KSK

I don’t know about a fusion explosion but the ITER central solenoid apparently produces a 13 Tesla field, which is comfortably lower than the field strengths used by modern (600Mhz +) NMR spectrometers. Those will have a safety line around them which you shouldn’t cross if you’re wearing a pacemaker (or are carrying credit cards - ask me how I know…) but the ‘danger’ zone around the magnet is not large. So I’m not sure that fusion rocket magnetic fields would be a particular problem, especially if you put it at a decent distance from the crew compartment.

They’re not exactly neutron mirrors but neutron reflectors are a thing. They work by scattering incoming neutrons, so a certain amount of them will be back scattered or reflected. Part of the control scheme for NERVA was based on neutron reflecting drums coated on one side with a neutron absorbing material. By turning the drums appropriately, neutrons escaping the nuclear reactor could either be absorbed or reflected back into it to increase the rate of fission. The other part of the control scheme was the fact that liquid hydrogen is a very effective neutron moderator, so the rate of fission could also be controlled by changing the propellant flow rate through the reactor. I believe that a number of shadow shield designs also incorporate neutron reflective layers. I’m unsure how ‘reflective’ neutron reflectors are but better reflectors would probably be massively useful in basic research. Powder neutron diffraction is a very powerful technique which complements powder X-ray diffraction, and is especially useful for studying magnetic materials (neutrons have a magnetic moment so neutron diffraction patterns can give you information about magnetic ordering in a material.) I’m thinking that better materials for neutron optics would make a lot of solid state chemists and physicists very happy. Source: I used single crystal X-ray diffraction a lot in my Ph.D. I knew quite a few of the shake-and-bake solid state guys down the corridor, and they did a lot of neutron diffraction work, which meant they got to go and hang out at synchrotrons and exciting Big Science facilities.

Well, I have a confession to make. I was firmly of the opinion that Obi-Wan Kenobi was a series that didn’t need to be made, and was basically Disney milking the Skywalker Movies for all they were worth. Then I watched the first three episodes back to back and I take it all back. Well - it may still be a shameless milking exercise but it’s done well enough that I don’t care! McGregor is doing sterling work and the actor playing his co-lead is absolutely knocking it out of the park. I agree with @MKI re Reva, and it’s looking like @JoeSchmuckatelliis getting his wish re Vader. Bring on Part IV when I get a spare moment.

Really interesting link - thanks! I’d also recommend it to @Spacescifi as a very nice and accessible reference article for near-future deep space missions based on a variety of propulsion systems.

You’ve got that backwards. It’s not that tumbling makes the fuel run out, it’s that the fuel running out causes the tumbling behaviour to change. I haven’t read the study that @SunlitZelkova refers to but it sounds like once enough propellant had been used, the vessel’s centre of mass was shifted sufficiently close to the crew compartment (or may even have been within that compartment) such that spinning the vessel was no longer useful for creating artificial gravity. Happy to be corrected. This is all quite general - it doesn’t matter whether the propellant is a tank of liquid methane or a rack of nuclear pulse propulsion units.

I’m quoting from your original post rather than your reply to Vanamonde. As far as I can tell, the rotating inner habitat cylinder is not required to make ‘down’ be towards the nose of the ship.

I don’t quite understand why you want this if you’re creating artificial gravity by having the whole vessel tumble. If your T-shaped spacecraft is tumbling end over end, then the centrifugal force will be acting along the long axis of the ship towards the cross-cylinder (and also towards the other end of the ship but we don’t care so much about that in this scenario). In other words ‘down’ will be towards the nose of the ship anyway - which is what you said you wanted. There’s no need for a centrifuge.

