You haven't been paying attention, have you? GWB's screwed the US economy so badly that the US$ has weakened to the point that it's no more valuable than some of those third world currencies.
I know you're trolling, but I just can't pass up a good fight.
GWB's administration lowered the rate of the dollar because they know what they're doing. Lowering the rate of the dollar makes US goods cheaper in foreign countries. If US goods are cheaper, then domestic companies can make more money via exports. If domestic companies are making more money, then they'll hire more employees. See how that works?
Be rest assured that the US Dollar will be at a crazy exchange rate again when strong buying power returns to the economy, and the US doesn't mind imports instead of exports.
Sincerest apologies to Kerry finatics who think the President of the United States of America is Hitler reincarnated.
Nope. No production engine was ever built for Project Orion. I was actually referring to NERVA.
Interestingly, the British Interplanetary Society studied an updated version called Project Dadelus that used much smaller fuel pellets, exploded them in a reaction chamber, and controlled the thrust much better than the Project Orion plans.
What I want to know is, when is someone going to build these things? Maybe it's just the engineer in me, but there's no point in simply theorizing about them. They actually have to be built! We've got the smarts and the technology. What are we waiting for?
...they probably won't use nuclear craft either. Nevermind that nuclear engines are the most efficient and workable solution. Nevermind that we were building nuclear ramjets in the 50's and production ready nuclear rockets in the 60's.
Oh wait. That stuff was done by the US. Has the EU ever even fired a nuclear engine? Nevermind.
Yeah, but you're developing a space probe. A land rover needs more power for the electronic drive. Given that one horsepower is 745 watts (i.e. 745 joules per second), you'd need to load a kilowatt RTG on the rover. The weight would be self-defeating. Thus, you have to use battery for the high draw situations and use an RTG capable of output slightly higher than is required by the rover at rest.
Do you hug trees or believe that RTGs will produce a nuclear explosion? If you do, you have issues. If you don't, you're probably just environmentally conscious.
But to supply a generator large enough to obviate the need for solar cells most likely would blow the weight budget (soft landing, remember?). Just my guess.
BZZT. 2.5 pounds of Plutonium per 75 watts of electricity. That's probably not that much heavier than the solar panels. The best part is that you'd need less battery with an RTG (just enough for large power draws) so you can save more weight there than your RTG costs you.
Different technology. Project Orion is/was a space travel/space launch method (now just space travel because of the fallout). Project Pluto was a nuclear ramjet that worked by superheating the air into plasma. A design that didn't throw out so much radiation was proposed, but 1950's technology made it unworkable. Modern GCNR engines however, may be able to power a ramjet without throwing out a lot of radiation.
You have your work cut out for you. I think we will get "clean" (as in no possiblity of radioactive pollutants) nuclear engines invented sooner then you will manage to convince enough people to use the ones you describe.
Perhaps. Doesn't stop me from trying tho. Even if we can get nuclear rockets in space, it would be a big step forward.
The way I understood, the mechanics of such a vortex would actually produce pressure on the sillica, not only due to pressure of the gas itself but of centrifugal force caused by the vortex. If you read the article you pointed me to, the guy there is talking about a system whereby a portion of the hydrogen is redirected to flow over the sillica in effort to cool it and more to the point: "equalize pressures".
Exactly the point. By maintaining equal pressure inside and out, the net pressure on the bulb is close to zero. Much like a kids balloon which would pop if not for the air pressure on the outside.
Not exactly, what would actually happen is that the whole mess: uranium fluoride, bits of sillica, hydrogen fuel and possibly some pellets from the emergency "scram shotgun" would be ejected through the venturi since for a brief period of time the engine would continue to function with the hydrogen propellant already inside and still expanding due to the residual heat.
Alright, you've got me. My opinion is that little to no materials would get ejected. However, the real problem here is that discussions on the subject are acedemic. The reason is that a production style engine has not yet been constructed (or even designed). Until someone gets the go ahead to build these engines outside of a labratory, there can be no discussion on how safe they are. After an engineer has a go at making the engine safe, then maybe we can revisit the issue. Unfortunately, that leaves us with a chiken and egg problem. How can we develop a safe design if no one will let us experiment with scale engines?
As others have pointed out, there's nothing precluding a nuclear powered ramjet. Such an engine was actually built in the 1950's when they believed that radioactive exhaust was a bonus in an atmospheric missile. Obviously, something so dirty would never be a viable choice for non-warfare technologies. But using a more modern design like GCNR, the air could be heated without the air and fissionable materials coming in contact. Most gasses in the atmosphere can't be made radioactive by fission, so that's not a major concern.
...as to other's thoughts on a nuclear powered RamJet/ScramJet. Project Pluto wasn't exactly something you'd want flying, but then again it was 1950's technology. What sort of problems do you see with something like GCNR converted for air breathing?
I am not sure if the medical estabilishment agrees with you on this one. What about all those warnings against sun-tanning? Virtually all the dermathologists are jumping up and down waving arms about how sun-tanning (exposure to UV radiation but it would be the same kind of principle) can lead to skin cancer later on in life (they are talking 40 years of age and later).
