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I never said it didn't.
The same criteria and soil bearing strength numbers apply to both the moon and Mars. Only the local weights are different, and only by approximately a factor of 2.
What I see routinely presented to the public in these press releases is not just wrong, but wrong by orders of magnitude.
GW
I've since learned the GEM 63XL solids do not have thrust vectoring. At least that is not the problem!
From the pictures I have seen, it is impossible to really tell whether the burn through and leaking plume occurred at the nozzle-case joint, the nozzle throat region, or somewhere in-between. It did not appear to be somewhere down on the supersonic expansion bell.
There have been 4 Vulcan flights. Two have had booster anomalies attributed to nozzle problems. The other one supposedly "lost its nozzle" entirely, whatever that really means.
All I can say is that somebody somewhere in the conglomerate that is Northrup-Grumman, specifically its solid motor outfit (which is one of the old large motor contractors from when I worked in that business decades ago), is not paying enough attention to adequate thermal ablative protection in that joint or in that nozzle throat approach design.
With aluminized propellants and AP oxidizer, you are looking at chamber temperatures approaching 6000 F, with a high solids content (mostly aluminum oxide particulates and droplets, in the exiting stream. This thermal environment is way worse than anything the liquid boys have ever seen, even when they tried hydrogen with fluorine at Santa Susanna back in the 50's and early 60's. It's worse in some ways than entry heat shields. Even today.
And a lot of that knowledge was engineering art that was lost in the mass layoffs of the huge industry drawdown about 1993-1996, after the Soviet Union fell apart.
I do have to wonder, though, if NASA insisted on yet another idiotically-dangerous multiple-O-ring "seal" at the nozzle to case joint.
GW
They still have not thought rough-field landings through, because they have never, ever made one! There are few alive today who ever really did. The young crowd today seems blissfully unaware of what it takes to make a rough-field landing on soft ground, with a rocket vehicle making a powered landing. The exception seems to be Firefly. Their design, which worked on the moon, appears to be inspired by what worked decades ago with Surveyor, Apollo, Viking on Mars, etc.
Lunar regolith might be a tad stronger than Martian regolith because the lunar particles are sharp and the Martian ones are not. But the difference is of order factor 2, not orders of magnitude. Both regoliths resemble nothing so much as sand dune sand here on Earth. The presence of scattered rocks within that do not touch provides no reinforcement whatsoever. Earthly sand dune sand is listed in most Earthly foundation design references as having an allowable bearing pressure of 1 to 2 US tons per square foot = 0.1 to 0.2 MPa. The failure pressure is factor 2 to at most 2.5 above that allowable. Those are VERY LOW values to deal with!
When landing, your vehicle is lightweight, unless it is to take off again. Whatever that local-gravity weight is, there are dynamics of touchdown, and off-angle effects leading to one pad touching first. Both require factoring up the static weight by a factor of 2, for a transient landing pressure under the first pad of 4 times what the static value would be. None of those dynamics affect takeoff, the pads see only the static weight, until the vehicle lifts off. But if you are refilling propellant locally, as is often proposed now, that weight is the full max takeoff weight. Which may be some 5 to 7 times the near-empty weight at touchdowndown.
I see nothing in the HLS illustration to show any recognition of those pad bearing pressure issues. I also see nothing in the illustration to suggest any cognizance of the risk of coming down on uneven ground, which is actually depicted nearby, in the illustration, and not as bad as some actually seen during Apollo! The cg is about halfway up the vehicle, with the weight vector hanging from it. If that vector points to a location on the surface outside the polygon defined by the landing pads, the vehicle WILL fall over (and explode)! And that is if there is zero horizontal speed at the moment of touchdown! If there is horizontal speed, the lead pad will dig-in and "trip" the vehicle, even if the weight vector falls well inside the polygon.
I see no cognizance in any of the press release illustration from SpaceX (or anybody else) about these issues and risks. The same ones that twice tripped-up Intuitive Machines on the moon, and the Japanese lander, too.
The criteria to avoid this have been known since the early 1960's. (1) Min dimension of the pad polygon must be greater than the cg height. (2) Make sure the transient bearing pressure under the pads is closer to the allowable bearing pressure than the failure pressure on landing, and similar for the static bearing pressure, for takeoff. (3) Tip the pads on spring mounts inward a little, so that the lead pad won't dig in so easily if you touch down with some horizontal speed. (4) Make sure that you can hover just above the surface, for a significant time, so that whatever is controlling the vehicle during the landing can "see and avoid" uneven high-slope ground, big boulders, and cavities or other holes.
And, also since the early 1960's, if you do not have test data for the target regolith, presume it is like Earthly sand dune sand, and use the lower range of values.
Only parts of this were ever formally written down. This was mostly the engineering art that was known among those who actually did those landings decades ago. Most of them are dead now. Apparently very little of this art was passed-on, and what of it was passed-on, was lost over the time since.
