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Not knowing where to put this, I put it here.
I see The New Glenn flew successfully today, including landing the booster on a barge. The second stage put the twin craft on their way to Mars.
The delay yesterday was too high a radiation environment due to the solar flares. Those Mars craft were judged at risk.
GW
I have split up the stuff discussed in posts 607 and 606 just above into two separate topics: (1) what is required of a vehicle design to be capable of rough-field landings on the moon, Mars, or even Earth, and (2) how to go about building the landing pads for vehicles not capable of rough-field landings, which involves spreading concentrated loads over larger areas to reduce bearing pressure, as well as rocket jet blast erosion.
I re-wrote and expanded these as two articles that will be posted on my "exrocketman" site in December and January. As soon as the search codes become available, I will post them here. The articles have not yet been posted, so there are no search codes for them as of yet. I did the research and was able to quantify the proper load spreading angle to use, as 30 degrees off vertical. That would be for the load-spreading ability of the layered packed rock substrate underneath the finish paved surface of the landing pad. The more concentrated the applied loads are upon the paved surface, the deeper the stone-backfilled excavation must be.
GW
These are good concepts, but they require being proven effective, before you risk lives upon them. To the best of my knowledge, that has not yet been done for any of these. Going to the moon to experiment with them in situ under harsh conditions, is a pretty good reason for going back to the moon, among others.
GW
Regarding the images Tahanson43206 posted for me in post 606 just above:
The "design for landing" image is what I estimated for a lunar "Starship" variant properly equipped for a rough-field landing on the moon. Mars would be similar, but the numbers would be different, and it would be very difficult to protect such legs during Mars entry. There are two critical design criteria a rough field lander must meet: (1) The transient pressure underneath the pads (or other contact surfaces) during the touchdown event cannot be allowed to be any greater than the bearing strength of the lunar regolith, which is rather similar to Earthly sand-dune sand. (2) The minimum span across the polygon created by the landing leg outer contact points must exceed the height of the vehicle center of gravity above the surface. These two critical design criteria were amply demonstrated appropriate by Apollo, and by Surveyor before it. There are too many today who ignore, or never learned, these well-established criteria. It shows in the recent overturned commercial lunar landers.
The "how to build a landing platform" image shows how roads and foundations are properly built upon weak soil, so that heavy concentrated loads do not crush or penetrate the paved surface. These techniques were developed and used with great success by the Romans, and are still used today. Unfortunately, doing it "right" is quite expensive, so today our roads are built with inadequate excavation and inadequate quantities and size-grading of the rock fill underneath the paved finish surface. So, they do not hold up nearly as well as the old Roman roads. Big heavy trucks do the most damage, by crushing the substrate down, "rutting" the road.
The image of the "Blue Ghost lander" is not what I sent, but it is the Firefly Aerospace commercial lander design that was actually quite successful landing on the moon. Note the squat low form relative to the leg pad span, and the large size of the landing pads. It meets the same criteria that the Apollo LM and the Surveyor probes were designed to. So, success at a rough-field landing should not be much of a surprise.
As for vehicle designs that do not meet rough-field criteria, they should not be sent to the lunar surface until a hard-surfaced, strong landing pad surface has been constructed. The same applies to Mars, most of its surface is similarly weak. The load-spreading effect of the backfill-rock substrate is how you spread a concentrated large force on the surface onto a much larger area at the bottom of the excavation, which reduces the applied bearing pressure to what the regolith or soil below can actually withstand. This is all civil engineering "dirtwork" just like what we do on Earth, except for the final pavement finish surface. To land rockets, that finish pavement must be both heat-resistant and blast erosion resistant. Concrete usually requires some repair after a rocket landing, but concrete as we know it is unavailable on the moon (or Mars). Some sort of tough, resistant tiles laid like flagstones might work. But they need to be thick, and as heavy as possible, not to get ripped away by jet blast shear forces. Laying such tiles directly upon the weak regolith will NOT work!
GW
Actually you don't need anything but pencil and paper to do analyze nozzle expansions, although having a spreadsheet or something to automate the iterations required to find Mach number from Area ratio helps. That's what you usually have to do, to have a vacuum bell. Bear in mind that there is no such thing as an "optimal vacuum rocket nozzle design", there are only constrained designs, the usual constraint being how big a device will actually fit behind your vehicle?
Pick your constrained Ae/At. Determine from it (and gamma) your exit plane Mach number. From Mach, determine the exit plane pressure ratio to chamber pressure Pe/Pc. Pick either an 18-8 degree curved bell shape to be detailed with method-of-characteristics, or else a 13 degree half angle conical bell. The conical bell is a bit longer, but will have identical performance! The performance index is kinetic energy efficiency nKE = (1 + cos(avg half angle))/2.
CFvac = (Ae/At)(Pe/Pt)(1 + gamma*nKE*Me^2) There is no backpressure correction term -(Pa/Pe)(Ae/At) because out in space Pa = 0.
Vacuum thrust Fvac = CFvac*Pc*At.
