The first is debt servicing arrangements capable of handling projects where payoff periods are measured in decades (if not centuries) that will need to be put into place (which is why debt servicing will be a most interesting challenge for this potential space business; although large scale projects such as terrestrial mines & skyscrapers - as well as the illfated Iridium consortium - seem to suggest that this problem isn't completely insurmountable).

Mind you: the payday from a large metal rich asteroid suddenly dropping a large load of processed material on terrestrial markets would certain put a new spin on the old traders' cry of optimism: When my boat comes in!....

(It is assumed here that debt servicing will be handled by futures sales of the processed raw material being mined... to avoid flooding the market, the ideal would be to have every gram of processed material presold before delivery; which could be incremental during nearEarth flybys - an especially attractive option if the final intent of the mining operation is to create some kind of spaceship/city/whatever - or dropping it en bulk from a final Earth orbit)

The second & third challenges have (probably) almost been met even now; & with development incentives could be tested in space within a couple of years. Both are technological - the bulk of space mining operations are almost certainly going to be robotic rather than human - & involve the creation of spacerated automated materials processing technology for turning floating piles of rock into valuable raw material; & mobile mining technology which can make the raw material available for processing. Elements of these technologies are almost available now (with a few systems existing on the drawing board... or should i say CAD nowadays?); & some systems testing has already taken place... the main challenge here would be to spacerate designs which are capable of the years of work they'll be required to do....

(It's worth noting that the same basic technology could also be adapted as Earth-impacting asteroid mitigation strategy... something we're going to have to develop sooner or later. Roll on real space industrialisation)

(On an internet mailing list, i suggested that a major prize should be raised for the first company to successfully deploy & demonstrate this technology... not that i'm generally a fan of prizes; but because this is such a crucial technology in the development of space industrialisation that anything which can fasttrack its development would be valuable. It's worth noting that the same basic technology could also be adapted as Earth-impacting asteroid mitigation strategy... something we're going to have to develop sooner or later.

(One particularly interesting challenge which needs to be met - @ least if we're trying to deliver processed material to the Earth's surface - is how to decelerate large inert masses from flyby velocities to ground zero safely & economically. This is a surprisingly difficult challenge (as MIR is about to demonstrate); & will probably require lightweight reusable heatshields; as a coating of slag from spacemining operations seems unlikely to be strong enough for our purposes)

The fourth challenge would be to develop propulsion systems capable of using local raw materials (probably light for power; with hydrogen as a fuel - although mass drivers using slag from the materials processing systems are certainly conceivable) to nudge the mined asteroid (with or without gravity assist manoeuvres) towards Earth orbit (assuming Earth orbit actually is the mine's final destination, of course). These thrusters don't have to be powerful; but they do need to be longlived... industrial strength Deep Space 1s; or more radical technologies - sails; or M2P2-based technologies - would be eminently suitable...

Ideally, you would be start by mining an asteroid like 1999 AN10, which make regular passes through terrestrial space; & use your propulsion system - in collaboration with the earth's own gravity - to trim the asteroid's orbit to keep the asteroid on an Earthgrazing (& therefore: potential processed materials deployment point) during most (& ultimately every) Solar orbit... under these circumstances, one should aim to make deliveries of processed material on every flyby. If this isn't possible; & the orbital mechanics mean that interim deliveries of processed material are rare or nonexistent, the most cost effective way of running this operation is for the mined asteroid to reach its final destination as close to the time when its raw materials have been completely processed as possible... it follows, therefore, that: as total materials processing of even a small NEO is likely to take decades; so can the propulsion system required to bring the processed material from space to Earth orbit....

(Which is why debt service is such an interesting challenge for this potential space business...

(By the way: the flight & operations strategy for a spacemine which is to be completely mined out is obviously different to one which is designed to be reformed as a spaceship of some form: in the former case, you essentially want to bring the mine into a final terrestrial orbit, from which it can be carved into nonexistance; whereas the later goal is continuous orbital trimming - or acceleration, if you're aiming for interstellar space - of an external shell while you strategically download processed material. More on these options below)

Substantial legal issues have to be addressed before any of this can happen, of course; & for Lunar mining in particular (the issues involving asteroid mining are rather different), these issues are likely to be the most intractable in the short term. Commercial operations on the Moon are currently banned under the Moon Treaty; & - given that only the US-Americans currently claim to have any motivation to industrialise space - there's little or no motivation on the part of the rest of the world to change this situation (Australia has made some noises about trying to change this treat as some bureaucrats can smell a cheap buck here; but noises are all that Australian politicians are generally any good at). Asteroid mining may be legal in the absence of any contradictory precedents; but few financiers are likely to invest in a project where the final product can be legally hijacked by independent parties because there is no legally enforceable ownership.

