sevenperforce

Oh, certainly unviable today.

A clean-sheet design could have used RD-180s on the first stage, a pair of J-2Xs on the second stage, and a single J-2X or a pair of RL-10s on a third stage, with SRBs to add impulse and reduce the number of RS-180s needed. Of course that obviates the SSMEs. If the SSMEs simply MUST be used, then a page could be taken from the Saturn S-IC Mega Atlas concept. Use a Shuttle ET but add a second common bulkhead, with RP-1 at the top, LOX in the middle, and LH2 at the bottom. Place a single SSME underneath, firing through a skirt where two F-1Bs are mounted, perpendicular to the SRB mounts. Keep the four-segment SRBs and use a J-2X on a larger EUS. The SRBs burn out first, and then the skirt with the F-1Bs drops away when the RP-1 tank runs dry, with the single SSME performing its role as a proper sustainer.

The hydrolox sustainer stage was always a bad design. You need methalox or kerolox for your first stage; otherwise you’re just needlessly lofting a bunch of superfluous tankage. If SLS had used the Jupiter-DIRECT approach and kept the same 734-tonne prop load of the Space Shuttle external tank instead of doing a tank stretch to a 988-tonne prop load, it could have saved roughly 16 meters of length, allowing for an upper stage nearly twice as large as the EUS. They would have needed to complete dev on the J-2X or looked into clustered MARC-60 engines, since the RL-10 wouldn’t be able to manage even in a large cluster, but that would have been easy enough by now. If the upper stage was essentially just a shrunk-down version of the core stage with two J-2X engines and the original four-segment boosters, it could send 117 tonnes to LEO, compared to the 105 tonnes that EUS can manage. With the modern five-segment boosters it could send 127 tonnes to LEO. But its throw to TLI is lower than Block 1B because the upper stage would then be oversized for BLEO operations. Hydrolox sustainer stages are just plain dumb.

The sea level thrust/area ratio of the Puff engines is horrible so unless you clip them wildly you end up with a ridiculously fat first and second stage, which tends to make parallel staging prohibitive.

Send Jeb to the Mun. Plant a flag. Bring Jeb safely back to Kerbin. Use monopropellant ONLY for your propulsion. Extra points: no electricity or reaction wheels for pointing; use monoprop for all attitude control. Lowest launch mass wins. I can do it at 127 tonnes...let's see who can do better.

That’s a good point. With calf-mounted propulsion, you need to flip around in order to land. Of course that’s not terribly hard to do; the hip+knee joint combo would make a fantastic (and, I suspect, very intuitive) gimbal. I imagine that rather than flying around looking straight up, you’d typically blast off in your desired direction, then flick your legs forward to rotate until you were facing largely in the direction of travel. Once you approached your destination, you’d flip further around and decelerate in order to touch down gently. Humans have fairly excellent binocular vision, so it would be pretty easy to get used to how fast you were moving relative to your destination and slow down as needed, accordingly. I could see the usefulness of wrist-mounted thrusters to supplement, but I imagine most people wouldn’t need them for long. And they wouldn’t have to be ducted fans; they could be simple compressed air lines providing only a slight nudge of an impulse here and there. Most microgravity habs would never be large enough to need this. However, it could be useful in a more-than-micro-gravity hab. If you have a large hab, it would be convenient to have a defined “up” and “down” and so you could have low rotation rates to produce a very slight artificial gravity gradient. Keeps things from floating all over the place, after all. In that kind of environment, the ability to hover and zip around would be really useful.

Agreed, in the sense that their basic concepts are not prohibited by the laws of physics. If you want to go to Mars in a bare-bones probable-suicide mission, this is the way to do it. But physical possibility doesn’t make it feasible.

We just have to first replace their book-lungs with hook-lungs for underwater utility.

