Those bulkheads only need to hold back 1bar, and realistically you could probably go down to 0.5 (while maintaining the same PPO2), and it'd still be fine. Your better design would probably be a series of bulkheads that progressively raise the pressure, which would also help for airlocking in and out (as going from 1bar to 1/3, as is typical in space suits, is a good way to give your astronauts the bends.
Except that I can think of three counter-examples: Seat Belts, Drunk Driving, and smoking. In each of these cases, we've made significant strides in changing the behvariour of the general population, and dramatically reducing the number of people injured or killed by these issues. None of these involved technical solutions, and instead were achieved through public education/advertising, changes to laws, and eventually changing expectations such that the problematic behaviours become socially unacceptable.
So yeah, can we change public behaviour? Sure, we've done it before, we can do it again. The best bet is to start doing this through kids, since they're the ones that are likely going to nag their parents to leave the phone alone.
I would argue the opposite, especially if you are a small company.
This exactly. I work with a midsized non-profit (roughly $3,000,000/year revenues), and we didn't do credit cards for years because we didn't have the ability (or desire) to have to deal with the security hassles associated with them. We finally found a good partner/vendor and were able to outsource the credit card portion of our online operations to them, and with the long delayed arrival of proper EMV terminals in the US, we can finally handle them on-site without having to take absurd security precautions.
In effect, the unencrypted/unsecured cardholder never, ever, touches our networks or computers. All we get from the payment processor is a hash that confirms the payment, and allows us to reconcile and/or reverse the charge if needed. It works great, and is far more secure than something I could have rigged up as a volunteer.
To be honest, I don't get this. Who cares if a network operator, or the person sitting next to you at a cafe next to you is snooping your data? With the advent of https everywhere, the data between my computer and the server is encrypted and secure, regardless of whether the underlying transport is compromised.
You always need to consider that the underlying network is insecure. I'll happily do my banking over public wifi, or satellite internet (where the packets are broadcast to the entire continent), because all an adversary sees is a stream of gobblygook.
Depends on the legal jurisdiction, but in 1948, a Saskatchewan farmer became trapped under his tractor, and scratched a short will into the bumper of his tractor. This survived court challenges, and that bumper is now on display of the library at the law courts. More info can be found here.
You're absolutely correct to say that correlation does not imply a causality. However, in this case, we do know the causal mechanism.
CO2 (and similar gasses) absorb infrared radiation at various wavelengths, and that absorbed energy translates into increased molecular motion, aka heat. This is a property that can be demonstrated experimentally in the lab, with completely reproducible results.
Those ice cores you dismiss? They're excellent time capsules of atmospheric gas composition. As the snow falls, and the cores build up, it traps small amounts of atmospheric gasses in the ice. You extract these tiny bits of gas, run them through a GCMS, and measure the concentrations of the various components. Typically these ice cores come from places that aren't subject to significant local human population (Antarctica, Greenland). They're also stratified, just like tree rings, so the date of the gas samples can be determined with a high degree of confidence.
These two things are undeniable facts. They are reproducible, and traceable.
So the real question is, if you're going to claim what you do, how has the increase in CO2 not caused an increase in temperature? What mechanism would prevent that?
We know the properties of Carbon Dioxide from reproducible lab experiments, in particular its interaction with infrared light, and at the concentrations found in the atmosphere.
We know with reasonable precision the concentrations of CO2 in the atmosphere for the past few thousand years, and that it has gone up dramatically in the past few hundred years.
We have pretty good temperature measurements since the dawn of the industrial age, and good proxies that go back much further.
We know, with reasonable precision, how much carbon dioxide we as humans emit into the atmosphere on an annual basis, based on analysis of fossil fuel consumption, industrial growth, and so forth.
All of these numbers jive, and point to us as the root cause.
The only extraordinary claim is that we as humans are not responsible, and that our very obvious release of CO2 has not caused the warming we have seen. Claiming that means either denying the rise in temperature, the known physical effects of CO2, or denying the known concentrations of CO2. That requires extraordinary evidence.
There's another important sense that this isn't tautological. Sputnik 1 had no scientific instruments- it really was just a beeping sphere.
Right, but in a sense it was a scientific instrument in and of itself. The beeping was transmitted on two frequencies to allow the density of the ionosphere to be measured, and the spherical shape allowed the density of the upper atmosphere to be measured by the changes in its orbit over time.
