SR03 Planetary environment II Flashcards
Planetary environment II
Van Allen radiation belt
The Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet’s magnetosphere. Earth has two such belts, and sometimes others may be temporarily created.
Impacts
No atmosphere means no protection
Causes and consequences:
Particle impact –> Mechanical damage, rupture, electrical failure
Secondary impacts –> Dust accumulation
Probability of a 1 km object impacting Earth
Impact probability info
- Sporadic meteoroid showers are more dangerous, with more smaller particles than regular showers
- Impact frequency decreases inversely to the diameter of the impactor
- The smaller the particles, the more secondary ejecta are produced
- A single impact with 20 km/s may eject 100 to 1000 time its mass in secondary particles
Probability of Jupiter impacts
Diameter 5–20 m: 10–65 per year
Diameter 300 m: 1/500 per year
Diameter 1600 m: 1/6000 per year
Name some shielding concepts
*Monolithic
*Whipple
*Stuffed Whipple
*Multi-shock
*Mesh-double Bumper
*Honeycomb panel
*Transhab
Methods of Protection of larger structures
- Making use of caves, partially roofed-over rilles
- Protection from impacts, but also temperature
- gradients and radiation
- Temperature inside a lunar cave likely <200 K
- 2 m layer could be stable over a 1 km wide tube
- Suitable for ISRU plants?
Basics on dust
- On atmosphere-less bodies: extremely fine grained, sharp-edged, adhesive
- On bodies with atmosphere: dust devils and sand-storms
- Lunar soil contains 0.5% respirable particles (Winterhalter et al. 2020)
- Lunar dust cleaned from Apollo suits was as much as 50% respirable dust
Dust effects
Causes and consequences:
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
Lunar Horizon Glow
Cause: Sunlight scattering off electrostatically charged lunar dust.
Observations:
Surveyor 7: Glow ~10 cm above surface near terminator.
Apollo 17: Glow up to ~10 km, seen before lunar sunrise.
Orbiting Cameras: Brightness suggests dust >100 km high.
Mechanism:
-UV radiation knocks off electrons, charging dust.
-Electrostatic forces levitate & loft dust, especially at the terminator.
-Micrometeoroid impacts & plasma interactions also contribute.
Significance: Forms a temporary dust atmosphere, affecting lunar exploration & instruments.
Dust Levitation and lofting natural causes
- Electrostatic transport (see previous slides), up to 300 g/m2/a (Rennilson and Criswell, 1974)
- Impact-generated dust, total dust accumulation from primary and secondary micrometeoroid impacts is
about 0.1 g/m2/a
Dust Levitation and lofting Anthropogenic sources
- Triboelectric charging, kicking-up dust by astronauts and machinery (drilling, driving, etc.)
- Engine plume (landing and launching; presumably the largest contributor)
- Dust accumulation on charged surfaces
Due to astronauts walking
* In reduced gravity, walking is rather „side-to-side wobbling with occasional shuffling […] inevitably
accompanied by the kicking of the fine lunar material“ (Katzan and Edwards, 1991)
* Dust travels on a ballistic trajectory
Due to rover operation
* Dust is thrown from the wheels in a “rooster tail” with particles traveling up to 20 m from their source
(Apollo lunar rover at 8 mph)
* Mitigation: fenders on the wheels
Due to 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
Due to 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/cm2
Dust levitation Mitigation strategies on Earth in mining and construction
- 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
Dust levitation Mitigation strategies due to spacecraft landing
- Landing pads
- Surface reinforcements
- Berms
Dust problems
Contamination/degradation of fabrics
Contamination/degradation of technical surfaces
Contamination/degradation of thermal surfaces
Rule of thumb:
0.2% per Sol decay in solar array output, assuming no dust removal
„at the end of two years, in the baseline case, the remaining power
is barely a quarter of the initial power“
Dust removal by wind was observed mainly for:
- MER Spirit
- MER Opportunity
- MSL Curiosity
Lunar dust emissivity and absorptivity
Lunar dust has high emissivity and high absorptivity
Dust Contamination/degradation of thermal surfaces of rover
- Lunar Roving Vehicle, battery radiators
- Dust cover protects radiator (fused silica second surface mirrors)
- Despite the cover, dust needed to be removed with a nylon brush
- This was not as effective as predicted, leading to overheating
Mitigation of 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
Small scale dust Mitigation and removal
Electrostatic cleaning
Magnetic cleaning
Large scale dust Mitigation and removal
Lotus coating
LN2 gas spray
Landing pad berms