I suspect, though, that this particular challenge will be ironed out - if only be default; probably by some group doing the job & challenging others to stop them (& so long as they don't try doing something stupid like hijacking the entire supply of Lunar ice or digging up the Apollo 11 landing site to sell on Earth, i doubt that the motivation to stop them will be particularly strong) - by the time the technology exists to really do the job....

The sixth challenge would involve reducing the cost of mass launch from Earth. In the early days of space mining operations, this would certainly be desirable; but perhaps not strictly essentially: if the first five cornerstones were in place, even expensive launch technology might appear cost effective due to the appropriately astronomical value of some asteroids; as the following reference article demonstrates: ---

Part One: Space Mining as Space Construction

It's worth noting that the chemical analysis of 433 Eros mentioned above was derived from a single spectrographic scan (a limitation caused by the bungled rendezvous burn last year) & is therefore very interim... the real value of this rock will only be established after the full NEAR mission is completed in 2001. However, the challenge outlined by the Beeb's scribe remains considerable: how do you turn the virtual asset of Eros is a realisable one; without flooding the market with the product your trying to sell. Financing the operation would presumably come from a mixture of sources; including conventional financial investments (loans, in other words; probably at high interest early in the operation; although the project can be refinanced as successively reduced rates as the minable asset goes from being simply a virtual asset (ie, unprocessed; in space) to a more obviously realised one (processed material; headed towards Earth); to presale investment (where a minerals company, says, effectively buys in advance the final product); while preselling the mine's processed material on the future's market would help with debt servicing.

Using space mines as the basis for large scale space construction is another possibility....

(The following scenario assumes that the final goal of your space construction is a city plying the Earth/Mars/return Hohmann transfer orbit; but it is adaptable to any inner solar system - & perhaps as far as Jupiter - trade route; as well as preparing arks for the longer jump into interstellar space. Modifications of this scenario specifically in terms of creating large interstellar ship will be discussed below)

You need to pick an asteroid using the following characteristics for judgement:

• useful raw materials to mine (metallic, obviously, although the actual mix of metals to be looked for is pretty much up for grabs... a good supply of consumables - water, in particular - would also be useful);
• easy of access from Earth (especially important where launch costs are high);
• & an orbit which is (relatively - we're almost certainly talking decades to play out the process described here) close to the basic Earth/Mars Hohmann orbit.

Land a basic mining technology package on the target asteroid; including automated mining units; materials processing units; control & command systems; & some kind of booster technology (currently, M2P2 - mini-magnetospheric plasma propulsion; currently under serious investigation by NASA - seems the simplest & most economically appealing system; although ion-style drives; solar sails & even mass drivers using mining slag could be considered)....

(I haven't mentioned space prospecting here; but this is obviously a crucial part of the space mining business. Much of the spectrographic ground work can actually be done from Earth, although this would require large, purpose-built telescopes; the rest would presumably be done with a constellation of nanosats)

Use automated systems to mine the asteroid (preferably by digging along the spin access, so you're effectively hollowing the asteroid in a basic space colony configuration from the start... at a certain point, you would also have to reinforce the walls of the asteroid to keep it from collapsing (non spherical - ie, less than about 200kms in diameter - asteroids appear to astonishingly weakly put together), especially at the seems between individual rocky masses; but this is unlikely to be an immediate mining priority), creating raw material for sale on Earth (or for inspace construction, if such construction is actually taking place @ this time... probably likely); electricity to power the operation & fuel for the boosters which will begin the agonisingly slow process of redirecting the asteroid into an Earthgrazing orbit... from which you can download processed material, upload new construction equipment; & use the Earth's mass to gravity assist your asteroid into its final Earth/Mars/return Hohmann transfer orbit.

At a certain point, the mined out part of the asteroid will become large enough to install people on board... if by this time, your mine has reached an orbital situation where it is regularly grazing the Earth; you essentially have an extremely large spaceship moving regularly in & out of terrestrial space. Operations can speed up considerably at this point; because the regular gravity assists make it cheaper & easier to trim your mineship's orbit to its final flightpath; while you can help financing your operations by dropping off processed material while uploading additional mining/processing/booster technology on each pass. If the mining operations have advanced sufficiently, you can even start installing people on your mineship; although automated technologies would still be the basis of our operation (for financial if no other reason... spacemining will almost certainly work on the principle that the only time you use humans is when it's too expensive - or dangerous - to send machines)... the odds are, therefore, that the manning of our mineship will need to take place as late as possible in the operation.

