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NASA's Journey To Mars May Use Nuclear Rockets (blastingnews.com)
MarkWhittington writes: NASA Administrator Charles Bolden has been making the rounds of congressional committees, defending the indefensible, that being the latest Obama space agency budget proposal. Thursday it was the turn of the House Science Committee to complain to Bolden that the budget underfunded the Journey to Mars and to vow that more money would be forthcoming. One of the other complaints Congress has been making is that NASA lacks a plan to get people to Mars, scheduled to happen sometime in the 2030s. Bolden was coy, suggesting that the time was not right to start firming up architectures and missions. However, he did drop an intriguing hint that a nuclear thermal rocket engine being developed at NASA's Marshall Spaceflight Center may take people to Mars quicker than chemical rockets.
Quick, hide the sensitive people like children and, people who are less rational and more spastic than children like MDSolar! Somebody used the word NUKULAR and there might even be a RAYDEEASHUN!!
We should ban all things nukular from space because polluting natural, artisanal, organic, and non-GMO space with radeyashun would be a crime!
AntiFA: An abbreviation for Anti First Amendment.
ESA: We made it to mars america! our rover is collecting samples and data.
ISRO: America! we need some help analyzing these samples! can you send a rover to kindly do the needful?
Russian space agency: Da. We are needing help with this outpost America. New supplies and ships needed for our colony.
NASA: look guys uh....we're in our fifth government shutdown, the supreme courts been vacant for 3 years, I think...i think most of our drinking water is lead these days and we just pledged another 800 billion to the terror war and the great wall of mexico. But if you can somehow work Mars exploration into religious freedom i think we can keep the radio comms up another month.
Good people go to bed earlier.
NASA had a nuclear thermal rocket program called NERVA back in the 60s (itself in part inherited from the US Air Force): https://en.wikipedia.org/wiki/NERVA
The program successfully developed a nuclear thermal rocket engine (successful test-firings and everything), and there were plans to build a Saturn V with a nuclear upper stage, but the program was killed by Congress because of the old "give a mouse a cookie" problem. NTRs are basically only useful for sending enormous things to Mars (or other planets), like human colony modules, since the engine and tankage is so heavy that the efficiency only becomes a benefit when the payload is even bigger. The fear was that if Congress let NASA continue NERVA development, it would lead to greater pressure for human Mars missions, which would be expensive (though I'm sure a campaign of human exploration of Mars pales in comparison to the cost of the campaigns in Vietnam and elsewhere -- and it will certainly pay off more technology dividends and look better in the history books).
We shouldn't pollute space with hard radiation!
I can see environmentalists objecting with something like that.
Who you calling fictional, Anonymous Cavedweller?
https://en.wikipedia.org/wiki/NERVA.
Sheesh...
Wow, finally there is someone who is even more clueless than MDSolar.
Excuse me, but please get off my Pennisetum Clandestinum, eh!
Wow...
To think that your vote counts as much as normal people's...
Mars is barren, extremely inhospitable, wasteland. Why are they in such a hurry to send meatbags there ?
No way. First there are international laws and treaties preventing ANY nuclear devices I space.
Way. In fact, it was already done long ago. The Voyager space probes have a nuclear power source.
Nae king! Nae laird! Nae yurrupiean pressedent! We willna be fooled again!
>> may take people to Mars quicker
Slowing down to catch the planet, getting back off the planet, and returning back to earth would all seem to be bigger problems.
Has it ever been used to push any mass whatsoever in space? No? It's fictional.
Following your definition, you're either fictional or surprisingly resistant to radiation, void, combustion and, presumably, landing at high speeds.
I believe the treat is nuclear WEAPONS... This is not a weapon, and besides which there have been numerous nuclear devices launched in recent years, New Horizons was powered by a radioisotope thermoelectric generator, which has PLUTONIUM!!
First there are international laws and treaties preventing ANY nuclear devices I space.
No, there aren't. The Partial Test Ban Treaty of 1963 bans nuclear detonations in space, which killed the Orion project (not that it would likely have gone anywhere anyway).
We launch nuclear devices into space all the time; that's how deep-space probes get their electric power. The recent proposal is to use nuclear heat generation to power a rocket, and the treaty is just peachy with that.
We need to launch a few nuclear tugs. They can be used to move spacecraft up to higher orbit, so we don't need to use large expendable boosters. Just get the craft into orbit, meet up with a tug, and push it to a higher orbit or even escape velocity. Then the tug can return to low orbit to be refueled and ready for the next mission. The tug still needs propellant, it just uses the nuclear power to heat it for propulsion.
A 0.01g constant acceleration ship gives you the Solar System.
A ship capable of a constant 0.01g acceleration would be a game-changer. Break the steps down as X-prizes. Build a 0.001g ship. Scale it up to a 0.005g ship. Next step is get it to 0.01g and you can reach Mars in three months and anywhere out to Pluto in just less than a year. First place to go? Prospecting the asteroid belt would be my vote. Find useful stuff, use it to build more useful stuff.
Nuclear would be much more feasible, no worries about long term health effects and less shielding, weight, propellant, and costs.
Also, they could just crash the craft into the planet, saving lots of cost for a lander.
Sheesh, evil *and* a jerk. -- Jade
>>>> Mars has like .6 the atmosphere of Earth
>> you might want to check again
I believe the poster meant: "The highest atmospheric density on Mars is equal to that found 35 km (22 mi) above Earth's surface. The resulting mean surface pressure is only 0.6% of that of Earth (101.3 kPa)."
Mars is barren, extremely inhospitable, wasteland. Why are they in such a hurry to send meatbags there ?