GW
Spacenut:
Did you see the paragraph in the linked report that described how they fixed the leaky seals? By going to a material that better resists NTO?
Q: If the better material was known in the first place, then why did Boeing use something different? Ans -- cheaper.
What does that tell you about the thrusters? Think "cheaper" might have something to do with those troubles, too?
Certainly did for the B-737MAX debacle. And there's a couple of other airplanes Boeing is in deep kimchee with troubles. One is the 777-X, the other is the new USAF tanker. All built by the same Boeing. As is the SLS core stage.
GW
Should not be a surprise. Money talks.
His SpaceX and Tesla baseline incomes come from government contracting. He is being paid to land people on the moon, if he can. He IS NOT being paid by anybody to go to Mars. If he defaults on his moon landing commitments, he will lose far too much credibility to be a major space contractor anymore, to NASA or DOD. That is "default" by not doing what he promised to attempt. "Failure" by not being able to do it, is a different issue.
GW
Whether the Starship really will be cheaper to launch than a Falcon-9 or Falcon-Heavy is still debatable. That answer CANNOT be known until experimental flight testing and design changes are done. Be aware that SpaceX is talking about an even larger Block 4, while the somewhat-larger Block 3 still has yet to fly at all! Block 2 pretty much worked mostly right in the last two experimental flight tests.
The change from "block to block" is somewhat closer to a new design than just a minor variation on an old one. Always has been, always will be. That's just the inherent nature of vehicle developments and the experimental flight tests to "prove them out".
The cost question also depends upon how big your crews are. If 3-7, a Falcon-9 or Falcon-Heavy and Dragon makes very good sense at ~ $90 M/(3 to 7) for $12-30M per seat. That may look like a high seat price, but if all you are flying is a small crew, that's a small portion of your overall mission cost.
If you are flying a big crew 20+, then you would need more than one Dragon, and something big like Starship makes a lot more sense to shoot them all up there in one launch. Per seat price? Nobody can know yet!
Early exploration does NOT need big crews! That comes later when you do some sort of experimental base where you can prove out and verify that you really can start to "live off the land". That capability will NOT be the case in the first explorations, and it will still NOT be the case, when you first set up that experimental base. That is inherent.
Let's just say I am extremely skeptical of the "$10 M launch cost" some have been bandying about for Starship. I rather think $100 M is a better wild guess! But it is ONLY a wild guess! NOBODY has anything any better than a wild guess! Not Musk, not ANYBODY! $100M / (20+) is under $5M per seat. Still a small portion of any real mission cost.
GW
from the AIAA email newsletter "Daily Launch" for Thurs 2-12-2026:
-----
Spaceflight Now
Vulcan suffers solid rocket booster problem during USSF-87 launch
ULA said an issue affected one of the four solid rocket boosters that helped propel its Vulcan rocket into space Thursday on a mission for the United States Space Force. Despite the problem the rocket, making only its fourth flight, continued on its planned trajectory, the company said. The rocket thundered away from pad 41 at Cape Canaveral Space Force Station at 4:22 a.m. EST but less than 30 seconds into the flight, there appeared to be a burn through of one of the nozzles on a Northrop Grumman-built graphite epoxy motor (GEM) 63XL solid rocket boosters (SRBs).
-----
My take: This is not the first such issue with this solid's nozzle. Somebody is not paying enough attention to the highly-erosive ablative insulation environment approaching and through the throat of a solid rocket nozzle. Whether out of ignorance or being too cheap is not knowable from this. If you complicate the design by adding thrust vector capability, you raise the odds of such burn-through or nozzle-loss failures, I do know that!
Reinforced rubbers do not hold up in the high shear flow. It takes hard silica phenolic plus a graphite throat insert, and that does NOT deflect to vector the nozzle bell! You have to deflect to vector out near the full case diameter where the scrubbing fluid shear, to get the rubber to hold up. Even then, you must do that deflection while still holding the full compressive thrust load aligned where you want it. Vectoring a solid rocket is a bad thing to attempt.
GW
Here's variation on what KBD512 suggested. Put together a reusable electric-drive transfer vehicle that is 2-way capable and reusable. Do this in LEO where humans can build the thing from docked modules like the ISS was. Load it there, too. Spiral it out unmanned to an orbit outside the outer Van Allen belt, say 60,000 or 70,000 km out. That's where you send the crew to board it, and to recover them coming home.
But, you do not need a Starship to do that!
