SAR Technology Incidental to Geosynchronous Asteroid Flyby

From: http://www.spacefuture.com/archive/t..._and_economic_
feasibility_of_mining_the_near_earth_asteriods.sht ml:

Application of celestial mechanics shows that (i) simple estimates of
"global minimum" delta-v can be made; (ii) low-energy opportunities
occur at approx 2-yearly intervals, for many NEAs; (iii) long synodic
periods militate against multiple-return mining missions; (iv) Earth-
return hyperbolic velocity should be kept low; (v) high-eccentricity
targets require Hohmann transfers, and a short mining season at
aphelion; (vi) low-eccentricity targets may use continuous-thrusting
propulsion, and extended mining season. There is a growing subset of
targets that are intermittently accessible for an outbound delta-v of
under 6 km/s, and offering return departure delta-v under 2 km/sec.

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How to acquire the spectral data? SAR mapping "flybys" utilizing
a data set similar to the Lunar Prospector Gamma Ray Spectrometer re-
vealed that the spectrometer was expected to be 2.5 to 8 times better
(w.r.t. peak intensity) than the NaI data from the Apollos. A higher-
Z Bismuth Germinate (BGO) crystal increases the filtering, or stopping
power of gamma rays, and returns two sets of data for the GRS at 32
second intervals:

"... a BGO spectrum from 0.3 to 9 MeV in each coincidence (rejected)
and anticoincidence (accepted) with the plastic shell. In principle the

accepted spectrum is the cleanest, since all full energy BGO photopeaks

will deposit no energy in the plastic. However, there is additional
information in the rejected spectrum which can be used to good
advantage
with respect to background reduction.

The rejected data consists of gamma rays that had one or more Compton
scattering events in the plastic, in addition to the partial peak
energy
deposited in the BGO. This scattering process mimics the Compton
scattering of the elemental spectral emission lines from the lunar
regolith before the gamma rays reach the LP spacecraft, and so are
similar
to the continuum background spectrum which rides below the elemental
line
spectrum. As such, a properly scaled version of the rejected spectrum
can
be subtracted spectrum to reduce continuum spectrum background from the

lunar surface. This second data set was not available in previous
measure-
ments for use in such background reductions."

(From Monte Carlo Simulation of the Gamma Ray Spectrometer Performance
on
Lunar Prospector, Robert E. McMurray, Jr., Marie C. Grimmer, William C.

Feldman, G. Scott Hubbard, and Steven D. Zins, NASA Ames Research
Center,
Moffett Field, CA 94035, Naval Postgraduate School, Monterey, CA 93943,

Los Alamos National Laboratory, Los Alamos, NM 87545, from the 1997
IEEE
Nuclear Science Synposium, Anaheim, CA p. 602)

For GAMS (Geosynchronous Asteroid Mapping Satellites, an orbital period
is
established to yield a ground track in x km. per y seconds (per 32
second
data set). The data sets are binned into square kilometer pixel bins
over
the maximum surface area. Dynamic x-ray imaging provides the resources
necessary for rapid processing (on the order of 8 ms per 7936 pixel
channels) for monochromatic photons. Monochromatic photons are single
frequency time-over-threshold photons with uniform pulse intensity. The

scintillation detector is tuned for reception of single frequency emit-
ted photons. I have a list of detector specific properties for
transition
frequencies of precious metals) that utilize PSPMT (Position Sensi-
tive Photomultiplier Tubes) yielding a hit (with pulse height and
frequency)
perform geosynchronization of coordinates transmission to an orbital or

earth-based GAMS mapping facility. The mapping facility then chooses a
des-
tination for the mining vessel and transmits new programming
instructions
for the rendezvous.

However, I do agree with the M.J. Sonter's link describing the types
of propulsion available, utilizing a "steam rocket" with "solar thermal
power is advantageous for extracting metals other than precious,
however
considering the time constraints for organizing such a mission for this
alone is not sufficient enough to pay for the entire mission - the
operation would have to require carefully selecting a landing site to
include both primary and precious metals in order to justify the cost.