Interesting topic. My own writing featured a rotating spacecraft, so I've done a bit of research and done a bit of thinking about possible designs. With that said, I'm not an engineer, so there will be a ton of things that I haven't considered. I found SpinCalc to be a useful tool for establishing spacecraft dimensions. Basically, it lets you play around with four interlinked parameters: radius, angular velocity, tangential velocity, and centripetal acceleration (i.e. artificial gravity) and see how they all affect each other. It also gives you an idea of whether a particular parameter is crew-tolerable or not, although I'm not sure how it calculates tolerability. That's not a particular problem though - if you want to be more conservative, you can just adjust the parameters to suit. For example, plugging 1g centripetal acceleration and 100m radius into the calculator gives me an angular velocity of 3 rpm and a tangential velocity of a bit over 31 m/s. So, whilst the ship isn't spinning particularly quickly, the crew would definitely notice the view outside whipping past at 31 m/s. Incidentally, the calculator marks up that tangential velocity with a yellow flag, meaning that it would be too fast for immediate crew comfort (although some authors disagree) and would require them to acclimatize. A rotating body will rotate about its centre of mass. So, taking your T-shaped ship and assuming that both short 'arms' of the T have equal mass (for simplicity), the ship will tumble about a point somewhere along the long body of the T. If all the mass is up at the crew compartment, then the centre of mass will be further up towards that end of the ship - which means that the crew compartment isn't as far from the centre of mass, giving a shorter effective tumbling radius for creating artificial gravity. Conversely, if all the mass is at the other end of the ship, near the engines, propellant tanks etc., then the crew compartment will be further from the centre of mass, giving a longer effective radius for creating artificial gravity. Centre of mass in any ship is likely to be strongly affected by the location of the propellant tanks - and will change as the propellant tanks empty out. How easy it is to get a ship rotating about an axis will depend on its moment of inertia about that axis. Moment of inertia is a function of mass and distance from the axis of rotation. So, consider two equally massed spacecraft attached by a tether. The centre of mass for that system will be at the mid point of the tether and the moment of inertia will depend on the length of the tether. Long tether = masses are further away from the centre of mass = higher moment of inertia. On the other hand, consider two balloons tied to opposite ends of a brick. Here, most of the mass is going to be the brick itself (unless you have really heavy balloons ), so most of the mass is a short distance from the centre of mass, so the moment of inertia for the system is going to be fairly low. If you're relying on tethers, you need to consider how the tethered compartment interacts with the rest of the ship and how the crew get in and out of it.

Agreed. At a minimum I think some kind of FTL capability will be required, which may not even be physically possible. Crewed interstellar travel at slower-than-light speeds, at least for 21st century wild type humans, strikes me as a last desperate option against some kind of overwhelming disaster. On the other hand, there are some interesting stories out there which deal with STL interstellar travel. One of my favourites is Greg Egan’s Diaspora, in which most of the main characters are sentient software running on molecular scale processors. Journey times are dealt with essentially by slowing down the running speed(?) of that software by arbitrary amounts so that a year of subjective time (from the character’s point of view) is equal to an arbitrary number of objective years. The technology is just as fantastical of course but it’s a different approach than the Star Trek style FTL spacecraft.

I don’t know - an 8 hour round trip to Alpha Centauri would probably make space interesting to more than just the pros. But yes - spaceflight per se is not terribly interesting. What makes it interesting is the human (or alien - this is sci-fi after all) angle, whether that’s an Apollo style leap into the unknown on bleeding edge but ridiculously primitive for the task at hand, technology, or how society evolves on board a generation ship, or everyone pulling together to rescue a stranded astronaut or whatever. Likewise for space exploration. Unless you’re seriously into the relevant science, most of the time it’s probably going to be rather dull. Science fiction tends to be about the times when the intrepid explorers find something interesting (and relatable) or set off to investigate something interesting that’s already been found. I’m struggling to think of any examples of stories about the geological and astronomical survey of System 2345b, which consists of a handful of rocky planets, a totally standard asteroid belt and a defiantly ordinary gas giant or two.

They absolutely don't. If you want a Star Trek like setting, you'll probably need Star Trek like technology. There's a reason it was written into the show after all. But all the problems you point out can be positives as well, if (as you mentioned in a previous thread) you want a story that shows that space travel is still hard. Needing everything to be pre-planned, having to obtain propellant for the journey home, needing to use shuttlecraft to land. These are all risks and places where things can go wrong, that make that exploration journey hard and dangerous. Star Trek (and epic scale space opera in general) is great but it's not the be-all-and-end-all of science fiction either.

Only if you insist on your fictional spacecraft being STABs (Single stage To Anywhere and Back again). If you're willing to accept any or all of multiple stage rockets, on-orbit assembly and refueling, some degree of infrastructure at the landing site, or use of a mothership and dedicated landers (which may be launched separately and make their own way to the destination to rendezvous with the main crew vehicle), then you can have pretty hard science-fiction journeys to anywhere in the solar system. Examples: Starship: Two stage to orbit vehicle, both stages reusable. Upper stage refuels in orbit, flies to and lands on Mars, refuels on the surface, returns to LEO. Saturn boosted Orion: Multiple stages to orbit, booster stages are discarded. Upper stage flies to Mars, deploys separate landers to get astronauts to the surface and back. Aldrin Cycler. Main spacecraft in permanent cycler orbit between Earth and Mars. Smaller shuttlecraft used at either end to get crew on and off the Cycler. Original Orion. Single Stage to Anywhere (but don't expect it to land anywhere). Would probably need dedicated shuttlecraft to land crew on another planet but has the mass budget to cope. The above have all been seriously studied. One is being built. It's not that hard to come up with plausible mission profiles for anywhere in the Solar System using currently available, or reasonably plausible propulsion. It's extremely hard to come up with one that only involves a single spacecraft. Yes they will have long journey times, yes they will have challenges to overcome (prolonged crew exposure to zero gravity, need for radiation shielding (either from background radiation or the ship's engines) etc. This is hard science fiction. No need to write an engineering treatise on any of those problems but showing that they've at least been considered adds realism to the story. Even if that's a throwaway description of the mothership and her rotating habitation module. If you don't want the story to be quite that hard, then handwave things a bit but keep the technobabble grounded. Use a 'fusion thruster' for example, without going into the nuts-and-bolts details of how it works. Everyone knows that fusion means lots of energy, so a fusion thruster must be really powerful right? As for 'not teaching the viewers that rocketry can do things far better than they actually do', in the immortal words of one starship medical officer. "You're writing fiction, dammit, not an engineering textbook."