The simple answer is that they don't know why the skin doesn't seem to fully repair the damage. There are however some theories.
Also should there ever be a release of some tiney particles of a few thousand atoms each of radioactive material which then would get into food/air/whatnot and get absorbed into the body and sit in one spot irradiating a small area of it, there is your continuous exposure scenario.
As I said, there is already radioisotope particles in the environment and most likely in your body. However, the small amount of isotope is not sufficient to guarantee any sort of ill effects. Only large doses of 1000 or more REM per year will do that.
e inherent issues like the fact that the sillica shield around the bulb can just explosively fail (because it is under pressure from inside and outside and is in fact that "mechanical" stress point I was eluding to earlier) and no amount of "scram" devices will help that one.
You can't get any more force out of an explosion like that than the structural materials are designed to handle.
Here's how I understand the engine. (I may get something wrong here, but I'll try to be as correct as possible.) The silica shield is thin like a light bulb. It's purpose is not to maintain gases under extreme pressure, but to maintain separation between the hydrogen and the uranium. The uranium itself is kept spinning in a vortex to reduce the amount of pressure on the silica. The uranium is hot enough to eat through most materials, so it wouldn't be advisable for the materials to be in constant physical contact.
Here's what I see happening in a situation where the uranium vortex failed and pressure were applied to the silica: The silica would quickly break (not much force there) and the uranium would splatter against the outer walls of the engine. The heat from the plasma will start to eat through whatever shell it's contained in, but it will cool quickly, and the materials will act as a moderator to stop the reaction. The hydrogen may continue pumping, but it would suddenly fail to become plasma. Since hydrogen cannot become radioactive via fission (only tritium via fusion) it presents no health risk.
Sir, the only one smoking crack is you. Swing is not inherently slow as is proven by many, many Swing programmers. (Check my sig, you'll find a very snappy Swing product.) I have tried Netbeans and Eclipse. On a machine with 256 MB, Eclipse is faster due to fewer features. On a 512 MB machine, it's all the same. Now take Eclipse on any platform *other* than Windows and it will start to suck big time.
The truth is that IDEs are a matter of preference. Many prefer Eclipse for its simplicity and pretty looks. I prefer NetBeans for its Java focused design, and features pouring out the wahzoo. You can change the default look of NetBeans (many prefer Windows or OS X looks), but I kind of like the cleanliness that the NetBeans developers have brought to the metal look.
As a word of disclosure, I had the distinct honor of hosting a recent poll on IDE usage. As a result, I have a rather unique perspective on all of this.
And thank goodness they don't. Sun's dev environment is slow, unwieldy, and generally a nuisance to use. As an end user I'm grateful for the Eclipse project.
Hardly. Netbeans just does more than Eclipse by default. As a result it hogs tons of memory. (Not a big deal on developer machines with 512 MB.) Eclipse is quickly matching Netbeans' bloat as more and more features are added.
You don't know what you're talking about. Sun gives away Forte for Java under an Open Source branding (think Mozilla/Netscape). The real reasons for this squabble go back to '01 when IBM released Eclipse after inviting every company except Sun to join the project. At the time, Netbeans/Forte was very mature and would have been a good choice for IBM to build their own platform off of. Instead, they named their product as a way of snubbing Sun, and used their own proprietary GUI API so the two projects could never interoperate.
Apparently it was simply too many files and the FS ran out of inodes. Remember that they're constrained to a 256MB file system. It wouldn't surprise me if they used an 8 bit or 16 bit number for the inode count. (Ah, the joys of Vx(Doesn't)Works.)
On another note, does anyone know exactly what they're deleting here? While I understand that they need to get this mission underway, is there a chance they could lose valuable mission or navigational information?
. Well your argument is good to explain a possiblity of dying from immediate exposure but what about long-term carcinogenic and other health risks.
Here's what most people don't realize: If you don't get cancer from radiation within a few months, it probably isn't the radiation! Your body is quite used to radiation. The Sun is spewing it out every day. While the Earth's radiation belts stop most of it, there's a significant amount of radiation that hits the Earth. (If there was none, the Earth would get pretty cold.)
Much of that radiation that passes through humans actually misses entirely. i.e. It passes through your body without hitting anything. Of course, some of it does strike. Alpha and Beta particles will simply bounce off your skin. Gamma and Xray radiation is what will usually penetrate. Most of the radiation will collide with something unimportant (e.g. water) But a small remainder may be lucky enough to hit your DNA.
When your body is healthy, it will usually notice the errors in the DNA and correct them. Otherwise you'd get cancer before you were even born! However, if you are lacking certain enzymes, or too many DNA molecules have been changed (as would happen if you were exposed to say 1000+ REM) then you may get cancer.
Now, radiation damage does take your body time to repair. As a result, you should be careful about constant exposure to high radiation. Constantly exposing yourself would cause more damage before your body is finished fixing the old damage.
