As others point out, things don't lose their mass just because they're in space.
However, the problem with reactors isn't that they're "too heavy", they're lighter than an RTG with equivalent power output would be. The problem is that they're too big. An RTG is a lump of passively decaying material surrounded by thermoelectric converters and heat sinks, there's no hard lower limit in size. A reactor has to have enough material to sustain a chain reaction, which imposes a stricter minimum mass.
If your mission's big enough to use one, a reactor makes much more sense than an RTG, but they only make sense for big missions. One example is the SAFE-400, which masses 512 kg but puts out 400 kW thermal and 100 kW electrical. A GPHS-RTG masses 57 kg and produces 4.4 kW thermal, 300 W electrical at the start of the mission. The reactor's a lot lighter for its output, but if you need 1 kW, what do you choose?
And if they'd been using a solid? They'd have been unable to do a hot fire test, and might have attempted to launch with a faulty vehicle, leading to a messy failure rather than a 2 week delay due to range contention. They've repeatedly demonstrated the benefits of being able to shut the vehicle down on the pad, among other advantages of liquids. (You can't make a launcher with engine-out capability using solid rockets, for example.)
Solids are a lot more trouble to manufacture, transport, and work around, can't be test fired or shut down when problems are encountered, have a nasty habit of exploding, are very difficult to scale up, and their performance sucks. In addition, just try restarting a solid and performing a precision landing as SpaceX intends to do with the Falcon 9-R. Even without that, SpaceX is launching for far lower prices than those other rockets.
Launch vehicles based on solid rockets are a dead-end carried over from and kept on life support by the ICBM industry, where they are required for their ability to sit in a silo for years and be ready to fire.
In fact, 1 billion dollars would fuel around 5000 Falcon 9 launches, each lifting 13 metric tons of payload to LEO, for 65000 metric tons total. For the Falcon 9 (one of the lowest cost launchers), propellant is about 0.4% of the launch cost.
The real costs are in the hardware and in operations. The problem is that there really hasn't been a huge amount of incentive to reduce costs. Especially in NASA's launcher programs, where things like Constellation and the SLS are specifically intended to keep Shuttle personnel employed and funds going to the important Congressional districts. This is just not an approach that will reduce costs.
The COTS effort is shaking things up a bit. SpaceX's prices are a lot lower than the competition's, and they are working on recovery and reuse of as much of the vehicle as is economical.
Perchlorate is a reactive and unstable anion that can easily be washed out of regolith, thermally decomposed by baking in an oven, or removed using chemical or microbial treatments. Similar treatments are likely going to be required anyway if you're going to be growing plants in it.
It's also not actually all that toxic. The thyroid absorbs it in place of iodine, reducing the amount of iodine absorbed...it has no other effects, and the iodine uptake interference stops when exposure to perchlorate stops...chronic ingestion is required to make it a problem, an acute exposure will only have a brief effect.
Basically: don't make a habit of eating untreated dirt, and monitor drinking water contaminants. Nothing they shouldn't already be doing. Iodine supplements might be a good idea in case drinking water becomes contaminated and it takes some time to correct.
You're missing the point. You have to make basically the same velocity change (somewhat more to actually rendezvous), but *you don't have to carry your radiation shielding while doing so*. A "cycler" carrying equipment and shielding only needed for the long duration port of the trip would only have to make minor maneuvers to maintain its orbit, the craft traveling to and from it could be much lighter because they only need to support their passengers for a relatively short trip.
"astronauts on even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts"
That is simply *not* the "huge amount of radiation" the article claims. It won't even cause any effects that can be tied to the radiation...it'll increase the long-term risk of fatal cancer by a few percent (for the 1000 mSv, 5% increase in cancer risk limit, that means you're still 20 times more likely to die of cancer from something else), provided the models are even accurate for such low exposures. Radiation exposure is something we'll obviously want to minimize, but this article is just radiophobic fearmongering.
They grind the plants up, extract the thylakoids from the chloroplasts in the plant's cells, and somehow bind them onto a base electrode covered in carbon nanotubes (it's not clear where the other electrode is). So no, the plant is not going to be doing anything with the energy produced. It's also not going to be doing any repair or replacement work on those extracted bits of cellular machinery, or reproducing, etc.
The "nearly 100 percent quantum efficiency" apparently refers to the fact that almost all of the energy of light of the appropriate wavelengths that is absorbed directly by a chlorophyll molecule ends up going into freeing electrons. The problem is that most of the light is of unusable or suboptimal wavelengths, a huge part of the remainder is reflected or absorbed by other things, and not all the freed electrons actually get put to useful work.
