Nuclear Thermal Propulsion

crix · Jul 4, 2006

ARES!! <img src="/images/icons/smile.gif" /> There's no "i"! I just found Mars DRM 4.0 using bimodal NTR propulsion. http://www.grc.nasa.gov/WWW/TurbineSeal/papers/2003/15Borowski.pdf Pretty neat. The artificial gravity idea doesn't look overly complicated and would help the crew a lot on their 7 month journey (even WITH NTR!). How would electricity be generated on a chemically propelled craft? Bimodal NTR would provide a ton of juice when the engine isn't firing. CalliEdit: This discussion started inside of the Multiple Ares V launches for on-orbit/surface assembly but grew too big for that thread. I have split it off and changed the title of the intial post to "Nuclear Thermal Propulsion".

barrykirk · Jul 4, 2006

Oops sorry about that. It is ARES.

JonClarke · Jul 4, 2006

There is even a "5.0" floating about somewhere! After 3.0 though the ideas moved off into different studies and no longer had the conherence of the original DRM. This tendenct is visible in the end of the 3.0 report which scope some alternative options also (nuclear and solar electric, inflatables). The problem with spin gravity is that it opens up a whole range of unexplored engineering and medical issues. Having it as a "must have" increases the development overhead for a Mars mission. The study assumes that this technology is simple and can be either developed cheaply or is already available. On Borowski et al's studies nuclear studies, the same is true. There are some very optomistic assumptions. It assumes as a baseline that a 950 Isp NTR is possible, that you can light up your NTR in LEO (400 km I think), and that NTRs can be clustered safely (earlier DRMs did this too). Some options discussed by Borowski et al. also assume that LH2 can be stored for years and that multiple NTR restarts over that period are possible. With these assumptions the EDS stage mas is about 62% of what would be possible with a chemical stage. Apologies if these numbers (and following) are a bit out, I am logging in from a conference and away from my usual resources! The problem is that these are assumptions. There is nothing wrong with this, Every study has assumptions, but they may or may not be reasonable. Analysis of any study must include an examination of the assumptions. For example the best Isp from an operating NTR is, as I recall, 920, but from Russian designs of the 80's. This is very poorly documented in the open literature. We must take on faith the assumption that this can be upped to 950 and meet modern safey and reliability standards. Clustering lightly shielded NTRs is a nighmare, apparently, because of neutron cross-coupling. It is an assumption that is problem will be solved or deemed irrelevant. Realistically nobod <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

gunsandrockets · Jul 4, 2006

"We must take on faith the assumption that this [NTR] can be upped to 950 [ISP]" Towards the end of the NERVA program a fuel element of composite construction was tested at a temperature high enough for 900 ISP. And 900 is good enough. "...multiple NTR restarts over that period are [probably not] possible." The NERVA I engine requirement was for 825 ISP, capable of 1 hour continuous operation, 10 hours total operation and 60 restarts. Experimental test engines had achieved those milestones. "Clustering lightly shielded NTRs is a nighmare, apparently, because of neutron cross-coupling." Experiments of clustering engine reactors as close as six feet apart were conducted during the NERVA program. Cross-coupling proved insignificant and clustered operations trouble free. " Long term storage of LH2 in orbit is a yet to be developed technology." Not a problem for TMI, the most important job, since long term storage isn't an issue for TMI. And more importantly the only way chemical propulsion can get around the very same long term hydrogen storage problem is by suffering under the inferior ISP of a storable propellant substitute. "[NTR] meltdown from coolant loss" In the NERVA program a mistake during an endurance experiment allowed an engine to run out of coolant while the engine was running at full power. Even though the engine core was damaged from the loss of coolant, the engine did not melt down. "problem of a fission product laden exhaust." Not an issue in the vacuum of orbital flight. I just finished reading, "To the end of the solar system: the story of the nuclear rocket." Very interesting information contained there. I'll have to buy a copy of my own since the book I read was from my local public library.

