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Nuclear Pulse Propulsion – Orion and Beyond (2000) [pdf]

sillysaurus3 10y ago
Happy to see this getting some attention. It's seemed like one of the only viable propulsion methods for interstellar purposes, though nuclear is unfashionable at the moment. I remember seeing a chart showing that it was possible to reach other stars using a technique like this. Unfortunately the problem is slowing down. You could get there, but you'd be going too fast to stop. And since the more fuel you carry, the harder it is to reach that speed, it ends up becoming completely impractical to carry enough fuel to both get there and slow down. Maybe it'd be viable to stop by smashing into a planet, but it's hard for anything to survive that kind of impact force.
- sien 10y ago
  This was considered by project Orion. Basically you turn the vehicle around and use the propulsion to slow you down. It would use a heap of fuel to do this but it was possible. Edit, also, great find of this by the poster.
  - api 10y ago
    But since you already used a bunch of your pulse propellant during acceleration, this is partly compensated for by the vehicle weighing less.
    - wiredearp 10y ago
      In "Death’s End", that’s a science fiction book by Cixin Liu, they use a variant of nuclear propulsion where the nukes are pre-distributed throughout the Solar System instead of being carried by the ship itself. This could free up even more mass and make room for an even bigger magnetic sail to be used for deceleration. Later in the same book, and much later in the fictional timeline, they build a circumsolar particle accelerator, which is easier than you would think [1], and this could be used to produce massive amounts of antimatter in space with a lot more propulsion power than conventional nukes. So I remain optimistic. It’s by the way a remarkable series of books that will freak out a lot of hackers, I recommend sticking with the series to the end. [1] https://books.google.dk/books?id=A_1oCAAAQBAJ&pg=PA451&lpg=PA451#v=onepage https://books.google.dk/books?id=A_1oCAAAQBAJ&pg=PA451&lpg=P...
  - sillysaurus3 10y ago
    In order to have fuel to do that, you'd need to accelerate it to begin with. It ends up being an exponential increase in the quantity of fuel required, far more than could be carried. The chart from the paper was pretty convincing. I'll see if I can dig it up. Making the explosions more efficient can only get you so far. I'd prefer to be optimistic about it, but the math was showing that even with an ideal ability to convert mass into energy, it would require too much fuel, to put it mildly.
    - sien 10y ago
      According to the wikipedia page on Project Orion: Later studies indicate that the top cruise velocity that can theoretically be achieved are a few percent of the speed of light (0.08-0.1c).[17] An atomic (fission) Orion can achieve perhaps 9%-11% of the speed of light. A nuclear pulse drive starship powered by Fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure Matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the max. speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant, this would allow the ship to travel near the maximum theoretical velocity.[18] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)#Theoretical_applications https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
      - sillysaurus3 10y ago
        The referenced paper [18] is informative: http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_superconducting_coils_for_near-term_interstellar_transportation_LenardAndrews.pdf http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_s... === 2.3. Deceleration: the canonical issue While accelerating to a sizable fraction of the speed of light is a daunting task, deceleration is a yet more challenging task. The reason is that no realistic scenario to provide the gravy-train approach to either momentum transfer or pellet energy transfer at distances of 4+ light years seems within known physics. We are therefore challenged with either sending sufficient numbers of pellet-sheath elements so that the spacecraft can decelerate with on-board energy, or to come up with some other innovative concept. 2.3.1. Fueling at departure point One option is to provide all necessary propellant at the departure location. If the specific power and specific impulse is sufficiently high, this is a potential approach. However, for our MMO concept, it is not particularly feasible. For example, our specific power is certainly high enough, but our specific impulse is dictated by the pellet-sheath combination, which limits the Isp to 128,955 s. While this may seem like a prodigious specific impulse, the ratio of spacecraft speed .1 c to g * Isp is 23. This means that the deceleration propellant must be e^23 times the spacecraft mass, which is an unworkable solution. 