[Thaeris]

The problem is inertia to a large degree, a rail-gun system would probably put stuff into space pretty economically, but I would have thought nothing organic would survive the launch. Oddly enough, the emerging system of piggy back as high as possible and then launching may be the best midway option for the forseeable future. Whilst it's still not cheap, taking the 'scenic route' of horizontal flight might prove to be far cheaper than getting out of the atmosphere as fast as possible, which is kind of ironic.

This is irrefutably the way to go - it requires no real brain power to recognize this after one has a basic understanding of physics and aerodynamics. And I do mean basic:

The basic rocket design is an attractive concept because it is readily understood and is fairly simple to make calculations for. A cylindrical design means that your center of mass along the line of action/flight is inherently in the center, and manufacturing components to fit in a cylinder isn't too difficult a task. It's still a lot of manufacturing time when you have a "specialty" product on that order of magnitude, however, and along with the cost of fuel it's not going to be cheap unless there was significantly more demand.

The problem of course is that you're fighting gravity for a long way up, and that fighting will be part of your initial engineering calculations. 0 to mach something almost straight up is not easy.

Fighting gravity at an angle of attack less than 90 degrees is a great way to not have to have a power-to-weight ration of greater than 1-1 when reaching launch-ingress speed and altitude. An easier climb means you use less fuel, less fuel means you have to lift less mass, etc., etc. And less mass is easier to accelerate with. I could go on, but this should be easy enough to understand.

Thus, level flight to altitude and launch point is a great idea. The problem is that now you're not just designing a spacecraft which must climb through the atmosphere (aka rocket), but a true aerospace system. Extra aeroplane is extra mass, which some would complain about with regards to the shuttle. A self-launched system is the ideal, though the combination of tried-and-true technology at this point is the limiting factor. Having separate fuel cells for air-combustible fuel and bi-fuel reactions/SRBs (should a system be so designed) as well as separate engines is a HUGE amount of mass to lug around. The best solution currently thus is a parasite launch vehicle scheme, similar to SS2. Otherwise, you need a system like Skylon, where you can reduce both the propulsion systems as well as the fuel loadings. We really need Skylon.

Another option is the air-launched rocket (which has been experimented with) which would be designed for conventional recovery (ala Shuttle SRB's).

[Luis Dias]

...and then there's that spinning monstrosity that gets its boost from microwave blasts from the ground.... pretty kewl stuff btw

[Thaeris]

The problem with that then is your dependence on ground-based systems.

However, if we begin to see more nuclear-powered spacecraft, the same engine concept you noted above, as see in sources here:

http://grasptheuniverse.com/star-travel/beamed-energies-propulsion/
http://en.wikipedia.org/wiki/Beam-powered_propulsion

...could power themselves in the atmosphere, while using the same reactor in space to drive engines such as VASIMR, etc. I feel this represents a very effective, low-mass propulsion system.

Combining the aerospike engine with the SABRE engine concept would assumably be a great design direction if using chemical reactants as fuel alone.

[esarai]

My personal take is that the space age will never be over as long as we rely on space-based systems so heavily.  We have a constant, if unmanned, presence in outer space, and until that changes, the space age lives on.

[watsisname]

That aint so easy to do. The orbit in question can be relatively far away as well.

And there's good chance you'll find stuff in orbit anyway already, specially in the Langrangian points

Unfortunately only L4 and L5 are stable, and are also quite a ways away from Earth.  There's also reason to doubt that many asteroids are there due to the influence of the moon which makes those points unstable in the long term.

On the other hand, asteroids in horseshoe orbits could make for easy mining targets, as they regularly and predictably get "fairly" close to earth without posing a significant impact risk.  Might even be able to capture one someday.

[666maslo666]

Regarding the space elevators - this concept does not require any new materials, substitutung tensile strenght with momentum:
http://en.wikipedia.org/wiki/Launch_loop

[Nuke]

merely catching an asteroid will be no easy task, since it will likely weigh more than every spacecraft and satellite ever flown combined. it would take a lot of missions just to determine if an asteroid is a viable canidate for capturing. you need to determine all this stuff well in advance:

composition (metal/rock/rubble)
mass
center of gravity
orbital parameters (this can be done with basic ground astronomy)

there's probably more you need to know, but thats all i could think of. you also have a couple modes of operation, do you want to catch a flyby asteroid, or do you want to pluck one out of a fairly stable solar orbit. catching a flyby will require that the asteroid come under sufficient gravitational influence from the earth. apophis is actually a fairly good candidate, assuming its not a rubble pile. all you need is a lot of retrograde thrust in a short amount of time while the asteroid is closest to earth. given the mass it would take a huge amount of thrust, and therefore fuel. srbs would probably be the best bet. the window of time for this is very narrow so you cant use slow burn engines like ion or solar sails. you could also use an aerobrake maneuver but thats just asking for trouble.

