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I see in the AIAA's email newsletter "Daily Launch" that Northrup-Grumman's "Cygnus" cargo craft is no longer launching to the ISS via ULA, now instead riding a Falcon-9 from SpaceX. It used to ride up on ULA's Atlas-5 launcher, which is now essentially gone except for a last few military missions.
I also see that Falcon-9 successfully put the Cygnus onto a transfer trajectory to the ISS, which I think is an ellipse with apogee near the ISS orbit, and perigee just out of the atmosphere. That would be a slightly shorter period, allowing the cargo craft to "wait out" the synchronization of ISS being there when Cygnus reaches its apogee. You circularize, and it's close-in maneuvering from there to docking.
I also see in the newsletter today that the circularization burn failed to work right, because the thruster shut down too early. Shades of Boeing and its Starliner thruster problems! Although, I'm not aware of this having been a problem on earlier Cygnus flights.
GW
I've been working on a stage sizing spreadsheet for TSTO vehicles, that will handle both expendables and reusables. Once I clean it up and finish the user's manual, I plan to add it to the course materials whose links are in this thread.
GW
Responding to, and mostly agreeing with, what Void said in the previous post. I do not usually even look at the politics thread, much less respond anymore. Because I get "flamed" when I do. But this really does need a response!
The conventional notion of left wing vs right wing in political thought is mostly an illusion. It is based upon the notion that political outlook corresponds to a straight line, from far left to far right. It does NOT! It never did!
The better model is a circle, which ranges from "middle of the road" near side, to oppressive military-supported dictatorship, on the far side. There are indeed 2 paths from here to there. But once they get all the way there, there's not a dime's worth of difference between them. It DOES NOT MATTER WHAT THEY SAY, it only matters what they do! ALL professional politicians lie! ALL the time! PERIOD!
I see NO operational difference between Stalin's Russia and Hitler's Germany. Both were military-supported dictatorships, with a secret police (or polices) to "disappear" opponents, concentration camps in which to hold opponents before finally "disappearing" them, total control of all published information, government agencies weaponized to persecute opponents, certain minorities demonized as "the enemy", all the corporate or business heads "bending the knee" to the dictator's every whim, stolen elections amounting to a sham democracy, and absolutely NO accountability upon the "fearless leader" in charge.
There are COUNTLESS other examples besides Stalinist Russia and Hitler's Germany. Putin's Russia today is only one of the latest. Xi's China is another. Kim's North Korea is another. The ruling "mullahs" in Iran are yet another. There are many more.
That ought to sound dangerously familiar to anybody in the US today.
Every one of these dictatorships which has already ended, ended in civil war at one level or another, sooner or later. They always do. And THAT ought to worry everybody in the US, too! Regardless of who you might have voted for!
Extremism is the real evil; left, right, no difference! Does not matter if it is political extremism, religious extremism, or both. And totally unregulated social media are completely rife with it! BELIEVE NOTHING FROM SOCIAL MEDIA, even if they tell you what you want to hear! They lie to you for profit! That is all they do. It is LITERALLY BUILT that way!
GW
My explanation for beginning students is that there are two kinds of numbers that you have to book-keep correctly, one being the numbers big enough to see (from math and algebra), and the others too tiny to see, called "differentials". You have to track them separately, but the two sets interact in two very specific ways.
First, if you ratio two of the tiny differentials to create a fraction, that fraction has a value that is a big number you can see, called a derivative. That is the fundamental notion behind differential calculus, and equations that have these ratios in them are called differential equations.
Second, if you add up an infinite number of these tiny little differential things, each too small to see any one of them, you get a sum that is a big number that you can see, and that summation process result is called an "integral". This is the fundamental notion behind integral calculus, and there are various formulas and procedures for actually computing those integrals.
Doing these same things with enough variable names to cover coordinates in 3-space (or more) is what we call "multivariate calculus".
The rest is merely learning all the rules and procedures to do these things correctly. It's very much like card games: you cannot win if you don't know the rules and procedures. Simple as that.
GW
Interesting diagrams. Thanks, Harold.
GW
Update 9-14-2025: I see in Spacenut's diagrams of Starship the evolution of the tankage dome designs, away from conical shapes, toward spherical-segment shapes, except under the bottom tank. There they need the conical shape to serve as an efficient load path (one of multiple paths) for engine thrust forces to reach the outer tank shell. Between the anti-slosh baffles (not shown), and whatever thrust truss supports there are, there's probably enough stiffness to keep the cone shape from ballooning-outward into "round", at only around 100 psi tank pressures. Too high a pressure, and the cone is where the burst failure is most likely to initiate.
