nuclear thermal rocket do better than chemical rocket

[nec208]

<p><font size="2">Read article.&nbsp;</font></p><p><font size="2">In a <strong>nuclear thermal rocket</strong> a working fluid, usually hydrogen, is heated in a high temperature nuclear reactor, and then expands through a rocket nozzle to create thrust. </font></p><p><font size="2">The nuclear reactor's energy replaces the chemical energy of the reactive chemicals in a traditional rocket engine. Due to the higher energy density of the nuclear fuel compared to chemical ones, about 10⁷ times, the resulting efficiency of the engine is at least twice as good as chemical engines even considering the weight of the reactor, and even higher for advanced designs.</font></p> <div class="Discussion_UserSignature"> </div>

 

[nec208]

<p>I don't think this will do to well if they use gas and not liquid?I would think gas will be less density .</p><p>Also if the article is true than the boosters can be made smaller.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[Cygnus_X_1]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think this will do to well if they use gas and not liquid?I would think gas will be less density .Also if the article is true than the boosters can be made smaller.&nbsp; <br /> Posted by nec208</DIV></p><p>&nbsp;</p><p>Not for orbital launch. &nbsp;&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[wick07]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think this will do to well if they use gas and not liquid?I would think gas will be less density .Also if the article is true than the boosters can be made smaller.&nbsp; <br />Posted by nec208</DIV><br /><br />Are you asking about the working fluid or the reactor type?&nbsp; A liquid working fluid (let's say LH2) would be turned into a gas and very likely a plasma by the intense heat that the engine creates.&nbsp; If you are talking about reactor type wikipedia actually has a good article on this that is pretty straight-forward.</p> <div class="Discussion_UserSignature"> <p><font color="#3366ff"><strong>_______________________________<em> </em></strong></font></p><p><font color="#0000ff"><em>"</em>If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum.  If you feel like trying to make a difference, you have to BE different.  How can you do that without interacting with those who are different from yourself?"</font></p><p><font color="#0000ff">-  a_lost_packet_</font></p> </div>

 

[annodomini2]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Are you asking about the working fluid or the reactor type?&nbsp; A liquid working fluid (let's say LH2) would be turned into a gas and very likely a plasma by the intense heat that the engine creates.&nbsp; If you are talking about reactor type wikipedia actually has a good article on this that is pretty straight-forward. <br />Posted by wick07</DIV></p><p>&nbsp;I get the concept, but you still have a ridiculously high mass to the vehicle at takeoff.</p><p>&nbsp;Safety wise its a tradeoff between fuel stability and radiation</p><p>Reusability is theoretically better, especially if you could use water as the propellant.</p><p>The real benefit would come if the engine could be combined with one of the nuclear powered Ion thrusters for deep space exploration.</p><p>&nbsp;Use this concept to achieve orbit and then the ion engine to travel on from orbit.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[Cygnus_X_1]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> Reusability is theoretically better, especially if you could use water as the propellant.</DIV></p><p>&nbsp;</p><p>Water is not a good propellant.&nbsp; Low molecular weight is better&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[publiusr]

Stan Borowski is doing fine work on NTR concepts.

 

[wick07]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I get the concept, but you still have a ridiculously high mass to the vehicle at takeoff.&nbsp;Safety wise its a tradeoff between fuel stability and radiationReusability is theoretically better, especially if you could use water as the propellant.The real benefit would come if the engine could be combined with one of the nuclear powered Ion thrusters for deep space exploration.&nbsp;Use this concept to achieve orbit and then the ion engine to travel on from orbit. <br />Posted by annodomini2</DIV><br /><br />This is true when you are talking about solid core NTR.&nbsp; However if you start talking gas core you can get ISPs in the 2500-4000 range and suddenly that weight trade-off doesn't seem so bad.&nbsp; Here is a link from the old uplink forum (unfortunately the interesting part of the post got truncated on the new software) that does some math to show what could be possible.&nbsp; Before anyone says it, yes Boris makes a few assumption, but I do not think they are unreasonable.</p><p>http://uplink.space.com/showthreaded.php?Cat=&Board=businesstech&Number=509814&page=12&view=collapsed&sb=5&o=0&vc=1</p> <div class="Discussion_UserSignature"> <p><font color="#3366ff"><strong>_______________________________<em> </em></strong></font></p><p><font color="#0000ff"><em>"</em>If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum.  If you feel like trying to make a difference, you have to BE different.  How can you do that without interacting with those who are different from yourself?"</font></p><p><font color="#0000ff">-  a_lost_packet_</font></p> </div>

 

[qso1]