2.3.2. Mag Sail deceleration In 2003 both Andrews and Lenard postulated using a large superconducting ring to intercept charge particles in interstellar space to slow the spacecraft down from high speeds. Additionally, the solar wind emanating from a star system provides an additional source of charged particles that can interact with the magnetic field. Deceleration can actually begin a sizable distance from the target star system. The following two charts indicate deceleration, velocity and time as a function of distance from the target star system. In this case the first phase of the deceleration starts at 21600 AU with a twoturn superconducting carbon nano tube reinforced loop. This loop captures the charged interstellar medium and deflects it to decelerate the spacecraft. This initial hoop size is 500 km in radius and carries 1,000,000 A of current. The spacecraft decelerates from .1 c to 6300 km/s by the time the spacecraft reaches 5000 AU. This will be quite a light show, so if there are any intelligent life forms with an observing system, they should be able to see the arrival.
- narag 10y ago
  I remember seeing a chart showing that it was possible to reach other stars using a technique like this. Unfortunately the problem is slowing down. So this is like being concerned how you will spend all that money, once you make it :-) There's a lot of discussion on interestellar travel, but "we" have almost frozen solar system travel. Yes, there are very nice probes out there doing important work, but manned vehicles are limited to keep ISS's lights on. The "impossible" tech needed to reach the stars will most probably be discovered or refined while conquering the solar system. Big sailing ships were developed along four centuries of sailing. The analogy may not be perfect, but I think it's eye opening.
  - triplesec 10y ago
    I agree with you in innovation terms, but there's a big economic difference: sailing used free energy and therefore could be developed over the long term by many actors. There are huge energy cost barriers to solar system travel which require bigger bets on economic return to be viable
- andygates 10y ago
  > nuclear is unfashionable at the moment It's more than that - this isn't just hippies, it's every major power on the planet. To fly Orion you have to put hundreds of nuclear explosives in orbit and pinky-swear that you're not going to use them to obliterate your enemies. Nobody is going to accept that. Orion's a fun paper rocket but will never be more. Engineers and they "yay nukes!" crowd will drag it out every couple of months for a repost, though.
  - jessriedel 10y ago
    > To fly Orion you have to put hundreds of nuclear explosives in orbit and pinky-swear that you're not going to use them to obliterate your enemies. To reiterate berntb's point: Every nation who has the ability to do this already has ICBMs that can deliver nukes anywhere on the planet in 20 minutes. So what difference does this make?
    - DennisP 10y ago
      True, but we still have a treaty that prohibits bombs in orbit, because they'd reduce the warning time enough to threaten deterrence. Maybe one day we can launch Orion from Mars.
      - maxerickson 10y ago
        Drive it to Earth, have lots of bombs left. From a strategic point of view, what's the difference between building on Mars and building it in orbit? Obviously there is a difference because the hostile faction has to seize control of it and move it to Earth, but once they do that, the calculation becomes the same. Do you commit to obliterating them the second they start moving it to Earth?
        masklinn 10y ago
        Best case scenario, Mars is 55 million kilometres from earth. Even using a ridiculous engine going full blast the whole way (in which case your payload will probably disintegrate when it hits the atmosphere) you won't get the transfer time under a month. If you want to actually deliver your payload in a useful manner you'll need twice that at the very least. 2+ months is a long lead time, and the engine you'll need will make the craft impossible to miss. What's the difference to building it in orbit? Building it in earth orbit you're dropping it from under 500km and your assembly makes 10~20 orbits a day, you can deliver it quickly at pretty much any time. The former allows countermeasure, the latter not really.
- deleted 10y ago
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tdy721 10y ago
I really love this stuff, this is a little more out there. (interstellar travel and all...) But I really believe that Nuclear power will be required to continue to explore our Solar System. Nuclear Thermal Rockets like Nerva[1] just seem like the only way to really colonize Mars in a sane way. I'm surprised that Elon Musk thinks it can happen with chemical rockets (and big tanks of LOX to keep cool and haul through the void). [1] https://en.wikipedia.org/wiki/NERVA https://en.wikipedia.org/wiki/NERVA
