> 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?
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
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.
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.
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.
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.
Henry Spencer on air breathing launchers (New Scientist, 2009):
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".'
I agree. I've played a LOT of kerbal space program, and yes, this is just a game, with simplified physics, and a MUCH lower orbital velocity required. But the fundamental problems with an air-breating spaceplane are still demonstrated:
1) Orbital velocity is FAST. VERY fast. In KSP orbital velocity for a low orbit is about 2,200 m/s. For earth its about 7,600 m/s 2) An air-breathing engine, by definition can only be used inside the atmosphere. 3) You will struggle to get anywhere close to orbital velocity while still in the atmosphere, due to drag, and heating.
At best, your air-breathing engine will only get you to a small fraction (less than 1/4th) of orbital velocity. Then you will have to a) climb higher, and b) use a different engine to accelerate to the required orbital velocity.
Yes, you will potentially save some weight by not having to carry oxidizer for while you gain that first 1/4 or so of your final velocity. But once your air-breathing engines, and wings and everything else are useless, you still have to carry their weight
https://web.archive.org/web/20090727013542/http://www.newsci...
(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.
See https://en.wikipedia.org/wiki/Lockheed_Martin_X-33
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.
And I strongly suspect Henry knew the "don't turn an airplane into a launcher" extended to using wings for landing and takeoff as well, although in 2009 that maybe wasn't quite as inescapable a conclusion as it is today.
I really wanted that thing to fly. Anyone know the fate of the IP?
> 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.
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.
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.
"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.
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.
> "Easier" in this context is still ridiculously hard
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.
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.
The point is more that 50 years ago, people thought we had sufficient understanding of fusion to build something like this. And thanks to advancements in inertial confinement research at the height of the thermonuclear arms race, they actually had a pretty good reason to believe so back then. There is very little reason to believe these new companies today when they say so, because fusion research is in a deep hole and running on a fraction of the funding it did during the cold war.
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?
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).
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.
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.
> "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 )
>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.
Actually spreading it out over a large area is much safer. What you don't want is a big hunk of highly enriched uranium landing somewhere. Not that it is very likely to harm anyone, but it becomes quite a nightmare to deal with it.
Any loss of containment is not going to play well in the news media.
We saw the hyperreactivity over Fukushima. I even know some very educated people who should know better like not wanting to eat any seafood caught in the Pacific.
It's not radioactive enough to matter.
Generally the sort of lightweight reactors NASA is looking at for space power use highly enriched uranium. U234 isn't particularly radioactive (it's lasted since the Earth was formed) and far less toxic than the hydrazine propellant our ships carry but it's a significant proliferation risk if it should all into the wrong hands.
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.
SpaceX let rockets explode because they're using chemical propellants and the consequences of that are low provided no one gets hit by debris.
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.
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.
You have to launch before 75-76 otherwise you're going to be chasing it for a long time before you make it there
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.
It was 25 years from V2 to Apollo 11.
55 years from Apollo 11 to Katy Perry
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.