5 ms·

> 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 missi

> 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?

zamadatix 1y ago
It was ~15 years between the V-2 rocket crossing the Karman line to a human walking on the moon. 15 years from now we will have time for a 10 year break followed by another 15 years before we'd need to launch such a 10 year mission to be there by 2075-2076. 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.
- SJC_Hacker 1y ago
  It was 25 years from V2 to Apollo 11. 55 years from Apollo 11 to Katy Perry
pfdietz 1y 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 1y 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 1y 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 1y ago
    I really wanted that thing to fly. Anyone know the fate of the IP?
  - nicktelford 1y 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 1y 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 1y 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.
imglorp 1y 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?
- loa_in_ 1y ago
  It makes sense for USA to not want to be the only ones pushing a solution to a challenge like this. America is the trailblazer in this domain and that's impressive enough.
- Robotbeat 1y ago
  Nuclear thermal was killed for pretty good reasons, one of which is the focus on nuclear-electric instead, which is better for this mission (along with a strong push by a refueled chemical stage in high Earth orbit).
- ajford 1y 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 1y 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/starship-rival-chinese-scientists-build-prototype-engine-nuclear-powered-spaceship-mars 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 https://archive.is/sGUJr )
JumpCrisscross 1y 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.
- kristianp 1y ago
  If Q < 1, aren't you better off with an ion drive that just shoots the hydrogen out the back? You still need to get most of the energy from somewhere other than the fusion drive.
  - thehappypm 1y ago
    Energy and thrust are not equivalent. There’s hardly any limit to how much energy you can generate in space (for example using a nuclear reactor), but fuel is the limiting factor.
    - TorKlingberg 1y ago
      By "fuel", do you mean reaction mass (stuff that shoots out the back of the rocket) or energy source? A nuclear reactor in space would require an enormous heat sink to get useful energy out.
- sigmoid10 1y 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.
  - b112 1y ago
    Da Vinci and others worked on flying machines, I expect designs go back thousands of years. Yet the result is now thousands of designs and working iterations. I think we're also getting better and faster at iteration and design. CAD, modelling, even wind tunnels from 50 years ago made a massive difference over jumping off a cliff with a glider for tests. I guess my point is, I don't see 50 years as validation of it being hard. And some of those designs were likely dismissed due to tech limits at the time.
wombatpm 1y 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.
- spartanatreyu 1y ago
  You have to launch before 75-76 otherwise you're going to be chasing it for a long time before you make it there

zamadatix 1y ago

It was ~15 years between the V-2 rocket crossing the Karman line to a human walking on the moon. 15 years from now we will have time for a 10 year break followed by another 15 years before we'd need to launch such a 10 year mission to be there by 2075-2076. 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.

SJC_Hacker 1y ago
It was 25 years from V2 to Apollo 11. 55 years from Apollo 11 to Katy Perry

pfdietz 1y 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 1y 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 1y 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 1y ago
  I really wanted that thing to fly. Anyone know the fate of the IP?
- nicktelford 1y 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 1y 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 1y 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.

imglorp 1y 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?

loa_in_ 1y ago
It makes sense for USA to not want to be the only ones pushing a solution to a challenge like this. America is the trailblazer in this domain and that's impressive enough.
Robotbeat 1y ago
Nuclear thermal was killed for pretty good reasons, one of which is the focus on nuclear-electric instead, which is better for this mission (along with a strong push by a refueled chemical stage in high Earth orbit).
ajford 1y 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 1y 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/starship-rival-chinese-scientists-build-prototype-engine-nuclear-powered-spaceship-mars 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 https://archive.is/sGUJr )

JumpCrisscross 1y 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.

kristianp 1y ago
If Q < 1, aren't you better off with an ion drive that just shoots the hydrogen out the back? You still need to get most of the energy from somewhere other than the fusion drive.
- thehappypm 1y ago
  Energy and thrust are not equivalent. There’s hardly any limit to how much energy you can generate in space (for example using a nuclear reactor), but fuel is the limiting factor.
  - TorKlingberg 1y ago
    By "fuel", do you mean reaction mass (stuff that shoots out the back of the rocket) or energy source? A nuclear reactor in space would require an enormous heat sink to get useful energy out.
sigmoid10 1y 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.
- b112 1y ago
  Da Vinci and others worked on flying machines, I expect designs go back thousands of years. Yet the result is now thousands of designs and working iterations. I think we're also getting better and faster at iteration and design. CAD, modelling, even wind tunnels from 50 years ago made a massive difference over jumping off a cliff with a glider for tests. I guess my point is, I don't see 50 years as validation of it being hard. And some of those designs were likely dismissed due to tech limits at the time.

wombatpm 1y 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.

spartanatreyu 1y ago
You have to launch before 75-76 otherwise you're going to be chasing it for a long time before you make it there