Spacenut:
That's exactly what Gerstenmaier said, no gap fillers! They know now that they need "something" in those gaps, and are, according to Gerstenmaier, looking at something he called "crunch wrap" to avoid having to do it with a caulking gun, or a prod to stuff something crushable in there.
Whatever those "metallic tiles" really were, it's quite clear that they oxidize rather rapidly. Iron is probably not the metal they want. Whatever, they have to do something else. Learning these lessons is what the flight tests are for.
GW
Generally speaking, small wind tunnel models and large vehicles correspond, as long as both have turbulent Reynolds numbers. Flow separation phenomena are the exception, particularly unsteady phenomena. That Reynolds number dependence is much more sensitive to the actual sizes.
I worked for a client only about 5 or 6 years ago, who had on his team a CFD expert working at a university as faculty. We used it to estimate both vehicle aerodynamics and the aerodynamics for a high supersonic/low hypersonic inlet. About 10-20% of the time the CFD model either failed to converge at all (despite saying it was converged), or else converged upon an obviously faulty result. It's good stuff, but it is NOT all that it is cracked-up to be! There's still convergence problems, GIGO problems, and not having the "right" turbulence (and other) models built into the code.
If you look in some of the photos, the loaded vehicle sits upon the engine bay skirt while on the pad. That is NOT one thickness of sheet metal. It is a double wall thing of around 6 inches thickness or more, probably with framing inside. It has to hold up over 5000 tons sitting on that firing stand.
I don't have any, but I have seen photos taken inside the big propellant tanks of the Starship upper stage. There were frames and stringers in there, visible on the tank wall, and some sort of significant baffles, sort of radial from sump drain to walls, down in the tank bottom. The images were distorted and confusing, so I cannot put numbers to them. So just presuming only a cylindrical barrel 4 mm thick carries all the loads is the wrong way to start any sort of structural analysis. For example, without something serving as circular framing here and there, the stainless steel barrel's circular form is completely unstable!
I've never seen any photos taken inside Superheavy, but it must be built similarly. Has to be. It holds up a loaded Starship. And Starship has to be tough enough to take reentry loads at about a 60-degree angle of attack. That's getting very nearly dead broadside.
GW
Don't forget that only the lowest part of the hull near the engine bay carries the entire weight of the loaded rocket.
However, as to pressurization stiffening, that is a real effect. But if you should get a burn-through hole into a propellant tank, you lose its pressurization. That is why the wise designer would not count on pressurization stiffening, not during entry, anyway.
GW
I still do not understand what the "metallic tiles" really are, but I did find this on LinkedIn. It is an evaluation by a NASA official (Gerstenmaier) that was reposted by another NASA figure (Yoon). It would appear that the booster flies its return a bit better than the CFD models would indicate. The gap fillers he talks about are put in there with what amounts to a caulking gun. Very labor intensive. The Dragon heat shield is the ablative PICA-X. - GW
Found on LinkedIn Wed 9-10-2025
Steven Yoon Steven Yoon • 1st1stNASA, air mobility, space explorationNASA, air mobility, space exploration9h • 9 hours ago • Visible to anyone on or off LinkedIn
Lessons from the last Starship Flight
Bill Gerstenmaier, a SpaceX executive in charge of build and flight reliability, presented the findings Monday at the American Astronautical Society's Glenn Space Technology Symposium in Cleveland.
“The metal tiles... didn't work so well," he said. “They oxidized extremely nice in the high oxygen environment.”
“In most of the tiles, there are fairly large gaps, and that's where we're seeing the heat get through and get underneath."
“The white patch was caused by heat seeping between gaps in the tiles and eroding the underlying material, a thermal barrier derived from the heat shield on SpaceX's Dragon spacecraft.” Technicians also intentionally removed some tiles near Starship's nose to test the vehicle's response.
"So, what that's showing us is that we're having heat essentially get into that region between the tiles, go underneath the tiles, and this ablative structure is then ablating underneath. So, we learned that we need to seal the tiles."
Not great, but SpaceX officials think they have a solution. Near the top of the ship, amid the patch of white, engineers noticed a few darker areas.
“We call it crunch wrap," Gerstenmaier said. "It's like a wrapping paper that goes around each tile, and then... these tiles are mechanically held in place. They're snapped in by a robot.” Using this "crunch wrap" material could seal the spaces between the tiles without using gap fillers.
Gerstenmaier also briefly mentioned the results of experiments with Starship's Super Heavy booster on the most recent test flight.
SpaceX engineers noticed the booster's performance on descent in flight doesn't match predictions from computer models or wind tunnel tests. In ground experiments, the booster encounters unstable buffeting as it slows below the speed of sound.
Based on those results, "[we] should not be able to do what we do with our maneuver coming back with a booster, but we've been able to essentially show through flight that we have more stability than either CFD (Computational Fluid Dynamics) or the wind tunnels show that we have.”
