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I do not understand part of the recent posts here. What is the problem with Sunni Williams?
GW
Nixon DID pull the plug on all human activity outside low orbit. Executive orders like that do not persist in perpetuity, we have recently seen that effect in action.
What I was pointing out was NASA goals being set by Congress to fit porkbarrel politics. That effect has persisted unchanged for decades, and it has shaped the space program for decades.
GW
This 1960's plan to use Apollo hardware for a Mars flyby ignores 2 fatal issues that were not very well understood back then: (1) the confinement effect of a crew living for months in a tight space (first demonstrated as a serious effect on Gemini-7), and (2) solar flare radiation exposure becomes rather likely, if you are out there for months-to-years. We know much more now, Zubrin was quite right to use a bigger habitat in his version. Every bit of extra space helps. Plus, in the 1960's, there was no recycling of life support materials. All the food, water, and oxygen for the entire trip had to be packed aboard "somewhere". There's no room in an Apollo CSM for that, not even with a bigger service module. It was a tight fit for 2 weeks support for 3 to the moon and back.
The artificial gravity thing at only Mars gravity levels is still an unsupported assumption, even today! Precisely because the experiments to verify its adequacy have never, ever been done! Until they are, the only level supported by evolution-as-evidence is 1 full gee. Anything else is an unethical or even immoral bet on human life and health.
There are huge developmental unknowns to overcome with cable-based spin systems, related to the transients of deployment and course correction burns, not to mention undoing the spin when the time comes. The traditional concepts for rigid spin systems are all very large, requiring the building of "Battlestar Galacticas".
Avoiding both of these perceived insuperable difficulties are why NASA has spent decades trying to figure out how to stay healthy in zero gee for more than a year mission time. But the available data so far says that will not be possible: we keep finding more and more bad effects of zero gee upon all sorts of body systems, way beyond just muscle atrophy and bone density loss.
No one has yet looked at baton spin. No one has yet looked at building large modules out of inflatables to be joined together (that can be launched deflated and folded tightly). No one has yet built a space station that spins in some way, to study how therapeutic reduced gee level might be (which ultimately drives your spacecraft design, by the way!!!).
This is the decades-long legacy of a technically-incompetent Congress micromanaging NASA projects to fit pork-barrel politics, instead of anything that makes any sense. And THAT is very most definitely NOT how a space program should have been run!
Ain't 20-20 hindsight wonderful?
GW
The impression I got from the Ars Technica article was that there is a time limit on how long the rocket can be stacked before it must be used. I saw no reason in the article as to why that is true, it was just stated as a given. Once the stages and SRB's are stacked, the Orion-and-service module-and fairing adapter "spacecraft assembly" is added.
That spacecraft assembly also apparently takes a lot of time to put together. I gathered from the story that there is not time to disassemble it and install a revised heat shield on the Orion, and then reassemble it, once the rocket stacking begins. Apparently, both processes have long schedules (which helps to partially explain the incredibly-high per-launch cost).
The Ars Technica article presumes that since rocket stacking has begun, there will be no heat shield revision to the Orion in the spacecraft assembly. The only other two options were a slight entry trajectory revision, or do nothing at all.
-- GW
From AIAA’s “Daily Launch” for Friday 11-22-2024, a short paragraph linking to a longer article published on Ars Technica:
ARS TECHNICA
NASA is stacking the Artemis II rocket, implying a simple heat shield fix
The Space Launch System rocket that will dispatch four astronauts on the first Moon mission in more than 50 years passed a major milestone Wednesday. NASA said ground teams inside the Vehicle Assembly Building (VAB) at Kennedy Space Center in Florida lifted the aft assembly of the rocket's left booster onto the mobile launch platform. Using an overhead crane, teams hoisted the left aft booster assembly—already filled with pre-packed solid propellant—from the VAB transfer aisle, over a catwalk dozens of stories high and then down onto mounting posts on the mobile launcher.