Falcon-Heavy with a Dragon has plenty of dV to take a crew of 4 to 7 (there are up to 7 seats in the capsule) across the belts quickly to board the ship there. It's not rated for usefulness beyond about 6 months, but I bet it could be. That's your emergency bailout capsule coming home. Falcon-Heavy also has the dV to fly up empty and bring a returning crew of 4 to 7 home. Once the reusable orbit-to-orbit craft is built, all you have to do is resupply it. It might be just about as easy to spiral in to LEO uncrewed for that, since the dV to LEO is only about 7.8 km/s + loss coverage, while the dV to 60-70,000 km circular is near 10.5 km/s + loss coverage + circularization.
Starship might be more appropriate for larger crews, but remember, its first and best role is as a transport to LEO, without any refueling tanker flights at all. Why use a big vehicle when a smaller one will serve? Just build some sort of tug based in LEO, which would require a lot fewer tanker flights to keep supplied if it is smaller than a Starship, and let it push a small hab about the size of Skylab at the most, for transporting crews quickly across the Van Allen belts. Just keep the tug and hab in LEO, based there.
The orbit-to-orbit interplanetary (or lunar) transport, ought to have spin gravity. Crews will be out there a long time, especially spiralling in and out at the moon or Mars. It will need a solar flare storm shelter, too. The rest of that stuff (the ordinary rockets and capsules) is short-term zero-gee stuff.
If we are going to send Dragons (or similar) out beyond the Van Allen belts, we will need better forecasting for solar weather, lest an unanticipated event kill a crew needlessly. And we will need a station in LEO at which to assemble things and to fill them up with mission propellants. It would seem likely one station could perform both functions.
All that being said, I am wondering why we would even consider sending tall, narrow Starships with landing legs and pads that are inherently too small, to the moon or Mars, before big, flat, hard-surfaced paved landing pads have been constructed. That's the fatal shortfall in Musk's vision. And don't kid yourself, it is a fatal shortfall.
GW
Same is true returning home, too! You have to cross the Van Allen belts fast, then either decelerate into orbit or do a free return. You cannot kill your crew trying to spiral-in slowly with electric.
GW
Void:
You cannot use electric propulsion to take humans from Earth orbit to Mars. Electric propulsion is extremely low thrust/low acceleration. It takes a month or two, maybe three, to spiral out through the Van Allen radiation belts. That long an exposure is a fatal dose for any crew.
You need to cross the Van Allen belts in only a day or so, something known since just before Apollo. That takes high-thrust chemical or nuclear rockets to get significant vehicle acceleration. You need around 0.1 to 0.5-ish vehicle gee capability to make that happen. Electric is typically under 1/10,000 gee.
The departure dV from Earth orbit onto the transfer trajectectory to Mars (or the moon, or anywhere else out there) is the biggest dV by far! If you have to use chemical (or nuclear) for that, then why bother with electric?
My point: there is a whale of a lot more to worry about than just Isp, when looking at travel to Mars, or the moon, or anywhere else. Focusing on only one aspect is a guaranteed trip down the wrong path.
GW
From AIAA's daily Launch email newsletter for Mon 9 Feb 2026:
Wall Street Journal
SpaceX Delays Mars Plans To Focus on Moon
SpaceX has put off a mission to Mars planned for this year, shifting its focus to a long-promised lunar voyage for NASA. The rocket company told investors it will prioritize going to the moon first and attempt a trip to Mars at a later time, according to people familiar with the matter. The company will target March 2027 for a lunar landing without humans on board, another person said.
GW
1. You have to have a way to do entry, descent, and landing. There just enough atmosphere to cause significant peak entry heating, but not enough to do subsonic touchdowns with wings or chutes. It's pretty much propulsive touchdown. With a heat shield at least during entry, and preferred to be retained if the craft is to be used more than once.
2. When you touch down, you must have either a smooth, flat, hard plain, or a vehicle short and squat enough not to tump over, if a landing leg hits a big boulder or a small ravine, or if you touch down on ground that is strongly-sloped locally. Whatever is flying the craft must be able to perceive such hazards and react real-time to avoid them, or else you must design the craft to cope with the worst cases as if you were flying blind. There are criteria that historically worked on the moon and Mars: (1) the polygon defined by the landing pads has a minimum dimension, which must be greater than the height of the center of gravity above the surface, (2) the landing pads have to be large enough to lower the bearing pressure created by a factored-up weight, so that the anticipated soil bearing strength is not exceeded, (3) tip the pads inward a few degrees on spring loading, so that the lead pad cannot dig in and tump you over, if you have horizontal speed at touchdown, and (4) you need the throttleable thrust for thrust/weight equal 1 to hover, for significant time, before attempting the final touchdown, so as to give whatever is flying the vehicle time to see the hazards and avoid them.
3. It would help if the crew cabin were close to the bottom of the craft to limit how far a crewman might fall when using stairs or ladders. The issue with a short fall in lower gravity on the moon or Mars is more about suit punctures and busted visors. Tractor rocket configurations lend themselves to this, plus easing the thrown debris problem. If you are tall and narrow with the crew cabin forward, you risk a very long, fatal fall. Even if you have a powered elevator of some kind.
