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Dave Ketchledge, Sunday, 11-20-11 November 21, 2011

Posted by The Space Show in Uncategorized.

Dave Ketchledge, Sunday, 11-20-11

“2033 The Nuclear Mission To Mars”


Guest:  Dave Ketchledge.  Topics:  Using nuclear power to do a humans to Mars mission.  You are invited to comment, ask questions, and discuss the Space Show program/guest(s) on the Space Show blog, https://thespaceshow.wordpress.com.  Comments, questions, and any discussion must be relevant and applicable to Space Show programming. Transcripts of Space Show programs are not permitted without prior written consent from The Space Show (even if for personal use) & are a violation of the Space Show copyright.  We welcomed back Dave Ketchledge to discuss his new book, “2033 The Nuclear Mission To Mars.”  The books is available in pdf format on a CD.  You can order the book from this website, http://rocketengineer.bravehost.com.  Later in the discussion Dave mentioned that the book can automatically download to a Nook e-reader and can be converted to be read on a Kindle.  We started our 2 hour plus discussion with Dave providing us with background as to why a humans to Mars mission was important, why we need heavy lift, SLS, and why nuclear propulsion was essential.  He shared reasons with us for going to Mars and talked about a Mars mission as being in our national interest.  We took listener phone calls asking for a clearer explanation of why we need to go to Mars.  One listener asked about the artistic side of the Mars flight, taking our focus away from technology and engineering. Terry wanted to know how many missions could be gleaned from a nuclear rocket and our guest spent considerable time going through the needed nuclear technology, providing us with a basic understanding of the technology, the risks, etc.  In fact, several times during the segment, Dave reiterated why a manned Mars mission was so vital to our nation & future. In our second segment, Dave continued taking us through the various chapters in his book and talked about radiation doses for people, space travel, NASA and more.  Fred, a space medicine radiation specialist, emailed in a note disagreeing with some of what Dave was saying about radiation doses.  Dave said Fred was partially correct, disagreeing with some of Fred’s comments. This exchange prompted Tim to call in objecting to negativity & naysayers such as Fred (in his opinion). I called Tim on this which caused me to do one of my notorious rants against la la land thinking & bad assumption making  I since apologized to Tim for my outburst, but strongly oppose la la land thinking & assuming valid disagreement to be the same as being negative, including assigning emotions to commonly used terms in science, medicine, and policy discussions such as “controversial.” Later in the segment, I asked Dave to explain the difference between nuclear electric and nuclear thermal propulsion.  Throughout the discussion, Dave advocated for the NERVA type  nuclear thermal engine.  He also explained the advantages re ISP via Pebble Bed technology.  As we neared the end of our discussion, Dave talked about the structure of his book, the references & data base along with the Orbiter freeware he has included with the CD.  At the end of our program, I asked Dave to give us a 5 minute talk were he to be invited to testify before Congress on nuclear propulsion & a manned mission to Mars.  I thought he did an excellent job in his off the top of his head 4.5 minute talk.  See what you think.  Post your comments/questions on blog URL above.  Dave’s email address is in the lower left hand corner of the above website used for ordering his book.



1. The Space Show - December 7, 2011

The following comment is from Dr. James Dewar. I have posted it to this blog with his permission.

Comments on David Ketchledge Interview on The Space Show, November 20, 2011

I was unable to hear your interview on The Space Show on November 20 and only found the time to listen to it in the last week. I would like to provide the following comments.

Manned Mars missions using a nuclear rocket have been around for as long as the Rover/NERVA program came into existence and that was from 1955-1973. Unfortunately, they have always been a poison pill; in the past, critics in the public, media, Executive branch and Congress have easily attacked and defeated such plans. My first book on the nuclear rocket, “To the End of the Solar System: The Story of the Nuclear Rocket,” tells this story and I hope you have had a chance to read it. It was a primary reason why the program was killed. Today I see no set of justifications for a new Manned Mars mission that could overcome those hostile to such a program, particularly when our fiscal and monetary structure is ready to collapse. Finding life on Mars, plus the technology/national interest arguments simply will not overcome the urgent need to find jobs for people here in the US as well as reduce the staggering national debt. In my opinion, national governmental missions such as Manned Mars are even deader now than they were fifty years ago. Our government is broke.

