Eh, while in general I agree with you, there are two other factors here. First, they really are short millions, not tens of thousands, of units. I have trouble coming up with simple reasons why they'd lie about that (apply Occam's razor for the rest of the argument). And second, they do have a certain amount of fiduciary responsibility to their shareholders (of non-zero but decidedly not infinite impact), which leads to a desire to place blame when possible (well in line with human nature as demonstrated by corporate execs, and so of high impact). So here it seems more reasonable than not to believe them.
No. Sony said it was due to shortages of the blue laser diode in the Blu-ray drives. Also, you'll note they're short a couple million PS3s, not a measley 16000.
Huh? I'm pretty sure the Egyptians didn't do a lot of work to decide if it was safe. The lead used would be unsafe regardless of the nanoparticulate nature of the compound. Lead was used in lots of other ways through history, too. That doesn't make it safe.
Yes, there is a distinction between available and announced. But I firmly believe that calling it a privacy issue is mislabeling at best. All of the info concerned was intentionally made public by the user in the first place (with, apparently, the exception of event invitations -- but I don't really think that's what people are whining about). The transition event isn't new, either. I check your page, see info A, come back tomorrow, see info B -- I now mentally create the transition event. It's not new, it's just announced instead of available.
I completely understand not wanting that much info about your friends for one reason or another, or not wanting that much information on your home page for UI / information overload reasons -- but that's a UI concern (potentially a very real one; I'm not trying to belittle it), not a privacy concern.
So yes, this changes how many people will see things about you. And yes, it reduces the effort required by strangers to track every detail about you and be a creepy stalker type. But anyone who believes it was hard to get all this information before is delusional.
I guess this is what confuses me: People aren't complaining because creepy stalker types have more info about them. And they're not complaining because their friends have more info about them. (Your friends read your page on a regular basis, right? That is what we mean by friends in this context, right? So therefore your friends notice these changes.) And they're not complaining that some set of people have access to this information that didn't previously have access. And as best I can tell, most people aren't complaining about the UI they're being presented (though clearly some are, that just doesn't seem to be the most vocal complaint). They're also not complaining that people can tell when they're online or not (they keep their IM name on the page, usually, right?). So, unless I'm mistaken, they're complaining because their acquaintences (people they know who only occasionally read their page) will, in all likelihood, get to know them a little bit better. And that seems to me to be a pretty minor complaint.
It's either that, or tens (hundreds?) of thousands of people are very, very confused about the meaning of the word "public." Either way, I'm truly amazed.
A better analogy would be if the county / state / country *alread* had a "type in a name to check for DUIs" web site that anyone could search, and then added a "recent DUI convictions" list below it. It's not putting the information anywhere it wasn't already, it's just making it more likely people will notice without thinking to explicitly look for it.
There's a little less privacy as a result, in the sense that more people will know more about you, but not in the sense that the information available to anyone who went looking has changed. It seems really weird to me that this many people think it's a big change (well, having not looked at it, there may be a big bad UI change that people don't like... that seems perfectly reasonable to complain about).
I'll just continue staring in amazement at the people who think this removed more than a small amount of privacy, and also at the ones who think this change didn't remove any privacy at all. As with many things, it seems the slashdot comments are completely polarized and miss what is most likely the real answer. Not that that's limited to slashdot, or anything...
BTW: Where will the lower parts of this thing fall when there is a disaster?....
To the west of the Earthside station, why?
It doesn't make a huge amount of difference, really. Your station will probably be near the ocean, so it won't get in anyone's way. Picking it up might be a bit of a pain, though.
Any material strong enough to make a space elevator out of will be light enough at the earth end that it will look more like a piece of ribbon fluttering in the breeze as it falls than anything else. It will land softly, except for the parts that are high enough up they don't survive reentry. Even for a fairly large elevator, the bottom is *very* thin.
There are plenty of obstacles to an elevator, but that one mostly takes care of itself.