Antarctica, the Mariana's Trench, the top of Mount Everest, the surface of the Moon and low earth orbit are all barren and extremely inhospitable wastelands and we've visited all of those. There are plenty of good reasons to want to put people on the surface of Mars too. We can learn a lot from inhospitable places and even more from figuring out how to get there and stay alive. Furthermore what is uninhabitable today may become a viable destination with an adequate application of technology. Nobody is asking you to go.
To be fair, NERVA did have problems. Good ISP (~850 sec), but abysmal thrust to weight ratio - depending on what numbers you look at, somewhere between 0,2:1 and 0,5:1 wet, 3-4 dry.
That really puts it as somewhere in-between chemical rockets and VASIMR, which has an even lower thrust to weight ratio but even higher ISP. The thing is... it's sort of an awkward middle ground. If you're going to Mars, you don't need your thrust to be delivered all that quickly. And VASIMR already exists. So unless you can dramatically improve on the NERVA concept, one has to wonder, what's the point?
(Totally ignoring the inevitable public opposition here)
You can't change that... by gettin' all... bendy.
Speaking of which, has anyone figured out how to get someone to Mars without being killed by exposure to the natural radiation in route?
There are Top People working on it. But that is just one of several show stopper problems we'll have to figure out before a visit to Mars becomes viable. And if we want to stay there for any length of time there are even more problems to solve. Probably doable but it's going to take a while to work them out. The precise length of "a while" will be contingent upon funding and societal motivation.
Comment removed based on user account deletion
There is a plan that would get us to Mars soon and in the budget we have. But Congress wouldn't like it because it wouldn't use their favorite pork rocket (SLS), and possibly not even Orion (which is a less-bad idea than SLS is, but still ultra inefficient).
But the fact is that we didn't even have a "plan" to get to the Moon when JFK made his Rice University speech. Or we did, but it was wrong. The original plan was to use direct ascent of the Apollo command module off the surface of the Moon and go straight back to Earth. But such a plan would've required a launch vehicle much larger than the Saturn V. Instead, we used Lunar Orbit Rendezvous, which allowed us to use just Saturn V. And of course, we had to shut down Saturn V production during the Apollo program because even Saturn V was too expensive and unsustainable. SLS is even worse, as it uses old Shuttle parts (developed in the 1970s, for God(dard)'s sake!) which were originally intended to be reusable but now we're just throwing away (the worst of both worlds... the upfront cost of reusable parts and the expense of throwing the whole thing away each time), and so we can afford to fly just once every other year (and each Mars mission will require several launches).
We can explore Mars entirely with EELV-class launch vehicles. Atlas V has a 7.2 meter fairing available, Delta IV Heavy can put about 28 tons in orbit (enough for the largest "single piece", provided we use docking... but no orbital assembly required), Falcon Heavy will launch within a year (it starts testing in Texas soon), can put over 50 tons to orbit (more with cross-feed), and Vulcan (the successor to Atlas V and Delta IV being designed now with Blue Origin's BE-4 engine) can handle a 8.4 meter fairing (same as SLS) and in Heavy configuration could also handle at least 50 tons to LEO.
We can also use either SpaceX's Dragon or Boeing's Starliner capsules, which are much more efficient, to get crew to space and back. The actual vehicle to bring astronauts to Mars vicinity wouldn't actually bring Orion along anyway, as the current plan is to rendezvous in a distant retrograde lunar orbit.
Our human exploration funding is dominated by SLS and Orion, both elements of which are way too expensive and will be available in full form much later than EELV-class vehicles (available now, with twice the capacity available sooner than SLS's first test launch) and Dragon/Starliner (set for 2017 crewed debut). Instead of wasting our funding on two elements we don't need, we could spend the money on a small transfer vehicle (perhaps using solar-electric propulsion, but chemical rockets would work, too) and a Mars lander/ascent vehicle in addition to surface elements.
Instead of duplicating effort, we should focus on what we actually need to do Mars. Lander and transit hab.
Congress (or rather, those in Congress who make a stink about space exploration because it provides jobs in their districtrs) knows SLS/Orion aren't strictly required, knows they're very expensive (which is why they're supportive of them... more cost = more jobs in their district), what they want is to somehow cement SLS/Orion in place so their districts are guaranteed to receive funds for decades. That's really the whole issue, here. ...there's also a huge revolution going on in spaceflight. Truly affordable reusable vertical takeoff, vertical landing (VTVL) rocket technology is now scaling up to enormous size. You have SpaceX with reusable flyback boosters for Falcon 9 and Heavy, plus Blue Origin tooling up for their own VTVL orbital vehicle. ULA (who makes Atlas V and Delta IV) is developing orbital refueling technology with Vulcan, which is hugely enabling. And we're just getting started. SpaceX has plans for an enormous reusable launch vehicle also using methane/LOx technology and intends to send people in 2025 (perhaps using Falcon Heavy and a Raptor-based lander, perhaps using the enormous vehicle). This is far earlier than any NASA plan could possibly hope for given its budget and Co
I should point out, I'm all for going to Mars! The scenario you lay out is exactly what I'd imagine it would go. A bunch of prebuilt habs along with a bunch of inflatable habs would be sent first. Along with all the machinery to start extracting O2 and methane out of the mostly CO2 atmosphere. I could imagine robots that would do nothing but basically stripmine the ice and then using solar and/or RTG's melt the ice, fliter the water and then store it in large tanks.
Then you drop in a small crew of people with lots of spare food and parts whose job it is to get the farming habitats up and running and producing food. Once you've got a good store of food going, then you start dropping more habitats or even better, you start looking around at the materials on mars and start building your own.
Imagine of each group of "settlers" basically came with their own habitat that the'd connect (or not!) to some network of habitats.
