https://www.wolframalpha.com/input?i=4.189%C3%9710%5E9+km%5E...
> Detailed spectroscopic analysis has revealed Sedna's surface to be a mixture of the solid ices of water (H2O),[15] carbon dioxide (CO2), and ethane (C2H6), along with occasional sedimentary deposits of methane (CH4)-derived,[16] vividly reddish-colored organic tholins,[15] a surface chemical makeup somewhat similar to those of other trans-Neptunian objects.[17]
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?
https://ia800108.us.archive.org/view_archive.php?archive=/24...
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...
Very cool.
I guess this will be the Niven-Pournelle thread.
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.
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.
https://en.wikipedia.org/wiki/Heavy_ion_fusion
but the accelerator needs like 100 barrels that are each 1 km. Maybe you can build a generation starship with that but whatever it is it's going to be big.
But, yeah, you probably don't want to be launching these routinely. People generally badly underestimate the number of nuclear explosions that have been set off on Earth and overestimate the badness of nuclear explosions. Putting one or two of these into orbit might be justifiable. It's certainly not a bad emergency plan to have in your pocket in case of emergencies. But you still certainly wouldn't want an entire industry routinely lighting these things off.
Still... the romance of it all...!
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.
If the DFD takes 10 years to get there it means it would need to be launched in 40 years. That's quite a timeline.
Amazing that an organization can keep budgeting and planning for such a long project.
Edit: The latter is "Fusion enhanced"[3]
The company’s the FireStar Drive uses is a water-fueled pulsed plasma thruster that uses a form of aneutronic nuclear fusion to boost its performance.
I watch the orbital observations closely to see if any altitude is being gained.[2] This is their second satellite in orbit, the first one had high voltage power supply issues so they never got to try the thruster.[1] https://www.nanosats.eu/sat/otp-2
[2] https://celestrak.org/NORAD/elements/graph-orbit-data.php?CA...
[3] https://www.aerospacetestinginternational.com/news/space/roc...
Perhaps there are some solid or non-cryogenic liquid fuels that could take place of the liquid hydrogen and make fission based systems far more feasible in the near term.
pavel_lishin•7h ago
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?
pfdietz•6h ago
In any case, it certainly cannot be ready next year, and would require large amounts of 3He.
nicktelford•6h ago
> Modelling shows that this technology can potentially propel a spacecraft with a mass of about 1,000 kg (2,200 lb) to Pluto in 4 years.
They're apparently targeting an in-orbit test in 2027. Even if this were to slip to 2030, and becomes commercially available in 2040, I expect that would be plenty of time for a rendezvous with Sedna's perihelion
moffkalast•6h ago
Hopefully this time round it goes a bit better than that.
ortusdux•6h ago
nicktelford•5h ago
My hope with Pulsar Fusion is that their existing thruster business provides the necessary revenue to both keep them solvent, and attract continued investment, until they're able to get their Fusion Drive off the ground.
JumpCrisscross•5h ago
PaulHoule•3h ago
It was bad enough that Richard Branson discredited private orbital spaceflight with the overly long development process for a vehicle that made the Space Shuttle look like a paragon of safety and low costs -- Skylon was so much worse.
pfdietz•18m ago
https://www.newscientist.com/blogs/shortsharpscience/2009/03...
'Trying to build a spaceship by making aeroplane fly faster and higher is like trying to build an aeroplane by making locomotives faster and lighter - with a lot of effort, perhaps you could get something that more or less works, but it really isn't the right way to proceed. The problems are fundamentally different, and so are the best solutions.
As Mitch Burnside Clapp, former US Air Force test pilot and designer of innovative launcher concepts, once commented: "Air breathing is a privilege that should be reserved for the crew".'
JumpCrisscross•6h ago
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.
sigmoid10•3h ago
PaulHoule•3h ago
JumpCrisscross•11m ago
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.
imglorp•6h ago
Was that the fossil fuel lobby's doing?
ajford•3h ago
Though with how SpaceX has been blowing up rockets left and right, probably a good idea to not have nuclear materials launching until that's been resolved entirely.
Boca Chica beach is a mess now, I can only imagine what new Fallout installment we'd get if South Texas became irradiated from a failed launch.
perihelions•3h ago
This isn't an issue at all: fission reactors aren't hazardous until after they first start up (go critical), which in the space electric-propulsion context means after (if) they've successfully launched, and are no longer in the vicinity of Earth.
At any rate, China is apparently[0] moving in this direction, regardless of what the US does.
[0] https://www.scmp.com/news/china/science/article/3255889/star... ("Starship rival: Chinese scientists build prototype engine for nuclear-powered spaceship to Mars" (2024)) (mirror: https://archive.is/sGUJr )
GolfPopper•2h ago
This is only true if the fission reactor's fuel isn't scattered over square kilometers after a launch failure.
perihelions•2h ago
Symmetry•1h ago
But yeah, it's not dangerous like the P238 in a radioisotope thermal generator (RTG). To put off enough heat to power a spacecraft just through natural decay you need something ferociously radioactive.
wombatpm•4h ago