I would say that the IT needs should sortof be postponed. They need to determine that the problem is solvable, and have some sense of how to go about it, but even if you need a high end supercomputer to do so, those can be built on a couple years notice; it will be 10 before the materials even start to look workable.
I'm pretty sure you're confused here. First, note that the padding is a 1 followed by some number of zeros, so no matter what the message actually ends with it is clear what is padding and what is message. That is, in all circumstances adding zeros to the end of the message changes what is being hashed, even when you ignore the file size part. And secondly, the message size as appended onto the message is the *original* message size, *before* any padding occurred. So appending zeros not only changes what the padded file looks like, it also changes the file size string that gets appended after the padding.
I really do think the mathematicians are doing exactly what you guys think they should be.
And actually reading the hash function descriptions is too complicated a solution for you? Oh, I forgot, you want your karma and most mods will assume you know what you're talking about because they don't read the specs either.
MD5, SHA, and every other hash function I've ever read the spec for appends some zeros followed by the original message size (the zeros are so it comes to an integer number of blocks) as the first thing it does. For exactly this reason.
At a guess, this attack requires that the two files be the same size. (But I haven't actually read TFA.) And attacks that delete or add data but can't manage to correct the file size are the minority anyway.
aka Constellation, and ditto the European manned space effort -- I hope they buy launch services from the likes of SpaceX.
Their first launch failed, but they found the cause (a rusted nut) and have fixed the problem and also implemented checks to catch it and many other potential problems in advance next time. They're planning to launch again in a couple months.
They are also at work on substantially larger vehicles, including a manned capsule.
If I were planning a manned space program 15-30 years out, I would be looking to buy my launch services and focus on the other parts, like what to do and how to do it once I got there.
Re:Telegraph didn't hurt anybody's grammar
on
It's OK to keep AIMing
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· Score: 3, Insightful
To be fair, there's a difference in quantity that could reasonably be expected to be relevant...
Also, most kids these days spend a fair bit of time on IM / SMS / etc, whereas kids almost never sent telegraphs. It is plausible that using bad grammar and syntax would hurt more when you're young and still learning.
I don't think telegraphs are a particularly relevant comparison.
Well, apparently you have to plug the cables into its eye sockets, and cramming more than one into each is probably hard. So more of a bridge than a router, I think...
IMHO, both licenses have their place. I prefer the GPL for my software, but could see using the BSD license if I wrote different software with different purposes in mind.
I believe it comes down to a question of goals (or, basically equivalently, what you think the word "free" is referring to) -- is your goal to set your software free, so that anyone can use it in any way you choose, or is your goal to maximise the amount of free software available in the world, by offering incentives to other developers to make their software free?
For my software, I choose the latter -- I have no burning need for others to be able to make a closed fork. I view my software as Free, but not without a price -- the price is, if you want to modify it, you need to make the modifications GPL as well.
Different views, different licenses. I don't see why it's such a big deal to some people what license other developers choose. If you don't like their license, don't use their software. And while we're at it, get off your high horse and make the world a better place by writing some code (or whatever other means you choose). With whatever license pleases you.
I agree. Mostly. And, given that scenario, I would indeed choose one of those options.
However, it's important to realize that because there are fewer manufacturers than there are consumers, and they often work together on decisions like this, an individual consumer has a lot less power than an individual manufacturer in shaping what products are out there. It might not be possible for me to buy an equivalent, non-DRM product.
This license is a way for a group of individuals to get together and bargain collectively, and thereby increase their power in the transaction to something closer to on par with the large corporations.
Unlike RMS, I don't believe I have a human right to run my software on hardware you're selling, and that it's immoral of you to try to stop me. But, I do want to be able to, and it matters to me. So, I plan to use this license as a bargaining tool by releasing software I write under it.
I don't mean to force anyone else to use this license, and I certainly see reasons for using GPLv2 or BSD-type licenses. They just aren't my reasons. I plan to vote not only with my wallet and my feet, but with the license of the software I write. If you don't want to do that too, that's fine, you're certainly welcome to make your own choices.