And they don't have anything that reproduces, they just use extracted plant bits as the active material in another type of PV panel. One that requires a large area carbon nanotube based substrate.
Except they're apparently harvesting the photosynthetic structures from plants and then incorporating them in something resembling a dye-sensitized solar cell using some exotic carbon nanotube substrate. That's not self-assembling, and given the lack of any cellular repair mechanisms, probably not very long-lasting.
Plants are nowhere near "the most efficient harvesters of solar energy on the planet". The most efficient plants, such as sugar cane, reach around 8%, on par with the very lowest efficiency photovoltaic modules. More typical efficiences are 0.1% to 2%.
Actually, it has a significantly better CPU. The Raspberry Pi CPU is an ARM11 (like the original APC) that, among other lacks, doesn't have hardware division. The Cortex A9 used in this thing is rather more sophisticated: http://en.wikipedia.org/wiki/ARM_Cortex-A9_MPCore#Features
Cesium doesn't bioaccumulate. It's not concentrated in any tissues, it's quickly excreted like sodium, potassium, etc. Strontium bioaccumulates, being treated like calcium and concentrating in bones, but at Fukushima it mostly stayed in the reactors...the stuff that escaped was mainly cesium and iodine (and the iodine has by now almost entirely decayed).
These fish are apparently maintaining a constant level by feeding in contaminated sediments that replace the cesium as fast as it is excreted. Predators will only have elevated levels while actively feeding on these bottom feeders.
However, with a 30 year half life, there aren't many plausible sources for the cesium, it pretty clearly came from Fukushima. Given that a major tsunami had just happened, it's not surprising that there's a layer of sediment trapping the cesium. Possibly something could be done to free up the cesium so it can dilute more thoroughly, or cover it in uncontaminated sediments so bottom feeders don't get into it so much.
The ISS orbits just 400 km above the ground, and experiences enough atmospheric drag to require periodic boosts back into higher orbit. About the only debris of concern is moving horizontally when it reaches the altitude of the ISS, anything that goes past it to lower altitudes hits atmosphere and quickly gets removed from orbit.
'many' does not imply a majority. The original poster was quite correct, many SF authors are in fact physicists, engineers, or others who are or have been active in those or related fields, and who actually do some research and analysis. Just offhand, there's Asimov, Heinlein, Clarke, Forward...
The computer did not in any way fail. Due to an unexpected configuration of the radar systems that was not tested on the ground, it became overloaded during the landing process. The LM AGC then functioned as designed, dropping or postponing low priority tasks (like updating displays) to stay responsive to more critical ones (such as controlling the craft) and giving 1201 and 1202 alarms, which an engineer on Earth recognized as being safe to ignore.
The LM AGC was never intended to land the craft on the surface, only to assist the pilot in doing so. It performed that task as intended, the alarms were only a distraction. If the AGC had failed, there's nothing the pilot would have been able to do.
That is true, but most of the code is still C-style. Aside from a few newer portions, it is basically a C program compiled as C++. It is definitely not a good representative of typical C++ programs.
That's not completely true. I don't see any reason it wouldn't be possible to lift human passengers through the radiation belts by rocket to a craft at the geosynchronous point, and crawl outward from there for a launch to some destination outside of Earth orbit. However, the elevator won't be a good way to get people into high orbit.
That'd be 120 Hz, one "refresh" for each half of the cycle. However, the phosphor used will not respond immediately, a slow responding phosphor will smooth things out and reduce apparent flicker.
In the case of LCD displays, the backlight is a cold cathode fluorescent lamp, which is likely driven by a high voltage power supply with an output frequency of a few hundred or thousand hertz.
By the time the Saturn V was 1 mile in the air, it was also moving at a very high speed. Simply starting from a high altitude doesn't give you much of an advantage. Climbing to orbital altitude is far easier than reaching orbit.
In addition, the fuel is one of the cheapest parts of a launch. Using a carrier plane makes things far more mechanically and bureaucratically complex, puts additional stresses on the vehicle that a pure vertical launch vehicle wouldn't need to withstand, and limits you to what an aircraft can lift, all in the name of saving a small amount (relative to the total amount required) of fuel which would almost certainly be cheaper than all the overhead of launching from a flying aircraft or a mountaintop.
And as others mentioned, you can get a bigger boost simply by moving toward the equator. An equatorial launch platform positioned at sea would provide security as well, from bad weather (very rare on the equator, especially compared to coastal Florida) or deliberate interference.
