Oh please, be serious. It's humans running the robots who make the decisions. The only benefit a human on Mars has is latency. But that's a really silly benefit, given that there's no urgency to get the data and just travel there takes months and the limiting factor on how much data you'll collect overall is how long your scientific equipment lasts. And no, an astronaut on Mars isn't going to be repairing a broken mass spectrometer or the like, it's a silly concept. And it'd, as noted, be orders of magnitude cheaper just to send a second robot.
I am correct, look it up if you don't believe me. The energy is primarily in the form of fission fragments. And no, chain reactions work exactly the same, the neutronicity doesn't vary. You're confusing fission fragments and neutrons.
I totally disagree. A dusty fission fragment reactor has been demonstrated using a non-nuclear substitute fuel, which demonstrated proper containment and thermal management. And modelling shows that such a configuration should produce a collimated fission fragment beam. So what's so grossly impractical? Have you come across a paper indicating that it's impractical? Because I sure haven't.
My previous comments apply to NEP
I'm not talking about NEP. I'm talking about generating a RF plasma and funnelling it through a nozzle, like in VASIMR, but with primary heating being from an IR nuclear lightbulb. And even if I wasn't, commentary on conventional nuclear reactors vs. solar is inapplicable when one is talking about totally different type of reactor.
Hmm... I'm not sure what you're thinking about doing with CAD, but a Sim that handles real inorganic (and potentially simple organic) chemistry and materials properties could be incredible for enabling the crowd-sourcing of simplifying the tech chains of refining and production, which on earth are just ridiculously long and totally impractical to just migrate to Mars. The users would be given a realistic distribution of raw Martian minerals, and would have to feed the 3d printers / molders / CNC machines / lithography / robotic assembly that makes products. These products would include a (long) fixed set of needs to keep colonists alive and comfortable, as well as spare parts for your refining / mining equipment and the manufacturing hardware's equipment. Users could then try to produce as much of a colony's needs as possible with as little imported hardware as possible.
Simulating wear and corrosion on the refining, transport, and mining hardware would be a must. I think requiring the users to design the full details of the 3d printing and other manufacturing hardware would be overkill, but they should be able to choose what materials different "major parts" for them are made out of and what they want to supply as raw materials, which would affect wear / corrosion rates / efficiency / etc. Game consultants should include a wide range of people with real-world experience in different industries to make sure it's realistic, and the game should be launched with a variety of real-world pieces of Earth mining and refining hardware so that new players have something to start out with and tweak (albeit starting out heavily reliant on imports from Earth). As each person designs a new piece of hardware and tries it out, it should be saved to a global database, along with a history of what it's been taking in (raw materials, parts, etc) and producing as an outputs. Others could then search through the global database for equipment that does a function that they need to incorporate into their hardware.
The game could run in a MMO mode or single-user sandbox mode. In MMO mode there would be multiple users each with their own mine, refining center, manufacturing center, or whatever they want to build) on Mars, while in single-user mode a user would have their own whole planet to play with on their own. Once they get a production line running they can dispatch transport to carry materials or goods to where they're needed, there can be mishaps along the way, etc - all of the elements of your typical enjoyable Sim game - except with real-world chemistry and mechanical properties underlying key aspects. The victory condition would be total manufacturing indepence from Earth. The loss condition would be overstraining Earth's ability to supply you, leading to shortages and colonist deaths.
I think something like that could, if well designed, be both potentially fun for users and useful for engineers designing real-world infrastructure.
Great! Now you just need to invent an actually functional confinement method for the absurdly-hot gaseous/plasma nuclear fuel to stop it from destroying its containment vessel or leaking out its fuel in short order. And while you're at it, you should probably go ahead and invent a way to stop the quartz / fused silica bulb from undergoing blackening when exposed to a neutron flux, something it's so prone to doing that people deliberately expose quartz to nuclear reactors to make opaque black quartz for jewelry. And of course, a way to start the whole thing, a process that's been so problematic that they've been investigating bombardment by sizeable amounts of bloody antimatter as a potential solution.
Easy as pie, surely! Riiight around the corner.
What isotope are you thinking of as fuel? Unicorn-235?
The shuttle wasn't thrown away, nor were the boosters - only the (rather simple) ET. How did that work out, price-wise?