(All that said, I find it unlikely that the software I write will be relevant one way or the other -- it's not media-handling stuff, or a kernel or compiler, or anything else likely to hit DRM restrictions. But I plan to voice my opinion by using the GPLv3 on it, assuming I like the final draft.)
Not so. If I write software, and release it under GPLv3, there's nothing that prevents me from also releasing it on a DRM'd platform. I lose nothing. I can dual license the software; I've always been able to.
What is happening, is that I'm saying that if you want to use *my* software on a DRM platform, *then* you have to hand out the keys or whatever else is needed. Which, for software I write, is exactly what I want. (Of course, I have trouble imagining how it would be relevant for things I write, but that's a different matter -- I don't write media players or kernels or other obvious targets).
As a software *author*, I lose nothing. As a user of other people's software, I lose out only if I'm trying to redistribute their copyrighted work in ways they don't want. And, in that case, too bad for me -- just like it's always been.
This license is about giving authors more choices, not less. And personally, this is an option I like.
While I'm reluctant to put a dollar value on lives, they clearly have *a* value -- we as a society repeatedly decide to risk the lives of our members for societal gain, be they astronauts, firemen, soldiers, or even just people commuting to work on the freeway.
The development project required to do substantial changes to the heat shield would be massive. You can't just attach another layer of tiles, for several reasons. Weight is the obvious one -- it cuts into payload capacity, probably quite substantially. Structural concerns are also very real -- those tiles are exceedingly weak, and it wouldn't surprise me if they couldn't support another layer if it was merely glued on. Providing supports through the existing layer would take a lot of work. And lastly, if the outer layer is damaged, it changes the aerodynamics. Probably not enough to affect control, but quite possibly enough to cause localized heating that the tiles underneath can't withstand. If that's the case, then you haven't bought nearly as much redundancy as you'd hoped for, since the failure modes are linked.
Just to be clear -- none of these things are impossible. They would just take time and money. And, my guess is they would take enough time and money that it would be better just to spend the money speeding up the CEV development project. And once you do that, you're back to the current question -- keep flying the shuttle fleet as is while waiting, or retire it now and have nothing in place until the CEV appears. Yes, you could argue that redoing the heat shield would provide an intermediate solution. I argue that it would be so short lived and so expensive as to be a waste of money that could be spent on other things.
That would be called an ablative heat shield. It's been done quite successfully -- Apollo, Soyuz, and almost every reentry vehicle except the shuttle.
That said, ablatives aren't easy, especially if you want aerodynamic control as you come in -- it's exceedingly difficult to get them to ablate evenly, which results in weird and unpredictable forces on the lifting and control surfaces.
If the shuttle had been a capsule reentry system, ablatives would have been fairly obvious. With wings, it's much less clear. What is clear is that it's cheaper to replace the damaged tiles than it would be to do the R&D to give the shuttle an ablative heat shield. And you can't just retrofit it on with an extra layer.
BTW, I think the choice of a winged orbiter was a mistake in the first place, and that a capsule and ablatives would have been better.
Commercial efforts so far? Almost, but not quite, recreating a 57 year old X-15 flight, courtesy of a couple of very rich angels. Commercial efforts will get there, but not anytime soon. Gotta satisfy those shareholders.
Don't sell SpaceX quite so short -- they've attempted one *orbital* launch, and will be trying again in a couple months. There's good reason to believe it will work -- the failure was a procedural one, not a design one, and they've added multiple checks to prevent it and similar problems. The current rocket (Falcon 1) is a small TSTO semi-expendable launcher; they have a larger Falcon 9 and some variants also already in production, and a much larger rocket (codename: BFR) and manned (!) capsule in development. I'd lay better than even money they repeat the Sputnik flight (with a useful payload) this year, and even money they do a manned launch in 5.