My take on it, after reading the linked article:
NASA managers have apparently decided to risk the crew with the evidently-defective heat shield design, and just modify the entry trajectory a bit to reduce peak heating as the “fix”, so that they can stack the rocket and fly as soon as possible before the “stacked lifetime” limit occurs. This would be the only way to fly during 2025 or early 2026. They are very close-mouthed about exactly what the “fix” to the heat shield really is, so that is what tells me they have decided to fly with what they have already installed on this Orion capsule.
They have decided to go ahead and risk manned flight with a poor heat shield design, in order to fly sooner and avoid the costs of a longer delay. And so they do not want that decision publicized, in case something bad happens. Where have we seen this pattern before?
Meanwhile, I have been in contact with David E. Glass at NASA, who is a real thermal protection engineer. I provided to him a copy of my original letter to Bill Nelson, with the 4 figures showing exactly how to put the hex into the bonded Avcoat tiles that they really want to use. I also provided to him two photos from ramjet combustor insulation tests I ran 3 decades ago, which show more-or-less the same cratering damage mechanism that they saw on the Artemis-1 heat shield, if there is only a weak tie between char and virgin beneath, under high fluid shear force conditions. These photos were from the presentation I took to the American Carbon Society meeting at NCSU last April.
Glass tells me that the NASA heat shield engineers trying to “fix” this problem now have all the materials that I sent to him. But I have heard nothing back from anyone, as of yet. But my contact was only just last week.
GW
I watched SpaceX's video of the mission, of course looking past the long times where nothing was happening. Launch looked good, hot staging looked good. The booster diverted to a water landing for no reasons I could understand watching their video.
The upper stage boosted itself onto the barely-suborbital trajectory just fine. The engine relight was about a 1 sec burn just before entry manifested itself. Entry went well, except for another hinge-line burn-through averted by the end of entry hypersonics, at the leading edge of one of the forward flaps, which forward-flap hinge line is where the other burn-through problems have occurred, except that they were at the aft end of that hinge line.
Booster recovery was aborted in favor of a splashdown, for no reasons given in the video.
The second-stage spacecraft entry and belly-flop looked fine, plus the flip to a thrusted water landing. This time, there seemed to be no explosion when the vehicle tumped over. However I saw some sort of shape change and some fires, after it did tump over. Looks to me like a methane tank broke open and started a methane-air fire. I saw no explosion from breaking open an oxygen tank, though.
GW
Here's one from AIAA's "Daily Launch" for Tuesday 11-19-2024 that is not worth the price of the paper it was written on.
The New York Times
SpaceX Starship’s Sonic Boom Creates Risk of Structural Damage, Test Finds
SpaceX’s new Starship rocket far exceeds projected maximum noise levels, generating a sonic boom so powerful it risks property damage in the densely populated residential community near its South Texas launch site, new data suggests. The measurements — of the actual sound and air pressure generated by the rocket during its fifth test launch last month — are the most comprehensive publicly released to date for Starship, the largest and most powerful rocket ever constructed.
My take:
I went and looked at the linked NYT article. Whoever wrote it was totally technically ignorant and confused the thrust noise made at launch with the sonic booms heard when the booster comes back. The sonic booms are never that loud, but the launch thrust noise is! There are no sonic booms heard at launch, period! The vehicle is subsonic until a handful of miles up and a handful of miles downrange eastward, out over the Gulf.
Coming back, the booster approaches some handful of miles up on 13 engines, and at much lower altitude on only three engines. That's all the thrust it needs to decelerate subsonic at a mile or two up, and then come down to land at roughly thrust equal to weight, with 3 engines, running throttled. You might hear a weak double boom for the sonic boom, and a stronger noise signal from the 13 engines as it reaches subsonic about a mile or so up, unless the thrust noise covers up the sonic boom. The 3 engines at touchdown are no noisier than any of the earlier Starship-only tests landing, which is also only thrust equal to weight on 3 engines, throttled.