It's simply not fair to pretend that launch costs are a minor issue. They are the limiting factor, and progress in reducing costs has been lethargic over the past decades. "in orbit operations" are expensive precisely because launch costs are so high. Bargain basement, pay-out-the-nose-for-insurance launch rates are $4-5k a kilogram. More typical Russian rates are about $6-7k, while typical US and European rates run about $10k. And that's for large payloads, for small payloads expect in the (very) rough ballpark of $20k. How do you expect to live affordably in space if launch costs are even within an order of magnitude of that?
That's not to say that rockets fundamentally can't provide cheap access to space. But today's rockets certainly can't.
Presently working or theoretical? If you want "presently working", then that would defeat the point of asking for suggestions, would it not? If you want theoretical, there's tons. I kind of like the Launch Loop concept - sort of like a space elevator except that it doesn't require unobtanium, avoids or reduces the countless other problems with space elevators (micrometeorite damage, oscillation modes, power transfer, lightning and ionospheric discharge, and about 50 other things), and it gives you much more ideal/customizable orbital momentum, plus is 1-2 orders of magnitude more energy efficient at lifting cargo (space elevator climbers have to rely on beamed power, there's no practical way to send it through the cable, and beamed power over great distances where one receiver is only a few square meters at best is very low efficiency) AND offers a far higher launch rate.
Earth-based space elevators, the stuff of sci-fi nerd dreams, really are an awful solution when you start looking at the details. There's far better solutions out there.
Space has resources. They're called asteroids. Often quite valuable resources, actually - although learning to mine in microgravity will be a trial-and-error process.
Let's be honest, the main sellable goods of a Martian colony would be martian minerals for the jewelry / collector industry (which would sell for many times their weight in gold... a fundamental requirement of martian exports, given the cost of return payload deliveries) and tourist trips for the few multi-billionaires obsessed with space. It's hard to envision in even the medium term much more coming from a Mars colony than that which could pay for itself. And these things wouldn't come close to paying for the cost of the colony, in any regard. I certainly don't expect to see, say, industrial minerals exports in the medium term; a "creative economy" means people which means ridiculously high upkeep costs; and the concept of martian manufacturing being competitive with Earth's is just laughable. And science is much more cheaply done with disposable robots. One could probably factory-produce a hundred Curiosity rovers and mass launch/land them in every corner of Mars for the cost of one manned mission (let alone a "colony"). One could probably launch an automated nuclear submersible-drillship into the oceans of Europa for less than the price of one manned Mars mission.
If you thermalize your fission fragments. Sure, that's what all current fission reactors do, but it's not a fundamental requirement. About 80% of a nuclear reaction's energy is in the form of fission fragments - high energy heavy ions - which can be decelerated for power without Carnot losses, without a thermodynamic sink. The key is that you can't use fuel elements with any serious thickness to them (otherwise most fragments will thermalize) - the fuel elements have to be wires, sheets, dust, things of that nature, with magnetic fields to separate the fragments from the fuel.
On the other hand, when it comes to propulsion, nukes are the bees knees. No form of currently-achievable propulsion yields a higher Isp than a fission fragment rocket, with the exception of photonic / magnetic sails, which are impractically low thrust for interplanetary travel. Some day I'd love to run some simulations as to whether you could have a spallation-driven subcritical dusty fission reactor get rid of much if not all of the moderator mass (power to drive the accelerator should be copious from a fission fragment reactor), and whether you could run one in an infrared nuclear lightbulb mode (making use of the electrostatically-contained dust's extreme surface area and low IR absorption spectrum to get high output, rather than using extreme, unmanageable temperatures to get high output as in a traditional nuclear lightbulb concept), thus opening up non-dirty high thrust power modes for surface operation (airbreathing, simple fuel heating, etc, including using electricity from fragment deceleration to run a microwave beam to help ionize the air/fuel and make it more opaque to IR) and a few other space options (such as a nuclear VASIMR-like mode)
That's not true, the mAh levels of batteries keep rising as the batteries themselves shrink. And while there have indeed been some improvements in electronics efficiencies, these have been largely offset by increased demands in various roles.
Li-ion loses a negligible percentage of its energy as heat. A li-ion pack charged over the course of an hour or so is usually around 99% efficient. Surge charging can drop it to 94-97%, depending on the chemistry and rate, but again, li-ion is very efficient. Flywheels are much lossier. They're also more expensive, larger, and have more catastrophic failure modes.