Commercial will get there, it's just a matter of putting enough investment in to get to the point that there's a market, and SpaceX has already sold 10 launches -- strongly suggesting that there is in fact a market for better, cheaper, more reliable vehicles.
Well, the CSO didn't choose to appeal the decision. Basically the CSO and chief engineer are worried about the loss of the vehicle, but not the crew. Everyone agrees the crew will be safe, since they plan to check out the tiles etc in orbit, and keep the crew in the ISS and land the shuttle remotely if it looks bad.
Griffin is taking a calculated risk -- he knows the shuttle might be lost, but has taken steps to make sure the crew isn't.
So basically, they object and think it's the wrong decision, but they believe that having gone on record as saying that is sufficient -- they don't think there's a need to override the person in charge of risk assessment since what's at risk is only the spacecraft and not the crew. Whether to risk the craft is legitimately a monetary / political decision, not a safety one, since the crew should be fine either way.
The reason it's hard is that now all the control moments are linked -- you can't roll the plane without causing pitch and yaw changes too. So you need to control all the surfaces in unison. This makes it complicated and hard to fly, but not necessarilly unstable. That's why there's a computer flying it, not a person -- once they get a good model of how it behaves, applying all the corrections at once isn't a hard thing for a computer.
LOX / Aluminum (better performance than Mg, easier to refine, and more abundant IIRC) optimizes at 2.4 O:F ratio -- way lean of stoichiometric, because Al2O3 is a crappy exhaust product -- you need a certain amount of O2 in the exhaust to make the nozzle work at all. It's also only 224s Isp. (All this at standard conditions, frozen equilibrium calculation). Compare to Lox / kerosene, which optimizes at 2.5 O:F (mildly rich because H2 in the exhaust is better than H2O / CO2 / CO) at 273s Isp -- substantially better performance.
Add to this that burning aluminum requires either a powdered metal pump / injector, which is hard, or burning in a hybrid mode. The hybrid requires a hydrocarbon binder and powdered aluminum -- pure metal conducts heat too well, it will all melt before you finish the burn. That kinda defeats the point since you need to ship the binder from earth.
Also, alumina particulates in the exhaust (which accounts for 25 mol % of the the exhaust) are hell on nozzles. You probably can't build a cooled nozzle that will withstand that abuse. That implies ablative nozzles, which are a continuing expense that has to be shipped from Earth (pesky hydrocarbons or graphite again...). Also, the *highly* reactive oxidizing exhaust of this engine is much nastier on any conceivable nozzle than a fuel rich exhaust. In an oxidizer-rich metal fire, anything you could make a nozzle out of looks a lot like more fuel.
Not to say it can't be done... But it would be hard, expensive, and require a large R&D budget just to make the motor work. Add to that ongoing lunar ops costs and non-reusable motors made on Earth. Lift+throw from the ground looks a lot more attractive at that point...
I'm not sure I follow. If/when launch costs are reduced, the cost of shipping mining machinery will just get lower. I don't see how the cost of the machinery itself would be more than $1000 per pound of fuel produced.
Because it's expensive to operate and breaks a lot. That means you either need a truly massive (and horrendously expensive, even if long term economical) on-site repair facility, or you need to ship lots of replacement parts from Earth. The process of mining the ice / regolith and cracking it is equipment intensive. If you have people there are non-trivial life support expenses. If you don't then the machinery is larger, more expensive, and more failure-prone. All this adds up to large R&D costs and equally large operating costs.
Put another way, each kg of machinery shipped has to buy you a bunch of kg of fuel delivered to be economical. And that machinery has to be shipped from Earth surface. It's the kg fuel delivered per kg machinery shipped ratio I'm questioning.
One reason it's so hard to operate is that Moon dust is nasty stuff: highly abrasive (sharp edges thanks to no erosion), statically charged so it sticks to everything, tiny enough to get into every join in sight, causes silicosis and other lung problems...