And that is why radiation early in life won't kill you later in life. If you get cancer at a later date, it probably is from all the radioactive uranium put out by Coal plants. Alternatively, you may have too many radioisotope particles in your system. There's a relatively high amount of Sr-90 and other radioisotopes in the environment from nuclear bomb testing. Or perhaps your cancer has nothing to do with radiation at all, and is instead caused by an error in your body while transcribing your DNA.
For a guy so well educated in the technology you surely have funny concept of human psychology. Lemme translate your statement for you this way:
Your little story is why Failure Is Not An Option(TM). NASA launches toward the ocean so that anything that blows up doesn't land on populated areas (wind or no). My comments are not meant to make people feel better if rocket ships do land on their home (although it would be nice if they did feel better), but rather make them feel better about nuclear technology in the here and now.
On another note the GNCR concept escapes me, it looks like the propellant is injected into a swirl of super hot uranium gas and then ejected along with portions of the gas via the venturi... isnt this producing a continuous stream of radioactive material out the back of the rocket?
If you look at the picture, you'll notice that the uranium plasma is kept in those middle oval areas, while the hydrogen in pumped around them in the outer tubes. Basically, the hydrogen will loop around the core once or twice, and become plasma on the way. By the time it reaches the exhaust, the hydrogen is as energetic as it's going to get.
Now, how do they manage containment? Well, they actually use something called a "nuclear light bulb". Instead of explaining what that is, I'm going to direct you here:
Make sure you read the next page as well. That's where the nuclear light bulb itself is explained. You might even want to read the whole article. It's a fascinating look at how nuclear propulsion can change space travel forever.:-)
P.S. I see that the evil Offtopic/Underrated mods have shown up. All my recent posts have suddenly been modded down, even though they're no longer on the front page. I wonder when they'll figure out that trying to reduce my Karma with abusive moderation is pointless.
Still, I take it you agree there's good reasons to be a little careful with strapping pounds of plutonium to the top of hundreds of tonnes of highly explosive rocket-fuel.
Of course. Anything will power deserves respect. I'm simply trying to point out that nuclear power is not somthing that should be singled out as world destroying. Most people think that being anywhere near plutonium will kill them all and mutate their children for 7 generations. The real truth is that it's no more dangerous than the chemicals in your cell phone/laptop/car battery. You treat battery acid with respect. Plutonium should be treated with the same respect.
Ha, while that is true for the Earth as a whole, it might add politically significant amount of uranium isotopes to some dude's backyard in Florida and that counts 100x more than all the output of coal plants combined globally.
Did you know that uranium is one of the most common substances on Earth? You probably already have some in your backyard. Raining some from an engine would NOT increase it by that much. It certainly wouldn't kill you in the time it takes for the nuclear energy commission to clean up your neighborhood.
Did you know that old style X-Ray machines would give you up to 10 REMs of X-Ray radiaition per X-Ray? Modern digital machines give off only about 10-100 millrems, but if you are older than 15 you may have had an X-Ray from an older machine.
You'll note BTW, that it did not instantly kill you or cause your skin to melt. In fact, doctors considered it quite safe as long as they made sure not to give you too many X-Rays.
When it comes to nuclear power, the real dangerous stuff is the heart of a very large reactor. Older reactor designs would keep hundreds of pounds of material under pressure so that they could produce large amounts of power. In the case of a melt-down and boiler explosion, a lot of hard radiation would be exposed to people near by. (And I mean people within about half a mile. Radiation falls off at the same rate as light, so give it just a little distance you won't get any more than you would from your CRT.)
Here's the upside about the "hard stuff". It doesn't last. In order to be energetic enough to kill someone, it has to have a very short half-life. Within an hour, a reactor's core has already lost much of its most potent stuff. Within a few days it may even be safe enough to approach. Within a month they could cement over it and forget it existed.
I should probably mention that modern reactors can't have a boiler explosion like Chernobyl. Those designs were deemed unsafe long before the incident, and were decommisioned here in the US. Chernobyl OTOH, was built with *decreased* safety precautions because the Russians thought they were unnecessary. Contrast that to Three Mile Island which shut down exactly as it was supposed to.
Some interesting statistics for you. Currently, there are ~500 nuclear reactors in the world, plus the 50+ used by US Navy Vessels (8 on the Enterprise alone, 2 on a standard Nimitz carrier, and 1-2 on each nuclear sub), plus about 550 research reactors operating worldwide. Nuclear reactors are well understood things at this point.
I must admit that from what you are describing the engine would look completely different from what I have seen in some old magazines, it must be some completely new concept, if you have some links to sites (with pretty diagrams for ignoramuses) I would appreciate.
You're probably thinking of NERVA engines. NERVA engines would melt off the back of a rocket and drop from the sky like a rock (a very heavy rock) if they were to melt-down (although they run pretty close to melt-down normally). Gas Core Nuclear Rockets (GCNR) use a uranium plasma vapour for heating the propellant. This is in many ways easier to contain in an emergency than a tradiational nuclear pile.
