Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

Comment Re: America (Score 5, Informative) 397

> IMHO I think "Star Wars" was actually more for defense from an invasion than to knock down missiles. I doubt it would have worked to do either goal; it's only now that we are developing lasers powerful enough to do anything to a distant flying object.

I worked on the Strategic Defense Initiative (the proper name for the project) in the 1980's. It was most certainly for knocking down missiles, all the math depended on it. As far as working or not, very few people understand the concept of "layered defense". SDI had 7 layers: two Boost Phase intercepts, three Midcourse intercepts, and High and Low terminal intercepts. Each layer only has to deal with what the previous layer missed. Assume, because the actual numbers were classified and I don't remember them after 30 years, that each layer is 60% effective, meaning 40% of warheads get through to the next layer. With 7 layers, only one in 610 warheads hits their targets. That kind of number is "survivable". Japan survived two warheads, and the US could survive about 15 or 20, due to being a larger country. This breaks the "Mutually Assured Destruction" concept, because the US would have plenty of undamaged assets to shoot back with.

But you don't need a fully functioning missile defense to apply leverage to the Russians. If you have only two functioning layers, and they are only 40% effective each, only 36% of Russian warheads get through. They have to build 2.78 times as many warheads to destroy their priority target list. The more functioning layers, and the higher their effectiveness, the worse their targeting problem gets, rapidly. The Russians may be deficient in some ways, but they had plenty of good mathematicians. They could see the threat of a layered defense, and they could not afford to build enough missiles to counter it. They could also not build their own SDI system, because Western technology was generally more advanced. So coming to the negotiating table to reduce missile counts was the only viable option, which is exactly what they did in 1991. In that sense, the SDI program helped win the Cold War.

Whether Reagan himself had a technical understanding of the project was irrelevant. That was between DARPA, Congress, and the defense contractors. As a former actor who did westerns, his job was making speeches other people wrote, and looking tough to the Russians. He was a figurehead for the nation. Tons of smart people did the real work.

Getting back to your lasers, we had two kinds as *advanced options* in SDI, airborne and space-based. Airborne were a boost phase system, designed to shoot at ICBMs while the rocket was still firing. That makes them an easy target, rockets have huge thermal signatures for targeting. But also they are fragile. Heat the nozzle of a rocket a few hundred degrees while operating, and it can easily fail, same for shock heating part of the fuel tanks. You don't have to melt them, just cause a gas explosion as the fuel boils, it does the rest. Space-based lasers were upper boost phase or early midcourse. They could get a clearer shot when the rocket was in the upper atmosphere, or starting on the ballistic trajectory. Physically the rocket was approaching the same altitude as the laser, so the distance was smaller. Both involved megawatt class lasers based on chemical combustion energy.

But remember, these were not the baseline, they were advanced options. And the US was making credible progress in laser technology. So it was not a matter of having them ready to use. It was a matter of the Russians believing the nation that beat them to the Moon could develop high powered laser weapons if they put their minds to it. After the Strategic Arms treaties were signed, the push to develop SDI technologies ended, so they have piddled along for the last few decades, and battlefield lasers and railguns are now entering field use. There was no rush because there was no enemy threatening enough.

Comment Re:It's not money it's a vision thing... (Score 1) 211

Phobos is a good spot for a control station while you are building up your Mars surface facilities. At first you have nothing on the Martian surface, and so not much in the way of support, or even level landing sites. It's not so good for keeping humans alive. So you send down some robots to start leveling and building roads, assembling greenhouses, unpacking solar panels. You can also send down drills to mine for ice, and an oxygen extraction plant (either from the atmosphere or the water). Once you have all that in place, *then* you can start sending down humans. Once on the surface, humans can continue to control robots locally, with the added capability to go outside and fix them as needed.

The other useful thing about Phobos is it's likely a Chondrite type asteroid, based on the very low density of 1.8 and spectroscopy. That type of asteroid can be mined for supplies like water and carbon compounds. Those can be reformed into Oxygen + Hydrocarbons, which are rocket fuel to land on Mars. Heat shields and parachutes don't give you accurate landings, because of variations in the atmosphere. You don't want the parts of your Mars base scattered across a 10 km landing ellipse, you want them to land at a preferred landing field, and *not* on top of other base parts. That requires a powered descent for at least a good part of the landing. A fuel station also simplifies returning from Mars.

So after the initial build up of the surface base, Phobos continues operation as a mining station and fuel supply point. The step-wise approach is more efficient in the long run, assuming you are going to Mars more than a few times to plant flags.

Comment Re:Budget? (Score 1) 211

About what the NASA budget is now. Currently they are spending several billion a year developing the SLS and Orion. Once their designs are done, they can turn to making the other necessary hardware and launch costs. The ISS is supposed to be retired in the 2020's, so that part of the budget can be reassigned to other missions. Don't think of it as a fixed project cost, government agencies don't work that way. Rather, they have an annual budget that is approximately the same from year to year, and projects are spread out to fit within that budget.

Comment Re:It's not money it's a vision thing... (Score 3, Interesting) 211

Which is exactly why as a space systems engineer, I'm working on Seed Factories ( http://en.wikibooks.org/wiki/S... ). Fully automated self-replication is hard. Instead, a Seed Factory grows grows from a starter set by three methods rather than one:

* Diversification - making new machines not in the starter set
* Scaling - making different size machines (usually larger), and
* Replication - making exact copies of what you already have

Your starter set allows you to make *some* parts and materials locally. The remainder is imported. As you add more machines, you can do other processes and make other products, and reduce how much you need to import.