However, I will assert that any industrial process worth pursuing in Earth orbit in the near future needs to make economic sense without the lunar base, and treat the lunar base as a cost saving measure.
That said, I think it's a lot cheaper (measured in dollars) to spend a bit more propellant getting things off the Earth than it is to make them on the moon, particularly since making propellant on the moon is non-trivial. I further think that this will continue to be the case until there is a *substantial* industrial base not on Earth's surface.
So I guess what I'm saying is, I can see why the Moon is interesting... eventually. But I don't see how it's worth pursuing before Mars the Near Earth Asteroids. Particularly when you consider the R&D costs (of which all too little transfers from Mars stuff to Moon stuff or vice versa).
Once you're willing to assume cheap Falcon 9's that are man-rated, I posit that it's cheaper still to use a SpaceX BFR to do a liftand throw.
Speaking of SpaceX... a reporter once asked Musk if he was doing this to get a ride into space. He replied that it would have been cheaper to buy a Russian ticket. Smart people have commented that the reporter should have asked about the ticket to Mars. Note that they seem to have all the major pieces in the works.
I agree, Shuttle derived things are far from the cheapest heavy lift vehicles imaginable. Zubrin likes them because the R&D cost is low, both in dollars and time.
The big reason against on-orbit refueling I see is simple... it's complicated, and complicated in space means expensive and risky. It can be a fair bit less efficient to use lift + throw and still be noticeably cheaper. Also, lift + throw has a lower R&D budget in all probability.
Slashdot Mirror
Eh, while in general I agree with you, there are two other factors here. First, they really are short millions, not tens of thousands, of units. I have trouble coming up with simple reasons why they'd lie about that (apply Occam's razor for the rest of the argument). And second, they do have a certain amount of fiduciary responsibility to their shareholders (of non-zero but decidedly not infinite impact), which leads to a desire to place blame when possible (well in line with human nature as demonstrated by corporate execs, and so of high impact). So here it seems more reasonable than not to believe them.
No. Sony said it was due to shortages of the blue laser diode in the Blu-ray drives. Also, you'll note they're short a couple million PS3s, not a measley 16000.
Huh? I'm pretty sure the Egyptians didn't do a lot of work to decide if it was safe. The lead used would be unsafe regardless of the nanoparticulate nature of the compound. Lead was used in lots of other ways through history, too. That doesn't make it safe.
I completely understand not wanting that much info about your friends for one reason or another, or not wanting that much information on your home page for UI / information overload reasons -- but that's a UI concern (potentially a very real one; I'm not trying to belittle it), not a privacy concern.
So yes, this changes how many people will see things about you. And yes, it reduces the effort required by strangers to track every detail about you and be a creepy stalker type. But anyone who believes it was hard to get all this information before is delusional.
I guess this is what confuses me: People aren't complaining because creepy stalker types have more info about them. And they're not complaining because their friends have more info about them. (Your friends read your page on a regular basis, right? That is what we mean by friends in this context, right? So therefore your friends notice these changes.) And they're not complaining that some set of people have access to this information that didn't previously have access. And as best I can tell, most people aren't complaining about the UI they're being presented (though clearly some are, that just doesn't seem to be the most vocal complaint). They're also not complaining that people can tell when they're online or not (they keep their IM name on the page, usually, right?). So, unless I'm mistaken, they're complaining because their acquaintences (people they know who only occasionally read their page) will, in all likelihood, get to know them a little bit better. And that seems to me to be a pretty minor complaint.
It's either that, or tens (hundreds?) of thousands of people are very, very confused about the meaning of the word "public." Either way, I'm truly amazed.
There's a little less privacy as a result, in the sense that more people will know more about you, but not in the sense that the information available to anyone who went looking has changed. It seems really weird to me that this many people think it's a big change (well, having not looked at it, there may be a big bad UI change that people don't like... that seems perfectly reasonable to complain about).
