled out of the discharge chamber by the ion optics
- Note that the higher the voltage of the discharge optics, the faster the exhaust speed of the ions
Step 5: Electrons are injected into the beam for neutralization
Ion propulsion used in spacecraft
Dawn spacecraft
- Most successful ion propulsion to date
Lunar Gateway
- Set to use the most powerful ion engines yet
Solar sailing
Arthur C. Clarke’s science fiction
Deployment of a large area, low mass “Solar sail”
Use the pressure of sunlight to change speed and direction
Acceleration generated is very small
Matter - Anti-Matter propulsion
When matter comes into contact with any matter, complete and spontaneous annihilation occurs
It offers 100% conversion of matter into energy
we can produce some anti-matter particles but strong them is the challenge
Nuclear powered rocket
Nuclear thermal rocket
The nuclear fission reactor heats and vaporizes the liquid hydrogen and generates thrust
Relatively low but long-term thrust
Concerns include safety of the environment during a lunch failure
Power for spacecraft
Power comes from solar panels that convert sunlight into electricity
Most efficient when close to the sun
Radioisotopes thermoelectric generators
RTG:
- A type of nuclear battery
Any radiation emitted must be easily absorbed so it wont impact the rest of the spacecraft
Only 3 isotopes are commonly used:
- Plutonium
- Strontium
- Americium
Exploring our solar system
Artemis project plans on return to the moon
- a permanent settlement seems likely within this decade
A human mission to Mars in the 2030s
Human settlements through our solar system are likey within this century
Artemis 1
Launched 2022
To the moon and back (uncrewed)
25 days
Artemis 2
Proposed launch 2025
To the moon and back with a crew of 4
- including a Canadian
~10 Days
Artemis 3
proposed launch 2026
to the moon and back with Crew 4 and with 2 astronauts landing on the moon
- First woman on the moon
~12 days
Artemis 4 and Beyond
Similar to Artemis 3
Use of lunar gateway, an orbiting station to facilitate long term stays on the moon
Lunar Living
Will not be self-sufficient in the short term
- But should be as soon as practical
Ice near the lunar poles provides water
Protection against harsh radiation is essential
2 weeks of sunlight and 2 weeks of night
- Battery power is important
Spacecraft Sterilization
Forwards contamination:
- The transfer of terrestrial organisms to another celestial body
Backward contamination:
- Aline life could be brought back into the Earth’s biosphere
How:
- Use of a clean room
- Heating to ~115C
- UV radiation
- etc…
Outer Space treaty
Came into effect on 10 October 1967 and has 112 signatures now
Attempts to guide a peaceful and free use of space for the benefit of humanity
- Weapons, specifically nuclear, will not be placed in space
- States will be responsible for nongovernment entities
- States will be liable for damages caused by their activity
Current interstellar spacecraft
Pioneer 10, 11
Voyagers 1, 2
Soon New Horizons
will take 10s of thousands of years to reach our nearest star
Interstellar travel
One way trip
- multi-generational ship ark is most likely
Sufficient number of people
- 100 or more likely 1000
Energy requirement for the trip
- Life support entails
- Air purification
- Heating
- Water purification
- Farming
Consumables for the trip
Interstellar hazards
- radiation
- particle
- collisions
Time dilation
Special relativity asserts that time measured by a moving clock appears to advance slower than for a clock in a rest frame
- For example, for astronauts aboard the international space station, time lags by about 0.01s for every 21 months elapsed on the Earth’s surface
The realistic time elapsed, T, for a clock moving at a speed v when compared to a reference clock elapsed time T0
T = T0/(root(1 - V^2/C^2))
Starshot initiative
Proposed that a nanocraft with a mass of a few grams could be accelerated to 20% of the speed of light
Which will reach a nearby star within 20 years