- jharohit 10y ago
  Well chemical rockets are at a stage where all it needs is scaling up to get more power. But I do agree with you, the complexity and sizes needed makes you wonder why waste so much effort on some technology which has inherent physical limits in terms of energy derived. Why not spend that money and effort on accelerating other forms of propulsion techniques (like nuclear) within the same timescales? We need another Manhattan Project for space tech.
jharohit 10y ago
What do you guys think of Laser sails & laser-based propulsion methods? The science exists now, seems like its only an engineering challenge. Phil Lubin has a paper on it as well https://www.nasa.gov/sites/default/files/atoms/files/roadmap_to_interstellar_flight_tagged.pdf https://www.nasa.gov/sites/default/files/atoms/files/roadmap...
- sprucely 10y ago
  That's what Breakthrough Starshot[1] is about, although scaled down to very small probes. I like the probe concept. If we really don't want all our eggs in this one basket, it seems to make more sense to put effort towards tech that can spread our seeds (whatever that may be) rather than humans physically traveling. [1] https://breakthroughinitiatives.org/ https://breakthroughinitiatives.org/
  - jharohit 10y ago
    Exactly - i think there should be more companies & organizations working towards pushing this. To become space-faring, we need to get from 1ev per bond of molecule level of energies obtained from chemical to 1GeV levels atleast!
    - IndianAstronaut 10y ago
      We are a long ways from becoming space faring. For the cost of sending one human to Mars, we could send ten rovers to Mars.
      - XorNot 10y ago
        Not if Elon Musk gets his way. If the cost profile works out, sending a human will be cheaper then sending a robot.
        Pinckney 10y ago
        His cost estimates depend on hundreds of thousands of people signing up, to diffuse R&D costs. That's dubious. Historically, colonists are self-interested. Typically they want to become rich, or they want to escape poverty or persecution. (Typically they're also poorly informed about just how dangerous their new life will be, and how much wealth they can expect to find, but in this age we shouldn't expect that to last much beyond the first landing). There's no precedent that I'm aware of for people leaving comfortable, privileged lives in mass to colonize someplace that has no wealth.
moseandre 10y ago
Please read Freeman Dysons's "Disturbing The Universe". This book is autobiographical and Dyson explains his arc of passion for nuclear propulsion and Orion. His strongest statement in this book is some deep respect for a biological scientist who, after seeing declassified army training manuals on chemical and biological warfare, supposedly discouraged the entire western hemisphere from further develomepment. This kind of nuclear research is, thankfully, over.
- jharohit 10y ago
  I would rather classify that as "unfortunate". Yes there are obviously biological harms in radiation exposure but that is what science & engineering is for. We know the power of nuclear energy so in order to harvest it, the right thinking should have been like "How can we safely extract it so that it does harm people in the mix?" rather than "Oh its harmful to humans so obviously we should give up and not use it". Current fission startups are working on versions of reactors which eliminate most of the harmful byproducts in the process.
  - moseandre 10y ago
    I'm not sure all of the opposition to nuclear research is about dangerous byproducts from the typical situation(s). It is about the improbable problematic situation which lead to exponential disaster that are scary, and, even if improbable, inevitable...
    - jharohit 10y ago
      well you have rockets which blow up on launch sites. so..
    - maverick_iceman 10y ago
      Yay, chicken little!
    - deleted 10y ago
      [deleted]
- 10y ago
fulafel 10y ago
There's also this great book about Orion: https://www.goodreads.com/book/show/21243.Project_Orion https://www.goodreads.com/book/show/21243.Project_Orion
jaunkst 10y ago
If only we could produce anti matter. A tiny amount would provide a fuel source viable for deep space exploration.
- jharohit 10y ago
  Anti-matter is produced at CERN for study https://home.cern/topics/antimatter https://home.cern/topics/antimatter. The problem is not production of it but the economy of producing it. It's still very costly to produce and then to build and engine around it which uses the energy efficiently is still at least 10-15 years. But do believe that the time to start actively looking into it is NOW.
  - flukus 10y ago
    Is it stable enough to survive a space launch?
    - jharohit 10y ago
      don't think so. I am guessing you would need really strong magnetic fields to contain the anti-matter.
      - dogma1138 10y ago