From AIAA's "Daily Launch" email newsletter for Tuesday, 9 Sept 2025:
Space
SpaceX test fires next Super Heavy booster for Starship's 11th upcoming launch
The company performed a static test fire of the Super Heavy booster slated for Starship's 11th launch. Secured to the launch stand at SpaceX's Starbase manufacturing and test facility in Texas, the booster, B15, fired its 33 Raptor engines for about 10 seconds Sunday, Sept. 7.
I did not follow the link to Space.com to see if there was a projected date for the launch yet. I'd hazard the guess of early October. I think they still need to static-test the ship, and it might still be in fitting-out. Last I heard it was another Block 2, not the newer block 3 that uses Raptor-3 engines.
GW
Beware the AI-generated results. It is confusing the hull construction materials with the heatshield materials.
All I know for sure is that earlier flights used some sort of ceramic tiles, probably resembling the outer layer of a Tufroc tile. The stainless steel hull can accept a higher temperature from the inward conduction through the denser ceramic, while the aluminum hull of X-37B could not; that's why the Tufroc tiles on the nose and leading edges of X-37B were two-layer, with a lower density underlayer. The denser outer ceramic can take a higher temperature, so they make it black to radiate away heat efficiently.
Somewhere along the line the last few flights, SpaceX has transitioned to what Musk termed a "metallic tile", whatever that really means. It's still put on the hull as tiles, you can see the joints. But I have no clue what they are actually made of, or how. Neither does anyone else outside SpaceX, near as I can tell. And the AI's certainly do not know. They don't even comprehend the question properly.
As for whether this was all worth it, 4 out of 10 mission successes all the way through reentry, and 7 out of 10 partial successes that made it into space at all, is actually a pretty damned good track record for a development flight test program of an advanced vehicle design that really pushes the state of the art rather hard. Complaining about low payload masses out of rapidly-evolving still-highly-experimental vehicles strikes me as grasping at straws for something to complain about!
I think they did really good on Flight 10, and pretty good all through the testing, even with the spectacular failures. The early histories of Atlas, Titan, Juno, Jupiter, Thor, and several others was actually rather similar. It's just what happens when you push the state of the art hard, with experimental flight testing the only real way to get credible results.
GW
Does anyone outside SpaceX really know what those so-called "metallic tiles" really are? I have not heard, myself.
They would appear to have worked well enough on Flight 10. And fewer tiles seem to have been lost on Flight 10, although that judgement is affected by the better camera coverage on Flight 10. I think the tiles on Flights 4, 5, and 6 were some kind of ceramic. But details like that were rarely given out.
Those are the four (flights 4, 5, 6, and 10) that have actually made it back through entry, descent, and landing. Flights 1, 2, and 3 were destroyed before ever reaching space. Flights 7, 8, and 9 were destroyed because they were tumbling out of control when they entered.
The worrisome thing from Flight 10 was the sudden creation of a hole in the engine bay skirt, in a process that appeared to be explosive, to the camera. Nobody yet seems to know what that was. It is the unknowns like that, which are the most worrisome things.
GW
There's a lot more to it than just wing loading (a first cousin to ballistic coefficient). Peak heating occurs somewhere about halfway down in speed, and more than halfway down in altitude, near Mach 12-ish (near 4000 m/s) at around 60 km. The driving temperature for that heating is something like 4000 K, no matter what else is going on. There is simply no way in hell ANYTHING USEFUL will ever come come through that, without some sort of heat protection, and that's regardless of how low its ballistic coefficient (or wing loading) is!
And saying that a delta wing is just "inefficient" is also plain wrong! It has a much lower lift curve slope behavior, yes, but it can go to far higher AOA without stalling, in subsonic flight, very useful when landing, although you cannot see over the nose while landing such a thing. That high stall AOA behavior is due to a rolling vortex pinned to the upper surface of the leading edge, which straight or swept conventional wings simply do not have! Whether that is good or bad is NOT inherent, it depends upon what you actually need!
What they found with the 2-stage airplane space shuttle studies, before it evolved into the cluster we actually flew, was that straight wings simply have too much stagnation heating compared to highly-swept wings. It's not that they cannot be heat-protected, it's just that protecting them is very much harder than protecting very highly-swept leading edges.
A delta is the ultimate in a highly-swept leading edge! That's a good thing for entry! Although, you have to do it as a double-delta or a strake-delta to avoid massive shifts in center-of-pressure location subsonic versus supersonic. That's not an entry issue, but it is a very real risk at approach and landing. If you don't do that job right, you can very easily end up killing crews! They did, with the B-58, which had a plain delta wing, not so much at landing, but at sudden deceleration subsonic after losing an engine. They had to move the cg to accommodate the change in cp, which was bigger than the capability of any trim system they could come up with. In the early 1950's nobody knew any better than any of that, yet. We do, today!
