|
|
Post by jageriv on Dec 9, 2016 3:11:53 GMT
I was considering making a "freight" challenge, where the goal was to move some amount of goods for the cheapest price (the example I was thinking of was moving as much methane from Titan Orbit to Earth, though an easier initial goal would probably be required). However, a problem I quickly came across was figuring out how to divide out the cost of the ship assuming the ship made multiple trips.
For example, lets say you had an earth mars freighter: Lets say it made a trip (either way) every two years: thus, if the ship lasted for 10 years of operation before scraping, or on average needed as much in repairs over that time as buying a new ship, the cost of the ship could be divided out over 5 trips. If the ship had an expected life of 20 year's however, it could be spread out over 10 trips, significantly lowering per trip costs.
Having an "expected ship life" also nicely adds a clear cost for having very long trips: If both ships have an expected life of 10 years, but one can make the mars earth trip in 1.5 years instead of 2, It could squeeze 1 more trip out of the hull than its competitor.
So, what are people's thoughts on the expected life of spaceship hulls in the future with our setting tech level?
|
|
|
|
Post by dragonkid11 on Dec 9, 2016 3:21:03 GMT
I think civilian space vessel would probably have rather long lifespan as the period of time it actually spent on burning is near minimal.
The maintainence required should be really low, thus increasing the lifespan of the vessel by a few years, even decades.
|
|
|
|
Post by newageofpower on Dec 9, 2016 4:20:35 GMT
I've designed a bunch of 'superior' civilian vessels. Let me know if you guys are interested in seeing them.
|
|
|
|
Post by amimai on Dec 9, 2016 4:51:25 GMT
A huge 20GW mercury MPD and appropriate sized nuclear reactor could cut the trip down from years to months easy. I have gotten really massive ships to have fairly high dV and surprising acceleration ratings using mercury MPD, and there really is no reasonable limits on how much power you can pump into one, I think it caps out at a couple TW but that's more then enough to burn a small country worth of mass to appreciable % the speed of light from just a couple kt of fuel across a week or 2.
Actually with the ingame MPD a mission to Alpha Centauri is probably possible using something the size of a city ship and a few very high power fission/fusion reactors.
|
|
|
|
Post by The Astronomer on Dec 9, 2016 5:22:13 GMT
Civilian spacecrafts, if maintained well, could easily live over 100 years. They might even outlive generations and generations of baseline humans. What might be a problem is that old, INFOAge striking 'outdated' problem, when people will abandon their old spacecraft in favor to the new fad. This will greatly reduce the ships' average life expectancy.
Anyways, do you guys have any GIGAWATT nuclear reactor plans?
|
|
|
|
Post by newageofpower on Dec 9, 2016 5:36:27 GMT
A huge 20GW mercury MPD and appropriate sized nuclear reactor could cut the trip down from years to months easy. I have gotten really massive ships to have fairly high dV and surprising acceleration ratings using mercury MPD, and there really is no reasonable limits on how much power you can pump into one, I think it caps out at a couple TW but that's more then enough to burn a small country worth of mass to appreciable % the speed of light from just a couple kt of fuel across a week or 2. Actually with the ingame MPD a mission to Alpha Centauri is probably possible using something the size of a city ship and a few very high power fission/fusion reactors. I would like to see the exhaust velocity of your best mercury MPD. I haven't gotten over 100MM/s on a sub petawatt design. Civilian spacecrafts, if maintained well, could easily live over 100 years. They might even outlive generations and generations of baseline humans. What might be a problem is that old, INFOAge striking 'outdated' problem, when people will abandon their old spacecraft in favor to the new fad. This will greatly reduce the ships' average life expectancy. Anyways, do you guys have any GIGAWATT nuclear reactor plans? Check out Tessfield's Solar System Standard Organization thread in the other forum. Apophys's 25 GW reactor is the most powerful practical reactor, power/weight wise (assuming paper thin radiators) and should be the main supply in any MPD based vessel. |
|
|
|
Post by thorneel on Dec 9, 2016 9:55:21 GMT
Mercury is the best MPD fuel, if money is not an issue, and not just because it is so fantastically dense.
With its highest molar mass, the rocket power equation means that it will give the most thrust for a given power. It will also give the less dV, but MPDs are not dV-limited, so this is not a problem.