Actually it was. The use of two radio frequencies in its transmission (20MHz and 40MHz) allowed the density of the ionosphere to be determined by receivers on the ground. The spherical shape was chosen so that it could be used to map the density of the upper atmosphere. It also provided information on the near space environment, as the internal temperature and pressure of the satellite could vary the duration of the beeps.
So yes, it was a scientific satellite, albeit a very basic one. It, of course, was also a big political F-U to the west, but that's realistically been the case for most things that have been done in the space age, especially the early part.
This exactly, or at least the cost part. I recently worked on a project where we undergrounded a private power distribution system for a retreat center located in an isolated location. The grid connects a small hydro-electric power plant with about 30 buildings, on a 25 acre campus. The total cost of this project was on the order of $3,000,000, and it was only that low because the Engineering work was done inhouse by a PE on a below market basis, and most of the labor involved was also donated. We're glad we did it, but it certainly was not cheap.
2) Test runs for Mars. All the same challenges of landing a mars mission are present on the Moon, but being so much closer it makes a much better place to test out the systems. If we cant do the moon, a mars trip is suicide. We havent actually tried since the days where the most advanced piece of tech around was a hand-held calculator. It's probably worth trying again with today's tech.
Landing on the Moon and Mars really aren't all that similar. Due to its lack of atmosphere, and lower gravity, landing on the Moon is a fairly simple propulsive affair. Kill your orbital velocity, which isn't that high to begin with, and use your engine to land gently on the surface.
Mars, on the other hand, has twice the gravity, and just enough atmosphere to be a problem. There's enough gas there that you need to have a heat shield, and can't build like you would for the moon, but you can't rely on it for the final stages of your landing (parachutes, propellers, what have you).
Thirdly, they represent very different situations once on the surface. Lunar dust is extremely abrasive, as it's had no water/wind to wear it down. This makes it absolute hell on any mechanical joint or seal that has to move. It's really hard to build equipment that will last a long time. On Mars, you probably don't have quite the abrasive issue, but you do have severe problems of toxicity due to the perchlorates in the soil.
As discussed in the above, it's incredibly difficult to actually "sink" a Venus habitat. Beyond how slowly large airships actually leak, the vast majority of the habitat's lift is dedicated to lofting the propellant on the ascent stage and (depending on the design decisions) the ascent stage itself. Meaning in the worst case you can ditch your ascent propellant (or even the ascent stage itself) and stay aloft on a tiny fraction of your peak design lift.
Heck, during the first world war, the Germans attacked London with Zeppelins, and those were incredibly difficult to shoot down, despite being filled with Hydrogen. The Brits would spray the Zeppelins with bullets, filling them with holes, but because the gas bags were at ambient pressure, there was very little escape.
Another example was a research balloon launched out of Canada in 1998. It's mission-ending systems failed to operate (detach the payload, burn a large hole in the envelope), and it drifted across the Atlantic. Canadian fighter pilots put more than 1000 rounds of ammunition through it, UK and US did the same, and it continued. Eventually, the Russians shot it with various air to air missiles, before it finally came down in Scandinavia.
The takeaway is that lighter than air craft are very difficult to take down when operating at ambient pressure.
ED: That should read "there's not even a large thermosphere temperature spike" like there is on Earth. You can see the temperature profiles here [astronomynotes.com] (I can dig up some graphics for higher up if you'd like)
That said, the thermosphere spike is largely of academic interest. The atmospheric pressure is so low at those altitudes that the thermal loading is close to nil. Basically the atoms/molecules in the atmosphere are moving really fast at those altitudes, so they're "hot", but there are just so few of them that they won't really heat anything of normal density up. I don't have a source handy, but I recall reading that it basically means that you could easily overcome it with radiators, and radiators are an incredibly inefficient way of rejecting heat.
Right, but overhead cables aren't insulated; the conductor is directly exposed to the air.
Underground cables, on the other hand, must be electrically insulated, and most electrical insulator materials are also pretty decent thermal insulators. Thus, in order to prevent the cable from heating up and destroy the insulation and/or blow up.
As both wireless and wired Internet access become cheaper and more ubiquitous, at some point that becomes the end of satellite/cable TV distribution.
For content distribution, and contribution, satellite will still be around for a long, long time. End user distribution? that's a different beast, but until we have the full demise of the networks, especially the sports networks, satellite will still be around. It's still the single cheapest way to distribute your content to the entire continent in real-time. A typical transponder costs about $1,000,000 a year to lease, and lets you stream out 4 or so HD streams, continuously. You're distributing that to 1000s+ clients at full resolution, it's going to take a long time to surpass that.