SpaceX is not attempting significant lifting flight during entry the way that the shuttle did, although they do get some hypersonic lift at about 60 degree AOA, to be used for detailed trajectory control, just like our early space capsules. It's L/D << 1 stuff. And they are not attempting lifting flight at all, after entry is over, which is what the wings on the space shuttle were REALLY for! SpaceX's flaps seem to work just fine aerodynamically, as the test flights have already shown, and with the "belly-flop" descent, are the very thing you want if you are trying to do vertically-oriented propulsive landings. The space shuttle did lifting horizontal airplane-type landings, except that it "flew like a brick" on approach.
Aeroheating-wise, SpaceX still has problems to solve with those flaps, there is no doubt about that!
Bandying vehicle concepts about, here on the forums, is all well and good, but take note! It's usually not the basic concepts, but the nitty-gritty details implementing them, that make or break their feasibility! Those details are rarely understood well enough to debate here on these forums, except by people who really do (or did) high-speed vehicle design for a living, like I did. And those nitty-gritty details can't be understood very well until you actually test the concept in some way.
I saw both sheet metal damage and repeated episodes of tile loss from the regions near the aft end of the hinge line on the aft flaps, during Flight 10's ascent, after staging. The camera views were better on Flight 10 than previously, so there is no real evidence as to whether this kind of damage happened on the earlier flights. But it quite evidently causes the aeroheating damages we see in those locations during entry.
There were 3 block 1 Starships, and now 1 block 2 Starship, that have made it all the way through entry, descent, and vertical water landings. All of these took place after implementing hot staging. I have to wonder whether these sheet metal and tile loss damages were done by reflected plume blast during hot staging. Nobody else is talking (in public) about that possibility yet. But it is a real possibility!
If that possibility turns out to be true, there are two fundamental paths to a solution: (1) stage some other way to eliminate the reflected plume blast, or (2) armor-up the vulnerable regions to take the reflected plume blasts with impunity. The exact details for either can vary in myriads of ways.
As for the heat shield itself, tiles or other, what difference does dis-colorization really make? Not very bloody much when you get right down to it! The thing either survived entry or it did not!
Flight 10 is now 4 Starships that have made it all the way through entry with tile heat shields of one kind or another. The other 6 were lost NOT because of heat shield failures in reentry! So the tile heat shield seems to be working, though perhaps not quite well enough yet. Drop the tile heat shield concept? Why change horses in the middle of the stream?
GW
Watch out with this AI stuff! It will "hallucinate" false data to spit at you. And it did, in this case. The shock impingement incident did NOT take place in 1961, although Joe Walker was indeed one of the several X-15 pilots. In 1961, all 3 birds were still flying on the two X-1 engines, not the XL-99 "big engine. Top speeds were Mach 3-ish at 2000-2200 mph. The "big engine came later.
Only bird number 2 was converted to the X-15A configuration during repairs after a crash. They lengthened it about 2 feet, and gave it drop tanks to reach higher speeds and altitudes (at which conditions it had already jettisoned those drop tanks). For flights above Mach 5, it was coated with a silicone rubber ablative heat shield, painted white with ceramic paint, because the silicone was pink, and the test pilots did not want to be seen flying a pink airplane!
The real incident was in the fall (I think October) of 1967, using the X-15A-2 with the drop tanks (that did not yet exist in 1961). The X-15 simply did not fly fast enough to have this problem until the advent of the X-15A-2 with the drop tanks. Pete Knight flew that test, which reached the very highest speed ever reached by the X-15: Mach 6.7 (4522 mph), at just barely under 100,000 feet (30 km).
I posted about this on "exrocketman" as the article "Shock Impingement Heating Is Very Dangerous", posted 12 June 2017, to which the search code 12062017 has been added. The article includes photos of the damages to some of the Inconel-X parts (today known as Inconel X-750). I have since found the 1968 NASA report that describes these damages in detail. That would be NASA TMX-1669 "Flight Experience With Shock Impingement and Interference Heating on the X-15-2 Research Airplane", October 1968, by Joe D. Watts at the Flight Research Center, Edwards, California.
GW
From AIAA’s “Daily Launch” email newsletter for Tuesday 3 September 2025, following a link to an Ars Tecnica article:
One of the more curious aspects of the 10th flight of SpaceX's Starship rocket on Tuesday was the striking orange discoloration of the second stage. This could be observed on video taken from a buoy near the landing site as the vehicle made a soft landing in the Indian Ocean.