What prompts these calls for Manned Mars missions is what I call this “mission-itus” thinking and this itself derives from the chemical rocket experience whose missions are very expensive with payloads costing thousands of dollars per pound. Since most space shots are governmental, a mission must be developed first to provide the justification for spending public monies on it. The much smaller private space program faces a similar situation because of the extreme cost, so a market justification mission (e.g., a communications satellite) must be developed first to see if it is profitable. If so, then it goes forward.

All thinking posture derives ultimately from the rigidity of the rocket equations, the heart of which is where thrust is proportional to the square root of the temperature of the exhaust gas over its molecular weight. In short, it’s T/M. In less fancy terms, it means that 90% of the weight of a rocket sitting on the launch pad is fuel and oxidizer and the remaining 10% is the rocket’s structure, engines and payload, which is then less 2% of the rocket’s gross takeoff weight. This is ironclad and no amount of research and development can change it. In other words, the best you can get is rocket engines with specific impulses of 330 seconds for solids and 450 seconds for LOX/LH2. T/M forbid it from going higher with chemicals except if you use some exotic and dangerous propellants. And even here the gain is not that much. Maybe 50 seconds of specific impulse.

The nuclear rocket changes this, as you noted it would have an ISP of 1000 seconds. In other words, it changes T/M. M is now 2 since only hydrogen is used instead of 18 for LH2/LOX while T is unlimited in theory – the temperature of the sun. However, in practice it is limited by the materials/procedures to hold the fissioning uranium. This new technology requires a new thought posture to handle it and take advantage of it properly. Think of the sub experience: if nuke subs had to operate like WWII diesel/electric subs, surfacing every couple of days to recharge the batteries, their advantages would be lost. So the navy adopted a new thought posture to take advantage of nuke subs ability to stay below the surface almost indefinitely. I hold that is required for nuclear rockets, new thinking to take advantage of them.

What is required, in my opinion, is the creation of a robust private sector space program funded by private money and a restructuring NASA to support it. In other words, NASA would cease to be an operational agency and turn into a NACA that supports this private sector space program (though I realize NASA would still have operational duties, but those quite different from the ones it has now). The technical centerpiece of this new space program should be a nuclear rocket, but one initially dedicated to go to and return from LEO. From 1955 to 1960 the nuclear rocket program had thoughts of using them to reach LEO and this was the norm, but NASA in 1960, for public relations reasons only, stated it would use nuclear rockets only from LEO outwards where they would pose “no harm” to people. It was a pure PR decision, not based on technical facts.

If you drop this ban – it was PR only for no technical reason exists on why it cannot be done – I see the payloads costs of $100 per pound to LEO as realistic with even lower costs to follow as more experience is gained and as even more capable nuclear rocket engines are developed. I’ll say this differently: 1000 seconds of specific impulse is not the ceiling for the solid core, but it may be around 1800 seconds. Such numbers are real game-changer. It creates a fundamentally different and extremely robust and profitable space program. In essence, it democratizes space and opens it up to the common man and thus will end the public’s tepid support of space. If the common man can make money out of it and have personal access to it, the support level would be quite high and overcome any opposition of the antis. I lay out my thinking for this new program to begin a debate and dialogue in my second book: “The Nuclear Rocket – Making Our Planet Green, Peaceful and Prosperous”. I urge you to get a copy of it either from Apogee Press or Amazon or Barnes and Noble.

I also hope you have read my first book on the nuclear rocket “To the End of the Solar System: The Story of the Nuclear Rocket.” It is with this that I wish to clarify some of your comments The Space Show.