<p><font color="#800080">I don't think this will do to well if they use gas and not liquid?I would think gas will be less density .Also if the article is true than the boosters can be made smaller.&nbsp; <br /> Posted by nec208</font></p><p>True, gaseous propellant would require a larger volume tank for storage until needed. Boosters would probably be smaller unless more LH2 is required when used with nuclear reactors.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[nec208]

&nbsp;<br /><p>Are you asking about the working fluid or the reactor type?&nbsp; A liquid working fluid (let's say LH2) would be turned into a gas and very likely a plasma by the intense heat that the engine creates.</p><p>-------------------------------------------------------------------------------------</p><p>Burning gas or burning liquid .The booster will have to be bigger if its going to hold gas.</p> <div class="Discussion_UserSignature"> </div>

 

[nec208]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think this will do to well if they use gas and not liquid?I would think gas will be less density .Also if the article is true than the boosters can be made smaller.&nbsp; Posted by nec208True, gaseous propellant would require a larger volume tank for storage until needed. Boosters would probably be smaller unless more LH2 is required when used with nuclear reactors.&nbsp; <br />Posted by qso1</DIV><br /><br />Its heated like a plasma gas.But still the boosters have to&nbsp;hold it.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[qso1]

<p>I'm not sure I get what your saying.</p><p>The booster size would first off be determined by how long the engines are to be utilized. How many propulsive burns and what duration which in turn determines tank size. So in that respect, say we want the S-IVB in conventional and nuclear flavor to do the same job. To have any advantage with a nuclear vesion, you want double the performance with either the same sized or smaller booster.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[nec208]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm not sure I get what your saying.The booster size would first off be determined by how long the engines are to be utilized. How many propulsive burns and what duration which in turn determines tank size. So in that respect, say we want the S-IVB in conventional and nuclear flavor to do the same job. To have any advantage with a nuclear vesion, you want double the performance with either the same sized or smaller booster.&nbsp; <br />Posted by qso1</DIV></p><p>I think you are talking more space travel.I'm talking more just&nbsp; to get up there...A nuclear rocket&nbsp; using gas to launch in space will need a bigger booster than liquid&nbsp;.</p><p>If you had&nbsp;2 boosters the same size&nbsp;,one with gas and one&nbsp;with liquid&nbsp;.To have the same power the one with gas would have to have a bigger booster.&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[qso1]

Gotcha, and yep your right, the gaseous hydrogen booster would have to be larger than a liquid hydrogen booster. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[annodomini2]

<p>I'm guessing liquid or gas the ISP will be determined by the thermal transfer capability of the material used and the Delta T provided by the reactor.</p><p>&nbsp;The reason I say water as a propellant is that it is easily available, very safe, stable and easy to store. i.e. safety risks are greatly reduced. Not to mention cheap.</p><p>&nbsp;The benefit of a gas engine is the propellant can be pressurised therefore reducing the size of the required tanks. However cooling may be required to provide suffcient Delta T in the Engine.</p><p>&nbsp;I personally dislike the concept of LH2 in this article, it is relatively expensive, volatile and difficult to handle. But may offer effciencies that water cannot provide.</p><p>&nbsp;I'm guessing an indirect cycle engine is needed? With lithium exchange or similar to the Ideas proposed in the 60's for nuclear powered jets?</p> <div class="Discussion_UserSignature"> </div>

 

[qso1]

<p>In hydrogen powered rocket engines such as the shuttle main engine, the hydrogen serves as coolant in addition to its main function as propellant. Another benefit of hydrogen is that while its still in a liquified supercold state, it is run through tubes along the thrust chamber that keep the chamber from melting during firing. Hydrogen is expensive and difficult to handle but the main thing, as you mentioned, is that it provides efficiencies water simply cannot provide.</p><p>Otherwise, I would think Robert Goddard would have used water to launch his rocket just on the basis of cost alone.</p><p>As far as indirect cycles. I'm no expert on this stuff but when they began studying nuclear rockets, they looked at as much as was feasible to do and in the NERVA designs, they had the least complex engines.</p><p>There are three basic designs to nuclear thermal rockets. Gas, liquid and solid core designs. Of the three, the solid core design is simplest and was the design that eventually resulted in a working engine for that reason. The other two designs have yet to be demonstrated as working engines.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[nec208]

<p>In hydrogen powered rocket engines such as the shuttle main engine, the hydrogen serves as coolant in addition to its main function as propellant. Another benefit of hydrogen is that while its still in a liquified supercold state, it is run through tubes along the thrust chamber that keep the chamber from melting during firing. Hydrogen is expensive and difficult to handle but the main thing, as you mentioned, is that it provides efficiencies water simply cannot provide.</p><p>----------------------------------------------------------------------------------</p><p>Could they use other fuel than hydrogen to cool the engine from burning up?</p><p>Why have a&nbsp;hydrogen and&nbsp;oxygen tank? Just have one hydrogen tank and design the rocket to breath air on the way up ?</p><p>In space have a hydrogen and&nbsp;oxygen tank.</p><p>Water does not seem to be powerful or we will be bak to the 1800's&nbsp;steam engine and using water for electricity.</p> <div class="Discussion_UserSignature"> </div>