I'll just continue staring in amazement at the people who think this removed more than a small amount of privacy, and also at the ones who think this change didn't remove any privacy at all. As with many things, it seems the slashdot comments are completely polarized and miss what is most likely the real answer. Not that that's limited to slashdot, or anything...
To the west of the Earthside station, why?
It doesn't make a huge amount of difference, really. Your station will probably be near the ocean, so it won't get in anyone's way. Picking it up might be a bit of a pain, though.
Any material strong enough to make a space elevator out of will be light enough at the earth end that it will look more like a piece of ribbon fluttering in the breeze as it falls than anything else. It will land softly, except for the parts that are high enough up they don't survive reentry. Even for a fairly large elevator, the bottom is *very* thin.
There are plenty of obstacles to an elevator, but that one mostly takes care of itself.
I would say that the IT needs should sortof be postponed. They need to determine that the problem is solvable, and have some sense of how to go about it, but even if you need a high end supercomputer to do so, those can be built on a couple years notice; it will be 10 before the materials even start to look workable.
A: None, everyone knows feminist activists don't change anything.
I really do think the mathematicians are doing exactly what you guys think they should be.
MD5, SHA, and every other hash function I've ever read the spec for appends some zeros followed by the original message size (the zeros are so it comes to an integer number of blocks) as the first thing it does. For exactly this reason.
At a guess, this attack requires that the two files be the same size. (But I haven't actually read TFA.) And attacks that delete or add data but can't manage to correct the file size are the minority anyway.
i386 netinst image.
That's the minimal network install image, which makes for a quick dl and then gets just what you need.
HTH.
Their first launch failed, but they found the cause (a rusted nut) and have fixed the problem and also implemented checks to catch it and many other potential problems in advance next time. They're planning to launch again in a couple months.
They are also at work on substantially larger vehicles, including a manned capsule.
If I were planning a manned space program 15-30 years out, I would be looking to buy my launch services and focus on the other parts, like what to do and how to do it once I got there.
Also, most kids these days spend a fair bit of time on IM / SMS / etc, whereas kids almost never sent telegraphs. It is plausible that using bad grammar and syntax would hurt more when you're young and still learning.
I don't think telegraphs are a particularly relevant comparison.
Well, apparently you have to plug the cables into its eye sockets, and cramming more than one into each is probably hard. So more of a bridge than a router, I think...
IMHO, both licenses have their place. I prefer the GPL for my software, but could see using the BSD license if I wrote different software with different purposes in mind.
I believe it comes down to a question of goals (or, basically equivalently, what you think the word "free" is referring to) -- is your goal to set your software free, so that anyone can use it in any way you choose, or is your goal to maximise the amount of free software available in the world, by offering incentives to other developers to make their software free?
For my software, I choose the latter -- I have no burning need for others to be able to make a closed fork. I view my software as Free, but not without a price -- the price is, if you want to modify it, you need to make the modifications GPL as well.
Different views, different licenses. I don't see why it's such a big deal to some people what license other developers choose. If you don't like their license, don't use their software. And while we're at it, get off your high horse and make the world a better place by writing some code (or whatever other means you choose). With whatever license pleases you.
However, it's important to realize that because there are fewer manufacturers than there are consumers, and they often work together on decisions like this, an individual consumer has a lot less power than an individual manufacturer in shaping what products are out there. It might not be possible for me to buy an equivalent, non-DRM product.
This license is a way for a group of individuals to get together and bargain collectively, and thereby increase their power in the transaction to something closer to on par with the large corporations.
Unlike RMS, I don't believe I have a human right to run my software on hardware you're selling, and that it's immoral of you to try to stop me. But, I do want to be able to, and it matters to me. So, I plan to use this license as a bargaining tool by releasing software I write under it.
I don't mean to force anyone else to use this license, and I certainly see reasons for using GPLv2 or BSD-type licenses. They just aren't my reasons. I plan to vote not only with my wallet and my feet, but with the license of the software I write. If you don't want to do that too, that's fine, you're certainly welcome to make your own choices.