They don't just "puff out a little", they puff out with a high internal pressure, making it very difficult to bend your limbs...hence the complicated joints. An elastic, form-fitting suit could be both far simpler mechanically and far less restrictive. Spray-on coatings sound far easier to deal with than rotating, vacuum-tight seals.
The higher the magnification, the smaller the field of view. Higher magnifications also require more specialized lighting and sample preparation, more precision parts, and a cleaner, more controlled environment. It's of little use for geology if you can't even see an entire grain of sand, and if vibration, vacuum, temperature changes and dust screw up the works so you can't see anything. It'd have to be a completely different microscope.
It was Marathon, an early Mac first-person shooter by Bungie, which first got me really interested in computers...especially when I discovered the tools for modifying the graphics and physics model, and for creating maps. I loved the idea of creating a virtual 3D environment.
Then I discovered POV-Ray (http://povray.org/), a photorealistic raytracing program with publicly available source code, and which uses a scripting language to generate the scenes. Getting an actual picture as feedback when you get a working program is far more encouraging than a simple blurb of text. By this time, I'd learned Pascal and C++, but the most complex projects I did were in POV-Ray. In the process, I learned a great deal of mathematics...the images I could generate provided motivation as well as an illustration of how things worked mathematically. It's a lot easier to learn the stuff when you have a practical need for it and can see how it works.
And perhaps best of all, when I decided the program was too limited, I was able to get into the actual source code and make my own changes and additions. I don't recommend doing this as an introduction for beginners, as the program is quite complex and has some rather messy code, but just generating images with the scripting language is a great way to start.
A couple things...it's a small asteroid, tiny really. And even a large asteroid wouldn't have a very strong gravity field. It would take a very close pass (near collision) with a very large asteroid to make much of a change in an object's trajectory. Objects in the solar system are very, very far apart, so this happens very rarely. This thing probably doesn't affect anything in the system more strongly than variations in solar light pressure due to sunspots.
Re:Water that "isn't wet" is hardly water...
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The Year In Ideas
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It's a fluorocarbon with one oxygen atom, four fluorine, and five carbon...NOVEC 1230, chemical formula: CF3CF2C(O)CF(CF3)2
And not only is it not water, but it is wet...it just evaporates quickly. It's quite possible it doesn't wet common substances as well as water, but it will wet some of them. "Water that isn't wet" isn't remotely accurate.
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As others point out, things don't lose their mass just because they're in space.
However, the problem with reactors isn't that they're "too heavy", they're lighter than an RTG with equivalent power output would be. The problem is that they're too big. An RTG is a lump of passively decaying material surrounded by thermoelectric converters and heat sinks, there's no hard lower limit in size. A reactor has to have enough material to sustain a chain reaction, which imposes a stricter minimum mass.
If your mission's big enough to use one, a reactor makes much more sense than an RTG, but they only make sense for big missions. One example is the SAFE-400, which masses 512 kg but puts out 400 kW thermal and 100 kW electrical. A GPHS-RTG masses 57 kg and produces 4.4 kW thermal, 300 W electrical at the start of the mission. The reactor's a lot lighter for its output, but if you need 1 kW, what do you choose?
And if they'd been using a solid? They'd have been unable to do a hot fire test, and might have attempted to launch with a faulty vehicle, leading to a messy failure rather than a 2 week delay due to range contention. They've repeatedly demonstrated the benefits of being able to shut the vehicle down on the pad, among other advantages of liquids. (You can't make a launcher with engine-out capability using solid rockets, for example.)
Solids are a lot more trouble to manufacture, transport, and work around, can't be test fired or shut down when problems are encountered, have a nasty habit of exploding, are very difficult to scale up, and their performance sucks. In addition, just try restarting a solid and performing a precision landing as SpaceX intends to do with the Falcon 9-R. Even without that, SpaceX is launching for far lower prices than those other rockets.
Launch vehicles based on solid rockets are a dead-end carried over from and kept on life support by the ICBM industry, where they are required for their ability to sit in a silo for years and be ready to fire.
In fact, 1 billion dollars would fuel around 5000 Falcon 9 launches, each lifting 13 metric tons of payload to LEO, for 65000 metric tons total. For the Falcon 9 (one of the lowest cost launchers), propellant is about 0.4% of the launch cost.
The real costs are in the hardware and in operations. The problem is that there really hasn't been a huge amount of incentive to reduce costs. Especially in NASA's launcher programs, where things like Constellation and the SLS are specifically intended to keep Shuttle personnel employed and funds going to the important Congressional districts. This is just not an approach that will reduce costs.