High power chargers are DC straight into the pack. You don't get to choose the voltage. If you tried to run high voltage in the cable and a converter in the vehicle, one that'd be a massive converter, and two, cooling it would be a huge problem in its own right.
20KW would *melt* domestic feeds even before you get to the meter.
I don't know about you, but my new house is going to have a 100A feed. It's not that unusual. 100A * 240V = 24kW.
Secondly, ulltra-fast home charging rates are irrelevant. Seriously, in what scenario is that necessary? Home charging is for overnight. Fast chargers are only needed on highways.
This is not going to suddenly "change everything". First off, there's so little info here you can't even see through the hype. There's nothing to get an idea of how hard this would be to commercialize, what its energy density would be, or any of tons of other things that make a big difference. And secondly, these are hardly the first lab-scale batteries to have properties like this. Heck, there have even been lithium titanate batteries commercialized before. Crazy charge / discharge times, but they were largely a flop except in niche applications - the cost was way too high and the energy density too low.
There is every week or two some great research breakthrough in battery storage. Most of them you'll never read about. Most of them will never go anywhere. But a few will. And they will slowly, inevitably make their way into the battery technology of tomorrow. Silicon anodes, for example, were once among those crazy lab future battery techs. Now they're in commercial cells. People never stop to think about how little the batteries in their phones have gotten in an area of increasing computing power, larger screens, greater demands on lifespan, etc. Energy density continues its inevitable march.... in the background. But the odds that any one tech that you read about is going to carry the industry is very small. And these things take half a decade to go from the lab to stores.
And of course, the assumption that if your station's maximum output is 10 MW that you have to have a 10 MW feed to the grid is also wrong. It presumes that you can't have a battery buffer in your station. Look at your typical gas station; pumps spend by far most of their time idle. A charging station with a peak output of 10 MW could probably meet all its needs with a 2 MW feed and a 20-minute battery buffer (although a statistical analysis of consumption patterns would be required for specifics)
It's not at all reasonable to reharge the entire pack every 17.5 hours. If your car has a 200 mile range, and you're charging that fully every 17.5 hours, then you're driving 274 miles per day.
In a naive calculation, one can easily determine that the charging cable would be way too heavy and unwieldy for a person to use.
Of course, that's the problem with naive calculations. The solution in practice for very high power charging is very simple, just cool the cable rather than requiring it to be passively air-cooled.
Personally, I think very high-power chargers should also provide coolant for the vehicle, through the charging port. It makes a lot more sense to me to make a small number of chillers (aka, part of the chargers) which can keep a store of coolant than making every single vehicle have to haul around a high power chiller and coolant reservoir. Coolant comes from the charger's reservoir, along its switching electronics, down the cable, into the vehicle, into its pack, and then heated coolant is returned on the cable's return line
And that's assuming you remember four random words easier than a sentence that you chose because it has meaning to you, which is quite the assumption to make. Was it "Right mule charger tape"? "Proper stallion storage glue?" "Accurate mustang AA stapler?"
Trust me, I've used both types of passwords. The sentence one is much easier to memorize. And it's shorter, faster and more accurate to type.
Bad analogy. You're applying rules to make my version more complicated, you should apply rules to make yours more complicated also. So it's no longer "correct horse battery staple", it's "c@553kt!H0rS3;8ATT3Ry^5Ta7E". And damn well yes the former is easier to memorize.
Of course not, no papers published at all. It's all part of the conspiracy, MAN! Because as we all know, scientists despise clean energy and grant money is given out in accordance with how much you don't do anything revolutionary. Fight the evil scientist cabal!
So why is a seven randomly-chosen word password, which would average in the ballpark of 50 characters, somehow less typo-prone than an abbreviation password a tiny fraction of its length for the same level of entropy?
The former being 13 characters long and the latter being about 50 characters long. Make a sentence that abbreviates to 20 characters and it's more secure than your "7 random words and two punctuation marks" example. And probably a heck of a lot easier to memorize than seven random words and two random punctuation marks at random locations.
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Oh please, be serious. It's humans running the robots who make the decisions. The only benefit a human on Mars has is latency. But that's a really silly benefit, given that there's no urgency to get the data and just travel there takes months and the limiting factor on how much data you'll collect overall is how long your scientific equipment lasts. And no, an astronaut on Mars isn't going to be repairing a broken mass spectrometer or the like, it's a silly concept. And it'd, as noted, be orders of magnitude cheaper just to send a second robot.