This color—so different from the silvery skin and black tiles that cover Starship's upper stage—led to all sorts of speculation. Had heating damaged the stainless steel skin? Had the vehicle's tiles been shucked off, leaving behind some sort of orange adhesive material? Was this actually NASA's Space Launch System in disguise?
The answer to this question was rather important, as SpaceX founder Elon Musk had said before this flight that gathering data about the performance of this heat shield was the most important aspect of the mission.
We got some answers on Thursday. During the afternoon, the company posted some new high-resolution photos, taken by a drone in the vicinity of the landing location. They offered a clear view of the Starship vehicle with its heat shield intact, albeit with a rust-colored tint.
Musk provided some clarity on this discoloration on Thursday evening, writing on the social media site X, "Worth noting that the heat shield tiles almost entirely stayed attached, so the latest upgrades are looking good! The red color is from some metallic test tiles that oxidized and the white is from insulation of areas where we deliberately removed tiles."
The new images and information from Musk suggest that SpaceX is making progress on developing a heat shield for Starship. This really is the key technology to make an upper stage rapidly reusable—NASA's space shuttle orbiters were reusable but required a standing army to refurbish the vehicle between flights. To unlock Starship's potential, SpaceX wants to be able to refly Starships within 24 hours.
So what comes next?
Tuesday's test was largely successful. There appeared to be an issue with one of the Raptor engines in the upper stage later in the flight, which has not yet been detailed by the company. Damage to the engine bay and one of the vehicle's flaps can be seen clearly in the new photographs. This did not appear to impact what was a soft and precise landing in the Indian Ocean, but obviously it was not nominal.
So, with this new information, what does it mean for SpaceX's plans to test future Starship vehicles? What follows is a mixture of informed guesswork and reporting. It is also very notional because SpaceX is known to change its plans rapidly in response to new data. So take this information with a pinch of salt.
Flight Test 11: SpaceX has not revealed a profile for this flight test. It will almost certainly be the last Starship based on the version 2 design, which has been an interim step before the company moves to the larger V3 vehicle, with newer Raptor engines and design improvements. For this reason, it is likely that the 11th test remains suborbital, with the goal of demonstrating Raptor performance in space and testing additional changes to the heat shield. It may also fly a different or steeper reentry angle to further stress the heat shield. This test could occur in the October time frame.
Flight Test 12: This likely will be the first flight of the V3 Starship. Because of this, it will probably follow a suborbital trajectory. Why is SpaceX flying all of these suborbital missions? When Starship flies into orbit, the company wants to be sure it can control where and when it comes back to Earth. Starship is the largest human vehicle to ever return from space, and large chunks would survive an uncontrolled reentry. So SpaceX wants to be confident in its operation of Starship before orbiting the vehicle. Consequently, the first flight of V3 will probably be a standard suborbital test of the ship, booster, and heat shield. Expect this flight in early 2026.
Flight Test 13 and 14: These missions will likely continue to test Starship V3. Assuming flight test 12 goes well, we could probably see a booster catch attempt on flight 13 and probably the first orbital flight, complete with operational deployment of Starlink satellites in this range. This is clearly the most important interim goal the company is working toward, as these larger Starlinks should improve network speeds and performance and increase direct-to-device capabilities.
Flights 15 to 20: At some point, we'll stop calling them test flights. During this range of missions, we can expect to see SpaceX make its first attempt to catch a Starship upper stage (Musk said recently this could occur on flight 13 to 15, depending on how V3 flights go). Somewhere in here, SpaceX is also likely to launch two Starships to conduct an in-orbit refueling test, demonstrating the ability of two Starships to transfer propellant. This is a key step toward allowing Starships to go to the Moon (for NASA's Artemis Program) and Mars. At this point, I think it is safe to predict this test will occur no earlier than the second half of 2026.
ERIC BERGER SENIOR SPACE EDITOR
Eric Berger is the senior space editor at Ars Technica, covering everything from astronomy to private space to NASA policy, and author of two books: Liftoff, about the rise of SpaceX; and Reentry, on the development of the Falcon 9 rocket and Dragon. A certified meteorologist, Eric lives in Houston.
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My take on it:
According to Musk, their heat shield tiles are now in some way “metallic”. He says the orange color is rust from the hot tiles, so at least some of that “metal” is iron. There’s some sort of thermal insulation blanket and adhesive beneath them. Musk says the white deposits come from that.
Where the individual tiles were missing, there’s white streaks among the orange. But on the bottom of the nose, right where the stagnation zone is, is a huge area of whitish discoloration. That underlayer has to be volatilizing and coming out from in-between the tiles.
That big white area is the zone of highest heating, with the highest equilibrium surface temperatures. The tiles cannot have all come loose there, because the vehicle would have broken up during entry.
link to that photo follows.