JonClarke · Jul 7, 2006

Apologies for the slow response, I have been out of circulation for a few days. Towards the end of the NERVA program a fuel element of composite construction was tested at a temperature high enough for 900 ISP. And 900 is good enough. A fuel element is not an entire system. As an entire system no NERVA design ever got above 825, as far as I know. The RD-0410 reached 910, but that was a much smaller system (about 10% of the larger NERVAs). Plus we need to ask under what circumstances is an Isp of 900 good enough? Under what circumstances is it not? The NERVA I engine requirement was for 825 ISP, capable of 1 hour continuous operation, 10 hours total operation and 60 restarts. Experimental test engines had achieved those milestones. NERVA did demonstrate restarts, but this is only relevant for earth departure. It did not demonstrate restart after several years on standby. This has yet to be achieved. Experiments of clustering engine reactors as close as six feet apart were conducted during the NERVA program. Cross-coupling proved insignificant and clustered operations trouble free. I would question the parameters of these tests. For example did they conduct them under normal or abnormal conditions? There has been quite some discussion of NTR technology on the NASA spaceflight site with the consensus from the engineers and physicists that this was an issue in the event of a failure. It is also worth noting that the final NERVA configuration was three engines side by side, 10 m apart, with only the other pair – separated by 20 m and an inert engine fired up for the initial EDS “burn”. There were a number of reasons for this approach were several, but it certainly would have reduced the risk of cross coupling. Not a problem for TMI, the most important job, since long term storage isn't an issue for TMI. And more importantly the only way chemical propulsion c <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

JonClarke · Jul 7, 2006

The Kiwi TNT test. Tis is what happens when coolant is lost to an NTR. The incandescent fragments are bits of core. The cloud contains between 5 and 20% of the core mass. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

JonClarke · Jul 7, 2006

Mutter mutter mutter. Here goes again with a resized image. <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

gunsandrockets · Jul 8, 2006

"Do you have a more complete citation? I would like to add this [To the end of the solar system: the story of the nuclear rocket] to my “to read” list, thanks." You could have just googled the title. Here is the amazon link... click here I don't have time right now and go do a point by point refutation of your last post. Maybe Sunday. Though if you read the book you might save us both a lot of needless bickering. I've seen the discussion threads about NTR over at nasaspaceflight.com and of course many recent threads here at space.com. Which is why the book is such a revelation. Because many of the posters claiming authority at those threads I now know are ignorant of much of the actual history, a prime example being clustering. Those 'authorities' who post on the discussion boards would lead you to believe clustering is some great and mysterious danger, when in reality the issue was fully investigated and experimented with during the nuclear rocket program. And that is just a single example, hence my subject heading 'NTR myths', for myths they are. CalliEdit: Shortened link for better thread display.

gunsandrockets · Jul 8, 2006

"The Kiwi TNT test. Tis is what happens when coolant is lost to an NTR. The incandescent fragments are bits of core. The cloud contains between 5 and 20% of the core mass." Read the book. I don't have the book in front of me so I'm guessing from memory, but it looks like the incident you are refering to had nothing to do with 'loss of coolant' or any kind of 'meltdown'. This looks like one of the very early test failures which used an early (and incorrect) design for holding the fuel elements secure in the core. What happened was the core was flapping around inside the pressure vessal of the rocket thrust chamber when under the stress of engine operation. So entire individual fuel elements would work loose and get ejected bodily out of the engine. Despite such a catastrophic failure of the experimental engine the testers were able to maintain engine power and functional control at an amazingly stable level, demonstrating the remarkably benign failure mode of the nuclear rocket under the worst of circumstances. The engine did not blow up. The engine did not melt down. The engine just kept cranking out power as the core slowly dissasembled itself by blowing chunks out the exhaust. Compare that to the notoriously tricky behaviour of chemical rockets which have reputations for 'hard starts' (blowing up) during ignition, or fires and explosions from leaking propellant. As one scientist put it, chemical rocketry is an art wheras nuclear rocketry is a science.

JonClarke · Jul 8, 2006

Thank you for the citation, as asked. Since you obviously had the reference to hand, the hassle of search engines seemed superfluous. The loss of fission products and fuel to the exhaust during normal operations are not myths. The lack of containment during accidents is not a myth. Address these issues, with references and quotes from your book and you will advance the discussion. If you dismiss them without discussion you will not. However this is off the topic of the thread. Why don't you start a new thread and address the "myths" item by item? Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