The nozzle mass flow rate wnoz depends upon c* ("characteristic velocity"), Pc, At, and the nozzle throat discharge coefficient CD that reflects boundary layer thickness. Wnoz = Pc CD At gc/c*. The flow rate drawn from tankage wtot is bigger than wnoz by the amount of any flow rate tapped off, used to drive turbopumps, and then dumped overboard without going through the nozzle. The dumped bleed flow fraction BF is dumped/wtot. Wnoz = wtot(1 - BF).
You must use wtot for your Isp calculation, because it is directly related to the mass ratio of the vehicle. This Isp = Fvac/wtot. Or you can divide the one relation by the other t tobtain Isp = CF c* (1 - BF) / (gc CD).
All you need to enable this is c*. That is chamber temperature and gas properties as c* = square root of [gc R Tc GF / gamma] where the gamma factor GF inside the square root is GF = c3^(c3/c1). In turn c1 = (gamma - 1)/2, and c3 = (gamma + 1)/2.
That's all there is to it.
As for the area ratio-Mach relation, it is Ae/At = (1/Me)(TR/c3)^c4, where c4 = c3/(2*c1). Now, TR = Tc/Te = 1 + c1*Me^2. You can find Ae/At directly, but finding Me is iterative, because the equation is transcendental in Mach.
As for the Pe/Pc ratio, PR = Pc/Pe = TR^c2, where c2 = gamma/(gamma - 1). Then Pe/Pc is just 1/PR. If you have a gamma and an Ae/At, you know Mach, and you know Pe/Pc. Given an nKE, you know CFvac. So you know thrust. And if you know CD, you know wnoz. If you know BF and wnoz, you know wtot. So if you know Fvac and wtot, you know Isp.
GW
I don't really know anything about "sulfacrete", except that the notion is to slurry rocks and fines into molten sulfur and let it cool off and solidify. That presents raw sulfur to the environment, because it is the matrix in a composite reinforced by the rocks and fines. If that gets hit by a rocket plume with H2O in it (and almost all do), that creates H2SO4 sulfuric acid anhydride, which is a strong acidic corrosive. Here on Earth, that's less of a problem, because there is much in the environment that is alkaline, which can help neutralize it. But on the moon or Mars, nearly all the rock and regolith materials are from volcanic-type rocks, which are also generally acidic. I think you will have an acid contamination corrosion problem with anything sulfur-based as a building material. But I could be wrong.
GW
I see in the news that NASA finally threw open the lunar lander thing to all of industry, seeking a "plan B". So far, there have been 2 responses, one from SpaceX, the other from Blue Origin, the same original HLS contractors NASA selected, then finally downselected to SpaceX. The news reports provide no clue as to what SpaceX and Blue Origin "plan B" items really are.
You can pretty much bet that the SpaceX "plan B" is still some variant of its Starship modified to land on the moon, which is exactly what they were contracted to do in the first place. You can also bet that the Blue Origin "plan B" will be based on the "Blue Moon" lander they were designing right up until the downselect. They both have too much effort invested in those ideas to switch horses now. Simple as that!
Both are too tall to be stable for rough field landings on the moon (they violate the "stance wider than the cg is tall" criterion that was successful with Surveyor and the Apollo LM). And, you have to worry also about landing pads sinking deep into the lunar regolith, because it is no stronger than an Earthly sand dune! I do not know how loaded the Blue Origin pads would have been, but as of yet I have seen nothing out of any SpaceX designs that take dynamic (transient) bearing pressures during touchdown into account. They only have touchdown experiences on a hard pad or steel deck.
NASA needs somebody else to respond with a different idea from either of these two. But, with the landing scheduled for only 1 or 2 years way, there is no reality to NASA's plans, either! The Apollo LM took 4 years paper to flight, and that was a crash program where money was secondary. This is not. The downselect was driven by insufficient money in the first place. This lander cannot be done "from scratch" in 1-2 years, even if it were a crash program.
The original SpaceX and Blue Origin ideas have about 2 years under their belts now. Some variants of those are the only feasible things that might get done in another 2 years. And that could ONLY happen if NASA funded both contractors at a crash program level, from now until then. That's the only way to have a viable option AND a viable backup option! Common sense says so!
But it ain't going to happen that way, people!
All you need do is look at what is happening to JPL to understand what has already been happening at the rest of NASA. So far, 25% of workforce laid off, and they were by far NASA's most capable people! Demonstrably so! THAT is what this government is really doing!
Just as I have always recommended: "look ONLY at what they really do; do NOT listen to what they say or promise!"
GW
These very large cruise missile concepts (several conventional like Snark, Mace and Matador, and Pluto's nuclear version) to replace manned bombers were designed in the early 1950's, long before there was any fieldable, practical ICBM technology. The Russians did the same things, too.
Yes, there was Atlas and Titan and Thor (and Russia's R-7), and there the initial IRBM-only Polaris on the submarines, by about 1959 if memory serves, but those liquid-propellant ICBM's and IRBM's were withdrawn as far too impractical for swift response purposes, as soon as Minuteman-1 became available in 1962. ICBM's have been instantly-ready solids ever since, on both sides.