4. Must limit thrown debris if there is to be anything at all on the site besides the landing vehicle itself! The rocket blasts striking the surface divert sideways, but still moving at very significant speeds measured in km/s. Any rocks, grit, sand, and even dust will get thrown outward at pretty close to that diverted rocket plume velocity. While the gas plume velocity slows as the plume(s) rapidly spread(s), once accelerated, the thrown debris does NOT slow down! Even small pebbles are quite dangerous at km/s speeds!
5. Once down, you must be close enough to straight upright to ensure that a takeoff that does not "fall over" too fast for the thrust vectoring to counter. That has to be built into the landing legs, most likely. Leg-adjust to level the grounded vehicle. Likely hydraulic, possibly electric. Probably NOT manually-operated!
6. When doing the early exploring, it is likely that the site is unoccupied by any assets other than perhaps pre-positioned supplies sent 1-way. Even so, thrown debris is a big risk, if it destroys the supplies your small exploration crew were going to live on. Early exploring is all about finding out what is really there, where exactly it is, roughly how much and what quality it is, and some notion of what is required to get at it. It is NOT about tinkering with in-situ life support or propellant manufacture or anything like that! At least not as a priority objective. That comes later at an experimental base site. Supplies and propellant must have come from Earth to support the early exploration crew for a stay of short-to-modest length (days or weeks). Not months! Not years! They will need a truck with a real drill rig on it, and they will need suits supple enough to work that rig like real oil field roughnecks. They can "camp out" in the landing vehicle for a surface habitation.
That's my two cents' worth.
GW
I finally found enough public information to understand what the heat shield tiles on Starship really are. They are a less expensive and more producible variant of TUFROC tiles used on X-37B. A lot of the savings comes from the fact that the same size and shape tile covers most of the ship, unlike the Shuttle or the X-37B.
These are a modified carbon-carbon composite type outer material, which has some sort of ceramic materials incorporated, which is tougher and higher temperature-capable than alumino-silicate ceramics. It is higher thermal conductivity than low-density aluminosilicates. The lower layer is low-density fibrous (in some way) alumino-silicate ceramic, which has the low thermal conductivity needed to keep the backside temperature down in a thin two-layer title.
I do NOT know exactly how these materials are made. But I have seen the black upper layer atop the white lower layer in photos of these tiles being installed on the pins, over a thin layer of some "ablative" that is a backup for lost tiles.
What they learned from flights 10 and 11 was that the alternative "metallic" tiles (whatever they were) were not reliable because of unexpectedly-high oxidation, and that they needed some sort of gap filler between the tiles. So they are going with this two-layer carbonaceous ceramic atop low density alumino-silicate (a variation on the TUFROC notion).
The gap filler has turned out to be some sort of crushable paper wrapping around each tile. I am only presuming that the excess paper sticking out of the gaps gets trimmed off during the installation process.
It is also my impression that the tiles are redundantly attached, with both adhesives and those pins. The pins may (or may not) stick up into the outer layer.
Sorry, but I am unable to pin it down any better that that! Not privy to internal specifications and data!
GW
Follow-up to post 60. I found another article that gave more information. There were two sets of hydrogen leaks during the wet dress rehearsal. The first was in the connections between the rocket and the infrastructure around it, very similar to the leaks seen during the Artemis-1 wet dress rehearsal. These were fixed the same way as Artemis-1. Then a second set of leaks appeared. I had the impression that these were inside the vehicle. The article said they "did not understand" those leaks, and shut it down at that point.
This is a Boeing-built first stage core having propellant leak problems. So did the Starliner capsule that stranded 2 astronauts on ISS. I think I might see a pattern here: being too cheap damages quality, causing unreliability. Same corporate management mistake as what caused the 737MAX disasters. If I am right, the odds of killing the crew while riding the SLS just got higher.
GW
Follow-up to post 59. I see also that Artemis-2 will now not launch until March at the earliest, since the propellant load rehearsal found hydrogen leaks. Reportedly, these were in the connections between the rocket and the launch pad structure, not the rocket itself. As I recall, the last SLS launch was delayed for the very same reason. So it looks like the leak problem might be chronic.
Meanwhile, I ran across this about severe solar flare activity:
From Space.com via AIAA’s Daily Launch email newsletter for 3 Feb 2026. Note that the “flare” is the burst of electromagnetic radiation that travels at the speed of light. The coronal mass ejection “CME”, if any, is the slower-moving mass of particles that constitutes the actual radiation exposure hazard. The bigger those are, and the more direct the impact upon “something”, the higher the radiation exposure that “something” receives. With big CME’s around, this might not be a good time to put crews out past Earth’s magnetic field in a spacecraft. Quote:
Sun unleashes extraordinary solar flare barrage as new volatile sunspot turns toward Earth
News
By Daisy Dobrijevic published yesterday
A rapidly growing sunspot has fired off at least 18 M-class and three X-class flares in just 24 hours, including an intense X8.3 eruption.
