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The mechanisms underlying breathing and combustion are different. Breathing depends upon the partial pressure of oxygen in the air being a bit greater than the partial pressure of oxygen in the blood. It is the difference in partial pressures across the lung membranes that drives movement of oxygen into the blood. And this gets complicated by the diluting effect of water vapor and carbon dioxide that lowers the partial pressure of the oxygen in the air that is actually inside the lungs.
Combustion is driven by a different mechanism, related, but not the same. Using the simple Arrhenius model of an overall chemical reaction rate, that rate is driven by a constant often multiplied by density to a power, multiplied by reactant concentrations raised to appropriate exponents, multiplied by an exponential in the temperature at which the reaction is proceeding. Reactants include the oxygen, the fuel, and often the water vapor produced (but not always). The sum of the exponents is usually pretty close to 2. If you use mass concentrations instead of volume concentrations, there is no density-to-a-power factor, and the value of the reaction rate constant is different.
The concentrations are related to volume percentages in the atmosphere, but they are not the same thing! They are closer to the partial pressures, but there is also a total pressure involved. I usually use mass per unit mass of atmosphere (mass concentration) instead of mass per unit volume of atmosphere (volume concentration), which gets rid of the density-to-a-power term out front with the reaction rate constant. If water does not figure into it, the exponents on the fuel and oxygen concentrations are usually pretty close to 1 on each factor.
Combustion proceeds at Earthly rates when the reaction rate predicted by the Arrhenius equation is the same. Breathing is the same when the partial pressure differences are the same.
Sorry, it's just complicated.
However, these things are exactly what I took into account, when I recommended hab and suit atmospheres. I checked fire danger as well as breathing. And also pre-breathe elimination for oxygen suits.
GW
Has anyone seen a date for the next Starship/Superheavy test flight?
GW
It finally showed up in a news story what the real hang-up was making a decision. The Boeing suits are so incompatible with Dragon that the two Starliner crew would have to ride back in shirtsleeves, exposing them to the capsule depressurization possibility that killed a Russian crew. That would be using Crew 8 Dragon as an emergency evacuation vehicle, with the Starliner crew riding in shirtsleeves on the cargo pallet installed below the 4 seats in that Dragon.
There is an ISS suit that fits Sunni Williams, but not one that fits Butch Wilmore. The Crew 9 Dragon only has 4 seats, but will bring a suit that fits Wilmore. That way, Wilmore and Williams could ride in pressure suits back aboard Crew 9 in February.
NONE of these stories addressed why Williams could not ride a Crew-8 emergency descent in that ISS suit, which would leave only Butch riding exposed in his shirtsleeves. That is part of why I know these news stories are still very flawed. It is hard to say how much of that flawed-ness is ignorant reporters, and how much is deliberate deception or evasiveness on the part of NASA and/or its contractors.
But there it is: did that lemon of a Starliner, or the risk of a shirtsleeve emergency descent on Crew-8, pose more risk to the Starliner crew? THAT is what they must have been debating all this time. And I notice NOBODY is talking about that! Apparently, the Starliner was considered more risky that a descent without a p-suit.
My advice to NASA on seats in Dragon still stands (and I know that some NASA folks see these forums): put all 7 seats back into Dragon! You don't have to fill them all, but if you should need them, then you have them. And you can always strap pressurized cargo into the empty seats. Just bag it up and tie it in with the seat belt! Whoever ruled otherwise (to the 4-sseat configuration) "for safety's sake" (worrying about speed of egress for the bottom 3 seats) was just dead wrong! 2020 hindsight clearly says so!
GW
At sea level on a US 1962 or an ICAO standard day, 535 mph is almost exactly Mach 0.7. For almost any shape, that would be close to, but still below, the start of the transonic drag rise.
GW
Anytime you do horizontal launch, you have to use lift to at least pull up into a near-vertical climb. Above about Mach 1 speed, the turn radius gets enormous at any practical turning gee (as does the wing). You will enormously increase your drag loss with parasite drag of the wing, and an enormous amount of drag-due-to-lift, over that incurred during a vertical launch into a non-lifting thrusted gravity turn.
As a result, such designs will inevitably need the theoretical dV factored up enormously to cover the huge drag loss, and they will have a higher-than-anticipated inert mass to incorporate the large wing.
Anyone who can run a rocket equation calculation with a proper weight statement can verify that the required mass ratio gets ridiculous, even with hydrogen-oxygen propulsion. Such numbers go with a huge propellant mass fraction, leaving very little for payload and inert mass fractions. And that is incompatible with the higher mass fraction needed for the big wing (and its heat shield).