The COTS effort is shaking things up a bit. SpaceX's prices are a lot lower than the competition's, and they are working on recovery and reuse of as much of the vehicle as is economical.
Perchlorate is a reactive and unstable anion that can easily be washed out of regolith, thermally decomposed by baking in an oven, or removed using chemical or microbial treatments. Similar treatments are likely going to be required anyway if you're going to be growing plants in it.
It's also not actually all that toxic. The thyroid absorbs it in place of iodine, reducing the amount of iodine absorbed...it has no other effects, and the iodine uptake interference stops when exposure to perchlorate stops...chronic ingestion is required to make it a problem, an acute exposure will only have a brief effect.
Basically: don't make a habit of eating untreated dirt, and monitor drinking water contaminants. Nothing they shouldn't already be doing. Iodine supplements might be a good idea in case drinking water becomes contaminated and it takes some time to correct.
You're missing the point. You have to make basically the same velocity change (somewhat more to actually rendezvous), but *you don't have to carry your radiation shielding while doing so*. A "cycler" carrying equipment and shielding only needed for the long duration port of the trip would only have to make minor maneuvers to maintain its orbit, the craft traveling to and from it could be much lighter because they only need to support their passengers for a relatively short trip.
"astronauts on even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts"
That is simply *not* the "huge amount of radiation" the article claims. It won't even cause any effects that can be tied to the radiation...it'll increase the long-term risk of fatal cancer by a few percent (for the 1000 mSv, 5% increase in cancer risk limit, that means you're still 20 times more likely to die of cancer from something else), provided the models are even accurate for such low exposures. Radiation exposure is something we'll obviously want to minimize, but this article is just radiophobic fearmongering.
They grind the plants up, extract the thylakoids from the chloroplasts in the plant's cells, and somehow bind them onto a base electrode covered in carbon nanotubes (it's not clear where the other electrode is). So no, the plant is not going to be doing anything with the energy produced. It's also not going to be doing any repair or replacement work on those extracted bits of cellular machinery, or reproducing, etc.
The "nearly 100 percent quantum efficiency" apparently refers to the fact that almost all of the energy of light of the appropriate wavelengths that is absorbed directly by a chlorophyll molecule ends up going into freeing electrons. The problem is that most of the light is of unusable or suboptimal wavelengths, a huge part of the remainder is reflected or absorbed by other things, and not all the freed electrons actually get put to useful work.
And they don't have anything that reproduces, they just use extracted plant bits as the active material in another type of PV panel. One that requires a large area carbon nanotube based substrate.
Except they're apparently harvesting the photosynthetic structures from plants and then incorporating them in something resembling a dye-sensitized solar cell using some exotic carbon nanotube substrate. That's not self-assembling, and given the lack of any cellular repair mechanisms, probably not very long-lasting.
Plants are nowhere near "the most efficient harvesters of solar energy on the planet". The most efficient plants, such as sugar cane, reach around 8%, on par with the very lowest efficiency photovoltaic modules. More typical efficiences are 0.1% to 2%.
Actually, it has a significantly better CPU. The Raspberry Pi CPU is an ARM11 (like the original APC) that, among other lacks, doesn't have hardware division. The Cortex A9 used in this thing is rather more sophisticated: http://en.wikipedia.org/wiki/ARM_Cortex-A9_MPCore#Features
Cesium doesn't bioaccumulate. It's not concentrated in any tissues, it's quickly excreted like sodium, potassium, etc. Strontium bioaccumulates, being treated like calcium and concentrating in bones, but at Fukushima it mostly stayed in the reactors...the stuff that escaped was mainly cesium and iodine (and the iodine has by now almost entirely decayed).
These fish are apparently maintaining a constant level by feeding in contaminated sediments that replace the cesium as fast as it is excreted. Predators will only have elevated levels while actively feeding on these bottom feeders. However, with a 30 year half life, there aren't many plausible sources for the cesium, it pretty clearly came from Fukushima. Given that a major tsunami had just happened, it's not surprising that there's a layer of sediment trapping the cesium. Possibly something could be done to free up the cesium so it can dilute more thoroughly, or cover it in uncontaminated sediments so bottom feeders don't get into it so much.
The ISS orbits just 400 km above the ground, and experiences enough atmospheric drag to require periodic boosts back into higher orbit. About the only debris of concern is moving horizontally when it reaches the altitude of the ISS, anything that goes past it to lower altitudes hits atmosphere and quickly gets removed from orbit.
'many' does not imply a majority. The original poster was quite correct, many SF authors are in fact physicists, engineers, or others who are or have been active in those or related fields, and who actually do some research and analysis. Just offhand, there's Asimov, Heinlein, Clarke, Forward...