it might actually be simpler to pull an asteroid from a solar orbit. you could land slow burn propulsion systems, like ion engines. solar sails would be good for this kinda thing if you have time to wait. so over the course of years or even decades you do a low thrust hohmann transfer. this is also safer because of the low rate of change of the orbit. if something goes wrong you have time to see in in advance, and react to it. using the previous method a misfiring of the srbs could take your pet rocks and drop in into the atmo, and you would have little time to do anything about it. but with low thrust engines you have super fine control of the asteroid's orbit and can completely avoid putting it into hazardous situations.

either way requires landing on the asteroid and installing engines, reaction control thrusters, and other equipment. this can probably be done with robots. it might be better just to mine asteroids in place though. having an asteroid in a less than lunar orbit would certainly provide a good place to build a large orbital industrial complex. you could also hollow one out for habitation, which would protect the interior installation from radiation and solar storms. you would definately need to do this for a space elevator, but i dont see that as being feasible at the moment. so i would use it as an infrastructure platform rather than anything else in particular.

[watsisname]

My main concern with trying to capture an asteroid during close approach from an elliptical orbit would be that since you have to apply a huge amount of thrust in a fairly short time interval you might shatter the asteroid in the process (IIRC many asteroids are essentially fairly loosely-agglomerated rubble piles).  If you could grab one from an earth-like solar orbit or horseshoe orbit then you might be able to very gently ease it into a more practical position and also have a lot more time during the process to react to any possible errors or unforeseen circumstances.  Might be more economical fuel-wise as well.

I'd imagine you'd also need to be especially wary of imparting unwanted spin to the roid during the maneuver.  Would require very good knowledge of its mass distribution (might be obtainable with gravity-measuring probes).

I'm all for trying aerobraking on a roid, that just sounds like a wonderful idea.

[Nuke]

My main concern with trying to capture an asteroid during close approach from an elliptical orbit would be that since you have to apply a huge amount of thrust in a fairly short time interval you might shatter the asteroid in the process (IIRC many asteroids are essentially fairly loosely-agglomerated rubble piles).  If you could grab one from an earth-like solar orbit or horseshoe orbit then you might be able to very gently ease it into a more practical position and also have a lot more time during the process to react to any possible errors or unforeseen circumstances.  Might be more economical fuel-wise as well.

I'd imagine you'd also need to be especially wary of imparting unwanted spin to the roid during the maneuver.  Would require very good knowledge of its mass distribution (might be obtainable with gravity-measuring probes).

I'm all for trying aerobraking on a roid, that just sounds like a wonderful idea.

youre gonna get spin just from gravitational gradient torque, especially if the asteroid is oddly shaped. you can gimbal your engines and/or add reaction control thrusters and use them to maintain orientation and steer. likely the asteroid will already be spinning when you rig it for moving.

as for aerobreaking (and i hope you were being sarcastic) an asteroid in the earth atmosphere, id completely avoid it for safety reasons. there are many bad things that can happen. the worst of which: asteroid could break up. anything that doesn't immediately hit the ground will come back around and hit on the next orbit. also you could damage the propulsion systems, aerobrake can only slow you down, but you will need to do a small pro-grade burn at apogee to lift perigee out of the atmosphere so that the orbit remains stable. if you cannot make the burn, then when it hits perigee again the orbit will decay further until it just falls out of the sky. a small hard asteroid will be your best bet for aerobreaking, but even with a solid asteroid you risk it breaking up because its suddenly going from freezing to hot which creates a temperature differential between the core and the outside, which could cause the rock to shatter.

[watsisname]

I wasn't being serious on aerobraking.  As cool as it'd be to see it happen in person (if it worked) there is simply far too much complexity and risk involved to be worth trying for real.

You bring up a good point on gravity-gradient torque, too.  Maybe a good way to go about it is to align the spin axis with the orbital path so that it acts essentially like a giant gyroscope for stability.  Then again, with a weirdly shaped rock you've got extra complications there.

[newman]

First of all, asteroids aren't readily available in low earth orbit. You have to go further than that to get one - a lot further. The Dawn mission arrives in orbit of Vesta, located in the asteroid field between Mars and Jupiter, tomorrow. It was launched in 2006 and the mission wasn't exactly cheap - and those were just the costs of sending a small probe over there, not something that would bring with it enough power to lug an asteroid back towards Earth. Anyway, in order to get an asteroid mined out in Earth orbit, you'd have to satisfy several criteria.

First, you'd need to know the exact size, composition, mass, and location of your target asteroid. You can't exactly send back Pallas or Ceres, those are way too massive, and right now we lack most of the data on smaller rocks present that would make such a mission feasible (hell, we lack most of the data on the larger rocks, which is why Dawn is out there on final approach to Vesta right now). This means years of sending probes to map out suitable asteroids - Dawn will just study Vesta and Ceres.