The sun has erupted in a relentless barrage of powerful solar flares over the past 24 hours, firing off at least 18 M-class flares and three X-class flares, including an X8.3 eruption — the strongest solar flare of 2026 so far. Solar flares are ranked by strength from A, B and C up to M and X, with each letter representing a tenfold increase in energy — meaning X-class flares are the most powerful explosions the sun can produce.
The culprit is sunspot region 4366, a volatile active region that has grown rapidly in just a few days. The flurry of activity began late Feb. 1 and has continued into Feb. 2, with multiple M-class and X-class flares erupting in quick succession. The prolific region appears to be far from finished. Spaceweather.com described the region as a "solar flare factory", warning that its rapid growth and magnetic complexity make further eruptions highly likely.
The X8.3 solar flare peaked at 6:57 p.m. EST (2357 GMT) on Feb. 1, unleashing a blast of extreme ultraviolet and X-ray radiation that ionized Earth's upper atmosphere. The flare triggered strong R3 radio blackouts across parts of the South Pacific, with shortwave radio disruptions reported across eastern Australia and New Zealand, according to NOAA's Space Weather Prediction Center.
Scientists are closely watching for signs of any coronal mass ejections (CMEs) that could follow these powerful flares. Early analysis of a CME linked to the recent X8.3 eruption suggests that most of the solar material is likely to pass north and east of Earth, with only a possible glancing blow expected around Feb. 5, according to NOAA's Space Weather Prediction Center.
If those glancing impacts materialize, they could briefly elevate geomagnetic activity and increase the chances of auroras at high latitudes. However, forecasters stress that it is too early to know whether conditions will be favorable, as much depends on the CME's speed, direction and magnetic orientation.
It's also possible that more eruptions are still to come. Sunspot AR4366 remains highly active and continues to rotate into an Earth-facing position, raising the chance that future eruptions could launch CMEs more directly toward our planet. NOAA forecasters say they expect more exciting space weather activity from this region in the coming days.
Solar flares are powerful explosions from the sun that emit intense bursts of electromagnetic radiation. They are ranked in ascending strength from A, B, C and M up to X, with each letter representing a tenfold increase in intensity. X-class flares are the strongest eruptions and the number following the X indicates how powerful the event is. Today's flare was measured at X8.3, putting it high in the upper tier of solar outbursts.
--- end quote
GW
Cosmic ray exposures in the inner solar system more-or-less in the vicinity of Earth vary between 24 and 60 REM per year, varying more-or-less sinusoidally with the nominally-11-year sunspot cycle. High solar activity is the lower value of cosmic ray exposure. Exceeding slightly the 50 REM/year exposure standard (twice that of Earthly workers in nuclear plants) increases the risk of cancer late in life beyond about 3%. 60 REM/year in a peak year is just not that much a risk!
The killer is solar flare events, not cosmic rays! Those occur erratically, though more often during high sunspot years, and they comprise an enormously-larger huge flood of much less energetic particles than cosmic rays. They can vary from 1 REM per hour to 10,000 or more REM per hour. Such exposures are a few to several hours long. Not the whole trip!
The older astronaut high-exposure limits are no more than 25 REM accumulated in any single month, and no more than 50 REM accumulated in a single short event. Somewhere near 200-300 REM accumulated in a short event is about a 50% chance of dying quickly from severe radiation sickness, and 500 REM accumulated in a short event is pretty much a 100% chance of dying quickly.
The outdoor fallout after a nearby fission bomb explosion is somewhere near 5000-50,000 REM per hour, for a few days after the event. That stuff requires feet of lead or yards of earth (and concrete) for adequate shielding.
However, solar flare radiation, being far less energetic particles than cosmic rays, is far easier to shield! It only takes about 15-20 gram/cm^2 worth of shielding on your craft's hull to adequately protect from a high-end solar flare event, such as what occurred in 1972 between two Apollo missions to the moon.
Cosmic rays are not impacted very much by any shielding we might use, but it is known that the lower the molecular weight of the atoms in the shielding materials, the lower the secondary radiation shower intensity produced by scattering events hitting atoms in the shielding. That's why you do not want metal shielding for cosmic rays!
Cosmic rays are just NOT the fatal problem! Anyone who points to that as a show-stopper is lying! The solar wind, and especially solar flare events, are! That exposure really does build up over time toward some kind of career exposure limit. The old one was 400 REM max lifetime accumulation, reduced by age and gender. There was a formula for that. NASA published this stuff, decades ago.