BTW, I should probably point out some of the safety features of nuclear rockets. For one, they have more power, so they can be built of more traditional and well understood materials. Many chemical rockets go for exotic composites to keep weight down. The other advantage is that the fuel is what cools the engine. In the case of a runaway nuclear reaction, the turbopumps can deliver more fuel to cool the reactor
I'm actually surprised that the Apple board felt comfortable with Jobs as the CEO of two companies. Even before he was with Apple, he was running NeXT (post-being kicked out of Apple in the first place, that is). Perhaps that's what made the Apple board feel more comfortable about it, but then why didn't the NeXT investors get squemish?
Vaccuum. I don't think there's any hard drive that will work in a vacuum.
By sealed, I meant "hermetically sealed". Since there's nothing living inside the case, the air can be sitting.
Radiation
As I said, shielded container. Although, someone pointed out that it wouldn't stop some of the most energetic stuff. The big question is whether a few inches of shielding would be enough to substantially reduce the radiation. We don't need it perfect, just good enough.
EMI/EMC, including Magnetic cleanliness
I didn't think that EMI would be a big problem. What would generate the interference? Hmm... perhaps a Faraday cage could be built into the casing?
Temperature range. Standard range is -34 deg C to +71, although that's usually negotiable. The less hardware you have to baby, the better.
Operating temp is 0C to 65C for microdrives. I originally stated that by sealing the device in lead, you would have a passively cooled system. (The lead would heat and bleed off the extra into space or atomosphere.) However, the more I think about it, the more I like the idea of having an active liquid or gas cooling system. This would also be built into the lead casing, and could be controlled by the computer itself. You'd need a temperature sensor inside the case, but that's not difficult or expensive.
the cost of a qualification program
Personally, I'd like to cut as much of this out as possible. "Cheaper, better, faster" remember? Probably the best way to handle this is to build the entire unit, and stress test the entire thing (Vibration, radiation, etc.). That would be cheaper than testing every component, and would give an good idea as to how sturdy shielded components are when compared to individual hardened components.
Reliability and life.
So far, Microdrives have been shown to be highly reliable and generally last. Given that flash cards are slowly destroyed by rewriting, microdrives may have a longer life time.
Here's an idea. Instead of triple redundancy, go for two microdrives and one CF card. RAID these together. Now if there truely is a failure in all drives, the CF can take over. Personally, I don't think it would be a problem, but that way you have a compromise between proven and unproven.
60 pounds is a hell of a lot. Mass is always tight, and there is no easy fix by "fueling the rocket." Would that there were!
Mass may be tight, but I find it difficult to believe that it's impossible to add 60 pounds to the craft. The craft is chosen based on the requirement for the mission, right? And the amount of fuel burned by the rocket is calculated for exact insertion into Mars orbit, right? So it's conceivable that the rocket could have extra capacity. (What are they using for interplantary missions these days? Titans?) I suppose I'd need to check the specs on the rocket.
The weight could be reduced by eliminating a computing unit. Instead, give the single unit dual processor capabilities. Both processors will attempt the same calculation in sync, which will be then checked by a simple bus controller. If the results don't match, the instruction is recalculated. That would reduce the power requirements as well. Say 30 pounds now? (Most of the weight is in lead shielding and plutonium.)
It would be interesting to be on one of these projects and have access to the mission limitations. I'm willing to bet that they could be pushed pretty far with a little creative thinking.:-)
You can't seal it because the case can't take the pressure.
Lead can't take pressure? Why not?
Also, moving parts are a lot more temperature-sensitive than silicon. They have lubricants which sieze up and thermal expansion which messes up all the tolerances.
Yep. That's why I wanted a sealed case with no airflow. Cooling would happen by heat passing through the lead case. Alternatively, you could better insulate it and build in some sort of active fluid cooling in the case.
CMOS generally works better at lower temperatures
In theory. I'm not sure that's really the case though, Thinking it through, the contraction of the memory is going to make it difficult for the UV rays to properly target the memory. Granted, I haven't paid much attention to the design improvements in flash memory for a very long time.
Now the problem with two processors - if they disagree, how do you decide who's right?
That's a standard problem with clusters. The best answer is to recalculate. Alternatively, you could go triple redundant, but that's starting to get extreme.
These guys are not idiots. They thought through the implications very carefully. The RAD6000 processor is very thoroughly tested in space and has an excellent reliability record.
Don't get me wrong. I think NASA is doing very well. After all, NASA's rovers are roving while ESA's aren't. That says a lot about NASA. I just have different idea on what "Cheaper, faster, better" means. My interpretation of that isn't going to penetrate NASA because that's not their culture. Their culture is that everything works right the first time, which is in direct opposition to the "cheaper, better, faster" idea.
And whoever complained that they were still developing the software after launch
Not me. I'm just glad they were able to recover.:-)
Slashdot Mirror
You haven't been paying attention, have you? GWB's screwed the US economy so badly that the US$ has weakened to the point that it's no more valuable than some of those third world currencies.
I know you're trolling, but I just can't pass up a good fight.
GWB's administration lowered the rate of the dollar because they know what they're doing. Lowering the rate of the dollar makes US goods cheaper in foreign countries. If US goods are cheaper, then domestic companies can make more money via exports. If domestic companies are making more money, then they'll hire more employees. See how that works?