To our point about the Moon, I almost think it makes more sense to go there as well... It's a much harsher environment, so technologies we sort out on the moon are going to transfer well to Mars. Also, only being three days away from Earth makes escape quite viable.
Yes Francis, the world has gone crazy.
Don't get your hopes up for gardens ;) Don't get me wrong, the first mission will surely involve plants. But they'll be more along the lines of something with a cutsie acronym like MAPLE (MArs PLant Experiment) or the like. It'll be a little self-contained box the size of a beach ball with its own self-contained grow environment that raises enough lettuce for a salad or two and the occasional sprig of basil. And NASA will make sure to get about 50 press releases out of it.
You can't change that... by gettin' all... bendy.
We'll never have small nuclear reactors capable of propelling anything. Why, next thing you know someone is going to propose nuclear submarines!
False.
Go away.
Slashdot still doesnâ(TM)t support Unicode after it was added to the HTML standard in 1997.
Don't get me wrong, nuclear does have some interesting avenues open to it. I just don't see nuclear thermal as among them.
I'm actually a big fan of fission fragment propulsion; I think that's a rather clever concept. It's about as high specific impulse as one could possibly get out of fission, and much higher than that of most fusion concepts, the vast majority of which we can't build today. In fact, I can't recall any fusion concept that beats it, except for fusion-driven photonic propulsion. Fission fragment concepts proposed thusfar provide thrust levels not that much less than VASIMR, but ISPs of over 100k sec.
Further in the future, I've pondered the concept of using Jupiter as an antimatter factory. Jupiter corrals the highest density of high-energy particles in the solar system into broad belts. They're of course still far too low energies and densities for antimatter production, but with a large enough magnetic pinch feeding it, I wouldn't be surprised if a realistic system could be designed to produce high flux beams in the dozens to hundreds of GeV energies required over a good-sized target (note: I haven't attempted to simulate this!). If you can get nature to provide your ion beam for you - a large/intense enough of one - then the concept of using antimatter as fuel could potentially become plausible. Here on Earth, the energy required to generate such beams renders antimatter implausible for direct spacecraft propulsion.
You can't change that... by gettin' all... bendy.
You don't need it to be delivered all that quickly, but you do need it to happen within some timeframe. (Important would be that you need to break orbit around the Earth and achieve your orbit to Mars within the same orbit around Earth, or you'll end up having to sped a whole lot more delta-v for the transfer. You can raise the orbit around Earth with a few different burns, so to minimize the delta-v needed for that final burn, but that burn is critical.) If you want to send a ship with a decent mass - like that you need for a manned mission, with habitation space and life support - than you need to have enough thrust to do so.
You typically want the highest ISP with enough thrust to do the job. The middle-ground engines can be useful sometimes then, for places where you need more thrust, but don't need the full lifting thrust of chemical rockets. We haven't done much in that space, as robotic probes can be an order of magnitude or more less massive, and therefore the VASIMR engines and other extremely-high ISPs can give enough thrust.
'Sensible' is a curse word.
Yeah, because nuclear thermal propulsion is SOOO science fiction and entirely impossible. No wait, it's just using a big box of heat to turn a liquid into an expanding gas, which you then eject out of a rocket nozzle. This, of course, has the advantage of rather simple, and massively cutting down the weight of what you're taking with you, because you're not bringing along several tons of chemical oxidizer so that you can use your traditional rocket for something besides mass. And it was already prototyped in the 1960s.
Slashdot still doesnâ(TM)t support Unicode after it was added to the HTML standard in 1997.
I can't wait to see the development budget on the world's first "no maintenance extraterrestrial stripmining robot fleet". Given that probes like Curiosity that slowly roll around making observations cost billions of USD.
And the budget for the prep missions that would be required to gather the data needed in the development of such robots.
Also: don't get your hopes up for Mars farms on early missions. Seriously. Farms that provide relevant food outputs to keep people alive are big even on Earth. Light is much scarcer on Mars, even when dust storms aren't blotting it out for weeks at a time. Anything "big" costs obscene amounts of money when you're talking about Mars. You can reduce the cost somewhat (although hardly as much as you'd want) by going with reduced-pressure greenhouses; plants can grow, with difficulty, at significantly lower pressures than humans can survive. But then you have to do all tending and harvesting while bungling around in a pressure suit, which hardly sounds like an efficient use of calories. You could instead credit a "large nuclear powered robot gardening fleet" to doing the harvesting for you... but wait until you see the price tag on that one. Also, wait until you see the amount of power it takes to supplemental-light and heat greenhouses sufficient to feed a colony. And the budget it would take to develop and deploy solar concentrators / nuclear reactors + lights to prove that.
Lets keep our expectations realistic. The first mission to Mars is not going to be growing crops and smelting steel out of regolith. Their water and fuel production rates are going to be the bare minimum trickle required to meet their needs and fuel their return vehicles. And even that won't be easy. We've been struggling for decades to find the budget for even a mission like that.
You can't change that... by gettin' all... bendy.
Actually, we've been using nuclear devices in space for years. How do you think Watney heated his rover?
The Moore-Murphy Law: The number of things that will go wrong will double every 2 years.
Nuclear would be much more feasible, no worries about long term health effects and less shielding, weight, propellant, and costs.
I would speculate that airing nuclear propulsion is precisely a way to get assistance with costs. If there is a tiny chance that it can have future military application, funding is much easier to attain. If nuclear space propulsion makes it easier or quicker to launch missiles at a future Chinese moon/Mars/Mercury base or even launch a missile from space towards an Earth target, it buys the votes of the large group of Jingoists in congress.
Things like finding out how rocks formed so we can know more about the formation of the solar system, not so much. When congress wants bang for the buck, the key word is bang.
