Most of us have pondered just how to 'kick start' commercial use of space resources, instead of the current paradigm of governments doing everything. I would like to suggest one possible method, which I cannot independently study much further, in the hopes the members of this email group may be able to help further develop this concept.

One of the probably necessities to construction of those large O'Neill cylinders is asteroid mining, which provide materials outside any planetary gravity wells, and in most cases volatiles like water that are absent in lunar regolith. However what is so far unclear is how to make a first mission to mine or otherwise utilize an asteroid pay for itself.

Production of fuel for GEO satellites is one definite option, however at present no orbiting satellite is capable of being refueled in orbit. An other issue would be the actual method of producing fuel essentially from rock. In his website (PERMANENT or http://www.permanent.com/index.htm ), Mark Prado mentions a human mission to take asteroid samples, and make a movie/documentary of the mission, and sell some of the samples to help pay for it. This may work, however it is still uncertain whether revenues generated by this type of scheme would be enough to cover the cost of the mission itself, and any follow-on missions would likely generate far smaller revenues due to it being a sort of 'second time' , allowing for a noticeable 'yawn factor' with the public. There is always the possibility of some multi-billion-air funding a mission out of his/her own pockets, however I have no idea how many rich individuals are so interested in spaceflight other than Elon Musk and
Robert Bigelow.

So I started thinking about one other concept: combine the first asteroid mining mission with the first SPSS mission, and you avoid many of the cash flow difficulties in other concepts. This could be accomplished if the target asteroid was a nickel-iron (aka stainless steel) asteroid (yes there are stainless steel asteroids floating around the solar system, for those who didn't know). If this asteroid, or part of it, was moved to a high-earth orbit, and later to GEO, it could be melted and cast (or otherwise formed) into a large solar concentrator and part of the structure for a steam (or Stirling cycle...) generator. However the main issue I have found in this concept is the actual (and extremely important) task of moving the asteroid from its initial solar orbit to a useful Earth orbit.

Many of us in this email group have considered using linear or centripetal mass accelerators to throw asteroid material at high speed, however this presents us with two problems. First, specific only to mass accelerators being used for propulsion, is they are essentially acting as electric propulsion engines, limited in thrust and specific impulse (or exhaust velocity) by the surface area of (and thus power produced by) the spacecraft's solar collectors, or by the output of a nuclear reactor. Electric propulsion systems are usually characterized by extremely low thrust, and high efficiency (but these can be traded for the other when using mass accelerators), lengthening the flight of any mission to retrieve that asteroid to a period of several years, extremely long for conventional manned spaceflight (unmanned flight may be necessary for at least part of the mission...). The second issue with asteroid propulsion via mass accelerators is specific to this type of
asteroid, being essentially solid metal. Whereas most 'rocky' asteroids are relatively easy to break up into small particles that can be used in a mass accelerator, metal does not turn to 'dust' so easily. This could be solved by using solar concentrators to melt the surface of the asteroid into small globules, magnetically hold and allow them to cool, then feed them to that mass accelerator, however this effectively wastes a huge amount of energy to melt the metal, leaving even less for the mass accelerator to use in actually accelerating it's reaction mass.

I have so far come to two possible alternatives to moving the asteroid via mass accelerator, both involving using that same (or larger) solar concentrator to melt parts of the asteroid. The first has already been considered for moving rocky asteroids deemed threating to Earth. It is to continually melt one spot on the asteroid, such that molten (or gaseous) metal comes streaming out vertically relative to the surface of the asteroid, creating thrust. This method would likely be fairly slow, but could be faster than using a mass accelerator. The second method may be the slowest option yet, but it has the advantage of needing very little work done once in Earth orbit. Melt most of the asteroid using the solar concentrator (or use some other method to form it) and make a solar sail, allowing the entire (or most of) the mass of the asteroid to provide propulsion. This has the advantage of needing very little work in Earth orbit (just bend the sail into a parabola),
but has the disadvantage of flight times of (or above) most solar sail designs.

Unfortunately, I have been unable to develop this concept any further. I would appreciate any comments, opinions, criticisms or even discussion on the topic from any of you.

Thank you for reading and thank you in advance for any replies;

Sincerely-
Michael P.