1. There was not a working nuclear engine in 1972 or any other time nor were there detailed blueprints for such an engine. The XE-1 was tested in 1969 and it was the first to a flight rated system. (All other tests were reactor tests or fuel tests). XE had at least a half dozen more tests scheduled and this was to be followed by about the same number of stage tests. The principal unknown with the latter was the gimbals. That was the program that was cancelled.
2. The belief that such as system could be built in 5 years is unrealistic if for no other reason that facilities do not exist. Jackass Flats is in tatters, Test Cell A is gone and the others would need extensive repair/refurbishment. I’ve not been there for 20 years, but some who have been there more recently say it might be best to start over. It’s too far-gone. Moreover, the records do not exist. Westinghouse records were lost in a flood; Aerojet’s at best are just lost and at worst destroyed. The only good records are those at Los Alamos and they are still classified. However, balancing this negative assessment is the fact that some inside Los Alamos have made a concerted effort over the years to reconstitute the record.
3. The shift from hexagonal fuel to pebble bed fuel is unlikely. The problem with pebble bed fuel is removing the heat where the pebbles contact each other; failure to do so would cause melting at the interface area and as it continued the core would likely be ejected out the nozzle. A similar core concept was studied early on in Rover/NERVA and rejected because it would lead to an unstable core, with pebbles starting to be ejected out the nozzle. In the 1980s, the Rover/NERVA alumni who were allowed to critique the Air Force Project Timberwind, which was also a pebble bed design, said the same thing. However, the Air Force disregarded that advice and proceeded to spend hundreds of millions on it until it became convinced that you couldn’t get the heat out. So rather than operate at 3000 C, you would have to operate at 1500 C, drastically lowering your specific impulse.
4. Delayed neutrons are not a problem. Pulse cooling was successful in removing the heat after a reactor/engine shut down. Using a nuclear engine to provide power is an intriguing idea and has been studied extensively, but not using delayed neutrons to power it because you would want power for a long duration e.g., months or years. To do this most studies I’ve seen feature a separate loop that circulates a working fluid through the core then back to a generator. But there are all sorts of concepts here.
5. Tungsten fast fission reactors were studied, but rejected for two reasons. First, fast reactors presented real control problems and second, graphite and carbide fuels were getting better and better thus negating tungsten’s refractory advantages.
6. There were never any accidents involving the loss of a nuclear rocket engine coming back to earth. The Russians have lost several space nuclear power reactors while the US had several losses of RTGs in the 1960s, but none since.

I hope you have a chance to read my two books, as they will answer many of your questions. For example, there is no need to go to a 46-inch core to get the thrust you need. You can expect increases in power density in future generation systems – the original NERVA was to have 75k thrust at 825 seconds of specific impulse while a second generation system was to have 925 seconds of specific impulse at 125k of thrust. There is room for growth beyond this. It’s like taking a Chevy small block and then seeing how much horsepower you can get from it by adding all sorts of bells and whistles. Here a doubling of the power is quite common and it is the same for a nuclear rocket engine, say starting with the 35×52-inch core. Double the thrust to 150k and more. Moreover, you can cluster nuclear engines to give you the thrust needed for any mission without worrying about stray neutrons. So there is no need for a 46-inch core. That was almost the size of the old 200-250k thrust NERVA II. Not needed. Finally, fuel life influences the thrust. Early in the program, the program featured massively large engines of up to 20,000MW firing for under a half hour to get the thrust needed for a manned Mars mission. That was because half an hour was the maximum the fuels would last. A decade the later the fuel goal was 10 hours at full power with 60 stops and starts. So the size of the engine dropped dramatically cause now one only had to take a long-life engine and run it longer to get the thrust needed for a mission.

If you provide me with your email, I will send you a 30-page analysis that outlines the potential of the solid core. It includes some preliminary analysis on how the $100 per pound to LEO can be attained.

Best wishes,

James A. Dewar

Dave Ketchledge - December 7, 2011

Dear Dr Dewar, thank you for ypur comment. I read your book The Nuclear Rocket and it was well worth reading,

We based the engine design out of Bess / INL report found in my book in the Reference section on a fast flux neutron core that also provided the Pebble Bed design, A thermal reactor is far easier to control since the neutron cycle is far longer. Since I wanted an Isp of 1000, this meant taking the fuel to 2000 MW thermal or MWt. But I used the same fission rate as the NERVA core, hence by increasing the core volume I got to the 46 inch diamteter as compared to the 35 inch diameter of NERVA. Either the NERVA or Pebble bed could send a crew to Mars.
The zirc carbide fuel pellet can operate at near 3100 deg K or 5120 deg F. So to reach the Isp of 1000. Both Zurbin and I prefer TNR’s over a plasma based engine. One can not fit a 500 MW power plant into a flight weight design. But a NTR fits the need for deep space. Since I have over 12 years as a Navy Reactor Operator and test engineer in Idaho I taught core physics and instrumentation. Thus my book is the blending of my career in nuclear and aerospace, I have the DOE / NASA 1991 report that includes the XE prime data and provided in the Reference section of the book. Certainly the B4 fuel can reach an Isp of 825-850 but going to ZrC offered the potential to reach an Isp of 1000.