JonClarke · Jul 8, 2006

You are confusing the Kiwi TNT test with one of the many excursions the Kiwis were prone to. Many of those resulted in the ejection of incandescent core fragments. Kiwi TNT was a deliberate destructive test. The 5-20% core vapourisation comes from the formal investigation. Silly statements about chemical rocketry being an art whereas nuclear rocketary in a science is exactly the reason why I do not trust proponents the proponents. they indicate an irrational level of advocacy and lack of connection with the bigger picture. Deal with the facts - fission product loss, lack of containment, core erosion (20% in 5 hours at the upper temperature regime according to one review in the 90's), the utter lack of containment - not rhetoric. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

gunsandrockets · Jul 9, 2006

"However this is off the topic of the thread. Why don't you start a new thread and address the "myths" item by item?" That's odd advice since you were the one on this thread who brought up the off-topic criticism of NTR propulsion in the first place. "Address these issues, with references and quotes from your book and you will advance the discussion. If you dismiss them without discussion you will not." As I already pointed out, I don't have the book. When I do I will be happy to use it. But I am not going to spoon feed you the book, you should read it for yourself.

gunsandrockets · Jul 9, 2006

"You are confusing the Kiwi TNT test with one of the many excursions the Kiwis were prone to. Many of those resulted in the ejection of incandescent core fragments. Kiwi TNT was a deliberate destructive test. The 5-20% core vapourisation comes from the formal investigation." Cite please. "Silly statements about chemical rocketry being an art whereas nuclear rocketary in a science is exactly the reason why I do not trust proponents the proponents. they indicate an irrational level of advocacy and lack of connection with the bigger picture." So what. Statements of fact and numerical reasoning can stand on their own merits no matter the personal interests of the source of information. But if you feel otherwise you can skip reading the book since the author, Dewar, is very much in favor of NTR. Pity, since the book has such great information.

gunsandrockets · Jul 9, 2006

"The Kiwi TNT test. Tis is what happens when coolant is lost to an NTR. The incandescent fragments are bits of core. The cloud contains between 5 and 20% of the core mass." Kiwi TNT is not what happens when a normally operating NTR accidentally loses coolant. It's what happens when an obsolete NTR is deliberately rigged to vaporize 20% of the core as part of an experiment to measure the contamination of the radiactive effluent. As explained in this link... http://www.gwu.edu/~nsarchiv/radiation/dir/mstreet/commeet/meet6/brief6/tab_l/br6l1k.txt

JonClarke · Jul 10, 2006

up to 20% core vapourisation during Kiwi TNT with 67% of the fission products released to the effluent cloud. http://www.gwu.edu/~nsarchiv/radiation/dir/mstreet/commeet/meet6/brief6/tab_l/br6l1k.txt Only 50% of the core was recovered inside a 7.62 km radius. The rest either vapourised (up to 15% in this source) or reduced to fine particles too small to recover. The largest fragment was part of the reactor vessel and weighed 67 kg. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19920005899_1992005899.pdf "Statements of fact and numerical reasoning can stand on their own merits no matter the personal interests of the source of information." Indeed. But saying that chemical rocketry is art and huclear rocketary is science is a stament that is factually wrong and mischievous in intent and therefore utterly without merit. "But if you feel otherwise you can skip reading the book since the author, Dewar, is very much in favor of NTR. Pity, since the book has such great information." What give you the idea I only read material I agree with? The facts speak for themselves, and a book can contain useful information even if the presnetation is incomplete and the interpretation flawed. Whether Dewar falls into this category is not something I can assess until I read the book. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

JonClarke · Jul 10, 2006

"Kiwi TNT is not what happens when a normally operating NTR accidentally loses coolant. It's what happens when an obsolete NTR is deliberately rigged to vaporize 20% of the core as part of an experiment to measure the contamination of the radiactive effluent." And in the process illustrates the consequences of a worst case catastophic failure. It's no good saying this won't happen in normal operation. It is the abnormal operations that make the messy accidents. It is this level of failure that must be containable if NTR technology is to be acceptable. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

gunsandrockets · Jul 16, 2006

Very interesting links. In fact what you characterize as a test of 'worst case accident' or a 'meltdown' from coolant loss and which you describe in near-apocalyptic terms is nothing of the sort. Your own links contradict you. Worst case accident? First off the Kiwi engine destroyed in the 1965 experiment was 4 times more powerfull than the NTR engines being considered today. Secondly the reactor was rigged to blow by modifying the control drums to move 100 times the normal rate so as to overload the reactor. Thirdly the experiment was not a test of possible engine failure or of coolant loss but an engine deliberately rigged to overload. And despite all this just how bad was the Kiwi "explosion"? About equal to 150 pounds of TNT. And how bad was the contamination? From the report..."Radiation effects from the cloud passage were less than predicted in the pretest safety evaluation report. The maximum off-site, integrated, whole-body exposure was 5.7 mrad about 15 miles from the test point." Some apocalypse.