I am correct, look it up if you don't believe me. The energy is primarily in the form of fission fragments. And no, chain reactions work exactly the same, the neutronicity doesn't vary. You're confusing fission fragments and neutrons.
I don't have anything backwards. As far as solar sails go, interplanetary travel is short distance.
The thrust is really, really, really tiny, for really, really, really huge sails.
I totally disagree. A dusty fission fragment reactor has been demonstrated using a non-nuclear substitute fuel, which demonstrated proper containment and thermal management. And modelling shows that such a configuration should produce a collimated fission fragment beam. So what's so grossly impractical? Have you come across a paper indicating that it's impractical? Because I sure haven't.
I'm not talking about NEP. I'm talking about generating a RF plasma and funnelling it through a nozzle, like in VASIMR, but with primary heating being from an IR nuclear lightbulb. And even if I wasn't, commentary on conventional nuclear reactors vs. solar is inapplicable when one is talking about totally different type of reactor.
Hmm... I'm not sure what you're thinking about doing with CAD, but a Sim that handles real inorganic (and potentially simple organic) chemistry and materials properties could be incredible for enabling the crowd-sourcing of simplifying the tech chains of refining and production, which on earth are just ridiculously long and totally impractical to just migrate to Mars. The users would be given a realistic distribution of raw Martian minerals, and would have to feed the 3d printers / molders / CNC machines / lithography / robotic assembly that makes products. These products would include a (long) fixed set of needs to keep colonists alive and comfortable, as well as spare parts for your refining / mining equipment and the manufacturing hardware's equipment. Users could then try to produce as much of a colony's needs as possible with as little imported hardware as possible.
Simulating wear and corrosion on the refining, transport, and mining hardware would be a must. I think requiring the users to design the full details of the 3d printing and other manufacturing hardware would be overkill, but they should be able to choose what materials different "major parts" for them are made out of and what they want to supply as raw materials, which would affect wear / corrosion rates / efficiency / etc. Game consultants should include a wide range of people with real-world experience in different industries to make sure it's realistic, and the game should be launched with a variety of real-world pieces of Earth mining and refining hardware so that new players have something to start out with and tweak (albeit starting out heavily reliant on imports from Earth). As each person designs a new piece of hardware and tries it out, it should be saved to a global database, along with a history of what it's been taking in (raw materials, parts, etc) and producing as an outputs. Others could then search through the global database for equipment that does a function that they need to incorporate into their hardware.
The game could run in a MMO mode or single-user sandbox mode. In MMO mode there would be multiple users each with their own mine, refining center, manufacturing center, or whatever they want to build) on Mars, while in single-user mode a user would have their own whole planet to play with on their own. Once they get a production line running they can dispatch transport to carry materials or goods to where they're needed, there can be mishaps along the way, etc - all of the elements of your typical enjoyable Sim game - except with real-world chemistry and mechanical properties underlying key aspects. The victory condition would be total manufacturing indepence from Earth. The loss condition would be overstraining Earth's ability to supply you, leading to shortages and colonist deaths.
I think something like that could, if well designed, be both potentially fun for users and useful for engineers designing real-world infrastructure.
Great! Now you just need to invent an actually functional confinement method for the absurdly-hot gaseous/plasma nuclear fuel to stop it from destroying its containment vessel or leaking out its fuel in short order. And while you're at it, you should probably go ahead and invent a way to stop the quartz / fused silica bulb from undergoing blackening when exposed to a neutron flux, something it's so prone to doing that people deliberately expose quartz to nuclear reactors to make opaque black quartz for jewelry. And of course, a way to start the whole thing, a process that's been so problematic that they've been investigating bombardment by sizeable amounts of bloody antimatter as a potential solution.
Easy as pie, surely! Riiight around the corner.
What isotope are you thinking of as fuel? Unicorn-235?
The shuttle wasn't thrown away, nor were the boosters - only the (rather simple) ET. How did that work out, price-wise?