        Magnetic fields aren't the only issue here. You won't be able to store large amounts of it since quantum tunneling will become a statistical problem.
        witty_username 10y ago
        Could you explain? How would quantum tunneling of antimatter be a problem? The probability of quantum tunneling is exponential so adding a little more separation or reducing the energy can change the probability from 10^-1 to 10^-100.
- berntb 10y ago
ramgorur 10y ago
"orion's death" (page 6-7) says it all, we might be able to see something like orion by today if there were no ban on the nuclear tests, and there wouldn't be any "ban" if there were no "nuclear attack in 1945".
luckystarr 10y ago
Nuclear salt-water rockets! https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket Powerful, fast, intriguing and disgusting. :)
- Tuna-Fish 10y ago
  Project orion has the name recognition, but nuclear salt water rockets would just be a much better use of the same amount of fissiles. Maybe we should start reposting the wikipedia link every month until people remember mr. Zubrin's creations more than project Orion?
  - Pinckney 10y ago
    The big advantage of Orion is that we're reasonably confident it would work, and could probably build one within the decade with a serious effort. Zubrin's NSW rocket, on the other hand, falls into the "hasn't yet been conclusively proved impossible" category. We're not sure if we can control the reaction, and we're not sure how much heat would be transferred to the rocket if we can.
  - maverick_iceman 10y ago
    Orion would have exhaust velocity ~1000-10000km/s. Compare that to NSWR's 66km/s. NSWR seems fast compared to today's chemical rockets but it's nothing compared to Orion.
  - Symmetry 10y ago
    It's hard to say which is a more efficient use of fissiles. It's easier to burn up all your fuels in the context of an explosion as in Orion than in a saltwater rocket. On the other hand by bulking out the fuel with water to form a larger mass of propellant the saltwater uses it's energy more efficiently at the cost of lower ISP. But really, if we're willing to leak radioactive byproducts I think an open cycle gas core might be the best bet in terms of not-yet-developed rockets. http://www.projectrho.com/public_html/rocket/enginelist.php#id--Nuclear_Thermal--Gas_Core--Open_Cycle http://www.projectrho.com/public_html/rocket/enginelist.php#...
- 10y ago
askvictor 10y ago
Eli5: how does a nuclear explosion create a change in velocity for the spacecraft?
- saulrh 10y ago
  Sort of like a sailboat, except the wind is the vaporized material from the nuke. The nuke explodes, throwing a ton of mass and energy in every direction. The rocket uses a sail or pusher plate to catch part of that mass and energy, which carries it forward.
  - askvictor 10y ago
    The mass is pretty tiny ( smaller than the ejected fuel pellet); I presume it's the fact it has huge velocity, hence huge momentum? What about photons; do they have the same effect as other particles, or is there a different effect?
    - Pinckney 10y ago
      You add a significant amount of mass to the bombs to act as propellant. I don't know offhand what fraction is typical for Orion designs.
- avmich 10y ago
  The explosion throws the products of the explosion - mostly plasma - into all directions. The spaceship is nearby, so some of the plasma hits the ship, which is hiding behind a strong plate. Plasma transfers momentum to the ship.
DrNuke 10y ago
Think of this as a startup case for 2016: an exciting idea on paper with a very improbable, cumbersome and practically impossible execution = non-viable, fail fast, goodbye.
Symmetry 10y ago
I think I like the recent work on pulsed fission-fusion better. Basically you have a normal z-pinch fusion system but surround the fusing hydrogen with U238. It absorbs the fast neutrons from the fusion, fissions, and creates more heat driving the fusion. There's some radioactive waste flying out the nozzle but if you're already in space that's not a huge problem. On the upside, people aren't going to get nervous about nuclear weapons in space since you can't trigger the fuel pellets outside the engine. And you don't need a massive pusher plate, you just direct the charged plasma with magnetic fields. And that means you can wait to turn this on until you're in orbit and avoid creating any fallout on Earth. https://www.nasa.gov/content/pulsed-fission-fusion-puff-propulsion-system https://www.nasa.gov/content/pulsed-fission-fusion-puff-prop...
- maverick_iceman 10y ago
  What's the Isp of this method?
  - Symmetry 10y ago
    The first paper mentions 19,400 seconds at one point; versus 450 for hydrolox and 3100 for Dawn's ion drive. I did a blog posts on the theoretical limit on this sort of drive a while ago, using propellant velocity instead of ISP. http://hopefullyintersting.blogspot.com/2015/04/rockets-vi-very-nuclear-rockets.html http://hopefullyintersting.blogspot.com/2015/04/rockets-vi-v...

