Bill Phil

SR2 is 3d. Has some interesting stuff in it too.

I’m more of a believer in stuff like launch loops and mass beam propulsion systems than space tethers - those just seem easier and offer better performance. But space tethers are still a very interesting concept to me. Anything that can make Earth to orbit launch easier is a cool concept. And space tethers can do quite a lot as well. But I don’t think tethers will offer as much capability as one would initally believe. Not to say that they can’t, but the geometry of space trajectories is incredibly complex. For example, launching from anywhere that isn’t the equator requires plane change manuevers to go to GEO. Pretty significant ones in some cases too. This means you have even more constraints on your system - launching from anywhere on Earth to the Moon requires a plane change unless the time and place is perfect or reasonably close. This is easy for rockets since you can just do it when the time is right. But for tethers you have even more time constraints on the mission - the tethers themselves require highly accurate timing both for capture and release but also for getting to the tether in the first place. Not to say that it isn’t possible, but it would definitely be more complicated and less capable without expanding the infrastructure considerably. You’ll need “out of plane” tethers that catch and launch out of plane, which creates some interesting issues as well. Still could be interesting to look into.

I didn't multiply acceleration by mass on a Dynamics test and still got most of the credit and even got a good chunk back when I talked to the professor about how I worked it out. So long as you get an answer, physics is generally quite lenient and forgiving.

I suspect that we lack the understanding necessary to really make that claim. The relationship between fundamental forces could make it so that such a thing just doesn't happen. Some process may create "negative" energy, so that the energy remains conserved. If not, it would be interesting if an advanced species tried to prevent the expansion of the universe by "creating" more energy, at least locally (perhaps within their local supercluster). Of course then you'd need to deal with entropy. And possibly proton decay. But if it is as you say this could be doable.

Hmm.... Might be able to make some ultra-strong materials. Still a fundamental limit to strength, but a Niven style ringworld falls well below it, and a Banks orbital is still smaller. But I doubt mass replication is possible - the energy has to come from somewhere even if you can manipulate it to be matter. Though it does become a lot easier to transmute elements.

From an energy used per unit thrust perspective, yes. But a photon rocket should have the highest possible specific impulse. Only in the case of rockets. A photon rocket may not use physical propellant in the same way a conventional rocket does but it does use mass to generate thrust. There are other propulsion schemes, however. For example, photon sails get 150MW per N, because of the reflection. Some concepts create a resonance cavity between the sail and the origin and can get hundreds of kW per N. And in theory a vehicle could reflect an incoming mass stream and get good performance as well. Such drives are not rockets, and can achieve better thrust per unit power than photon rockets. This is because photons are extremely inefficient at transferring momentum. This can be improved by reflecting photons as many times as possible before they become impossible to reflect or by using particles with mass. Within the context of interplanetary travel a network of beam stations (likely firing a mass stream but laser beams are possible too) could provide reasonably fast travel. And in theory such technology could be scaled up to provide interstellar launch capability as well, though that would be a far future endeavor.

Vernier engines can actually be part of the RCS, though Apogee Motor is a bit weird. Though by the time of the Universal Century it's possible that a number of terms have changed... I guess aerospikes just aren't really well known enough or considered desirable for the "cool factor".

Fair enough.

Information can't travel faster than light. As for the speed, I'm not sure if it would be the speed of sound or not. However, the application of a force would create a stress locally, and that stress would have to propagate. Stress waves propagate differently depending on whether or not the stress is normal stress or shear stress. I believe normal stress propagates at the material's speed of sound, provided that it's isotropic and of constant density. However, shear stress propagates at much lower speeds generally since it's based on the shear modulus of the material which is usually lower than its elastic modulus. Basically, the impulse is only applied locally. The force applied creates local stress which then propagates like a wave. Interestingly, this would also mean that the material would have an infinite elastic modulus - infinite tensile/compression strength.

Well he could theoretically do something. I mean there’s a version of him that has god like powers.

Ceres is also immensely more massive. It's not stability. It's that asteroids aren't structurally sound. And even if you don't spin the asteroids up you want a rotating habitat of some kind and excavating that material leaves you with a huge amount of stuff that you could build rotating habitats with since it's likely to be denser than the air you fill it with.