Some real life numbers - or as close as they get for Orion. This is from a 1963-64, General Atomics study for NASA on a 10m diameter Orion craft designed to be launched on a Saturn V. The ship is launched ‘dry’ (mass at launch is 100 tons) with propellant and crew (and presumably supplies) loaded on-orbit. Departure mass is 600 tons, payload to Mars is 80 tons, with a round trip duration of 450 days. Artificial gravity created by slow tumbling of the ship in transit. Propellant requirement - 2782 kiloton yield pulse units weighing about 300 lb each This is all taken from George Dyson’s ‘Project Orion’. A couple of thoughts. Firstly, even with nuclear pulse propulsion, about 2/3 of the ‘wet’ vehicle mass is propellant. (We’ll ignore the political issues involved in launching nearly 3,000 kiloton yield weapons into space). Secondly, a single pulse unit is equivalent to nearly double the ‘wet’ vehicle mass of TNT. Even accounting for the fact that modern high explosives are likely more performant than TNT (I have no knowledge on this point), the mass of explosives required seems to make an HE propelled Orion a non starter. Thirdly, if one wanted to make this an SSTO as per the original post, a 600 ton vehicle would be… challenging to launch with reusable chemical boosters, whatever propellant combo one uses. In that regard hydrolox is a poor choice due to the low density of liquid hydrogen (although I agree that it’s probably the easiest choice for in-situ refuelling) - witness the size of the main tank for SLS, which still requires a hefty SRB assist to get off the ground.

Hmmm. The modified g-suit I had in mind would have more air bladders than normal and would be able to operate them in sequence to move fluids around. A bit like peristalsis. Would that be enough to avoid pressure sores (and you’re right - I could see those being a problem) especially if the suit wasn’t on all the time? I have no idea. As I said, the g-suit idea was just speculation. Edit. Without a g-suit or similar restraint, I wouldn’t have thought pressure sores would be a problem in zero-g. As for the effects of zero-g on eyesight? Again, you’re probably right but again, the deterioration in vision clearly isn’t bad enough to stop astronauts going into space again. I know we’re not in the 60s any more and that astronauts are no longer expected to be perfect physical specimens but I’d have thought you still need to be in pretty good shape to be strapped into a spaceship - and to have pretty good eyesight before you’re allowed to fly them.

Havoc is a bit strong in my opinion. Long duration spaceflight is a thing and, whilst it certainly doesn't sound pleasant to come back to Earth after an extended period in zero-g, astronauts are still quite capable of undergoing multiple gees on reentry - which suggests that they're still reasonably fit and healthy. Plus all the effects you mention are mostly reversible. They certainly haven't prevented astronauts from doing multiple tours on the ISS - two appears to be pretty standard, three is quite common, and Yuri Malachenko has apparently served on five ISS crews. But hibernation. I doubt it'll mitigate any effects due to fluid displacement but it might actually help to prevent bone atrophy. One of the points of hibernation for space travel is to lower the astronaut's metabolic rate, thus reducing life-support requirements. Bone remodelling doesn't happen instantly and is an active process involving specific enzymes and whatnot (the technical description, you understand. ). So if overall metabolism is lowered, it would make sense to me (which doesn't necessarily make it correct!) that bone remodelling is slowed down as well. On a purely speculative note, I wonder if a modified g-suit could be used on a hibernating astronaut to help move fluids around the body and stop them pooling as much.

This thread puts me in mind of "Blue Remembered Earth" by Alastair Reynolds. It's set in a near future Solar System and interplanetary travel plays a reasonably large part in the story, although mostly for getting the characters from place to place rather than going into great technical detail. The gist of it is that ships are propelled by VASIMR thrusters and are generally described as mostly being propellant tanks and radiators. VASIMR gives them good ISP but rather underwhelming thrust so journey times, whilst being better than we can do with current technology, are measured in weeks and months rather than days and weeks. Hibernation is used to get around the journey times - as a passenger you're put into hibernation, loaded onto the ship, unloaded at your destination and revived. You'll wake up in hospital, feeling like hand-carved mulch, with temporary amnesia and reduced motor control, both of which come back after a couple of days. For longer journeys you're most likely going to be walking around with an exoskeleton assist for a week or two until (and probably getting medical treatment) until your muscle tone rebuilds. The ships themselves are relatively flimsy. They're as light as possible and, much like current rockets, built to be strongest along the axis of thrust. Try and maneuver too hard in them and you'll end up snapping them in two, which doesn't tend to go well. I quite liked this as a reasonably well thought out, consistent depiction of near-future spaceflight with (recalling another recent @Spacescifi )thread), well optimized ships, given the available technology, and which also did a decent job of showing that spaceflight was still hard by leaning into the medical after-effects of relatively long duration spaceflight, especially for regular folks.