. Single gender bathrooms in retail. Most places can't really afford having separate facilities, so you'll probably see most places just have a room with both fixtures. Exception: bars, restaurants.
Actually, these are going away in bars and restaurants as well, at least here (Western Canada). A number of the local bars/restaurants have moved to a design where you have a genderless restroom, which is surrounded on all sides by full-height stalls. These aren't the stupid stalls like you see in most places, but rather completely enclosed, with a full door/lock on it. They're just marked as to whether they contain a toilet or a urinal+toilet.
I'll admit that the first time I walked in, I backed out thinking I had walked into the wrong one (there was a woman touching up her makeup at the window), but once I figured it out, it's no big deal. Plus, if you're really worried about safety, having it brightly lit, and more foot traffic, is going to improve that far more than anything else.
That's still no reason to ignore the colregs (collision regulations), which require adequate watch to be kept at all times while underway. This includes both visual watch keeping (aka the mk1 eyeball), and in the case of limited visibility (fog and/or smoke), a requirement to maintain an auditory watch (so listening for other ships), and produce sounds on your own, namely fog signals, gongs, and bells.
GPS has an omni-directional antenna. You don't know the angle to the satellites. GPS coordinates are based off the difference in time from the various satellites the receiver gets signal from.
Right, but the Ku-Band and X-Band communications antennas are highly directional, and calculate their lookangles to the satellite based on the known position of the satellite and the GPS position on the ground. Furthermore, many TDMA based modems depend on knowing the precise position of the transmitter so that they can synchronize the transmissions properly. if the ground position doesn't match the time-of-flight for the signal, collisions start happening and error lights go on.
Right, but think about how GPS actually works. Each satellite is transmitting a precise time signal, and the receiver determines its position through trilateration. It basically measures the distance to each of the satellites in orbit, based on the path delay between the satellite and the receiver. Spoofing works by replacing the signals received from the satellite with one of earth origin.
What you can't do when spoofing a position is replicate the geometry (and thus differences in path delay) that makes GPS work. What will suddenly happen is that everyone's GPSs in the area affected by spoofing are suddenly going to give exactly the same outputs. The same lat/long, the same Course over Ground, the same Speed Over Ground.
So let's take the example of a ship doing 14 knots, heading 90 degrees true, and located at 123.03W by 49.05N. As a bad actor, I want to misguide them, and cause them to move to 123.04W and 49.03N, so I setup my spoofer and start broadcasting the signal. Here's the rub: as soon as I turn the spoofer on, everyone in the region is suddenly going to have their GPS readout "123.04W and 49.03N, doing 14kt SOG at 90 True COG. Furthermore, if I have two GPSs onboard with decently separated antennas (say on either side of the bridge), they're both going to be showing the exact same values, which should also trigger alarms in the navigation system.
Now, you're absolutely right, none of this should eliminate proper watch keeping and situational awareness.
With all that said, though, AIS & Radar massively improve safety by radically improving your situational awareness, especially in foul weather. I was sailing up in the Broughton Archipelago. On a couple of occasions we got stuck out in dense fog, where we could see maybe 150m or so. We kept an appropriate watch, with the other guy onboard maintaining a bow watch, emitting appropriate fog signals, etc... but the radar was a huge help, especially to ensure we remained in channel.
On that same trip, we were crossing Queen Charlotte Straight, and passed (in fog) within 2 nautical miles of the Crystal Serenity (largest cruise ship on the Alaska run this year), and the only reason we knew she was there was due to AIS, seeing her on radar, and her crew being active on the VHF. Had we not known she was there, our original course would have brought us too close for comfort.
So yes, it's doable, but done right, the modern aids are a huge improvement in situational awareness and safety.
The thing is that with modern navigational systems, it's pretty easy to detect GPS spoofing. Let's say it happens.. Suddenly, the data coming off your GPS unit isn't going to match up with the rest of the sensors installed on the ship. In addition to the GPS, ships carry gyrocompasses, speed logs, and other sensors.
Modern navigational suites are supposed to compare the SOG derived from the GPS with the STW (Speed Through Water) from the speed log. If they're more than, say, 6kt out from each other (to allow for current), it throws an alarm. Same thing with gyro heading and COG from the GPS.
