charles@stb.info.com (Charles (from bbs)) (06/17/91)
How do we mine the El Dorado asteroid ? Is it one big stainless steel
nugget, or is it differentiated ? Either way, I propose blasting it
to pieces using high explosives. If it is a homogeneous stainless
steel nugget I would drill a hole right to the center and insert a
small nuclear device. If it is differentiated, conventional
explosives might suffice. Nuclear gives more bang per pound, so
better than chemical and takes less propellant to send it to El
Dorado.
We do not want lots of fragments flying everywhere, all we need
is to create a powerful shock wave to disrupt the asteroid structure.
The shock should be small enough that gravity will continue to hold
the pieces together. We could literally surround the asteroid with a
safety net to ensure most of it is retained. Once shocked the
pieces can be individually transported or processed by a robot
smelter. If it is well differentiated it might be possible to
visually separate out nuggetts of rare metals, and discard the
silicates and iron. A weak acid could dissolve reactive metals (
alkali earth and alkali metals and iron ) and heavier metals like Gold
and Platinum would be beneficiated. If desired the acid solution
could be electrolysed with low energy to recover the lighter metals.
Beneficiating by weight might be possible, would have to spin the
nuggetts in a centrifuge to find out how dense they are. Each nugget
could also be scanned by alpha particle back scattering or other
radio-spectroscopy means, and then sorted into valuable and less
valuable bins. Probably cheaper than electrolysis too. Most efficient
might be to use minimum size ( ie critical mass only ) nuclear
charges, and progressively shock parts of El Dorado, that allows more
margin for error in case we guess wrong about the quantity of shock
needed - do not want to over do it ! Would need rather a lot of
diamond drills if it is steel, maybe somebody could design a laser
cutting torch so we can burn our way in. How about a deliberate
nuclear pile meltdown on the surface, the hot pile melts to the center
via gravity - al la China Syndrome.
An advantage of a single blast dead center would be that the
surface structure would be least affected, so it might be possible to
the centre, and leaving a large hollow structure which could be turned
into a human habitat. I like that better than progressively blasting
it completely to pieces from the outside. Residual radiation might
be a problem for future colonists, I wonder what the half-life would
be.
In the immediate term it would be interesting to send a probe to
El Dorado, to see if it is differentiated or homogoneous.
El Dorado is probably spinning, so the blast could be timed such
that the exhaust coming out of the drill hole would cause a reaction
which would tend to propel the asteroid towards the Earth a little.
We do not have controlled fusion, but maybe a large thermonuclear
device could be designed as a shaped charge. After the initial
fission explosion and hollowing out some of the interior, the
thermonuclear shaped charge could be inserted into the interior of El
Dorado, and the drill hole widened. The blast would then be mostly
directed out through the vent hole, creating a more substantial thrust
reaction, which could maybe manouver El Dorado within a few million
miles of Earth. This would be most useful if the blast could be done
at perihelion, thus lowering the aphelion, making collection of the
asteroid pieces much cheaper.
Perhaps the nuclear shocking and thrusting could be a government
program. Then collection and benefaction of the pieces could be by
private prospectors.
* Origin: Ventura Co NSS 805-649-5314 STS final approach
(1:206/2403.0)
szabo@sequent.com (06/17/91)
In article <1991Jun16.195153.9959@stb.info.com> charles@stb.info.com (Charles (from bbs)) writes: >We do not want lots of fragments flying everywhere, all we need >is to create a powerful shock wave to disrupt the asteroid structure. >The shock should be small enough that gravity will continue to hold >the pieces together. We could literally surround the asteroid with a >safety net to ensure most of it is retained. Any significant shock wave is going to be greater than the escape velocity (a few m/s). The net, perhaps nylon, is a better idea. Also, if possible set up the explosive(s) so that they fracture the insdide of the asteroid while leaving a surface shell intact. (Charles suggests this also later in his post). The combination of the net and the shell may be sufficient. Cold metal is brittle, but I am not sure whether it would fracture in the way we like, rather than just melting and recondensing. Data from underground nuclear explosions would help here. It would be best if we could produce powerful ultrasound with little heat. >pieces can be individually transported or processed by a robot >smelter. Pumping a very thin atmosphere, and/or magnets may suffice to move the gravel through tubes in microgravity. >In the immediate term it would be interesting to send a probe to >El Dorado, to see if it is differentiated or homogoneous. It is mostly likely homogoneous, I am afraid. The metal asteroids that have struck earth (iron meteorites) are homogenous. Another interesting thing we need to know is how much metal regolith exists on the surface. This saves us the blasting and grinding steps. In general, exploration is cheaper than mining, and we should search widely to discover the most easily extracted resource before committing $billions to mining projects. >thermonuclear shaped charge could be inserted into the interior of El >Dorado, and the drill hole widened. The blast would then be mostly >directed out through the vent hole, creating a more substantial thrust >reaction, which could maybe manouver El Dorado within a few million >miles of Earth. Some issues here: * We can't use Earth gravity assist or aerobraking for such a large asteroid and unpredictable propulsion scheme. Therefore, the delta-v is likely to be quite large (several km/s). * The energy required to achieve that delta-v would likely disrupt or vaporize the asteroid. For example, to achieve 4,000 m/s the power output is (1e10 kg)(4,000 m/s)^2/(.01 s) = 1.6e19 watts assuming a propogation time of .01 second. Of course, we could do multiple explosions, but hundreds to thousands of small nuclear warheads starts to get expensive. * The Christic Institute et. al. don't like things called "nuclear". There is also a treaty that ban putting nuclear explosives in space which would have to be changed (this is a good idea anyway -- it would be much better to allow nuclear explosives in space and ban them on Earth!) Interesting brainstorm. -- Nick Szabo szabo@sequent.com Embrace Change... Keep the Values... Hold Dear the Laughter... These views are my own, and do not represent any organization.
