Submitted by Creepy_Toe2680 t3_10ozjk9 in space
Comments
corsairealgerien t1_j6hn22i wrote
>It would also make the journey to Mars significantly shorter, from six months to just 45 days.
Is this with RDRE or the proposed nuclear-powered system?
Creepy_Toe2680 OP t1_j6hnffp wrote
Nuclear powered
>This isn’t the only way that NASA is looking at revolutionizing deep space travel. The space agency is reportedly looking into nuclear-powered spacecraft, which would allow spacecraft to travel further distances without needing liquid fuel. It would also make the journey to Mars significantly shorter, from six months to just 45 days.
corsairealgerien t1_j6hnt3s wrote
Is there a similar estimate as to the difference RDRE would make? Or is it more the case of RDRE being more efficient in fuel terms, allowing for longer flights, rather than making them faster per se?
danielravennest t1_j6ih89p wrote
In theory the RDRE would improve chemical rocket efficiency by about 10%. There is a finite amount of energy in any fuel/oxidizer combination set by the chemistry. Regular rocket engines use a turbopump to push the ingredients into a combustion chamber at high pressure. The expansion of the resulting hot gas is what turns into thrust.
The RDRE feeds the ingredients at lower pressure, and uses a detonation to create the high pressure for expansion. The energy otherwise used to run the turbopumps is then directly used for thrust. Turbopumps generally tap off some of the fuel and oxidizer flow to power themselves.
ProgressBartender t1_j6jsmk4 wrote
It’s all about exhaust velocity, there’s just a limit to have fast a combusting gas will expand out of your nozzle. Faster velocities can be reached with Ion engines, nuclear pulse engines or other future technologies.
[deleted] t1_j6imp08 wrote
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danielravennest t1_j6io6qc wrote
> Bakugo's Howitzer Impact
Not familiar enough with manga physics to answer your question. I only do physics for this world :-).
rawbleedingbait t1_j6joy60 wrote
Okay that's fine, but why haven't we been looking into spirit bomb technology?
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dave200204 t1_j6ll589 wrote
A person's chi just doesn't provide enough energy to power a rocket, IRL.
A Chi Chi powered engine might at least give you a ballistic trajectory.
[deleted] t1_j6j2huv wrote
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zcleghern t1_j6jpnpq wrote
What the heck did i just read
Caboose_Juice t1_j6kvl32 wrote
from what i gather, no. RDRE is basically sourcing its fuel pressure from detonations rather than a turbo pump, eliminating an auxiliary system that consumes energy. i’m not sure about anime
AlmennDulnefni t1_j6jm5pz wrote
Those are the same thing if you have the same thrust. More efficient means less fuel mass means more acceleration from a given thrust.
Creepy_Toe2680 OP t1_j6how4h wrote
uhh looks like i have to do some research and math here soo..
i am gonna use the second one (but i don't know if it is talking about the vehicle or the wave.)
distance from mars (130,000,000 km)
speed of detonating engine = 2km/s
so, 130000000/2= 65000000 seconds = 752.31481481 days or 2 years and 22 days.
not sure don't quote me on this.
edit: YES I knew it i was right that i was wrong!
wgp3 t1_j6iebfv wrote
Unfortunately that's just all wrong. The part you took from the second source isn't even about the rotating detonation engine but the detonation pulse jet engine. Maybe the exhaust velocities are the same but I doubt it. And the figures used aren't even the actual exhaust velocities. That's the speed of the Shockwave from the detonation and the speed of the wave from deflagration.
But rocket engines use something called a de laval nozzle. Designed for the flow to speed up to Mach 1 at the throat and then go supersonic out the back. So the exhaust velocity of a typical rocket engine is already in the several km/s range. For example, rs25 has an exhaust velocity of about 4 km/s. Twice that of the figure you used for the detonation engine.
You can't easily just take an exhaust velocity and calculate how long a trip to mars would take. The exhaust velocity is not a limit on how fast the rocket can go. It's more about showing its efficiency. Higher exhaust velocities are more efficient. This is also measured in a term called Isp, specific impulse. Which is why ion thrusters are so efficient. They cam have effective exhaust velocities of about 40 km/s.
With effective exhaust velocity (which I'm not sure 2km/s is it for an rde) you'd at least need the initial (or wet mass, aka fully fueled rocket mass) and final mass (dry mass, mass after burning all propellant) to get the total delta v from the rocket equation. That would give you a rough idea of where the rocket can get you. The more delta v the faster you can get somewhere.
danielravennest t1_j6ii1ae wrote
That's not how rockets work. Vehicle speed changes as your run the engine and produce thrust (push). Earth and Mars already are in orbit around the Sun. To get to Mars, you have to change your orbit so the other end crosses Mars' orbit at the same time Mars is at that point.
corsairealgerien t1_j6hppu5 wrote
2 years and 22 days? But the original quote said it takes 6 months to get to Mars at the moment?
