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Post by The Astronomer on Jan 22, 2017 8:47:19 GMT
Note: NTR is Nuclear Thermal Rocket, and SEP is Solar Electric Propulsion.
Scrolling though the internet, I came across one particular page.
'Forget NTR, use SEP!' Result: TRIGGERED.
I mean, there is problem about SEP and all: that pathetic sub-1kN thrust that would take you forever to climb out of the deep gravity well of the low Terra (Atomic Rocket reference, but yes I like this name) orbit, compared to millions (sometimes tens of millions) of newtons achieved by the NTR-maker players of CoaDE.
For most people, switching from NTR to SEP is probably the most favorable choice, but as both type of propulsion may have different favorable fuel, I decided to ask this question.
If you have to choose either NTR or SEP for your year 2030 Mars manned mission spacecraft, which type of propulsion will be your choice?
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Post by bigbombr on Jan 22, 2017 8:54:31 GMT
Note: NTR is Nuclear Thermal Rocket, and SEP is Solar Electric Propulsion. Scrolling though the internet, I came across one particular page. 'Forget NTR, use SEP!' Result: TRIGGERED. I mean, there is problem about SEP and all: that pathetic sub-1kN thrust that would take you forever to climb out of the deep gravity well of the low Terra (Atomic Rocket reference, but yes I like this name) orbit, compared to millions (sometimes tens of millions) of newtons achieved by the NTR-maker players of CoaDE. For most people, switching from NTR to SEP is probably the most favorable choice, but as both type of propulsion may have different favorable fuel, I decided to ask this question. If you have to choose either NTR or SEP for your year 2030 Mars manned mission spacecraft, which type of propulsion will be your choice? SEP, if 'boosted' by a laser. |
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Post by The Astronomer on Jan 22, 2017 9:28:16 GMT
Note: NTR is Nuclear Thermal Rocket, and SEP is Solar Electric Propulsion. Scrolling though the internet, I came across one particular page. 'Forget NTR, use SEP!' Result: TRIGGERED. I mean, there is problem about SEP and all: that pathetic sub-1kN thrust that would take you forever to climb out of the deep gravity well of the low Terra (Atomic Rocket reference, but yes I like this name) orbit, compared to millions (sometimes tens of millions) of newtons achieved by the NTR-maker players of CoaDE. For most people, switching from NTR to SEP is probably the most favorable choice, but as both type of propulsion may have different favorable fuel, I decided to ask this question. If you have to choose either NTR or SEP for your year 2030 Mars manned mission spacecraft, which type of propulsion will be your choice? SEP, if 'boosted' by a laser. Wait, SEP does not contains heating the propellant. If you are talking about heating the propellant, that's the thermal rocket, which is literally just a resistojet. |
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Post by bigbombr on Jan 22, 2017 9:40:41 GMT
SEP, if 'boosted' by a laser. Wait, SEP does not contains heating the propellant. If you are talking about heating the propellant, that's the thermal rocket, which is literally just a resistojet. I mean an MPD powered by beamed power (higher energy intensities than solar light). |
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Post by n2maniac on Jan 22, 2017 9:46:28 GMT
Either a fission reactor goes into space, chemical rockets are used, or some sort of very gradual acceleration involving solar. It is saddening to see how little fission reactors get to be used in space IRL, but maybe that is for the best.
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Post by zuthal on Jan 22, 2017 10:22:58 GMT
For a manned mission, I would definitely use an NTR. Even if you use a centrifuge system to provide artificial gravity, you still have radiation concerns, and want to minimise travel time. Electric propulsion simply does not give you the acceleration needed to take the relatively time-efficient Hohmann trajectories you'd want to take.
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Post by darthroach on Jan 22, 2017 10:29:08 GMT
Solar energy based propulsion systems may work well enough out to the orbit of Mars, but we're never going to go any further with them. If we're serious about space exploration, we're going to have to go nuclear at some point. The only way nuclear powerplant and propulsion tech is going to advance is if it's used. So I'm for either NTR or at least NEP. And as to the type of NEP, I'd suggest using the Fusion Driven Rocket - Magneto-Inertial Fusion. It may well be the first type of fusion reactor we get going and would probably end up paying dividends in many other areas of technology. And the best part is, it will probably work if we build it. www.projectrho.com/public_html/rocket/enginelist.php#id--Pulse--Inertial_Confinement--Magneto_Inertial_Fusion |
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Post by thorneel on Jan 22, 2017 12:10:02 GMT
External Nuclear Pulse Propulsion - ok, so apparently this is not allowed by some old treaty and silly concerns about "frying half the LEO satellite net and causing a Kessler syndrome". Come on, people, we've got to take risks if we want to achieve something!
...fine (who needs satellites anyway).
External Chemical Pulse Propulsion, then. You'll need high-power artillery guns to lob said explosives at the pusher plate of the craft.
Laser thermal launch (using atmosphere as remass) would be better, but 2030 is too short to build an extensive laser launch system.