I do hear that those older astronaut exposure limits have recently been reduced some, but that is small change compared to what I am talking about! And the truly high-exposure limits have been known since the atmospheric atomic tests in Nevada in the 1950's, not to mention the two Japanese cities that were A-bombed in 1945. Only the really low-dose exposure limits were found in the decades since.
GW
The Artemis-II mission was delayed because of cold at Cape Canaveral. I don't know any details about the delay, but the reason (cold, just below freezing soak-out) is comparable to what killed Challenger back in 1986. That decision on NASA's part is unsurprising, since the SRB's on this launch vehicle are basically a 5-segment form of the Shuttle 4-segment SRB's. It would be incredibly stupid to make the Challenger mistake twice!
I am not sure how accurate this is, but one posting I saw on LinkedIn had an animation of the orbit Artemis-II is "going to use" (supposedly, anyway). It launches into an ellipse that apogees somewhere in or between the two Van Allen belts, then figure-8's around the moon (like Apollo, but further out from the moon), before making a free return and entry. There has to be a perigee burn to get from the ellipse onto the lunar transfer trajectory, but no other burns, other than course corrections.
If true, these astronauts will spend more time (twice or more) exposed to Van Allen belt radiation than the Apollo astronauts ever did. This is a high solar activity year. From what I read, that increases the radiation exposures from the Van Allen belts (it does decrease cosmic ray exposure outside Earth's magnetic field).
Notice also that I said nothing about the Orion heat shield risk. That is well covered in other postings. Peak convective heating occurs at about half the entry interface speed, which is near escape in a free return from the moon. Convective heating rate varies roughly as speed cubed. Plasma radiation heating rate varies by an exponent of 6 or more with speed. The effective plasma temperature in degrees K is crudely numerically equal to speed in m/s. You decide if flying a known-to-be-defective heat shield with a human crew was a "good risk to take".
GW
So we have a revised airframe and a new engine, neither of which have flown before. Remember, this is still experimental flight test. Very experimental indeed!
I hope it goes well. The risk is rather high that it will not. There's a lot of changes between this and the earlier version that last flew.
GW
Some of these reporters and press release writers are abysmally ignorant. The phrase "moon's immense gravity" in paragraph 5 of the second article quotation is proof enough of that.
Plus I noticed the real reason they will not orbit the moon was NOT given: SLS block 1 with Orion does not have the delta-vee capability to enter lunar orbit and get back out of it! Block 1B might, but that's not what this SLS is.
As for the heat shield, I have previously posted how they are making the same kinds of bad management decisions as killed 2 shuttle crews. It's been 2 years since Artemis 1 flew. They have had the time to have replaced the heat shield, despite the article claiming there was not enough time. They spent that 2 years trying to analytically show changing entry trajectory was enough safety margin, and not everybody inside (or outside) NASA agrees with that.
Once again we see schedules and budgets prioritized above crew safety, while either/or thinking and "not invented here" attitude prevented looking for a third alternative besides flying flawed or doing it with the expensive Apollo method.
GW
Based on the color in Spacenut's photo, the resin in the hex may be phenolic. The fiber definitely looks like glass, but could be a mineral fiber like fire curtain cloth, although that's not likely due to the high costs compared to glass.
I've never seen anything definitive about those material choices, so I do not know.
But look at Spacenut's photo once again! That's a chunk of the hex held in the hand, to show how the gun nozzle fits the hex cell, for hand-gunning the heat shield. It also shows almost EXACTLY my alternative!
Put a bottomless mold around that chunk of hex, and attach it to the outlet of a plastic extrusion press. Use the press to fill all the cells in the hex at once, plus the border between hex and mold wall. Trowel off the excess on the bottom, install the mold bottom, take the mold off the press, trowel some of that excess onto the top, and install the mold top. Then go cure the thing.
You have to think outside the either/or trap! They've spent 2 years now trying to justify-with-analysis flying a defective heat shield with a crew! They could have replaced that heat shield with a hand-gunned one in that 2 years, or they could have tried my idea and proven it worked in that 2 years, with the hand-gunned option as a backup.
THEY DID NEITHER!
They did not want to pay the labor to hand-gun any more heat shields, and I cannot fault that aversion. But they did NOT value crew safety high enough to NOT fly a known defective heat shield! And, they were too bound up in their either/or thinking to consider any other options! Not to mention "not invented here" thinking, since my idea came from outside their organization. (I had to use a friend at NASA just to get it inside!)
Either/or thinking and "not invented here" attitude. Not prioritizing crew safety above cost and schedule! THAT is the fault here! And it has NOT changed since Challenger and Columbia! The real lessons of those disasters were quite apparently NEVER learned!
Those shuttle loss inquests were around a billion dollars, and 18 months or more, each! There really is nothing as expensive as a dead crew! Especially crews dead from bad management decisions! Just like my by-line says!