It's the launch on 33 engines at full thrust, that is the real noise generator! I warned about this being a problem before they ever got started trying to test things there, if you will recall. At around 12-15 million pounds of thrust, about twice the Saturn-5, this thing is about as "thrusty" as the smaller end of the old "Nova" paper designs Von Braun brought with himself when he went to NASA in 1958 from the Army at Huntsville, AL. NASA could not use any of the "Nova" designs, as the launch noise level was thought to be too dangerous, for the 3-mile clearance they had to populated areas. Note that the launch pad at Boca Chica is only 5 miles from the Brownsville, TX, city limits. And there's many houses closer than that, and I am not referring to those few that were right next to the office building at Starbase. Not to mention civilians in Mexico, too.
Why would anybody be surprised when someone finally flagged the noise risk? I warned of this years ago! The writeup breaking this news is a piece of crap, but the data it refers to are quite real! I totally expected this! All I wondered was why this did not come up sooner!
GW
See what I just posted in meta new mars/GW Johnson postings, where the same question was asked, and I answered it there.
GW
Question: could a “Starship” without any payload reach LEO without a “Superheavy” booster?
Answer: it’s complicated. But it is very likely not possible.
Details:
As being currently flown, which is not yet fully fitted out, the inert mass of “Starship” is somewhere in the vicinity of 120 metric tons. These notions of getting that down to something in the 50-90 ton range are utter bullshit! That inert will grow, if anything. But let’s use it anyway. That same configuration has tanks that can hold a max of 1200 metric tons of propellant. That puts the vehicle at just about 1320 metric tons mass, ready for ignition with no payload.
To get efficient launch kinematics and not waste propellant by climbing too slowly, the very-well-verified rule-of-thumb is that you need thrust/weight = 1.5 at launch (basically half a standard gee above the local pull of gravity). For 1320 metric tons mass, that is 1980 metric tons-force of thrust that you need at liftoff on Earth.
As currently flown, “Starship” has a total of 6 Raptor engines, those being 3 sea level and 3 vacuum variants. These are Raptor 2’s for which the sea level variant has a sea level thrust somewhere in the vicinity of only about 200 metric tons-force. The vacuum variants cannot be used at sea level; they are on the verge of bell separation and with a much-reduced thrust. Raptor-3 is reputed to be nearer 250 metric tons-force sea level thrust in the sea level variant. There might be room to mount 9 engines in the “Starship” engine bay, if all 9 were sea level variants. The inner 3 would gimbal, but the outer ring of 6 could not gimbal.
If these 9 sea level engines were Raptor-2, total takeoff thrust would be 9*200 = 1800 metric tons-force, only a little bit short of the rule-of-thumb. If they were instead Raptor-3’s, total thrust would be nearer 9*250 = 2250 metric tons-force, more than enough. So you could successfully launch with either Raptor model, but you would get significantly better overall performance results at the higher thrust level of the Raptor-3 sea level design. Especially if inert mass grows, as I think it will.
As you burn off propellant on the way up, you will need to shut some engines down, or else overstress the structure with too much acceleration gee. 9 Raptor-3’s at 1/3 thrust on a dry-tanks 120 metric tons is still too high at 6.25 gees thrust-induced acceleration, near-horizontal and exo-atmospheric. The 3 gimballing center engines, at half-thrust, would produce about 3.1 gees, which is much more realistic. And don’t forget: at reduced thrust, Isp is always somewhat lower. You really have to look at this thrust stuff, otherwise, the rocket equation will lie to you, because of a GIGO problem!
The ascent-averaged Isp of the Raptor-2 (or -3) would be in the 350-360 sec Isp class. Call it 360 s just to be optimistic about what Raptor-3 will eventually be capable of! That puts the effective ascent-averaged exhaust velocity pretty near 3.53 km/s. For the rocket equation, that puts the no-payload mass ratio at 1320/120 = 11.00, producing a deliverable dV = 8.46 km/s. That has to cover the theoretical energy needed, plus at least the drag and gravity losses. (There’s also rendezvous and deorbit to worry about, plus maybe a landing burn.)