And the SLBM range improved dramatically as they left the early Polaris models behind. Liquid propellant missiles persisted for several years on Russian subs, including the K-129 the CIA tried to salvage. Once the flirtation with Regulus 1 and 2 was over, our subs went all-solid with the Polaris SLBM IRBM. And our subs have used solids ever since.
No leaks, no drips, no toxic fumes, no delays fueling up, you just push the "go" button and it goes, right then. That is precisely why solids are very much preferred for ballistic missile weapons.
GW
I do not know, but I am hazarding the guess that this thing is a nuclear turbojet, not a nuclear ramjet. It seems most likely subsonic, their equivalent to a Tomahawk, just with an effectively-infinite range. I've seen one source making that claim among a bunch making other claims, and that rounded but fairly-blunt nose does imply subsonic cruise. Ramjet works at high subsonic, but turbojet works a whale of a lot better. If this thing really is a nuclear-powered Tomahawk equivalent, it not only flies subsonic, it also flies at low altitude.
The heating rate for turbojet is lower than for ramjet: you only need to take the air to turbine inlet temperature (at or under 2000 F). You do not see the kind of full rich combustion temperatures needed for ramjet (nearer 3000-4000 F). That means a smaller unshielded reactor core that will actually fit inside such a modest-size airframe. But it does mean you have to get that heat into the airstream between some compressor, and the turbine that drives it. Maybe the core is in that stream, maybe not. Who knows? There are such things as heat pipes today.
The Project Pluto nuclear ramjet missile was a high-speed design using supersonic inlets, and early 1950's reactor core technology, with the air going through passages through the reactor core. Such were simply much larger cores, partly because of the old technology, and partly due to the presence of the air passages, which could not be small.
It was a very large missile, unlike Tomahawk, that was to fly "forever" at about Mach 3 and under-500 feet above the ground. The hazards that forced its cancellation were actually two-fold: (1) the exhaust plume was densely radioactive with materials eroded from the core, and (2) flying that fast that low, has the bow shock still lethally-strong as it "drags" along the ground. It would have killed a lot of our people on its way out of our country, from both radiation poisoning and violent death by blast wave effects.
This Russian thing won't have the shock wave problem, being subsonic. But it does present the same radiation poisoning problem, even though the core is smaller and there is less total plume mass. It has to fly over their people while leaving their country, just like the radiation risk the Project Pluto ramjet posed. Putin probably does not care about killing his own people, though.
GW
I saw the videos, plural. The first one takes on their rough field landing system. The second takes on refueling in space, and cut off before it was finished.
It appears that if you decide to land tall things, you need a discerning pilot to target the right spot amongst all the hazards, and who can adapt the positioning of landing surfaces to the unevenness just before the touchdown. That has to happen faster than humans can act. This is going to be based on AI, apparently.
Tip-over after touchdown on rough surfaces with tall, narrow objects is a real thing, and some recent commercial landers have demonstrated that ugly little fact of life. Any horizontal speed at touchdown can tump you right over in a split second, even in low lunar gravity. That was the proximate cause of the Japanese failure, and at least one of the two US failures. Both designs were tall and narrow, presuming the controls were good enough to adapt.
Given the track record of failures and crashes because of events unanticipated by the programmers with Tesla self-driving software, I would hesitate to take the same approach with a crewed device as the Japanese and that one American commercial lander company. The other American commercial lander was more squat and more successful.
Controls can only be so good, not perfect. And the moon is infamous for having unevenness and randomly scattered but dense distributions of obstacles and hazards.
But my fears may or may not be justified. I just do not trust AI, because I see lots of errors and falsehoods out of the ones available to the public. I still think the term AI is an oxymoron: there is NO intelligence or understanding of anything there, there is only imitation of style plus very high speed. Computers process bad data as well as good data. It all looks the same when it comes out of them.
GW
SLS started out as the Ares-5, yes. It's still the same first stage core made of space shuttle engines.
Orion is intentionally overweight, to absorb the otherwise lethal thrust vibrations seen with the original 5-segment expansion of the shuttle solid booster. Orion atop one of those was Ares-1.
That same 5-segment booster rocket is used as the boosters on SLS Block-1. I'm guessing that they finally tamed the thrust oscillations in that design, not seen in the 4-segment shuttle design, or else the huge SLS core is enough mass to absorb and attenuate them.
Whether Ares or SLS, this is reusing shuttle components built at the same plants in the same states where the shuttle was built, to the max extent possible, for maximizing senatorial race votes. These vehicle designs are NOT what real engineers would do on a clean sheet of paper! These configurations were dictated by politicians.
All the engineers could do was cope: try to find some way to fly these things and still get to the moon. And THAT is why SLS Block-1/Orion cannot even reprise Apollo-8, much less the other lunar landing missions!
And THAT is what multiple launches to mount 1 mission, from that boondoggle Gateway station, in the idiotic unstable halo orbit about the moon, is all about!