Be rest assured that the US Dollar will be at a crazy exchange rate again when strong buying power returns to the economy, and the US doesn't mind imports instead of exports.
Sincerest apologies to Kerry finatics who think the President of the United States of America is Hitler reincarnated.
You mean Project Orion?
Nope. No production engine was ever built for Project Orion. I was actually referring to NERVA.
Interestingly, the British Interplanetary Society studied an updated version called Project Dadelus that used much smaller fuel pellets, exploded them in a reaction chamber, and controlled the thrust much better than the Project Orion plans.
What I want to know is, when is someone going to build these things? Maybe it's just the engineer in me, but there's no point in simply theorizing about them. They actually have to be built! We've got the smarts and the technology. What are we waiting for?
...they probably won't use nuclear craft either. Nevermind that nuclear engines are the most efficient and workable solution. Nevermind that we were building nuclear ramjets in the 50's and production ready nuclear rockets in the 60's.
Oh wait. That stuff was done by the US. Has the EU ever even fired a nuclear engine? Nevermind.
*sigh*
Yeah, but you're developing a space probe. A land rover needs more power for the electronic drive. Given that one horsepower is 745 watts (i.e. 745 joules per second), you'd need to load a kilowatt RTG on the rover. The weight would be self-defeating. Thus, you have to use battery for the high draw situations and use an RTG capable of output slightly higher than is required by the rover at rest.
Do you hug trees or believe that RTGs will produce a nuclear explosion? If you do, you have issues. If you don't, you're probably just environmentally conscious.
But to supply a generator large enough to obviate the need for solar cells most likely would blow the weight budget (soft landing, remember?). Just my guess.
BZZT. 2.5 pounds of Plutonium per 75 watts of electricity. That's probably not that much heavier than the solar panels. The best part is that you'd need less battery with an RTG (just enough for large power draws) so you can save more weight there than your RTG costs you.
Sorry, tree huggers are the problem.
Different technology. Project Orion is/was a space travel/space launch method (now just space travel because of the fallout). Project Pluto was a nuclear ramjet that worked by superheating the air into plasma. A design that didn't throw out so much radiation was proposed, but 1950's technology made it unworkable. Modern GCNR engines however, may be able to power a ramjet without throwing out a lot of radiation.
Other rocket propulsion methods
You have your work cut out for you. I think we will get "clean" (as in no possiblity of radioactive pollutants) nuclear engines invented sooner then you will manage to convince enough people to use the ones you describe.
Perhaps. Doesn't stop me from trying tho. Even if we can get nuclear rockets in space, it would be a big step forward.
The way I understood, the mechanics of such a vortex would actually produce pressure on the sillica, not only due to pressure of the gas itself but of centrifugal force caused by the vortex. If you read the article you pointed me to, the guy there is talking about a system whereby a portion of the hydrogen is redirected to flow over the sillica in effort to cool it and more to the point: "equalize pressures".
Exactly the point. By maintaining equal pressure inside and out, the net pressure on the bulb is close to zero. Much like a kids balloon which would pop if not for the air pressure on the outside.
Not exactly, what would actually happen is that the whole mess: uranium fluoride, bits of sillica, hydrogen fuel and possibly some pellets from the emergency "scram shotgun" would be ejected through the venturi since for a brief period of time the engine would continue to function with the hydrogen propellant already inside and still expanding due to the residual heat.
Alright, you've got me. My opinion is that little to no materials would get ejected. However, the real problem here is that discussions on the subject are acedemic. The reason is that a production style engine has not yet been constructed (or even designed). Until someone gets the go ahead to build these engines outside of a labratory, there can be no discussion on how safe they are. After an engineer has a go at making the engine safe, then maybe we can revisit the issue. Unfortunately, that leaves us with a chiken and egg problem. How can we develop a safe design if no one will let us experiment with scale engines?
As others have pointed out, there's nothing precluding a nuclear powered ramjet. Such an engine was actually built in the 1950's when they believed that radioactive exhaust was a bonus in an atmospheric missile. Obviously, something so dirty would never be a viable choice for non-warfare technologies. But using a more modern design like GCNR, the air could be heated without the air and fissionable materials coming in contact. Most gasses in the atmosphere can't be made radioactive by fission, so that's not a major concern.
...as to other's thoughts on a nuclear powered RamJet/ScramJet. Project Pluto wasn't exactly something you'd want flying, but then again it was 1950's technology. What sort of problems do you see with something like GCNR converted for air breathing?
Done
I am not sure if the medical estabilishment agrees with you on this one. What about all those warnings against sun-tanning? Virtually all the dermathologists are jumping up and down waving arms about how sun-tanning (exposure to UV radiation but it would be the same kind of principle) can lead to skin cancer later on in life (they are talking 40 years of age and later).
The simple answer is that they don't know why the skin doesn't seem to fully repair the damage. There are however some theories.