Happy to see this getting some attention. It's seemed like one of the only viable propulsion methods for interstellar purposes, though nuclear is unfashionable at the moment. I remember seeing a chart showing that it was possible to reach other stars using a technique like this. Unfortunately the problem is slowing down. You could get there, but you'd be going too fast to stop. And since the more fuel you carry, the harder it is to reach that speed, it ends up becoming completely impractical to carry enough fuel to both get there and slow down. Maybe it'd be viable to stop by smashing into a planet, but it's hard for anything to survive that kind of impact force.

sien 10y ago
This was considered by project Orion. Basically you turn the vehicle around and use the propulsion to slow you down. It would use a heap of fuel to do this but it was possible. Edit, also, great find of this by the poster.
- api 10y ago
  But since you already used a bunch of your pulse propellant during acceleration, this is partly compensated for by the vehicle weighing less.
  - wiredearp 10y ago
    In "Death’s End", that’s a science fiction book by Cixin Liu, they use a variant of nuclear propulsion where the nukes are pre-distributed throughout the Solar System instead of being carried by the ship itself. This could free up even more mass and make room for an even bigger magnetic sail to be used for deceleration. Later in the same book, and much later in the fictional timeline, they build a circumsolar particle accelerator, which is easier than you would think [1], and this could be used to produce massive amounts of antimatter in space with a lot more propulsion power than conventional nukes. So I remain optimistic. It’s by the way a remarkable series of books that will freak out a lot of hackers, I recommend sticking with the series to the end. [1] https://books.google.dk/books?id=A_1oCAAAQBAJ&pg=PA451&lpg=PA451#v=onepage https://books.google.dk/books?id=A_1oCAAAQBAJ&pg=PA451&lpg=P...
- sillysaurus3 10y ago
  In order to have fuel to do that, you'd need to accelerate it to begin with. It ends up being an exponential increase in the quantity of fuel required, far more than could be carried. The chart from the paper was pretty convincing. I'll see if I can dig it up. Making the explosions more efficient can only get you so far. I'd prefer to be optimistic about it, but the math was showing that even with an ideal ability to convert mass into energy, it would require too much fuel, to put it mildly.
  - sien 10y ago
    According to the wikipedia page on Project Orion: Later studies indicate that the top cruise velocity that can theoretically be achieved are a few percent of the speed of light (0.08-0.1c).[17] An atomic (fission) Orion can achieve perhaps 9%-11% of the speed of light. A nuclear pulse drive starship powered by Fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure Matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the max. speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant, this would allow the ship to travel near the maximum theoretical velocity.[18] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)#Theoretical_applications https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
    - sillysaurus3 10y ago
      The referenced paper [18] is informative: http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_superconducting_coils_for_near-term_interstellar_transportation_LenardAndrews.pdf http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_s... === 2.3. Deceleration: the canonical issue While accelerating to a sizable fraction of the speed of light is a daunting task, deceleration is a yet more challenging task. The reason is that no realistic scenario to provide the gravy-train approach to either momentum transfer or pellet energy transfer at distances of 4+ light years seems within known physics. We are therefore challenged with either sending sufficient numbers of pellet-sheath elements so that the spacecraft can decelerate with on-board energy, or to come up with some other innovative concept. 2.3.1. Fueling at departure point One option is to provide all necessary propellant at the departure location. If the specific power and specific impulse is sufficiently high, this is a potential approach. However, for our MMO concept, it is not particularly feasible. For example, our specific power is certainly high enough, but our specific impulse is dictated by the pellet-sheath combination, which limits the Isp to 128,955 s. While this may seem like a prodigious specific impulse, the ratio of spacecraft speed .1 c to g * Isp is 23. This means that the deceleration propellant must be e^23 times the spacecraft mass, which is an unworkable solution. 