You absolutely do NOT want politicians micromanaging your space program! They are totally (and reliably) technically incompetent! But THAT is exactly where we have been since the 1970's!
GW
PS - that same incompetent micromanaging to optimize votes instead of designing to a sensible spec, is also EXACTLY why it take many years and $billions to get a new airplane, tank, or ship. Military procurement is hobbled by congress the same way, and has been for decades.
The most famous example showing how to do it right was the P-51, way back before congress screwed everything up. About 90-100 days from paper to a flying prototype! And, like SpaceX, there was a fix-it-in-the-field aspect. The P-51 got re-engined with a better engine and a bigger prop, before it was effective enough. The final bubble canopy that fixed the "see the enemy before he sees you" problem did not get fixed until the introduction of the P-51D model, which is the one everybody thinks of.
Artemis II is the Orion atop the SLS with the flawed heat shield discovered on Artemis-I's Orion (which was the first Orion flown atop an SLS), but this one already built before they ran that uncrewed test flight. Orion flew once before, atop a smaller booster, and not under the name "Artemis"; that one (unlike the Artemis-I Orion) had a heat shield that was built and functioned properly. They changed the processing and screwed it up, for Artemis-I, building at least both the Artemis-I and Artemis-II capsules this new way, to save $.
They have decided to fly it anyway, crewed, flawed as it is, even though there has been more than enough time to switch it out with one built "right". It just cost more $ to do that. So now try to tell me NASA top managers value crew safety above $ and schedule, the way that they claim! They claimed that before the Challenger loss (and attempted a cover-up afterward), and they claimed it again before the Columbia loss. They lied, both times. I have seen nothing since to indicate that those attitudes have ever changed since the loss of Challenger.
The Artemis-II mission is a loop around the moon, then heading out into cis-lunar space for a while, before coming home. This is without orbiting the moon. This mission does not even reprise Apollo-8, much less Apollo-10 through 17! That is how uncapable the Orion's service module is, and how uncapable SLS Block 1 is. The closest comparison is Apollo-13, which looped around the moon without orbiting, to save the crew after one of the O2 tanks in their service module blew apart.
The Apollo service module had the dV capability to enter low lunar orbit off the transfer trajectory with both the command module and a lunar module, and enough more dV to get back onto the transfer trajectory from low lunar orbit with just the command module. The Orion service module does NOT have that capability: it is too small, and the Orion capsule is too big and heavy for it. This configuration was selected by politicians, not real engineers! As was the SLS Block-1 configuration.
Artemis-III is another Orion already built, and as I understand it, already being stacked atop an SLS. I do not know if they fixed the flawed heat shield, not having seen a word about that. People should be asking questions about its heat shield! While it is slated to land astronauts on the moon, they do not yet have a working lander to take those astronauts there, with the landing only a year or 2 away, supposedly.
Now I see in the news that Musk has begun a pissing contest with the acting NASA administrator, over NASA re-opening the lander contract to Blue Origin and anyone else, because the Starship variant "HLS" is behind schedule and seems unlikely to be ready in a year or 2 (and I agree with that assessment). Big money correlates with big egos that simply do not know how to behave.
The real problem here is that neither Blue Origin nor anybody else can possibly man-rate a lunar lander in only 1-2 years. It took 4 on Apollo, and that was a crash program where costs were of secondary importance. Blue Origin has built things for its small Blue Moon prototype, but has built nothing for the larger one which was to be the crewed version.
The mistake here is that a serious lander program should have started about 5 or more years ago, maybe even 10 years ago, since this was not to be a "crash" program. But none did. And nobody at the modern NASA seems to have been keeping track of the factors Musk time/real time and Bezos time/real time. There has never been any reality to NASA's Artemis program: contracts, plans, or schedules.
There is plenty of fault here, to go around. A lot of this is the Senate's fault, since they micromanage not only what is to be done, but with what hardware, to be built in whose states. And no one is taking responsibility for all this gross mismanagement. I predict no one will.
Apollo succeeded because NASA and its engineers did the work without much in the way of congressional pork-barrel politics interfering with things and micromanaging things. The Space Shuttle, however, was NOT a fully reusable two-stage airplane, precisely because of congressional mismanagement. And the ISS suffered from the same congressional mismanagement flaws, which is why there were never any human centrifuges aboard it. And why it is in an orbit that is easy for the Russians to reach, but which is quite wrong for dispatching missions to anywhere outside Earth orbit.
The only part of NASA that really worked well in the years after Apollo was JPL with the planetary probes and landers. And now this particular congress and that idiot who is our president have now gutted JPL. 25% laid off, so far. Those idiots are firing the government workers that have demonstrably done good work! Just how STUPID is that?
And everybody forgets what the other A in NASA stands for: "aeronautics". The X-59 has still not yet flown, which was to demonstrate how to fly supersonic with reduced sonic boom. Meanwhile, Boom Supersonic has already accomplished that feat, and on private money. They got there faster. And they did a really good job!
The rot in government that needs rooting-out goes deep, yes, but that process should start in Congress and the White House, not with the general federal workforce.
