Realistic STL Interstellar Missions

[AlexanderHowl]

50% is not that much in 50 years. Even if we continued with that date of increase, it would take six or seven centuries to get to 5% c. For reasons specified above, we are unlikely to get above 5% c unless one of the FTL schemes end up working.

[Joseph Paul]

Originally Posted by David Johnston2

A realistic interstellar ship requires vast resources. It would be a global scale project.

How vast? More than what it takes to build a city?

[AlexanderHowl]

Well, the cost is around $10 million per person at TL10 assuming mature technology. If you are producing a one-of-a-kind spacecraft, you are probably increasing the cost by 100x, as you have to include research and development, infrastructure costs, training costs, etc. If it is the only spacecraft produced of that type, the cost would probably end up being $1 billion per person, meaning $10 trillion for a mission of 10,000 people. By comparison, the average city would cost around $500,000 per person in total infrastructure costs (including housing), so $10 trillion would build a city of 20 million people.

Realistically, a society would be unlikely to invest more than 5% of GDP per year on interstellar missions, with 1% of GDP per year being more likely after the first decade. A mature and developed TL10 society with 10 billion people has a GDP of ~$670 trillion per year, so 5% is ~$33.5 trillion per year and 1% is ~$6.7 trillion per year. A one-of-a-kind mission could be launched, though it would be difficult to justify, so a continuous production would make more sense, meaning that the society would likely send out 670,000 people per year, as well as employing millions of people directly and supporting millions of people indirectly.

If we assume construction in the Neptunian Trojans, it would probably be the reason for the colonization of the outer edge of the Sol System. With ~6.7 million people working directly on it, another ~26.8 million people would provide support services for those people. When you include dependents, spouses, retirees, etc., the total population impacted by the construction of the missions would probably be around ~53.6 million, meaning >0.5% of the entire system would depend on the missions.

[Johnny1A.2]

Originally Posted by David Johnston2

A realistic interstellar ship requires vast resources. It would be a global scale project.

So would an airplane have been...to the Romans.

The scale of resources necessary to build an STL starship are relative to the overall wealth and size of the society. For us today, yeah, it would be a global project. In fact, it would be super-global, beyond us for all practical purposes.

But a Solar System wide society, multiple orders of magnitude wealthier than our own, would be a different critter. Likewise, exactly how big the cost (broadly defined) of such a project would be would depend on what tech was required to instantiate it.

'Realistic cost' is relative.

[Johnny1A.2]

Originally Posted by DanHoward

This is an increase of almost 50%. It seems pretty dramatic to me.

Compared to the previous time period, it's peanuts. The time period from 1850 to 1950 (roughly) saw orders of magnitude increases in speed and performance. People who travelled west in covered wagons lived to see astronauts travelling at multiple miles per second.

[Anthony]

Interstellar travel at .05c requires a minimum energy budget of 1.125e+14J/kg, and no rocket will achieve even half that, call the actual energy budget 3e+14J/kg. Low end of current electricity prices is about $4e-8/J, but less useful energy might go less, call it $1e-8/J, putting a low end price of $3M/kg or $3B/ton. It seems unlikely that we can manage less than a ton per person, so based on TL 10 wealth of $75k/person, we only need 40,000x starting wealth per person you send.

[cptbutton]

Originally Posted by AlexanderHowl

Of course, it would be relatively easy for a spacecraft to divert when 1+ ly from Earth in order to go to another system. Unless the governments of Earth were willing to waste resources to monitor a spacecraft on a ballistic trajectory, most people would assume a tragedy had occurred when they do not find evidence of the new colony a few years or decades after it was supposed to arrive (light lag is always annoying). Lost colonies will probably be a popular theory concerning missing colony missions.

This ties in to my idea. You have an STL ship as described, but you aren't sure what system is suitable. So you pick 4-5 likely possibilities in the same direction, and send a smaller manned probe or probes that can make 5-10% c. When they get there, they survey the system and either say "Come on in , the water's fine!" or "This place bites, go somewhere else."

For extra complication, if the probe crew waves the main ship off, they are doomed. Might bias their results.

[David Johnston2]

Originally Posted by Johnny1A.2

So would an airplane have been...to the Romans.

The scale of resources necessary to build an STL starship are relative to the overall wealth and size of the society. For us today, yeah, it would be a global project..

No. It wouldn't. For us today it would just be an impossible project. We aren't rich enough to do it at all.

[AlexanderHowl]

Originally Posted by Anthony

Interstellar travel at .05c requires a minimum energy budget of 1.125e+14J/kg, and no rocket will achieve even half that, call the actual energy budget 3e+14J/kg. Low end of current electricity prices is about $4e-8/J, but less useful energy might go less, call it $1e-8/J, putting a low end price of $3M/kg or $3B/ton. It seems unlikely that we can manage less than a ton per person, so based on TL 10 wealth of $75k/person, we only need 40,000x starting wealth per person you send.

I think you are basing the cost on an inflated cost of energy. The cost of energy dramatically declines from TL9 to TL10. We can tell that by the change in delta-v between engine systems by TL. For example, the delta-v for fusion engines increase 5x between TL9 and TL10, suggesting that energy costs 4% as much at TL10 as at TL9 since energy is the square of delta-v.

Since 96% of the energy from the 0.05c spacecraft comes from a ramscoop, you can further discount the effective cost of energy by 96%, since energy is the square of velocity. That would reduce the cost of energy to effectively 0.16% as much as at TL9.

In addition, you can use processes that would be wasteful for electricity generation but perfectly fine for propulsion generation. Since you do not have the infrastructure for generating and transmitting electricity, and since you to not need to protect 100% of the environment from radiation, you can reduce the associated costs of energy by effectively 96%. That would reduce the cost of energy to effectively 0.0064% as much as electricity at TL9.

The end result would be the 3.125 PW-h of kinetic energy per person would be worth as much as 200 GW-h at TL9. If we assume a wholesale price of $30,000/GW-h, that ends up being $6 million per person, less than the $10 million per person budget.

[ericthered]

Originally Posted by AlexanderHowl

Since 96% of the energy from the 0.05c spacecraft comes from a ramscoop, you can further discount the effective cost of energy by 96%, since energy is the square of velocity. That would reduce the cost of energy to effectively 0.16% as much as at TL9.

correct me if I'm wrong, but I thought ramscoops ended up being inefficient for propulsion -- though they still work for slowing down, which might give you a sizable chunk of savings... but its going to end up being under half.