Also should there ever be a release of some tiney particles of a few thousand atoms each of radioactive material which then would get into food/air/whatnot and get absorbed into the body and sit in one spot irradiating a small area of it, there is your continuous exposure scenario.
As I said, there is already radioisotope particles in the environment and most likely in your body. However, the small amount of isotope is not sufficient to guarantee any sort of ill effects. Only large doses of 1000 or more REM per year will do that.
e inherent issues like the fact that the sillica shield around the bulb can just explosively fail (because it is under pressure from inside and outside and is in fact that "mechanical" stress point I was eluding to earlier) and no amount of "scram" devices will help that one.
You can't get any more force out of an explosion like that than the structural materials are designed to handle.
Here's how I understand the engine. (I may get something wrong here, but I'll try to be as correct as possible.) The silica shield is thin like a light bulb. It's purpose is not to maintain gases under extreme pressure, but to maintain separation between the hydrogen and the uranium. The uranium itself is kept spinning in a vortex to reduce the amount of pressure on the silica. The uranium is hot enough to eat through most materials, so it wouldn't be advisable for the materials to be in constant physical contact.
Here's what I see happening in a situation where the uranium vortex failed and pressure were applied to the silica: The silica would quickly break (not much force there) and the uranium would splatter against the outer walls of the engine. The heat from the plasma will start to eat through whatever shell it's contained in, but it will cool quickly, and the materials will act as a moderator to stop the reaction. The hydrogen may continue pumping, but it would suddenly fail to become plasma. Since hydrogen cannot become radioactive via fission (only tritium via fusion) it presents no health risk.
Call me sad, but I've had no reason to upgrade my 512MB dual PIII 550MHz box. It runs Eclipse well enough, unlike Netbeans... Just my tuppence 'worth.
That is sad. Netbeans runs great on my 733PIII w/512MB box. Dunno what your problem is.
Sir, the only one smoking crack is you. Swing is not inherently slow as is proven by many, many Swing programmers. (Check my sig, you'll find a very snappy Swing product.) I have tried Netbeans and Eclipse. On a machine with 256 MB, Eclipse is faster due to fewer features. On a 512 MB machine, it's all the same. Now take Eclipse on any platform *other* than Windows and it will start to suck big time.
The truth is that IDEs are a matter of preference. Many prefer Eclipse for its simplicity and pretty looks. I prefer NetBeans for its Java focused design, and features pouring out the wahzoo. You can change the default look of NetBeans (many prefer Windows or OS X looks), but I kind of like the cleanliness that the NetBeans developers have brought to the metal look.
As a word of disclosure, I had the distinct honor of hosting a recent poll on IDE usage. As a result, I have a rather unique perspective on all of this.
And thank goodness they don't. Sun's dev environment is slow, unwieldy, and generally a nuisance to use. As an end user I'm grateful for the Eclipse project.
Hardly. Netbeans just does more than Eclipse by default. As a result it hogs tons of memory. (Not a big deal on developer machines with 512 MB.) Eclipse is quickly matching Netbeans' bloat as more and more features are added.
You don't know what you're talking about. Sun gives away Forte for Java under an Open Source branding (think Mozilla/Netscape). The real reasons for this squabble go back to '01 when IBM released Eclipse after inviting every company except Sun to join the project. At the time, Netbeans/Forte was very mature and would have been a good choice for IBM to build their own platform off of. Instead, they named their product as a way of snubbing Sun, and used their own proprietary GUI API so the two projects could never interoperate.
...Slashdot is days late on the scoop. The Java community has already figured out that this is business as usual between Sun and IBM.
Those probably didn't exist when they started development. Or if they did, they weren't yet certified for space travel.
Apparently it was simply too many files and the FS ran out of inodes. Remember that they're constrained to a 256MB file system. It wouldn't surprise me if they used an 8 bit or 16 bit number for the inode count. (Ah, the joys of Vx(Doesn't)Works.)
On another note, does anyone know exactly what they're deleting here? While I understand that they need to get this mission underway, is there a chance they could lose valuable mission or navigational information?
.
:-)
Well your argument is good to explain a possiblity of dying from immediate exposure but what about long-term carcinogenic and other health risks.
Here's what most people don't realize: If you don't get cancer from radiation within a few months, it probably isn't the radiation! Your body is quite used to radiation. The Sun is spewing it out every day. While the Earth's radiation belts stop most of it, there's a significant amount of radiation that hits the Earth. (If there was none, the Earth would get pretty cold.)
Much of that radiation that passes through humans actually misses entirely. i.e. It passes through your body without hitting anything. Of course, some of it does strike. Alpha and Beta particles will simply bounce off your skin. Gamma and Xray radiation is what will usually penetrate. Most of the radiation will collide with something unimportant (e.g. water) But a small remainder may be lucky enough to hit your DNA.
When your body is healthy, it will usually notice the errors in the DNA and correct them. Otherwise you'd get cancer before you were even born! However, if you are lacking certain enzymes, or too many DNA molecules have been changed (as would happen if you were exposed to say 1000+ REM) then you may get cancer.