Creepy_Toe2680 OP t1_j6hpwar wrote
various factors affect this such as vehicle size and many more
maybe my calculation is wrong.
buffetcaptain t1_j6hup2p wrote
The distance to Mars changes depending on the respective orbits, at the closest point it's about half that.
Testimones t1_j6lv9yr wrote
No no, you have it all wrong, the planets are all fixed to transparent spheres rotating around Earth, even the old greeks knew that!
LegitimateGift1792 t1_j6mynsv wrote
I gave you an upvote even though you did not use the obligatory /s. It was the transparent spheres i liked the best.
mvpilot172 t1_j6idy94 wrote
It stills needs liquid fuel though doesn’t it? Just does not need an oxidizer so it saves that portion of liquid fuel.
cjameshuff t1_j6iswvx wrote
Yes, that part is completely wrong. Nuclear rockets still use propellant. Nuclear thermal rockets use about half as much by mass as the best chemical rockets, but they only get their peak performance with LH2, which takes up about 5 times as much volume for the same amount of mass. A nuclear thermal spacecraft will be a big pile of propellant tanks (likely drop tanks so you don't have to carry empty tank mass around) strapped together with a nuclear rocket engine at the back and a small payload tacked onto the front.
The "45 days" claim appears to be in reference to the "wave rotor" stuff that's been getting massively overhyped. Basically, as described, they propose sticking a widget between the nuclear reactor and the nozzle that somehow doubles the specific impulse while halving the flow rate.
This means doubling the power output of the reactor. Since the power output of the reactor is already limited by the need to keep it from melting, and the reactor is cooled by the propellant flow which you've just cut in half, it's not clear how this doesn't result in the reactor, well, melting. Also, even if it worked, doubling the specific impulse isn't nearly enough of a gain to allow a 45 day trip to Mars.
They then throw in nuclear-electric propulsion, which requires heat exchange loops, many megawatts of electrical generation capacity, giant radiator arrays, and arrays of ion thrusters. They assume all this can be done "with minimal addition of dry mass", and this is how they double the performance again to get their 4000 s number. However, it doesn't actually appear to have anything to do with the wave rotor.
NASA's giving one guy $12500 to look at it. It's not taking anyone to Mars any time soon.
Worldofbirdman t1_j6kxwsf wrote
I'm sure they could figure out a way to use the temperature of outside the space craft for cooling. As soon as I read your comment I did a quick look and it's -455f or something similar. I guess an issue could be heat exchange from a vacuum to whatever the cooling system is, but that's above my brain grade.
Edit: temperature I'm referring to is the vacuum of space.
Phoenica t1_j6l207z wrote
> I guess an issue could be heat exchange from a vacuum to whatever the cooling system is, but that's above my brain grade.
That's sort of the whole problem though. Whatever particles are around in a near-vacuum might be very cold, but there are also very very few of them. There just isn't anything to exchange the heat to. A vacuum is an insulator, that's how Thermos bottles work for example.
andrew_calcs t1_j6lbekx wrote
The problem with space being cold is that it’s also empty. You know how a windy day at 40 degrees out feels much colder than when it’s 20 degrees out but with no wind? Take that to its logical extreme. Things do cool down in space, but not by convection or conduction so it’s very slow.
-Prophet_01- t1_j6lliz1 wrote
Heat exchange in vacuum largely works with a different principle and is much, much less efficient. Without other molecules to transfer heat to, we're left with black body radiation. Lower efficiency means bigger radiators. It's basically trying to cool down by giving off infrared light.
Something that could be done with a small coolant loop through a river or a glorified AC on earth, requires large sail-like structures in space (sails because it maximizes the surface to throw out that thermal radiation).
Karcinogene t1_j6klrbl wrote
The thermal nuclear engine has propellant, technically not fuel. It's not combusted, just ejected backwards at high speed. It's gets used up, but it's not a source of energy.
Jobotics t1_j6ls3fu wrote
The detonation engine still uses both fuel and oxidizer. It isn't nuclear. The nuclear engine was just mentioned at the end as another engine being worked on.
Tylerdirtyn t1_j6lbc24 wrote
That's a hell of a starting point. I bet within a decade they get it from 45 days to 5 if they aren't already capable now. We usually find out about new technology 2 decades after the government gets a hold of it.
newtoallofthis2 t1_j6j8k6v wrote
So dusting off the Orion project plans?
urmomaisjabbathehutt t1_j6ho8ye wrote
this is an engine showcasing newer material manufacturing tecnics such as additive manufacturing, these tecnics allow more resilience and temperatures needed for this type of engine
in theory ths will allow a type of engine that is simpler and more efficient but it has its own challenges, for instance solving instabilities
I-Pop-Bubbles t1_j6ikx5k wrote
Integza has a really neat video about RDE, and in addition to going over some of the science behind it, he makes a homemade one. It's very cool.
1SweetChuck t1_j6iyowy wrote
Scott Manley has a video on the subject as well. https://www.youtube.com/watch?v=rG_Eh0J_4_s
Hampamatta t1_j6lt7er wrote
Was about to say integza just recently made a video about this.