Now, estimate the dV and losses: conveniently, Earth circular orbit speed at the surface is 7.913 km/s. That’s a good measure of the energy we have to achieve going to low circular orbit (say near 200-300 km altitude), in a low-inclination eastward direction. It is also a good basis for figuring the losses. If we achieve launch thrust/weight near or above 1.5, gravity losses will be only on the order of 5% of surface circular, or 0.396 km/s. The “Starship” shape is aerodynamically pretty clean and of a nice L/D ratio, so the drag losses can be low, near 5% of surface circular, also 0.396 km/s. So the energy and losses total so far to 8.705 km/s, already greater than what the stage design can deliver (which is only 8.46 km/s)!
Conclusion: it won’t work!!! It cannot work!!! But even if it did, you would reach orbit with dry tanks. You would be unable to rendezvous with anything, which budgets somewhere around another 0.1 km/s as a minimum, so what good would that be as something delivered on-orbit? And you would also be incapable of doing a de-orbit burn, to dispose of this massive launched hardware safely, which is just about another 0.1 km/s from low circular orbit. How unethical would not being able to safely dispose of this thing be?
The real velocity requirement with losses would include both the rendezvous and deorbit burns, for a total of just about 8.905 km/s (or maybe a bit more) that your rocket equation delivery must meet. And that would be for a crash landing after deorbiting. You need even more, if you actually intend to land the thing and reuse it. Say, at or just above 9.1-9.3 km/s.
Only if you believe in the bullshit numbers for incredibly low inert mass, can you reach a mass ratio that could deliver near 9.2 km/s dV (or even only 8.9!!) at an ascent-averaged Isp of 360 s. I do not believe in crap like that! And with my background, I ought to know. I have never, not in all my life, seen a vehicle inert mass that did not grow during development and testing. They ALWAYS grow!
GW
It's kind of hard to evaluate your idea, because I have no clue as to the mass and weight statement of the "mini-Starship" upper stage. It's also a bit hard to know what the real thrust of a Raptor-2 or Raptor-3 engine is, and which configuration those data are for (sea level or vacuum).
Starship as it has been flying is somewhere in the vicinity of 120 metric tons inert, and 1200 metric tons propellant in the tanks. It has been flying at zero payload, and not with all the features of an operational LEO freighter. We will ignore those very fundamental difficulties.
I will just do a wild guess of 200 tons for an upper stage "mini-Starship", which might carry 10-30 tons of deliverable payload. Maybe. Maybe not.
Weight statement for launch configuration: payload = loaded "mini-Starship" = 200 m.tons, + 120 m.tons 1st stage inert + 1200 tons 1st stage propellant = 1520 m.tons ignition mass.
Kinematic requirement: T/W ~ 1.5 at liftoff in order not to waste propellants accelerating too slowly.
Take a wild guess as to the max thrust per engine of a sea level Raptor-3: call it 250 m.tons-force. Raptor-2 is not that high. But we are looking to the future here.
Starship as we know it is 9 m diameter. The three center engines are sea level, and they gimbal for thrust vectoring. The outer 3 are vacuum with much larger bells, but are fixed in mounting. Take a wild guess that we could replace these three vacuum Raptors with 6 sea level Raptors, also fixed in mounting. That is a total of 9 sea level engines, for a total of about 2250 m.tons-force at liftoff.
The thrust/weight ratio at liftoff is then about 2250/1520 ~ 1.5, which is adequate to fly efficiently. But, the 200 ton upper stage mass limits your deliverable payload to a low number, likely down near 10-30 m.tons! Raising the upper stage mass lowers the launch thrust/weight. That means the gravity loss dV is going to be much higher!
I'm quite unsure this is a good approach at 9 m diameter. The requirements on the first stage are quite different from those imposed on the second stage. You have to look at thrust/weight as well as the rocket equation. If you fail to look at thrust/weight, you get bad answers from the rocket equation.
GW
I just saw an article linked from AIAA's "Daily Launch". Sierra Space has pushed back the launch date for its first Dreamchaser from late this year to May '25. No reason given. They have a second Dreamchaser under construction. And they are building and ground-testing big inflatable modules, to include hypervelocity gas gun tests for meteor impact effects.
