[HN Gopher] The Quest for a Fusion Drive
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The Quest for a Fusion Drive
Author : tectonic
Score : 57 points
Date : 2022-11-09 17:05 UTC (5 hours ago)
(HTM) web link (orbitalindex.com)
(TXT) w3m dump (orbitalindex.com)
| Symmetry wrote:
| In terms of fusion drivers I've always liked NASA's PuFF[1] or
| Pulsed Fission Fusion. The idea is to use a normal z-pinch pulsed
| fusion setting, which won't normally be self sustaining. But if
| you surround the D-T mix with depleted uranium it'll adsorb a lot
| of the fast neutrons from the fusion and trigger a round of
| fission generating more energy. The recoil against the magnetic
| compressor/nozzle should be enough to generate enough energy for
| the next pulse and the reaction byproduct are emitted to become
| your propellant.
|
| [1]https://www.nasa.gov/puff
| zabzonk wrote:
| we don't have fusion power on earth (except for bombs) so why
| could we magically create it (and launch it) in space?
| zizee wrote:
| There is value in creating designs that are feasible if some
| technological breakthroughs is made. If we manage to make
| fusion work, then someone can then capitalise on the existing
| designs. It's also a great motivator for people to work on
| those hard problems that could enable many fantastic
| possibilities. It's also just fun to let your imagination not
| be constrained by what is possible today, but what might be
| possible in the future.
| [deleted]
| yummypaint wrote:
| Fusion on earth (that people talk about) is about generating
| electricity. Fusion on spacecraft is about shooting out
| exhaust gas as quickly as possible and storing energy at high
| density. The rocket equation relates the exhaust rate to the
| propelent mass requirements, which determines the feasibility
| of the spacecraft. It's a completely different optimization
| problem, and one that has historically favored nuclear energy
| sources in general.
| traverseda wrote:
| Well, you don't need to care about safety nearly as much.
| zabzonk wrote:
| safety is not what is limiting fusion development on earth
| - we simply can't do it effectively
| sbierwagen wrote:
| In 1998, Robert A. Freitas published a detailed design of an
| artificial red blood cell with several useful properties,
| (stores 236 times as much oxygen as a natural red blood cell,
| indefinite shelf life) but with the minor downside that it
| would require atomically precise diamond fabrication to
| actually construct. https://www.tandfonline.com/doi/pdf/10.31
| 09/1073119980911768...
|
| Was that paper a waste of time?
| bobsmooth wrote:
| NASA needs to stop being wimps and bring back Project Orion
|
| https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
| api wrote:
| Ahh, the old devil's pogo stick...
|
| The thermonuclear Orion could, on paper, achieve up to 10% the
| speed of light on an interstellar trajectory at least for a
| small payload. It's possible that it could send a probe to the
| Centauri system that would arrive in 40-50 years, short enough
| to be feasible on human time scales.
| choeger wrote:
| I never got the fascination for Orion. Why on earth should a
| spaceship carry a gigantic pusher plate? Carry hydrogen instead
| and put through a conventional fission engine. That gives you a
| much more controllable engine and should save you a lot of dry
| mass.
| api wrote:
| As far as I know the iSP (specific impulse) of Orion is a lot
| higher, which may result in better overall performance.
|
| There are some high temperature nuclear rocket engine designs
| though, like nuclear gas core rockets. They're crazy reactor
| designs you would never try running down here inside a
| biosphere but have energy densities far higher than anything
| else save a bomb.
| pinewurst wrote:
| (a) Much much higher ISP even including pusher plate mass
|
| (b) We can build bombs and pusher plates now ;)
| zabzonk wrote:
| no "conventional fission engine" has ever flown - there may
| be reasons for this
| voldacar wrote:
| Yeah the reason is that Richard Nixon cancelled Project
| Rover, which had long since demonstrated that a safe and
| reliable nuclear engine was totally feasible
| cjtrowbridge wrote:
| There are a lot of reasons why this is a bad idea, not least of
| which is the effects of the resulting electromagnetic pulses on
| satellites, the earth, and the equipment on board the vehicle
| itself.
|
| There is also the radioactive fallout that would affect human
| populations all over the world.
|
| Detonating nuclear weapons at high altitudes or in space would
| also disturb or damage the van allen belts and expose the
| surface of the earth to high levels of radiation from solar
| winds and cosmic rays.
|
| And of course there is the fact that it's a violation of
| international law to bring nuclear weapons to space or to test
| or detonate them in the atmosphere or in space.
| politician wrote:
| > Detonating nuclear weapons at high altitudes or in space
| would also disturb or damage the van allen belts and expose
| the surface of the earth to high levels of radiation from
| solar winds and cosmic rays.
|
| Could you please elaborate on the effects of high nuclear
| altitude testing on the belts? Preferably, a link to a paper.
| pfdietz wrote:
| https://en.wikipedia.org/wiki/List_of_artificial_radiation_
| b...
|
| It wouldn't expose the Earth to cosmic rays, but it would
| damage satellites.
| Rooster61 wrote:
| I've always wondered if we could mitigate this issue by
| burning the spacecraft into a parking orbit around the L2
| Lagrange Point on the far side of the moon using conventional
| propellant, and then beginning detonation there. Irradiating
| Earth is of course a bad idea, but the Earth Moon L2 point
| should be plenty far enough away, provides a stable spot from
| which to begin pulsing in whatever direction they like as the
| moon orbits, and has the added benefit of the moon itself
| acting as a shield for the Earth from the radiation.
|
| It doesn't really matter if we irradiate the hell out of the
| far side of the moon. It's been pelted by solar wind and
| cosmic radiation since time immemorial. A bit of radiation
| from a few nukes should be negligible by comparison.
| toss1 wrote:
| Sure, those are problems if the Orion method is used inside
| the orbital region.
|
| However, if used after escaping from Earth's gravity well to
| accelerate towards distant destinations, the only remaining
| issue is international law. Electromagnetic pulses decay as
| the inverse square law, radioactive fallout would be outside
| the Earth's gravity well and disperse harmlessly in space,
| the Van Allen belts are also not near enough to be affected.
|
| The only real risk would be from accidents while lifting that
| much fissile material to space, which could be mitigated by
| proper containment vessels (which do add weight and reduce
| effective payload, but the total lift may still be worth the
| cost)
| kappuchino wrote:
| Am I the only one to admit thinking "Odd, It makes no sense
| returning to hybrid disk + ssd drives(1)".
|
| Anyway. Way more cool.
|
| (1) https://de.wikipedia.org/wiki/Fusion_Drive
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