GW
Well, NASA managers are "playing the odds". Yes, the Artemis-2 heat shield is going to spall out chunks, maybe more of them since it was built less permeable, or so the story says. The Artemis-1 heat shield was mostly identical, and spalled out chunks. But those ugly and alarming craters left behind were not enough to cause a burn through.
Less likely would be two craters close enough together to be one big crater, at the bottom of which another chunk happens to spall out! That would penetrate most of the way through the heat shield, leading to a burn-through, in turn very likely fatal for the crew.
You have to understand what Avcoat really is. It is a cycolac polymer loaded with little microballoons to lower its density and increase its ablation rate. Denser is lower ablation rate. Too dense, and gas has more difficulty getting out of the less permeable char. But the more filled with microballoons, the more viscous it is, and hard to mold into where you want it to go. Artemis 2 has fewer microballoons in more of the tiles they made, according to the story. That's denser, with a slower ablation rate, but a less permeable char, increasing the risk of the gas not getting out, and so causing chunks to spall off.
Their theory is that gas unable to get out fast enough blows off chinks of char, exposing virgin material beneath too soon. That’s probably right. Probably.
Have you ever handled real charcoal? Not the pressed crap they sell for your grill, but an actual charred piece of wood? Depending upon the species, it can be quite weak. The more fibrous and stronger the virgin wood, if the charred fibers hold together, the physically tougher a charred piece of it is. Think of oak as strong char (good coals in the fireplace), versus mesquite as weak (doesn't even form coals, just burns immediately to soft ash).
The fundamental mistake NASA made with the Orion heat shield has NEVER BEEN ADDRESSED! That was deleting the fiberglass hex from the Avcoat! They continue to think of that as an either/or decision. Either we build it like Apollo, or we make tiles. That is just plain BS !!!!
You can put the hex back into every tile you make, where as the hex chars and melts, but at a rate slower than the cycolac, its fibrous structure ties the cycolac char together, as a sort of composite material. THAT is why the heat shields built Apollo-style did not spall chunks! THAT is the real difference! Not piddling around with more or less microballoon content in the cycolac polymer!
Here is where you have to see beyond the either/or thinking, in order to put the hex back into the Avcoat. Apollo (and EFT-1 Orion) had the hex bonded to the capsule structure. Into each and every hex cell, you had to manually gun viscously-stiff cycolac with a high microballoon content, to make sure its ablation rate was faster than the fiberglass hex (likely epoxy or vinyl ester resin on glass fiber, I don't know such details). There were 300,000-ish cells on Apollo, and nearly 400,000 such cells on Orion EFT-1. That's a LOT of manual labor to be paid!
Managers do not like to spend money. The good ones will spend what it takes to protect lives. The bad ones will not. There are more bad ones than good ones, we’ve already seen that during 2 shuttle-loss inquests. In fact, the good ones might well now be extinct, near as I can tell.
Here is how you do it OUTSIDE their either/or thinking:
Put a hex core into a tile mold with no bottom. Instead of pouring your cycolac /microballoon mix into an empty mold with a bottom, put that hex-containing bottomless mold on the outlet of an extrusion press (such are very common in the molded plastics industry). Load your cycolac / microballoon mix into the press, and extrude it through the cells in the hex inside that bottomless mold. Use a trowel to scrape most but not all of the extruded strings of mix off the bottom of the hex, and install the bottom of the mold. Then remove the mold from the press, add a bit more mix on top with the trowel, and install the top of the mold. Go cure the thing.
Result: hex-reinforced tiles that will not spall, because they are fiber-reinforced AND you used the correct high-microballoon mix ratio to get the correct ablation-rate ratio! AND you did it with low labor, saving scads of money! The labor relates to a few dozen tiles, not a third of a million cells. But you filled a third of a million cells doing it this way!
I gave that notion free of charge to NASA long ago. I was able to confirm that their heat shield group in Houston actually got it, and that some folks in that group thought very well of it. Then I never heard another word from anybody at NASA about it.
Meanwhile, NASA has had the 2 years necessary to make tiles that way and confirm that the process actually works. But they DID NOT DO THAT! They instead spent all their time and money trying to make unreinforced tiles look OK by analysis, while ONLY considering the hand-gunned Apollo process as the alternative!
Either/or thinking among top managers. The very same as what killed 2 shuttle crews! They so very clearly do NOT listen to their own engineers, much less engineers from outside the agency!
And THAT, sadly, is my assessment of NASA, regardless of who leads it!
GW
Spacenut:
I have a pretty good idea why it happened. These things are made by owned subsidiaries of Northrup-Grumman and one other company. The leaders of these corporations know nothing and care less about high-quality engineering of anything. We just saw that with the Boeing MAX disaster. They fire experienced hands and hire kids fresh out of school they can under-pay. Typical corporate thinking. But aerospace energetics in general, and rockets in particular, ESPECIALLY SOLIDS, do not do well in that environment!