There's a little bit of a difference between thermal decay generators and nuclear propulsion. All deep space probes have an RTG, solar panels don't work when you're far from the sun. Even with the RTGs there's been concern about what to do if there's a launch accident. But direct nuclear propulsion is inherently dirty--in Project Pluto it was actually considered a feature that in addition to dropping nukes the platform could just be flown around irradiating the target. AFAIK nuclear propulsion is only envisioned for extra-atmospheric use, but even getting the fuel up there is a tricky question if every launch runs a risk of dirty bombing a launch facility.
There's a little bit of a difference between thermal decay generators and nuclear propulsion.
RTG's are not the only nuclear power sources -- look up RORSAT and the BES-5 reactor.
VASIMR can provide more than sufficient thrust for a quick Mars journey, so long as you have a good-sized power source to pair to it.
There's no point to a rocket that exhausts its fuel in a few minutes or even hours when you're talking about a journey that even on a fast route will take many weeks to complete.
You can't change that... by gettin' all... bendy.
They built and tested at least one nuclear rocket design in the 1960s.
High ISP but heavy. Useless for an ICBM.
Play some KSP, you'll understand.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
While the Outer Space Treaty of 1967 does specifically ban nuclear WEAPONS in Article IV, as mentioned elsewhere, nuclear power, either as a power source or propulsion source is not banned.
This could become interesting if someone built an ORION-drive spacecraft. Even so, calling the bombs in question "impulse devices" would technically make them allowable under the Outer Space Treaty. . .
Yeah, it'd be great if we could just wish new physics into being.
Might as well wish for wormholes or teleportation.
In reality, we need rockets. And chemical rockets actually work just fine. Nuclear-thermal would cost about as much as SLS, and wouldn't even be that useful, it'd just be a nice in-space stage. Reusable launch tech (which we're getting thanks to SpaceX, Blue Origin, Masten Space Systems, and others) gets you cheap launch which makes a nuclear-thermal stage an unnecessary frivolity. Nuclear-thermal rockets tend to be much lower thrust than chemical rockets, too, so you don't get as full advantage of the Oberth effect without multiple passes through the Van Allen belts. Not as low thrust as electric propulsion (which has MUCH higher Isp than nuclear-thermal, so still pays for itself), but still bad compared to chemical rockets. You gain a little lower launch mass, but still not as good as electric propulsion can do.
Cheap launch with in-orbit refueling, high mass fraction chemical stages (like ULA's Centaur or ACES), aerocapture, and ISRU are ultimately much, much better than nuclear-thermal with it's deeply cryogenic (i.e. very high boil-off) liquid hydrogen and low-thrust-to-weight ratio and enormous, heavy tanks for that liquid hydrogen. Also, methane/oxygen is a LOT easier to produce on Mars (or even the Moon) than the same amount of liquid hydrogen. For the same amount of water, you can produce fully TWENTY times as much stoichiometric methane/oxygen for a chemical rocket as you can liquid hydrogen for a nuclear thermal rocket.
Electric propulsion (using either solar or nuclear for electricity production--solar is higher performing in the inner solar system and nuclear-electric is higher performing in the outer solar system) is close to constant-acceleration. Solar-electric especially would be a good choice for Mars transport (at very least for cargo), and improving solar technology (mainly producing lighter weight solar panels) can allow continual improvement in the amount of acceleration you can achieve. But chemical propulsion would work just about as well, though would require more mass (but if mass is cheap, who cares?).
Or they might use an improbability machine. Maybe, or an inertialess drive, or maybe -
sigh. another maybe article.
Useless for an ICBM.
I don't think anyone has suggested ICBM. IPBM, on the other hand....
but abysmal thrust to weight ratio, depending on what numbers you look at, somewhere between 0,2:1 and 0,5:1 wet
To go to Mars from LEO, you need about a 3600m/s impulse. At an Earth TWR of 0.2:1 (or more properly expressed, an acceleration of ~2m/s^2), you're looking at around a 30 minute burn. Hardly anything unusual. Upper stage boosters routinely use these kinds of accelerations.
Now on to the VASIMR claim. VASIMR exists insofar as a essentially a baby size version of it. Like the VX-200, a 200kW system, capable of, hold on to your seats, a whopping 5N of thrust! Wonderful! Now I'm sure you know of a simple and sufficiently light-weight electrical system capable of delivering several hundred MW into a spacecraft, but unfortunately, NASA doesn't, short of putting a crazy complicated and delicate nuclear power reactor on board. So it's gonna be nuclear power either way. Only question is: how complicated would you like your mission-critical propulsion unit to be?
I am typically first in line to balk at mysterious propulsion systems that are claimed to work while violating our current understanding of physics. We have them by the truckload and they are bullshit.
But wait...
Back in 2001 a small satellite propulsion research company was investigating different techniques involving electric engines. That in itself is nothing spectacular. For whatever reason, they developed and tested a closed cavity microwave drive. I do not now the story of why they did such a thing, since it would not be viable under the law of conservation of momentum. But their data showed otherwise. When the announcement hit the conspiracy theory world, I remember debating the matter with my conspiracy theory friends, citing said law as proof the data is wrong or outright faked.
Over the years scientists here and there have got wind of the original research, built the device, achieved similar results, wrote a paper and moved on. More recently NASA, or at least a propulsion research group at NASA has been messing with it. Despite not knowing how the thing works fundamentally, they have been able to make modifications that have brought it to a level of viability and foresee being able to increase it's thrust even greater. Pretty much the final argument against data showing it works was the proposal that thermal currents accounted for the extra energy. So it was tested in a hard vacuum. Still works.