jdnicoll@watyew.uwaterloo.ca (James Davis Nicoll) (06/17/91)
In article <1991Jun17.052228.8112@sequent.com> szabo@sequent.com writes: > >Some issues here: > >* We can't use Earth gravity assist or aerobraking for such a large > asteroid and unpredictable propulsion scheme. Therefore, the delta-v > is likely to be quite large (several km/s). > >* The energy required to achieve that delta-v would likely disrupt or > vaporize the asteroid. For example, to achieve 4,000 m/s the power > output is (1e10 kg)(4,000 m/s)^2/(.01 s) = 1.6e19 watts assuming a > propogation time of .01 second. Of course, we could do multiple > explosions, but hundreds to thousands of small nuclear warheads starts > to get expensive. This is probably a stupid question, but is the change in kinetic energy (and a power rate based on a time value that appears to me to be arbitrary, unless I missed something) a particularly useful number to look at? Hmmm. That is phrased poorly. Maybe an example: Take a 1 kilo object and change its velocity by 1000 m/s. That's a change in Ek of 0.5(1 kg)(1000 m/s)**2 or 5 x 10**5 Joules. Now, let's assume we're using a rocket to cause the delta vee which has an Isp of 400. Mass ratio will be something like: M1/M0 = e**delta vee/exhaust velocity = e**(1000 m/s)/(4000 m/s) = 1.28 If M0 = 1 kg, then M1 = 1.28 kg, so we have to throw .28 kg to get our delta vee. Ek = .5(.28)(4000)**2 = 2.24x10**6 Joules. To power the system we're using, we have to come up with 2.24x10**6 J, but the change in Ek in the object is only 5x10**5 J, a bit more than a fifth of the energy we actually use. The ratio between the delta Ek of the object and the energy we actually use for a given propulsion system goes up as Isp increases, of course. In your example up above, while the delta Ek is 1.6x10**17 J, the actual energy we'd need would be higher (How much higher depends on the Isp of the system we use). As an aside 1.6x1017 J is about the amount of energy we could produce using all the the world's current off- the-shelf supply of nuclear explosives (Actually, it's two or three times as much), so we'll need to build more nuclear explosives to move the above rock, perhaps much more, depending on hw we use them. Anyone out there have an idea how much nukes cost per megatonne? If there's some painfully obvious reason you used the delta Ek and the .01 second values you did, take it as written I pound my head shapeless in contrition. James Nicoll
szabo@sequent.com (06/18/91)
In article <1991Jun17.144137.23456@watdragon.waterloo.edu> jdnicoll@watyew.uwaterloo.ca (James Davis Nicoll) writes: > If there's some painfully obvious reason you used the delta Ek and >the .01 second values you did, take it as written I pound my head shapeless >in contrition. No, I was being pretty arbitrary. The energy of the explosion is given off over less than .01 seconds. The actual sound shock wave propagation takes on the order of 1 second. The power output of a nuclear explosion might blast a cold metal asteroid into smitherenes. That's what I get for brainstorming on the net. :-) For a more accurate analysis, we need to look at the actual results of underground nuclear tests. -- Nick Szabo szabo@sequent.com Embrace Change... Keep the Values... Hold Dear the Laughter... These views are my own, and do not represent any organization.