Lastly, an observant crew should notice that something is wrong as if they get spoofed to a place far enough away, their satcom suite should become very unhappy as the computed angles to the satellites they're targetting will be wrong enough they can't track any more.
As far as the AIS thing goes, all I have to say is "Finally"... The US Navy is pretty much alone in western nations in not participating in AIS during peacetime. As a recreational sailor, I always follow the rule "If it's grey, stay away" but that's hard to do if you don't know they're there. I'm in the PNW, and more than a few times I've been out sailing in the islands, come around a point, and been surprised to come across a (small) warship that was hidden by the headland. Had they been participating in AIS, I could have better avoided them.
However in order to be sold in the USA, they must comply with the law that forbids reception on the old AMPS bands. Of course, this is usually just a pinkyswear on the part of the manufacturers, and can be unlocked either through accessing a calibration mode, or by snipping a diode/resistor on the main circuit board.
A satellite with this size and cost is often built without ROM, simply because of the cost of space-qualified ROM which must be rad-hard for decades of operation.
I thought it was the other way around? A PROM, and especially a mask ROM is an incredibly simple device, effectively just a single diode between a given row and column on the die. Not counting the address decoder (which you would have in both RAM and ROM), a ROM chip only has a single PN junction per bit. An SRAM cell has 6 transistors per bit, and DRAM is a capacitor plus a transistor (not to mention the required refreshing).
I'd love to be shown the error of my ways, but I would have thought the KISS principle would hold.
As I recall, the other primary reason why AMSAT typically uses this configuration is due to doppler. The frequency shift at VHF is only something like +/- 15kHz, which is usually within the capture window of a VHF receiver, whereas at UHF it's +/- 45 kHz, which is beyond your typical receiver. Since we can retune our earth based receivers on the fly, the whole thing works.
Generally in a software project "under-resourced" means the milestones aren't being reached, which either means you have bad milestones, bad requirements, or bad coders.
I guess I didn't make myself sufficiently clear, and you hit the nail on the head. By resources I was meaning not just people, but equipment, tools, requirements, knowledge, plans, or is it just bad milestones to begin with. Adding more people to a failing project is a recipe to make it fail faster, the solution is to figure out what's going on early so the problems can be resolved.
Slashdot Mirror
Those bulkheads only need to hold back 1bar, and realistically you could probably go down to 0.5 (while maintaining the same PPO2), and it'd still be fine. Your better design would probably be a series of bulkheads that progressively raise the pressure, which would also help for airlocking in and out (as going from 1bar to 1/3, as is typical in space suits, is a good way to give your astronauts the bends.
Except that I can think of three counter-examples: Seat Belts, Drunk Driving, and smoking. In each of these cases, we've made significant strides in changing the behvariour of the general population, and dramatically reducing the number of people injured or killed by these issues. None of these involved technical solutions, and instead were achieved through public education/advertising, changes to laws, and eventually changing expectations such that the problematic behaviours become socially unacceptable.
So yeah, can we change public behaviour? Sure, we've done it before, we can do it again. The best bet is to start doing this through kids, since they're the ones that are likely going to nag their parents to leave the phone alone.
I would argue the opposite, especially if you are a small company.
This exactly. I work with a midsized non-profit (roughly $3,000,000/year revenues), and we didn't do credit cards for years because we didn't have the ability (or desire) to have to deal with the security hassles associated with them. We finally found a good partner/vendor and were able to outsource the credit card portion of our online operations to them, and with the long delayed arrival of proper EMV terminals in the US, we can finally handle them on-site without having to take absurd security precautions.
In effect, the unencrypted/unsecured cardholder never, ever, touches our networks or computers. All we get from the payment processor is a hash that confirms the payment, and allows us to reconcile and/or reverse the charge if needed. It works great, and is far more secure than something I could have rigged up as a volunteer.
If it's not your wifi, it's not secure.
To be honest, I don't get this. Who cares if a network operator, or the person sitting next to you at a cafe next to you is snooping your data? With the advent of https everywhere, the data between my computer and the server is encrypted and secure, regardless of whether the underlying transport is compromised.
You always need to consider that the underlying network is insecure. I'll happily do my banking over public wifi, or satellite internet (where the packets are broadcast to the entire continent), because all an adversary sees is a stream of gobblygook.
Depends on the legal jurisdiction, but in 1948, a Saskatchewan farmer became trapped under his tractor, and scratched a short will into the bumper of his tractor. This survived court challenges, and that bumper is now on display of the library at the law courts. More info can be found here.
