Thor Wotansen

You'd have to design new earth regolith-moving equipment anyways, to handle the unique environments on both Mars and the moon separately. The moon has some pretty interesting requirements for cooling, since you're in a vacuum and those are known to be good insulators. Also diesels don't work in either place.

One thing that has always bugged me in discussions about colonizing the moon or Mars is the casual way everyone overlooks the growing of food. I have a fairly well rounded background in agriculture, and I have spent a lot of time learning about the complex symbioses that a lot of plants depend on to survive. I know that NASA has been growing salad greens and some types of wheat in a very small experimental area on the ISS, but I don't think it's enough to get a good picture of what agriculture will look like on space colonies. First of all, any system that has colonists reliant on it for sustenance must be 99% sustainable at a minimum. NASA's experiments have been very closely monitored with sensors giving real-time data on all sorts of parameters to a team back on Earth, and the most they've gotten out of it is a few salads. For a serious system, it has to be somewhat robust, and able to handle some shocks and variation to conditions. It also needs to be able to reprocess all the wastewater produced by the colonists in a safe and efficient manner. These things are very possible to achieve, but they do present some challenges. Growing food is maybe one of the easier ones to handle. The most logical solution, in my mind, is aquaponics. Aquaponics is like hydroponics, but with fish. Turns out that fish poop has pretty much everything plants need to grow, and the plants are great at filtering the water for the fish. This means you only have to figure out how to feed the fish. Initially, formulating food for the fish might require some supplemental nutrients, but over time, it should be possible to stabilize the intake/output of the various micro-nutrients in the system. Probably the best species of fish to use is Blue Nile Tilapia, a fast growing breed used around the world in commercial fish farms. The other challenge to the system is processing the human poop. If composted properly, human waste makes a fantastic fertilizer for plants, but it is illegal to use human waste for growing food crops in the US. This is due to the possibility of spreading disease via unwashed vegetables. This can be avoided in our application, since we aren't growing our plants in soil. We can, however, reduce the possibility of spreading disease by using human waste to grow things like cereal grains and even fruit trees. The cereal grains can be used to formulate food for the fish, as well as for things like bread or beer. Obviously, setting up a self-sufficient system like this will require a large enough population to support it, but the advantages are many. Fore one, you won't have to have carbon scrubbers, since the plants will easily take care of that. Another aspect is the psychological benefits of having green things growing about the base. One of the largest challenges, however, will be maintaining healthy populations of bacteria in the system. Here on Earth, bacteria do a lot of the work in the treatment of wastewater, and in converting waste from both fish and humans into nutrients plants can use. These bacteria are everywhere on Earth, and can be relied on to just show up and start growing where conditions are favorable, but on an off world base, we'll have to bring our own. This could be extremely challenging, due to the high radiation environment in space, and any system on a moon or Mars base will have to be buried deep underground to protect it from radiation. There is also the potential issue of symbiotic organisms that are present here on Earth, that could affect how various plants in the system grow, or don't grow. It is also likely that we will have to introduce some species of insects into the ecosystem to pollinate plants for us. We might also bring earthworms and other species that help decomposition, so we can compost things like food scraps, plant fibers, and solids that settle out of the various wastewater systems. Worms would make great food for the fish, and they are excellent at breaking down fibrous materials. As you can see, the biodiversity of a sustainable life support system is immense and complex, and certainly not possible in a sterile space station. Sure, you could grow only certain plants and feed them with chemical fertilizer, but this would be very difficult to make self-sufficient. Anywho, I'd love to hear other folk's thoughts on the topic, this is just what's been rattling around in my head for a few years now. I'm currently thinking about going to school for engineering and soil science, either as a double major, or minoring in soil science with an engineering major. I've seen little to no discussion of the actual mechanics of "just growing food in greenhouses" and I'm hoping I can kick off a bit of discussion on the topic. I suspect that a lot of the folks into rockets and space travel aren't really into the sustainable farming movement, and vice versa, which might be why the topic is so often dismissed as a triviality or just glossed over by enthusiastic future Martians.

Interplanetary rock festival anyone? Everyone is expected to bring their own rocks.

I don't think anyone will be using a Starship as a source for building material, unless it is deemed unfit to fly again because of a rough landing that damaged the engines or something. Besides, you'd want a lot more mass between you and the surface of the moon, for radiation shielding. More likely we'll be using things like a Bigelow inflatable module, or an inflatable concrete building. If indeed the Starship can soft land 150t on the surface of the moon, delivering earth regolith moving equipment won't be an issue, especially if you're committed to moving in for the long haul. Andy Weir's book Artemis has a pretty decent outline of what a moon base might become, although I'm more in favor of burying it under a few meters of regolith, especially the farming area.