The critical issue resides in the flight time to Mars due to GCR and SPE rad dose. With estimates of 60 Rem unshielded over a 3 year nmission. Cut this to 4.5 months and the Rad dose drops by a factor of 4. Now arrange the water, food and some shielding for a tenth factor or a total dose of 1.5 Rem. While someone got annoyed at my comment of what is the minimal acute dose before you see blood changes at 25 Rem, any expose has a small degree of risk. I provided a chapter on radiation control in the book. So on many points we can agree on. The intent of the pebble bed fuel was to increase the fuel surface area and build a core able to achieve 2000 MW thermal to reach 3100 deg K. You can drop me a direct note via my web site. At the bottom left is an email link. Again I found you book a excellent resource des above my desk that represents books I want on hand/

Your comment pn the flooding explains the lack of more core data from NASA/DOE such as rod worth data. If NASA did get back into development it would be at least 6-10 years till we had a floight ready system. Currently the Engineering points this way.

James A. Dewar - December 8, 2011

Thanks for your comments, but I have some differences with it. I am unconvinced a fast reactor is the way to go over thermal, the ability to control it being a major reason. Getting to 1000 seconds of ISP does not require ZrCarbide fuels. At the tail end of the Rover/NERVA program, ZrC fuels made their appearance and several were tested in the Nuclear Furnace. That highlighted a difference of opinion between Los Alamos and Y-12. Don MacMillan, who has since passed away, was head of the Rover materials group and told me he believed ZrC was the future. I believe he was right, but ZrC fuels could not use the B-4 core design. Los Alamos had not yet evolved a new core design for these fuels and Bill King later said a relook at the Dumbo concept for them might be useful. The Russians started working on these carbide fuels in 1968 when they mysteriously changed their program from graphite to carbide. Why? Who knows? They evolved a twisted ribbon core concept for these brittle fuels. The bottom line here is carbides offer great promise, but no core design has been developed, tested or proven to my knowledge. On the other hand, Y-12 was a believer in graphite and I believe they are right. When the program ended in 1973, Los Alamos ended all its materials research but Y-12 kept its research and development on graphite going and to my knowledge it is still going today. One of their experts, with 40 years or so experience here, told me graphite still has a lot of room for growth, meaning it could give fuels with ISPs of 1000+ for the B-4 core. Here I have to give the nod to Y-12, as they have continued to work on graphite and carbon and they are the preeminent materials experts within the government and probably the nation.
On a different subject, perhaps you have not had access to my first book on the nuclear rocket “To the End of the Solar System: The Story of the Nuclear Rocket.” I urge you to obtain a copy, as it will clarify some of your thoughts, such as the need for going to a larger core, i.e., a 46-inch diameter. That thinking was widespread through about 1966, but after that date it was discarded because of technical advances in getting long-life fuels. Also clustering of nuclear rocket engines next to each other was demonstrated not to be a problem. It’s difficult to find copies of my first book. Apogee Press might have several copies of the paperback it issued several years ago and Amazon has listings for some who are selling the first edition hardback. That is expensive, however. Amazon is also offering a Kindle version, which surprises me because Apogee Press, which holds all the rights to my book, has not issued an electronic version. I know where you can buy a brand new hardcover first edition of my book for $100. It’s still in its wrapper and the original price from the publisher was $75.
Finally, I’ve sent Dave Livingston a copy of my 30-page analysis to post. I’m not certain where he would post it, but you should read this. It contains further argumentation on why breaking the ban on using a nuclear rocket to take payloads to and from LEO is the way to go. So it supplements my second book. Obviously, I’m convinced that is the way to go and not manned Mars. If you can’t get this, please let me know and I’ll see about getting you a copy.

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