(All that said, I find it unlikely that the software I write will be relevant one way or the other -- it's not media-handling stuff, or a kernel or compiler, or anything else likely to hit DRM restrictions. But I plan to voice my opinion by using the GPLv3 on it, assuming I like the final draft.)
What is happening, is that I'm saying that if you want to use *my* software on a DRM platform, *then* you have to hand out the keys or whatever else is needed. Which, for software I write, is exactly what I want. (Of course, I have trouble imagining how it would be relevant for things I write, but that's a different matter -- I don't write media players or kernels or other obvious targets).
As a software *author*, I lose nothing. As a user of other people's software, I lose out only if I'm trying to redistribute their copyrighted work in ways they don't want. And, in that case, too bad for me -- just like it's always been.
This license is about giving authors more choices, not less. And personally, this is an option I like.
The development project required to do substantial changes to the heat shield would be massive. You can't just attach another layer of tiles, for several reasons. Weight is the obvious one -- it cuts into payload capacity, probably quite substantially. Structural concerns are also very real -- those tiles are exceedingly weak, and it wouldn't surprise me if they couldn't support another layer if it was merely glued on. Providing supports through the existing layer would take a lot of work. And lastly, if the outer layer is damaged, it changes the aerodynamics. Probably not enough to affect control, but quite possibly enough to cause localized heating that the tiles underneath can't withstand. If that's the case, then you haven't bought nearly as much redundancy as you'd hoped for, since the failure modes are linked.
Just to be clear -- none of these things are impossible. They would just take time and money. And, my guess is they would take enough time and money that it would be better just to spend the money speeding up the CEV development project. And once you do that, you're back to the current question -- keep flying the shuttle fleet as is while waiting, or retire it now and have nothing in place until the CEV appears. Yes, you could argue that redoing the heat shield would provide an intermediate solution. I argue that it would be so short lived and so expensive as to be a waste of money that could be spent on other things.
That said, ablatives aren't easy, especially if you want aerodynamic control as you come in -- it's exceedingly difficult to get them to ablate evenly, which results in weird and unpredictable forces on the lifting and control surfaces.
If the shuttle had been a capsule reentry system, ablatives would have been fairly obvious. With wings, it's much less clear. What is clear is that it's cheaper to replace the damaged tiles than it would be to do the R&D to give the shuttle an ablative heat shield. And you can't just retrofit it on with an extra layer.
BTW, I think the choice of a winged orbiter was a mistake in the first place, and that a capsule and ablatives would have been better.
Don't sell SpaceX quite so short -- they've attempted one *orbital* launch, and will be trying again in a couple months. There's good reason to believe it will work -- the failure was a procedural one, not a design one, and they've added multiple checks to prevent it and similar problems. The current rocket (Falcon 1) is a small TSTO semi-expendable launcher; they have a larger Falcon 9 and some variants also already in production, and a much larger rocket (codename: BFR) and manned (!) capsule in development. I'd lay better than even money they repeat the Sputnik flight (with a useful payload) this year, and even money they do a manned launch in 5.
Commercial will get there, it's just a matter of putting enough investment in to get to the point that there's a market, and SpaceX has already sold 10 launches -- strongly suggesting that there is in fact a market for better, cheaper, more reliable vehicles.
Griffin is taking a calculated risk -- he knows the shuttle might be lost, but has taken steps to make sure the crew isn't.
So basically, they object and think it's the wrong decision, but they believe that having gone on record as saying that is sufficient -- they don't think there's a need to override the person in charge of risk assessment since what's at risk is only the spacecraft and not the crew. Whether to risk the craft is legitimately a monetary / political decision, not a safety one, since the crew should be fine either way.
The reason it's hard is that now all the control moments are linked -- you can't roll the plane without causing pitch and yaw changes too. So you need to control all the surfaces in unison. This makes it complicated and hard to fly, but not necessarilly unstable. That's why there's a computer flying it, not a person -- once they get a good model of how it behaves, applying all the corrections at once isn't a hard thing for a computer.