The layers of material for the inflatable are thick, to provide insulation and meteor protection, plus they are said to provide good radiation protection. These modules have a core with walls and decks folded inside, very much like what I presumed for the habitat modules of my orbit-to-orbit transport concept in my 2016 version of a clean-sheet-of-paper Mars mission plan.
Bigelow may be gone, but inflatables are about to be here. Looks quite promising.
GW
To fill the LOX tank before the vehicle topples would take an opening about the same size as the diameter. I don't think there's any practical way to do that. You only have a single handful of seconds to get the job done.
GW
I can't figure out how to use it. I see nothing intuitive there.
GW
At Starship upper stage landing, there's essentially nothing in the main propellant tanks but pressurized vapors. I don't know what pressure they are using, but it's enough to use those vapors for cold-gas attitude thrusters. That's a bomb waiting to go off, once the tanks crack open, letting the propellant gases mix. All you need is an ignition source to set it off. Methane-air lights easily. Methane-oxygen even easier.
The landing is done using propellants in the small header tanks in the nose. There's not a lot of propellant to begin with, as not a lot is needed to land an essentially-empty vehicle, but there would still be some liquid residuals in these header tanks after landing. Mass at landing is little different from dry-tanks mass, by maybe a single handful of tons at most, maybe at ton or so at minimum.
At 9 m outside diameter, the cross-sectional blockage area is some 63.6 sq.m. For a ship standing vertical in the water, you pick up 63.6 cu.m worth of displacement volume for each meter of length you have submerged. At about 1 ton/cu.m density of water (fresh, sea water is very slightly denser), that's 63.6 tons of buoyancy for every m worth of displacement volume you have submerged.
We will ignore the buoyancy of trapped air in the open-ended engine bay, some 3 m long, from what I read. If you believe the dry-tanks mass to be around 120 metric tons, you only need 2 m worth of length of submerged displacement volume to float the vehicle. 3 m for 180 tons inert, 1 m for 60 tons inert, etc. Adding in for the engine bay, at 120 tons inert, the tail end is 2+3 = 5 m below the surface to float statically, with buoyancy equal to weight. You might penetrate 2 to 3 times that temporarily, during dynamic landing transients.
(And those transients are far shorter than the time it would take to fill the main LOX tank even partly full of water!)
This vehicle is about 50 m long. The center of gravity is pretty near its middle, or it would not have flaps of roughly the same size at each end. That puts the cg some 25 m from the tail. Maybe 20, who knows for sure? Let's use 20 m for a nice round number.
Statically, that puts the cg some 20-5 = 15 m above the water surface. With the center of buoyancy under that surface by half the buoyant length, which is around 1 m. Cg above buoyancy center by about 16 m, compared to only 9 m diameter. That is wildly unstable! It must fall over! And rather quickly.
Now look at the dynamic transient during touchdown on the water. Let's assume worst case 3 times the static penetration of 5 m for 120 tons inert. That's 15 m penetration, subtracted from a 20 m cg position, for a cg still 5 m above the water, with a center of buoyancy located about 6 m below the surface, well below the cg. Cg above buoyancy center by 11 m, compared to a diameter of 9 m. It's still very unstable. It must fall over.
Note that for ships to be stable, they use heavy ballast down in the bottom. The idea is to pull the cg below the buoyancy center, although it will still be sort-of-stable as a rule-of-thumb, if the cg height above the buoyancy center is significantly less than the hull width. However, that's not a ship you can ride-out a storm in, without being capsized! Storm-proof is cg below buoyancy center. Period. ***
If it topples over and smacks the sea surface, things are going to break. Period. There are no flight-weight structures that will not break when that happens, as a sort of broadside impact. The forces are comparable to toppling over and smacking a concrete pad. Water starts behaving like concrete in terms of impact forces, at about 20 mph impact speeds and higher. That why you don't do a belly-flop off the high board at the pool!
If things break, the contained propellant gases will be released. All it takes is any source of ignition, like a flaming plume from a methane vent outlet, or a still-hot piece of anything from entry (there's multiple tons of still-hot heatshield tiles, plus recently-molten steel from the hinge line burn-through), to set off the explosion.
