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=== Meteorites ===
Near Earth Resources with Low Cost Delivery
As of August 2016, the NASA Near Earth Object Program has estimated Orbital Elements and absolute magnitudes for almost 15,000 objects that cross the 1 AU spherical shell that contains Earth's orbit. The rate of discovery is rapid. From those magnitudes, we can estimate size and volume, more than 1E14 cubic meters.
Over a very long time, we arrange impacts between the near earth objects to break them into 50 meter or smaller chunks, and we tag them with milligram-weight laser retroreflectors for high precision tracking. We also use lasers for ablative thrust. We line these up for delivery orbits to the Moon.
Meteorites are about 5% nickel-iron. Assuming a density of 8000 kg/m3, that's more than 4e16 kilogram supply - 20,000 years worth at current global consumption rates; which MUST diminish over time, as we have depleted everything but lower grade iron ores. Heating iron from cold solid to a hot liquid requires about 1 MJ/kg.
We construct a 30 kilometer geodesic grid of 20,000 "smelting tunnels" across the back side of the Moon, deep holes with 100 meter throats and slight bends partway down. Over a very long time, each object is arranged to fall straight down a tunnel at high speed, to impact a melting chamber at the bottom, while a lid is fired over the top to contain impact ejecta. The objects will impact at greater than 2.6 kilometers per second (the squared sum of lunar escape plus orbital velocity), and have at least 3.4 MJ/kg; after an elastic collision into lunar rock, enough energy should remain in the object to melt it.
This would a very long term project, because arranging the impacts and planarizing the material, then delivering it at a steady rate, may require thousands of orbits of the Sun - thousands of years on average. However, the assumption of continued exponential growth into the far future is contrary to every observed system in nature. All growth (at best) follows an S curve, or worst case an bell curve impulse followed by extinction.
Asteroid orbits are chaotic in the long term. Newton's Clock by Ivar Peterson (1993) says on page 189: "Near-circular orbits can suddenly stretch after a few hundred thousand years of placid behavior, becoming so elliptical that they cross the paths of Mars and Earth." See work by Jack Wisdom when he was a grad student at Caltech in the 1970's (thesis adviser Peter Goldreich). 1982 paper in The Astromomical Journal, March 1982, 599-593 and Nature 315 (27 June 1985): 731-733.
Later recent references suggest some Mars-influenced NEOs have Lyapunov times (errors increase by e) of 100 years or less. Steering them into orbits predictable enough to hit the Moon 1000 years from now requires calculating their position, velocity, and future trajectory to better than 100 meter precision now. On the other hand, an intentional centimeter-per-second velocity change today can evolve into the Earth-Moon distance in 1000 years. So, if we can measure these objects to optical wavelength precision now (5e-7 meters), and model and nudge them accurately enough (BIG if), then a 50 year Lyupanov time over 1000 years multiplies that optical error into a 0.25 kilometer error, which can in turn be corrected with another centimeter-per-second velocity change 7 hours earlier.
Deflecting useful potential impactors into the Moon (or Mars or Venus for the potential impactors deemed "useless") will require much continuous measurement and correction for a very long time, but the cost of protection is eternal vigilance.
A 140 meter diameter round asteroid has a surface area of πD² or 61575 m² ( 6.16 hectares, 15.2 acres ). If the bulk density is 2 g/cm³ (2000 kg/m³), the mass M is πρD³/6 or 2.87 million tonnes, and the surface gravity is 4GM/D² = ⅔πGρD = 3.9e-5 m/s² = 4μ gee.
A 1 acre round asteroid is 36 meters in diameter.
Relics of Ancient Time
Michael K. Shepard (Bloomberg U.), Central 523.44 s5474a 2015
A pretty good lay description of asteroids and how we learned about them. The connections between specific asteroids and specific meteorite classifications is fascintating. I read the book in late 2019, and significant progress has been made in the five years since the author wrote the book.