Why? Because rocket "science" is not science, the science being what was actually written down for others to use. In production work, rocket "science" is only about 40% science. It is about 50% art, that being the also-essential knowledge passed on from oldsters to newbies, one-on-one, on-the-job. Why? Because no manager wanted to pay for writing it down!
But this gets done ONLY if those oldsters are still there to do that! And today's corporate "wisdom" specifies getting rid of anybody older than about 45-50 years old as "too expensive".
The other 10% is just plain old blind dumb luck!
This has been going on for decades, and is almost universal among today's gigantic (and almost totally unaccountable) corporations. Competition was once a brake on that evil behavior, but no longer. We only have monopolies or oligopolies now, in government contracting, and other arenas, too.
It's actually worse with development items: the art and luck percentages are higher, and the "science" written down is very much lower!
High-level managers ignoring or being unaware of these truths are EXACTLTY why bad management decisions killed two shuttle crews and 2 sets of MAX passengers. That plus a completely unwarranted arrogance that they know better than their engineers, when in truth they do not!
You don't take shortcuts with solids! You will blow them up if you do! And if it's a big solid, that can be quite the spectacular (and expensive and possibly lethal) event. Effective managers for such dangerous things (and there are many besides solid rockets, such as heat shields) will prioritize success over money and schedule. It is possible to get 1/million failure rate reliability out of solids (I once worked in a plant that did exactly that and was profitable)! But, such effective managers are now rare, if not totally extinct!
GW
Once you get gas flow and it warms up a bit, you are probably "thermal choking" somewhere in the heater tube. That leads to a sonic or very low supersonic speed at the exit, which really does produce a thrust. You need either less massflow or a much larger flow cross-section area to avoid that thermal choking. It does raise the pressures inside the heater tube. Although, maybe you really want the thermal choking. I honestly dunno. -- GW
Those old pictures of S-4 are priceless. She was lost, you know. Collision with a ship. They could not raise her in time to save a few survivors.
GW
It was 3.7 psi pure oxygen in the Mercury, Gemini, and Apollo (and X-15) suits. The cabin of the spacecraft would have been similar with a pure oxygen system. Biggest problem on Apollo was scrubbing out the CO2 from the exhalations. Stupidly enough, different shaped canisters of CO2 absorbent were used in the capsule from those used in the LM. This nearly cost the Apollo-13 crew their lives, until a contrived work-around adapter could be built from scrap and tape.
The pre-breathe criterion: oxygen suit pressure must equal or exceed the hab atmosphere nitrogen partial pressure divided by a factor of 1.2. Higher hab pressures near 1 atm are driving the push toward 8+ psi suits to avoid pre-breathe! The science supporting that is bad! Their blood oxygen model mis-predicts what mountain climbers experience above about 2500 meters elevation! Which is not very high at all (2500 m = 8200 feet). There is a distinct shift in body metabolism at elevations above 2500 m, not reflected in the model (or the input data to that model) being used for blood oxygen.
3-5-8 (37.5% oxygen 62.5% nitrogen for 8.00 psia hab pressure) is not the only gas mixture that would work! I have one even better, and just as easy to remember!
"Rule of 43" (2.72 psia oxygen, 3.60 psia nitrogen, for 6.32 psia hab pressure, or 43% by volume oxygen at 43% of an atmosphere pressure) also works and allows a low enough oxygen suit pressure (only 3.00 psi, or anything higher) to use far-easier-to-develop MCP suits at only 3-4 psia. Webb did his MCP work at 3.3 to 3.7 psia in the oxygen MCP suit. All without any pre-breathe time! Tested way above the vacuum death point in a altitude chamber at a simulated 87,000 feet, for 30+ minute exposures, with the test subject pedalling a bicycle ergonometer. That was long enough to see any effects of not-perfectly-distributed compression upon the body.
3-5-8 requires a higher suit pressure to avoid pre-breathe time: 5 psi nitrogen/1.2 factor = min suit pressure 4.17 psia or higher). The higher the min suit pressure, the more difficult it is to design MCP suits! But you don't want to go below about 3.00 psia, because of drying out lung and nasal tissues with work shift-long exposures. Although for short-term survival and rescue purposes, even 2 psia oxygen works!
"Rule of 43" has a higher oxygen partial pressure than Earthly air at 2500 meters, below which elevation there are no differences in rates of pregnancy and birthing issues compared to those at sea level. People actually live all the way up to 4500 meters, but experience higher pregnancy difficulty rates and chronic hypoxia diseases up there. Yet the oxygen mass concentration with "rule of 43" is less than that of 77 F air at sea level pressure, restricting the fire danger to only that of warm sea level air, despite the over-40% by volume oxygen! It's the less-than-1-atm [pressure that lets you get away with that! You can even leak down significantly more than 10% before you even start getting close to any troubles.
GW