Now, radiation damage does take your body time to repair. As a result, you should be careful about constant exposure to high radiation. Constantly exposing yourself would cause more damage before your body is finished fixing the old damage.
And that is why radiation early in life won't kill you later in life. If you get cancer at a later date, it probably is from all the radioactive uranium put out by Coal plants. Alternatively, you may have too many radioisotope particles in your system. There's a relatively high amount of Sr-90 and other radioisotopes in the environment from nuclear bomb testing. Or perhaps your cancer has nothing to do with radiation at all, and is instead caused by an error in your body while transcribing your DNA.
For a guy so well educated in the technology you surely have funny concept of human psychology. Lemme translate your statement for you this way:
Your little story is why Failure Is Not An Option(TM). NASA launches toward the ocean so that anything that blows up doesn't land on populated areas (wind or no). My comments are not meant to make people feel better if rocket ships do land on their home (although it would be nice if they did feel better), but rather make them feel better about nuclear technology in the here and now.
On another note the GNCR concept escapes me, it looks like the propellant is injected into a swirl of super hot uranium gas and then ejected along with portions of the gas via the venturi... isnt this producing a continuous stream of radioactive material out the back of the rocket?
If you look at the picture, you'll notice that the uranium plasma is kept in those middle oval areas, while the hydrogen in pumped around them in the outer tubes. Basically, the hydrogen will loop around the core once or twice, and become plasma on the way. By the time it reaches the exhaust, the hydrogen is as energetic as it's going to get.
Now, how do they manage containment? Well, they actually use something called a "nuclear light bulb". Instead of explaining what that is, I'm going to direct you here:
http://www.nuclearspace.com/a_liberty_ship7.htm
Make sure you read the next page as well. That's where the nuclear light bulb itself is explained. You might even want to read the whole article. It's a fascinating look at how nuclear propulsion can change space travel forever.
P.S. I see that the evil Offtopic/Underrated mods have shown up. All my recent posts have suddenly been modded down, even though they're no longer on the front page. I wonder when they'll figure out that trying to reduce my Karma with abusive moderation is pointless.
Still, I take it you agree there's good reasons to be a little careful with strapping pounds of plutonium to the top of hundreds of tonnes of highly explosive rocket-fuel.
Of course. Anything will power deserves respect. I'm simply trying to point out that nuclear power is not somthing that should be singled out as world destroying. Most people think that being anywhere near plutonium will kill them all and mutate their children for 7 generations. The real truth is that it's no more dangerous than the chemicals in your cell phone/laptop/car battery. You treat battery acid with respect. Plutonium should be treated with the same respect.
Ha, while that is true for the Earth as a whole, it might add politically significant amount of uranium isotopes to some dude's backyard in Florida and that counts 100x more than all the output of coal plants combined globally.
Did you know that uranium is one of the most common substances on Earth? You probably already have some in your backyard. Raining some from an engine would NOT increase it by that much. It certainly wouldn't kill you in the time it takes for the nuclear energy commission to clean up your neighborhood.
Did you know that old style X-Ray machines would give you up to 10 REMs of X-Ray radiaition per X-Ray? Modern digital machines give off only about 10-100 millrems, but if you are older than 15 you may have had an X-Ray from an older machine.
You'll note BTW, that it did not instantly kill you or cause your skin to melt. In fact, doctors considered it quite safe as long as they made sure not to give you too many X-Rays.
When it comes to nuclear power, the real dangerous stuff is the heart of a very large reactor. Older reactor designs would keep hundreds of pounds of material under pressure so that they could produce large amounts of power. In the case of a melt-down and boiler explosion, a lot of hard radiation would be exposed to people near by. (And I mean people within about half a mile. Radiation falls off at the same rate as light, so give it just a little distance you won't get any more than you would from your CRT.)
Here's the upside about the "hard stuff". It doesn't last. In order to be energetic enough to kill someone, it has to have a very short half-life. Within an hour, a reactor's core has already lost much of its most potent stuff. Within a few days it may even be safe enough to approach. Within a month they could cement over it and forget it existed.
I should probably mention that modern reactors can't have a boiler explosion like Chernobyl. Those designs were deemed unsafe long before the incident, and were decommisioned here in the US. Chernobyl OTOH, was built with *decreased* safety precautions because the Russians thought they were unnecessary. Contrast that to Three Mile Island which shut down exactly as it was supposed to.
Some interesting statistics for you. Currently, there are ~500 nuclear reactors in the world, plus the 50+ used by US Navy Vessels (8 on the Enterprise alone, 2 on a standard Nimitz carrier, and 1-2 on each nuclear sub), plus about 550 research reactors operating worldwide. Nuclear reactors are well understood things at this point.
I must admit that from what you are describing the engine would look completely different from what I have seen in some old magazines, it must be some completely new concept, if you have some links to sites (with pretty diagrams for ignoramuses) I would appreciate.
