Pusher plates on orion nuclear pulse propulsion vehicles.

[vogon13]

Also keep in mind, your first detonation following a 'dud', (and assuming the shock absorber system copes successfully with the dud) will need to be either a reduced yield device, or a standard issue one detonated at a greater distance.<br /><br />The problem being in this case the pusher plate being at rest relative to the detonation rather than approaching it. With no momentum in the plate to cancel, a full yield hit will over accelerate it.<br /><br />This would be ungood.<br /><br /><br />Another problem with a dud would be if the chemical explosives detonated, but no nuclear reaction occured. In this case, 'chunks' of debris from the nuke might spall or penetrate the pusher. You would want to be sure this has not occured before resuming powered flight.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[qso1]

vogon13:<br />The construction of an interstellar Orion was envisioned to take centuries...<br /><br />Me:<br />And therien lies the problem. We have spent half a century now...just deciding whether we are going to go back to the moon and on to mars. Not only that, NASAs budget has only been a steady flatline at best since it was cut by around half in the post Apollo budget cut frenzy.<br /><br />vogon13:<br />Additionally, examining 20 to 30 million nukes in isolation is not the point, the point is the cost per delivered kilogram to the target star system.<br /><br />Me:<br />Cost of nuclear bomb production is not all that expensive I would agree. However, I think whats not being realized here is bomb making capacity. How many nukes can the U.S. or say, an international effort produce in a given amount of time? Keeping in mind the two arms racing powers produced maybe 100,000 nukes tops, to be generous, over a period of half a century.<br /><br />vogon13:<br />Orion beats anything in that analysis. Recall the interstellar Orion is delivering 50,000 people, and sufficient materials to found a viable colony. The pilgrims would be envious to have been able to take so much 'stuff'. Should we be so inclined, Orion could take the Great Pyramid of Cheops along for the ride . . .<br /><br />Me:<br />In this case, I think too much reliance on unproven data is a problem. All sorts of hard data was trundled out to justify the inexpensive reusable shuttle system in the early 1970s. 60 flights per year with 7 orbiters. The shuttle did eventually show that it could theoretically fly 24 missions per year, but at what cost? Manpower would have to be increased to have full coverage for all four orbiters.<br /><br />Today, the initial optimistic data is the butt of jokes and the fodder for shuttle critics worldwide. What do we really know about the cost of delivering something to a star system?<br /><br />I should also point out that I can see Orion as a viable system if it advances from the 1960s prop <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>

 

[qso1]

By the time we build something like Orion, it should be advanced enough to account for radiation exposure. Radiation protection has to be built in anyway to protect the crew from radiation already present in space. <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>

 

[vogon13]

Many improvements to the original Orion concepts have been floated. The 1960s Orion interstellar vehicle envisioned taking the entire pusher plate all the way to the target star. The vehicle efficiency improves if the plate is annularly segmental, and portions are jetisoned along the way. Additionally, with a reducing plate area, the propulsion charges can be rather more seriously gradated, providing another bump in performance, either speed or payload, or a combination of both.<br /><br />Advances in weapon design also helps, it seems the Soviet era Tsar Bomba would make a rather good basis for a propulsion unit (without either the lead, or the design called for DU tertiary stage)<br /><br />Distributing inert payload (discussed above) across the pusher rather than in the crew area dramatically reduces the mass and complexity of the shock absorber system. This gives another big bump in performance. <br /><br />With advances in storage technology, books will not have to be taken.<br /><br /> We may take far fewer colonists and instead take frozen eggs, sperm, and gametes to supplement the genetic diversity of the crew. Savings in food and supply mass can be translated into more propulsion units for a faster traverse.<br /><br />In the 60s, Orion might have done 3 light years per century, an advanced 2nd generation Orion might do 8 or 9 per century.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[lampblack]