This sort of design approach is feasible with Isp values corresponding to nuclear thermal propulsion. But not hydrogen-oxygen chemical. And anything less than hydrogen-oxygen Isp is just totally infeasible. I have already shown that in verifiable bounding calculations.
In my opinion, this thing is more marketing hype to attract investors, than any real promise of anything that might ever fly with chemical propulsion. It would have to be nuclear to work.
GW
Edit same-day update: Go see the current posting on my "exrocketman" site, titled "Rocket Equation-Based Launch Vehicle Analyses", dated 1 September 2024. In particular, see Figure 11 and Figures 21, 22, and 23! Know also that this was all done with the spreadsheet tools made available with the "orbits+" courses. Any of you can use those tools and do this as well as I can. Both the course materials and this "exrocketman" posting show you exactly how to use those tools correctly.
You might be right about the outcome of a ramming incident with any ship under my command. But I'd rather save my ship and be court-martialed, than be "right" in some political sense. I come from an earlier time, as you can tell.
GW
Brian likes to differ with me because I am not a Trump supporter and he is. Yet on most practical things, he and I agree.
I'm not sure either where to put conversations like that. But they do arise.
GW
FAA's rules for airplanes were developed from failures and deaths, as were the fire codes. In the 1940's and 1950's not so much was known about metal fatigue as today, but the net effect was that there was a maximum number of takeoff/landing cycles that an airframe could withstand (especially a pressurized airframe). You must rebuild or replace something, when you approach that limit. And there are design features that raise it or lower it, which you must take into account.
I suspect that there is a similar life-cycle number limitation for rocket engines and propellant tankage, as well as heat shielding and any other subsystem you care to name. Nobody yet knows what those limitations might be, and they will be different for each subsystem. But we are just beginning to get an idea with SpaceX's Falcon stages. Bear in mind that spaceflight is far more stressful on materials and designs than atmospheric flight is. The limits might well turn out to be rather low, but that is just speculation on my part.
Remember the DeHavilland Comet jet airliner? With square window corners, and some other design features we now know to be faulty, its pressurized fuselage fatigue life turned out far too low. That cost 2 or 3 plane-loads of passengers. The Comet entered service as the last of the unpressurized and much slower DC-3/C-47 aircraft were built. It had redundant structures that lowered the stresses on any individual piece, to values below the infinite fatigue life now known (but not back then) for the aluminum alloys from which it was constructed. Which is why some 80-year-old examples are still flying.
GW
Kbd512:
I can't disagree with anything you said. I just know that if I were Captain, and a Chinese ship actually succeeded in ramming my ship, I would sink him. In little pieces, if possible.
GW
Returning to the original topic, Starship/Superheavy is a rocket still early in flight test development. The Starship upper stage configuration still bears only superficial resemblance to what the final product might become. Estimates of its inert mass are still completely bogus, which makes the weight statements to be used in the rocket equation bogus as well.
Because of the exponential nature of the rocket equation, results are very sensitive to those weight statements that support any burn analyses. It's a GIGO thing, if you input garbage, you're going to get garbage. And THAT is precisely where we, SpaceX, or anybody else, are, when estimating what kind of performance to expect flying this thing anywhere, including Mars! There is no way around that.
I can put in weight statement numbers that indicate a Starship refilled on-orbit might take significant payload mass to Mars one-way. That ignores the rough-field landing issue, it ignores the propellant boiloff issue, it ignores the life support issue for any crew, it ignores the radiation protection issue for any crew, and it ignores the in-flight electrical power supply issue. It also ignores the electrical power issue on Mars. And it ignores the issue of an adequate heat shield, which is getting better, but still "not there yet" for an 8 km/s entry.
I can use those same weight statement numbers and reduce the return payload some, to show that a Starship refilled on Mars could fly single stage from the surface of Mars to a free-return at Earth. That ignores all the issues listed above, plus the issue of making propellant on Mars in situ. Which is a "biggie". So is the adequacy of a heat shield capable of free return at Earth, at something in the 12-17 km/s speed range! To the best of human knowledge, that requires ablatives. Refractory ceramics will not do that job! Which is what they are flying, as near as I can tell.
What I saw in the Nature article was way too many things assumed about inert masses and propellant losses, leading to inherently-bogus weight statements that correspond to the assumptions made. Their assumptions led to infeasibility. Other assumptions lead to feasibility. All assumptions anyone makes are currently bogus, and the rocket equation analysis is critically, drastically, sensitive to those assumptions. That's just the nature of the beast.
Basically, until better data become available, this is all "how many angels can dance on the head of a pin" crap. Give the flight tests a chance, and pray that Musk does not rush it too hard.