2.3.2. Mag Sail deceleration In 2003 both Andrews and Lenard postulated using a large superconducting ring to intercept charge particles in interstellar space to slow the spacecraft down from high speeds. Additionally, the solar wind emanating from a star system provides an additional source of charged particles that can interact with the magnetic field. Deceleration can actually begin a sizable distance from the target star system. The following two charts indicate deceleration, velocity and time as a function of distance from the target star system. In this case the first phase of the deceleration starts at 21600 AU with a twoturn superconducting carbon nano tube reinforced loop. This loop captures the charged interstellar medium and deflects it to decelerate the spacecraft. This initial hoop size is 500 km in radius and carries 1,000,000 A of current. The spacecraft decelerates from .1 c to 6300 km/s by the time the spacecraft reaches 5000 AU. This will be quite a light show, so if there are any intelligent life forms with an observing system, they should be able to see the arrival.
narag 10y ago
I remember seeing a chart showing that it was possible to reach other stars using a technique like this. Unfortunately the problem is slowing down. So this is like being concerned how you will spend all that money, once you make it :-) There's a lot of discussion on interestellar travel, but "we" have almost frozen solar system travel. Yes, there are very nice probes out there doing important work, but manned vehicles are limited to keep ISS's lights on. The "impossible" tech needed to reach the stars will most probably be discovered or refined while conquering the solar system. Big sailing ships were developed along four centuries of sailing. The analogy may not be perfect, but I think it's eye opening.
- triplesec 10y ago
  I agree with you in innovation terms, but there's a big economic difference: sailing used free energy and therefore could be developed over the long term by many actors. There are huge energy cost barriers to solar system travel which require bigger bets on economic return to be viable
andygates 10y ago
> nuclear is unfashionable at the moment It's more than that - this isn't just hippies, it's every major power on the planet. To fly Orion you have to put hundreds of nuclear explosives in orbit and pinky-swear that you're not going to use them to obliterate your enemies. Nobody is going to accept that. Orion's a fun paper rocket but will never be more. Engineers and they "yay nukes!" crowd will drag it out every couple of months for a repost, though.
- jessriedel 10y ago
  > To fly Orion you have to put hundreds of nuclear explosives in orbit and pinky-swear that you're not going to use them to obliterate your enemies. To reiterate berntb's point: Every nation who has the ability to do this already has ICBMs that can deliver nukes anywhere on the planet in 20 minutes. So what difference does this make?
  - DennisP 10y ago
    True, but we still have a treaty that prohibits bombs in orbit, because they'd reduce the warning time enough to threaten deterrence. Maybe one day we can launch Orion from Mars.
    - maxerickson 10y ago
      Drive it to Earth, have lots of bombs left. From a strategic point of view, what's the difference between building on Mars and building it in orbit? Obviously there is a difference because the hostile faction has to seize control of it and move it to Earth, but once they do that, the calculation becomes the same. Do you commit to obliterating them the second they start moving it to Earth?
      - masklinn 10y ago
        Best case scenario, Mars is 55 million kilometres from earth. Even using a ridiculous engine going full blast the whole way (in which case your payload will probably disintegrate when it hits the atmosphere) you won't get the transfer time under a month. If you want to actually deliver your payload in a useful manner you'll need twice that at the very least. 2+ months is a long lead time, and the engine you'll need will make the craft impossible to miss. What's the difference to building it in orbit? Building it in earth orbit you're dropping it from under 500km and your assembly makes 10~20 orbits a day, you can deliver it quickly at pretty much any time. The former allows countermeasure, the latter not really.
deleted 10y ago
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tdy721 10y ago