If you have never heard it, NASA has a very in depth article on it here: Evaluating NASA’s Futuristic EM Drive
I highly suggest reading the whole thing. As it currently appears, it could be used, right now, to dramatically reduce the cost and time involved in getting humans to Mars. My brain is fighting itself on this. First, it appears it should not work. Second, should we use a highly effective space propulsion system without knowing how it works?
Brought to you by Carl's Junior.
Nuclear pulse engines are much more fun!
As we still don't know how it works, no one knows how to scale it up to use it to push something big. Currently it doesn't have enough force for something the size of a snowblower to push a pencil across the desk.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
And yet, once nudged out of Earth's gravity, and being that it would be in a vacuum, that is a fantastic amount of continuous thrust.
Brought to you by Carl's Junior.
I'm sorry, but were you under the bizarre impression that anyone in this thread was saying that the burn time on NERVA would be too long to be useful? And if so, why?
And with the 620kg full system mass, plus 170kg propellant at 5000 ISP, the system could accelerate a 1605kg payload to 3600m/s in a 20 day period. For a matching reactor, we could use RAPID-L for estimates of what the mass would be - 670kg for 200kWe (space-based reactors have been made before - the Soviets used them heavily - but they're all old and obsolete now). Hence simply strapping 10-20 of them together and the corresponding reactors as-is would accelerate a 9,35 to 18,7 tonne payload in that time period. Of course, if you engineer a larger VASIMR and a larger reactor rather than many small ones, as is the general rule, you'll get a better mass ratio.
You're going to Mars. There's no point to trying to keep your burn down to 30 minutes.
You can't change that... by gettin' all... bendy.
You do realize that there have been RTGs that reentered, and even ones involved in launch accidents where the rockets broke up explosively. You know what happened? They bounced.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
What always made me wonder about that in the book and movie was why he didn't use the RTG to also charge the batteries. It wasn't big enough to power the rover, but would have provided a good amount of baseload power for the rover.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
I'm not sure what they have to do with deep space probes or with nuclear propulsion (they were used for electrical generation just like RTGs, but at a much higher power output and with much greater weight.) But yes, they do exist and are a good example of why there's so much skepticism about nuclear power in LEO.
Maybe, maybe not. The EM drive which the comment references had so little thrust it was difficult to measure it from a device using a ton of power and that was quite large and heavy. The Star Trek style Alacumbre drive in the link is still only theoretical, and unlikely to be within our power budget for centuries.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
And there have been other failures in space based nuclear programs which have caused detectable leaks. The RTGs themselves are pretty safe, but that's because they have a pretty small amount of material (and generate very little power). Reiterating the point a couple of posts up, yes, there are current systems using RTGs--but that says pretty much nothing about the safety of, or tolerance for, nuclear propulsion.
A drive that has had full size test units built is hardly theoretical. It is a nuclear reactor with an open cooling loop. The water (or other liquid) is run over the reactor which causes it to turn into a gas which is allowed to exit the rear of the ship. This isn't a terribly hard concept to get, it is actually quite easy to understand. It isn't some fictional warp drive.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
Yeah, I wondered the same thing. After all it's a freakin' electrical generator.
The Moore-Murphy Law: The number of things that will go wrong will double every 2 years.
Those were really interesting points. I was actually thinking of a fission fragment rocket or stuff like nuclear electric.
They have a more or less working technology to bring astronauts in 6-7 month to Mars and not a budget to fund it, and now they propose using a technology which has not been implemented and used? Interesting, I thought the wanted to go 2030+ and have not enough funding. How is developing a new technology cheaper? Yes I saw there is an article on the principle here https://en.wikipedia.org/wiki/... and yes it is not the crazy nuke drive which would not work reliable.
I know that. Still from a working propulsion technology to Mars is much easier than creating a new device and using that.
anyone in this thread was saying that the burn time on NERVA would be too long
Yes, that would be you and I quote:
NERVA did have problems ... abysmal thrust to weight ratio
So make up your mind. Is it a problem, or is it not a problem? Also, don't shift the goal post by tacking on qualifiers like "to be useful". You didn't say that originally. You said it's a problem. I showed you it isn't. TWR of 0.2 on an orbital booster is a non-issue.
And with the 620kg full system mass, plus 170kg propellant at 5000 ISP, the system could accelerate a 1605kg payload to 3600m/s in a 20 day period.
I think you may have forgotten to carry a one somewhere. 2400 kg at 5N of thrust gives .0002 m/s^2 of acceleration. So not 20 days, but 200 days! And even if you weren't off by one order of magnitude, even a 20 day burn is no longer a classical Hohmann transfer from down low near the Earth (for maximum Oberth-effect awesomeness), so the delta-V requirements go up tremendously (probably around double). So using the correct acceleration, you're looking at over a year-long burn. THAT'S why even the VASIMR creators envision nuclear-powered spacecraft using VASIMR for interplanetary travel.
Glad to see you at least know the rocket equation.
Scrap that latter point about a 200 day burn, I shouldn't be doing math at 12 at night.
Thermocouples are really inefficient. From the book: 1500 W of total energy from the RTG. 1400 W of it gets radiated as heat, 100 W is produced as electricity. The rover had (IIRC) 14000 Wh - 14 KWh - of capacity in each battery. You could charge that off the RTG, sure, but only if you gave it 140 hours (approximately six days) per battery. I think he did actually plug it into the system - got a few percent more range that way - but it was the difference beteen depleting the battery in 4.5 hours and in 4.7 hours or something similarly inconsequential.
On the other hand, the fact that the RTG mostly produces heat is really useful, because it meant he didn't have to sacrifice a bunch of the rover's range running its own heaters. 1400 W of heat would drain one of the rover's batteries in 10 hours (electricity converts very directly to heat; it's the reverse that's hard) even if it wasn't used for propulsion at all. That was actually more heat than the rover was designed for; he had to remove some insulation.