LOX / Aluminum (better performance than Mg, easier to refine, and more abundant IIRC) optimizes at 2.4 O:F ratio -- way lean of stoichiometric, because Al2O3 is a crappy exhaust product -- you need a certain amount of O2 in the exhaust to make the nozzle work at all. It's also only 224s Isp. (All this at standard conditions, frozen equilibrium calculation). Compare to Lox / kerosene, which optimizes at 2.5 O:F (mildly rich because H2 in the exhaust is better than H2O / CO2 / CO) at 273s Isp -- substantially better performance.
Add to this that burning aluminum requires either a powdered metal pump / injector, which is hard, or burning in a hybrid mode. The hybrid requires a hydrocarbon binder and powdered aluminum -- pure metal conducts heat too well, it will all melt before you finish the burn. That kinda defeats the point since you need to ship the binder from earth.
Also, alumina particulates in the exhaust (which accounts for 25 mol % of the the exhaust) are hell on nozzles. You probably can't build a cooled nozzle that will withstand that abuse. That implies ablative nozzles, which are a continuing expense that has to be shipped from Earth (pesky hydrocarbons or graphite again...). Also, the *highly* reactive oxidizing exhaust of this engine is much nastier on any conceivable nozzle than a fuel rich exhaust. In an oxidizer-rich metal fire, anything you could make a nozzle out of looks a lot like more fuel.
Not to say it can't be done... But it would be hard, expensive, and require a large R&D budget just to make the motor work. Add to that ongoing lunar ops costs and non-reusable motors made on Earth. Lift+throw from the ground looks a lot more attractive at that point...
Because it's expensive to operate and breaks a lot. That means you either need a truly massive (and horrendously expensive, even if long term economical) on-site repair facility, or you need to ship lots of replacement parts from Earth. The process of mining the ice / regolith and cracking it is equipment intensive. If you have people there are non-trivial life support expenses. If you don't then the machinery is larger, more expensive, and more failure-prone. All this adds up to large R&D costs and equally large operating costs.
Put another way, each kg of machinery shipped has to buy you a bunch of kg of fuel delivered to be economical. And that machinery has to be shipped from Earth surface. It's the kg fuel delivered per kg machinery shipped ratio I'm questioning.
One reason it's so hard to operate is that Moon dust is nasty stuff: highly abrasive (sharp edges thanks to no erosion), statically charged so it sticks to everything, tiny enough to get into every join in sight, causes silicosis and other lung problems...
However, I will assert that any industrial process worth pursuing in Earth orbit in the near future needs to make economic sense without the lunar base, and treat the lunar base as a cost saving measure.
That said, I think it's a lot cheaper (measured in dollars) to spend a bit more propellant getting things off the Earth than it is to make them on the moon, particularly since making propellant on the moon is non-trivial. I further think that this will continue to be the case until there is a *substantial* industrial base not on Earth's surface.
So I guess what I'm saying is, I can see why the Moon is interesting... eventually. But I don't see how it's worth pursuing before Mars the Near Earth Asteroids. Particularly when you consider the R&D costs (of which all too little transfers from Mars stuff to Moon stuff or vice versa).
Speaking of SpaceX... a reporter once asked Musk if he was doing this to get a ride into space. He replied that it would have been cheaper to buy a Russian ticket. Smart people have commented that the reporter should have asked about the ticket to Mars. Note that they seem to have all the major pieces in the works.
I agree, Shuttle derived things are far from the cheapest heavy lift vehicles imaginable. Zubrin likes them because the R&D cost is low, both in dollars and time.
The big reason against on-orbit refueling I see is simple... it's complicated, and complicated in space means expensive and risky. It can be a fair bit less efficient to use lift + throw and still be noticeably cheaper. Also, lift + throw has a lower R&D budget in all probability.