Planetary Environments Flashcards
What is the surface gravity on the earth / moon / mars?
9,78, 1.62, 3.71 ms^-1
What is the rotation period of the earth / moon / mars?
23.93, 655.72, 24.62 sidereal hours
What is the average surface temperature on the earth / moon / mars?
185/331 , 26/396, 200/70 K
Does Mars / Moon have a global magnetic field?
No
What are the 7 main environmental factors?
- Vacuum
- Gravity
- Illumination
- Temperature
- Radiation
- Impacts
- Dust
What is Galilean invariance?
Gravitational acceleration is independent of objects mass
How does solar intensity vary with distance?
Inversely proportional to square of distance
What is the effect of the 14 day lunar day?
- Limited Power
- Reduced Radiation Intensity
- Extreme Temperature Gradients
- Psychological Effects
What is the formula for solar radiation?
q^dot = \sigma T^4 (R/r)^2
What are PEL and PSR’s
Peaks of eternal light and permanently shadowed regions
What are the sources of radiation?
- High energy cosmic rays
- Solar particle events
What are the effects of radiation?
- DNA and cell damage –> Cataracts, gene mutations, increased chance of cancer, sterility
- Jamming/damage of electronics –> Computer errors (glitches, bit flips, latchups, burnouts)
What are three philosophies of shielding electronics against radiation?
- Radiation Hardening by architecture
- Radiation Hardening by design
- Radiation Hardening by process
What are some causes and consequences of impacts and why are they relevant?
- Relevant because of lacking atmosphere on most celestial bodies, so no protection
- Particle impact –> Mechanical damage, rupture, electrical failure
- Secondary impacts –> Dust accumulation
What are the eight impact shielding concepts?
- Monolithic (simple and heavy)
- Whipple (thin bumper shocks the projectile, debris cloud less harmful)
- Stuffed Whipple (variation of Whipple with layers of Nextel and Kevlar, further impact energy reduction)
- Multi-Shock (staggered layers of Nextel)
- Mesh Double Bumper (double layer bumper of aluminum mesh, aluminum rear wall)
- Honeycomb Panel (light and rigid)
- Foam Panel (light and rigid, better shielding than honeycomb)
- Transhab (layers of Mylar, Nextel, Kevlar and foam, compressible for launch, prototype for Mars habitat)
What are some consequences of dust?
- Inhalation of respirable fines –> Toxic, causes cancer
- Skin exposure –> Allergic response (allergen unknown, might be nickel)
- Abrasion and wear –> Decrease of lifetime
- Particulate contamination –> Reduced seal tightness, clogging of moving parts, clouded solar cells
What are the natural sources of dust clouds?
- Electrostatic transport, up to 300 g/m^2/a
- Impact-generated dust, about 0.1 g/m^2/a
What are the mitigation strategies for dust for spacecraft landing?
Landing pads
Surface Reinforcement
Berms
What are some strategies for mitigating surface dust contamination?
- Surface coatings that repel the dust
- Removal of the dust
- Altering the local lunar surface environment
- Charged brushes
- Systems that are designed to be tolerant of the dust
- Redundant systems that use a combination of these approaches
- Adjustment of operational procedures
What is the ambient pressure at sea level of Earth, Moon and Mars?
- Earth: 1013 mbar
- Moon: 10^-11 to 10^-10 mbar
- Mars: 6 mbar
What are the effects and consequences of vacuum?
- No oxygen –> life support system
- Pressure difference –> pressure suit, reinforced structures
- No convection –> highly variable thermal stress (sunlit planes/shadowed craters)
- Material outgassing –> degradation, damage, contamination
- No atmospheric drag –> meteoroid bombardment
What happens to a human in space?
- Air sucked out of lungs (holding breath causes tissue rupture)
- Blood boils off
- Other liquids boil off (Eyes, Tongue)
- Local freezing
- Ultimately full freezing, slower
What are effects and consequences of reduced gravity?
- Reduced contact to ground –> reduced traction and control, risk of bouncing off
- Increased dust aggregation –> compromised vision, increased contamination
- Varied fluid behaviour –> bubble growth/detachment and reduced convection (for reactors)
What are effects and consequences of decreased illumination?
- Limited power supply –> energy storage, other power sources
- Reduced radiation intensity –> other power sources
- Extreme temperature gradients –> thermal stress, damage, wide design envelope
- Psychological effects –> psychological stress, mood
Where can PEL’s and PSR’s be found and what are their benefits?
- No evidence for “eternal light”, but peaks with illumination 80% of the time
- Moon, Mercury, Ceres
- Benefit: continuous power close to potential resource deposits
What are effects and consequences of temperature?
- Temporal/spatial gradients –> thermal stress (dynamic/static), thermal expansion
- Extreme values –> enhanced outgassing, increased power demand
What are some effects of Earth’s magnectic field?
- Shields radiation
- Traps highly energetic particles in the Van-Allen Belts
Where are the 2 Van-Allen Belts located and where is a relatively safe zone?
- Inner belt: 0.2 to 2 Earth radii, mainly protons
- Outer belt: 3 to 10 Earth radii, protons and electrons with highest intensity around 4 to 5 Earth radii
- Safe zone inbetween
How much radiation dose is experienced on a trip to Mars compared to the recommended value for an average career?
> 60%
Can individual solar eruptions be forecasted and what is the time between an observation of an eruption and its arrival in the Earth-Moon system?
- Impossible to forecast
- Time between observation of an eruption and arrival in
the Earth-Moon system is <1 h up to 4 h
How many of the solar flares result in a particle event?
About 20%
What are some countermeasures against radiation exposure?
- Timing of a mission
- Careful planning of orbital trajectory
- Shielding (Aluminum provides limited shielding, Propellant tanks much more efficient)
- Risk of secondary radiation depending on material and thickness
- Different materials for different types of radiation
How can radiation hardening by architecture be achieved?
- Redundancy (increases overhead in voting logic, power consumption, mass)
- Multiple levels of redundancy (i.e. component, board, system, spacecraft level)
How can radiation hardening by design be achieved?
- Triple Modular Redundancy (TMR) strategies within the chip layout
- Dopant wells and isolation trenches in the chip layout
- Error detecting and correction circuits
- Device spacing and decoupling
How can radiation hardening by process be achieved?
- Employ specific materials, processing techniques
- Usually performed on dedicated rad-hard foundry fabrication lines
What is triple modular redundancy?
Three systems perform a process and the result is processed by a majority-voting system to produce a single output
How do radiation-hardened components and commercial components compare?
Radiation-hardened components lag behind commercial devices by several technology generations (~ 10 years)
What is LUMIO and what is its purpose?
- Newly approved CubeSat mission to observe meteoroid impacts on the lunar farside
- Conduct observations of the lunar surface to detect impacts and characterise flux, magnitudes, luminous energies, sizes and locations
What is an example of how larger structures could be protected from impacts and what are some aspects of this example?
- Utilize caves or partially roofed-over rills
- Protects from impacts, but also temperature gradients and radiation
- Temperature inside lunar caves likely <200 K
- 2 m layer could be stable over a 1 km wide tube
How does dust differ on atmosphere-less bodies and bodies with atmosphere?
- Atmosphere-less: Extremely fine grained, sharp-edged, adhesive
- With atmosphere: Dust devils and sandstorms
What is a general rule of thumb for solar array output decay?
~0.2% per Sol decay assuming no dust removal
