sevenperforce

Oh yeah, you're right -- I forget that the Dragon 2's capsule mass includes its maneuvering propellant and engines. Why the hell is it so heavy? Yeah, I think it's proprietary. I wonder how it could be estimated. In the pad abort test, Starliner's coast from abort motor cutoff to apogee lasted 11 seconds and its ascent angle was about 41°. It is dense AF so I will ignore air resistance for a first-order estimate. This means the vertical component of its velocity was 11s*9.81m/s2 or 107.9 m/s, making its total velocity 164.5 m/s. This accords fairly well with the observed plume expansion during cutoff (the first diffuse plume travels 336.6 pixels in 11 frames, and since Starliner is 31.4 pixels wide and the playback framerate is 31 fps, that's 48.9 meters in 0.355 seconds or 137.7 m/s which is to be expected since the plume needs time to slow down). Boost duration was 5.355 seconds, split equally between 2.677 seconds nearly straight up and 2.677 seconds at 45 degrees, which is exactly what you want to get as far away from the fireball and from the exploding rocket as possible. It covers 70.3 meters in the 1.806 seconds it takes before the tower drops out of view, which tells us via kinematic equations that the acceleration during initial vertical boost is 43.1 m/s2 (the felt-equivalent of about 5.4 gees for those with weak stomachs) and a speed of 77.8 m/s at an angle of 68.6°. Treating the burn as two separate boosts (the first half at 68.6° and the second half at 45°) which are each split into vertical and horizontal components and then and solving like a good first-year physics student predicts a speed of 184.2 m/s at 47.8°, about 10% higher than estimated from the coast period. Of course this doesn't account for wind resistance so we would expect it to be slightly higher, so we know we're in the right ballpark. Finally, Boeing has said that the four engines generate 40,000 pounds-force each or a total of 711.7 kN. The engines are just slightly canted out (my visual estimate is about 6.8°) so cosine losses will bring the effective thrust down to around 706.8 kN. If Starliner's pad weight is 13 tonnes, then they should supply a total acceleration of 54.4 m/s2, which is just 3% more than my visual estimate once you subtract gravity (and it should be slightly over because, again, air resistance). All this gives us a good degree of confidence that the pad abort burn was full-thrust. Specific impulse for hypergolic pump-fed SL engines range from the Viking's 248 s to the RD-273's 296 s. There aren't many numbers for pressure-fed hypergolic SL engines (mostly because they aren't often used) but of course we know the SuperDraco comes in at 235 s, so let's ballpark Starliner's abort motors (which are each roughly 2.5X the thrust of a SuperDraco) at the same number. At full thrust these would consume 308.7 kg/s which means a 5.355-second burn requires at least 1,653 kg of propellant. A pad abort would deplete most of the propellant...let's give it a 5% reserve and round it off to 1,750 kg. It's tough to estimate the mass of these engines, but that won't stop me from guessing. According to SpaceFlightNow, each service module propulsion kit contains 24 additional OMS engines which each provide 6.7 kN as well as 28 RCS engines of unspecified thrust, but we can assume they are the modern version of the R-4D, since Aerojet Rocketdyne now manufactures those. They provide 490 N. All together the thrust capability of the service module is 886 kN, and since I'm lazy I will just borrow the 80:1 T/W ratio of the Viking first-stage engine, which would give them a combined mass of 1.1 tonnes. The Agena A carried about about 1100 kg more propellant than Starliner, but at least we are in the right ballpark. Its dry mass (less its XLR81 engine) was 751 kg. Scaling with the square-cube law gives us a total tank and structural mass of about 536 kg, for a total service module mass of 3.4 tonnes. That sounds about right if you compare the gross mass and propellant load of the larger (and lacking-in-abort-engine) ESM. So that suggests a loaded capsule mass of around 9.5 tonnes. Not much less than Orion.

Reducing the propellant load can't possibly hurt things

Interesting how tiny Orion is. It's the service module that cripples it.

Haha!! It is much easier to pump a liquid than to pump a gas. So there's an advantage. Any decent high-efficiency rocket engine is going to use regenerative cooling at some level, which transfers waste heat to the propellant which makes the whole engine more efficient. There is usually going to be plenty of waste heat available to heat your propellant as warm as necessary. If he had 16,000 psi hydrogen at 0°C then it would get EXTREMELY cold if allowed to exhaust and expand to ambient...fairly certain it would self-liquefy. He has very little information about his fancy rocket engine's closed-cycle mode, but if what he's proposing is simply a pressure-fed gas-gas rocket, then....I mean, yes, that would work. Exhaust the GH2 and the GOX straight into the combustion chamber. Keep the chamber pressure high enough and it's fine. It's the propellant containment that's an issue. Ullage might be an issue eventually though.