Wikipedia explanation of various proulsion methods
NERVA and GCNR engine descriptions
You're probably thinking of NERVA engines. NERVA engines would melt off the back of a rocket and drop from the sky like a rock (a very heavy rock) if they were to melt-down (although they run pretty close to melt-down normally). Gas Core Nuclear Rockets (GCNR) use a uranium plasma vapour for heating the propellant. This is in many ways easier to contain in an emergency than a tradiational nuclear pile.
BTW, I should probably point out some of the safety features of nuclear rockets. For one, they have more power, so they can be built of more traditional and well understood materials. Many chemical rockets go for exotic composites to keep weight down. The other advantage is that the fuel is what cools the engine. In the case of a runaway nuclear reaction, the turbopumps can deliver more fuel to cool the reactor
I'm actually surprised that the Apple board felt comfortable with Jobs as the CEO of two companies. Even before he was with Apple, he was running NeXT (post-being kicked out of Apple in the first place, that is). Perhaps that's what made the Apple board feel more comfortable about it, but then why didn't the NeXT investors get squemish?
Vaccuum. I don't think there's any hard drive that will work in a vacuum.
:-)
By sealed, I meant "hermetically sealed". Since there's nothing living inside the case, the air can be sitting.
Radiation
As I said, shielded container. Although, someone pointed out that it wouldn't stop some of the most energetic stuff. The big question is whether a few inches of shielding would be enough to substantially reduce the radiation. We don't need it perfect, just good enough.
EMI/EMC, including Magnetic cleanliness
I didn't think that EMI would be a big problem. What would generate the interference? Hmm... perhaps a Faraday cage could be built into the casing?
Temperature range. Standard range is -34 deg C to +71, although that's usually negotiable. The less hardware you have to baby, the better.
Operating temp is 0C to 65C for microdrives. I originally stated that by sealing the device in lead, you would have a passively cooled system. (The lead would heat and bleed off the extra into space or atomosphere.) However, the more I think about it, the more I like the idea of having an active liquid or gas cooling system. This would also be built into the lead casing, and could be controlled by the computer itself. You'd need a temperature sensor inside the case, but that's not difficult or expensive.
the cost of a qualification program
Personally, I'd like to cut as much of this out as possible. "Cheaper, better, faster" remember? Probably the best way to handle this is to build the entire unit, and stress test the entire thing (Vibration, radiation, etc.). That would be cheaper than testing every component, and would give an good idea as to how sturdy shielded components are when compared to individual hardened components.
Reliability and life.
So far, Microdrives have been shown to be highly reliable and generally last. Given that flash cards are slowly destroyed by rewriting, microdrives may have a longer life time.
Here's an idea. Instead of triple redundancy, go for two microdrives and one CF card. RAID these together. Now if there truely is a failure in all drives, the CF can take over. Personally, I don't think it would be a problem, but that way you have a compromise between proven and unproven.
60 pounds is a hell of a lot. Mass is always tight, and there is no easy fix by "fueling the rocket." Would that there were!
Mass may be tight, but I find it difficult to believe that it's impossible to add 60 pounds to the craft. The craft is chosen based on the requirement for the mission, right? And the amount of fuel burned by the rocket is calculated for exact insertion into Mars orbit, right? So it's conceivable that the rocket could have extra capacity. (What are they using for interplantary missions these days? Titans?) I suppose I'd need to check the specs on the rocket.
The weight could be reduced by eliminating a computing unit. Instead, give the single unit dual processor capabilities. Both processors will attempt the same calculation in sync, which will be then checked by a simple bus controller. If the results don't match, the instruction is recalculated. That would reduce the power requirements as well. Say 30 pounds now? (Most of the weight is in lead shielding and plutonium.)
It would be interesting to be on one of these projects and have access to the mission limitations. I'm willing to bet that they could be pushed pretty far with a little creative thinking.
You can't seal it because the case can't take the pressure.
:-)
Lead can't take pressure? Why not?
Also, moving parts are a lot more temperature-sensitive than silicon. They have lubricants which sieze up and thermal expansion which messes up all the tolerances.
Yep. That's why I wanted a sealed case with no airflow. Cooling would happen by heat passing through the lead case. Alternatively, you could better insulate it and build in some sort of active fluid cooling in the case.
CMOS generally works better at lower temperatures
In theory. I'm not sure that's really the case though, Thinking it through, the contraction of the memory is going to make it difficult for the UV rays to properly target the memory. Granted, I haven't paid much attention to the design improvements in flash memory for a very long time.
Now the problem with two processors - if they disagree, how do you decide who's right?
That's a standard problem with clusters. The best answer is to recalculate. Alternatively, you could go triple redundant, but that's starting to get extreme.
These guys are not idiots. They thought through the implications very carefully. The RAD6000 processor is very thoroughly tested in space and has an excellent reliability record.
Don't get me wrong. I think NASA is doing very well. After all, NASA's rovers are roving while ESA's aren't. That says a lot about NASA. I just have different idea on what "Cheaper, faster, better" means. My interpretation of that isn't going to penetrate NASA because that's not their culture. Their culture is that everything works right the first time, which is in direct opposition to the "cheaper, better, faster" idea.
And whoever complained that they were still developing the software after launch
Not me. I'm just glad they were able to recover.