It's simply not fair to pretend that launch costs are a minor issue. They are the limiting factor, and progress in reducing costs has been lethargic over the past decades. "in orbit operations" are expensive precisely because launch costs are so high. Bargain basement, pay-out-the-nose-for-insurance launch rates are $4-5k a kilogram. More typical Russian rates are about $6-7k, while typical US and European rates run about $10k. And that's for large payloads, for small payloads expect in the (very) rough ballpark of $20k. How do you expect to live affordably in space if launch costs are even within an order of magnitude of that?
That's not to say that rockets fundamentally can't provide cheap access to space. But today's rockets certainly can't.
Presently working or theoretical? If you want "presently working", then that would defeat the point of asking for suggestions, would it not? If you want theoretical, there's tons. I kind of like the Launch Loop concept - sort of like a space elevator except that it doesn't require unobtanium, avoids or reduces the countless other problems with space elevators (micrometeorite damage, oscillation modes, power transfer, lightning and ionospheric discharge, and about 50 other things), and it gives you much more ideal/customizable orbital momentum, plus is 1-2 orders of magnitude more energy efficient at lifting cargo (space elevator climbers have to rely on beamed power, there's no practical way to send it through the cable, and beamed power over great distances where one receiver is only a few square meters at best is very low efficiency) AND offers a far higher launch rate.
Earth-based space elevators, the stuff of sci-fi nerd dreams, really are an awful solution when you start looking at the details. There's far better solutions out there.
Space has resources. They're called asteroids. Often quite valuable resources, actually - although learning to mine in microgravity will be a trial-and-error process.
Let's be honest, the main sellable goods of a Martian colony would be martian minerals for the jewelry / collector industry (which would sell for many times their weight in gold... a fundamental requirement of martian exports, given the cost of return payload deliveries) and tourist trips for the few multi-billionaires obsessed with space. It's hard to envision in even the medium term much more coming from a Mars colony than that which could pay for itself. And these things wouldn't come close to paying for the cost of the colony, in any regard. I certainly don't expect to see, say, industrial minerals exports in the medium term; a "creative economy" means people which means ridiculously high upkeep costs; and the concept of martian manufacturing being competitive with Earth's is just laughable. And science is much more cheaply done with disposable robots. One could probably factory-produce a hundred Curiosity rovers and mass launch/land them in every corner of Mars for the cost of one manned mission (let alone a "colony"). One could probably launch an automated nuclear submersible-drillship into the oceans of Europa for less than the price of one manned Mars mission.
If you thermalize your fission fragments. Sure, that's what all current fission reactors do, but it's not a fundamental requirement. About 80% of a nuclear reaction's energy is in the form of fission fragments - high energy heavy ions - which can be decelerated for power without Carnot losses, without a thermodynamic sink. The key is that you can't use fuel elements with any serious thickness to them (otherwise most fragments will thermalize) - the fuel elements have to be wires, sheets, dust, things of that nature, with magnetic fields to separate the fragments from the fuel.
On the other hand, when it comes to propulsion, nukes are the bees knees. No form of currently-achievable propulsion yields a higher Isp than a fission fragment rocket, with the exception of photonic / magnetic sails, which are impractically low thrust for interplanetary travel. Some day I'd love to run some simulations as to whether you could have a spallation-driven subcritical dusty fission reactor get rid of much if not all of the moderator mass (power to drive the accelerator should be copious from a fission fragment reactor), and whether you could run one in an infrared nuclear lightbulb mode (making use of the electrostatically-contained dust's extreme surface area and low IR absorption spectrum to get high output, rather than using extreme, unmanageable temperatures to get high output as in a traditional nuclear lightbulb concept), thus opening up non-dirty high thrust power modes for surface operation (airbreathing, simple fuel heating, etc, including using electricity from fragment deceleration to run a microwave beam to help ionize the air/fuel and make it more opaque to IR) and a few other space options (such as a nuclear VASIMR-like mode)
That's not true, the mAh levels of batteries keep rising as the batteries themselves shrink. And while there have indeed been some improvements in electronics efficiencies, these have been largely offset by increased demands in various roles.
Li-ion loses a negligible percentage of its energy as heat. A li-ion pack charged over the course of an hour or so is usually around 99% efficient. Surge charging can drop it to 94-97%, depending on the chemistry and rate, but again, li-ion is very efficient. Flywheels are much lossier. They're also more expensive, larger, and have more catastrophic failure modes.
Nope, can't do that.