I really love this stuff, this is a little more out there. (interstellar travel and all...) But I really believe that Nuclear power will be required to continue to explore our Solar System. Nuclear Thermal Rockets like Nerva[1] just seem like the only way to really colonize Mars in a sane way. I'm surprised that Elon Musk thinks it can happen with chemical rockets (and big tanks of LOX to keep cool and haul through the void). [1] https://en.wikipedia.org/wiki/NERVA https://en.wikipedia.org/wiki/NERVA

jharohit 10y ago
Well chemical rockets are at a stage where all it needs is scaling up to get more power. But I do agree with you, the complexity and sizes needed makes you wonder why waste so much effort on some technology which has inherent physical limits in terms of energy derived. Why not spend that money and effort on accelerating other forms of propulsion techniques (like nuclear) within the same timescales? We need another Manhattan Project for space tech.

jharohit 10y ago

What do you guys think of Laser sails & laser-based propulsion methods? The science exists now, seems like its only an engineering challenge. Phil Lubin has a paper on it as well https://www.nasa.gov/sites/default/files/atoms/files/roadmap_to_interstellar_flight_tagged.pdf https://www.nasa.gov/sites/default/files/atoms/files/roadmap...

sprucely 10y ago
That's what Breakthrough Starshot[1] is about, although scaled down to very small probes. I like the probe concept. If we really don't want all our eggs in this one basket, it seems to make more sense to put effort towards tech that can spread our seeds (whatever that may be) rather than humans physically traveling. [1] https://breakthroughinitiatives.org/ https://breakthroughinitiatives.org/
- jharohit 10y ago
  Exactly - i think there should be more companies & organizations working towards pushing this. To become space-faring, we need to get from 1ev per bond of molecule level of energies obtained from chemical to 1GeV levels atleast!
  - IndianAstronaut 10y ago
    We are a long ways from becoming space faring. For the cost of sending one human to Mars, we could send ten rovers to Mars.
    - XorNot 10y ago
      Not if Elon Musk gets his way. If the cost profile works out, sending a human will be cheaper then sending a robot.
      - Pinckney 10y ago
        His cost estimates depend on hundreds of thousands of people signing up, to diffuse R&D costs. That's dubious. Historically, colonists are self-interested. Typically they want to become rich, or they want to escape poverty or persecution. (Typically they're also poorly informed about just how dangerous their new life will be, and how much wealth they can expect to find, but in this age we shouldn't expect that to last much beyond the first landing). There's no precedent that I'm aware of for people leaving comfortable, privileged lives in mass to colonize someplace that has no wealth.

moseandre 10y ago

Please read Freeman Dysons's "Disturbing The Universe". This book is autobiographical and Dyson explains his arc of passion for nuclear propulsion and Orion. His strongest statement in this book is some deep respect for a biological scientist who, after seeing declassified army training manuals on chemical and biological warfare, supposedly discouraged the entire western hemisphere from further develomepment. This kind of nuclear research is, thankfully, over.

jharohit 10y ago
I would rather classify that as "unfortunate". Yes there are obviously biological harms in radiation exposure but that is what science & engineering is for. We know the power of nuclear energy so in order to harvest it, the right thinking should have been like "How can we safely extract it so that it does harm people in the mix?" rather than "Oh its harmful to humans so obviously we should give up and not use it". Current fission startups are working on versions of reactors which eliminate most of the harmful byproducts in the process.
- moseandre 10y ago
  I'm not sure all of the opposition to nuclear research is about dangerous byproducts from the typical situation(s). It is about the improbable problematic situation which lead to exponential disaster that are scary, and, even if improbable, inevitable...
  - jharohit 10y ago
    well you have rockets which blow up on launch sites. so..
  - maverick_iceman 10y ago
    Yay, chicken little!
  - deleted 10y ago
    [deleted]
10y ago

fulafel 10y ago

There's also this great book about Orion: https://www.goodreads.com/book/show/21243.Project_Orion https://www.goodreads.com/book/show/21243.Project_Orion

jaunkst 10y ago

If only we could produce anti matter. A tiny amount would provide a fuel source viable for deep space exploration.

jharohit 10y ago
Anti-matter is produced at CERN for study https://home.cern/topics/antimatter https://home.cern/topics/antimatter. The problem is not production of it but the economy of producing it. It's still very costly to produce and then to build and engine around it which uses the energy efficiently is still at least 10-15 years. But do believe that the time to start actively looking into it is NOW.
- flukus 10y ago
  Is it stable enough to survive a space launch?
  - jharohit 10y ago
    don't think so. I am guessing you would need really strong magnetic fields to contain the anti-matter.
    - dogma1138 10y ago
      Magnetic fields aren't the only issue here. You won't be able to store large amounts of it since quantum tunneling will become a statistical problem.
      - witty_username 10y ago
        Could you explain? How would quantum tunneling of antimatter be a problem? The probability of quantum tunneling is exponential so adding a little more separation or reducing the energy can change the probability from 10^-1 to 10^-100.
berntb 10y ago

ramgorur 10y ago

"orion's death" (page 6-7) says it all, we might be able to see something like orion by today if there were no ban on the nuclear tests, and there wouldn't be any "ban" if there were no "nuclear attack in 1945".