 

[qso1]

<p><font color="#800080">Could they use other fuel than hydrogen to cool the engine from burning up?</font></p><p>They could, but its easier to just use the hydrogen for both purposes, and cost effective. Not to mention its been successfully done for the better part of four decades.</p><p><font color="#800080">Why have a&nbsp;hydrogen and&nbsp;oxygen tank? Just have one hydrogen tank and design the rocket to breath air on the way up ?In space have a hydrogen and&nbsp;oxygen tank.Water does not seem to be powerful or we will be bak to the 1800's&nbsp;steam engine and using water for electricity. Posted by nec208</font></p><p>On the way up, you essentially are in space once you reach approximately 20 miles or so. Not enough oxygen to support combustion in a rocket engine beyond that point. During the National AeroSpace Plane (NASP or X-30) studies, there were configurations of the craft that had jet engines for takeoff, scramjets to boost the craft to near orbital velocities, and rockets to insert into orbit.</p><p>This of course, was something that would actually have been quite complex, but probably doable. Of course, this means it may have been like the shuttle. Too expensive for commercial operation. X-30 was eventually canceled as it met the cost barrier.</p><p>http://en.wikipedia.org/wiki/Rockwell_X-30</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[KosmicHero]

<p>&nbsp;</p><p>Nuclear Thermal Rockets do NOT derive their added efficiency over chemical rockets from the increase in energy density of nuclear material or from significant increases in heat transfer to the working fluid (i.e. propellant).&nbsp; The advantages from NTRs are almost entirely derived from the independence in working fluid.&nbsp; </p><p>&nbsp;When you&nbsp;operate a chemical rocket you require a fuel and oxidizer but when you&nbsp;operate an NTR the source of your energy (heat) is not chemically dependent on the fuel/oxidizer you choose.&nbsp; Because of this, you want to choose the lowest molecular weight propellant you can.&nbsp; This is hydrogen.&nbsp; Hydrogen is the only propellant that will make an NTR&nbsp;competitive with a chemical rocket.&nbsp; </p> <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

 

[qso1]

Makes sense to me. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[wick07]

Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Nuclear Thermal Rockets do NOT derive their added efficiency over chemical rockets from the increase in energy density of nuclear material or from significant increases in heat transfer to the working fluid (i.e. propellant).&nbsp; The advantages from NTRs are almost entirely derived from the independence in working fluid.&nbsp; &nbsp;When you&nbsp;operate a chemical rocket you require a fuel and oxidizer but when you&nbsp;operate an NTR the source of your energy (heat) is not chemically dependent on the fuel/oxidizer you choose.&nbsp; Because of this, you want to choose the lowest molecular weight propellant you can.&nbsp; This is hydrogen.&nbsp; Hydrogen is the only propellant that will make an NTR&nbsp;competitive with a chemical rocket.&nbsp; <br />Posted by KosmicHero</DIV><br /><br />KosmicHero, could you expand on this because it is quite to opposite to what I have always heard about NTR.&nbsp; Thermodynamically your efficiency should increase as you exhaust temperature increases (assuming your "heat sink" temperature remains constant).&nbsp; Why does increased temperature not translate to greater efficiency in NTR?&nbsp; Assuming you keep the temperature constant shouldn't increased molecular weight of the fuel/working fluid translate to increased power due to increased momentum? <div class="Discussion_UserSignature"> <p><font color="#3366ff"><strong>_______________________________<em> </em></strong></font></p><p><font color="#0000ff"><em>"</em>If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum.  If you feel like trying to make a difference, you have to BE different.  How can you do that without interacting with those who are different from yourself?"</font></p><p><font color="#0000ff">-  a_lost_packet_</font></p> </div>

 