GW
Tahanson 43206 is correct. Back to topic.
There was the recent second stage failure that left Starlinks too low to survive. I know there was a cold cryo-propellant leak, because of the ice seen in the on-board video footage, not seen in prior launches. It had to be the oxygen, because kerosene is not a cryogen.
They had the leak sitting on the pad, because the ice forms when atmospheric humidity comes in contact with a cryogen. There is no humidity in space. The ice was already there when they staged and started the second-stage on-board video.
Why they didn't catch the leak before they launched, nobody has said.
The more recent first stage recovery failure on the barge is more puzzling. There was a bit of a greenish tint to the fire about the base of the stage, which would suggest copper burning. I know they use that metal in the engines. That in turn suggests there was an engine failure as it landed. But nobody has said anything, except the FAA, which first grounded all Falcon-9's, and then cleared them to fly a couple of days later. All without any explanations from anybody at FAA or SpaceX.
I still think there is more to that incident than meets the eye. Somebody in SpaceX knew what happened, and how to fix it, or FAA would not have cleared them so fast. I suppose the corrective action might simply be "don't fly them quite so many times". But I certainly do not know, and both FAA and SpaceX have been silent about it.
GW
Free speech is NOT an absolute right, despite what Musk and several others claim. If you yell "fire" in a crowded theater, there had bloody well better well be a fire in there, or you are going to jail for endangering the public. The critical elements are (1) truth, and (2) public danger.
Musk's version of X is rife with lies, racist crap, neo-nazi crap, and much disinformation. The disinformation can incite violence, which is why it is a public danger. Why is anyone surprised when a legal system would disallow such things?
Musk is operating within another country, which means he has to obey their rules to operate within it. If he fails to obey their rules, he must take the consequences of that failure.
GW
I second Kbd512's motion. There is a vast difference between what we do and what the Chinese do (and several other bad actors).
I understand the "optics" of our having allies and bases all around China. We had to do the same thing with Russia after WW2, and we still need it today, given Putin as its insane autocratic leader. "Optics" do NOT tell the whole story. Most often, they are used to issue lies and propaganda.
You'll notice the Chinese do NOT use use water cannons or ramming against US warships. That would be an act of war, rating a sinking of the offender. If I were commander-in-chief, I would specify exactly that in the operating rules. If I were a ship's captain, I would defend my ship very vigorously, and I have believed in tactical overkill since the Cold War. Orders or not, I would sink the bastard.
I hope the current president already has done that, but I'm unsure, because such orders are classified, never shown to the public (which is as it should be). There's a small navy of the Iranian Revolutionary Guard that certainly needs to be sunk on sight, along with the pirates.
But as long as Iran suffers no consequences for what its proxies do, outfits like the Houthis, Hamas, and Hezbollah (and more besides) will continue to cause death and destruction. Iran funds them, arms them, and gives them their marching orders, allowing for the fact that terrorists are an unruly bunch who will sometimes kill without being ordered to.
GW
As I wrote in a different thread, I think there was more to this grounding than met the public eye. The rapid re-approval sort-of confirms that, in the sense that whatever was "wrong" was so easily fixed.
This may or may not have had something to do with a Merlin engine failure. It may have had a lot more to do with something Musk said or did that pissed off the FAA.
He's gotten a lot of notoriety lately for his public misbehaviors. Including getting his precious X banned in Brazil.
GW
This is a highly-experimental mission. It is the first attempted flight for Blue Origin's New Glenn rocket. Most first flights do not go well. But if this one does go well, then (maybe) there's a twin probe set heading to Mars.
GW
I'm unsure whether China or the US can do anything crewed very fast, although China seems less hog-tied bureaucratically. I've seen nothing out of either country that is credible as a means to land crewed on the moon any time soon.
As for a "race" to the moon, there is nothing official about anything, and I see no reason to race. We've already been there, although we need to go back. China is wanting to go there. And that's OK, if they as a nation behave themselves.
Something they are most definitely NOT doing in the South China Sea. Ah, such are autocrats!
GW
Hi Bob:
Let's just say I am unsurprised!
GW
The moon is unique because it rotates so slowly. There is almost no speed associated with the moon's rotation at any latitude, so that orbits in pretty much any direction, even retrograde, all cost about the same from the lunar surface. This circumstance explains why the figure-8 orbit was used by Apollo, which was a retrograde low orbit, at very low inclination. This circumstance obtains on no other body we might wish to visit anytime soon.