Extracting the maximum specific impulse from a Mentos+Diet Cola combo would require a long, narrow precipitation chamber which would allow the fluids to exit but redirect the gases back upwards in order to maintain pressure. Two liters of diet cola contain approximately 12 grams of dissolved carbon dioxide. I’m going to go out on a limb and make the entirely unscientific estimate (based on my prodigious bartending capabilities) that the empty space in an average 2-liter bottle is about 6 fluid ounces or 177 mL. The molecular weight of air at standard mix is 28.97 g/mol while the molecular weight of carbon dioxide is 44.01 g/mol, so using the ideal gas equation carbon dioxide will occupy 65.83% as much volume as an equivalent mass of standard-mix air. The density of air at STP is 1.225 kg/m^3 or 0.00122 grams per mL. That 177 mL can hold approximately 0.216 grams of air at STP (although we assume it already contains air at STP). A little math and we learn that precipitating all the carbon dioxide from two liters of diet soda would raise the pressure in that 177 mL from 1 atm to 38.6 atm. Now, in order to expand that 177 mL of gas from 38.6 atm to 1 atm, you’d need 6.83 Liters. But we only have 2 Liters to work with. So the work done by the gas in expanding, using the pressure-volume law, comes to 489.4 Joules. Soda has a density equivalent to water, so two liters of the stuff weighs 2 kilograms. KE=mv^2/2, so the exhaust velocity is 22.2 m/s or a miserable 2.26 seconds. Mars, here we come! I will note FWIW that the maximum achievable height for a perfectly optimized mentos+coke geyser is, by basic math, 25.1 meters.

The USSF-52 launch in Q3 will use a fully-recoverable FH; it is only sending 6.2 tonnes to GTO (which I must point out is well within the capability of an expended EOL F9, thus supporting the cannibalization claim). The ViaSat-3 launch this August will supposedly use a fully-recoverable Falcon Heavy for direct-to-GEO ascent, but at 6.4 tonnes I have my doubts about the core surviving. I dunno beyond 2022.

They have used F9 sticks as side cores, although they have recovered them all. It’s not entirely trivial but it’s not far from it, either. It would absolutely make sense to use EOL F9s for the rare expendable FH mission. It is not possible to use a F9 booster as a FH core. They are incompatible. The Merlin clusters on F9 have sufficient gimbal to do a cursed 3-2-1 FH launch, where one booster is jettisoned early for boostback and landing and the other booster is expended, but the FH core cannot handle the unbalanced thrust forces.

Technically, Diet Coke is a monopropellant; Mentos are the (consumable) decomposition catalyst. Although even more technically/pedantically, it’s not chemical decomposition but rather runaway physical precipitation of a dissolved gaseous solute in a liquid solvent. The presence of aspartame in Diet Coke (in lieu of sucrose in regular cola) decreases the viscosity of the solvent, allowing higher exhaust velocities; there is also some speculation that aspartame tends to help stabilize bubble formation. I believe the maximum theoretical specific impulse of a Diet Coke+Mentos combo is somewhere in the neighborhood of 20 seconds. All the Pythom team needs to do is convert all the water in Earth’s oceans into Diet Coke and they’ll be at least 0.03% of the way to reach the amount of propellant they’ll need to reach orbit.

All speculation of course, but in the future this could lead to customers paying a premium for the extra capability of “swan song” expendable booster flights, and SpaceX will officially discontinue offering expendable flights of new boosters. “Sure, we’ll expend a booster for you, but you’re gonna have to get in line because we only have three EOL flights per year.” This also tends to cannibalize Falcon Heavy. There’s little incentive to pay for a Falcon Heavy flight to send your 7-tonne megasat to GTO when you could just adjust your schedule and use a swan song flight of a Falcon 9. Falcon Heavy looks increasingly less useful for full reuse; its use case is primarily government/science missions BLEO with the core expended. FH reusable can send frankenstages direct to GEO in the 6-8 tonne range, I believe, but since comsats always carry their own propulsion, it’s almost always more efficient just to let the comsat circularize. With the inclination change needed for GEO, bi-elliptic transfers are just ridiculously more efficient than direct Hohmanns.

Yeah, insectoid (and avian) wings are completely focused around resistance to gravity. In microgravity, there’s no “down” and speed is not necessary for flight. In a future where it became necessary to traverse significant open corridors in microgravity, the most intuitive solution would probably be calf-mounted ducted fans, actuated by ankle articulation. That way your source of force is located near your feet, which is precisely what we happen to be accustomed to.

The moths and flies that went to space as adults kept trying to fly and kept failing. The moths and flies which were “born” in space, on the other hand, rapidly gave up on powered flight and learned to glide by simply shoving off surfaces and floating across to a destination. The first group of live bees which went to space on Columbia in STS-3 were ill-fated as they received insufficient nutrition and never learned to navigate in microgravity. However, subsequent missions which sent an entire hive into space showed much better results. In-colony, the bees rapidly learned how to fly straight paths in microgravity and worked together to define a “front” and “back” of the hive and hung out at the front and beat their wings together to create a consistent airflow path. They were hopelessly lost when it came to keeping their combs consistent, though. Not as bad as spiders, though. The spiders that went up on Skylab proved utterly incapable of weaving consistent webs. I suspect that a spider’s intuitive orb-weaving instinct is highly algorithmic and thus extremely gravity-dependent.

No, I think the crush of a pythom is called constrictiom. I don’t see why they are bothering with nitric acid and alcohol when all they really need is a bottle of vinegar and some baking soda.

Nilesat-301 is only four tonnes. I wonder what kind of performance enhancement they’ll be able to get out of expending the booster. Nominally, Falcon 9 can take up to 8.3 tonnes to GTO if the booster is expended. By my math, the upper stage has a whopping 1.21 km/s more dV with a four-tonne payload than with an 8.3-tonne payload. Circularization in GEO is only 1.63 km/s. I wonder if they’ll make the upper stage a frankenstage and try to do a near-GEO injection. Of course the upper stage still needs enough residuals to either graveyard or deorbit itself.

So one of the critical questions is whether we are only comparing dV costs from the surface to LEO, or if we are also considering the cost of getting the necessary propellant to the lunar surface. To bring the discussion back to the thread topic: consider a bog-standard Starship (85 tonnes dry mass, 1200 tonnes propellant, 150 tonnes to LEO, 380 s). Suppose your goal is to get 150 tonnes of raw materials into LEO. Is it easier to get it from a mine on Earth or a mine on the Moon? Well, obviously, you can get that 150 tonnes into LEO in just one Starship launch if you're bringing it from Earth. On the other hand, if you're starting on the lunar surface and aerobraking at LEO, then you'll need 2.74 km/s. Starship will need to burn 265 tonnes of propellant to transport itself and the materials to LEO. And since that 265 tonnes has to get to the moon, you're obviously going to need to lift more than 265 tonnes of propellant into LEO in the first place, so you might as well just lift the 150 tonnes of raw materials into LEO in the first place. What about 450 tonnes of raw materials? Well, if you're starting from Earth, that will require three Starship launches to LEO, quite obviously. On the other hand, if you're starting from the moon, it will cost you 583 tonnes of propellant. Now, that's a better trade-off; 583 is a lot closer to 450 than 265 is to 150. But you're still losing, overall.

Don’t part-clip ad nauseum but sure, you can mess around with aero exploits if you think that will do the trick.

It’s very Kerbal; I’ll give them that. I tested a two-Kerbal expendable unpressurized descent/ascent vehicle like the one they proposed. It was a bit chunky, but it was able to do lunar ascent/descent, Martian ascent/descent, and Kerbin abort-capable launch and descent without any issues. Quite robust, really.

What’s more energy-expensive: sending ore from Earth to LEO or sending ore from the lunar surface to LEO?

As a bare-bones mission goes, it's not the worst concept ever proposed. Presumably non-cryogenic fuel transfer is easier than cryogenic fuel transfer, right? But also absolutely no way in hades.

This is a simple challenge, but I'm very, very curious to see what people do in order to try and beat it. You're allowed a vessel weighing up to ten tonnes, nothing more. Your sole source of propulsion must be monopropellant or bipropellant rocket fuel; no jet engines, nuclear engines, or ion engines allowed. You can, of course, use the rocket fuel with a fuel cell to power a propeller, but if you do that then you cannot use solar panels or an RTG. No infiniglide or other hacks/cheats; no part mods. Without ever leaving the atmosphere, how far can you go before you land? Specifically, on the F3 menu, you want to maximize "Ground Distance Covered" between liftoff and touchdown/splashdown/crashdown/burnup. "Highest Altitude Achieved" on the F3 menu must be below 70,000 meters. You have to be airborne. If you need a takeoff roll on the runway, that's fine, but once you touch down again it's over (no rovers allowed). Let's see what you've got!

That's super cool! See what I did there

It is friendly to the environment in the sense that it removes things which are known to be bad for the environment, such as humans.