Submitted by Creepy_Toe2680 t3_10ozjk9 in space
corsairealgerien t1_j6hn22i wrote
Reply to comment by Creepy_Toe2680 in NASA tested new propulsion tech that could unlock new deep space travel possibilities by Creepy_Toe2680
>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?
[deleted] t1_j6kvfst wrote
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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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[deleted] t1_j6jrqpf 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
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