Details, details. Chewing up a stick of celery only takes about half a calorie of your energy, but your body burns 80-something calories per hour when you're just sitting there, and so the amount of calories you get from a stick of celery is less than the amount of calories you burn during the same time period. He is very loud and proud about how he doesn't use liquid propellant; all his designs use GH2 and GO2 but supposedly stored at 16,000 psi. That's 1,100 bar. Most pressure-density graphs for GH2 don't even go that high, but at 0°C it's about 54 kg/m3 and at -100°C it's about 68 kg/m3. Liquid hydrogen has a density of 71 kg/m3 and that's at just 2.3 bar. So he expects us to believe that he can make conforming-shape thin tanks that hold 480X higher pressure than cylindrical tanks with a 31% better mass fraction. I feel like he has very odd ideas about the interplay between density, mass, and volume.... "Overall fuel capacity for Raven is beyond 18,000 gallons (which liquid fuel weight would be beyond 140,000lbs), which since it is designed to be fueled by hydrogen; and oxygen for orbital capabilities, that reduces overall take off weight greater then 140,000 LBS." Does...does he think that compressing hydrogen produces a higher energy density but not a higher volumetric density??

As someone who gained entirely too many pounds during the pandemic, I feel volume is more a problem than bulk density

Sorry. If I am a trustworthy source 99.9% of the time then it does make that 1-in-1000 prank all the more believable, I suppose.

You jest but if we could build an Orion drive then aliens could too. How far away could you see one of those operating (for given thrust-class levels)? Which of our telescopes would be ideal?

RIP SN15!!!!! NOOOOOOOOO

That's probably even more mean but I won't say no

I wonder how preposterous this is...this might not be fair. These engine nacelles are able to rotate "60 degrees forward" for cruise. My mind is blanking -- does that mean the component of forward thrust is F*sin(60°) = 0.866 and the component of upward thrust is F*cos(60°) = 0.5, or is 100% of the thrust split at those proportions? Let's just say it's the former, which would tend to help him out (although that feels like a violation of the conservation of energy). So upward thrust will be 58% of whatever our forward thrust setting ends up being. Where does that get us? Well, let's start with form drag. We know F = 0.5*CD*A*ρ*v2 but we don't know the drag coefficient CD. We can guess, though. A Tesla Model S has one of the lowest drag coefficients of any vehicle at 0.24 but let's say we reduce this even further to 0.2, which is as "unheard" as many of his other claims. That same pixel count as before (completely ignoring those gigantic nacelles) gives me a frontal area of about 1.11 square meters. 250 knots is 129 meters per second. Plug and chug, and you get a form drag of around 2.36 kN (note: we haven't even touched on parasitic drag or interference drag). So just to deal with form drag at 250-knot cruise, the engines are going to need to be operating at a minimum of 681.3 N each (to account for the sine losses), or 34%. However, this does provide some cosine gains, since they'll be pushing 340.1 N downward, which helps reduce the needed lift and thus the lift-induced drag. What about that lift-induced drag, then? Well, the Martin X-24A lifting body had a subsonic L/D ratio of about 3.5, which was remarkably good for its size. I can't imagine the "Blackjack E" having a body-lift L/D ratio nearly this high with literally no wings at all. But let's assume it does. Loaded weight is 1,500 lbs which would require 6.67 kN of lift in fully lift-based flight, but the 340 N of upward lift from each engine will reduce the necessary lift to just 5.3 kN. With that very generous L/D ratio of 3.5 this means induced drag is 1.5 kN so we need to spin up the engines a little higher. Increasing power to 50%, my BOE estimate, reduces needed lift to 4.7 kN and reduces induced drag to 1.3 kN, but we're still going to come up a little short. At 53% power, you can finally break even. Each nacelle is pushing 1.06 kN and the lift, drag, and thrust are all in balance. To achieve the 160-mile range you need 33 minutes of cruise at 379.5 kW or 208.7 kWh. Liftoff takes place at 633 kW with a net upward acceleration of 0.067 gees. Let's assume you need to get at least 100 meters in the air before you begin transitioning to cruise. Kinematic equations tell us that the time t it takes to climb a certain distance Δx at a constant acceleration a is given by t = sqrt(2Δx/a). So ascent takes about 18 seconds. Flip those rotors forward and start accelerating. Drag builds up quickly but you've got a decent amount of power, so you hit 129 m/s after about 17 seconds. However, you need about 2 minutes of hover time to ensure a clean landing approach at your destination. So ascent and descent require about 155 seconds at 633 kW for an additional 27.3 kWh, bringing the energy requirement to 236 kWh. Add a 5% reserve and a 96% depth-of-discharge limit, and your battery pack needs to carry 258 kWh. It will have a mass of around 1.6 tonnes or 3,614 pounds. This is actually a really good demonstration of why personal electric drones just don't make much sense.