GW
I found this in today's "Daily Launch" email newsletter from AIAA. It refers to a longer article in the NY Times:
New York Times
With SpaceX Behind Schedule, NASA Will Seek More Moon Lander Ideas
The acting administrator of NASA said on Monday that the agency was looking for a Plan B to carry astronauts to the moon’s surface because SpaceX, Elon Musk’s rocket company, is behind schedule. In appearances on CNBC and Fox News, Sean Duffy, the temporary leader of the space agency, said he would open bidding on a contract to build a new lunar lander to other companies.
-----
my take on it:
I doubt SpaceX will lose its contract to do a "HLS" lunar lander version of Starship, unless Musk does something further to piss off Trump. Big egos seem to go with big money.
The "behind schedule" thing is the inevitable difference due to "Musk time" vs "real time". This is an effect well known and demonstrated to be a factor of about 3, since Musk started SpaceX and almost went bankrupt with it learning to successfully stage supersonic vehicles (Falcon-1, which failed its 1st 3 out of 4 flights).
There is no excuse for NASA not to have known about this effect. They apparently erroneously believed he could do it on a "Musk time" schedule. Which is where we are now.
All the contractors have this time factor schedule lie problem. It's a part of the marketing hype that wins contracts, unfortunately. It's just a different schedule time factor for each one. The government is supposed to track those things and be aware of about how long it will really take.
Boeing's time factor has risen since the merger with McDonnell-Douglas. It is now over 3, approaching 4. (Same goes for Lockheed-Martin.) The difference is that about the same jigger factor now applies to budget estimates with Boeing, not so much at all with SpaceX.
This inevitably pushes back the manned landing. It took 4 years to develop and fly the Apollo LM, and that was a crash program, where cost was secondary. It'll take longer to do this one, because the people who did this before are long-retired or dead, and took their know-how of the unwritten engineering art with them (which is close to half of what you need to know, in order to do what they did). This "plan B" thing should have started about 2-3 years ago.
And that NASA need for a "plan B" also reflects the Blue Origin delay, although nobody said a word about that! They have been funded to build and fly their "Blue Moon" lander, right alongside SpaceX, ever since SpaceX got its contract. Bezos also seems to have a time factor of about 3. And he's been busy trying to get his own big rocket flying, just like Musk.
Surprise, surprise!
GW
In the previous post, the "kaowool" is a low-density ceramic or mineral fiber insulation. That low density means it has a low thermal conductivity, letting the tile get hotter without the tank shell seeing that heat addition so very much. You can only do that if you have a separate means of "tying" the tile in place over the insulation. In SpaceX's case, that is the tile retention pins.
That low density insulation has to be a mineral/ceramic fiber to take the temperatures at the interface with the tile. That way the tile can be a denser and therefore stronger and tougher ceramic (or other material, but apparently not iron-based from Flight 10). Denser is higher thermal conductivity, inherently. Which makes the inner tile face temperature much closer to the outer face temperature. Which is why they need the "kaowool" layer.
The "Pyron" ablative layer is not something I understand yet, except that it is the backup in case the tile is lost. It is related to PICA-X, based on what little there is to be read about it. PICA-X is what the Dragon uses for its ablative heat shield. "PICA" is an acronym for "phenol impregnated carbon ablator". The carbon is likely in a woven fabric form. This was originally a NASA thing, but it was expensive and difficult to fabricate. SpaceX subsequently did a cheaper- and easier-to-fabricate variant, and named it PICA-X. It is still phenolic reinforced with carbon fibers (likely in woven fabric form) and who knows what else, either way. I have seen no material specs for either form, much less "Pyron".
Apparently, the tiles used on Flight 10 were "metallic" in the sense of high iron content in some way. I know NOTHING about the actual material! But apparently it oxidized very fast during the one entry, quite unexpectedly. Whatever Flight 11's tiles were made of, it was something different, likely some kind of firebrick-like material. And those tiles worked a lot better.
Bear in mind that there was no insulation or backup underneath the space shuttle heat shield tiles. Those were a fragile and vulnerable low density ceramic, combining the high temperature resistance of the alumino-sililcate material and the low thermal conductivity of the very low density, into a single material. The new nose and leading edge tiles on X-37B are the first step away from that approach, they being a high-density ceramic locked onto a low-density ceramic underlayer. SpaceX seems to be pioneering yet a different approach. And it would seem to be working.
GW
Update on post 2223 just above:
I saw in today's "Daily Launch" email newsletter from AIAA with a similar very positive assessment of Flight 11. It had a link to a longer Ars Technica article. I looked at that article. About the only new piece of information is that the "crunch wrap" variation of installing heat shield tiles seems to have solved the gap flow problem.
It may be a while before they fly the next one. That will be a version 3 ship with Raptor-3 engines. Who knows what they will do to the booster. They are rebuilding test stands and launch pads for the newer versions. That work is currently ongoing.
GW
I saw this story, too. The South Atlantic Anomaly is growing. That's not good news, as the effective "bottom" of the Van Allen Belts is at lower altitude there, down to LEO itself, instead of generally higher at ~1600 km ~ 900-something miles. Things in higher-inclination orbits (like the ISS) often pass through that lowered bit of Van Allen radiation.