The computer did not in any way fail. Due to an unexpected configuration of the radar systems that was not tested on the ground, it became overloaded during the landing process. The LM AGC then functioned as designed, dropping or postponing low priority tasks (like updating displays) to stay responsive to more critical ones (such as controlling the craft) and giving 1201 and 1202 alarms, which an engineer on Earth recognized as being safe to ignore.
The LM AGC was never intended to land the craft on the surface, only to assist the pilot in doing so. It performed that task as intended, the alarms were only a distraction. If the AGC had failed, there's nothing the pilot would have been able to do.
That is true, but most of the code is still C-style. Aside from a few newer portions, it is basically a C program compiled as C++. It is definitely not a good representative of typical C++ programs.
That's not completely true. I don't see any reason it wouldn't be possible to lift human passengers through the radiation belts by rocket to a craft at the geosynchronous point, and crawl outward from there for a launch to some destination outside of Earth orbit. However, the elevator won't be a good way to get people into high orbit.
Except that POV-Ray is not "Open Source" and it doesn't support direct rendering of NURBS...
That'd be 120 Hz, one "refresh" for each half of the cycle. However, the phosphor used will not respond immediately, a slow responding phosphor will smooth things out and reduce apparent flicker.
In the case of LCD displays, the backlight is a cold cathode fluorescent lamp, which is likely driven by a high voltage power supply with an output frequency of a few hundred or thousand hertz.
By the time the Saturn V was 1 mile in the air, it was also moving at a very high speed. Simply starting from a high altitude doesn't give you much of an advantage. Climbing to orbital altitude is far easier than reaching orbit.
In addition, the fuel is one of the cheapest parts of a launch. Using a carrier plane makes things far more mechanically and bureaucratically complex, puts additional stresses on the vehicle that a pure vertical launch vehicle wouldn't need to withstand, and limits you to what an aircraft can lift, all in the name of saving a small amount (relative to the total amount required) of fuel which would almost certainly be cheaper than all the overhead of launching from a flying aircraft or a mountaintop.
And as others mentioned, you can get a bigger boost simply by moving toward the equator. An equatorial launch platform positioned at sea would provide security as well, from bad weather (very rare on the equator, especially compared to coastal Florida) or deliberate interference.
They don't just "puff out a little", they puff out with a high internal pressure, making it very difficult to bend your limbs...hence the complicated joints. An elastic, form-fitting suit could be both far simpler mechanically and far less restrictive. Spray-on coatings sound far easier to deal with than rotating, vacuum-tight seals.
The higher the magnification, the smaller the field of view. Higher magnifications also require more specialized lighting and sample preparation, more precision parts, and a cleaner, more controlled environment. It's of little use for geology if you can't even see an entire grain of sand, and if vibration, vacuum, temperature changes and dust screw up the works so you can't see anything. It'd have to be a completely different microscope.
It was Marathon, an early Mac first-person shooter by Bungie, which first got me really interested in computers...especially when I discovered the tools for modifying the graphics and physics model, and for creating maps. I loved the idea of creating a virtual 3D environment.
Then I discovered POV-Ray (http://povray.org/), a photorealistic raytracing program with publicly available source code, and which uses a scripting language to generate the scenes. Getting an actual picture as feedback when you get a working program is far more encouraging than a simple blurb of text. By this time, I'd learned Pascal and C++, but the most complex projects I did were in POV-Ray. In the process, I learned a great deal of mathematics...the images I could generate provided motivation as well as an illustration of how things worked mathematically. It's a lot easier to learn the stuff when you have a practical need for it and can see how it works.
And perhaps best of all, when I decided the program was too limited, I was able to get into the actual source code and make my own changes and additions. I don't recommend doing this as an introduction for beginners, as the program is quite complex and has some rather messy code, but just generating images with the scripting language is a great way to start.
A couple things...it's a small asteroid, tiny really. And even a large asteroid wouldn't have a very strong gravity field. It would take a very close pass (near collision) with a very large asteroid to make much of a change in an object's trajectory. Objects in the solar system are very, very far apart, so this happens very rarely. This thing probably doesn't affect anything in the system more strongly than variations in solar light pressure due to sunspots.
It's a fluorocarbon with one oxygen atom, four fluorine, and five carbon...NOVEC 1230, chemical formula: CF3CF2C(O)CF(CF3)2
And not only is it not water, but it is wet...it just evaporates quickly. It's quite possible it doesn't wet common substances as well as water, but it will wet some of them. "Water that isn't wet" isn't remotely accurate.