However, it is so expensive that I never used it in any serious design. I prefer neon due to it being cheap and not particularly awful in any way (like hydrogen density or its Houdini tendencies), and with the reactors we have, we can throw pretty much anything with MPD, it will work. With the added bonus of being chemically completely neutral, I expect to see many civilian using it.
I also tend to use large MPDs as they have a better mass flow at a given power level.
(Technically, radon has a higher molar mass than mercury, but not only is it so absolutely stupid expensive, its half-life is actually measured in days, so I am not sure how they manage to hold it in a tank for months...)
For Alpha Centauri missions, does that include the 6-months life of nuclear fuel? Or do you count nuclear fuel and means to change it with cargo bays?
In fact, what kind of dV do you need for such a mission for a given number of decades?
|
|
|
|
Post by amimai on Dec 9, 2016 12:15:19 GMT
i think ~10% light speed will get you there in 133 years, so its not really that far...
|
|
|
|
Post by The Astronomer on Dec 9, 2016 12:30:46 GMT
Mercury is the best MPD fuel, if money is not an issue, and not just because it is so fantastically dense. With its highest molar mass, the rocket power equation means that it will give the most thrust for a given power. It will also give the less dV, but MPDs are not dV-limited, so this is not a problem. However, it is so expensive that I never used it in any serious design. I prefer neon due to it being cheap and not particularly awful in any way (like hydrogen density or its Houdini tendencies), and with the reactors we have, we can throw pretty much anything with MPD, it will work. With the added bonus of being chemically completely neutral, I expect to see many civilian using it. I also tend to use large MPDs as they have a better mass flow at a given power level. (Technically, radon has a higher molar mass than mercury, but not only is it so absolutely stupid expensive, its half-life is actually measured in days, so I am not sure how they manage to hold it in a tank for months...) For Alpha Centauri missions, does that include the 6-months life of nuclear fuel? Or do you count nuclear fuel and means to change it with cargo bays? In fact, what kind of dV do you need for such a mission for a given number of decades? I made a 176 km/s Mercury MPD, but the design is far too power hungry. Currently trying HD, will try Ne soon, thanks. |
|
|
|
Post by cutterjohn on Dec 10, 2016 4:53:30 GMT
I think civilian space vessel would probably have rather long lifespan as the period of time it actually spent on burning is near minimal. The maintainence required should be really low, thus increasing the lifespan of the vessel by a few years, even decades. The engines seem like one of the more easily replaceable components of a ship, and at fractions of a G of acceleration, there would be little mechanical stress on the framework. I don't think burning less would have an appreciable effect on the lifespan of the ship. Especially since, in zero-g, swapping engines honestly becomes an almost trivial exercise. An engine can be swapped out on an airliner in just a few hours. Meanwhile, on a longer trip, all of your power systems and life support systems would continue accruing hours. |
|
|
|
Post by The Astronomer on Dec 10, 2016 5:08:46 GMT
Why not just 'LUNA IS DYING IN 10 YEARS, WE NEED TO FERRY AS MANY PEOPLE TO MARS'
|
|
|
|
Post by Pttg on Dec 10, 2016 7:28:04 GMT
I suspect that ships would last at least as long as naval vessels, and probably longer since they aren't sitting in saltwater.
|
|
|
|
Post by dragonkid11 on Dec 10, 2016 7:40:51 GMT
They most likely have tons of spare parts for air support and power system for long journey.
And if they need more food, put them in cargo bay or something.
|
|
|
|
Post by dpidz0r on Dec 15, 2016 19:08:36 GMT
As far as propulsion goes, do you guys think there might be regulatory limits placed on the power plants or engine performance? A suicidal commercial airline pilot isn't unprecedented ( en.wikipedia.org/wiki/Suicide_by_pilot#By_pilots_in_control_of_whole_flight ), and I'd imagine a suicidal space captain dropping his ship on a planetary population center at relativistic speeds would be pretty bad. Would it even make sense to see regulations limiting performance of civilian engines as an attempt to mitigate that (either from a technical standpoint or a clueless politician doing it "for the children" because "if it saves just one life it's worth it"). |
|
|
|
Post by beta on Dec 15, 2016 19:27:04 GMT
That would be like trying to govern all vehicle traffic to no more than 20 km/h because a lot of people can get killed in accidents when going 100 km/h. Completely impractical to the operation of moving around quickly.
|
|