You're absolutely correct to say that correlation does not imply a causality. However, in this case, we do know the causal mechanism.
CO2 (and similar gasses) absorb infrared radiation at various wavelengths, and that absorbed energy translates into increased molecular motion, aka heat. This is a property that can be demonstrated experimentally in the lab, with completely reproducible results.
Those ice cores you dismiss? They're excellent time capsules of atmospheric gas composition. As the snow falls, and the cores build up, it traps small amounts of atmospheric gasses in the ice. You extract these tiny bits of gas, run them through a GCMS, and measure the concentrations of the various components. Typically these ice cores come from places that aren't subject to significant local human population (Antarctica, Greenland). They're also stratified, just like tree rings, so the date of the gas samples can be determined with a high degree of confidence.
These two things are undeniable facts. They are reproducible, and traceable.
So the real question is, if you're going to claim what you do, how has the increase in CO2 not caused an increase in temperature? What mechanism would prevent that?
It really isn't that extraordinary of a claim.
We know the properties of Carbon Dioxide from reproducible lab experiments, in particular its interaction with infrared light, and at the concentrations found in the atmosphere.
We know with reasonable precision the concentrations of CO2 in the atmosphere for the past few thousand years, and that it has gone up dramatically in the past few hundred years.
We have pretty good temperature measurements since the dawn of the industrial age, and good proxies that go back much further.
We know, with reasonable precision, how much carbon dioxide we as humans emit into the atmosphere on an annual basis, based on analysis of fossil fuel consumption, industrial growth, and so forth.
All of these numbers jive, and point to us as the root cause.
The only extraordinary claim is that we as humans are not responsible, and that our very obvious release of CO2 has not caused the warming we have seen. Claiming that means either denying the rise in temperature, the known physical effects of CO2, or denying the known concentrations of CO2. That requires extraordinary evidence.
There's another important sense that this isn't tautological. Sputnik 1 had no scientific instruments- it really was just a beeping sphere.
Right, but in a sense it was a scientific instrument in and of itself. The beeping was transmitted on two frequencies to allow the density of the ionosphere to be measured, and the spherical shape allowed the density of the upper atmosphere to be measured by the changes in its orbit over time.
Actually it was. The use of two radio frequencies in its transmission (20MHz and 40MHz) allowed the density of the ionosphere to be determined by receivers on the ground. The spherical shape was chosen so that it could be used to map the density of the upper atmosphere. It also provided information on the near space environment, as the internal temperature and pressure of the satellite could vary the duration of the beeps.
So yes, it was a scientific satellite, albeit a very basic one. It, of course, was also a big political F-U to the west, but that's realistically been the case for most things that have been done in the space age, especially the early part.
This exactly, or at least the cost part. I recently worked on a project where we undergrounded a private power distribution system for a retreat center located in an isolated location. The grid connects a small hydro-electric power plant with about 30 buildings, on a 25 acre campus. The total cost of this project was on the order of $3,000,000, and it was only that low because the Engineering work was done inhouse by a PE on a below market basis, and most of the labor involved was also donated. We're glad we did it, but it certainly was not cheap.
2) Test runs for Mars. All the same challenges of landing a mars mission are present on the Moon, but being so much closer it makes a much better place to test out the systems. If we cant do the moon, a mars trip is suicide. We havent actually tried since the days where the most advanced piece of tech around was a hand-held calculator. It's probably worth trying again with today's tech.
Landing on the Moon and Mars really aren't all that similar. Due to its lack of atmosphere, and lower gravity, landing on the Moon is a fairly simple propulsive affair. Kill your orbital velocity, which isn't that high to begin with, and use your engine to land gently on the surface.
Mars, on the other hand, has twice the gravity, and just enough atmosphere to be a problem. There's enough gas there that you need to have a heat shield, and can't build like you would for the moon, but you can't rely on it for the final stages of your landing (parachutes, propellers, what have you).
Thirdly, they represent very different situations once on the surface. Lunar dust is extremely abrasive, as it's had no water/wind to wear it down. This makes it absolute hell on any mechanical joint or seal that has to move. It's really hard to build equipment that will last a long time. On Mars, you probably don't have quite the abrasive issue, but you do have severe problems of toxicity due to the perchlorates in the soil.