You’d need to pull the cord pretty fast though - do you think that tying it to a rocket would work?

Correct about the microwave heating but ultrasound and microwave radiation can't really be compared. Different frequencies (by several orders of magnitude) and one is electromagnetic and the other isn't. Having said that, focused ultrasound has been approved for certain surgical applications where it's used to raise local tissue temperature. Soundwaves (I'm unsure about the frequency used) can also be used in lithotripsy to break up gallstones or kidney stones for easier removal. On the gripping hand, ultrasound is commonly used in the lab to disrupt or lyse cells. Useful for isolating proteins or nucleic acids - lyse the cells, centrifuge to remove membranes and other debris, extract what you want from the supernatant. My concern with using ultrasound in cryogenics is that you'd want to interrupt ice crystal formation at an early stage before they become large ice crystals, at which point the damage is done. However, I suspect (but do not know) that dispersing small ice crystals with ultrasound would simply lyse the very cells that you're trying to protect. My best guess is that it would be possible in principle (ultrasonication is used to homogenize mixtures after all, so homogenizing ice crystals doesn't seem like too much of a stretch) but difficult and dangerous in practice. For space travel, some kind of induced hibernation might be a better bet, with or without induced hypothermia. Cooling the traveler down in other words, but not freezing them. Edit: One thought about any sort of microwaving or ultrasonication of tissues - low level, uniform, heating or ultrasonication is going to be difficult to achieve because the human body is decidedly non-uniform (spherical cow physics jokes notwithstanding ). I'm thinking about the brain in particular which is encased in an inconvenient bony reflector and is probably one of the more essential organs to safely preserve.

Late to this party but I, for one, welcome our RoboTurtle overlords.

Probably best not to imagine what happens if someone lets the balloon go and all the air shoots out of one end.

This is not my analogy but I quite like it. Imagine a balloon. Paint a bunch of dots on it to represent stars (or galaxies - whatever). Now inflate the balloon. The radius of the balloon represents the time axis. The surface of the balloon represents 3D space. As we move forward in time, all the stars move away from each other but they’re not moving away from any single point in space although they are moving away from a single point in time.

God does not play dice with the universe.

You’d need a very big tube if I’m understanding your description correctly. Let’s assume a 40,000 km acceleration tube (circumference of the Earth to a reasonable approximation). Let’s assume constant 4g acceleration and deceleration, so half of that tube is used for charging the Drive. Starting from rest, s = 1/2 at^2. Solving for t, I get 1000 seconds, approximating 4g to 40ms^2. So a fully charged Drive can accelerate for 1000s at 4g. So what delta-V does that give? Delta-v = a.delta-t Solving for v, I get 40km/s. Thats… curiously unimpressive for the infrastructure involved. So much so that if someone could check my maths, that would be appreciated. For reference, the Saturn V could accelerate the Apollo CSM+LM stack to around 10km/s.

Just for comparison purposes, according to Wikipedia, the world Maglev speed record is 603 km/h, achieved on an 18.4 km track. That's from rest to full speed and back to rest. A little bit of back-of-the-envelope maths gives me an acceleration of approximately 0.15g and a time to reach maximum speed of 110s or just under 2 minutes. Put a Maglev in a vacuum tube so that it can keep accelerating and you very quickly get to some pretty ridiculous speeds even at .15g. Again, for comparison, commercial passenger jets travel at about 600 mph (from a quick online search) or 965 km/h. The above Maglev in a vacuum tube would hit passenger jet speed in about 3 minutes and about 14 km into its journey, assuming my arithmetic checks out. In that context, accelerating at 1 or 2g looks a bit like overkill. Edit: This is a very rough calculation of course - for one it ignores air resistance completely and, for two, it assumes a constant acceleration to the half way point and then constant braking to rest. But I think it gets the main points across - it should only take a relatively modest constant acceleration for a vacuum tube train to comfortably beat out commercial air travel for raw speed, and those kinds of acceleration are quite achievable with current technology. Whether a vacuum tube train can be made as reliable and safe as commercial air travel is another matter.

Good to see this one back! Glad college life is going well too!