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200 points speckx | 2 comments | | HN request time: 0.422s | source
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pavel_lishin ◴[] 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 ◴[] 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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kristianp ◴[] No.44442331[source]
If Q < 1, aren't you better off with an ion drive that just shoots the hydrogen out the back? You still need to get most of the energy from somewhere other than the fusion drive.
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1. thehappypm ◴[] No.44443712[source]
Energy and thrust are not equivalent. There’s hardly any limit to how much energy you can generate in space (for example using a nuclear reactor), but fuel is the limiting factor.
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2. TorKlingberg ◴[] No.44446301[source]
By "fuel", do you mean reaction mass (stuff that shoots out the back of the rocket) or energy source?

A nuclear reactor in space would require an enormous heat sink to get useful energy out.