It is possible. And it may be done one day. But it's something that is considerably difficult compared to orbital habitats. Indeed. Such a project would be quite a challenge. But it's a question of scale. Escape velocity in high Earth orbits can be on the order of hundreds of meters/sec. At 1 hundredth of a gee such a maneuver wouldn't take too much time. Of course, for a habitat (and some other stuff) massing around 50 million tonnes, that's still a lot of force. Something like 5 giganewtons. But again, that's a question of scale. We can use a huge cluster of rocket engines, or we could use mass drivers. Or perhaps some nuclear pulse drive system. Not too crazy, really. Indeed nuclear pulse drives generally work better at larger scales, though this doesn't apply to all such drives. Though one based on Mag-Orion could do it well, and at high ISP too. Though you wouldn't want it to use actual bombs. Doesn't seem any more advanced than the settlement itself to me. Sure, there's a minimum degree of self-sufficiency. But what I was getting at is that the individual settlements themselves will be more akin to cities or even neighborhoods than nations. A nation-state could be capable of self-sufficiency, but could that be said of the cities within it? Or individual neighborhoods? As a whole system the space settlements and space based industries could be self sufficient, but individual settlements need not be. That's too much to ask. I think it's reasonable to expect them to grow their own food, but even that would require some regular inputs over time. Even settlements on a planet have a limit to their modularity. The question is what is the optimum size for a given module? This is a limitation of orbital settlements, but it isn't a deal breaker. We can start small as we build up the infrastructure. Some rather small designs exist but still have reasonable populations. And over time the size of new colonies grows until we reach the optimum for size and ease of construction. There are concepts for expanding rotating habitats but I am not too familiar with them. However, it is definitely possible to inhabit a small portion of the colony and not pressurize the rest until you need it. Beyond that there are a few ideas where a cylinder can be lengthened while under rotation. I personally don't like that idea since it's overly complicated. It definitely requires more infrastructure, but I would argue that it's not that much more. The industry in space can be bootstrapped to an extent and once it reaches the necessary size building space colonies can be done without too much trouble. It's essentially a giant pressure vessel - and cylinders are well suited to having a huge number of identical parts. Once the industry reaches a certain point building a new colony could become easy enough that doing it for just a few hundred people isn't seen as a problem. Especially since you'd want to have a continuous production of colonies - maybe even with a stable population. Don't get me wrong, using the Moon as a resource is definitely great. But I don't really think the Moon or Mars are suitable for human habitats. We can do much better with artificial environments built in space.

British Engineer? Pretty sure he was from the American South, at least in-universe.

Not necessarily. Certain planets would make excellent sources of raw materials like Mercury or Mars, provided civilization is suitably energy rich. Actually using asteroids and comets as habitats isn't a great idea. It seems great at a surface level, but consider that asteroids aren't all that structurally sound. And even if they were, the amount of material that you'd excavate would be large enough that you could build more habitat space. It's not self-replication in the context of microscopic things. It's self replication on an industrial scale - that is, using industry to self replicate industry. All you need to bring is a population to provide labor and the means of production for them to work on. If every space habitat has its own industrial block that can build another space habitat (with another industrial block) then said habitat can self-replicate, provided the population is large enough to provide the labor necessary and the needed inputs are provided. This isn't nanomachines, but rather more conventional machines (though adapted for use in the free fall environment if necessary). So really it's a symbiosis of nonliving things and living things that work together to self-replicate, provided the right energy and material inputs. The only strict problem with orbital habitats is material resources. The fuel will be solar energy (or nuclear energy if necessary). Even then, with enough energy this problem becomes rather solvable by sourcing materials from places that have those materials. Some places will have everything in varying quantities and others won't. But to build a space habitat 95 to 99% of the mass will be shielding, so it can be basically anything. It's still desirable to place habitats near material sources though, in energy terms. So in orbit over a planet or large asteroid. Possibly bring some other asteroids with good resources nearby. How is that any different from settlements on Earth? They need regular resupply as well. No space settlement should ever be considered to be an isolated system and no large human settlement should be expected to be entirely self-sufficient. Every settlement is but one part in a much larger whole, and should be considered as such. Even settlements that are sent to other planets to then self-replicate won't be completely isolated unless they're going on an interstellar voyage. In fact, you could send a cluster of settlements at once along with a decent cache of necessary resources to use while en route and shortly after arrival. No human settlement is ever completely self-sufficient. Even a Moon or Mars settlement would require the infrastructure to receive regular cargo and manufacture things. Not to mention large scale infrastructure to build the settlement. Not only that but the vast majority of the mass of orbital habitats is just that: mass. It can be anything. This is because most of it is radiation shielding. So in terms of mass that provides living space, it'll likely be quite similar to the mass requirements for any settlement on a planet/moon, but this one can provide a full 1g. No one should live on the Moon. People can work there - to provide resources for orbital habitats and other purposes - but no one should live there. The gravity could be much too low for healthy development. But it can be a decent source of some materials. Space habitats are basically housing (with some more stuff but that's basically what they are). Resources can be gathered from other places, and manufacturing can be done either on a space habitat or wherever is convenient. But housing should be as comfortable and healthy as possible. These requirements necessitate 1g. And the only way to get that is rotation. This could also be done on a surface but that's highly complex in comparison and the surface itself limits expansion. So building such habitats in space would be the best option.

But what can you do if you die in a car accident? Or anything else? Risk of death will still exist. The life expectancy may rise to thousands of years, but that's a blink of an eye compared to the half life of proton decay. Sure, there may be a way to save someone, but there's a new debate about whether or not that's even the same person. Biological immortality isn't the total elimination of death. Just a large reduction in the risk. But that risk still exists.