gunsandrockets · Jul 16, 2006

Towards the end of the NERVA program a fuel element of composite construction was tested at a temperature high enough for 900 ISP. And 900 is good enough. "A fuel element is not an entire system. As an entire system no NERVA design ever got above 825, as far as I know. The RD-0410 reached 910, but that was a much smaller system (about 10% of the larger NERVAs)." The people doing the testing during NERVA were not idiots. Most of them worked for Los Alamos or Lawrence Livermore and developed scientific modeling to aid development as much as possible. It's one of the reasons the speed of nuclear rocket development exceeded all expectations and estimates. It isn't neccessary to build an all-up complete engine and fly it in space to know whether a new design fuel element can resist higher reactor temperatures and propellant erosion. That was the reason for the 'furnace reactor', for testing advanced fuel element design. "Plus we need to ask under what circumstances is an Isp of 900 good enough? Under what circumstances is it not?" Existing fuel element design showed performance high enough for 900 ISP. That is good enough to rebut the notion that 950 ISP is some ridiculous pie in the sky figure. The NERVA I engine requirement was for 825 ISP, capable of 1 hour continuous operation, 10 hours total operation and 60 restarts. Experimental test engines had achieved those milestones. "NERVA did demonstrate restarts, but this is only relevant for earth departure. It did not demonstrate restart after several years on standby. This has yet to be achieved." If an NTR uses ammonia for propellant, the challenges for successful restart after years in space are less than for any chemical engine including those using hypergolic propellant. An NTR can control it's thermal environment, unlike a cold chemical engine, and ammonia is much more easy to store than any oxidizer/fuel combination

CalliArcale · Jul 17, 2006

Let's please get back to the topic of "Multiple Ares V launches for on-orbit/surface assembly". Nuclear thermal rockets are a fascinating topic and really deserve a separate thread. BTW, if there is more interest in continuing this particular NTR discussion than starting a new one, I can break it off cleanly into its own thread; it looks like the off-topic discussion had kept itself neatly contained in a single subthread. Would that be desired? <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

gunsandrockets · Jul 17, 2006

I don't know what your powers of splitting can do. The NTR sub-thread started here... http://uplink.space.com/showthreaded.php?Cat=&Board=missions&Number=528794&page=0&view=collapsed&sb=5&o=0 My response to Jon Clarke's response was the first one with the subject heading changed to "NTR myths". So the NTR subthread is entangled in the original thread in terms of times of postings and subject headings of postings. I also note no-one has responded to the original thread subject for some time. So far I was the last one to post on it.

CalliArcale · Jul 17, 2006

My hope is that by splitting it, we can get the original discussion going again. Most people view the thread in "flat" mode, 10 posts per page, so they won't see the original discussion for several pages. I'll split off starting at crix's post. I know his post related to travel to Mars, but it didn't seem so specifically related to the topic of whether multiple Ares launches for a single mission would be feasible or beneficial, and is better kept with the NTR replies I think. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

gunsandrockets · Jul 17, 2006

Seems fine.

crossovermaniac · Jul 19, 2006

Electricity on a chemically proplelled craft would be solar panels. The power requirements are quite modest, solar panels are mature technology that is rapidly advancing in terms of mass, efficency and storage capability, and they are highly reliable and intrinsically redundant. And how far away from that big fusion engine in the sky can the 'highly reliable' and eco-friendly solar panels stray before going dead? And Heaven help the astronauts in the solar-powered Mars habitat designed by granola-munching hippies when the Martian weather goes bad and those global dust storms kick up? Or what about the hippy moon base and the two-week long night. What's that you say, you got batteries. I hope it's a lot because batteries are crap when it comes to energy density. That's why a car can go farther on a few gallons of gasoline than with several hundred pounds of batteries. And it's even worse on spaceships that have weight constraints. Not only that, but the panels have to be over twice as big to store electricity in the batteries during the time when power available. If nuclear power in space has problems, then solar-powered manned missions to Mars and the Moon is begging for one royal &%$#@! up.

nyarlathotep · Jul 19, 2006

Hear, Hear!

baktothemoon · Jul 19, 2006

NS, we need nuclear power in space. Go green, boil a treehugger.

Nuclear Thermal Propulsion

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