The final form of the cryo-propellant transfer tank eliminates all the dock and undock operations I listed in post 121 above. Cryo-propellant payload tanks in the tanker resupply vehicle, and the storage tanks at the depot space station, can all be vane tanks. You would not want this for your main propulsion tanks (extra hardware mass), but it makes cryo transfer as easy as storable transfer otherwise. I even figured out out to zero-out all the gyroscopic forces of the vanes and propellant that are spinning inside the tanks. And I filed a Provisional Patent Application (PPA) on this design approach.
Here is a link to a concept sketch. The actual patent has a lot more of the details worked out.
http://40.75.112.55/phpBB3/download/file.php?id=9
GW
You have to remember, there are simply fewer payloads to be launched that require the heavy-lift Falcon-Heavy. Most of the current business is down at a size that Falcon-9 can handle. It did take some effort to fix the troubles that both rockets exhibited not long after they went into service, and that seems to be done now. The record since then is exemplary, and Falcon-9 is "routinely" launching crews. Falcon-Heavy is there when and if it is needed, but there just isn't much business in that payload class. And with NASA science missions being cancelled, there won't be much in that size class.
What SpaceX is doing now, developing the gigantic Starship/Superheavy, is risky but twofold: (1) to provide a gigantic launch capability and mission flexibility that the government (NASA) is going to need if it is to do anything in manned explorations (aimed at government business), and (2) to make up for the lack of giant commercial payloads by doing the "rideshare" thing in a huge way (aimed at commercial business).
Once they get this rocket working right and reliably, its reusability results in a price so low that no one will be able to compete for some time to come (same thing as they already did with Falcon-9). The hope is that the extremely low price will draw in a huge "rideshare" business of the small payloads currently riding the existing and new-entry launch fleet (Falcon-9/Falcon-Heavy-class things). That enormous payload bay can hold an awful lot of those smallish payloads.
We will see if this strategy actually plays out the way they want. But, they have to make the rocket reliable first! And they know that! When the giant payloads aren't yet there, you can only justify such a giant launcher in the commercial launch business by doing "rideshare" at a scale we have not yet seen. If that does not work out, they will likely go out of business just flying the occasional NASA exploration mission with it. And they know that, too!
GW
Spacenut:
Here is a link to a sketch I drew showing how the drag and the heating vary for high speed flight in the atmosphere, getting into hypersonics, as you approach orbital-class speeds.
http://40.75.112.55/phpBB3/download/file.php?id=7
The hypersonic heating is best done by simplified correlations for stagnation point heating, and scaled to other locations by means of experimental data. The oldest and simplest of those stagnation point convective heating correlations is the one used by H. Julian Allen for warhead entry in the early 1950's: Q/A = constant * sqrt[density/nose radius]*[velocity^3]. Plasma radiation heating is somewhat similar, but has a much higher exponent on velocity.
The image showing where ionization starts "kicking in" shows about Mach 6. It gets to be more than a 10% error in estimated temperature at about Mach 7.
Hope that helps.
GW
Spacenut:
Looking at the video SpaceX has posted on the website, I would agree that the relight burn was short. They did say it raised the perigee of their orbit above the Earth's surface, though. I'm just guessing it was slightly below the surface and after about a 1 sec burn, it was slightly above the surface. Apogee was only about 200 km, though.
Their video did not show much regarding the Starship's condition as it hovered to touch down, but I've seen some other images from elsewhere that show it with considerable clarity. A great portion of the heat shield was some sort of orange color, and up near the stagnation point on the bottom of the nose, it was a weird white color. You could see the streaks indicating surface flow direction, especially in the white stuff. I have NO CLUE as to what either color represents.
There was some burn-through damage to the aft flaps. Not as much as was on that first one that came back. I saw sheet metal damage near the aft end of the flap right near the hinge line, plus lost tiles repeatedly coming from that same region, during the ascent after staging. Not sure what that really means, either, although I am beginning to wonder whether the Starship engine plumes bounced off the Superheavy and struck the rear of Starship. There was also some sort of sudden damage (resembling an explosion, actually) to the engine bay skirt, that happened as entry began. I have to wonder if that might not also have been caused by a bounced plume strike at staging.
But, I know nothing for certain.
GW
Void:
Here is a sketch I drew to illustrate what I was trying to explain in post 2160 above.
http://40.75.112.55/phpBB3/download/file.php?id=6
GW
Well, 3-D printing is long after my time, so I could not say for sure.
But I have observed that 3-D printing of metals initially produced weaker strengths and brittle, low-elongation only just several years ago. The 3-D metal printers now have the strengths up near those of traditional wrought materials, and a few of them are getting better elongation to avoid the brittle failure modes. But how that is done, I do not know.