There's no place I could be, since I've found Serenity...
Are you speaking a language other than English here? How on Earth are you reading "abysmal thrust to weight ratio" as "unreasonably long burn time"?
An abysmal thrust to weight ratio means that you can't use it as an ascent stage. Not "it takes an unreasonably long time to burn". Seriously, how could you possibly think I was saying NERVA takes too long to burn while recommending VASIMR, and saying that NERVA fits in between chemical rockets and VASIMR?
No, you shouldn't.
You can't change that... by gettin' all... bendy.
An impulse system using pellets of uranium or plutonium would be far more realizable than a fusion system. Electron or ion beam systems the size of a dishwasher can achieve pellet compression sufficient to reach critical density for fission. We could have a vehicle that could take off from the Earth's surface, go to the moon, and return with a soft landing. Only problem: lots of radiation emitted into the atmosphere, so such a system would have to be beyond Earth orbit. But it would be ideal for Earth/Moon and Earth/Mars.
Are you speaking a language other than English here? How on Earth are you reading "abysmal thrust to weight ratio" as "unreasonably long burn time"?
Then you shouldn't have said it's a problem. Honestly, quit weaseling. NERVA's TWR wasn't a problem. Period. There were plenty of other problems, but TWR wasn't one of them.
There are already a large number of abandoned reactors in space, shitty old fission ones that are due to fall back to Earth in about 10,000 years from now.
About 20 years from now nanotechnology, 3D fabrication systems, AI and fusion power will be very far ahead of what we have now so the plan seems viable except for one little detail, why would we need to send humans at all?
You know what? A solar thermal rocket could work as well as any electric thruster, be even slightly more efficient than a nuclear thermal rocket, it doesn't require tremendous R&D money the way that space-based nuclear power does, and we know how it actually works.
Ezekiel 23:20
The funny thing is, I distinctly recall that providing additional power to the rover was exactly what he did with it (beyond heating with it). Not sure about the movie now.
Ezekiel 23:20
Now I'm sure you know of a simple and sufficiently light-weight electrical system capable of delivering several hundred MW into a spacecraft, but unfortunately, NASA doesn't, short of putting a crazy complicated and delicate nuclear power reactor on board.
Space-based solar is currently somewhere around one tonne per those 200 kW you'd need for a VX-200. Projected to improve further still.
Ezekiel 23:20
So apparently I'm to blame for your lack of ability to read English? Wow.
You can't change that... by gettin' all... bendy.
Neat, rather than admit you were wrong, you go with insults. I'm going to stoop to your level.
So if NERVA's TWR wasn't a problem, why did you say it was? What's the nature of that problem? Just to illustrate, VASIMR's incredibly low thrust is a significant issue, insofar as it's not really conducive to escape burns. Ideally, main propulsion rocket engines need to provide a short, intense impulse. Not a long, gentle nudge. Even a 20 day burn means you're going to be spiraling out, not burning out, giving much worse delta-V (and consequently lengthening the burn).
Moreover, the proposed nuclear power reactors you describe are merely concepts at this point. No real hardware. By contrast, NERVA was effectively mission-ready in the 70s. It's easy for you to be handwavy that "it'll get resolved somehow", but unfortunately, there's a fairly big step between "concept study" and "mission ready hardware".
Sources? A single 32kW solar array assembly on the ISS weighs around 16t. I hope you won't try to claim that designers weren't motivated to make it as lightweight as possible, given that the ISS experiences no accelerations of any kind.
Which of the following words:
"Abysmal"?
"An"?
"As"?
"Ascent"?
"Burn"?
"Can't"?
"It"?
"Long"?
"Means"?
"Not"?
"Ratio"?
"Stage"?
"Takes"?
"Time"?
"That"?
"Thrust"?
"To"?
"Unreasonably"?
"Use"?
"Weight"?
"You"?
Please help me out here because I'm not sure what part of that has been flying over your head.
Nope.
Dozens of them have been launched over the years.
Nope.
Got that? That's from an overall rather fawning report from proponents of resurrecting NERVA at NASA; even they aren't pretending that these were flight engines. It was simply an engine feasibility demonstration program. It wasn't flight hardware. And all of that is just concerning the engine. An engine is not a stage in and of itself. And even when you have a stage, it's not proven until running flight success (as the soviets saw with the N1). And even if it had been a full, tested flight stage, it'd be no more resurrectable than Apollo. Like with Apollo, most of the individual hardware components components and systems used in the manufacture no longer exist.
(In case you're curious why there's that talk of small-scale scrubbers as if their development was an afterthought... it was! Partway through development they were hit with a new enviro
You can't change that... by gettin' all... bendy.
Sources?
ATK MegaFlex, for example.
I hope you won't try to claim that designers weren't motivated to make it as lightweight as possible, given that the ISS experiences no accelerations of any kind.
I could, but I won't, since that argument doesn't make sense, for two reasons. First, if you make it heavy, it will have to support its own weight under small accelerations. If you make it lightweight, it will have to support its own weight under small accelerations as well. Either way, any of the two would work (since the forces are never that high regardless of what design and materials you use), so no clear weight preference comes from this consideration. Second, because your argument actually works exactly the other way round: you could make it as heavyweight as possible, given the low loads on the ISS, but if high loads are expected, a more lightweight design (not needed for the ISS) will work better than a heavyweight one (ATK's arrays are an example of that). So where the load-induced limitations are present, it's lightweight designs, not the heavyweight ones, that are favored. You got it the wrong way.