GW
I saw the news story that Starship/Superheavy flew successfully yesterday (Monday), and I went and watched the video of it on SpaceX's website today (Tuesday). It looked to me like they met every objective and suffered less damage than the last flight.
I saw one engine that failed to light for the Superheavy boostback burn, but it lit up for the landing burn.
I did see the heating discoloration on the Starship rear flap trailing edges from the reflected jet blast of the hot staging, but I did not see actual sheet metal damage there, this time. And I saw nothing suggesting any plasma leakage through the rear flap hinge lines, so whatever they did to stop that, seems to have worked.
I didn't see much in the way of pieces coming loose during entry, but I saw lots of small bits coming off as it hit the dense air just before and during its landing burn and splashdown. I did not see a view of the heat shield as it touched down, although I thought I heard words to the effect that such coverage was actually obtained.
All in all, it looked like it got through in even better shape than the last time. Supposedly the next one will be v3 Starship with the Raptor-3 engines. It's pretty close to time for trying to recover them at launch site. They'll learn a lot more, and more quickly, from real hardware with which to do "scratch and sniff" tests, after the flights.
Kudos, SpaceX! You did it again!
GW
If power is beamed as a coherent bean, beam spread is very much reduced. A power density that is quite dangerous leaving the satellite is still rather dangerous 30,000 km away. So you have to aim the beam with utter reliability. This is an inherent phenomenon with coherent beams. We've seen it before, with both laser and maser.
You do not have that risk to mitigate, if you could use an extension cord "fat" enough not to lose very much in I^2*R losses. The problem with that concept is the materials from which to build it do not yet exist! I think I said that when I posed the concept in a post elsewhere on these forums. I used the words "manurium", "unbelievium", and maybe "unobtainium", when I wrote the post.
But once they do exist, one could use the alternate extension cord approach to lower the cost of that electricity further, by simplifying and eliminating so many safety controls and devices.
The danger posed by the extension cord is the same as that posed by a space elevator: what if the thing breaks? Part of it will fall to Earth, ultimately at very high speeds. So you have to build it to reliably not break, if you do it at all, no matter what the available materials are, in the future.
GW
I have actually looked at the Centaur as a possible small space tug. There is a larger version, but it still features the common bulkhead between the LOX and LH2 tanks. Though that is an insulated bulkhead, it still limits the stage life to several hours or maybe a day or so, which is too short to be a useful tug. The periods of the elliptic capture and departure orbits are the best part of a week long.
I really like the steel balloon approach to lighter weight, which depends critically upon control of tank pressure with both evaporation and appropriate venting. I also greatly admire the reliability of the RL-10 engines. Put those together in a scaled-up stage that has separated LOX and LH2 tanks, with anywhere from 2 to 5 RL-10 engines, and cover those tanks with low-density insulation and a very reflective outer foil layer, and you would have a LOX-LH2-powered tug with a stage life long enough to serve as a tug: more than a week or so. Without adding cryocooler equipment, which is not all that heavy, but not all that light either.
SpaceX does not face quite the same stage life problem with its Starship, because the LOX and LCH4 temperatures are not very far apart. They are already doing pressure control of evaporation and venting. But they are not relying upon the inflated balloon approach for strength. At that size scale they cannot, and they also must make this thing a survivable reentry craft, plus land the thing. Centaur does none of those things. SpaceX's design is similar to monocoque construction, with frames and stringers. Their stage life is long enough that a Starship could be a very large space tug. It would have to be fitted for external docking features in one way or another, though.
You would choose a large tug when flinging a large craft into interplanetary space. You would use a small tug (like my conceptual Centaur variant) when flinging a small craft into interplanetary space. The tug (of either size) takes you from LEO speed to just under escape, so that your interplanetary craft need add only a little more to get fully beyond escape to the c3 needed for its mission. The tug (whichever it is) stays on the extended ellipse, and burns (unladen!) back into LEO about a week or so later, then must rendezvous with "something". The unladen burns need not much propellant, despite the large LEO-entry dV (rendezvous budgets are small), precisely because it is unladen (very much lighter in nonpropulsive weight).
GW
Data on the moon's orbit about the Earth, from the "data" worksheet in the "orbit basics spreadsheet" file, part of the "orbits+" course materials available by links from the forums site.
Rmax = 405,506 km, Rmin = 363,299 km, Ravg = ellipse a = 384,403 km, eccentricity = 0.0549 (some 5.49%). speed V at apogee = 0.9632 km/s, V at perigee = 1.0751 km/s, avg V at R = a is 1.0176 km/s. Mean surf gravity 162.3 cm/s^2. Mean surface escape V = 2.376 km/s, mean surf circular orbit V = 1.680 km/s. Mean radius = 1738.3 km, polar radius = 1737.6 km, equatorial radius 1738.7 km. Mass = 7.354 x 10^22 kg.