I have heard that a few out there are now 3-D printing solid propellants for rocket motors. But I have no clue how they are doing that. Or what kind of propellants they are making. The ones I know were traditional processing of composite propellants (solid powders added to polymeric binders), double base (gelatinizing nitrocellulose onto a plastic charge of the shape you want by dissolving it temporarily in nitroglycerin), and "composite-modified double base" where an oxidizer and other additive powders are added to the pelletized nitrocellulose for double base processing. All of those processes are quite hazardous, even with the low energetics associated with fireworks propellants (which are mostly a variation on liquid-processed black powder).
I'd be surprised indeed if anybody is 3-D printing fiber-reinforced composite structural materials, which might be the only way to improve on the strength-to-weight ratios of traditional wrought materials.
Basic answer here is "I really do not know".
GW
Void:
If I understand you correctly, you are talking about a slightly suborbital transfer trajectory to final orbital altitude, followed by a circularization burn when you get there. That's pretty much how it works for just about any trip to LEO now.
The slightly-suborbital transfer trajectory is an ellipse with its apogee at LEO altitude, and its perigee at, below, or above the surface. You don't get onto this right at perigee, you fly a non-lifting but thrusted and dragged ballistic trajectory and get onto the transfer ellipse at about or just barely above the entry interface altitude. "Getting onto it" means you hit the right altitude at the right path angle above horizontal, and with just the right speed. You coast from there to apogee.
If you fail to make the circularization burn, you will re-enter when you come back down the transfer ellipse and hit the entry interface altitude. In point of fact, that is what all 7 Starship/Superheavy flights that made it into space at all have done, and it was intended for the other 3, they just didn't make it that far.
Typically, when I run a surface-grazing ellipse as representative of the transfer trajectory, with apogee at 300 km LEO, I get a circularization burn magnitude of just about 0.1 km/s, or 100 m/s. Almost any engine or thruster could be used for that, although you want that burn to last only for a minute or two at most, to avoid wasting energy in gravity losses. That's an easy thing to model with the spreadsheet I came up with and provided for the "orbits+" course and materials, posted on these forums for free use.
Ballistic missiles usually fly "suborbital trajectory" transfer ellipses with rather high apogee altitudes, and perigees well within the Earth. This has been standard practice since ICBM's and SLBM's first began appearing in the 1950's. The longer ranges are usually associated with higher apogees, but they do not have to be.
This sort of transfer trajectory does address inherently your space junk concern, for the entire coasting period between main engine cutoff getting onto it, and any circularization burn. That entire path is suborbital in the sense that it may apogee-put, but without a circularization burn, it will return back down the other side of the transfer ellipse. That applies to any junk lost, and the entire vehicle if it does not make the circularization burn.
The one SpaceX has been using apogees-out over the far South Atlantic or tip of Africa, and hits entry interface altitude way out across the Indian Ocean somewhere. It resembles a really long-range ICBM trajectory, except that the apogee altitude is lower. ICBM's use a bit lower dV, and need the higher apogee altitude to reach adequate range. Their exit and entry angles relative to local horizontal are generally steeper. Spacecraft generally come in much shallower (from lower altitudes) to decrease the gees and the peak heating.
GW
Update 9-1-2025: Here is a link to a image I created to help explain the "suborbital ascent trajectory".
Trouble is, materials are no stronger at large size than they are at small size. To make it strong enough at large size you have to make it disproportionately thicker, and so you gain inert mass disproportionately faster as you scale up size. That's the square-cube law.
It's why there have been very few really large airliners like the Airbus 380, and none of the really big ones hang together very well in otherwise-survivable crash landings. And it is why ships at sea longer than about 1300-1500 feet are too fragile to survive hogging and sagging on the ocean swells.
GW
Void:
What I was talking about is the ice that forms on any rocket using cryogenics, while it is sitting on the pad waiting to launch. The humidity in the air freezes to the very cold tank surface, and this can build up to an ice coating an inch or more thick. Most of this is shed in the seconds just after launch, due to the tank shell deflections under stress and the intense vibrations. However it is possible (however unlikely) that pieces here and there may get stuck on protuberances, and shed later in the ascent trajectory, presenting a very severe impact hazard. Ice like that should be long gone before ever reaching orbit, because of the vibrations and the acceleration forces.
After thinking about the ice impact scenario for flap damage, I realized that there is another scenario to worry about, due to the hot staging. Lighting the upper stage engines to blast away from the lower stage will always run the risk of engine plumes reflecting off the lower stage surfaces and striking the upper stage. There is likely some spreading angle off axial involved. This is the first rocket with aerosurfaces (the flaps) on the upper stage, to attempt such hot staging. I would think that both the aft flaps and the engine bay skirt wall itself might be at serious risk from this damage mechanism. (So would any engine bell not producing a thrust plume.)
