About the "Mars in two weeks" nuclear rocket.

[exoscientist]

There was a study announced a few years ago on a more efficient nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:<br /><br />Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks.<br />Date: 2001-01-03 <br />http://www.sciencedaily.com/releases/2001/01/010103073253.htm<br /><br /> Taking the number 75,000,000 km for the distance at closest approach for Earth and Mars, we can calculate the acceleration required to reach the half way point in 7 days, or 608,000 seconds. The formula for the distance travelled (s) at constant acceleration (a) over time (t) is:<br /><br />s= 1/2 * a * t^2<br /><br /> So: <br /><br />37.5E9 = 0.5 x a x (608000)^2 = 0.5 x a x 3.7E11 , <br />so a = 0.2 m/s^2 . <br /><br /> Then the max velocity is: 0.2 x 608000 = 120960 m/s, about 121 km/s. <br /><br />I found a report on line that derived some design elements for this propulsion method: <br /><br />FISSION FRAGMENTS DIRECT HEATING OF GAS PROPELLANT FOR SPACE ROCKET. <br />http://www.crs4.it/Areas/cfd/10-IWCP_article.pdf <br /><br />It gives the Isp as 2500s, maximum. <br /><br />This page gives the formula for the mass ratio in terms of the velocity change over the trip, or delta V, "DESIGN-CENTERED INTRODUCTION TO AEROSPACE ENGINEERING", http://www.adl.gatech.edu/classes/dci/space/dci10.html , as:<br /><br />M1/M2 = e^(deltaV/g*Isp) <br /><br /> So in this case: M1/M2 = e^(4.937) = 139. If the ship itself weighed 100 tons the ship plus propellant would weigh 14,000 tons.<br /><br />This is large, but the DESIGN-CENTERED INTRODUCTION TO AEROSPACE ENGINEERING web page gives the mass ratio to reach Earth escape velocity for standard chemical rockets as with the Apollo missions as 18.7. So this nuclear Mars mission would be less than <div class="Discussion_UserSignature"> </div>

 

[spacester]

Very refreshing. Usually I feel the need to pounce on a "two weeks to Mars" thread and provide corrections. This is not particularly fun, because as I've said, one of my motivations behind learning what I have is to be able to provide positive feedback. It seems that orbital mechanics experts are mostly interested in what cannot be done, whereas I am interested in the art of the possible.<br /><br />But I see no factual errors here. It's arguably more in the science fiction realm than a viable technology, but still.<br /><br />At a trip time this fast, the flight path is not all that far from a radial line between orbits. Of course it's actually a segment of an elliptical path on a very very energetic orbit, but the estimate given for deltaV is reasonable. A very very large deltaV of course, and if you lose the brakes, you're going to go way way out there before coming back and grazing the sun. <div class="Discussion_UserSignature"> </div>

 

[mikejz]

What sort of Thermal/G-Forces would we be looking at if they did a direct-entry?

 

[spacester]

Lithocapture. <img src="/images/icons/laugh.gif" /><br /><br />Actually, if you had enough dV to match velocities with the planet, the piddly little extra needed for a direct entry would be an afterthought. <div class="Discussion_UserSignature"> </div>

 

[the_ten]

Sounds good. Let's make it happen!

 

[mikejz]

Just one question: Is that stuff water soluble? If it is there might be some safety issues.

 

[silylene old]

I wonder how many smoke detectors one would have to disassemble to get enough Am to fuel this rocket?<br /><br /><img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[tap_sa]

<font color="yellow">"Could Am 242 be used in inertial confinement fusion?"</font><br /><br />IAmNotANuclearScientist, but the way you described is unlikely to work. It looks like you expect the whole Am-layer to go through instant fission causing implosion and ignite d+t fuel, correct? This will not happen. If you remove the moderator <i>nothing</i> happens. In a nuclear reactor it's not the moderator that moderates the reaction down, quite the opposite. Moderators purpose is to slow down the neutrons from previous fissions to levels where their probability to cause another fission is much bigger. Without moderating material the reactor is unable to reach criticality. It is the control rods that are used to keep things from not going supercritical. They are usually cadmium which absorbs the neutrons.<br /><br />To get Am going critical without moderation you need a certain minimum mass of it and then were start to talk about bombs, not reactors. <br /><br />Btw you'd want to replace tritium with lithium, use something like lithium-deuterium hydride. Tritium is very rate and radioactive, halflife only 12 years. LiD is a solid, stable material, cheap and easy to make. Neutrons from fission (and fusion once it get going) turn lithium into tritium. This is how thermonuclear bombs work, only first prototype used tritium.<br /><br />Hmm I wonder if this post hampered my chances in diversity visa lottery ... echelon, cia, I was just kidding, I know nothing about nucular devices...

 

[the_ten]

I've never witnessed a real life conversation about Star Trek'ish stuff. Please, continue! <img src="/images/icons/wink.gif" />

 

[haywood]

It's pronounced "nu-clee-ar". LOL.<br />

 

[dan_casale]

>Here's a thought <img src="/images/icons/smile.gif" /> Could Am 242 be used in inertial confinement fusion? <br /><br />Would that be electro-static inertial confinement or laser initiated inertial confinement?