Transhuman Space/Avatar

[Cyclone]

Originally Posted by Fred Brackin

I wouldn't. There's just much in the books for _everything_ to have caught somebody's attention in the years since this forum was established.

"Alien world with actual life on it that people are visiting in setting" is not something that people would just skip over like "another asteroid colony with funny people on it."

Originally Posted by Fred Brackin

Your "probe" (assuming you mean something beyond Starstream swarms) timeline may have problems. The highest amount of Delta-V i can recall in the setting was a very specialized courier with a bit over 100 miles per second. Spaceships gives a figure of 4000 mps for a 400 hundred year voyage to Alpha C at 0.01 c. Your timeline requires even more Delta-V than that.

Use of the phrase "Moonshot!" doesn't necessarily cover the problem. The ramp up from a V-2 to a Saturn-5 required a little less than a 6x increase in Delta-V most of which came from building _much_ bigger. You need an ikncrease of Delta-V more than 10x that.

I don't mean something beyond Starswarm and the like. I mean something like a small drone with laser beams fired at its light sails, like Breakthrough Starshot. The 2080 date would be a first look with whatever can get there the absolute fastest. The "modern era" expeditions would be the ones with some kind of actual "manned" vessel, though presumably something extremely specialized and expensive, basically designed for exactly one trip. Probably not even a return trip, since the setting has lots of "expendable" sapients and infomorphs.

[TGLS]

Originally Posted by Fred Brackin

This is about 43 miles per second per day and you'd use up 5% of your ship's mass in antimatter fuel every 79 days. I don't think you can do this for 10 years even with using multiple stages.

I'm kind of half-assing a beam riding spacecraft (i.e. ground station accelerates small amounts of matter to relativistic velocities, which impact the spacecraft, pushing it along without need for reaction mass) and hand-waving all the implications with regard to the engineering steps here. Given the assumption is, "THS but they really really want starships guys" I think that it could be doable.

Though it could plausibly take much longer to get the ship moving. If we're going with a 20 year lead time on the probe, that implies a ship that can stop would take about 29 years, and with a 30 year lead time, the ship would take 36.5 years.

[Fred Brackin]

Originally Posted by Cyclone

"
I mean something like a small drone with laser beams fired at its light sails, like Breakthrough Starshot.

Maybe one of the more math-oriented people will come along and tell us how many GW or TW such a scheme would require but I suspect it's a lot and running it continuously for 10 years is a lot too.

[TGLS]

Originally Posted by Fred Brackin

Maybe one of the more math-oriented people will come along and tell us how many GW or TW such a scheme would require but I suspect it's a lot and running it continuously for 10 years is a lot too.

According to the wikipedia article it's on the order of a TJ necessary to push the craft and it could be done with a 100 GW array of 10 KW lasers (I suspect this is output power). This is ~10 million lasers. Even assuming a lasers of 10% efficiency (some lasers have efficiencies of <10%), we're looking at 1/18th of humanity's total energy consumption.

My ridiculous 86% speed one would need roughly a 4 TW laser output, assuming a 40 ton payload. The ship that stops would need about 1.83 TW laser output over ~4.34 years, again assuming a 40 ton payload. Also, it would need a power supply for the breaking magsail over ~18.662 years. Better start tiling Mercury with solar panels.

[Fred Brackin]

Originally Posted by TGLS

A Also, it would need a power supply for the breaking magsail over ~18.662 years.

I think magsails only need power in the turn when they are first deployed. so at least that may not be a stumbling block.

[Cyclone]

Originally Posted by TGLS

According to the wikipedia article it's on the order of a TJ necessary to push the craft and it could be done with a 100 GW array of 10 KW lasers (I suspect this is output power). This is ~10 million lasers. Even assuming a lasers of 10% efficiency (some lasers have efficiencies of <10%), we're looking at 1/18th of humanity's total energy consumption.

Per second, yes. The laser sails are only fired for a few minutes, though - they're supposed to hit accelerations of 100 km/s^2, and are shot at very tiny drones, so they don't need to fire for years. Assuming you launch one per day, and each launch requires 10 minutes, that's more like 1/2,592th of Earth's energy consumption.

[Fred Brackin]

Originally Posted by Cyclone

Per second, yes. The laser sails are only fired for a few minutes, though - they're supposed to hit accelerations of 100 km/s^2, and are shot at very tiny drones, so they don't need to fire for years. Assuming you launch one per day, and each launch requires 10 minutes, .

Eek! That's over 10,000 Gs and for 10 minutes means it has to be handled as a static load.

Thermal issues might be worse though. Even if your sail is .98% reflective it's still absorbing the rest. 2% of 4 TW is 80 GW and you have to absorb and re-radiate all of that for 10 minutes without your sail melting. You'd need a big sail to be able to spread your laser thin enough to avoid that melting and that would probably make your sail mass too much to get those accelerations.

[TGLS]

Originally Posted by Fred Brackin

Thermal issues might be worse though. Even if your sail is .98% reflective it's still absorbing the rest. 2% of 4 TW is 80 GW and you have to absorb and re-radiate all of that for 10 minutes without your sail melting.

Numbers are a bit off there boss. Each sail needs on the order of 1 TJ, which implies on the order of 1 GW power applied to the sail for 10 minutes. If only 2% of the power were absorbed as heat, that implies a waste heat on the order of 10 MW.

This is still on the "very speculative" end of the scale, to say nothing of the large fast design.

I still feel this discussion is getting hung up on technical details when the real questions ought to be revolving around why people/AIs/etc. in Sol really care about Alpha Centauri.

[Cyclone]

Originally Posted by TGLS

I still feel this discussion is getting hung up on technical details when the real questions ought to be revolving around why people/AIs/etc. in Sol really care about Alpha Centauri.

It is an alien world, located nearby, that has a functional biosphere (and later, confirmed intelligent life). Even in THS mainline, they were almost ready to spend however much money Starswarm cost to go to what was almost certainly a completely dead system, in between trying to find trace biological life on Mars and Europa.

It is hard for me to imagine anything that would be better for NASA's budget than "turns out that there is a world with a complete biosphere around Alpha Centauri," other than, I suppose, "turns out there is a world with a complete biosphere around Proxima Centauri."

[TGLS]

Originally Posted by Cyclone

It is an alien world, located nearby, that has a functional biosphere (and later, confirmed intelligent life). Even in THS mainline, they were almost ready to spend however much money Starswarm cost to go to what was almost certainly a completely dead system, in between trying to find trace biological life on Mars and Europa.

Oh, sure launch a starswarm there between 2046 and 2056. Problem is that the starswarm does a fast pass of Alpha Centauri before heading off into deep space until it eventually runs out of power and then hits something. A craft that can stop and look around is several steps beyond a starswarm. A craft that can stop, look around, and return (well I suppose AI could return, but if the goal involves anything involving unobtanium...) is even more steps beyond that.

Even ignoring the difficulties of getting there and stopping, I fail to see what this adds to the setting beyond, "Great powers are sinking lots of treasure and effort into attempting establishing a colony far away." Unless the adventure is at the colony, of course.