Could you make light-based transistors that require little to no power to operate? Maybe, but the bigger problem is memory. What are you going to use for RAM and long term storage? I don't know of any way to keep light just hanging around waiting for you to use it. Sure, we could certainly have a read only memory that could be used to execute programs with a purely light based system, but you won't be writing anything to memory without a high power laser or an optical sensor that reads to a more conventional disk.

Yeah, the term you're all looking for is specific thrust. The Ignition book has a bit about developing a fuel for SAM missiles that used mercury for this reason.

@kerbiloid I am 100% certain that reuse of the Falcon 9 first stage is increasing SpaceX's profits. You mentioned the cost of the engines earlier, saying that if you take one or two off and reduce the tank size by 15% you'd save in the long run. I think you're over estimating the mass and value of a restartable engine vs a one time use one. The hypergolic starter fuels that SpaceX uses to relight engines on the F9 1st stage are quite potent and don't weigh very much at all. The engines are designed to be radiatively cooled, making them quite reliable over multiple burns. It is known that engines are the most expensive single components of any large flying machine, so based on that alone, reusing a stage 3 times with 9 engines on it is more profitable than expending 3 stages with 7 engines each. The Falcon 9 is also a very inexpensive rocket to make. ULA and some others that make aluminum rockets form the skin out of thicker metal and then machine the inside of the skin with massive milling machines. This has the effect of making a very strong and lightweight skin, and measurably increases the performance of the rocket, but it contributes to the incredible cost of the rocket. SpaceX on the other hand, uses what amounts to high quality sheet metal to build their rockets, with little to no machining required, other han drilling holes, I presume. This makes the rocket slightly less efficient, but massively reduces build costs. The performance hit is fine, since the F9 design is quite capable, expendable or otherwise, and the cost savings in manufacturing can be passed on to the customer. SpaceX also saves vast sums of money by making most of their stuff in house, instead of subcontracting things to other companies like ULA does. In short, I suspect it costs SpaceX a fair bit less than $50m to make a brand new Falcon 9, and if they can reuse one even once, they can save quite a bit of money by not having to manufacture another one. Combine all this with Gwen Shotwell's claim of significantly less than 50% of manufacturing costs to refurbish the first reuse (they've presumably gotten better after ~35 times) and you have some very significant financial reasons for reusing the first stages. I think the argument that 'SpaceX is losing money therefore reuse of medium rockets isn't worth it' is disingenuous. We don't, and never will, know all the things that SpaceX is spending money on, and if they are indeed losing money, it is not because of the Falcon 9. SpaceX is pushing the boundaries of rocket technology in a remarkable number of directions, and regardless of your opinions of their motives, you can at least give them credit where it's due. Both the Merlin and the Raptor are amazing engines, and you really can't beat the price to performance of them. Whatever other R&D they're crunching in the background might be eating their profits, but I'm certain the Falcon 9 is more than capable of paying it's own way at current pricing.

RE the leg hinge structural question: front end loaders are articulated with a hinge right under the cab. The largest ones have operating weights north of 250t and payload ratings (what they're rated to lift) well over 50t. That's a lot of force on a hunger and you never hear of them folding in half. Granted there's a bit of a weight disparity, but SpaceX has a much longer hinge to play with giving them better leverage against the forces at play.

Since nobody has posted it yet. [seems I suck at embedding things]

Gosh darn it Florida, first Florida Man and now this?

Uh, they're called Space Marines, heretic. WH40k reference

It would be trivial to program that with a KAL 1000. You gave me some ideas though, so thanks

Not after seeing that. It seems I was operating under the mistaken impression that the craft had to be manned.

@boolybooly who is the current minimalist record holder and what is the current record?

I did this yesterday. It handles surprisingly well. KerbalX link

It would be cool if someone uses it to haul ridiculously outsized things around, like heavy equipment to disaster areas or luxury yachts for absurdly rich people.