I know. I'm getting tired of converting back and forth. I want to take a closer look at these not-prop rotors that can produce a combined 1800 lbs-force. That's about 2 kN per rotor and by my pixel count these rotors each sweep out an area of approximately 0.56 square meters. To manage that, the exhaust velocity needs to be 74.9 m/s, which doesn't seem that bad, does it? But since you can get power by multiplying thrust * exit velocity, you find that the actual power for each rotor is 149.8 kW. Variable-pitch propellers cannot get much more than about 80% efficiency, but even if we stretch and give him 85% efficiency, that means the total electrical power requirement is actually a whopping 712 kW at liftoff. The new combined powerplant mass is going to be 800 kg or 1,764 pounds. Now it makes sense!! If the powerplant is over 1,700 lbs but the maximum takeoff weight is 1,500 lbs, the airframe must actually have negative weight! That's his secret! "These techniques include using exotic materials and advanced assembly processes that are currently unheard" "Note, all technologies internally, engineering, and physics involved with U-TBCC are proprietary and non disclosable" That's the secret! When he says "exotic materials" he actually means negative mass!! No wonder the "physics involved" is "proprietary and non disclosable"! I know I'm just being mean at this point but this is funny AF

The VTOL commuter craft are fun too. I feel like his modeling software took a turn here. "The rotors are not props, but variable pitch 7 blade rotors with IO Aircraft QUIET TECH© built in." So they aren't props, just...propellers. "If catastrophic failure occurs, it is also equipped a BRS (Ballistic Recovery System), which can deploy deploy and the entire aircraft will come down safely." I want to know how to deploy-deploy too. "Ballistic Recovery System" sounds like "lithosphere-assisted braking" or "rapid unscheduled disassembly". Supposedly its power supply is a 600,000 milliamp-hour lithium polymer battery. That doesn't tell us about its energy contents, but its motors are supposed to have 120-140 hp for each of four nacelles, so the discharge rate for these batteries needs to be on the order of 422 kW during hover, assuming 99% efficiency electric motors. The most weight-efficient electric motor in the world, the Emrax 268, outstrips a Tesla motor by 36% at a featherweight 11.56 kW/kg. So the engines in those nacelles are going to mass something on the order of 36 kilograms alone. He says, "this aircraft will take off easily and the rotors can spin up further to produce up to 1,800 LBS thrust then cycle down during forward flight." If we take the utterly preposterous assumption that level forward flight at 250 knots is possible at just 50% motor load, that's still 211 kW. A range of 160 miles at 288 mph requires about 33 minutes of flight so he needs a 69 kWh battery just for cruise. Consider that the Tesla 85 kWh battery comes in at 540 kg, so scaling for weight that gives us a combined battery and engine mass of 474 kg, or 1,045 lbs. Add 400 lbs for 2 passengers brings us to 1,445 lbs. We can then subtract from the quoted maximum takeoff weight of 1,500 lbs to arrive at the vehicle dry weight of...55 pounds or 25 kilograms. 25 kilograms for the "composite ultra strong chambered airframe" that is made of a "fireproof composite resistant up to 2,500F" and is "multi layer chambered" along with the weight of the rotating nacelles and 8 variable pitch rotors. No wonder it is "able to float in case of catastrophic failure over water"!!

Leaving much more volume! For extra thrust! It clearly needs its wings for very height! He says the Discovery SSTO contains 8,000 gallons of "hydrazine or similar" which comes to what -- 32 tonnes of hydrazine? Let's give him the benefit of the doubt and say it's a 200,000-pound vehicle (about 91 tonnes) empty. The best hydrazine thrusters can provide about 240 s of specific impulse. That's 710 m/s of dV....which, admittedly, is enough for a deorbit burn, but it's not anywhere near 2 km/s.

He calls compressed GOX "CO2" apparently not realizing what CO2 is. Translating orbital speed into ground speed is just the best.

