sevenperforce

Is COPV resin inert to oxidization? The COPVs used for helium in Falcon 9 are Al-lined.

Kinetic penetrators and radiation shields, yeah.

Uh, the speed of electric current is 0.95c. So a little bit more than 70 km/s. More like 295,000 km/s. Yes. If nothing else, the synthesis of superheavy stable elements would allow for advanced experimentation and testing. If you have big heavy stable atoms to play with, you can test all kinds of predictions of string theory and similar cutting-edge physics. What happens when you smash Element 120 into Element 122? String theory A predicts that you get particle X; string theory B predicts that you get particle Z; string theory C predicts that unicorns pop out and dance to Schoolhouse Rock. Let's see which one is right! If we found a way to make them in quantity, superheavy elements could also be used in all kinds of novel tech as well.

I saw this, hinted to my wife about a Father's Day present, and tried to avoid saying anything on the board for fear that it would sell out.

There's no problem with your maths; the maths are fine. I'm saying that the case you've set up doesn't match any as-yet-defined formulation of the problem. What I'm taking issue with is the feedback loop in the conveyor belt's programming. You have to define what the conveyor belt is attempting to do in order to figure out what is going to happen. I think that you could arrive at the formulation you're describing by using the following programming: IF (AirplanePosition > 0) BeltSpeed++; ELSE IF (AirplanePosition < 0) BeltSpeed--; ELSE Return; ...and repeat.

I wonder if pressure-testing includes sequential removal of bolts to test failure. That would explain why they are as-yet uncovered. I doubt it, of course, because it would be very difficult to ensure non-destructive failure testing.

Whether the wheels are powered or not is important. If the wheels are geared to something that is RPM-limited, then the plane will not be able to take off. Of course, no plane actually has wheels geared to anything...or, if they do, they are in neutral during the takeoff roll. In the earliest formulation I've found, the phrasing is, "designed to match the speed". So even if you're interpreting the speed as the rotation of the wheels, as above, you are left with a treadmill which will attempt to keep the vehicle (plane or car) stationary, but its ability to do so is not a given. I would question this. In order to match the interpretation above, the belt must be programmed thus: FOR GetSpeed(Wheels); IF (GetSpeed(Wheels) > GetSpeed(Belt)), IncreaseSpeed(Belt); ELSE IF (GetSpeed(Wheels) < GetSpeed(Belt)), DecreaseSpeed(Belt); RETURN; We can suppose that the belt runs this subroutine an arbitrary number of times each second. Now, with the above programming, the belt cannot turn at all until it receives a signal that the plane has begun moving forward. Once the plane has begun moving forward, the belt will immediately detect GetSpeed(Wheels) > GetSpeed(Belt) and will run IncreaseSpeed(Belt); as a result. However, this will cause the result of GetSpeed(Wheels) to increase in response, because the wheels are held to an axle which is not force-coupled to the treadmill; increasing belt speed directly increases wheel speed. So the only way to satisfy the programming is for the speed of the belt to increase to infinity, instantly. It's like running IF (GetSpeed(Belt) = GetSpeed(Belt)), IncreaseSpeed(Belt).

Right. Running LH2+LOX at stoichiometric ratio will melt the engine, so adding unburnt hydrogen reduces chamber temperature while simultaneously decreasing molecular mass in order to kick Isp up a little bit. The key is that Isp is the combination of average propellant specific energy and average propellant molecular mass, and there is a porkchop plot which defines the maximum Isp. True tripropellant engines (which mix three propellants at essentially the same mixture ratio the entire time) exist to pair a high-specific-energy fuel combination with a low-molecular-mass propellant. The main fuel tanks aren't made of composites. The interstage and fairing are. As are the COPVs. Unlined composite, which is scary.

This is not the case. I mean, it's possible. But it's not accurate. The uprated Merlin 1Ds can still run on LOX and RP-1 at boiling point. They do in every mission; by the time that the entry and landing burns roll around, the tank temperature has increased enough that the propellants are no longer as densified as when they started. Plus, Word of Elon. They can run on the non-densified propellants. Payload decreases slightly, but sending D2 to the ISS is a sandbag for Falcon 9 Block 5. If R3* R1 is on the order of R2, then it's not a concern. R3 is very very low, and so R2 would have to be nearly as low (or R1 would have to be ridiculously high) in order for the risk analysis to preclude load-and-go. No, the trunk burns up. That's a relief. Cosine losses during orbit adjustment maneuvers look like they would be really high.

Oh, using compressed hydrogen gas as a monopropellant by itself is a very bad idea; it has no specific energy. But hydrogen gas is the lightest thing (short of doing something like monatomic hydrogen) you can use as a propellant, so mixing it with a high-specific-energy heat source (like fluorine and lithium, or a nuclear thermal reactor) will give you the best specific impulse.

I do suppose that there is nothing terribly different than existing metro lines. I ride a major subway system every day and it's pretty normal. If there's an emergency while you're zipping through a tunnel with 6" of clearance at 40 mph, there's really not much that can be done.

Damn, so that's what a spaceship looks like.