GW
As I indicated in my news post about this, I think there is more to this than anyone is talking about in public. Either the FAA suspects strongly an engine problem (which could be a risk to humans on ascent), or else something Musk did or said pissed them off. There's just not any other possibilities that come to my mind. And certainly there's no risk to humans (excepting possibly bystanders, which there have been none) if a booster crashes upon landing. On the surface, grounding the Falcon-9 fleet looks like a way-over-reaction by the FAA. But they rarely over-react to companies (example: Boeing until very recently). So, something else is going on, and nobody is talking publicly about it.
GW
update 9-2-2024: whatever it was all about, FAA seems to have gotten over it quickly. I saw one posting about Falcon-9's being cleared to launch again, here on the forums. There hasn't been one word either way on the major news services.
I did not know where to really post this. Concerns a Falcon-9/Starlink launch.
Apparently the last Starlink launch succeeded except for not recovering the booster. The stage landed on the drone ship, but its bottom was immediately enveloped in fire, and it toppled over and exploded.
The fire seemed to have a greenish tinge to it. I would SPECULATE the green was copper being oxidized. That might (might !!!) mean some sort of engine burn-through or explosion, as it touched down, breaching a kerosene tank or line and creating a big fire. It toppled slowly, as if one of the landing legs gave way in the heat.
GW
Update minutes later: a story on CBS News says the FAA has grounded all Falcon-9's until this booster landing crash gets figured out and any corrective actions approved and taken. On the surface, that seems like overkill, since it worked right up to the landing. I think there may be more to this than meets the eye. We'll see in coming days.
I see that the Polaris Dawn mission has been delayed twice now: once for a helium leak and once again for expected bad weather in the landing zones.
It is really hard to tell from the news reports, but as best I can make out, the helium leak was in ground equipment, not the Dragon. That's quite distinct from the Starliner helium leaks, which were in the Starliner spacecraft itself.
Both craft use helium to pressurize the thruster propellants and drive them into the thruster combustion chambers. These are hypergolic bipropellant thrusters that are pressure-fed. I know Dragon uses MMH and NTO. I think Starliner uses the same. Or possibly a different hydrazine and NTO.
Aerozine-50 was once commonly used with NTO by "old space" companies. It is a 50-50 blend of UDMH and simple hydrazine. But the trend in recent years has been toward MMH.
GW
My inverters tie through a manual switch and a manual circuit breaker directly to the meter installations (I have two, one for the house, one for the shop and my renter). There is no "automatic switch" of any kind! My solar is directly tied to the meter, on my side of the meter. It senses the sine wave coming in from the grid, to synchronize its phase to the grid's phase. If the grid is down, it cannot sense anything, so it makes no AC from the solar DC.
GW
Today's new carries stories that Butch and Sunni will ride home this Feb in the Crew 9 Dragon.
The same stories indicate that the Crew 8 Dragon will be rigged with an extra makeshift 2 seats so that if emergency evacuation of ISS were to happen, they could ride back with the 4 members of the Crew 8 mission.
The Boeing suits might not be "compatible" with Dragon, but apparently they can serve for an emergency ride home.
Meanwhile, if NASA would pull its head out of its collective ass, they would realize that if makeshift seats could be rigged out of junk aboard ISS, the two extra seats could be rigged in Crew 9, which is still on the ground waiting to go, where you could have the right stuff" in days. They don't have to reduce Crew 9 to 2 members, just to have seats to bring Butch and Sunni home.
And as a lesson for the future: just put all 7 seats back into Dragon! You don't have to fill them. But if the need arises for the extra seats for some emergency, they would already be there. You wouldn't have to jury-rig anything!
GW
I addressed this in the other thread. If that was ever classified at all, it was declassified long ago.
It might have been some sort of company trade secret, but I think NASA had control of it, because both McDonnell and North American Rockwell used the very same technology on Gemini (McDonnell) and Apollo (North American Rockwell), and they were competing companies back then.
The original versions of the technology actually flew on Mercury (also built by McDonnell).
There is a rather complete Wikipedia article on Avcoat. It pretty much tells you what it is, what it is made with, and how it was made. There's absolutely NO excuse for NASA not to have detailed specifications and process instructions in its Apollo records!
GW
update 8-23-2024 4:44 PM CDT --here is the link: https://en.wikipedia.org/wiki/AVCOAT
What would be wrong with using a simple press and a single press operator, instead of some expensive high-tech robots, to squish the polymer down into the cells of a block of the phenolic-impregnated fiberglass hex, inside some suitable mold tooling? Then force that uncured item down into the mold of a heat shield tile, and then butter it over with the polymer, and smooth its surface with a trowel? Then cure the whole thing at once?
Anybody who has ever actually built stuff putting goo into structures with his own hands could have thought of that!
GW