Dude_Oner t1_j6m4byn wrote
Whats the vid, very interesting. Thanks for linking it.
Parliamen7 t1_j6jnmsm wrote
Nowadays everybody wanna talk like they got something to say But nothing comes out when they move their lips Just a bunch of gibberish And motherfuckers act like they forgot about RDRE
grchelp2018 t1_j6je9au wrote
> It would also make the journey to Mars significantly shorter, from six months to just 45 days.
What about a mission to places like Neptune?
internetlad t1_j6jugzb wrote
Uh just go to California it's right near the ocean smh
ButtPlugJesus t1_j6lstfw wrote
Assuming the same relative time decrease, 3 years
dependency_break t1_j6m3t8h wrote
that's totally manageable, or at least within reach once we sort out renewable food, necessities, etc
could go three threes. 3 to get there, 3 to stay do shit, 3 to return. i'm sure there's people who would sacrifice just under a decade of their life for that experience
Rowlandum t1_j6meiuu wrote
My kids are bored after 30mins in the car. I won't be sailing them on a 6 year round trip to Neptune
curiousauruses t1_j6isdwg wrote
Does this mean the scify art where spaceships emit little rings from their exhaust isn't that far off?
a10t2 t1_j6jvqt1 wrote
The "blue glow" type of propulsion is probably an ion engine, which is essentially just propellant + electricity. From a sci-fi perspective you'd want to generate that electricity with a fusion reactor.
Hampamatta t1_j6lthgq wrote
Theoretically ion engines are the pinnacle of propulsion. Far more efficient than normal combustion engines. And doesn't satellites already use small ion engines for realignment?
Earthfall10 t1_j6lv6wv wrote
Eh, there are other electric engine options that are better than ion engines, such as plasma engines or mass drivers. And if power isn't a limiting factor the ultimate in propellent efficiency is a photon rocket, aka a light bulb. No need to carry propellent, though you need 300 megawatts of photons to get a pathetic newton of thrust, so whatever reactor is powering it will need a shit ton of fuel. Though if you're using a laser array to push a mirrored sail that power plant can remain on the ground.
FrozenChocoProduce t1_j6mb7oo wrote
I remember reading about a fusion reactor variant, that, while not ouputting a net gain, might be used (while using up porpellant) to accelerate particles in a rocket engine (usable only in the vacuum of space)...and some well-funded startup already developing this?
andrew_calcs t1_j6lb24j wrote
> nuclear-powered spacecraft, which would allow spacecraft to travel further distances without needing liquid fuel
Nuclear thermal rockets still use a liquid fuel. There still has to be some mechanism for momentum transfer, and that means shooting something out the back of the rocket really fast.
Specifically, NTR thrusters use hydrogen superheated from passing over a nuclear reactor. Exhaust velocity of tested variants from the 60s and 70s were up to roughly twice the exhaust velocity of typical chemical propulsion systems.
The disadvantages are the ones you’d expect: putting a nuclear reactor on top of a giant controlled explosion is risky, and mounting a nuclear reactor makes the engine weight significantly higher so thrust to weight ratios are much lower. Still, it’s expected they would provide a significant performance advantage if engineered to fruition.
Hampamatta t1_j6ltpxi wrote
Nuclear propulsion would likely need to be assembled in space and when needed, the spacecraft would need to attach to it in orbit. Critical malfunction tends to happen in atmosphere.
ThatDoesNotRefute t1_j6me6b0 wrote
Hey I'm the guy that approves this shit, I'm not at my desk right now so if you guys could just go ahead and get started that would be great.
CrackyKnee t1_j6k22we wrote
Shockwave through atmosphere? How does that enables travel through deep space possible? Wouldn't you miss atmosphere there?
Caboose_Juice t1_j6kwf4c wrote
shockwaves are sent through the fuel as it’s combusted
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Linktry t1_j6j68q2 wrote
Reminds be of the sonic burst from learn how to fly
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wiwalsh t1_j6kcccw wrote
But did they measure thrust and ISP? This has been the issue with testing I’m aware of so far.
CraftsyDad t1_j6kkmu1 wrote
How do we know you’re not Joshua Hawkins?
WilyDeject t1_j6klz44 wrote
I watched a YouTube video on these recently and they are something else for sure! Interesting and exciting stuff.
Interesting-Space966 t1_j6lc9cr wrote
Another 20-25 years and 60 billion before they got something that can lift off…
But its all money well spent, we all get to spend 30 seconds watching a rocket take off on live tv, that’s if we can afford cable or internet access of course…
ThatDoesNotRefute t1_j6mem29 wrote
No chance look at what we accomplished via nuclear propulsion in the 50s and 60s. The tech and and tooling we have now, combined with the new space race I'll be shocked if a unmanned- spacecraft doesn't fly past voyager in the next 15.
MikeTheGamer2 t1_j6lkjzv wrote
I fell like I've heard of this before, somewhere.