So, given all of this, why would anybody ever be surprised by the explosion fireball seen on flight 5 when the Starship ditched into the sea? That's pretty much a given, for just about any Starship ditch-at-sea scenario imaginable.
GW
*** Most cruise ships violate cg-below-buoyancy center. They have to steer clear of even minor storms, or else be capsized. Which is why I have no wish to ever travel aboard one of those top-heavy things! So far, they have not had a capsizing. But it is only a matter of time. And there is no getting aboard the lifeboats if you capsize! Thousands will die. Profit vs a low-probability with absolutely-intolerable consequences. Where have we seen that prioritization before?
The Starship upper stage is 50 m (165 ft) tall. When it touches down, the water will snuff the engines, but maybe not quite fill the engine compartment. That means any engine compartment fires may or may not be snuffed-out. The weight will shove that tail somewhere around 20-30-40 feet into the sea, leaving around 120-130-140 feet sticking out. That will fall over to one side and smack the sea at a pretty good clip. The odds of not breaking open a tank or busting a big plumbing line are close to nil.
The trouble here is that they have to do almost the same things as were done in flight 5 to stay within the launch license. To me, it seems more important to solve the hinge-line burn-through problem and demonstrate that solution, plus maybe try a Raptor re-start in space. Doing anything beyond crashing the Starship into the Indian ocean will require a new launch license from scratch. And that takes time to get approved.
They ought to be working on the next launch license already with the FAA. That assumes they already know what they want to try next, given better success with flight 6.
They dodged a bullet purely by chance on flight 5, being a reported 1 second away from commanding an abort instead of catching that booster. The words of SpaceX's own employees clue you in, as to why that happened: they didn't have all the software "saucered-and-blowed" the way they wanted.
Why wasn't it all done "right" before they flew? Musk pushing too hard. Pure and simple. He doesn't listen to his employees enough, and he has way too big a mouth; there's quite a track record of that, screwing up the FAA launch license processes, causing them to drag out.
GW
According to Musk, they are targeting Nov 18 for flight 6. We will see if the team is really ready. He pushes too hard, has a history of that. It shows in "Musk time" being factor 2 to 3 shorter than reality. The flight profile has to be similar to flight 5, or it would require a new launch license from FAA. Watch for (1) no more flap hinge line burn-throughs, and (2) touching down on the ocean without exploding. Actually, I rather doubt that 2 is possible. It's bound to bust a tank, toppling over into the sea. If oxygen hits a fuel-air fire, the fire always explodes.
GW
From the 11-6-2024 “Daily Launch”:
ARS TECHNICA
After 31 cargo missions, NASA finds Dragon still has some new tricks
As space missions go, the latest Cargo Dragon one was fairly routine, ferrying about 6,000 pounds (2,700 kg) of cargo and science experiments to the space station. However, there is one characteristic of this flight that may prove significant for NASA and the future of the space station. As early as Friday, NASA and SpaceX have scheduled a "reboost and attitude control demonstration," during which the Dragon spacecraft will use some of the thrusters at the base of the capsule. This is the first time the Dragon spacecraft will be used to move the space station.
My take on it:
If Dragon can be used for re-boost and debris avoidance, docked to an American-style docking port, then there is an alternative to the Russian-style docking port on the leaking Zvezda module. Soyuz craft on the Russian docking port have so far has been the only means of re-boost and debris avoidance. If this works, there is no excuse not to close the hatch into the leaking tunnel in Zvezda, and letting the cracked tunnel depressurize.
Problem: doing that then deprives the station of its ability to receive Soyuz and Progress craft.
NASA and Roscosmos will need to send up some kind of adapter to fit Soyuz and Progress craft to the American-style docking ports. Otherwise, they lose the crew transport capability of Soyuz, and the cargo transport of Progress. That deprivation and docking compatibility problem is why the Russians have so far resisted closing that hatch.
GW
I made note of that same unfortunate news in Meta New Mars/GW Johnson postings .../post number 442.
With all the legal battles, the SABRE engine, and the fast cooling technology (that was integral to SABRE, but has other applications) is basically lost to users. It will remain lost until the lawyers quite fighting over it.