luckystarr 10y ago

Nuclear salt-water rockets! https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket Powerful, fast, intriguing and disgusting. :)

Tuna-Fish 10y ago
Project orion has the name recognition, but nuclear salt water rockets would just be a much better use of the same amount of fissiles. Maybe we should start reposting the wikipedia link every month until people remember mr. Zubrin's creations more than project Orion?
- Pinckney 10y ago
  The big advantage of Orion is that we're reasonably confident it would work, and could probably build one within the decade with a serious effort. Zubrin's NSW rocket, on the other hand, falls into the "hasn't yet been conclusively proved impossible" category. We're not sure if we can control the reaction, and we're not sure how much heat would be transferred to the rocket if we can.
- maverick_iceman 10y ago
  Orion would have exhaust velocity ~1000-10000km/s. Compare that to NSWR's 66km/s. NSWR seems fast compared to today's chemical rockets but it's nothing compared to Orion.
- Symmetry 10y ago
  It's hard to say which is a more efficient use of fissiles. It's easier to burn up all your fuels in the context of an explosion as in Orion than in a saltwater rocket. On the other hand by bulking out the fuel with water to form a larger mass of propellant the saltwater uses it's energy more efficiently at the cost of lower ISP. But really, if we're willing to leak radioactive byproducts I think an open cycle gas core might be the best bet in terms of not-yet-developed rockets. http://www.projectrho.com/public_html/rocket/enginelist.php#id--Nuclear_Thermal--Gas_Core--Open_Cycle http://www.projectrho.com/public_html/rocket/enginelist.php#...
10y ago

askvictor 10y ago

Eli5: how does a nuclear explosion create a change in velocity for the spacecraft?

saulrh 10y ago
Sort of like a sailboat, except the wind is the vaporized material from the nuke. The nuke explodes, throwing a ton of mass and energy in every direction. The rocket uses a sail or pusher plate to catch part of that mass and energy, which carries it forward.
- askvictor 10y ago
  The mass is pretty tiny ( smaller than the ejected fuel pellet); I presume it's the fact it has huge velocity, hence huge momentum? What about photons; do they have the same effect as other particles, or is there a different effect?
  - Pinckney 10y ago
    You add a significant amount of mass to the bombs to act as propellant. I don't know offhand what fraction is typical for Orion designs.
avmich 10y ago
The explosion throws the products of the explosion - mostly plasma - into all directions. The spaceship is nearby, so some of the plasma hits the ship, which is hiding behind a strong plate. Plasma transfers momentum to the ship.

DrNuke 10y ago

Think of this as a startup case for 2016: an exciting idea on paper with a very improbable, cumbersome and practically impossible execution = non-viable, fail fast, goodbye.

Symmetry 10y ago

I think I like the recent work on pulsed fission-fusion better. Basically you have a normal z-pinch fusion system but surround the fusing hydrogen with U238. It absorbs the fast neutrons from the fusion, fissions, and creates more heat driving the fusion. There's some radioactive waste flying out the nozzle but if you're already in space that's not a huge problem. On the upside, people aren't going to get nervous about nuclear weapons in space since you can't trigger the fuel pellets outside the engine. And you don't need a massive pusher plate, you just direct the charged plasma with magnetic fields. And that means you can wait to turn this on until you're in orbit and avoid creating any fallout on Earth. https://www.nasa.gov/content/pulsed-fission-fusion-puff-propulsion-system https://www.nasa.gov/content/pulsed-fission-fusion-puff-prop...

maverick_iceman 10y ago
What's the Isp of this method?
- Symmetry 10y ago
  The first paper mentions 19,400 seconds at one point; versus 450 for hydrolox and 3100 for Dawn's ion drive. I did a blog posts on the theoretical limit on this sort of drive a while ago, using propellant velocity instead of ISP. http://hopefullyintersting.blogspot.com/2015/04/rockets-vi-very-nuclear-rockets.html http://hopefullyintersting.blogspot.com/2015/04/rockets-vi-v...