What clued me in to this scenario was the evident sheet metal damage right at the trailing edges of the aft flaps near and adjacent to their hinge lines, and the persistence of heat shield tile shedding from those same locations. All the "birds" that showed aft flap damage, whether block 1 or block 2 versions, flew after the start of hot staging. The block 2's show less leakage of reentry plasma through the hinge lines, but they all showed some entry plasma leakage and they all showed tile losses during ascent, after staging from the aft hinge line regions. And the sheet metal damage seems to have finally showed up in the even-better camera coverage on Flight 10.
Just something else to worry about. Given the right beef-up and heat protection, any such reflected plume blast damage should be avoided. Or at least minimized.
It's hard to catch risks like this until you actually start recovering vehicles for detailed inspection of post flight damages. Quite understandable that it might get missed through multiple flights without vehicle recovery.
GW
I went to the SpaceX website and reviewed their recording of the live coverage. Overall, it looked pretty successful to me. They did all their objectives, right through to both splashdowns. Whatever was going wrong before, looks to be mostly fixed. I have to wonder whether the quieter tests I have heard have anything to do with that outcome. I don't get the 10 Hz house-shaking pressure oscillations any more. But, honestly, I do not know.
I saw tiles coming loose during the ascent before staging, in the camera view of the aft portside flap. They seemed to be coming from around the hinge line near the aft end of that flap. That and some other "bursts" of tiles or tile fragments in various views make me wonder if possibly these might be related to ice chunk impacts as it sheds the coating of ice that builds up before launch. I would have thought most of that should be shed before about max q. But maybe not all. Plus, I also think I saw some sheet metal damage to the aft end of one or more of the flaps. It was hard to tell which one was in each camera view. Ice impact might explain that, too. But I did not see any such ice impacts actually happen.
Update 8-28-2025: there is another possibility for both sheet-metal and tile-loss damage near the aft end of the aft flaps. There might be some sort of reflected engine-plume blast hitting them during hot staging, especially with some of the stage shield vent ports closed to enable the fast flip procedure for the booster.
The sudden damage to the engine bay skirt seemed to catch even SpaceX by surprise. I'm glad it did not seem to damage any engines. It certainly could have. Whether this had anything to do with any of the "missing tile" testing is unclear at best.
The vulnerability of the flap hinge lines to hot gases during reentry, particularly the aft flaps, seems similar to what we saw on the first 3 successful flights (4, 5, and 6?). They still have that issue to resolve, but that is tempered by the fact that in 4 successful reentries now, we have not seen the loss or incapacitation of any of the flaps (such loss would likely cause loss of the vehicle).
Update 8-28-2025: I went back and researched what flew and what happened on all 10 flights. Everything was lost on flights 1-3. The upper stage Starships for flights 4-6 all made splashdowns in the Indian Ocean. They were all Block 1. All the Starship upper stages on Flights 7-9 were lost, ostensibly for different reasons. They were all Block 2 design upgrades. Flight 10's Starship was the first Block 2 upgrade to survive all the way to splashdown. It suffered flap damages that included tile loss, sheet metal damage, and consequent entry heating damage, although not as much hinge line burn-through as the 3 Block 1's that survived showed.
I only saw one engine that shut down and failed to relight: one of the middle ring of 10 in the booster. Hopefully they have the data to figure out what went wrong with that one.
I'm wondering whether it's not time to start catching boosters again. They've now learned about how hard they can push that stage to higher-AOA, "draggier" entry, without actually crushing it by flying too broadside in the windstream pressures. If you actually have the post-flight hardware to look at, you can learn even more, a lot more, from the test. Losing it in the splashdowns does cost you that kind of data, but I understand that it's a tradeoff of what is more important to learn on any given flight.
It will be very interesting indeed if they can start recovering or catching or landing the upper stage Starships in some way, pretty soon. That will require going into full orbit. And they'll have to satisfy the FAA that they are ready to do that. Once they have post-flight hardware in hand for the upper stage Starship, fixing the damages and hot gas leaks in the flap hinge lines will proceed much faster.
Congrats to SpaceX indeed! Very successful test flight!
GW
Update Wed. 8-27-2025 -- this from the Wed 8-27 version of AIAA's "Daily Launch" email newsletter:
AEROSPACE AMERICA
Starship Flight 10 aces test objectives
A SpaceX Starship-Super Heavy rocket lifted off from South Texas at 6:30 p.m. Central on Tuesday, marking the design’s 10th integrated flight test. SpaceX has to review the flight data, but early indications point to the majority of the test objectives being accomplished, communications manager Dan Huot said at the conclusion of the livestream.