GW
The builders of Sabre, in the UK, just went broke.
GW
No one can argue with you about landings, Kbd512. Capsules with chutes seem to work pretty good here on Earth, and so did the shuttle. I would say there might be a difference landing lower stages always unmanned, and upper stages that could be manned craft, like "Starship". There's no reason other than the costs of failures not to land lower stages as powered landings. SpaceX has already proved you can reach a good track record for that, as long as these are always unmanned.
It's the upper stages that are a different case entirely. If they are to be recoverable at all, they must be more than just a rocket stage, they have to be independent spacecraft that are entry capable. It is the entry capable that is the hard part, because only certain shapes are allowable, and the heat shielding will always be a heavy thing. Even the super ceramics are dense, and once fully hot, there's no practical way to hang onto them.
So, you are back to one of 3 things: capsules, spaceplanes, or powered landings. Only the first 2 of those 3 have any sort of track record yet. SpaceX is attempting the unproven one. But their results do show promise somewhere down the road.
What I was getting to with the short article was not about landing, it was about launch. Vertical launch into a non-lifting gravity turn leaving the sensible atmosphere at only modest supersonic speed gets you the lowest gravity losses, and the lowest drag losses by far!!!! You also have very modest ascent heating. Payload protection on these ascents is as much, or even more, about windblast protection.
Trying to fly entry-in-reverse with a lifting trajectory runs afoul of far-hypersonic speeds way down in the atmosphere, for the same heating rates as entry, but far longer exposure times, because you won't reach orbital-class speeds until you are almost above the entry interface altitude anyway. You heating problem is actually worse than entry, because of the longer exposure times. Your gravity loss is higher. And your drag losses to be covered are very likely larger than the orbital speed itself. Between that fatal issue, and the fact that in the extremely thin air above 60 km, there's just no sensible thrust available from any sort of airbreather (not even scramjet), that's really why the X-30 project went nowhere.
Those issues apply to any sort of upper stage spacecraft, be it a capsule, a spaceplane, or SpaceX's powered landing vehicle. You'll note that both shuttle and X-37B launch vertically onto a non-lifting gravity turn. Even the original early staged-airplane designs for shuttle launched vertically. Pretty much all the other lifting craft designs that had any real potential did, too. X-33 for one. The X-20 that was never built was another.
GW
From AIAA’s “Daily Launch” for 1 Nov 2024:
BREAKING DEFENSE
UK vows to ‘closely monitor all our supply chains’ after collapse of hypersonic supplier
The UK Ministry of Defence said it will continue to “closely monitor all our supply chains” as it reels from the collapse of Reaction Engines, the high speed propulsion manufacturer and industry lead on London’s quest to develop a reusable Mach 5 and beyond aircraft under the Hypersonic Air Vehicle Experimental (HVX) program.
My take on it: both the SABRE engine technology and the innovative cooling system used in it are now lost to industry. Very sad outcome. The detailed story said they never got completely out of start-up-style fundraising, which is not a way to indefinitely sustain a business.
From AIAA’s “Daily Launch” for 1 Nov 2024:
SPACE
Boeing can recover from its Starliner troubles, but it can’t afford any other misfires
The partial failure of Starliner’s mission doesn’t help Boeing’s effort to bounce back from its problems. The company’s reputation has not been irreparably...
My take on it: the full article discusses many things beyond just Starliner. Those include the 737MAX crashes, and the general notion of reputation damage. The article does not take on top corporate management’s causing this by prioritizing profit far above safety and reliability, with way too much cost-cutting in areas of activity that reduce safety and/or reliability.
From AIAA’s “Daily Launch” for 1 Nov 2024:
SPACENEWS
Chinese launch startup Cosmoleap secures funding for rocket featuring chopstick recovery system
Chinese launch firm Cosmoleap has secured more than 100 million yuan for the development of its Yueqian reusable rocket and a recovery system inspired by SpaceX. Cosmoleap announced more than $14 million in funding Nov. 1. Shenergy Chengyi, a Shanghai-based state-owned enterprise focusing on innovative investments, Tiangchuang Capital, an investment firm with a focus on emerging technologies, venture capital firm Baiyan Fund, Legend Capital, a venture capital firm supporting technological advancements, and investor Zhang Chao participated in the funding round.
