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Feasibility study of a mission to Sedna – Nuclear propulsion and solar sailing

(arxiv.org)
200 points speckx | 5 comments | 01 Jul 25 14:08 UTC | HN request time: 0.697s | source
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pavel_lishin ◴[01 Jul 25 14:46 UTC] No.44434403[source]▶
> Sedna is expected to pass through the perihelion of its orbit in 2075--2076 and then move again away from the Sun. Considering the distances involved, a mission targeting the object would need to be launched "relatively" soon, especially if using conventional propulsion systems, which could require up to 30 years of deep-space travel.

Sedna's perihelion is ~76 AU - more than twice as far as Pluto, which took New Horizons nearly a decade to reach.

Sedna's apehelion is over 500 AU.

> The Direct Fusion Drive rocket engine is under development at Princeton University Plasma Physics Laboratory

Is it ... is it actually working? How close are they? And even if they get it to work next year, will it be something well-engineered & reliable enough to send it into space for 10 years and expect it to work?

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JumpCrisscross ◴[01 Jul 25 15:20 UTC] No.44434787[source]▶
> How close are they?

Not very. That said, DFD is a technology with tremendous moonshot potential.

Fusion propulsion is inherently easier than fusion power on Earth because you don’t have to worry about converting heat to electricity and the breakeven threshold is far lower; depending on the mission, even Q < 1 could be fine.

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1. sigmoid10 ◴[01 Jul 25 18:24 UTC] No.44436727[source]▶
"Easier" in this context is still ridiculously hard. Fusion rocket designs were first seriously researched 50 years ago and not a single one of the countless designs proposed since then has reached readiness for in-space use.
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2. PaulHoule ◴[01 Jul 25 18:53 UTC] No.44436975[source]▶
Note the economics might be better than for terrestrial fusion energy because you're not paying for watts you're paying for thrust and something like D-He3 has a great exhaust velocity.
3. JumpCrisscross ◴[01 Jul 25 21:44 UTC] No.44438270[source]▶
> "Easier" in this context is still ridiculously hard

Absolutely. I’ve just noticed that a lot of people think, correctly, that fusion power is hard and space is hard so doing them together is stupidly difficult. Not so in this application—the relaxation of requirements on fusion outweigh the difficulties of doing it in space.

Put another way, the dollars going into fusion power might be better spent on DFD.

4. bbarnett ◴[02 Jul 25 05:04 UTC] No.44440395[source]▶
Da Vinci and others worked on flying machines, I expect designs go back thousands of years. Yet the result is now thousands of designs and working iterations.

I think we're also getting better and faster at iteration and design. CAD, modelling, even wind tunnels from 50 years ago made a massive difference over jumping off a cliff with a glider for tests.

I guess my point is, I don't see 50 years as validation of it being hard. And some of those designs were likely dismissed due to tech limits at the time.

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5. sigmoid10 ◴[02 Jul 25 09:18 UTC] No.44441592[source]▶
The point is more that 50 years ago, people thought we had sufficient understanding of fusion to build something like this. And thanks to advancements in inertial confinement research at the height of the thermonuclear arms race, they actually had a pretty good reason to believe so back then. There is very little reason to believe these new companies today when they say so, because fusion research is in a deep hole and running on a fraction of the funding it did during the cold war.