Rather than try to make it all automated, you use remote control and *some* live humans where necessary. Thus an asteroid processing plant in near-Lunar orbit, or robots building a Lunar base can mostly be controlled from Earth, with occasional human visitors to fix things. Once you are producing food, water, oxygen, fuel, etc , then you can bring in more permanent occupants. The same goes with Mars. Start with a control station on Phobos, which is close enough for real-time VR. The crew remote control surface robots who prepare the landing site. Once enough equipment is set up down there, humans can follow.

Other people are working on finding asteroids and how to bring them where you need them. That's why I'm working on self-bootstrapping factories. Once you have the raw materials, you have to make useful products out of it. Launching whole industrial plants is too heavy and expensive. So you want to make most of the equipment on-site if you can, out of the materials you are mining.

Comment Re:Actually Not (Score 1) 130

That's the real problem with this mission plan - not enough bang for the bucks. An alternate approach follows up the small asteroid retrieval mission (4 meter/60 ton rock) with a bigger asteroid tug that can haul 11 meter/1000 ton loads, and repeat missions every few years. After you science the shit out of the first rock, you then use it as a testbed for mining and processing. You deliver a crew habitat and surround it with the first load returned by the bigger tug, creating radiation shielding. Keep adding modules, and start setting up a greenhouse too.

You make fuel, water, oxygen, and basic metals out of the asteroid rock you bring back. These supplies can be used for a lunar lander, which you can remote control in real-time from the high-orbit processing station. Explore the Moon, set up basic mining there too. Your asteroid tugs return more fuel than they consume bringing back the next rock, so they are self supporting. A high orbit station can refuel and repair GEO satellites, and supply fuel for planetary missions, helping cover the cost of operation.

Eventually you boost a habitat to a Mars transfer orbit, and protect it with more rock your tug collects from nearby asteroids. You repeat the mining and processing in that orbit, then move on to Phobos, and finally the Martian surface. You now have a string of stations from here to Mars, each of which can produce basic supplies to support itself, and which is radiation protected. Instead of a few weeks on Mars, your are remote-controlling robots from Phobos that build a permanent base, which the crew eventually go down to occupy. You already learned how to remote control stuff on the Moon from Lunar orbit, so this is building on past experience.

This is a plan that leads to occupying the whole solar system eventually, and probably fits in the same 1-2 SLS size launches a year. The main difference is using electric tugs wherever possible, cutting down fuel and increasing useful cargo, and mining wherever you go, so your locations are mostly self-supporting. There are already 13,000 known Near Earth Asteroids, just as many between Earth and Mars, and *lots* more once you get just past Mars into the inner Asteroid Belt. The Moon, Phobos, and the Martian surface also have lots of mineable resources.

What it requires is a change in thought patterns from rockets and capsules to more mining and processing equipment

Comment Re:Huh? (Score 1) 130

> akin to the level of background radiation on the surface of the earth,

It's not required to get the radiation that low. Astronauts already accept higher levels flying on the ISS (5 REM/year, equal to radiation workers), and for a one-time Mars mission can accept 50-70 REM total dose. Part of that dose is solar flare risk, for which they can hide in a "storm shelter" surrounded by water tanks and water-bearing supplies like food. Flare radiation only lasts a day or two - the time between the fastest vs slowest particles to get from the Sun to you. The background dose from cosmic rays is more steady.

Comment Re:Better (Score 2) 130

> Humans are super-expensive

They are only super-expensive because we have crappy logistics support from Earth. If we had space mining and production of basics like fuel, oxygen, and water, keeping people alive wouldn't be so darned expensive because we would not have to bring it all from down here.

Comment Re:Huh? (Score 1) 130

Radiation isn't a big problem if you make several assumptions. First, is the Mars/Phobos crew only make *one* trip in their lifetime. Second, you have a "storm shelter" for solar flares, which produce high peak radiation doses. The storm shelter is a small space surrounded by water or water-bearing items like food. That provides enough shielding to keep the crew from excessive doses, and anti-radiation drugs can help a bit. They just hide in the storm shelter for a day or two until the radiation from the flare passes. Third, the crew knowingly accept the risk they are taking.

We're talking exposure equivalent to 10-14 years for nuclear workers or LEO astronauts (50-70 REM). If you got that dose all at once, you would get slightly sick and recover, and your risk of cancer goes up a bit. More typically you get a lower dose at a steady rate, plus short term spikes if flares happen. Overall, the radiation risk is in line with the other risks they are taking (engine explosion, life support failure, etc.)

Now, for a colony transport this level of exposure is unacceptable for the general population, but these are exploration missions, and the crew is expecting some big risks.

Comment Re:Difficult investigation, or difficult charges? (Score 2) 99

> I don't think there's a single government that has decided what Bitcoin actually is - a currency or personal property.

It's a scarce digital commodity. Word documents or mp3 files are easily copied. Control of a bitcoin address, and whatever balance it holds, cannot. The control comes from a private 256 bit key, which is required to transfer control of the balance to another address. The balance can't be copied because you can trace it back through previous transactions to the point where the coins were first generated, and that history (the blockchain) can't be altered, but *can* be verified by anyone who wants to check it. Inability to copy it, and a limited supply ( no more than 21 million units, ever) makes it a scarce good in the economics sense.

Digital means it is easy to transfer, scarcity means it is in limited supply, and other technical features make it useful to people, creating a demand. Supply and demand establish a market value, like for other commodities. It's a commodity because one bitcoin is pretty much like any other bitcoin, in the way barrels of oil or bars of gold are pretty much the same. So most people don't care *which* bitcoin they get, just *how many* they get. That makes them easily traded, unlike, say, houses. Houses are all different sizes and shapes, and every one of them has a different physical location. People care very much *which* house they get, so they are not easily traded for other ones.

Saliva causes cancer, but only if swallowed in small amounts over a long period of time. -- George Carlin