By the classical tsiolkovsky equation, a 95% fuel ship has to have an effective exhaust velocity of 1/3 of its final velocity. Protons at c/30 have an energy around 1 MeV. Meaning they'd have to be accelerated through a million volt potential in an ion drive. Or 2+ million volts if we're dealing with heavier atoms that have neutrons. That seems challenging from an engineering standpoint but perhaps doable. Plenty of materials with a dielectric strength >50Mv/m

@RobertCousineau I wouldn't say the below is truly a truly a crux as I don't think fusion is required for this to be likely (although it definitely does make it more likely), but it is a strong characteristic disagreement.

I added a new 10k Yes limit at 66%.

the trouble with a small ship is that the ratio of surface area to mass is worse so it gets pummeled to death by space dust and radiation much faster. At 10% c even cold protons are hitting it at energies around 9 MeV

@JonathanRay 9 MeV protons striking anything will produce gamma rays and neutrons

@JonathanRay and if you want to protect it with a magnetic deflector there are problems:
1. a lot of the interstellar medium is neutral hydrogen
2. deflector drag scales as the square of ship radius, but available fuel scales as the cube of ship radius, so this probably doesn't work at small scales.

it might be feasible with fission powered ion drive to get enough delta-v to transfer to a highly elliptical orbit around the milky way which passes close enough to the supermassive black hole to reach 10% c -- if the ship isn't destroyed by radiation or collisions with debris in that high density zone first

never bet on a 2000x increase in a world record (4000000x in terms of energy)

@JonathanRay This makes no sense. Here’s a very obvious counter-example (I guess it’s only a 1500x increase but it’s also only in about 130 years, vs 8000 in this market)

https://en.m.wikipedia.org/wiki/List_of_production_cars_by_power_output#Timeline_of_most_powerful_production_cars

@JonathanRay put a new limit of 10k at 60%.

@benshindel there were a lot of low hanging fruit when cars were first invented and most of that increase on the log scale was frontloaded in the first 20 years

@JonathanRay Space travel was making that kind of rapid progress in the 1950s but it's been a mature industry for half a century

Would tiny lightsails like these qualify?

https://en.wikipedia.org/wiki/Breakthrough_Starshot

@benshindel if it is capable of sending us a message from alpha centauri, yes. I doubt anything that small could hold an adequate transmitter.

@JonathanRay Why is that a condition? I don’t understand why that’s relevant.

What happens if we pass 9999 but then reverse the arrow of time and subsequently develop such capabilities after we pass back below 9999 CE?

@benshindel Time doesn’t work that way

@JonathanRay say that to yourself in (9999-2024)*2 years

a highly elliptical orbit passing close to a neutron star or black hole to take advantage of the oberth effect is one way of achieving this but you get less than a second above 10% c unless it's a supermassive black hole.

@JonathanRay and the ship would be spaghettified

Before 9999 or before 10,000?

More importantly, what if such a ship is built and launched from space, with no identifiable planet of origin (e.g. assembled in a multi-planetary station)?

@BrunoParga Velocity relative to the station it was built on

@JonathanRay makes sense, thank you.

Project Daedalus, with 70's (expectation of) very plausible tech, was estimating it probable to get up to around .12c using a fusion rocket.

https://en.wikipedia.org/wiki/Project_Daedalus

a potential crux: https://manifold.markets/JonathanRay/dark-matter-used-as-reaction-mass-b

@JonathanRay some way of interacting with dark matter efficiently to push it around would make this a zillion times easier because then you don't have to carry all the reaction mass with you.

@JonathanRay Ridiculously easy. If you don't need to throw away reaction mass to accelerate, it's just a matter of dumping energy into your motor. For example, at 100% drive efficiency, a 100 ton craft with a 1 Gigawatt reactor could reach .1 c in ~41 years. Adjust for whatever efficiencies your drive might have and how good a reactor we might have once such a thing would be discovered. For many values, the time required is quite short.

Still voting No on that question though. I think dark matter really only interacts with gravity, and there's no way we're getting some kind of gravity-wave-ramscoop in 100 years.

Yes on this question though. 9999 is a long time to build Project Daedalus.