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Post by someusername6 on Jun 16, 2017 21:48:34 GMT
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Post by tortugagreen on Jun 18, 2017 23:58:01 GMT
Oh, this is very cool. Having flights going by 2023? that's very soon. I'm inclined towards "that's way too fast, it's probably going to be more by 2030 at least" but if Elon Musk can pull that off, then I'm excited for this. I'd prefer if Nuclear Thermal Rockets were used to get higher Delta V, but I doubt Musk wants to tell people "we want to send you to space on top of a nuke instead of just a bomb." It would help, but I expect it would mean delaying things further for all the testing and safety inspections, because people are a lot more nervous about nuclear energy.
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Post by Hicks on Jun 19, 2017 0:30:03 GMT
Honestly, I was a NTR girl until CoaDE, and would have said that if you wouldn't get on a NTR because it had a nuclear reactor you didn't deserve to go to space; dV is king and NTRs have more. And then CoaDE converted me to 2 things: Boron, God's wonder material, and MPDs.
MPDs are just too efficient, their exaust velocity too great, and their propellants too abundant and cheap and easy to extract. You take a nuclear reactor, but instead of just dumping its coolant out the back through a nozzle you hook it to a thermocoupleand radiator and have that electrical energy drive the MPD. And the dV is nuts. It's just nuts.
So though I understand that flying a nuclear reactor to space would require testing, anyone who wouldn't get on a nuclear powered MPD because it has a nuclear reactor dosen't deserve to be in space. That's a hard line, but they'd have never reached where we're going to go anyway.
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Post by ross128 on Jun 19, 2017 1:05:47 GMT
MPDs are nice if you're an immortal machine intelligence that can take their sweet time getting up to speed, but short-lived humans with their needs for things like food might still prefer the extra gs that an NTR can pull.
Of course, being an immortal machine has so many other perks that long-term it probably is a desirable state to achieve if possible anyway.
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Post by The Astronomer on Jun 19, 2017 5:28:06 GMT
Honestly, I was a NTR girl until CoaDE, and would have said that if you wouldn't get on a NTR because it had a nuclear reactor you didn't deserve to go to space; dV is king and NTRs have more. And then CoaDE converted me to 2 things: Boron, God's wonder material, and MPDs. MPDs are just too efficient, their exaust velocity too great, and their propellants too abundant and cheap and easy to extract. You take a nuclear reactor, but instead of just dumping its coolant out the back through a nozzle you hook it to a thermocoupleand radiator and have that electrical energy drive the MPD. And the dV is nuts. It's just nuts. So though I understand that flying a nuclear reactor to space would require testing, anyone who wouldn't get on a nuclear powered MPD because it has a nuclear reactor dosen't deserve to be in space. That's a hard line, but they'd have never reached where we're going to go anyway. I see you've became a MPD girl, but this ship is intended to be landed on Mars and work in low planetary orbits. MPD-powered ships won't do anything except taking forever getting out of orbit or crashing into the planet.
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Post by Hicks on Jun 19, 2017 5:49:39 GMT
That line of reasoning is fallicious, and my proof to counter you is the home comming mission race. NTRs have thrust, but only matters in the context of overcoming gravity, in orbital freefall its thrust is nearly irrelevent; dV is nearly everything.
You orbit, accellerate, coast, decelerate, and orbit again. Methane NTRs get ~6 km/s dV, Hydrogen NTRs get ~9 km/s dV; both take ~10 minutes to achieve maximum velocity, but can only coast at 3 and 4.5 km/s. And, IIRC, they take 6 months to go from Earth to Mars and years to get to Jupiter. A Methane MPD gets 56~100 km/s dV, which means they coast at 28 to 50 (!) Km/s, and can do the Earth-Mars run in 2-3 monthss and MONTHS to get to Jupiter.
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Post by Hicks on Jun 19, 2017 6:04:27 GMT
Civillians should use Resistor-jet/MPD combo, Military ships use NTR/MPD. The only reason to have an NTR is if you needed the power to thrust AND something else is using all your reactor power, e.g. a big laser.
Reactor+resistor jets / MPD is cheaper and grants equivalent thrust to NTR, and easier to maintain because you don't have N nuclear reactors on gimbals hanging off the back of the ship. Civillian RJ/MPD ships can also support their ports with power generation while they sit at their docks.