Chaff5 t1_j6lq1h1 wrote
Wow a 45 day trip to Mars... that's absolutely incredible.
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RickAdtley t1_j6mxtvy wrote
Looking forward to the private spacecraft companies appropriating this and saying that "the free market" gave us deep space travel.
NoSoupForYouRuskie t1_j6nq7h8 wrote
They are also funding research into EM drives and resonance drives!
venir t1_j6igzkw wrote
Scott Manley did a really good video on RDE propulsion. Definitely worth a watch.
Buckwheat469 t1_j6jbyyf wrote
Integza also did a really good video on it. He visited a test bed engine to see how powerful it was.
The_Bombsquad t1_j6kqlv4 wrote
Scott Manley does a lot of really good videos. Highly recommend.
Escapyst t1_j6j1hqe wrote
Am I the only one who sees the great flame sword descending from space?
enilea t1_j6jjf7m wrote
Yea lol I saw the thumbnail without looking at the title or sub and my first thought was a flameblade from botw on the ground at night.
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NoThoughtsOnlyFrog t1_j6jzf1z wrote
I thought it was a lightsaber and got excited thinking we finally made one..
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Bobandis458 t1_j6i5sr4 wrote
I've heard about this RDRE, it's a cool concept but I've seen very few details on performance. Does anyone have a number for its specific impulse? Has it been tested in vacuum yet?
danielravennest t1_j6ilyom wrote
Nope. This test was a proof of concept engine. The next version will be a fully functional engine that they can measure specific impulse, thrust, and engine life for.
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snowmunkey t1_j6ipgcr wrote
Early calculations for solid core engines could be as high as 800-1000 seconds using hydrogen as the propellant.
Edit: nevermind, I didn't realize this article was about rotating detonation engines, I thought it was about nuclear-thermal engines
BackflipFromOrbit t1_j6ky8nv wrote
Japan launched a small scale RDE into space on a sounding rocket. Iirc they ran it for a few seconds in a vacuum.
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RenuisanceMan t1_j6m1gzx wrote
It's not a great as the article seems to think, it's around 500 secs from hydrolox according to Scott Manley. A few pictures I've seen make it look like an aerospike which makes sense with an annular combustion chamber, so may well be good for a first stage or an SSTO. Another concept I've seen recently is a sort of nuclear thermal/ion hybrid with an ISP of a few thousand whilst generating serious thrust, this makes more sense for deep space.
Dragongeek t1_j6jr8yv wrote
iirc hydrogen-fueled air-breathing RDEs are theorized working up to Mach 5 at 8000-9000 isp and hydrocarbon fueled ones about half or a third that isp.
It's all theory though, but very attractive
cjameshuff t1_j6k5pl3 wrote
Air-breathing engines aren't comparable to rocket engines. They have big specific impulse numbers because the specific impulse is no longer the impulse available from the propellant, but what's available from just the fuel after that fuel's been combined with the air. And since it's wildly variable with airspeed, it only makes sense for craft that cruise in a given range of airspeeds...in this case, Mach 5 and less.
a10t2 t1_j6jw269 wrote
I haven't seen numbers anywhere near that. For a hydrolox RDRE they're hoping to hit maybe 550 s.
A_curious_fish t1_j6hyovl wrote
Now what about crazy stuff like assembling a nuclear engine to be only used in space and get it into space via a regular rocket? Don't we have nuclear powered boats floating around aka the carriers and subs with nuclear engines? Granted idk how in gods name they work but I feel like toss it in space it'll be fine
GeorgeOlduvai t1_j6i7073 wrote
Nuclear powered and nuclear propulsion are two very different things.
A_curious_fish t1_j6i7pti wrote
That's a good point and more so what I meant when I don't know how it works
GeorgeOlduvai t1_j6i8j5m wrote
The subs and carriers have nuclear power plants aboard to generate electricity. While that power is used for propulsion, it's not the same thing as a nuclear engine. A nuclear rocket engine operates on the same principles but rather than using the heated water to turn a turbine, the water is directed through a nozzle to create thrust.
danielravennest t1_j6ilp8k wrote
Nuclear rockets use pure hydrogen as propellant. Lighter molecules move faster, and H2 is much lighter than H2O.
cjameshuff t1_j6j0557 wrote
And you can use heavier things as propellant, like ammonia (water and methane are both bad choices for various reasons), but anything but LH2 gives you only slightly more performance than chemical engines.
Meanwhile, instead of a pile of steel, copper, and nickel alloys carefully arranged to burn stuff really well, you need enriched uranium arranged to sustain a nuclear fission chain reaction. That's a huge step up in cost and regulatory complications, and nobody's going to do it for something barely better than a chemical engine, so LH2 it is.
stanspaceman t1_j6jhkvt wrote
They don't use high enriched Uranium FYI, it's HALEU, mandated for all space systems currently being designed.
cjameshuff t1_j6jk6m5 wrote
I didn't say HEU, I said enriched uranium. HALEU is enriched to a U-235 content of 5-20%, natural uranium is only 0.72% U-235.
stanspaceman t1_j6jm0na wrote
Okay still important point to make.
