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?
> 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
Hopefully this time round it goes a bit better than that.
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.
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.
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".'
(The original link says "Page is Gone")
And here's some more quoting
Could a single-stage-to-orbit spaceship, something that could operate rather like an aeroplane, be built with just rocket engines? Well, actually, yes. In the 1980s, NASA and the US Air Force spent about $2 billion trying to build the X-30, a single-stage spaceship powered by scramjets (with help from rockets, of course). It never flew. At the same time, for comparison, NASA's Langley Research Center studied building a single-stage pure-rocket spaceship. The results were interesting.
The pure-rocket design was more than twice as heavy as X-30 at takeoff, because of all that LOX. On the other hand, its empty weight - the part you have to build and maintain - was 40% less than X-30's. It was about half the size. Its fuel and oxidiser together cost less than half as much per flight as X-30's fuel. And finally, because it quickly climbed out of the atmosphere and did its accelerating in vacuum, it had to endure rather lower stresses and less than 1% of X-30's friction heating. Which approach would be easier and cheaper to operate was pretty obvious.
The Langley group's conclusion: if you want a spaceship that operates like an aeroplane, power it with rockets and only rockets.
There have been some other discussions of this lately, but I would say the pursuit of SSTO resulted in a lost decade for spaceflight in the 1990s.
SSTO is just barely possible, the problem is that you have a big rocket that carries a tiny payload so you are driven to exotic engines, exotic materials, and various risky technologies.
If Musk had any good idea it was not only falling back to two-stage-to-orbit reusable rockets but also recognizing that it was worth just reusing the first stage. A SSTO gets closer to aircraft-like operations in that you don't need to stack two stages on top of each other, but given how much TSTO improves everything else it's probably worth just optimizing the stacking.
The real question "is there actually fund this engine and mission to bring that to completion in the next 40 years" than whatever the completion and reliability is today.
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.
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.
Was that the fossil fuel lobby's doing?
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.
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 )
This is only true if the fission reactor's fuel isn't scattered over square kilometers after a launch failure.
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.
It's bizarre to suggest that the same strategy would be used with nuclear materials onboard. Developing the "can not fail" rocket is the sort of thing NASA does well, and kind of highlights how we've squandered them.
In any case, it certainly cannot be ready next year, and would require large amounts of 3He.
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]
The word 'just' is doing a whole lot of work in that sentence!
New Horizons, to use your example, weighed a thousand pounds and used a 2 meter dish transmitting at something like 12 watts to compensate for the fact that the receivers are billions of miles from earth and hidden beneath a blanket of RF noise. The inverse square law can't really be beaten at that kind of distance so everything becomes inefficient by design.
If we can pick up that tiny 12 watt whisper of a signal from billions of miles away, surely we we could design much lower power omnidirectional signals that relay between mesh nodes closer together using far less power?
Imagine a string of probes that are all within a few thousand miles of each other with clear line of sight. Yes, we might need six million of them to cover that same distance, but if they were cell phone sized devices produced using what we've learned about consumer electronics it should be feasible to just keep launching them forever, for a few hundred bucks apiece, until we eventually build a large network that could assemble high resolution data by combining multiple sources.
We keep trying to fight the rocket equation, but that's not a battle that can be won. Mass is always going to be the limiting factor for space exploration, so maybe we can just start launching lots of intelligent low mass things regularly instead of the occasional big dumb thousand pound lump of metal.
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.
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.
[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...
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?
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.
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...!
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.
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.
https://ia800108.us.archive.org/view_archive.php?archive=/24...
Very cool.
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...
I guess this will be the Niven-Pournelle thread.
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.