So... that trip to Gliese 581 C -- at 20 light years -- might take 220 years, assuming an Orion 2.0 upgrade? Would that be the apparent lapsed time from the perspective of the colonists? Or the observed lapsed time from the perspective of folks on earth? The times would be different, of course, due to relativity -- and the fact that the ship is traveling at almost .1 cee.<br /><br />Anyhow, 220 years seems a long time to store frozen eggs, sperm, and gametes, especially in an environment likely to have higher-than-nominal radiation levels.<br /><br />And what sort of g-forces would the folks be experiencing inside the ship? All of that nifty fusion bomb-driven acceleration would hardly seem worth it if it smashes folks flatter than pancakes. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>

 

[qso1]

vogon13:<br />Many improvements to the original Orion concepts have been floated...<br /><br />Me:<br />I agree, and the books and storage technology analogy is an excellent example of taking advantage of current tech advances where practical. Now its only a matter of imagination to see what could occur in the next half century or so. <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>

 

[vogon13]

Acceleration (on average) for the interstellar Orion is quite low. Dyson envisioned 30 years to accel to (IIRC) .003C.<br /><br />Note that 1 G for roughly a year gets you close to 100% C, so 30 years to even .1 C isn't going to be much of a strain for the crew.<br /><br />Still, it is significant structurally for a vehicle massing 300 million tons.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[vogon13]

Oh, and time dilation under .1C (hell, even .5C) doesn't amount to much.<br /><br />Also, Dyson envisioned a DU pusher plate, and the neutron flux (so big of a problem for a steel pusher) breeds plutonium, to be recovered on arrival at the target to be recycled into a nuclear power plant for the colony.<br /><br />Maybe even fuel for nuclear powered aircraft carrier derived vehicles and submarines to explore the oceans of the target world.<br /><br />Or perhaps, during the 'cruise' phase of the flight, to keep the crew busy, they recycle the Pu made on the voyage so far into plutonium triggers for their propulsion modules. Kind of like bootstrapping your way to the star.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[qso1]

What I see here is that Orion, if we decide to build it...in the end, will probably only vaguely resemble the Orion of the 1960s and even the Orion of today based on the 1960s model.<br /><br />The discussion here seems to focus mainly on building something based on todays known technology and science. Little room to account for possible advances which is understandable because we don't actually have a way of knowing what those advances might be.<br /><br />They may be advances that allow for frozen commodities to be stored more efficiently, radiation protection may see some advances that could counter one of the problems you mentioned. I also tend to think that advances in laser fusion propulsion technology will lead to a system that will not have to rely on exploding bombs behind a pusher plate, or at the very least, we should be able to calculate the bomb force vs the G force on the crew.<br /><br />In this hypothetical scenario...imagine its 1869 and there is a group who advocates the idea of going to the moon in the way described in "From The Earth To The Moon" by Jules Verne which was written IIRC, in 1865. The discussion centers around how powerful the cannon has to be to get people to the moon. Nobody imagined rockets ultimately being utilized. Rockets in 1865 were little more than fireworks and a few rockets used on the battle field but nothing like todays rockets. But the most important advancement, one not envisioned at all by Verne or anyone else AFAIK...the advent of liquid rockets which made the journey not only possible...but practical to the extent possible for modern day rockets.<br /><br />Man eventually went to the moon in a manner similar in some ways as Verne wrote, but there were some major differences as well. Its those differences here in Orion discussions of early 2000s that we have no way of seeing, that make the big difference in say, 2207.<br /><br />Or at least thats my take for what its worth. <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>

 

[steve82]

"Shock absorber design between the pusher plate and the payload remains a challenge, and one of the greatest problems occurs when a nuke propulsion charge fails to detonate. In that instance, the recoil of the plate from the prior blast would remain a considerable design problem. "<br /><br />Another great concern they had in the failure to detonate scenario was a fission dud wherein the conventional charge went off to initiate the bomb but fission did not occur and, instead of vaporizing, all of the metal components of the bomb turn into shrapnel and hurl themselves against the ship.<br /><br />