As discussed in the above, it's incredibly difficult to actually "sink" a Venus habitat. Beyond how slowly large airships actually leak, the vast majority of the habitat's lift is dedicated to lofting the propellant on the ascent stage and (depending on the design decisions) the ascent stage itself. Meaning in the worst case you can ditch your ascent propellant (or even the ascent stage itself) and stay aloft on a tiny fraction of your peak design lift.
Heck, during the first world war, the Germans attacked London with Zeppelins, and those were incredibly difficult to shoot down, despite being filled with Hydrogen. The Brits would spray the Zeppelins with bullets, filling them with holes, but because the gas bags were at ambient pressure, there was very little escape.
Another example was a research balloon launched out of Canada in 1998. It's mission-ending systems failed to operate (detach the payload, burn a large hole in the envelope), and it drifted across the Atlantic. Canadian fighter pilots put more than 1000 rounds of ammunition through it, UK and US did the same, and it continued. Eventually, the Russians shot it with various air to air missiles, before it finally came down in Scandinavia.
The takeaway is that lighter than air craft are very difficult to take down when operating at ambient pressure.
ED: That should read "there's not even a large thermosphere temperature spike" like there is on Earth. You can see the temperature profiles here [astronomynotes.com] (I can dig up some graphics for higher up if you'd like)
That said, the thermosphere spike is largely of academic interest. The atmospheric pressure is so low at those altitudes that the thermal loading is close to nil. Basically the atoms/molecules in the atmosphere are moving really fast at those altitudes, so they're "hot", but there are just so few of them that they won't really heat anything of normal density up. I don't have a source handy, but I recall reading that it basically means that you could easily overcome it with radiators, and radiators are an incredibly inefficient way of rejecting heat.
Right, but overhead cables aren't insulated; the conductor is directly exposed to the air.
Underground cables, on the other hand, must be electrically insulated, and most electrical insulator materials are also pretty decent thermal insulators. Thus, in order to prevent the cable from heating up and destroy the insulation and/or blow up.
As both wireless and wired Internet access become cheaper and more ubiquitous, at some point that becomes the end of satellite/cable TV distribution.
For content distribution, and contribution, satellite will still be around for a long, long time. End user distribution? that's a different beast, but until we have the full demise of the networks, especially the sports networks, satellite will still be around. It's still the single cheapest way to distribute your content to the entire continent in real-time. A typical transponder costs about $1,000,000 a year to lease, and lets you stream out 4 or so HD streams, continuously. You're distributing that to 1000s+ clients at full resolution, it's going to take a long time to surpass that.
. Single gender bathrooms in retail. Most places can't really afford having separate facilities, so you'll probably see most places just have a room with both fixtures. Exception: bars, restaurants.
Actually, these are going away in bars and restaurants as well, at least here (Western Canada). A number of the local bars/restaurants have moved to a design where you have a genderless restroom, which is surrounded on all sides by full-height stalls. These aren't the stupid stalls like you see in most places, but rather completely enclosed, with a full door/lock on it. They're just marked as to whether they contain a toilet or a urinal+toilet.
I'll admit that the first time I walked in, I backed out thinking I had walked into the wrong one (there was a woman touching up her makeup at the window), but once I figured it out, it's no big deal. Plus, if you're really worried about safety, having it brightly lit, and more foot traffic, is going to improve that far more than anything else.
That's still no reason to ignore the colregs (collision regulations), which require adequate watch to be kept at all times while underway. This includes both visual watch keeping (aka the mk1 eyeball), and in the case of limited visibility (fog and/or smoke), a requirement to maintain an auditory watch (so listening for other ships), and produce sounds on your own, namely fog signals, gongs, and bells.
GPS has an omni-directional antenna. You don't know the angle to the satellites. GPS coordinates are based off the difference in time from the various satellites the receiver gets signal from.
Right, but the Ku-Band and X-Band communications antennas are highly directional, and calculate their lookangles to the satellite based on the known position of the satellite and the GPS position on the ground. Furthermore, many TDMA based modems depend on knowing the precise position of the transmitter so that they can synchronize the transmissions properly. if the ground position doesn't match the time-of-flight for the signal, collisions start happening and error lights go on.
Right, but think about how GPS actually works. Each satellite is transmitting a precise time signal, and the receiver determines its position through trilateration. It basically measures the distance to each of the satellites in orbit, based on the path delay between the satellite and the receiver. Spoofing works by replacing the signals received from the satellite with one of earth origin.