The Osprey VTOL Testbed is an experimental airplane built to test the amazing new invention, the hinge! It handles well in forward flight, but nobody cares about that. The engine tilting is controlled with the 1 and 0 keys. The 1 key reverses the movement and the 0 key plays/pauses the movement. The Osprey takes off best with a bit of forward cowbell and will tend to pitch up until aerodynamic control can be established, so be quick with the transition to forward thrust once you take off. The plane is unstable in the full down position, but it’s useful for slowing down. To get a true hover you need to adjust the position of the hinges by reversing and play/pausing until the perfect angle is achieved. If you develop any lateral or reverse movement at sub 20m/s airspeed, you will crash. For vertical landing it’s best to carry about 10-15m/s forward velocity just to keep the nose pointing the right way. At that point it’s just a matter of controlling descent rate with the throttle. Enjoy. KerbalX link

I came to the realization today, whilst engaging in drudgery, that it should be possible to make a self balancing bipedal or even monopedal walk(ish)er using a probe core set to hold radial out and a number of balance weights with their actuation bound to pitch and yaw. I would build a demonstrator, but I have 3 more hours of drudgery yet.

That moment when you buy the DLC and try to play it before the update to the game that recognizes it hits.....

A warp dive will conserve momentum. If you want to make your scifi obey the laws of physics, you'll have to figure some other way of fixing the problem. One interesting thing about RKVs is that a sewing needle in the path of the missile, a few hundred miles above Earth would be enough to completely destroy it, and Earth would be saved. Having railguns or gauss guns that can fire tiny projectiles at high speed, and the computing power to calculate an intercept in a few milliseconds would be a believable counter to a ship massed RKV that needed some run-up. A ship is not a good RKV though. They have a tendency to be as light as possible, so hitting the atmosphere at, say, 5%C would make a very big fireball and perhaps cause local devastation, but not really destroy the planet. A more effective RKV would be an aerodynamically optimized slug of Tungsten or Uranium massing a few kilotons. This would be able to release it's energy far deeper in the planet and cause massive tectonic instability and enormous earthquakes that would pretty much level any buildings and rearrange the geology of the planet suddenly enough to kill most everything. If you want to blast the planet into little bits, you need to go big.

There's much easier ways of wiping out all life on earth than engineered viruses. Roundup is a systemic herbicide that targets specific protein generation systems of a plant, and shuts them down, resulting in death. Creating a similar substance to kill really any type of life on earth is most likely trivial. This type of xenoforming is not what I consider to be conquering; rather, it is exterminating. Conquering, in my mind, is the subjugation of the sentient life on the planet, for whatever purposes you need them for, be that biological computing, breeding for assault armies (but why?), or to fulfill some holy prerogative of some alien god. Again, if they want to kill us and take our planet, they will not show up with a big fleet and do some planetary laser art. They will send a tiny probe or a relativistic missile. But really, the only thing of value to aliens, that they can get nowhere but here is us. If they need materials, there's innumerable tons of whatever they need far closer to wherever they come from than Earth. If they need alien soldiers, it's far easier to bio-engineer their own. The only logical reason to come here is to meet humanity and study it's culture and biology, and if they show up with a strong display of force, then they are worried that we are a bunch of petty, violent apes that are scarcely past beating each other with clubs, and generally can't be trusted to be civilized. And if you say that alien logic is inscrutable, it's not. If they have a survival drive, which they would have to have to survive, they will be cautious, and if they suspect we have a small chance of beating them in a fight, they will either eradicate our military means or not come at all.

Alien races might be very alien, however, there are some things that stand true, regardless of how different they might be. No alien race will attempt to conquer earth without a very good, logical reason. If they intend to keep us humans alive, then they will have some form of communication, and will likely have already figured out how to communicate. If they want the resources of our planet for some reason, they would get far more stuff by blowing the planet into tiny pieces. The only reason aliens approach earth with a large armed force is to intimidate us into accepting what they have to say with very little question. The only thing that makes earth special is life and unbound oxygen.

I disagree. Any life form that wins at evolution long enough to develop space travel has quite a few things in common with humans, like a drive to survive and proliferate it's genetic code in whatever form that takes. Math is math, and the only difference will be the symbols used to describe it. Physics also dictates the types of weapons that are viable, although we might learn a thing or two. Generally speaking, if they come in force with a bunch of huge warships bristling with weapons, they want us alive, if we get annihilated by a relativistic kill missile, we won't likely notice.

The easiest way to move a planet is a gravity tractor, which would be fairly trivial, since we have a nice convenient moon. All we need is a nice beefy fusion torch on the front and back of the moon and we just fire it for a day when it's in line with Earth's prograde direction.

The livestream has the time pushed to 8 right now.