4 ms·

This direct fusion drive is a really interesting concept. Maybe something like this could be used for interstellar travel in a century (or five), it is very enc

This direct fusion drive is a really interesting concept. Maybe something like this could be used for interstellar travel in a century (or five), it is very encouraging that there is active research on it. ~5kg of thrust is not a lot, but over time... This sounds significantly more feasible than nuclear pulse propulsion ("project orion" style) which I used to think was the only feasible approach to get to another star. One thing that was unclear from the paper to me: How does the fusion drive "pick" D/He3 fusion over D/D? Can this be "forced" by just cranking the plasma temperature way up? Or do you still just have to deal with a bunch of neutrons from undesired D/D fusion?

floxy 1y ago
Roundtrip Interstellar Travel Using Laser-Pushed Lightsails https://ia800108.us.archive.org/view_archive.php?archive=/24/items/wikipedia-scholarly-sources-corpus/10.2514.zip&file=10.2514%252F3.8632.pdf https://ia800108.us.archive.org/view_archive.php?archive=/24...
- myrmidon 1y ago
  This is very interesting. Apparently beam collimation is much less of a show-stopper than I would have assumed. But I don't see us putting a a 1000 kilometer lens into orbit anytime soon, and that multi-terawatt (sustained!) laser system sounds like a bit of a headache, too...
  - cnity 1y ago
    See: https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot
- pavel_lishin 1y ago
  > This paper discusses the use of solar system-based lasers to push large lightsail spacecraft over interstellar distances. The laser power system uses a 1000-km-diam. lightweight Fresnel zone lens that is capable of focusing laser light over interstellar distances. A one-way interstellar flyby probe mission uses a 1000 kg (1-metric-ton), 3.6-km-diam. lightsail accelerated at 0.36 m/s2 by a 65-GW laser system to 11% of the speed of light (0.11 c), flying by a Centauri after 40 years of travel. A rendezvous mission uses a 71-metric-ton, 30-km diam. payload sail surrounded by a 710-metric-ton, ring-shaped decelerator sail with a 100-km outer diam. The two are launched together at an acceleration of 0.05 m/s2 by a 7.2-TW laser system until they reach a coast velocity of 0.21 c. As they approach a Centauri, the inner payload sail detaches from the ring sail and turns its reflective surface to face the ring sail. A 26-TW laser beam from the solar system, focused by the Fresnel lens, strikes the heavier ring sail, accelerating it past a Centauri. The curved surface of the ring sail focuses the laser light back onto the payload sail, slowing it to a halt in the a Centauri system after a mission time of 41 years. The third mission uses a three-stage sail for a roundtrip manned exploration of e Eridani at 10.8 light years distance. Very cool.
- foobiekr 1y ago
  The Mote in God's Eye I guess this will be the Niven-Pournelle thread.
topynate 1y ago
The easiest way (perhaps the only practical way) to favour the aneutronic reaction is to run a helium-rich mixture. The trade-off is lower power density.
MadnessASAP 1y ago
> This sounds significantly more feasible than nuclear pulse propulsion ("project orion" style) which I used to think was the only feasible approach to get to another star. I still carry a torch for project Orion, it's impossible to not love. * Feasible 50 years ago, not 50 years from now. * No ultra lightweight fancy space age materials, steel and lots of it. * Seriously, lots of it, let's launch a battleship to to Mars, * or Jupiter, * or Alpha Centauri. * Gives everyone something way better to do with all those nuclear bombs they have laying around.
- marcosdumay 1y ago
  > it's impossible to not love As an idea, yeah. But if somebody actually tried to build it, the entire world would oppose for very good reasons. Still, it's something that maybe we should build on space (outside of Earth's magnetic field).
- randallsquared 1y ago
  > Gives everyone something way better to do with all those nuclear bombs The counterpoint there is it gives lots of reasons to make so many more, increasing proliferation worries. However, there's an SF novel that just came out that features nuclear pulse: Fenrir, by Ryk Spoor and (posthumously) Eric Flint. I enjoyed it.
  - pavel_lishin 1y ago
    I should re-read Footfall, by Larry Niven. Quite a few banger lines in there.
    - m4rtink 1y ago
      Orion drive is one long line of bangers by definition! ;-)
  - eszed 1y ago
    My favorite SF along those lines is King David's Spaceship, by Jerry Pournelle. https://en.m.wikipedia.org/wiki/King_David%27s_Spaceship https://en.m.wikipedia.org/wiki/King_David%27s_Spaceship
voxleone 1y ago
Project Orion was the promise of my youth [70/80s]. It speaks to both the technological courage and the philosophical optimism that once characterized space exploration — and how that momentum seems to have faded. By all accounts, it was technically feasible. And yet... Of course there was 'the shadow of the Bomb'. From bold, almost reckless experimentation (Mercury, Gemini, early Apollo, things shifted to safety-optimized, cost-constrained engineering. And there was Cost and Politics; the post-Apollo world didn’t want to colonize the solar system. It wanted low Earth orbit, and safe returns. Budgets followed. Kinda sad.