What you can't do when spoofing a position is replicate the geometry (and thus differences in path delay) that makes GPS work. What will suddenly happen is that everyone's GPSs in the area affected by spoofing are suddenly going to give exactly the same outputs. The same lat/long, the same Course over Ground, the same Speed Over Ground.
So let's take the example of a ship doing 14 knots, heading 90 degrees true, and located at 123.03W by 49.05N. As a bad actor, I want to misguide them, and cause them to move to 123.04W and 49.03N, so I setup my spoofer and start broadcasting the signal. Here's the rub: as soon as I turn the spoofer on, everyone in the region is suddenly going to have their GPS readout "123.04W and 49.03N, doing 14kt SOG at 90 True COG. Furthermore, if I have two GPSs onboard with decently separated antennas (say on either side of the bridge), they're both going to be showing the exact same values, which should also trigger alarms in the navigation system.
Now, you're absolutely right, none of this should eliminate proper watch keeping and situational awareness.
With all that said, though, AIS & Radar massively improve safety by radically improving your situational awareness, especially in foul weather. I was sailing up in the Broughton Archipelago. On a couple of occasions we got stuck out in dense fog, where we could see maybe 150m or so. We kept an appropriate watch, with the other guy onboard maintaining a bow watch, emitting appropriate fog signals, etc... but the radar was a huge help, especially to ensure we remained in channel.
On that same trip, we were crossing Queen Charlotte Straight, and passed (in fog) within 2 nautical miles of the Crystal Serenity (largest cruise ship on the Alaska run this year), and the only reason we knew she was there was due to AIS, seeing her on radar, and her crew being active on the VHF. Had we not known she was there, our original course would have brought us too close for comfort.
So yes, it's doable, but done right, the modern aids are a huge improvement in situational awareness and safety.
The thing is that with modern navigational systems, it's pretty easy to detect GPS spoofing. Let's say it happens.. Suddenly, the data coming off your GPS unit isn't going to match up with the rest of the sensors installed on the ship. In addition to the GPS, ships carry gyrocompasses, speed logs, and other sensors.
Modern navigational suites are supposed to compare the SOG derived from the GPS with the STW (Speed Through Water) from the speed log. If they're more than, say, 6kt out from each other (to allow for current), it throws an alarm. Same thing with gyro heading and COG from the GPS.
Lastly, an observant crew should notice that something is wrong as if they get spoofed to a place far enough away, their satcom suite should become very unhappy as the computed angles to the satellites they're targetting will be wrong enough they can't track any more.
As far as the AIS thing goes, all I have to say is "Finally"... The US Navy is pretty much alone in western nations in not participating in AIS during peacetime. As a recreational sailor, I always follow the rule "If it's grey, stay away" but that's hard to do if you don't know they're there. I'm in the PNW, and more than a few times I've been out sailing in the islands, come around a point, and been surprised to come across a (small) warship that was hidden by the headland. Had they been participating in AIS, I could have better avoided them.
However in order to be sold in the USA, they must comply with the law that forbids reception on the old AMPS bands. Of course, this is usually just a pinkyswear on the part of the manufacturers, and can be unlocked either through accessing a calibration mode, or by snipping a diode/resistor on the main circuit board.
A satellite with this size and cost is often built without ROM, simply because of the cost of space-qualified ROM which must be rad-hard for decades of operation.
I thought it was the other way around? A PROM, and especially a mask ROM is an incredibly simple device, effectively just a single diode between a given row and column on the die. Not counting the address decoder (which you would have in both RAM and ROM), a ROM chip only has a single PN junction per bit. An SRAM cell has 6 transistors per bit, and DRAM is a capacitor plus a transistor (not to mention the required refreshing).
I'd love to be shown the error of my ways, but I would have thought the KISS principle would hold.
As I recall, the other primary reason why AMSAT typically uses this configuration is due to doppler. The frequency shift at VHF is only something like +/- 15kHz, which is usually within the capture window of a VHF receiver, whereas at UHF it's +/- 45 kHz, which is beyond your typical receiver. Since we can retune our earth based receivers on the fly, the whole thing works.
Generally in a software project "under-resourced" means the milestones aren't being reached, which either means you have bad milestones, bad requirements, or bad coders.
I guess I didn't make myself sufficiently clear, and you hit the nail on the head. By resources I was meaning not just people, but equipment, tools, requirements, knowledge, plans, or is it just bad milestones to begin with. Adding more people to a failing project is a recipe to make it fail faster, the solution is to figure out what's going on early so the problems can be resolved.