One of the problems of using an Orion drive or any pulsed based drive, is that the occupants will feel a sudden jolt of force instead of a smooth constant acceleration for artificial gravity. Is there a way of alleviating this problem for pulsed drive ships?
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1$\begingroup$ I had several colleagues who had programmed military rockets for life. According to them electronics can withstand about 10g. More than a human but not much more. I do not know the details but a complex system incorporating GPS, cameras, perhaps even radar - apparently has enough moving parts to fail when kicked hard. $\endgroup$– VoracJun 29, 2022 at 11:40
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9$\begingroup$ @Vorac This does not sound right. Air-to-air missiles handle accelerations of 30-50 g. And guided gun rounds over 1000g. Maybe a Tomahawk is limited to 10g? But that's because it lacks the maneuvering capability anyway. $\endgroup$– TheracJun 29, 2022 at 19:08
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3$\begingroup$ @Robbie I hate to disagree but I think this is not quite so simple a question...Camille's answer is pretty interesting $\endgroup$– 0xDBFB7Jun 29, 2022 at 23:32
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3$\begingroup$ @Vorac - There are gun launched electronics. Hardening things for 10,000+ (ten thousand) G is relatively straightforward, if you follow the appropriate design practices. $\endgroup$– Fake NameJun 30, 2022 at 7:35
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2$\begingroup$ @Vorac Also note that SpinLaunch has shown that an unhardened iPhone can survive massive g loads if they are applied gradually (which admittedly is not the use case here, but is still relevant I think). $\endgroup$– Charles StaatsJun 30, 2022 at 13:03
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4 Answers
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You need to realize that the ship is not accelerated by the atomic blast, it is accelerated by the springs(*) that exist between the push plate and the ship. I.e. while the push plate experiences insane g-forces, the momentum of the push plate is transferred to the ship continuously over an extended period of time. If you detonate the next charge before the springs have pushed the plate all the way back down, you will have uninterrupted gravity on your ship.
Of course, the further forward the push plate is, the higher the force transmitted by the springs will be for virtually any spring design. However, if you give the springs a sufficient preload, you can limit the transmitted force to a pretty narrow range, and thus provide for a smooth ride. How much you are willing to preload the springs is simply a matter of compromise between a smooth ride and beefiness of the springs structure. The higher the preload, the more energy is already stored in the extended springs, and thus the heavier the springs need to be, eating into the the payload capacity. Nevertheless, continuous acceleration of the ship is always possible by using a high enough blast frequency.
*) With a very general definition of "springs": They could be anything from large pneumatic cylinders to electric systems. The point is, that they continuously act to accelerate the push plate downwards.
answered Jun 29, 2022 at 19:16
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$\begingroup$ Thank you, but I have one more question. What is the ideal amount of momentum a pulse unit must impart to the ship for a smooth g-1 force. $\endgroup$ Jun 30, 2022 at 2:36
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6$\begingroup$ @spaceamoeba1010 That is a question which is way too specific to a particular ship design, and opens too many cans of worms for me to even attempt to answer. It's a complicated optimization problem where I'm sure that I would miss key components. $\endgroup$ Jun 30, 2022 at 9:27
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1$\begingroup$ This seems like a fancy way of saying that the ship has a suspension. $\endgroup$– benrgJul 1, 2022 at 7:47
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The short answer is to use a lot of pulses/second. They'll more or less average out into a steady(ish) push.
That's why a 12 cylinder engine vibrates far less than a 1 cylinder engine.
answered Jun 29, 2022 at 12:21
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$\begingroup$ That's not a good analogy. Engines with many cylinders can be very smooth because the movements are nearly sinusoidal and thus the forces can be made to cancel out almost completely. With an Orion drive, you may be able to make the jolts smaller by making more pulses, but it only scales down linearly. This would never be something you could call "steady" without the suspended pusher plate. $\endgroup$ Jul 1, 2022 at 16:18
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Wikipedia's long article says:
The pusher plate would be mounted on large two-stage shock absorbers that would smoothly transmit acceleration to the rest of the spacecraft.
A diagram there confirms two shock absorbers, but lacks hard numbers about stroke length, energy dissipation, time constants, variation of acceleration transmitted, etc.
answered Jun 29, 2022 at 16:43
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$\begingroup$ The answer may be "yes, for a brief time". The real engineering problem is having a high enough specific impulse to be able to accelerate continuously (or continually). $\endgroup$ Jun 29, 2022 at 16:56
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1$\begingroup$ The original design was limited to mechanical shock absorbers. There's no reason a modern system couldn't be handled almost entirely by hydraulic actuators under electronic control. $\endgroup$– GrahamJun 29, 2022 at 17:42
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1$\begingroup$ @spaceamoeba1010 See cmaster's reply to that question. $\endgroup$ Jun 30, 2022 at 13:55
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Dan suggested lots of pulses per second. Using lasers to create fusion in pellets might offer a route to large numbers of small pulses through thermonuclear fusion. Do lots of tiny 'bombs' still count as an Orion drive?
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1$\begingroup$ Sure, that counts, as long as the pellets are big enough to not be confused with a liquid! $\endgroup$ Jun 30, 2022 at 14:00