floxy 1y ago

Roundtrip Interstellar Travel Using Laser-Pushed Lightsails https://ia800108.us.archive.org/view_archive.php?archive=/24/items/wikipedia-scholarly-sources-corpus/10.2514.zip&file=10.2514%252F3.8632.pdf https://ia800108.us.archive.org/view_archive.php?archive=/24...

myrmidon 1y ago
This is very interesting. Apparently beam collimation is much less of a show-stopper than I would have assumed. But I don't see us putting a a 1000 kilometer lens into orbit anytime soon, and that multi-terawatt (sustained!) laser system sounds like a bit of a headache, too...
- cnity 1y ago
  See: https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot
pavel_lishin 1y ago
> This paper discusses the use of solar system-based lasers to push large lightsail spacecraft over interstellar distances. The laser power system uses a 1000-km-diam. lightweight Fresnel zone lens that is capable of focusing laser light over interstellar distances. A one-way interstellar flyby probe mission uses a 1000 kg (1-metric-ton), 3.6-km-diam. lightsail accelerated at 0.36 m/s2 by a 65-GW laser system to 11% of the speed of light (0.11 c), flying by a Centauri after 40 years of travel. A rendezvous mission uses a 71-metric-ton, 30-km diam. payload sail surrounded by a 710-metric-ton, ring-shaped decelerator sail with a 100-km outer diam. The two are launched together at an acceleration of 0.05 m/s2 by a 7.2-TW laser system until they reach a coast velocity of 0.21 c. As they approach a Centauri, the inner payload sail detaches from the ring sail and turns its reflective surface to face the ring sail. A 26-TW laser beam from the solar system, focused by the Fresnel lens, strikes the heavier ring sail, accelerating it past a Centauri. The curved surface of the ring sail focuses the laser light back onto the payload sail, slowing it to a halt in the a Centauri system after a mission time of 41 years. The third mission uses a three-stage sail for a roundtrip manned exploration of e Eridani at 10.8 light years distance. Very cool.
foobiekr 1y ago
The Mote in God's Eye I guess this will be the Niven-Pournelle thread.

topynate 1y ago

The easiest way (perhaps the only practical way) to favour the aneutronic reaction is to run a helium-rich mixture. The trade-off is lower power density.

MadnessASAP 1y ago

> This sounds significantly more feasible than nuclear pulse propulsion ("project orion" style) which I used to think was the only feasible approach to get to another star. I still carry a torch for project Orion, it's impossible to not love. * Feasible 50 years ago, not 50 years from now. * No ultra lightweight fancy space age materials, steel and lots of it. * Seriously, lots of it, let's launch a battleship to to Mars, * or Jupiter, * or Alpha Centauri. * Gives everyone something way better to do with all those nuclear bombs they have laying around.

marcosdumay 1y ago
> it's impossible to not love As an idea, yeah. But if somebody actually tried to build it, the entire world would oppose for very good reasons. Still, it's something that maybe we should build on space (outside of Earth's magnetic field).
randallsquared 1y ago
> Gives everyone something way better to do with all those nuclear bombs The counterpoint there is it gives lots of reasons to make so many more, increasing proliferation worries. However, there's an SF novel that just came out that features nuclear pulse: Fenrir, by Ryk Spoor and (posthumously) Eric Flint. I enjoyed it.
- pavel_lishin 1y ago
  I should re-read Footfall, by Larry Niven. Quite a few banger lines in there.
  - m4rtink 1y ago
    Orion drive is one long line of bangers by definition! ;-)
- eszed 1y ago
  My favorite SF along those lines is King David's Spaceship, by Jerry Pournelle. https://en.m.wikipedia.org/wiki/King_David%27s_Spaceship https://en.m.wikipedia.org/wiki/King_David%27s_Spaceship

voxleone 1y ago

Project Orion was the promise of my youth [70/80s]. It speaks to both the technological courage and the philosophical optimism that once characterized space exploration — and how that momentum seems to have faded. By all accounts, it was technically feasible. And yet... Of course there was 'the shadow of the Bomb'. From bold, almost reckless experimentation (Mercury, Gemini, early Apollo, things shifted to safety-optimized, cost-constrained engineering. And there was Cost and Politics; the post-Apollo world didn’t want to colonize the solar system. It wanted low Earth orbit, and safe returns. Budgets followed. Kinda sad.