High power chargers are DC straight into the pack. You don't get to choose the voltage. If you tried to run high voltage in the cable and a converter in the vehicle, one that'd be a massive converter, and two, cooling it would be a huge problem in its own right.
I don't know about you, but my new house is going to have a 100A feed. It's not that unusual. 100A * 240V = 24kW.
Secondly, ulltra-fast home charging rates are irrelevant. Seriously, in what scenario is that necessary? Home charging is for overnight. Fast chargers are only needed on highways.
This is not going to suddenly "change everything". First off, there's so little info here you can't even see through the hype. There's nothing to get an idea of how hard this would be to commercialize, what its energy density would be, or any of tons of other things that make a big difference. And secondly, these are hardly the first lab-scale batteries to have properties like this. Heck, there have even been lithium titanate batteries commercialized before. Crazy charge / discharge times, but they were largely a flop except in niche applications - the cost was way too high and the energy density too low.
There is every week or two some great research breakthrough in battery storage. Most of them you'll never read about. Most of them will never go anywhere. But a few will. And they will slowly, inevitably make their way into the battery technology of tomorrow. Silicon anodes, for example, were once among those crazy lab future battery techs. Now they're in commercial cells. People never stop to think about how little the batteries in their phones have gotten in an area of increasing computing power, larger screens, greater demands on lifespan, etc. Energy density continues its inevitable march.... in the background. But the odds that any one tech that you read about is going to carry the industry is very small. And these things take half a decade to go from the lab to stores.
And of course, the assumption that if your station's maximum output is 10 MW that you have to have a 10 MW feed to the grid is also wrong. It presumes that you can't have a battery buffer in your station. Look at your typical gas station; pumps spend by far most of their time idle. A charging station with a peak output of 10 MW could probably meet all its needs with a 2 MW feed and a 20-minute battery buffer (although a statistical analysis of consumption patterns would be required for specifics)
It's not at all reasonable to reharge the entire pack every 17.5 hours. If your car has a 200 mile range, and you're charging that fully every 17.5 hours, then you're driving 274 miles per day.
In a naive calculation, one can easily determine that the charging cable would be way too heavy and unwieldy for a person to use.
Of course, that's the problem with naive calculations. The solution in practice for very high power charging is very simple, just cool the cable rather than requiring it to be passively air-cooled.
Personally, I think very high-power chargers should also provide coolant for the vehicle, through the charging port. It makes a lot more sense to me to make a small number of chillers (aka, part of the chargers) which can keep a store of coolant than making every single vehicle have to haul around a high power chiller and coolant reservoir. Coolant comes from the charger's reservoir, along its switching electronics, down the cable, into the vehicle, into its pack, and then heated coolant is returned on the cable's return line
We can play this game until the correct horse battery staples come home.
Is it...
"Correct Horse Battery Staple"
"Correct horse battery staple"
"correct horse battery staple"
"CORRECT HORSE BATTERY STAPLE"
"CorrectHorseBatteryStaple"
"Correcthorsebatterystaple"
"correcthorsebatterystaple"
"CORRECT HORSE BATTERY STAPLE"
And that's assuming you remember four random words easier than a sentence that you chose because it has meaning to you, which is quite the assumption to make. Was it "Right mule charger tape"? "Proper stallion storage glue?" "Accurate mustang AA stapler?"
Trust me, I've used both types of passwords. The sentence one is much easier to memorize. And it's shorter, faster and more accurate to type.
Bad analogy. You're applying rules to make my version more complicated, you should apply rules to make yours more complicated also. So it's no longer "correct horse battery staple", it's "c@553kt!H0rS3;8ATT3Ry^5Ta7E". And damn well yes the former is easier to memorize.
Of course not, no papers published at all. It's all part of the conspiracy, MAN! Because as we all know, scientists despise clean energy and grant money is given out in accordance with how much you don't do anything revolutionary. Fight the evil scientist cabal!
So why is a seven randomly-chosen word password, which would average in the ballpark of 50 characters, somehow less typo-prone than an abbreviation password a tiny fraction of its length for the same level of entropy?
The former being 13 characters long and the latter being about 50 characters long.
Make a sentence that abbreviates to 20 characters and it's more secure than your "7 random words and two punctuation marks" example. And probably a heck of a lot easier to memorize than seven random words and two random punctuation marks at random locations.