"It is better to fail in origionality than to succeed in imitation."
-Herman Melville

Greeting Michael

I to have pondered 'asteroid mining' on a commercial
scale. Where shall I start?

A few year ago in a USC Astronautics class I did a
project and paper on a Solar Thermionic Electric
Generator (STEG) for use at a Lunar Colony on Malapert
Mountain in the southern latitudes of Luna.

After the class I thought of how easily this design
could be converted to Space Solar Power Satellites
(SSPSs). I also took another USC Astronautics course,
Advanced Propulsion, from which I came away from with
a rudimentary design for a Hybrid Solar Powered Rocket
(HSPR).

In high thrust mode it works on Solar Thermal, but in
high efficiency mode it works on Solar Electric. The
engine has a specific impulse of ~3000 sec in the
electric mode, 500 to 1500 sec (adjustable) in the
thermal mode. The working fuel is water, although
some additional degradation of the engine must be
designed away.

Anyway a 15 ton (empty) spaceship, engine tankage,
structure, Solar collectors / STEGs and 2 automated
Service arms plus 30 plus tons of fuel (water) plus a
4 ton Asteroid Tool Kit (ATK) (more on this later).
If the design proved out and was constructed and
tested, the HSPR could be launched on 4 Falcon 9 -
heavys, for $312M (2006) USD. My actual plan is to
launch the HSPRs using a low-cost electromagnetic
launch system (which is the key part of a much bigger
plan that includes Space-Gas-Stations, Automatic
Assembly of small 2 to 20 MW (electric to earth grids)
Space Solar Power Satellites, and a whole lot more),
then assemble and test them in space. However it
would quite probably be worth the effort to launch the
fully tested prototype in this manner as the mission
times are fairly long (3 years minimum, but 5 to 6
years and longer are more typical).

Once the HSPR is checked out and fueled, and at a
precise moment, it accelerates from GTO to a lunar
flyby, and on to a pre-selected Asteroid. There it
will open the ATK, monitor the motion of the asteroid
and determine which, if any large boulders may to
collected for return. The HSPR will land on the
asteroid (or possible a smaller remote walker?) and
collect large boulders, sands and dust and possibly
volitiles (including water) in plastic bags. The ATK
has many large plastic bags, rope/cable, and
transponders to further track the asteroids orbit. It
also has several Laser Spectroscopes and other devices
for chemical analysis. Once the million or so tons of
samples (the Chunk) were collected and bagged, the
HSPR (or the walker?) will wrap a long cable (with a
good anchor and automated release mechanism) several
times around the asteroids equator, attaching the
sample bags and HSPR to the free end. After extensive
earth based calculations are radioed back, the HSPR
blasts off, despinning the asteroid and picking up
several Km/sec Delta-Vee for the trip back toward
earth. The HSPR uses most of it's propellant aiming
itself and the Chunk, into a Lunar flyby resulting in
a 2X Lunar Periodic Orbit. This orbit is quite easily
attained and is very stable.

Once in this orbit, STEG powered machinery will start
to process it. The details have not yet been
completely worked out, indeed they really cannot be
until the asteroidal materials have been analyzed.

If we were fortunate enough by be able to sent 3 HSPRs
out to 3 NEOs, we would like 1st a metallic chunk
(especially heavy in Platinum Group Metals), 2nd an
asteroid or comet nucleus chunk (in a plastic bag)
containing volatiles such as water, methane, CO2,
etc.,
and 3rd, probably more metals, but that's very
tennative at this point. Then each of these 3 HSPRs
would refuel and repeat similar missions, many times.

Anyway once we start processing metal from asteroids
in HEEO, we would use our STEG technology plus MHD
technology to form tanks, pressure vessels, and space
habitats, (with Rad. shielding). Most of these would
be given propulsion systems, and the 100% automated
system would change over to a 99.5% automated system,
with human supervision and enhancement. After humans
live in these colonies, we would probable move these
asteroid recovery operations to earth's L-4 or L-5
zones for safety.

I don't want to discuss costs, time frames, or
technical details. This is just my personal
perception of what may come about. I would very much
like to be a part of this, and indeed I will if I live
long enough.

Dave Handwerk

--- Michael Persohn-Costa wrote: