sevenperforce

If you have a high-performance cryogenic tug performing both TLI and the initial braking burn, then you can launch a very respectably-sized hab (maybe even a hab and pressurized rover combo) into LEO, loiter until the tug shows up to ferry it to suborbital lunar descent, then use its own hypergolic propulsion to perform the final braking and landing.

Thank you! The reason for the three-stage approach was that NASA seemed to be dead set on assembly at LOP-G, where each component would be boosted to TLI by its cryogenic launch vehicle and then brake itself into NRO for rendezvous with LOP-G. The three-stage design was forced solely because no commercial LV has a large enough lunar throw to get a component large enough to brake itself into NRO and then perform LLO transfer and lunar descent with the ascent vehicle. If we had larger commercial launch vehicles, a two-component, separate-launch architecture or even a monolithic two-stage architecture would be vastly preferred. Introducing an expendable, cryogenic tug on the front end rather than a hypergolic tug on the back end changes a lot of the math. Depending on the size of the tug and the capability of your launch vehicles, there are numerous ways to solve the problem: Constellation Redux Launch descent and ascent modules, already mated, into LEO Launch cryogenic tug to LEO and rendezvous Cryogenic tug performs TLI Either cryogenic tug or descent module performs insertion at NRO Apollo-C Launch an ascent module and a descent module to LEO in two separate launches Mate the two modules together in LEO Launch the cryogenic tug to LEO and rendezvous Cryogenic tug throws stack to TLI Either cryogenic tug or descent module performs insertion at NRO Artemis Lite Use a commercial vehicle to send lightweight ascent vehicle to TLI Ascent vehicle brakes for its own insertion at NRO Use a commercial vehicle to send lightweight descent stage to LEO Launch cryogenic tug to LEO and rendezvous Cryogenic tug throws stack to TLI Cryogenic tug performs insertion at NRO, rendezvous with ascent stage Orion reaches NRO on SLS Cryogenic tug uses residuals for transfer to LLO Crasher Chaos Use a commercial vehicle to send a reusable crew capsule to TLI where it brakes itself into NRO Use a commercial vehicle to place a landing/ascent stage in LEO Launch cryogenic tug to LEO and rendezvous Tug performs TLI and injection; loiters until Orion arrives Tug performs transfer and most of descent In the last version the tug needs better loiter or ZBO. One thing to note is that no commercial launch provider is going to be able to send both the HLS and the tug to LEO. The cryogenic tug will need to be launched separately. The cool thing is that if the tug is delivering surface assets, you don't necessarily have to have a 1-to-1 correspondence between the surface asset placements and the missions. You can put stuff down way in advance, and you might have missions without any surface-related launches at all.

For reference: if we assume that a surface component delivered to a suborbital lunar staging point will need to provide the last 300 m/s of its own braking (not including margins for hover and touchdown), then a cryogenic tug will need to provide a total of 5.67 km/s to take it from LEO to lunar suborbital staging. Crew modules (whether delivered in piecemeal or all at once) will need to get a total of 3.63 km/s from LEO to the Orion rendezvous point. If the cryogenic tug is kerolox, then surface assets can be up to 55% the mass of whatever is delivered to the Orion rendezvous point. If the cryogenic tug is methalox, then surface assets can be up to 58% the mass of whatever is delivered to the Orion rendezvous point. If the cryogenic tug is hydrolox, then surface assets can be up to 63% the mass of whatever is delivered to the Orion rendezvous point. That should give us a good starting point.

Let's drill down on this optimization problem a little farther. Suppose we take the following assumptions as givens: SLS will never launch anything but Orion and a uselessly small payload; Orion will never reach anything but NRO/EM-2/DRO; Orion will always need an abort-to-Earth option; and Our goal is lengthy, manned polar surface missions. With these assumptions, we articulate our forcing function: we want our missions to achieve maximum cadence with the lowest cost. The following factors will impact this: Cost amortization won't help us much because NASA will be depending on commercial partners, who will absorb a good deal of the development cost. Component reuse (whether via commonality of components or actual hardware reuse) can help to improve mission cadence even if NASA does not benefit in absolute cost. Mission risk is folded into mission cadence; if you have an architecture that cannot accommodate schedule slip, your overall mission cadence drops. Are we agreed so far? I think, given the high dV cost of going to the Orion rendezvous stopover, all surface components MUST be emplaced in advance using direct Hohmann transfer rather than stopping off midway. Given these variables, component commonality seems strongly preferred. I think that one of the major elements which can be broadly useful in mission design is a cryogenic, high-performance, expendable tug with no more than a week of persistence. Such a tug could be used in two different ways: both to deliver human-rated mission components from LEO to the Orion rendezvous point and to deliver surface components from LEO to a suborbital lunar staging point. Any components used to deliver crew from the Orion rendezvous point (with or without involving LOP-G) to the lunar surface need to be as small as possible, due to the significant delta-v costs of braking into the rendezvous point and then proceeding to the lunar surface. Going from TLI directly to low lunar orbit costs 900 m/s, while going from TLI to LOP-G (or equivalent) and then to low lunar orbit costs 1,160 m/s, a 30% dV penalty. If the cryogenic tug is very large, it could be used to deliver very large surface assets as well as delivering an entire descent/ascent mission stack to the Orion rendezvous point. If it is small, it could be used to deliver smaller surface assets and individual components of the descent/ascent mission stack. This approach offers a nice constraint on mission building; whatever is delivered to the lunar surface will have a specified mass ratio with respect to whatever is delivered to the Orion staging point.

A further observation... Given the high dV cost of taking anything from NRO/EM2/DRO down to the surface, there is a strong forcing factor in preference for placing surface assets directly, without a stopover.

I mean, we can constrain some things. Realistically, SLS is never going to launch anything but a manned Orion to TLI. It will never be useful for distributed launch. It will never reach Block 2, so Block 1B is the only configuration we will actually be able to make use of. So the primary constraint is that we are going to be having Orion and up to 8 tonnes of comanifested cargo coming toward the moon. The cargo will never be able to provide propulsion to Orion, so Orion will have to burn to deliver it to wherever we're going. Orion is never going to be beefed up (because then SLS can no longer deliver it), so it cannot reach LLO. It can reach a high prograde circular orbit, a frozen orbit, or an elliptical orbit, but only marginally. NASA won't want that. So realistically Orion will never be sent anywhere other than NRO, EM-2, or a distant retrograde orbit. NASA will always want an abort-to-Orion option, so Orion cannot be moved around by a tug. Everything else will need to be emplaced by commercial rockets, and it will need to be sent well in advance. It's also generally agreed that we are targeting the poles. So those are the constraints: Stage a polar lunar surface mission, Using commercial rockets to place everything in advance, At NRO, EM-2, or DRO, Permitting no more than an 8-tonne module to arrive along with Orion, And without moving Orion after it arrives. Aaaand....go. Not much better.

Incidentally I must have added it up wrong -- the stdev is 6 and my score is 136. But nbd. Constrained rankings do pose a challenge. But maybe there's a way around it. Suppose an infinite number of students, each having a certain score S = A+B+C+D where each stdev is 6 and the mean of all S is 80. That would generate a Gaussian distribution. I could then find the percent of students with a total score greater than 136, which gives me my percentile and thus can be used to determine rank.

Over and over, I come back to this exact conclusion. There's no good way to optimize, no good solution, because there's no consensus on goals.

If all students have the same standard deviation of 6.697 in their original scores (which, again, is only one data point but is all the data we have, and probably is pretty representative) then that should be able to tell us something about the shape of the curve.

The class rankings I've posted are derived from more complete data -- in some cases, the full known distribution of grades; in others, a bucketed distribution of grades. For example, I have one of only 3 As in Class A, with 40 total students, so my expected class ranking is 2 +/- 1 of 40. In class D, the professor simply told me outright that I am #2 in the class. Since everyone takes the same classes, end-year class rankings are based on a raw total grade point score. Ranking in each individual class is a decent proxy because each class is curved to the same mean, so a #4 ranking in Class A should correspond to the same grade as a #4 ranking in Class B, and so on. The classes are weighted differently, but because of my grade distribution it will yield the same results if you weight them all equally. For these purposes I think you can treat each rank as a discrete number of points. So #2 would be 39 points and #10 would be 31 points and so forth. My gross point total would be 135. I'm not sure how to estimate what percentile that corresponds to, though. There COULD be someone who is #1 in every class but it is very unlikely....most people probably have the same standard deviation (6.697) as me.

Revisiting this now that I have more data. The ranks of each class are now known. In Class A, I am ranked # 2 (+/-1) of 40 In Class B, I am ranked #10 (+/-3) of 40 In Class C, I am ranked #14 (+/-2) of 39 In Class D, I am ranked #2 (+/-0) of 40 Based on statistics, and the assumption that most students have a similar grade distribution to my own, what is my estimated overall class rank?

I am always excited to see the small fairing because it usually means a high-energy payload.

Now to build and test in KSP... You'd need planes trimmed to lift off automatically at a certain speed so you could get them off the ground together. Then it would be a matter of choosing pre-set trim action groups so they would essentially fly themselves into a suborbital parabola. I really like the idea of dumping precooled oxidizer into the intake of a COTS fighter jet engine in order to squeeze out extra performance. Wouldn't be as efficient as SABRE but would be considerably cheaper, easier to achieve, and more robust.

I always had a soft spot for Black Horse. This seems better.

The volume and mass of a black hole are related by the equation rs = 2GM/c2, where rs is the Schwarzschild radius, G is the gravitational constant, M is the mass contained within the black hole, and c is the speed of light. Quite by coincidence, the mass of the observable universe is such that if you calculate its Schwarzschild radius, you get 24 billion light years, which is around 60% of the radius of the observable universe. So a lot of people like to speculate that the universe is a "white hole" -- a black hole turned inside out with a wormhole from another universe. It's a nice idea, but it doesn't really work. One of the big problems is that it suggests that the position of the Milky Way is near the actual, physical center of the universe, which violates the Copernican principle. And a white hole wouldn't really work the way our universe appears to have worked. Also, the universe is spatially flat and is not ever going to collapse on itself, so positing this theory as a means of explaining the universe's past origin fails too. https://www.discovermagazine.com/the-sciences/the-universe-is-not-a-black-hole

Additionally, they're "stuck" to each others via rugged bumpers to begin with, so those would be the only contact points anyway. I wonder if wind conditions are just always going to be so unstable that fairing catches never reach a high success rate. Then, in turn, I wonder how much of a success rate is needed to pay back the dev work and investment in the two boats.

Not proposing the concept. Thought experiment.

As @Space Nerd said, noap. I had the same thought with planets -- if we merged all the superfluous moons, could we get a super-earth? Of course the answer is no, not even close.

OML = outer mold line. And yes, I am quite aware of the basic underlying principle of orbital flight. TWR may not be entirely irrelevant, but it is not nearly as big of an issue as it is on the ground. Lower TWR requirements, higher vacuum efficiency, and the obviation of the bulk of atmospheric and gravity drag bring the dV requirements down to manageable levels for SSTO -- you can achieve orbit with an 82% propellant ratio if you use RL-10s. Large, draggy tanks aren't an issue and provide a huge advantage during re-entry. Hence the question -- what vehicle shape, engine configuration, and EDL profile would be favored if you could "jump" to the edge of the atmosphere for free?

If you can lift something to the edge of space with NO regard to cost or size or shape, it would open up a lot of additional options, OMLs, and so forth.

That's the part I'm trying to figure out how to do. Nah, no need to predict final grades. I am satisfied if I can predict my current rank.

The internet will really only lose it if we attempt a sample return from Uranus.

The trick here is that you can't do a gravity turn because you can't deviate from a vertical ascent using the laser. The laser can't follow the vehicle downrange. It seems arbitrary, yes, but I wanted to do a thought experiment about what kind of rocket you would design if you couldn't do a gravity turn.

Sure, that would work, but I actually have much more data than that. I know what I made in all four classes, and I know the actual discrete scores in each class. For example (these are not the real numbers because it would probably be some sort of crime to post them online): grades/class Class 1 Class 2 Class 3 Class 4 As 3 2 4 1 Bs 12 16 13 5 Cs 11 9 11 18 Ds 2 1 0 3 Fs 0 0 0 1 (my grades) A B A C I could simply take the average grade and make a bell curve, but I think that having the actual grades above would make a placement/percentile distribution curve more accurate. As an added complication, Classes 1 and 3 are 6-hour classes while classes 2 and 4 are 4-hour classes, so they each count 50% more.

My question assumed you only had the ground laser, and that it could only accelerate the vehicle vertically, not horizontally. It would be more than launching from a very tall mountain because no mountain is as tall as you could achieve using this. You could also give it significant vertical velocity, enough to get well out of the atmosphere. Let's handwave the cost of the laser and electricity to run it. The way I see it, you have two basic paths: Slow rise. By using the atmosphere as your sole propellant source on ascent, you need only carry engines for the boost into horizontal flight, and you need no particular aerodynamic shape. It is still an SSTO requiring 7.8 km/s of dV but that's easier than it sounds when you can optimize for vacuum at the outset and TWR is virtually no object. High boost. You can make your ship aerodynamic and carry inert propellant, allowing the laser to push you at high speed through the lower atmosphere and then heat your propellant to propel you much higher. Once your apogee reaches MEO altitudes, you can burn efficiently at apogee to lift your perigee out of the atmosphere, then burn at perigee to circularize.