Lecture 3 Flashcards
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
How can some mechanical damages on the JWST be corrected and how can it be protected from them?
- Some deformations are correctable through mirror realignments
- Meteor-shower forecasts generated, allowing reorientation
Where and how often are impacts on the Moon visible from Earth?
- Impact flashes on the dark portions of the Moon, sometimes visible with the naked eye
- Hundreds of detectable impacts per year
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
How dangerous are sporadic meteoroid showers and how does the impact frequency relate to the diameter of the impactor?
- More dangerous than regular showers, as they have more smaller particles
- Impact frequency decreases inversely to the diameter of the impactor
How do secondary ejecta and particle size relate and how much does a single impact with 20 km/s eject in secondary particles?
- The smaller the particles, the more secondary ejecta are produced
- May eject 100 to 1000 time the impactors mass in secondary particles
How often do impacts on Jupiter happen per year with impactor diameter of 5-20m, 300m and 1600m?
5-20m: 10-65 per year
300m: 1/500 per year
1600m: 1/6000 per year
What are 8 shielding concepts from impacts and how do they work?
- 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 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
How much respirable particles does lunar soil contain and how much respirable dust was cleaned from the Apollo suits?
- Lunar soil: 0.5% respirable particles
- Apollo suits: 50% respirable dust
What are some causes and 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 is Lunar Horizon Glow (LHG) and what causes it?
- Faint glow near lunar horizon
- Variable lunar “atmosphere” of dust extending to >100 km
- Dust scatters sunlight from beyond the horizon
- Levitation and lofting caused by electrostatic forces (UV radiation, charged particles knocking out electrons, creating positive charge on Sun side and negative in craters and dark side)
What are some natural sources of dust?
- Electrostatic transport, up to 300 g/m^2/a
- Impact-generated dust, about 0.1 g/m^2/a
What are some anthropogenic sources of dust?
- Triboelectric charging, kicking up dust by astronauts and machinery
- Engine plume (landing and launching)
- Dust accumulation on charged surfaces
How is dust generated from astronauts walking?
- Walking is rather “side-to-side wobbling” with occasional shuffling in reduced gravity, leading to kicking of fine lunar material
- Dust travels in ballistic trajectory
How is dust generated from rover operation and how can this be mitigated?
- Dust is thrown from the wheels in a “rooster tail” with particles traveling up to 20 m from their source (Apollo rover at 8 mph)
- Mitigation: fenders on the wheels
How is dust generated from mining and construction?
- Mining and construction includes much “earthmoving”, digging, dumping and transporting of soil
- Operating speed might be low, but mass manipulation generates loads of dust
What are some mitigation strategies for mining and construction on Earth?
- Ventilation in mine shafts
- Capturing airborne dust with water spray
- Wetting broken material
- Dust collectors / filtration
- Optimising cutting geometry / reducing dust generation
- Reducing dropping material
- Using enclosed conveyors
What is an example of dust generated from spacecraft landing?
- Apollo 12 landed 150 m away from Surveyor 3, whose camera was sandblasted by dust
- Ejecta impacted Surveyor 3 at ~3 km/s (escape velocity)
- Surveyor 3 accumulated a layer of dust of 1 mg/cm^2
How can dust from spacecraft landing be mitigated?
- Landing pads
- Surface reinforcements
- Berms
What is an example of dust impacting performance of solar power cells?
- InSight Mars lander
- Generated 5000 Wh per day in December 2018
- Generated 500 Wh per day in April 2022
What is a general rule of thumb for solar array output decay?
~0.2% per Sol decay assuming no dust removal
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
