Feasibility study of a mission to Sedna - Nuclear propulsion and solar sailing

129•speckx•5h ago

Comments

pavel_lishin•5h ago

> 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?

pfdietz•4h ago

It's a scheme based on rotating magnetic field drive (RMF) of field reversed configurations. The claim is that they can preferentially accelerate and recover energy from 3He ions, greatly reducing DD fusion and associated neutrons. I question the recovery part (how is the entropy that is introduced by ion-ion collisions removed?), but do not have the expertise to fully evaluate the claim.

In any case, it certainly cannot be ready next year, and would require large amounts of 3He.

nicktelford•4h ago

There's also Pulsar Fusion, a UK company currently building a Dual Direct Fusion Drive (DDFD). They claim:

> 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•4h ago

When it comes to the UK space industry all I can think of is Skylon and Reaction Engines Ltd. Or more how they spent 20 years working on an engine that never left the ground until going bankrupt.

Hopefully this time round it goes a bit better than that.

ortusdux•3h ago

I really wanted that thing to fly. Anyone know the fate of the IP?

nicktelford•3h ago

Yeah, the British space industry has struggled; principally with investment. Reaction Engines largely went under because they ran out of money and their investors declined to put more money in.

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•3h ago

I remember when Reaction turned down relocating to America in favour of some minor support from London. It was around 2014 and we all figured it was D. O. A.

PaulHoule•1h ago

Frankly it seemed like an idea that made no sense for multiple reasons. For one thing the density of atmospheric oxygen is a fraction of the density of liquid oxygen so it's hard to picture getting enough oxygen in the thing to make a difference. If you're liquifying it you're going to slow your rocket down by bringing O2 as well as 4 times as much N2 on board, then there is the weight of the liquification plant. Investing in Skylon is like investing in cold fusion.

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.

JumpCrisscross•4h ago

> 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.

sigmoid10•1h ago

"Easier" in this context is still ridiculously hard. Fusion rocket designs were first seriously researched 50 years ago and not a single one of the countless designs proposed since then has reached readiness for in-space use.

PaulHoule•55m ago

Note the economics might be better than for terrestrial fusion energy because you're not paying for watts you're paying for thrust and something like D-He3 has a great exhaust velocity.

imglorp•4h ago

And tragically, nuclear propulsion at NASA has been aggressively singled out for the axe so humanity will be counting on more advanced countries to finish that research.

Was that the fossil fuel lobby's doing?

ajford•1h ago

I always figured it was from Nuclear pearl-clutching and genuine fear about launch disasters. Especially after the various Apollo and shuttle disasters.

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•1h ago

> "probably a good idea to not have nuclear materials launching until that's been resolved entirely"

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•31m ago

>fission reactors aren't hazardous until after they first start up (go critical)

This is only true if the fission reactor's fuel isn't scattered over square kilometers after a launch failure.

perihelions•27m ago

It's not radioactive enough to matter.

wombatpm•2h ago

So 75-76 for closest approach. How far away will it be in 2100? Given that orbit size I think we have some slack in the launch date.

chuckledog•4h ago

https://en.m.wikipedia.org/wiki/Sedna_(dwarf_planet)

imglorp•4h ago

They know its radius is ~1000km but interestingly, there is no way to determine its mass without a flyby or other gravitational interaction. I guess you could swag it by using the lunar density, which gives ~~~ 10^22 kg.

https://www.wolframalpha.com/input?i=4.189%C3%9710%5E9+km%5E...

_joel•4h ago

Wouldn't it's composition be of more ice and rock (like pluto), therefore lower density than the moon?

sapiogram•2h ago

That's a reasonable assumption, but given Sedna's unusual orbit, its origin could also be quite different from Pluto's.

benbayard•1h ago

In the wikipedia post you are replying to has the chemical composition of the surface of the planet, obviously we can't know what is beneath that, but to me, indicates this is closer to Pluto than it is to our Moon.

> 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]

myrmidon•4h ago

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•4h ago

Roundtrip Interstellar Travel Using Laser-Pushed Lightsails

https://ia800108.us.archive.org/view_archive.php?archive=/24...

myrmidon•4h 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•3h ago

See: https://en.wikipedia.org/wiki/Breakthrough_Starshot

pavel_lishin•2h 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•1h ago

The Mote in God's Eye

I guess this will be the Niven-Pournelle thread.

topynate•4h 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•3h 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.

randallsquared•2h 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•2h ago

I should re-read Footfall, by Larry Niven. Quite a few banger lines in there.

eszed•2h 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

MadnessASAP•1h ago

Yeah, if I'm being really honest, I don't want to give anyone an excuse to put a 1000+ nuclear bombs in orbit. Plus the few dozen you'd have to detonate in quick succession to even get it above the karman line.

PaulHoule•1h ago

The electron beam ignition they talked about doesn't work. Heavy ion probably does

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.

hermitcrab•36m ago

I once spoke to Freeman Dyson at a book signing and asked him if Orion would work. He said he thought it would. And I asked him if it should be launched. He said probably not (IIRC due to the amount of radiation that would be put into the atmosphere).

jerf•17m ago

It is almost the epitome of steampunk romance. Launch an entire mid-20th century city and economy into space! And it might even work!

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...!

voxleone•3m ago

Project Orion was the promise of my youth. 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.

accrual•4h ago

Very fascinating mission idea. Given how Sedna reaches so far away (>500AU), I wonder if the flyby would also reveal some details about conditions that distant. Maybe the surface contains some unexpected molecules that could shed light on its origin and what it's like that far out.

pier25•3h ago

> relatively soon

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.

ananddtyagi•3h ago

Sound like something out of 3 Body Problem

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