Pharisaeus t1_j6i84r2 wrote
> Don't we have nuclear powered boats floating around aka the carriers and subs with nuclear engines?
The issue with nuclear reactors in space is waste heat. Boats you're referring to have literally whole ocean around them to use as coolant. In space you don't have such luxury and you need massive radiators to dump the heat.
hawaiianthunder t1_j6ivu6m wrote
Wouldn't the lack of our atmosphere make it easier to cool a radiator?
carbonbasedlifeform t1_j6j5gfl wrote
Actually it makes it harder. Without air to use as a heat transfer medium you don't have anything to bleed heat into.
MetallicDragon t1_j6j73zf wrote
On the contrary, it makes it much harder. On earth, you can radiate away heat by direct contact with air. No air in space means the only way to dump heat is by black body radiation.
p-d-ball t1_j6jdjy3 wrote
So, now we have to bring an atmosphere with our ships???
​
(kidding, kidding)
hawaiianthunder t1_j6jhftu wrote
That's a new term for me, thanks for the reading material
Pharisaeus t1_j6jgwal wrote
It's a common misconception that space is "cold". This is due to the definition of "cold" -> the kinetic energy of particles in certain volume is low. But while on Earth is means you have lots of particles, each with low energy, in space it's very different - you have very few particles, often with very high energy.
In order to cool something down, you need to transfer the energy. On Earth particles with low energy will steal some of the energy of your hot thing, cooling it down. The more particles, the better. In space this effect doesn't exist, there are no particles to steal the energy. You need to radiate the heat as infra-red.
Polygnom t1_j6k65zb wrote
Heat can be transferred in three ways: Radiation, Conduction and Convection. Conduction is heat transfer by two solids touching. Or when you put your hand on your heater, you feel your hand getting warmer. Convection is heat transfer to fluids (gases). That is why the air in your room heats up when you put a heater in it. Radiation is the weakest form of heat transfer, by far. But if you aren't surrounded by an atmosphere or ocean to dump heat into, and instead are surrounded by a vacuum, radiation is the only way to get rid of heat. Conductive transfer will constantly heat up the spacecraft until parts start to melt if you cannot radiate the heat fast enough. Hence the need for large radiators on spacecraft that produce a lot of heat, e.g. the ISS or even the shuttle, whose whole payload bay doors were used as radiators and needed to be opened somewhat quickly once in orbit or the shuttle would overheat.
DownvoteEvangelist t1_j6ig1d2 wrote
They produce electricity and electricity powers electric motor... This wouldn't work in space...
Shrike99 t1_j6jofu2 wrote
It would work if you added some propellant to the mix. For example, add a big water tank and use that electric motor to drive a pump that sprays the water out the back at very high pressure.
Realistically you're not going to get a very good exhaust velocity with that method, so you'd instead use a different kind of electric engine to accelerate the propellant; electrostatic, electrothermal, or electromagnetic.
Indeed, the only example to date of nuclear propulsion actually being used in space was on SNAP-10A, which featured a nuclear reactor powering an electrostatic engine with cesium as the propellant.
Granted, it only worked for about an hour before it broke down, but it did work. It's a shame there hasn't been any followup in the 58 years since then.
DownvoteEvangelist t1_j6jv4q5 wrote
Probably because you don't get much thrust with that type of engine.
Shrike99 t1_j6jxdxg wrote
We've had plenty of solar powered electric propulsion since. The Dawn mission was a great example of what electric propulsion can do. Solar power just doesn't scale up well to larger vehicles, or work very well as you get furthur from the sun.
A nuclear electric system has the potential to be much faster than a chemical rocket over long distances, i.e to Mars or especially beyond.
The real issue has been the reluctance to put nuclear reactors into space. SNAP-10A remains the only example the US has ever launched, even though much better designs like the SAFE-400 and KRUSTY have since been developed.
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iheartbbq t1_j6i9j8s wrote
And then what? Nuclear power on earth just steam power. Propulsion in space requires Newtons 1st law - to go forward you gotta shit some stuff out the back. You can't just heat up water and shoot it out the back, I mean, you can, but that's a lot of squeezing for not a lot of juice.
Just permanently emitting a stream of decayed nuclear atoms would produce a tiny amount of thrust, but it could build up to tremendous speeds over time. But again, not really practical for transit during human life time scales.
danielravennest t1_j6ilews wrote
> You can't just heat up water and shoot it out the back,
That's exactly what the third stage of the Artemis I rocket did on Nov 16th. Except the water was carried as separate hydrogen and oxygen tanks, and burning them is what produces the heat. What comes out the nozzle is superheated steam.
iheartbbq t1_j6imc8u wrote
Groan. Worst kind of pedant.
It's also what the main boosters of the shuttle system did.