The real motivation to make it reasonably lightweight (for its time) most likely came from the need to lift it into orbit, preferably with an appreciable amout of other useful cargo on the Shuttle. That costs money. Having said that, waiting many years for newer designs costs money, too, so they used what they could use at that time. Shuttle flight delays had already made the ISS more expensive by that point in time anyway, so waiting for newer panels instead for launching the existing heavy ones would have been a financial disaster.
Ezekiel 23:20
NERVA did have problems. Good ISP (~850 sec), but abysmal thrust to weight ratio
YOU said one of its problems was TWR. Now you're changing the claim by tacking on the "too long to be useful" qualifier. I'm not going to let you get away with that. Quit ducking and dodging. YOU said it's a problem. I showed you it's not a problem.
Nope [discovery.com].
Are you seriously going to quote a news article interviewing the rocket engine's creator as a source worthy of detailed analysis? Containing gems such as:
A journey from Earth to Mars could in the future take just 39 days — cutting current travel time nearly six times — according to a rocket scientist who has the ear of the U.S. space agency.
Oh hold on to your hats! It *could* take just 39 days? That's practically ready to fly!
Dozens of them have been launched over the years.
I was talking about the concept 200kWe reactor you mentioned. I know TOPAZ were flown, but those were few-kW units. I also kinda doubt the amount of red tape there would be much different to NERVA (high-enriched Uranium either way, so the greenies are gonna go crazy), but I don't really care about it from a technical analysis POV.
And even if it had been a full, tested flight stage, it'd be no more resurrectable than Apollo. Like with Apollo, most of the individual hardware components components and systems used in the manufacture no longer exist.
I should have been more clear. NERVA wasn't flight-ready. It was mission-ready, in that the system had been tested at full scale and that a detailed plan existed to construct one. Your point on the ressurectability, I will happily yield. Unfortunately, with the state of society today, it might well be very difficult to build a flight-ready engine, as you correctly noted in the environmental concerns.
The rest of your points, I have no problem with. My original contention was simply with you saying that NERVA didn't have the TWR. It did and was pretty straightforward to complete (it was considered for the Apollo upper stage). The real technical killers for a Mars mission, in my mind, are:
a) the environmental regs today make large-scale reactor development pretty difficult
b) the propellant was awful. LH2 is a bitch to work with. For deep-space missions requiring deep-space maneuvers, it's essentially a non-starter.
The state of the art in space solar today is 200W/kg
Source to flight-ready hardware please. I don't buy that the ISS has a very inefficient array.
Overall, I like VASIMR better than NERVA as a future prospect, especially when coupled to a high-power source. But that development is very much in the not-so-near future. If we want to get people to Mars within a decade, it's either biting the bullet and building a flight-ready NERVA or chemical and of the two, the latter seems more doable.
An abysmal thrust to weight ratio means that you can't use it as an ascent stage
That's not true either. You can't use it as a LIFT stage (i.e. low-atmosphere). But you can certainly use it for ascent (upper atmosphere, circularization) and escape (the aforementioned 3.6km/s). TWR of Delta Cryogenic Second Stage, gross ~30t /w ~20t payload = ~50t. RL-10B thrust is ~11t Earth equivalent, so Earth TWR is 0.22:1. Yes, the burns are long (often over 15 minutes), but if you design your trajectory right, it's doable.
ATK MegaFlex, for example [orbitalatk.com].
Interesting stuff, thanks! However, these are just the solar panels themselves. Not the rest of the on-board components needed to support them. The radiators, the electrical equipment, etc. My guess is, when all is said and done, it'll be a lot more than the manufacturer-quoted 150W/kg figure for just the panels themselves (as they themselves claim only 1/3 mass/W compared to rigid solar panels, not 1/100).
You got it the wrong way.
I think you may be misunderstanding what I'm talking about. It's not "heavy" vs "light", it's "highly loaded components" vs "lightly loaded components". A massive design has lower component loading, simply because there's more material to carry the stress. That's why we build bridges out of thick steel girders, not sheet metal. Of course, as long as the component's structural limits aren't exceeded, making it heavier doesn't help.
Interesting stuff, thanks! However, these are just the solar panels themselves. Not the rest of the on-board components needed to support them. The radiators, the electrical equipment, etc. My guess is, when all is said and done, it'll be a lot more than the manufacturer-quoted 150W/kg figure for just the panels themselves (as they themselves claim only 1/3 mass/W compared to rigid solar panels, not 1/100).
I'm not sure what you mean by that. Radiators are not for the panels, they're for the ISS coolants. You're conjuring up needlessly pessimistic figures without any justification for them (also called "shit-talking" by some). The 100+ W/kg figure/200 kW/kg for some cell configurations is real, why do you think the ARRM mission is going to use ~50 kW of these panels? Do you think NASA doesn't know how much their own stuff weighs? In a 2013 concept paper, NASA expects a maximum of 3950 kg of dry total weight for a spacecraft with 50 kW of solar panels, how does that compute to you? And that's including the spacecraft structure, engines, large fuel tanks, the capturing equipment, and all the other stuff besides solar panels.
A massive design has lower component loading, simply because there's more material to carry the stress. That's why we build bridges out of thick steel girders, not sheet metal.
But a bridge carries vehicles, whereas the panel assembly only carries itself. Load bearing is not its primary purpose. And given a certain acceleration, the more lightweight design carries a proportionally smaller load.
Ezekiel 23:20
Radiators are not for the panels, they're for the ISS coolants
You're gonna get heating in the panels, the electrical equipment, etc. Those need cooling. Hence the rads. I'll admit, it's not going to be very much, but it's there.