- p049 1983/01 10mo IRAS 2K Superfluid Helium 12/25/60/100 μm infrared channels, observed 2000 asteroids over 10 months
- p054 2009/12 10mo WISE 20K Solid Hydrogen 3.4/4.6/12/22 μm, 12/22 1000x more sensitive than IRAS
- p055 2013 radiative cooling to 75K "staring" at deep sky
- p108 Carbonaceous chondrites 5% of all falls
- CI rare stony no chondrules most primitive remaining from solar system formation
- CV large chondrules with CAI calcium-aluminum inclusions
- CM primitive with amino acids and water-formed clays
- CO small chondrules and some metal phases
- CK, CR, CH and CB (both high metal)
- Enstatite, magnesium-only pyroxine with some metal and iron sulfides
- p110 Fig 4.5 solar elemental abundances
p114 HED howardites (breccias of both:) eucrites (fine grained volcanic basalt) diogenites (coarser grained)
- p157 K-Pg (former K-T) extinction, may be both impact and Deccan Traps eruption
172 "The environment 100 km above our heads is quite hostile to life - no air to breath and a greatly reduced magnetic field
- er, no to the latter; the field at 100 km above the equator is 95% of the field at sea level (inverse cube radius). Radiation effects (such as the South Atlantic Anomaly) are entirely due to the lack of atmosphere intercepting van Allen belt particle trajectories.
p201 v6 secular resonance perturbation by Saturn, megayears?
p203 Poynting-Robertson effect is retrograde light pressure on small particles due the incoming light seeming to come in from a small angle (orbit velocity divided by radial speed of light).
p216 The asteroid 490 Veritas seems to be the largest fragment of a 150 km asteroid shattered by a collision 8.2 Ma, creating a cloud of He-3 laden dust that forms an 8.2 Ma dust in the Greenland ice sheet and in deep ocean sediments.
p269 25143 Itokawa S-class Apollo NEA 500 meters long, appears closest to LL-chondrites
MUSES-C spacecraft became Hayabusa (falcon)
p279 ESA Herschel Space Telescope sees water vapor plumes from Ceres in 2014, perhaps liquid water
From wikipedia, Bennu close approach 400,000 km on 23 September 2060 some lensing, close approach 300,000 km on 25 September 2135, 300,000 km ( +/- 200,000 km? ). The Moon will be 89% full and 311,000 km.
p305 2010 NRC Report objects up to 1 km in diameter ... 1 cm/s ... heavy lift launch vehicle ... 15000 km in 10 years
- 10 × 3e7 x 0.01 = 3e6 meters = 3000 km; divergent process somewhere
Carrie Nugent Tigard TEDbooks 2017 523.44 NUG
Caltech/IPAC., NEOWISE thermal infrared (earth orbit)
p03 by 2011, found 90% of >1km NEA, next target 90% of 140m NEA
p09 NEA = perhelion < 1.3 AU, 14,445 NEA discovered at time of writing
- p11 90,000 kg/day of dust and small rocks hit Earth
- p15 2013/02/15 Chelyabinsk 20 meters, pancaked and exploded at 38 km altitude, 53 km away, flash of light, shockwave broke windows
- p19 shockwaves circled globe twice in three days, registered on 20 of 283 UN infrasound monitor stations
- came from sunside where telescopes can't be used
- every 100 years or so
- p24 diagram/map of northern hemisphere observatories at night
- p29 Minor Planet Center Cambridge MA processes 50,000 observations per day
- p29 to p33: 2008 TC3 3m object over Sudan
- p48 Kodak T-Max 400 film for 6 to 10 minute exposures, stereo microscope
- p54 CCD survey NEAT ( NEA Tracking), Glo Helin
- p55 now Spacewatch, Catalina (near Tucson) Sky Survey, Pan-STARRS, LINEAR, 95% NASA funded
- p72 2014 HQ124 300 m class 1.2M km closest approach
- p74 bistatic radar, transmit from Goldstone and receive from Aricebo
- p80 1994 Shoemaker-Levy 9 into Jupiter 200,000 km/h (56 km/s) 24,000C fireball
p82 1998 movies Armageddon and Deep Impact
- p87 NASA Planetary Defense Coordination Office in DC, Lindley Johnson Planetary Defense Officer
p89 Deep Impact Probe, 372 kg at 37,000 kph (10.3 km/s) into 7.6km × 4.9km 9P/Tempel 3e14 kg?