The combustion process adds significant velocity to the propellant when properly nozzled. What is the point of adding the danger of a nuclear energy source in space when the propellant is completely expended? Just use chemistry.
danielravennest t1_j6imxym wrote
> What is the point of adding the danger of a nuclear energy source
Because a nuclear-thermal engine can use pure hydrogen rather than a hydrogen-oxygen mix. Lighter molecules go faster at a given temperature, and H2 is much lighter than H2O. So you get roughly twice the exhaust velocity/specific impulse.
iheartbbq t1_j6ipagh wrote
Again, the juice is simply not worth the squeeze. You're adding nuclear complexity to every launch (nobody wants a dirty bomb going off in the sky) and you're just not getting significant benefits. You're still going to run out of propellant after an X minute burn. And now you're stuck with a super complex, hazardous, expensive boat anchor on your space craft that's VERY hard to cool because you only have radiation as conduction and convection don't exist in space.
Also
>Lighter molecules go faster at a given temperature, and H2 is much lighter than H2O. So you get roughly twice the exhaust velocity/specific impulse.
Oh, twice huh. H2 weighs 2 grams per mole, it will need to be ejected at nine times the velocity of a water molecule at 18 g/mol to have equal the force.
danielravennest t1_j6ivn9h wrote
> (nobody wants a dirty bomb going off in the sky)
Before you start up a reactor for the first time, the core is low radiation. Reactors produce short-life fission products, which is what makes nuclear waste dangerous.
Rocket mass is in kg, not moles. Exhaust velocity is ~9 km/s for hydrogen, vs ~4.5 km for H2-O2 engines.
I'm a space systems engineer, who has worked on nuclear rocket designs. My opinion is the time for nuclear-thermal propulsion is past. Solar-thermal can get the same performance - both heat H2 to the limits of the materials. But solar doesn't have all the nuclear baggage to deal with.
Nuclear-electric has much higher performance (3-20 times), though like all electric systems it has longer burn times. The reactor can be much smaller (1 MW rather than 1 GW), making radiators and such easier to do.
iheartbbq t1_j6iwpzo wrote
Right, and I'm a SUPER spaceman Thunderbirds engineer.
All that matters is mass and rate of the amount of shit that gets shot out the back, doesn't matter if it's in moles or kg, according to your claim 18x more H2 coming out the ass, is that true?
danielravennest t1_j6j7zjo wrote
I'm writing a textbook on Space Systems Engineering. Check the "view history" tab on any page to see who wrote it.
>according to your claim 18x more H2 coming out the ass, is that true?
That's your number, not mine, and it is wrong.
Shrike99 t1_j6js9tu wrote
You seem to be ignoring the minor fact that lower molar mass also means more moles, so it cancels out.
If you pump 1kg of water into the engine, that's 55.5 moles. If you pump 1kg of hydrogen into the engine, that's 500 moles.
So hydrogen produces 1/9th as much force per mole, but it also has 9 times as many moles per kg of fuel. The end result is that both produce the same total force when that kilogram is expelled from the engine.
Or at least, they would if they were both expelled at the same speed. Since hydrogen actually comes out twice as fast, it produces 1/4.5th as much force per mole, while still having 9 times as many moles, and hence produces twice as much total force.
MetallicDragon t1_j6j7y4l wrote
>Oh, twice huh. H2 weighs 2 grams per mole, it will need to be ejected at nine times the velocity of a water molecule at 18 g/mol to have equal the force.
Or just with 9x the mass flow rate. And thrust doesn't matter too much in space, what matters is fuel efficiency. A weaker nuclear rocker might need to do longer burns, but for the same mass of fuel as a conventional engine, it will get you going a lot further.
Shrike99 t1_j6jstqe wrote
>Or just with 9x the mass flow rate
You need 9x the molar flow rate, not the mass flow rate. And since hydrogen has 1/9th the molar mass of water, it ends up cancelling out.
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FirstTarget8418 t1_j6jegwt wrote
Hasn't this been like a working theory since the 50's or something and never went anywhere?
cjameshuff t1_j6jof4l wrote
The idea of using detonation to improve efficiency is quite old. The V1 "buzz bomb" used a pulsejet engine in 1944-1945, and experimental versions of pulsejets using detonations are about as old. The vibrations inherent in pulsejets of any sort have prevented them from being used much.
The basic concept of using continuous detonation waves in some form has probably been around for just as long, but has been more difficult to implement.
BackflipFromOrbit t1_j6l01s2 wrote
Standing oblique detonation ram jets are also a thing. Instead of the detonation wave revolving around an annulus it occurs in a static position downstream of a really interesting series of C-D nozzles and fuel injectors. It uses the ram effect for oxygen intake and compression but undergoes a pre-burn through an upstream CD nozzle to accelerate the gas further to higher mach numbers. The gas then flows into another CD nozzle where more fuel is injected at the throat. This mixture then accelerates again and just downstream of the throat there's a ramp that causes a standing oblique shock wave. The rapid increase in heat and pressure crossing the boundary of the oblique shock causes the fuel rich hypersonic gas to detonate constantly.
cjameshuff t1_j6l0p7t wrote
Oh, the shcramjet (not a typo). Yeah, I'd forgotten about those.