My take on it: one has to wonder how serious this really is, or just copycat stuff aimed at looking good in the PR world.
GW
I suspect it (the mission profile) will be similar to flight 5, except that they may attempt to circularize outside the atmosphere, to test the in-space restart capability. If they do, then the Starship might proceed around multiple orbits, instead of a fractional orbit, then do a second restart to do the deorbit burn. They might even attempt more simulated propellant transfer by venting pumped liquid to space.
They might bring this one down in the Pacific off California, or in the Gulf off of Florida. I doubt they would attempt a drone ship landing, because this thing is way too big for the drone ships they have. I doubt they would try to land on a pad in Florida, because overflying inhabited land to get there is a major launch license change. But I REALLY doubt they would attempt a catch landing at Boca Chica, for 2 reasons: (1) bringing it down over the US land mass is a major change to the launch license, and (2) they won't have had time to clear the tower of the attempted booster recovery. They only have the one tower so far.
Just my opinions, I have no facts.
GW
I don't know anything for sure, but it certainly appeared like a fuel-air fire in the engine bay of the descending Superheavy booster on Flight Test 5. As I indicated in the other thread.
There are a lot of possibilities as to where the leaking methane might be originating. This same effect has been seen at smaller scale in Raptor ground test videos, as flames enveloping some of the plumbing about the engine power head. Whatever is leaking, and there may be more than one thing, SpaceX really needs to identify it and fix it.
An oxygen leak is a much lower probability, but not zero. If such happens, sending pure oxygen into a fuel-air fire in the engine bay, then a huge, catastrophic, and fatal-to-the-vehicle explosion is inevitable. You shouldn't man-rate things with such problems unfixed.
GW
Bob:
I think you may be right. That sure looked like a fire to me.
I noticed the white "vapor" of some kind being vented from the engine compartment, in the thin air several seconds ahead of the first sign of the fire. It's not possible to say whether that is an unintended propellant leak or an intended flowing of cold propellant to pre-cool the engines to operating temperature.
Whatever it was, the gases in the engine bay did seem to catch fire as the booster descended into thicker air. There is a pressure below which fuel-air ignition is not possible. That fire started nearer leeward in the bay, but quickly extended all across it, around the center 13 engines. I did not see any fire around the outside ring of 20 engines, and I do not understand that at all, not yet, anyway.
I am glad there was no apparent oxygen leak into this fire. That would have precipitated an immediate (and fatally destructive) explosion.
GW
I repeat: what are you going to use for a piston ring or seal, with cryogens? There are NO polymers that remain flexible enough at usable sizes and thicknesses, to do any good at such temperatures!
Anything that gets past your piston may still be inside the housing or cylinder, but at low pressure. How will you increase its pressure to get in back into the tank?
Such a piston pump/syringe will have a pushrod that moves the piston. There will have the be a seal around that rod, or any leakage will go right to space. Same question applies: what are you going to use for that sliding rod seal, when cryogenics rules out all polymers?
You can get away with a static O-ring seal on valves and plumbing fittings, as long as you obtain the seal before you expose the fitting to cryogenic cold, AND you ensure there is absolutely NO chance of motion at all, at the seal in that fitting! Moving seals are an entirely different sealing problem, and currently an impossible, non-existent, technology at cryogenic temperatures.
The spinning-tank approach simply avoids every single one of those fatal difficulties.
I went "spinning tank" for the cryogens, because there are no usable polymers at cryogenic temperature to support bladdered expulsion, which I would have greatly preferred. I recommend bladdered expulsion heartily for the (room-temperature) storables (which includes kerosene!), as a solution proven for decades. But you simply cannot do that with LOX, LCH4, or LH2. If we could, it would have already been done! It has not been done, so QED, it still cannot be done with any known technology.
GW