GW
The moon's orbit about the Earth has a low, but nonzero, eccentricity. That eccentricity will overcome anything based on pure circles. But that effect at low eccentricity is still low.
There is also the issue of local topography. Few places on Earth are really an approximation to the "ideal sphere" used to estimate both sunrise and moonrise, and sunset and moonset, here on Earth. 1 degree of topographical deviation is a deviation of about 4 minutes in sunrise or moonrise, and in sunset and moonset.
Even the adjacent tree-line is a serious effect on this. Locally, the adjacent tree-line variations correspond to angle deviations up to 1.5 degrees (6 minutes) from the "ideal" horizon. Where I am, this is the central Texas prairie. But there really is topological deviation, plus the heights of adjacent tree-lines. Other locations with more pronounced deviations will have even larger time differences for sunrise, moonrise, sunset, and moonset. It is inherent.
Complicating that is some light refraction effects upon what you term sunrise and sunset. Even those definitions have a serious effect: about 2 minutes, whether you use tip-of-sun (or moon) at horizon, or the centerpoint of the disk. Both the sun and the moon are roughly half a degree in diameter as viewed from Earth.
Sorry, but that is the real-world stuff you have to deal with.
Now, who did a better job explaining it. Me, or ChatGPT?
I still say that the term "artificial intelligence" is an oxymoron. Precisely because no computer has any understanding of truth vs falsehood. If all you know is only what others have said, how can you possibly know what is right vs wrong?
Dare trust no machine, and very few real humans!
GW
The Carnot efficiency is an upper bound upon what can be done, from classical thermodynamics. The disparity between what actually can be done and what that upper bound is, is usually quite large: around a factor of 2.
Carnot efficiency is 1 - Tcold/Thot, where the temperatures must be in absolute units.
These low pressure concepts are attractive ONLY if you can tolerate the low inherent energy conversion efficiency. Crudely factor 2 below Carnot efficiency.
Sorry, but that's just the way it is. There have been NO observed exceptions to classical thermodynamics for about 300 years now!
GW
Spacenut:
Here's best notion I've been able to come with yet. Use the Dragon with the bigger trunk, and use a refuelable version of Blue Origin's smaller lander prototype as the LM. I'm not sure, but I think the Blue Origin lander designs were to be 1-stage in order to be reusable. I also think they were going to use LOX-LH2 propellants in order to make 1-stage reusability happen.
Then we need a scaled-up Centaur with the anti-boiloff gear installed, because we are going to use it as a reusable tug, and we need about a 2 week stage lifetime. The lunar trajectory is a 3-body-disturbed ellipse to the moon at its apogee, and LEO at its perigee. The period is about 10 days. If you do not burn for capture at the moon, you will return to LEO, where you can burn to recover there.
Transport the Dragon/big trunk fully loaded with one Starship freighter to LEO, transport the reworked Centaur fully loaded to LEO with another Starship freighter to LEO. After that, you only need to send up propellants for them, and more Dragons with the big trunks. All with Starship freighters to LEO. No big tanker refill flights
Use the modified Centaur to put the loaded Dragon-big trunk/Blue Origin LM onto the lunar trajectory, then detach and let the modified Centaur come back, where it burns unladen to recover into LEO, requiring very little remaining propellant to do so. Thay's about a 3 km/s dV fully laden and another 3 km/s unladen. I am assuming the big trunk has enough propellant to put the whole cluster into low lunar orbit (dV ~ 1 km/s), and to get back onto the trajectory to come home without the lander (another ~1 km/s at a lighter mass), which lander is left in lunar orbit. The trunk is lost and the Dragon makes a direct free return.
The next mission does not need another lander, just the propellant tanks by which to refuel the one left in lunar orbit. All you need are those tanks, and another Dragon with a big trunk. You are out one trunk per mission, and the lander refuel tanks. The Dragon capsule is reusable a few times. Nothing else! Two Starship/Superheavy launches for the first mission, maybe only 1 per mission after that. But no more than 2.
If you can figure out how to use the modified Centaur as a tug, You can course-correct not to make a free entry return with the Dragon/big trunk, but to stay on the ellipse instead. The tug can retrieve you, but that will require another 10 day trip around the ellipse. That's the cost of not losing the Dragon (which is actually reflyable after entry) and the big trunk (which cannot survive entry). Dragon currently has 2 weeks life support for up to a crew of 7. Smaller crews could ride for a longer duration.
If you capture into polar instead of equatorial orbit at the moon, the dV to capture is higher, perhaps double. That would require a really big trunk for Dragon. But that does put the south pole within reach. You capture into an extended equatorial ellipse, instead of low circular. Then you do the 90 degree plane change at its apogee where speeds are low. Then you finally enter low circular polar. There will be a rendezvous budget for rendezvous and dock with the lander, on subsequent missions.
Of course, there is nothing reliable as a cost estimate per launch of Starship/Superheavy. But even if that is $100M per launch, you are looking at no more than $200M per mission in launch costs to go back to the moon. SLS might be able to put these clusters into low lunar orbit with one launch, and it might not, but the price using it is supposedly past $4B per launch.
