Terwin

I am under the impression that x-rays tend to interact weakly unless you have a lot of mass/density, and that is not something deuterium is known for(having an atomic mass of 2). This is why x-rays pass through flesh easily and can be more easily blocked by denser bone. That being the case, you would need exceptionally high reflectivity. If, for example, there is a 1% chance of an x-ray being caught by a deuterium atom each time it encounters the atom, and a 1% chance of encountering such an atom with each pass through the reaction chamber, then you would need the average reflection to be better than 99.99% or else the majority of your x-rays will escape before imparting any energy into your fuel mass. Also, conduction is a very potent means of transferring heat, and even with all your perfect x-ray mirrors, you lose most of your accumulated heat should any of the fuel you are heating come in contact with your containment vessel. Then there is the need to extract work from your closed fusion system, so you need a controlled way to extract accumulated heat from your reaction chamber without stalling the reaction. So perfect x-ray mirrors are not enough, you also need perfect insulation to keep the heat contained in the fuel, which is made harder because you would then need to extract the generated heat from any helium you made so as to pass it on to the incoming deuterium which needs to be hot enough to continue the reaction.

I remember walking through one of those during one of my NASA visits. I think it was at Houston, but it might have been the cape , or possibly even the infinity science center just east of Louisiana on I10. Ah, it was the infinity science center, and they just have a mock-up of the destiny module: https://www.visitinfinity.com/galleries-exhibits/

You either need a large O2 tank for this, or you will or you will evaporate all the O2 and still need filters in the main O2 tank because you are no longer catching all of the H2O and CO2. This is also a separate tank that needs filling and emptying, little better than a he tank. A large enough O2 tank with adequate filters will always be heavier and more complex than the main O2 tank with the same filters . (Filter size and mass is relative to the amounts of ice it needs to catch, not the size of the tank, so your solution will either clog or have more weight. Possibly both)

At 400km altitude(ISS altitude) it only takes 90 minutes to orbit, so if you have the dV to get to an equatorial orbit with each flight you can fly up to 16 times per day, more if you have a lower orbit or use multiple launch pads. (but tandem launches might be a bit much for now)

Using cryogenics is a choice, it is entirely possible to get to orbit using compressed oxidizer and non-cryogenic fuel, but compressed o2 does not seem to be the best choice. Dumping oxygen rich exhaust into the LOX tank my or may not prove to be the superior choice, but we do know that on previous launches the draw-backs of doing so were not properly accounted for. Probably because it is something new which may or may not prove to be superior to the old preferred choices once everything has been accounted for. We also know that the refurbishment requirement of using the standard choice of compressed He for pressurization would preclude the stated design goal of rapid reusability. Perhaps that design goal is not possible, but until it has been discarded as such, autogenous pressurization is the only viable option, and pumping oxygen rich exhaust into the LOX tank still looks like a lower-mass and lower failure-rate option than adding a heat exchanger. Just because trying new things also introduces new problems does not mean we should never try anything new. If there were cargo or passengers, then new failure modes would be a concern, but as the only launch product for these test-launches is data, this is the best time to try out new things that may have new failure modes. Think of it as 'unlocking new rocket parts by trial and error' or 'exchanging funds for science'

You know some other bad ideas: * high pressure combustion * transporting large tanks of cryogenics * large tanks of fuel and oxidizer close together * lighting or re-lighting rocket engines in flight All of these have major down-sides that need to be accounted for and designed around. But without all of them, we would never get to orbit. Just because something is a bad idea in isolation does not mean it is unnecessary when trying to achieve a specific goal.

This sounds like a balancing act between 'starting' velocity(aka orbital altitude) and the oberth effect. If you assume that the initial velocity is 'free' then there is a point where additional 'free' velocity is less advantageous than the oberth effect for the acceleration needed to achieve the new trajectory. On the other hand, if you are starting from the ground, there is no 'free' starting velocity other than the rotational velocity of the surface, which is pretty minor, making 'not hitting the ground or enough atmosphere to matter, but just by a hair' the ideal orbital altitude so as to maximize the oberth effect.

As of yet, no starship has been lost due to loss of a tile. I consider the assumption that ss can be lost due to the loss of a single tile to be an assumption made to maximize safety. Ss is intended to come home safe from Mars, and anything that can reenter from a Mars return trajectory will be more robust than what is needed for a return from the moon trajectory, which in turn is more robust than what is needed for reentry from low Earth orbit. But musk wants 100+ passengers per SS to Mars, so he needs safety well beyond what is normal for manned flight. Focusing his engineers on making SS safe for re-entry from Mars may give him that safety margin It is also possible that he does not want to make the same mistake that the shuttle program made with regards to loss of tiles being normal.

As far as I am aware, Hubble is intended to be grasped by the Canada arm, not a standard docking adapter. I remember seeing a proposal to install a standard adapter as part of repairs by a dragon launched team, but I do not believe this has happened as of yet.

Using lots of input energy to maintain a fusion reaction seems to be a fairly reasonable activity: https://www.itnonline.com/content/world-record-strongest-nuclear-fusion-reaction-steady-state-system-achieved-phoenix-and Sounds like they have been using sustained fusion reactions as a neutron source for manufacturing medical materials since before 2019. Seems like fusion itself is not hard, just self-sustaining fusion.