Shrike99 t1_j6k8b6k wrote
Sometimes it takes quite a while for a theory to be practically implemented.
Work on Scramjets started in the 50s, with engines working in laboratory conditions in the 60s, but didn't operate in real flight conditions until the 90s and have only recently started to approach practical use - it's hard to say exactly where they are today since most such projects are classified.
I'm not sure when the theory for FFSC engines dates to, but the first example was built in the 60s. However it was unable to sustain stable combustion and the first stable engine wasn't tested until the early 2000s. The first test flight of an FFSC engine wasn't until 2019, and the first practical use will probably occur this year.
The basic theory for fusion dates back to the 1920s, with proposals for fusion power specifically dating to the 1950s, but it still hasn't gone anywhere, yet. We have been making steady progress, so it may still go somewhere given more time. The recent scientific breakeven at the NIF was a significant, if not directly applicable milestone.
Advances in computer control technology have been instrumental to a lot of the recent progress in the aforementioned applications. Having the theory is one thing, being able to control a complex and delicate process in practice is another.
Maintaining continuous rotating detonation has proven quite challenging in the past, typically breaking down due to instabilities in a matter of milliseconds. The fact that NASA were able to run this engine for what looks like about 8 seconds is very promising indeed.
Decronym t1_j6iixue wrote
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
|Fewer Letters|More Letters| |-------|---------|---| |DARPA|(Defense) Advanced Research Projects Agency, DoD| |DoD|US Department of Defense| |FFSC|Full-Flow Staged Combustion| |H2|Molecular hydrogen| | |Second half of the year/month| |HEU|Highly-Enriched Uranium, fissile material with a high percentage of U-235 ("boom stuff")| |Isp|Specific impulse (as explained by Scott Manley on YouTube)| | |Internet Service Provider| |LH2|Liquid Hydrogen| |NTR|Nuclear Thermal Rocket| |SSTO|Single Stage to Orbit| | |Supersynchronous Transfer Orbit|
|Jargon|Definition| |-------|---------|---| |EMdrive|Prototype-stage reactionless propulsion drive, using an asymmetrical resonant chamber and microwaves| |hydrolox|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer| |turbopump|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust|
^(11 acronyms in this thread; )^(the most compressed thread commented on today)^( has 15 acronyms.)
^([Thread #8497 for this sub, first seen 30th Jan 2023, 16:09])
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mauore11 t1_j6jhwif wrote
Slingshooting blue whales out the back of the ship would get you 1 Kyle of force...
qa2fwzell t1_j6ipmm7 wrote
Shame anything earth-like is hundreds of lightyears away :/
cjameshuff t1_j6j2cwu wrote
Realistically, anything Earth-like would likely be uninhabitable. Aside from the forward and backward contamination issues, an entirely alien biosphere wouldn't contain any diseases or poisons adapted to us, but would be saturated with things that are moderately to severely toxic or just noxious, and complex organic substances that our immune systems have never encountered before, some of which would be likely to cause severe allergic reactions.
In short, it'd probably stink horribly and send you into anaphylactic shock, and if it didn't, it'd probably have environmental toxins that would kill you slowly. Habitable environments are those with the natural resources needed to support habitats where we can support Earth life, not those already filled with alien life.
Mars? Oh no, perchlorates! Yeah, about 0.5-1% of the regolith consists of salts twice as toxic as table salt that are unstable, easily washed out with water or decomposed by heat or reducing agents, and which do not bioaccumulate. Worry more about heavy metals and long-lived organic compounds leaching out of plastics and such.
Who_DaFuc_Asked t1_j6j9e2h wrote
I was about to say, if you tried breathing on a habitable planet you'd probably inhale some super toxic or deadly stuff almost immediately. You would 100% need an extremely reliable and high quality filter to make the air safe to breathe even if it's the same composition as on Earth.
Multiple generations of humans would need to gradually develop immunity to the planet's natural threats, unless we could make some insane tech to compensate for it
steveoscaro t1_j6jtu2o wrote
This is the type of comment I love to read
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laxkid7 t1_j6jwrkf wrote
Kinda off topic, but whatever happened to using sails in space. Never really heard much about it after the hype a little while back
Shrike99 t1_j6k1i1e wrote
By my count there have been 9 solar sail demonstration missions launched, the first being Cosmos 1 in 2005 and the most recent being the NEA Scout launched just a few months ago.
However, the vast majority of these missions have either outright failed or been a dubious success at best. The only one which has been truly successful and demonstrated practical use of a solar sail was IKAROS in 2010, which operated successfully until 2015.
It only takes one success to prove that the concept works, but the large number of failures seems to have tempered expectations and dampened enthusiasm somewhat.
There was a proposed follow-up to IKAROS called OKEANOS intended to go to the Trojan asteroids, which would have been the first real use of a solar sail for a scientific mission.