I'd say my idea not only saves beaucoup launch cost money, but it also saves on mission hardware costs by reusing nearly everything. How could it NOT be a far better idea? Its only fault is that we are not using hardware made in former shuttle-item plants in the states of powerful senators. Which is why under the current government operating procedures, nothing better than SLS will ever be done by NASA.
GW
It's worn out, Spacenut. Particularly the Zvezda module, which keeps cracking and leaking. Sooner or later, something is going to split wide open, and decompress the entire station, killing the entire crew.
It's not pressurization / depressurization cycles like an airplane, but hot-to-cold thermal cycling every orbit. Sunlight vs shadow. That's roughly 4000 cycles per year, for over 2 decades now. 80,000 + cycles? A lot of airplanes were only designed for 40,000 cycles. Same aluminum structures! Unlike most other metals, aluminum does not seem to have a low stress value below which fatigue life is infinite. Or if it does, that value is very low indeed.
You are correct in pointing out that NASA has no valid follow-on space station plan of any credibility! The powerful senators that dominate what NASA's big projects are, are simply too stupid to understand what is really needed next. We do not elect our best and brightest to Congress. Or had you not noticed that?
Myself, I think it is way past time we-the-people got Congress out of the business of micromanaging NASA projects for pork barrel outcomes instead of real space program outcomes. Congress has been doing that to NASA since Apollo. We have NOT seen a logical next-project-notion for NASA, since John F. Kennedy set the moon-landing-objective-before-1970, way back in 1961.
As for this last Cygnus cargo flight, word has it that the trouble was in the flight control software, not the actual engine system hardware. Still, that kind of nonsense is no longer tolerable. Starliner showed that lesson for certain and for true, plus the other lesson about not being so damned cheap.
GW
Spacenut:
Look at it this way. If there were still in existence the Apollo CSM and LM, that entire cluster could fit within the cargo bay of an operational Starship, and be within its anticipated payload capability to LEO. We still do not have a good figure for the cost of a Starship/Superheavy launch, but whatever it finally proves to be, it will be way less than the cost of a Saturn-5, and truly way-to-hell-and-gone less than an SLS (which even makes a Saturn-5 look cheap)!
We could put some sort of Centaur upper stage with an appropriately scaled-up set of propellant tanks into another Starship cargo bay, and send it to LEO to be docked with the Apollo CSM/LM cluster. That scaled-up (slightly) Centaur could put that cluster into the lunar transfer orbit from LEO (doing what the S-IVB did before), and the service module of the CSM has enough dV capability to enter low lunar orbit with the LM, and to return from lunar orbit without the LM. That reprises any of the Apollo missions. You lose the Centaur and the LM, and eventually you lose the service module. But you DO NOT lose a Saturn-5! And you did it with two Starships from LEO without any refueling.
Wanna do it even better? Leave the LM in lunar orbit for the next mission, but modified for refueling in orbit. Substitute a Dragon and the ISS-deorbit trunk with the extra propellant, for the Apollo CSM. Make sure the modified Centaur is just big enough to fetch along propellant tanks for the LM's left in lunar orbit. Do the same mission as before, except refuel and reuse the lander on subsequent missions (maybe 1 or 2 more). All you throw away is the trunk and the extra propellant tanks that refueled the LM in lunar orbit. But you must send a loaded lower LM stage with each subsequent mission!
Wanna do it even better than that? Use the smaller 1-stage Blue Origin lander instead of the old 2-stage Apollo LM. Landing from low lunar orbit requires a lower dV than from that idiotic halo orbit. That way, the smaller Blue Origin lander can carry even more payload down, and maybe even back up, from the lunar surface. Refuel it with the tanks sent for each mission after the very first one that put it there in low lunar orbit. Just make sure your modified Centaur stage can do trans-lunar injection with the Dragon, the bigger trunk for it, and the Blue Origin smaller lander. You still only need two unrefueled Starships to launch the Centaur, and the Dragon/trunk/small Blue Origin lander cluster, to LEO. You throw away only the trunk and the lander refuel tanks. The Blue Origin lander will likely have a longer service life being re-used, than the old Apollo lander ever might have had. Probably much more than 2 missions.
Now think about a third Starship, one that is at least partly refueled in LEO. Use it as a tug to reach the perigee speed of the transfer orbit to and from the moon (just barely under Earth escape at LEO altitude). If you match with the Centaur stage, you can recover it and bring it back to LEO for refuel and re-use. A fourth such Starship could do the same thing to retrieve the big trunk from the Dragon (and maybe even the lander refuel tanks), for refuel and reuse based in LEO. Now, you throw away nothing except maybe the lander refuel tanks! Although, it would help to have a propellant depot and vehicle assembly space station in LEO!
Not even Musk has proposed using Starship as a tug to retrieve returning-from-the-moon things to LEO. But now I have!
And if you do the tug departure thing using yet another partly-refueled Starship, you don't even need the modified Centaur stage!
It's all about thinking outside the usual boxes. Not even Musk does THAT!
GW