 

[vogon13]

Um, yeah . . . .<br /><br />{posted 5/10/07, 10:58 PM}<br />Also keep in mind, your first detonation following a 'dud', (and assuming the shock absorber system copes successfully with the dud) will need to be either a reduced yield device, or a standard issue one detonated at a greater distance. <br /><br />The problem being in this case the pusher plate being at rest relative to the detonation rather than approaching it. With no momentum in the plate to cancel, a full yield hit will over accelerate it. <br /><br />This would be ungood. <br /><br /><br />Another problem with a dud would be if the chemical explosives detonated, but no nuclear reaction occured. In this case, 'chunks' of debris from the nuke might spall or penetrate the pusher. You would want to be sure this has not occured before resuming powered flight. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[christine16]

so you think we can start to biuld it?

 

[vogon13]

If anyone was wondering about DU:<br /><br /><br /><br />Sorry, I tend to lapse back into techno prattle so often. <br /><br />DU is Uranium 238 (depleted uranium). <br /><br />When zapped with neutrons it eventually transmutes into Plutonium 239, a very handy material to have. Considering most of the uranium we do have is 238 and until it is transmuted it isn't much good for anything besides armour piercing shells. <br /><br />Hydrogen fusion 'propulsion units' emit copius neutrons, by the way. <br /><br />When a steel pusher plate is zapped with neutrons, some of them lodge in the steel and decay into hydrogen atoms. As the hydrogen builds up, it mechanically degrades the steel and tends to make the pusher plate brittle. <br /><br />Not good for something that might be getting walloped with nukes every minute for seveal years. <br /><br />So, a DU pusher plate might be an interesting thing to take to alpha Centauri . . . <br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[docm]

Problem is a pusher plate made of DU big enough to do the job would weigh as much as a small moon <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> </div>

 

[vogon13]

A DU clad steel pusher would be fine, the expected neutron flux and the amout of Pu needed would be computed to determine the thickness of the DU layer on the pusher.<br /><br />No point in taking more DU than is needed.<br /><br />With inert payload distributed across the pusher, perhaps a DU clad aluminum pusher would work. Good use for lunar aluminum, and the weight savings would be millions of tons. Power from a Pu refueled reactor could be used to resmelt/anneal the pusher as needed during the flight. Another task to keep the crew busy during cruise mode.<br /><br />More speed, more payload.<br /><br />It just keeps getting better and better. Maybe a .1C Orion is possible . . . <br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[tomnackid]

Back to the original question for a moment. The version of Orion shown below (from astronautix.com) was designed to be launched into space by a Saturn V -- hence the modest size of the pusher plate. Orions designed to take off under their own power or built in space have much larger pusher plate designs. However, you reach a point of diminishing returns where the added mass of a pusher plate is not offset by any increase in propulsive force. It was found that the most efficient designs feature a Nuclear Pulse Unit (a fancy name for a nuclear bomb!) with a shaped charge that would direct most of the blast toward the vehicle. The NPU would also be packed with with a substance like polyethylene the would vaporize upon detination and help improve the coupling of the explosive force to the vehicle. For these reasons the size and therefore the mass of the pusher plate can be kept to a minimum. Earlier Orion designs partially enclosed the blast with spherical or bell shaped structures--sometimes spraying water into the blast to increase the thrust. These concepts suffered from poor performance do to the mass of the enclosing structures.<br /><br />

 

[strandedonearth]

For reference, here's a pic of somebody's visualization of <b>Micheal</b>, as described in the novel <b>Footfall</b> by Larry Niven and Jerry Pournelle.

 

[webtaz99]

Don't second-guess engineering until <b>you do the math</b>.<br /><br />That's the difference between design and egineering. <div class="Discussion_UserSignature"> </div>

 

[publiusr]

I like NSWR better--a smoother ride--if you can keep it from melting.