Whatever the flight status; you need to continue the orbital manoeuvres until the asteroid's flightpath also touches Mars's orbit regularly, reinforce the wall structures (it appears that most asteroids are extremely weakly constructed) & add all the essentials of life (atmosphere, which can be derived from local material; or mined from other, cometary NEOs; additional sources of power: solar; nuclear & tether are all exceedingly viable here; golf course; wildlife sanctuaries; etc); & you have a O'Neill-style space city mining itself out while plying the traderoute between the Earth & Mars....

(Notwithstanding my point about delaying the arrival of people, it doesn't necessarily follow that a mineship/space station need be fully converted before you open the doors for people: a large asteroid - a couple of kilometres or more in length - need only be partially mined before conversion to human habitation begins in the mined-out section; & this habitable zone can be occupied as soon as there is a viable reason for doing so... presumably: @ the point where you start to achieve a successful Earth/Mars/return trajectory; even if this isn't the final Hohmann transfer orbit)

Whether or not this strategy is eventually used to build space stations (& this approach makes rather more sense than many of the strategies currently under serious consideration), this scenario reinforces my belief that space mining & construction is more of a financial challenge than a technological one... not that the technological challenges aren't considerable, of course.... ---

Part Two: The Mineship as Interstellar Ark

There are a bunch of ways of beating the challenges of extraterrestrial flight with robotic probes; & no doubt we'll use all of them... some possibly in the not-too-distant future (before the current budget chaos, Dan Goldin was on record as expecting a probe into interstellar space - which may or may not be the same thing as an interstellar probe - as likely to be launched within 40yrs... if M2P2 propulsion (potentially: a fine cost/speed compromise for exHeliopause research) really stacks up, this estimate might actually be conservative.

Launching a small interstellar probe is a very different challenge to simply flying a micro- or nanoprobe; but no doubt people will eventually want to try & make the trip (especially if useable life expectancy continues to expand beyond the biblical three score years & ten). Assuming that there are no transEinsteinian shortcuts to the found here, what's the cheapest way to build a space colony fleet?

The above mineship scenario is an obvious starting point; but further modification is required before the system is fulling practical. Obviously: you're orbital strategy will be different if your a priori position is to launch the mineship into interstellar space rather than synchronise it with a solar system trade route like the Earth/Mars/, cisLunar or Earth/Jupiter/return orbits... instead of trying to trim your mineship's orbit, you want to accelerate it as fast as possible. Multiple flyby scenarios will be the order of the day here; as you attempt to synchronise the flight of several metalrich mineships so that @ the chosen launch date, they're all flying in the same direction @ more or less the same speed....

(As mentioned previously, this concept has the peculiar corollary that you might begin mining your ship decades - even centuries - before it becomes anything resembling a ship; giving you plenty of time to pick up speed using solar system gravity assists as well as making it easier to synchronise the launch of multiple interstellar arks)

The goal would be to launch the fleet before any of them are completely built; with only a skeleton crew on board each (you might be talking about leaving with less than 10% of final capacity prepared)... this gives your colony the freedom to expand through the dark light years of space; collecting consumables from comets as they fly (in this context: comets will be a fine, flying resource base, rich in water & carbonaceous compounds & their value for interstellar colonists - if not their robotic predecessors - will be considerable... mining of such resources would presumably begin before the interstellar arks are even being used as arks: once these ships begin looping through transJovian space, the capture & processing of slow, barely Sun-modified comets into useful raw materials will be comparatively easy). Presumably, there will also metalrich asteroids out in interstellar space (this comment remains highly speculative)... if so; these, too, could be captured; & slowly redirected towards the target star, adding to the fleet.

Given that you're carving your ships from the inside of metalrich rock rather building from the outside, the walls could be almost arbitrarily thick to avoid particle damage at low relativistic speeds... it might even be possible to generate electromagnetic fields around the ship to charge & deflect particles headed towards the ship. Interestingly, it would be feasible to restock your ark with consumables when you arrive at your target star; or simply abandon it in flight: either to colonise an interstellar world; or - probably more likely - to build a bigger ark for the next leg of your endless journey.

(Given the technical feasibility of this design, it's entirely possible that abandoned ark ships could be drifting through solar space; but it would be difficult to establish a system for detecting them without a cheap space prospecting nanocraft. There could even be a cultural drive to equipment a kind of space museum of ETI existence for humanity (Dr Clarke's TMA-1 meets Rama, if you like) to discover a safe distance from the Earth... the main asteroid belt, for instance. In this context, i note that the mainbelt asteroid 16 Psyche has a spectrum which suggests near-pure metallic content; covered with dust... anyone planning a quick visit to 16 Psyche?...)

In the longest term, though; smaller sailcraft flying on beams of energy between stars will eventually provide the most cost effective means of interstellar travel. I wonder if it would be possible to detect these energy beams as evidence of a technological ETI?...