Very very strange

Rocket propellant chemistry is (unsurprisingly) a rather complex issue. Maximizing specific impulse is a porkchop plot of two variables: specific energy and product molecular mass. Both have to be maximized in order to get highest average exhaust velocity. Specific energy is the energy released when one kg of reactants is burned and converted into (slightly less than) one kg of reaction products. To get a high specific energy, you want lightweight atoms which can each form multiple bonds and have high bond energies in the reaction product. At the same time, you want its pre-combustion molecular configuration to have low-energy bonds, because energy you use to break those bonds has to come out of your reaction. Atoms like nitrogen have really high bond energies, but their pre-combustion state has as much energy as their post-combustion state and so they don't really contribute. Product molecular mass is the average molecular mass of your reaction product. You want this to be low, because exhaust velocity is inversely proportional to the weight of each exhaust molecule. The lowest possible product molecular mass (barring molecular disassociation in nuclear thermal rockets) would be simple compressed heated hydrogen gas. Of course, compressed hydrogen gas isn't very high-energy, so it's not exactly ideal as a monopropellant. But if you have an effectively-infinite heat source (like a nuclear reactor or a solar thermal rocket) then hydrogen (probably in liquid form, for storage considerations) is def the way to go. The highest specific energy is achieved by operating an engine in stoichiometric ratio, but adding low-molecular-mass fuel can increase specific impulse (as in the SSME) because you can sometimes get better exhaust velocity if you lower your average product molecular mass, even when that decreases temperature (because some of the hydrogen passes through unburnt). Beryllium has higher specific energy than lithium because even though it's heavier and has lower bond energies, it can form multiple bonds with a single atom. Laying aside silly foibles like extreme toxicity, it's a better rocket propellant, as long as sufficient quantities of diatomic hydrogen are available to carry that energy away at high exhaust velocity. Liquid ozone beats out liquid oxygen because its precombustion bonds are weaker and therefore require less energy to break, but deliver the same amount of energy in the reaction products. Fluorine beats out liquid oxygen, even though it only forms one bond per atom to oxygen's 2, because its bond energies are so much stronger. FOOF beats out fluorine and ozone because it is even denser than liquid ozone, but has single-bonds in its precombustion state, which require less energy to break than LOX or ozone or liquid fluorine. So FOOF + LH2 + Be, in perfect ratio, is pretty much the highest-specific-impulse triprop combination chemically possible. Eh, that's probably a reference to fuel LEL/UEL. It means that when mixed with air at STP, it will detonate when ignited below 42% but conflagrate when ignited above 42%. LEL/UEL stand for Lower Explosive Limit and Upper Explosive Limit. As an example, natural gas has its explosive limit between 5% and 15%. When natural gas is mixed with air at standard temperature and pressure, ignition will result in simple conflagration below 5% (because it is too oxidizer-rich to detonate) or above 15% (because it is too fuel-rich to detonate) but will explode in a destructive, supersonic wavefront if the ratio of methane to air is between 5% and 15%.

2,113.3

If I am climbing on top of a giant bomb, I would very much like for the bomb to be empty until I have my ejection seat primed and ready to go. If I am helping someone else climb on top of a giant bomb, I would very much like for the bomb to be empty until I am far, far away. There's a simple answer to all this. Let R1 be the probability of pad RUD during fueling Let R2 be the probability of pad RUD while fueled Let R3 be the risk of death or serious injury during a capsule abort Let T1 be fueling duration Let T2 be ingress duration Let nC be the number of crew Let nS be the number of support personnel If R1 * nC * T1 * R3 > R2 * T2 * (nC + nS), then it is safer to load fuel before the crew enters the capsule. Otherwise, it is safer to load fuel after the crew enters the capsule.

I'd say to do oxygen difluoride...or, even more exciting, dioxygen diflouride (FOOF). The former combo would have a specific impulse of 432 seconds; the latter we don't know. Of course, pentaborane is nasty enough to make hydrazine seem tame; the only reason to use it is that it gives you cryogen-level performance with hydrocarbon density and hypergolic storability. If you replace it with good old liquid hydrogen in an engine with oxygen difluoride, you can joyously ride all the way up to 477 seconds, blowing past LOX/H2. Your thrust suffers in comparison to pentaborane, though. From a pure-chemistry standpoint, your maximum possible isp is going to be FOOF, liquid hydrogen, and powdered beryllium, with a projected isp of 568 seconds. I don't want to be anywhere in the same state when that sucker test-fires, though.

How many nerds discussing video game rocket science?

You could try stabilizing ozone with nitronium perchlorate to make a medium-cryo pumpable slurry.

In all seriousness, the higher rolling friction of treads and velocity-dependent drag might make this more like the "upstream seaplane" than the "jet on a treadmill".

I don't recall whether it was Ignition or Things I Won't Work With that said liquid ozone was volatile in comparison to "nice stable things like nitroglycerin".

All rocket launches are bespoke. Sure, a team making 50 bespoke suits a month can probably sell them cheaper than a team making 5 bespoke suits a month, but the reductions are fractional. Economies of scale can only take you so far. Beyond that, you need reuse. Or you need a ridiculously cheap, ridiculously powerful expendable rocket (like Orbital ATK, but without the RL-10s) that can service a wide range of payloads and profiles without alteration.

LOL...are you intentionally trolling? do wheels spin if the surface they are resting on moves? Yes. The purpose of wheels is to spin...they love it and don't care if they're spinning forwards or backwards. Yes, I was being obtuse. And yet even now we have variant answers.

If the conveyor belt pushes the plane forward, will the wheels spin?

That's what I meant. The next two launches (Iridium-6 and SES-12) will be reused B4s. The next launch, Telstar 19V, may be a Block 5 if there is no B4 available for reuse. CRS-15 is next, which will reuse the TESS booster. After this is the final Iridium launch on B5.