Someone please stop me I'm laughing too hard to breathe!! "Fuel weight with maximum fuel load, is only around 6,700 LBS of compressed hydrogen. That's right, only around 6,700 LBS; because it no longer uses liquid fuels. "To compare that to a regular fixed with aircraft, Raven is like taking off on empty, when considering the weight. It's light, which means it can fly very height without the drag from huge volumes of fuel. Instead, it's fuel is 8.000-16,000 PSI compressed hydrogen providing a massive volume of fuel capacity; which is required for such extreme thrust and velocities." So are "huge volumes of fuel" a bad thing because of the drag, or are they "required for extreme thrust and velocities"? And what is "very height"? Is that like "very doge"? And don't even get me started on BlueEdge..... "Kerosene, ie Jet A is 6.7 LBS per gallon, and that would easily be 335,000 LBS of fuel. 8,000 PSI compressed Hydrogen, is only 5% of the fuel weight.... That means, take off for BlueEdge at MAX fuel load, is only a rounding error compared to empty weight. The aircraft is light as a feather, making high altitude flight possible, but also efficient due to weight = drag." Whyyyyyyy And the VTOL two-passenger hypersonic aircraft with 90 DEGREE THRUST VECTORING AEROSPIKE SCRAMJET Oh and the weapons systems, the weapons systems: "This version is ground launchable, in which the Stage 1 booster accelerates the platform to 225,000-250,000ft, then releases. The semi internal booster then accelerates the missile platform to Mach 20 at an altitude of 300,000 ft very rapidly and let inertia continue it's arc in LEO. At that time, the missile platform is flying inverted operating in glide mode and can navigate; similar to Lockeed's BGV and China's HTV. Except when it has re-entered atmosphere around 150,000ft, it rolls over and converts to scramjet under power. At this time the missile platform can turn and bank, change attitude, etc. What any advanced radar system that could detect the craft and plot it's trajectory; well that trajectory just changed. "The hypersonic platform can either choose to extend the range for glide to target after fuel is expended, or it can choose to hit its target at full momentum and scramjet propulsion system is in full burn mode hitting its target at Mach 20 at impact, releasing over 120,000 LBS of Kinetic energy." What......what sort of energy measurement is "120,000 LBS" here? TNT equivalent? Blast wave overpressure? Pure mass-enegy conversion? "The Zircoff Hypersonic Missile is designed and engineered for low altitude high atmosphere density. It is meant to replace Hellfire Missiles, TOW Missiles, and expand Missile capabilities. "The missile can be ground or air launched; from fixed positions, mounted to armor and wheeled vehicles, AH-64 Apache's, Drones, A-10's, F-16's, F-18's, F-35's, etc. If it can be mounted, it can be launched. Including tripod's for non vehicle ground troops. "For example if troops are requesting air support, they instead can provide the GPS location of target, while an FOB can input those coordinates and launch. Within 60 seconds or less, that target will be eliminated with extreme prejudice." Yes, it DEFINITELY sounds like a good idea. Ground troops! How would you like to fire a Mach 10 scramjet from this tripod?

Maybe it's just that this is a much smaller rocket with lots of extra mass fraction to play around with but it is SPORTY off the pad. Makes an Atlas V or a Falcon 9 look positively sluggish.

Almost 100% Graphene and Kevlar according to the guy. It's like he never learned what COPV stands for.

I, for one, am LOVING the idea of making an SSTO that burns compressed hydrogen gas and compressed GOX. Whatever THOSE tanks are made of, I want to build a car out of them.

Good point. "Rest mass" I know, and "relativistic mass" I know, but what are "current mass" and "dynamic mass"? At present my diagram just has a (?) exponent for the neutrinos. EDIT: **to clarify, I currently have a (0) exponent for the photon, Higgs boson, and Z boson, an (8) exponent for the gluon, a (+/-) exponent for the positively-charged leptons, a (-/+) exponent for the negatively-charged leptons, and then the aforementioned (?) exponent for the neutrinos because I have no freaking idea what they are.

But aren't the Z and Higgs bosons also their own antiparticles?

Ooooooooh there it is. That's the bit I was missing. I wondered why flavor oscillation required mass but I didn't connect that anything which requires the passage of time cannot happen to something massless. So if we measure a sinusoidal neutrino oscillation wavelength of ~1067 km/GeV, then we have a relationship between neutrino mass and neutrino oscillation rate. If the mass is on the order of 0.2eV/c2, then the proper time oscillation period is on the order of 5.02e-12 s. I suppose that at these energies, there are huge problems with trying to even design an experiment to determine the proper time oscillation rate. While I have you -- I've gotten conflicting statements on whether the three flavors of neutrinos are their own antiparticles or not. What's the current state of our knowledge here?

Our numbers are different because we came at the equation from two different angles, but they are at the same order of magnitude so we are in the right place. I think the issue here is heat conduction rate. Your body is basically water, but you don't have any convective heating going on, so you are limited by the direct heat conduction rate. And water is an insulator. So the "change in temperature" doesn't even come close to reaching your entire body; it's limited to the outer layer of your skin. The non-convective thermal conductivity of water is about 0.606 W/(m*K). The sun is 5800 K and your body temperature is 310 K. Unfortunately I am blanking on how to effectively drag a "heat transfer wavefront" speed out of that.

Doesn't that require you to bake in (heh, no pun intended) the assumption that your speed at Earth is not matched with your speed on the surface of the moon?

In this situation you are functioning as a heat engine. One of the consequences of the second law of thermodynamics is that radiative heat transfer is reversible and so you cannot raise the temperature of your target above the temperature of a source, no matter how much focusing you do.