Then, you'd need to transport over an incredible amount of whatever it is you plan to use to get your target asteroid out of it's trajectory and on course for Earth. This would involve years of R&D and transporting costly material first into Earth orbit and then towards your target asteroid. Then you'd need to somehow remotely attach whatever it is you're using to propel the asteroid towards Earth - an array of boosters, a large explosive device, whatever. You'd also need to be very accurate or you may very well end up being responsible for wiping out every living thing on Earth. No pressure. Thousands of billions of dollars later, your most expensive space project to date (hell, most expensive project in the history of mankind, period) has produced a giant rock in orbit of Earth you can now mine at a hefty price (since it's still expensive as all hell to transport stuff up and down from just low Earth orbit - and you wouldn't park such an object in LEO due in no small part to extreme risks involved - you'd park it further out exponentially increasing the costs of reaching it). That rock better be made of Unobtanium laced with the purest processed heroin to justify the costs and risks.

Just wishing for a more elaborate space program isn't going to make it feasible. Fact of the matter is, while we have the technology to "get there", barely, we don't have the technology to actually do anything with it while making it cost effective and at least moderately safe. We're simply not there yet in terms of technological advancement.

[Nuke]

seems to me mining would be better do do in place. it would be a lot cheaper to send back refined ore than it would be to send back the whole asteroid. the only reason to put an asteroid into earth orbit is as a building platform. i wouldn't put it in leo at all. you need to at least be at geosync or higher. otherwise youl have a situation like you have with the moons like phobos, which will eventually hit mars due to tidal deceleration. point is you dont have to go all the way to the moon to have a stable platform for large scale industrial complexes. then again we could always build some mega rockets that can lift some serious tonnage, and build our own platform.

when i say layered approach i mean there are things that absolutely need to happen that open the door for other things. before we even think about orbital industrial complexes, moon bases, asteroid mining, or capturing and re-purposing asteroids. good place to start is orbital re-fueling. engine technology really isnt the issue there are plenty of engines on the drawing board and in use that can be used in space and use very little fuel/propellant and can deliver a lot of useful deltav. electric engines (ion, plasma, magnetic) use very little propellant and are meant to operate for long durations. the only thing really holding them back is the availability of electrical power. if those problems could be solved then a mission can be carried out with sufficient fuel for a return trip, refueled and sent out on another mission. so you get two missions essentially for the price of one (assuming the fuel depot can be used multiple times).

problem with electric engines is they are not launch engines. they dont provide enough thrust in a short enough time. you are never gonna see a nuclear launch engine for obvious reasons. launches for the most part will remain a chemical engine buisness for some time. sabre is a step in the right direction. cover as many bases with a single engine as you can, reduce oxidizer requirements, etc. we are going to need to lift a lot of tonnage into space with chemical engines to do anything mentioned so far. point is, one step at a time.

[Kosh]

Just wishing for a more elaborate space program isn't going to make it feasible. Fact of the matter is, while we have the technology to "get there", barely, we don't have the technology to actually do anything with it while making it cost effective and at least moderately safe. We're simply not there yet in terms of technological advancement.

Read my post please. Granted I wasn't referring to capturing asteroids because I'm not totally sold on the idea, but going to them isn't such a bad idea. What that is isn't building a more elaborate space program, it's building private industry in space. As I said, government dominated space programs are not the answer.

[newman]

The private sector hates negative profits even more than governments do. When governments overspend they can break the backs of taxpayers to make it up. When private industries overspend they generally go out of business.
That private industry in space would still be completely unprofitable with our current levels of technology. The whole concept would fail financially at the first step - getting your equipment into geosync orbit, let alone traversing the distance to the nearest asteroid belt, mining the stuff and getting back. It's simple math. If 1kg of some ore costs 2000$ on Earth (expensive ore), start calculating the costs of getting the automated mining equipment into orbit, then sending it over there, then sending the stuff back here, landing it on Earth and processing it. The costs rise exponentially if you want this to be manned.
It would make sense if you had some elaborate space infrastructure - space stations, research bases, shipyards, etc. At that point yes, if we find it's cheaper to mine something in space rather than lugging it from Earth we'll probably do that. But we're decades, if not centuries away from this. Before we get economical means to go out there safely and quickly I wouldn't expect the private sector to go much further than LEO.

[Unknown Target]

Space needs another attraction besides just raw materials or people who want to go to it saying we need to go to it.

Much of my work on my Venus colony concept was based off the idea that space should look like a better place, something that you can't get on Earth. Why would anyone want to live on Mars, if you think about it? Dead, cold, covered in rust...you can't exactly sell photos of the place beyond "hey look we're on a different planet".