It was a finalist for ISAS's consideration in 2019, but ultimately lost to LiteBIRD. Unfortunately there just isn't enough space science funding for all the missions people would like to do, so a lot of neat stuff gets passed on.
Old_Toby2211 t1_j6k1or1 wrote
I read snails and bust a gut laughing
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_Weyland_ t1_j6k3dva wrote
Is this tech only suitable for space travel or can be used to launch from the planet as well?
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Scrumpchy t1_j6lenrm wrote
45 days to Mars. Wow Elon may actually return home within my lifetime.
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Vauld150 t1_j6jk6nx wrote
Doesn’t the Air Force already have a spy plane that uses this tech?
acelaya35 t1_j6k7g0b wrote
A Pulse Detonation Engine was proposed for DARPA's Blackswift hypersonic test vehicle from the late 00's. Pulse Detonation Engines are engines that use the same detonation concept but are still inherently air breathing jets and not rockets. I'm not aware of if one was ever built though. It's my understanding that contemporary hypersonic missiles use solid rocket motors to get up to speed and then glide to their target.
derphurr t1_j6ljjiv wrote
No that's why nasa is testing it. Most of this was developed at AFRL. I'm guessing for upper atmosphere unmanned drones.
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kujasgoldmine t1_j6m47hu wrote
Interesting! I'm satisfied when they come up with propulsion that emits blue-ish fire.
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Larry_Phischman t1_j6hlktj wrote
The US government has a pulse detonation jet engine technology which would be useful for SSTO applications. They’ve kept it secret.
Creepy_Toe2680 OP t1_j6hmcpq wrote
iheartbbq t1_j6i6sie wrote
Pulsejets require an atmosphere to operate. By definition they can't reach orbit with a single stage. There's no kind of conspiracy to hold back technology to prevent cheaper cost per kilogram to space or reusability.
Aerospike rockets are a FAR more practical SSTO technology (and pretty reusable, btw). Just never got serious funding because of the intense costs up front.
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Tylerdirtyn t1_j6lb47f wrote
I would like to see some testing of subsonic drivers for deep space propulsion. As they have discovered that low frequency vibrations can produce thrust in the vacuum of space a ship outfitted with a wall of specially designed and built "subwoofer type" drivers could very well get us to much higher speeds than ever before. My concept is similar to the guy with the piezo electric drivers but going the opposite direction and using low frequency energy rather than high frequency energy. The system could even be solar powered and would require less energy than any previously or currently designed system.
JustAPerspective t1_j6iq57z wrote
The best part about this discovery?
They used existing tech that had been assumed not to work... & made it work better than anyone had ever thought.
Discovery oft comes in simply finding the assumptions others missed.
cjameshuff t1_j6j4eq9 wrote
This isn't a discovery, it's not existing technology, nobody assumed it wouldn't work, and it's not clear yet how well it actually will work. It's an early test of a new technology that has been in the conceptual stage for decades, has only recently been gotten to work, but which has been expected to improve performance.
wombat5003 t1_j6jzbml wrote
This will be the future not of space exploration, but mining ore… this is the start of humans building out past the confines of our planet to making possibly a series of rings around Mother Earth using ore from asteroids as material.. think I’m crazy?? Maybe not… Ask Larry Niven :)))) Ringworld is coming!!
Seriously I say this because if ya think about it, it takes 18 months currently to get to the asteroid belt with what tech we have. With this new way, we could cut the round trip significantly which makes mining a viable prospect..
cjameshuff t1_j6k76wg wrote
This will give you 10% or so better performance. That's not nothing, but it's not the difference between asteroid mining being viable or not.
TheOtherAisle t1_j6n568q wrote
10% is huge, given that the weight restrictions are so harsh that astronauts have to pick and choose on how much underwear they bring.
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Creepy_Toe2680 OP t1_j6hkn5m wrote
The new tech is called a rotating detonation rocket engine, or RDRE. This propulsion system uses detonations to generate thrust. To do this, the tech relies on the accelerating of a supersonic exothermic front, which similarly creates thrust to the way a shockwave travels through the atmosphere after an explosion, which could make deep space travel easier to build for.
The point of the design is to use less fuel while also providing more thrust than the current propulsion systems that NASA and other rocket-building companies rely on. Using less fuel makes it easier to prepare these spacecraft for deep space travel, as you can mete out smaller amounts of fuel that won’t weigh down the rocket when it is lifting off.
With the success of this test, NASA is now looking at building a working, fully reusable 10,00-pound RDRE that it can then compare to the performance of traditional liquid rocket engines – like those used in the Space Launch System. If those tests prove successful, too, and the comparisons play out well, it could revolutionize how we think about deep space travel in the future.
This isn’t the only way that NASA is looking at revolutionizing deep space travel. The space agency is reportedly looking into nuclear-powered spacecraft, which would allow spacecraft to travel further distances without needing liquid fuel. It would also make the journey to Mars significantly shorter, from six months to just 45 days.
by Joshua Hawkins (not me)