Then, once in deep space, I have an affection for solar thermal. Cheap, simple, and you can achieve surprisingly high temperature with big enough mirror.
Bar that, chemical-boosted SEP would use tried and tested tech, so for 2030 there may be no other options.
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Post by zuthal on Jan 22, 2017 14:35:46 GMT
Standard solid-core nuclear-thermal is actually fully tested and developed already, minus being tested in actual flight hardware, and as I said, for manned missions you want short travel time.
Though, especially when using advanced Methalox engines, doing it with just chemical engines doesn't seem entirely unfeasible either.
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Post by coaxjack on Jan 22, 2017 16:59:53 GMT
Ah! While the 1972 NERVA prototype never actually flew, it was flight-rated, and probably would have eventually ended up doing some lunar type missions if Apollo wasn't cancelled. In my opinion that was a huge setback, especially considering how beefy the INT-21 was. Imagine the payload you could get into a 30 foot diameter fairing!
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Post by zuthal on Jan 22, 2017 21:18:41 GMT
Saturn INT-21 would have had 75 tonnes capacity to LEO. A LEO-Mars Surface-Earth Surface trip, assuming that all velocities that can be reduced with aerobraking are fully reduced with aerobraking, required about 10 km/s of delta-V. Assuming a 6 km/s methane NTR, we can get away with a mass ratio of 5.3, i.e. we can have 14 tonnes of payload+structural mass - with an 8 km/s hydrogen NTR, we can instead get a mass ratio of 3.5 and ~21 tonnes payload+structural mass - though I'd be a bit more doubtful about that being able to develop TWR>1 on Mars's surface - and that is without any ISRU, of course.
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Post by darthroach on Jan 23, 2017 0:29:54 GMT
Saturn INT-21 would have had 75 tonnes capacity to LEO. A LEO-Mars Surface-Earth Surface trip, assuming that all velocities that can be reduced with aerobraking are fully reduced with aerobraking, required about 10 km/s of delta-V. Assuming a 6 km/s methane NTR, we can get away with a mass ratio of 5.3, i.e. we can have 14 tonnes of payload+structural mass - with an 8 km/s hydrogen NTR, we can instead get a mass ratio of 3.5 and ~21 tonnes payload+structural mass - though I'd be a bit more doubtful about that being able to develop TWR>1 on Mars's surface - and that is without any ISRU, of course I am not sure direct launch is the best mission architecture for Mars exploration, let alone colonization. The current idea, courtesy of the ever active mr Zubrin and featured in the book/movie "the Martian", is to have separate cargo and crew launches, with the possibility of using a separate high-speed interplanetary shuttle for crewed use introduced in the latter. You launch the hab, supplies and return vehicle ahead of time, and send the crew with the next mission's start supplies in the next launch window. Allows lighter launches, because the return vehicle spends the 2 years on Mars gathering propellant. Either way, we should really stop thinking in terms of what will get a crew of scientists over there one time, and more in terms of stable, quick and safe transport infrastructure for colonization. We landed on the moon with chemical rockets, but it's unlikely any moon colony will be sustained without long-use refuellable NTR shuttles. Same with Mars. |
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Post by apophys on Jan 24, 2017 2:40:47 GMT
Methane NTR + MPD is an excellent propulsion method in CoaDE, so it would be a great choice for a Mars mission. Alternate propellants can work well too, like RP-1.
Of course NSWR is sexy for interplanetary travel, but probably not for use in the vicinity of any zone of human habitation. So it would need alternate propulsion up to orbit.
Solar thermal is very appealing in the inner solar system (solar furnaces on Earth melt steel at industrial scales). High heat = high dV. I haven't checked it out, but I expect low thrust, so getting off Mars again would be a bit of a challenge (and that's why I voted NTR).
Ultimately, what will be used is what will be cheap and simple.
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Post by zuthal on Jan 24, 2017 18:55:03 GMT
Solar thermal would have to be low thrust, yes - that is because the maximum thrust power is limited by the solar constant and your collector area. Assuming you are at Earth (solar constant of 1370 W/m^2) and have a 10000 m^2 collector (e.g. a 100 m by 100 m square of alumised mylar), you have 13.7 MW of thrust power available. At 8 km/s for hydrogen, you can get, with 100% efficiency, at most 3425 Newton of thrust. At Mars, with only 600 W/m^2 of solar irradiance, you only get 1500 N - and it only gets worse from there.
Also, the methane NTR has another advantage over more exotic fuels used in SEP or NEP - the potential for ISRU on Mars. Since Mars probably has large amounts of subsurface ice, and has a carbon dioxide atmosphere, it would be possible to, using electrolysis of the ice and then the sabatier reaction, produce methane on mars - along with oxygen, which can be funneled to the crew ECLSS or liquefied and stored on-board for use in a LANTR-type "reverse afterburner", to generate a brief boost in thrust e.g. for takeoff at the cost of exhaust velocity (basically, switching to low gear to climb out of Mars's gravity well).
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