The idea behind my Venus concept is that it would offer something you can't get on Earth, something that might make space more interesting to many people. Living in a floating sky ship whose interior looks like something humans would want to live in (as opposed to current space effort) I think would attract more people and more interest in the idea of colonization.

Tbh I view the ISS as a money hole for NASA, and the Shuttle has too much weight in politics for it to fly well, I think.

In regards to future flight, I see things being a lot stranger than many people expect. I see people downloading their minds into mechanical bodies, or undergoing genetic alteration to adapt to the harsh climates of space travel. I think sentient robots (probably us in robotic bodies), and real life furries are in the cards for future space travel.

[Luis Dias]

Future space **** will start by curiosity by wealthy billionaires that are just plain sick and tired of our planet's shenanigans, AKA luxury tourism. Then some billionaire will die, and the bubble pops. Then quietude again, until it gets cheaper. Then this economy will bubble up again and won't stop until we invent the warp drive. Then the 4th protocol of Zerblexians that state that any space-faring species with the ability to warp should be genocided to the last gene will take place and it'll be all over in less than a day.

[Kszyhu]

What do you need aliens for? Humans can exterminate themselves faster, cheaper, and with less hassle.

[Luis Dias]

But not completely. I was going for total anihilation, not "return to caveman age".

[Kosh]

The private sector hates negative profits even more than governments do. When governments overspend they can break the backs of taxpayers to make it up. When private industries overspend they generally go out of business.

And yet NASA was perfectly willing to shell out a billion to launch the Ares 1 while SpaceX was able to launch a rocket with the same amount of payload capacity for $50 million. NASA routinely goes over budget on nearly everything precisely because they are fundementally inefficient, with a bloated bureaucracy and highly protected jobs. One of the biggest reasons the shuttle lasted as long as it did was because it was viewed more as a pork barrel earmark rather than an asset, each shuttle took several thousand people for each orbiter just to keep it airworthy (for comparison the Skylon is intended to have a support crew of just 200).

That private industry in space would still be completely unprofitable with our current levels of technology. The whole concept would fail financially at the first step - getting your equipment into geosync orbit, let alone traversing the distance to the nearest asteroid belt, mining the stuff and getting back. It's simple math. If 1kg of some ore costs 2000$ on Earth (expensive ore), start calculating the costs of getting the automated mining equipment into orbit, then sending it over there, then sending the stuff back here, landing it on Earth and processing it. The costs rise exponentially if you want this to be manned.

Ah but mines crank out continual streams of said expensive ores. Once the machinary is up there it stays there, forever. Once the rock you're currently mining is depleted, you move it to another one. The machinery is a one time investment and people get rotated and resupplied on each trip. But you're also forgetting something important, what happens to the other metals? They stay in space where they will be used to build the infrastructure in space needed for future expansion. That greatly reduces the cost of space construction allowing for great expansion beyond the initial infrastructure you claim wont happen for centuries.

It would make sense if you had some elaborate space infrastructure - space stations, research bases, shipyards, etc. At that point yes, if we find it's cheaper to mine something in space rather than lugging it from Earth we'll probably do that. But we're decades, if not centuries away from this. Before we get economical means to go out there safely and quickly I wouldn't expect the private sector to go much further than LEO.

We've had much better propulsion technology than the simple chemical rockets since the 70's, with a greatly improved version developed in the 80's. Granted they aren't the best possible designs, they are adequate for getting to the asteroid belt.

[Polpolion]

That private industry in space would still be completely unprofitable with our current levels of technology. The whole concept would fail financially at the first step - getting your equipment into geosync orbit, let alone traversing the distance to the nearest asteroid belt, mining the stuff and getting back. It's simple math. If 1kg of some ore costs 2000$ on Earth (expensive ore), start calculating the costs of getting the automated mining equipment into orbit, then sending it over there, then sending the stuff back here, landing it on Earth and processing it. The costs rise exponentially if you want this to be manned.

Ah but mines crank out continual streams of said expensive ores. Once the machinary is up there it stays there, forever. Once the rock you're currently mining is depleted, you move it to another one. The machinery is a one time investment and people get rotated and resupplied on each trip. But you're also forgetting something important, what happens to the other metals? They stay in space where they will be used to build the infrastructure in space needed for future expansion. That greatly reduces the cost of space construction allowing for great expansion beyond the initial infrastructure you claim wont happen for centuries.

But sending the rockets there and back, even unmanned and with an empty hold, is still the most expensive part of the mission. Not only would you need enough fuel to get there, but you'd need to carry enough excess fuel to get back with a lot more weight added onto the ship. I really don't think that any of this is going to happen until current materials are near-expended and it happens to be cheaper for companies to go to the asteroids to mine than search the Earth for whatever scraps of precious materials are left. And at that point I'd bet that the world's economy would already be so crippled from thrashing that simply no one will be able to afford those missions aside from the richest nations and corperations.