NASA expects a maximum of 3950 kg of dry total weight for a spacecraft with 50 kW of solar panels
That seems a lot more realistic. It's kinda difficult to split the difference here between what of that are necessary because of the panels and how much of it is the spacecraft without a more detailed analysis. Still, even this kind of spacecraft, without any payload or fuel, using electric thrusters would need around 1/2 year of acceleration to get to escape velocity. That's why I think it'll take a lot more dense power source to make it viable for human flight. Now if you could place a 0.5 MW power source in that footprint it starts to become practical for human travel.
You're gonna get heating in the panels, the electrical equipment, etc. Those need cooling.
The panels are perfectly happy with re-radiating any heat they are receiving. The Stefan-Boltzman equilibrium for bifacial re-radiation of 1000 W/m^2 of incident heat is three hundred Kelvins. Slightly more if the cell side is suboptimal, emissivity-wise. Slightly less if 30%-efficient cells are used, and/or beyond 1AU.
That seems a lot more realistic.
"Seems a lot more realistic"? It's perfectly in line with what I quoted. The panels will weigh something like 500 kg, or somewhat more or less than that, depending on configuration.
Still, even this kind of spacecraft, without any payload or fuel, using electric thrusters would need around 1/2 year of acceleration to get to escape velocity.
And? You wouldn't use that for reaching escape velocity. You'd most likely use a hydrolox tug for that. It's the most obvious option. At least until some kind of orbital boosting stations gets built, which is a long-term prospect, though.
Ezekiel 23:20
The panels are perfectly happy with re-radiating any heat they are receiving.
Well argued, point taken on the rads.
It's perfectly in line with what I quoted.
It's half of what you quoted.
You wouldn't use that for reaching escape velocity. You'd most likely use a hydrolox tug for that.
The Hohmann transfer delta-V breakdown is about 3.2 km/s for Earth escape and about 0.4 km/s for Mars transfer. So you'd have already spent around 90% of the delta-V using hydrolox. Why not spend the little bit extra and just do the whole escape burn in one go? Fewer systems, fewer components. And what about the journey back? From Mars, it's about 2/3 of the delta-V requirements to go to Mars (assuming direct re-entry and no capture attempt into Earth orbit), so again another 1/2 year burn to return.
Every time I see a "some jackass proposes Mars mission" post on /., I pop in, read the article, and close it in disgust when I see the clown didn't mention NERVA or thermal nuclear rockets. A nine month journey to Mars is simply not possible with our current level of technology - the life support mass alone would be nigh impossible to orbit, from both a technical and financial standpoint. A nuclear thermal rocket (such as the NERVA) offers a specific impulse of 850 or more, at least four times better than most conventional chemical rocket engines can manage. Moreover, it also provides enough raw thrust to perform important time-sensitive maneuvers (such as orbital insertion and circularizing) once it gets there, unlike an ion engine, and scales up to a human-sized craft quite well. A NERVA engine gives you a transit measured in weeks, not months. It's basically a prerequisite for any serious Mars mission - especially in the timeframes being discussed, because it's the only one that's had actual R&D work done on it before and reached the prototype stage.
It is extremely satisfying to be vindicated by NASA itself - clearly, they can add as well as I can, and came to the same conclusion, as evidenced by this exciting news that they are actually continuing development of thermal nuclear propulsion.
We will need one of those Antimatter / Positronic / Dilithium Generators. That will be the only thing that will get us up to warp speed and finally allow us to traverse the Multiverse.
Paul E. Bahre
It's half of what you quoted.
The panels in question don't have a single fixed power-to-weight ratio, it depends on the size of the array and the type of cells chosen. I've gone for the lower end in that estimate, just to be sure.
The Hohmann transfer delta-V breakdown is about 3.2 km/s for Earth escape and about 0.4 km/s for Mars transfer. So you'd have already spent around 90% of the delta-V using hydrolox. Why not spend the little bit extra and just do the whole escape burn in one go?
An escape tug can be reused between any interplanetary missions for GTO and cislunar traffic. It would lower the requirements for the interplanetary craft while simultaneously sharing common in-space infrastructure with other projects (heavy satellite tugging, lunar traffic etc.). But if you want to escape from cislunar space using electric propulsion, you could always start from one of the Lagrange points, for example. Or from a high Earth orbit.
Ezekiel 23:20
An escape tug can be reused between any interplanetary missions for GTO and cislunar traffic. It would lower the requirements for the interplanetary craft while simultaneously sharing common in-space infrastructure with other projects (heavy satellite tugging, lunar traffic etc.).
Let me be clear. I like the idea, but you're describing infrastructure that's just way outside of practicality right now. In 20-30 years? Maybe. But in the next decade. Highly unlikely.
But if you want to escape from cislunar space using electric propulsion, you could always start from one of the Lagrange points, for example. Or from a high Earth orbit.
But that's the crucial bit. Getting to any Lagrange point or high Earth orbit is the costly bit. LEO to GTO is 2.5 km/s. And it's another 0.7 km/s to the Moon's orbital radius and that's only at apogee. To circularize at GEO is more than a simple escape & Mars transfer together - that's the power of the Oberth effect. Using the slow spiral-out method, you can almost double the delta-V requirements. That's why even Ad Astra says on their website that for practical human spaceflight, you'd need a nuclear reactor.
Does Ad Astra say how you make a nuclear reactor more lightweight and reliable than modern or even future solar panels? Frankly, I don't consider their stuff vital anymore. For smaller applications, it's eclipsed with magnetically shielded hall thrusters; for higher trust applications, there's the very viable solar thermal rocket concept, also applicable for delivering water from asteroids all over the inner solar system. Also, yes, the tugs are an idea for the distant future, but so are regular Mars trips, so there's that. But there's already been some interesting studies with regards to making Mars trips much more viable with conventional tech and some clever engineering.
Ezekiel 23:20