[KosmicHero]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>KosmicHero, could you expand on this because it is quite to opposite to what I have always heard about NTR.&nbsp; Thermodynamically your efficiency should increase as you exhaust temperature increases (assuming your "heat sink" temperature remains constant).&nbsp; Why does increased temperature not translate to greater efficiency in NTR?&nbsp; Assuming you keep the temperature constant shouldn't increased molecular weight of the fuel/working fluid translate to increased power due to increased momentum? <br /> Posted by wick07</DIV><br /></p><p>Those are excellent questions and I would be happy to explain.&nbsp; For a rocket that is acclerating a fluid through converging-diverging (C-D) nozzle, the equation for the exit velocity of the fluid is given by </p><p><span style="font-size:12pt;font-family:'TimesNewRoman'"><span style=""><img src="file:///C:/DOCUME%7E1/JOSHUA%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image002.gif" alt="" width="95" height="47" /></span></span> (I hope this works)</p><p>&nbsp;</p><p>&nbsp;This is the simplified equation if you assume that the pressure is expanded to ambient which is usually what nozzles are designed to do so we'll ignore that part.&nbsp; It doesnt really impact this explaination anyway.&nbsp; So in this equation the gamma is the ratio of specific heats which is affected slightly but the type of propellant that you use but its pretty small (1.6 for hydrogen, 1.4 for air).&nbsp; The R is the gas constant and the M is the molecular mass of the propellant (2 for hydrogen (actually since it will disassociate at these high temperatures it will be closer to 1, and water is 18 which is the primary product of combusting hyrdogen and oxygen which is the highest performing liquid combination).</p><p>The last term is the 'stagnation' or 'chamber' temperature.&nbsp; This is how hot we can get the combustion (or in the case of the NTR the reactor).&nbsp; You are right when you say that a higher chamber temperature will give you higher Isp (specific impulse), and an NTR can be run to extremely high stagnation temperatures.&nbsp; Unfortunately the reactor (made from some very exotic materials usually tungsten/nickel alloys) cannot handle the temps the reactor can put out.&nbsp; A liquid rocket can produce around 2500 K to 3000 K.&nbsp; NTRs are run upto maybe 3500 K but after that material limitations start to become the constraint.</p><p>One more thing, the connection between specific impulse and exhaust velocity is from the ideal rocket equation and the definition of Isp.&nbsp; Ue = Isp*g.&nbsp; There is a lot of confusion here, but the g you use is the g at sea level no matter where you are.&nbsp; This is because this is converting velocity and 'weight' and weight as it is thought about here is weight at sealevel. &nbsp;</p><p>Let me know if this suffices or if you have any more questions.&nbsp; If the equation doesnt work I'll just make a cruder one.&nbsp;</p> <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

 

[KosmicHero]

<p>&nbsp;</p><p>Bah!!</p><p>&nbsp;</p><p>Ue = sqrt( gamma * R/M * T_0)&nbsp;</p> <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

 

[nec208]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Nuclear Thermal Rockets do NOT derive their added efficiency over chemical rockets from the increase in energy density of nuclear material or from significant increases in heat transfer to the working fluid (i.e. propellant).&nbsp; The advantages from NTRs are almost entirely derived from the independence in working fluid.&nbsp; &nbsp;When you&nbsp;operate a chemical rocket you require a fuel and oxidizer but when you&nbsp;operate an NTR the source of your energy (heat) is not chemically dependent on the fuel/oxidizer you choose.&nbsp; Because of this, you want to choose the lowest molecular weight propellant you can.&nbsp; This is hydrogen.&nbsp; Hydrogen is the only propellant that will make an NTR&nbsp;competitive with a chemical rocket.&nbsp; <br />Posted by KosmicHero</DIV><br /><br />If you what better efficiency it is better to go with a fuel&nbsp;&nbsp;than&nbsp;gas has gas takes up more space and you need a bigger tank = &nbsp;more weight for take off.If the core is splitting atoms the&nbsp; engergy will be more than any chemical&nbsp; , Chemical has less power than atomic energy.</p> <div class="Discussion_UserSignature"> </div>

 

[KosmicHero]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If you what better efficiency it is better to go with a fuel&nbsp;&nbsp;than&nbsp;gas has gas takes up more space and you need a bigger tank = &nbsp;more weight for take off.If the core is splitting atoms the&nbsp; engergy will be more than any chemical&nbsp; , Chemical has less power than atomic energy. <br />Posted by nec208</DIV><br /><br />There is more energy production capacity from a nuclear fission reactor than from chemical reactions.&nbsp; What I said was that this is not the reason nuclear thermal rockets give you better efficiency (Isp) than chemical rockets.&nbsp; The reason it gives you better efficiency is because you can use a low molecular weight propellant (hydrogen).&nbsp; </p><p>Tank mass is a consideration.&nbsp; When you use hydrogen you usually store it in a liquid state (I'm guessing this is what you mean by fuel versus gas)&nbsp;which drastically reduces the size of the required tankage but adds some inert mass in the form of coolers (Hydrogen is cryogenic so it has to be kept at extremely low temperatures and high pressures... on the other hand LOX is also cryogenic, so you have the same problem on LOX/LOH designs).&nbsp; You will actually save some mass on an NTR versus a LOX/LOH system because you only have to have 1 set of tanks and pumps and coolers.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>