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Post by bigbombr on Jun 19, 2017 6:41:48 GMT
MPDT's are unbeatable for interplanetary travel with current tech. For surface to orbit, laserlaunch/lightcraft/laser thermal pulsed plasma propulsion craft seem the best option. Using the atmosphere as a propellant for a lot of your delta-v means you can have a reusable SSTO with a decent mass fraction. Making interplanetary craft land would be folly, so you interplanetary craft only need high thrust to get out of the gravity well.
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Post by Hicks on Jun 19, 2017 7:02:26 GMT
So I know there was research in NTR ramjets, but was there ever any research into resistor/ram jets?
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Post by bigbombr on Jun 19, 2017 8:34:59 GMT
So I know there was research in NTR ramjets, but was there ever any research into resistor/ram jets? Sure. People are plenty creative when trying to go fast.
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Post by The Astronomer on Jun 19, 2017 9:32:35 GMT
Wait, you guys are designing an entirely new spacecraft? Okay, so, why don't you use NTRs in civilian ships? You'll still need the nuclear reactor anyways.
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Post by apophys on Jun 19, 2017 20:51:21 GMT
The cruising speed in my Homecoming ship is ~200 km/s, and the trip is 65 days (Themis and Mars being far apart in their orbits at the time). You can't get such ludicrous speeds using NTRs (or methalox). Wait, you guys are designing an entirely new spacecraft? Okay, so, why don't you use NTRs in civilian ships? You'll still need the nuclear reactor anyways. You need a reactor to power your MPDs (essential). A resistojet can take electricity from the same reactor. An NTR on the other hand requires its own dedicated reactor, for each engine, in addition to the one you use for your MPD. So it is strictly inferior if resistojet thrust could be adequate (which it is, according to CoaDE) and if nothing else is using the electricity (which is the case for civilian craft, but not military craft).
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Post by EshaNas on Jun 25, 2017 4:00:45 GMT
Again, the problem with MPDs and stuff like VASIMR is the power plant. They're great, they're environmental, but they need huge amounts of power for manned missions in a timely manner. That points us to nuclear reactors. Civilians on Earth handle nuclear reactors now, I see no reason to bar them for space civilians. If you're barring nuclear *motors*, that's a bit different, but even then, why? Even that can have a civilian version using lesser enriched fissiles while the military hogs the 80-90%+ enriched stuff.
But back to ion drives of all types. Zubrin, for instance, knows that the math on the VASIMR is solid, but because NASA doesn't have nuclear power plants on hand to churn out 10 MW, we're not going to Mars in 30 days and until NASA churns out capable nuclear tech all money into VASIMR is basically wasted, in his words, a 'hoax'. Last I checked, the nuclear space reactors we've made and tested are as follows:
SNAP 10A - 590 watts SNAP 2 - 3.5 kilowatts TOPAZ-I - 5 kilowatts TOPAZ-II - 10 kilowatts SP100 - 17 kilowatts SAFE 400 - 100 kilowatts Some Los Alamos Design, light nuclear fission reactor of some type, apparently 1 negawatt.
There are also some nuclear submarines which are 'light', I think my criteria was under 10,000 tones for total tonnage, but those reactors are well, for submarines, not spaceships, and conversion might not be worth the hassle. And because they're often military, numbers on the reactors themselves are hard to come by. The NR-1 apparently clocked out 144 kilowatts, the French K48 around 48 megawatts, and the American? S2C around 1.8 megawatts. Other subs might have 'small' nuclear reactors but their total tonnage conceals the tonnage of the reactors themselves.
Keep in mind these might be watts thermal or electric, I didn't note down which.
Of those, only the French sub reactor is useful for VASIMR, or 10 of those Los Alamos reactors, which I couldn't even find a number for. But putting the space reactors with a NERVA, or Project Timberwind or whatever came out of Project Prometheus or the Nuclear Cryogenic Propulsion Stage Project or the RD-0410 nuclear motors? Now there's something promising and relatively available.
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Post by princesskibble on Jun 25, 2017 7:05:02 GMT
I'm a chemical rocket girl lol :3
They do everything, and if you have propellant depot infrastructure, they go everywhere! No expensive radiation toxic powerplants or enormous solar panels needed!
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Post by bigbombr on Jun 25, 2017 8:48:51 GMT
I'm a chemical rocket girl lol :3 They do everything, and if you have propellant depot infrastructure, they go everywhere! No expensive radiation toxic powerplants or enormous solar panels needed! Getting to orbit is expensive though, and they take forever to get anywhere. Laserlaunch or lofstromloops to get to LEO, laserthermal or resistojets to get out of the gravity well, and MPDT's for inter body travel.
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