While fusion reactions taking place at temperatures and pressures that melt or vaporize normal materials is a serious problem, another problem, just as large is that we need to keep the high temp and pressure inside the reaction. If we pump out heat by cooling the walls, then the reaction gets too cold to continue. Even just reaching out and touching the walls of the containment vessel means losing too much heat for fusion to continue. If you have a better idea for focusing and containing heat at temperatures that melt structural materials, and without letting any of that heat escape, then that would be a big help, but just cooling thee walls does no good if you want to sustain the reaction. Note: even Jupiter cannot sustain the heat and pressure needed for an ongoing fusion reaction, it is that hard.

I rather expect that this is the working assumption until proven otherwise. It is safer to assume that even with a tougher skin, Starship will be vulnerable to the same sorts of thermal management failures to which the shuttle was vulnerable. Remember: Musk wans mars colonies, so even if SS could re-enter fine from LEO or even the moon without any tiles at all, SS reentry is not safe until it is safe for SS to reenter from Mars.

Previously the US had a 'fast breeder reactor'(I think the navy had it) that could take 'used' nuclear fuel and re-enrich it. Unfortunately, this process also creates Plutonium, which is a proliferation risk, so that type of reactor is strictly controlled. Considering that NASA cannot get their hands on any new plutonium, I suspect no one is 'allowed' to have that sort of reactor, meaning the most cost-effective thing to do with 'spent' fuel rods is bury them and buy new ones. (or store them under water while waiting on a place where you can bury them)

Doesn't the quick disconnect mitigate this to some extent? While I suspect they cannot pump the fuel into the tanks as fast as the engines pump it out, hopefully they can at least reduce the losses due to hold-down and engine stabilization.

Being able to parlay a project to support a funding-required but poor capability component into multiple systems with superior capabilities sounds like quite the coup to me .

It sounds like the 'cooling LEDs' might be a viable option for rejecting heat to space if: 1) do the wavelengths where cooling LEDs work match those wavelengths where the atmosphere is most transparent (otherwise we are not getting any heat out to space) 2) the solar panel efficiency* led cooling efficiency * atmospheric transparency at cooling wavelengths > 50% (otherwise we are generating more heat than we reject with this project) Has anyone looked at those numbers to see if this is even feasible?

Glacial period Ice age: somewhere on the planet has year-round Ice (covers the last 2.6my) Glacial period: glaciers are advancing and covering more of the earth. last one was 110ky-11.7ky ago Interglacial period: glaciers are retreating and cover less of the earth . Includes the last 11.7ky We are still in an ice age. You can tell by the poles being frozen wastelands. People trying to encourage the next glacial period to start sooner to 'save the planet' make me worry about the goals of modern educational systems.

The heat must go somewhere and any time you move energy up a gradient (ie moving heat from cool to warm) you generate waste heat. As the atmosphere acts as a thick blanket, how do you plan to remove more heat from the planet(including the air) than you generate in waste heat? Also, as we are already in an ice age(polar ice caps are NOT normal for the earth nor are glaciers), is further cooling even a good idea?

I would very much refuse to put a used battery of unknown providence into any of my devices. (even with less risky batteries like 12v car batteries, I stick to new or refurbished by the manufacturer) I have no objections to the batteries themselves, only to swapping in a potentially adulterated battery to save a few minutes of charging time. From google: A battery typically makes up around 40% of a new EV's price. How that battery is treated is key.

In spite of movies, shooting a can of gas will not cause an explosion. Having a battery-pack land on a sharp rock or bit of metal will likely cause a chemical fire that will destroy the entire battery facility. Just plugging in a damaged or faulty battery pack could do the same. Also, Batteries and tires are the two most wear-sensitive parts on a BEV, and who wants to get an 'old' pack with only 2/3 the range of their brand new pack?

Google says that up to 25% of EV mass is the battery, and 25% looks like a good estimate when I spot checked a couple vehicles(model 3: 26-27%, Cybertruck: ~24%). I cannot imagine that 'swapping out' ~25% of a multi-ton automobile is something that either automotive engineers or public safety officials would find appealing, or even tolerable. That is entirely ignoring the fact that a newer battery is worth much more than an older battery and that anything with that much power density *will* be explosive if it is mishandled. The fact that merely puncturing a battery with the currently favored automotive battery chemistry will start fires/explosions is probably a consideration as well. note: v8 engines weigh 400-700 lbs, so this is similar to swapping out the engine multiple times to fill the fuel tank. Edit: This is also ignoring that a lot of EVs look like they are incorporating the battery hardware into the undercarriage super-structure to improve handling and reduce weight/cost, making a swappable BEV even more of a premium item than current BEVs)

I thought most microwaves running at X% power were actually turning on and off so that they run x% of the time at full power and 100-x% of the time it is off and just giving the heat time to spread out.

Still a couple days early for that

Fusion does not have the same waste, but it still produces neutrons and thus neutron activates near-by materials(something reactors hope to use for lithium production) so the pusher-plate of either will quickly become radioactive and thus dangerous for proximity.

I do not see either engine being useful on pusher-plate sized vessels. Sub-sonic airliners need 10-20% of their mass in engines, and that would be totally inadequate for something as unaerodynamic as a pusher-plate vessel, and also would be far from sufficient for the types of speeds you would need for them to be useful. Just use disposable solid boosters to get it to orbit and never let it land. (Once the pusher plate is used, you never want it near people again, so landing would be a war-crime even if you use a parachute instead of nukes to slow down)