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The real problem with asteroid/comet defense of Earth is detecting the threats in time to be able to do anything about it. That detection capability still demonstrably does not exist, and the solution has been known for several years, but never built. Multiple in-space detection satellites looking outward in the far infrared, and located well inward of Earth, orbiting the sun.
Once you have some years of warning, you have the option of going out there and trying to deflect the threat with a "small push", which way far out like that, is not a problem even if the body disrupts. If it does, the cloud of fragments will have spread to a size far larger than Earth, so that most of the fragments will miss, even in a dead-center hit.
M-types (metal) are mostly one big solid piece. You can "push" on that pretty hard and not break it up. Which makes a last ditch defense with a big impactor or a nuclear weapon feasible. S-types ("stony") may not be one big piece, perhaps several large chunks. It is still unknown how hard a "push" you can use on it and not break it up, so it is still unknown whether a last-ditch "big push" defense is even feasible with those.
The most numerous by far are the C-type (carbonaceous chondrite) types, which so far have been devoid of ices to bind their small particles together, even when coming from as far out as the main asteroid belt. These are loose rubble piles bound only by mutual gravity, which is vanishingly weak. No last-ditch defense is feasible: you just end up converting the single bullet strike to a small dense shotgun blast, if you try.
If you have multiple years warning (AND you have developed the right kinds of spacecraft and ion engines !!!), you can employ the gravity tractor. But ONLY if you have multiple years of warning! That kind of deflection does not significantly disrupt even the C-types, because the applied "push" is the same magnitude of strength as the binding force.
I see absolutely no progress since the 2009 meeting that I attended, toward fielding ANY of the right equipment to accomplish any of this defense need. With one (and only one) recent exception: NASA is (finally !!!) launching an infrared asteroid detection satellite, to be at one of Earth's LaGrange points. That's the right detection method, but not yet the right place to put it.
And, until you have multiple years of warning, you are faced with only last-ditch "big push" defense, which cannot work with the vast majority of these objects, those being C-types that are dry and thus loose rubble piles.
GW
The Vanguard that failed right after Sputnik in 1957 was a Navy program. PR said it was for science, but the Navy was running it. The Explorer-1 launch in Jan 1958 was put together out of a Redstone and some other solid motors, by Werner Von Braun as part of the Army ballistic missile program. The Navy went on with solids as the simpler, safer solution for the missile submarine concept, and had Polaris flying by about 1959 or 1960, as I recall. [EDIT UPDATE 10-2-2024: DOD went on to success later, going all solids with Minuteman for the USAF and the Army's battlefield missiles. Not the liquids that NASA needed.]
Then there numerous failures of Atlas (USAF), Thor (USAF), Juno (US Army), Jupiter (US Army), and many others, before there ever was a NASA. These continued as NASA was getting started late in 1958. Which was about the time Von Braun left the Army and went to work for NASA, bringing his Saturn ballistic missile designs and much of his Peenemunde team (Operation Paperclip) with him. All of that stuff from 1954 to 1958 was DOD, and NASA got started in 1958 using DOD rockets. Including what became Saturn-1 and Saturn-5.
So the premise that NASA is screwed up and DOD needs to take over is based on a false reading of history.
Those frequent failures happened less out of incompetence and more out of the fact that space is just hard to do. And the Russians had them, too, just not ever publicized the way ours were.
That is still true today, which is why anything that is a large step ahead always sees serious troubles; eg, Starship/Superheavy. That is simply to be expected. And you should expect to see more of it with ULA's Vulcan, Blue Origin's New Glenn, and probably any other heavy lifter out there.
GW
PS -- Saturn-1 was originally a huge ICBM meant to carry the oversized thermonuclear warheads of the mid-1950's. By 1958, thermonuclear warheads had shrunk to the point that even a B-47 could carry one, and the giant Saturn-1 ICBM was no longer needed. But NASA needed it for Apollo. And now they employed Von Braun with his paper Saturn designs. They had Saturn-1 flying by about 1962 or 1963, as I recall.
The Saturn-5 was originally a giant suborbital troop transport for sending 100 men one-way to Russia for a pre-emptive war scenario (that involved LSD-25 bombs, as well). It was originally 2 stages, with a huge payload that landed with chutes and rocket braking. Replacing that payload with a Saturn-1 second stage switched it to the 3-stage Saturn-5 that NASA needed for Apollo lunar missions. Which is how and why Saturn-5 was flying by about 1967.
But until NASA (and even Von Braun) got over their "not invented here" attitude, it was going to take two Saturn-5 launches per mission to the moon. On-orbit propellant transfer was going to involved, and they just did not know how to do that with storables then, much less cryogenics. Learning was going to push the first landing past 1970. It was the lunar orbit rendezvous idea from outside NASA that finally got us down to one launch per mission, and still meet JFK's due date.
These things usually do not follow a logical progression. They never did before!
The ISS leak was in today's "Daily Launch", for the second straight day. This time the article was far less clear, and read like an attempt to calm the fears the first article would create. It claimed they all-of-a-sudden reduced the leak rate by some undescribed repair, but did not identify what that was, while simultaneously claiming they still did not understand why they had a leak (which is quite contradictory, so I know the second article is just PR BS from NASA management to the media).
The first article said they closed the door to the leaky module when it is not being used, to limit the atmosphere leakage from the ISS to just that module, into space. It is a tunnel module connecting the rest of the ISS to a Soyuz docking port module, in the Russian portion of the station.
It is quite unclear whether this is a hole somewhere (like two previous Soyuz capsules), a crack in a panel, or a cracked weld. A hole could be a drilling or space debris impact. The first article said they have been looking for it for a long time but still have not located what is leaking or why. That I believe!
But if it is a cracked weld or panel, that is extremely serious. Such cracks always grow in cyclic loading, and how far they can grow before catastrophe happens, is quite finite. We are talking air leak rates on the order of a kg a day or more. This is no pin-hole leak. Which is why the ISS team classified it and its consequences as their worst case evaluations.
GW
I think you ought to make one and try it out, before expending the resources to tool up and make a bunch. That's just prudence in a manufacturing operation. Which I did study for my PhD.
GW
There is nothing in Mil Handbook 5 about any materials that are "self-healing". If a material is not listed in there, it is considered not yet ready for application. And that's for the military, who get away with doing things civilians are just NOT allowed to do, under a variety of laws and regulations. A notable exception was beta-phase titanium, which is still not in Mil Hndbk 5, but was used to build the SR-71's long ago. As I said, the military can get away with things that civilians are not allowed to do.
GW
If you just need to make one, cut it from a scrap of board with a simple jig saw. Then use a rasp to shape it as desired. Having a pattern to use with a router is how you make lots of them. But you might want to try it out, before tooling up to make lots of them. That's what prototyping is all about.
GW
There are two kinds of cyclic stresses: (1) actual alternating loads, and (2) cycling thermal stresses. But stresses are stresses, regardless of how produced, and if they cycle, fatigue is the risk. If you design down at the infinite fatigue life stress level, aluminum's low density advantage disappears, because you have to use so much of it. But all the metals need to be used at their infinite fatigue life stress levels, unless you can justify accepting a finite life just to get a lighter structure. They do that with airplanes: usually at 40,000 cycles. That gives you many years, even decades of service life at the cycling rate aircraft see: a single handful of flights per day.
Spacecraft are different: there is thermal stress cycling for anything in orbit, as it sees day and night on a rate equal to the orbital period. Exposure to occasionally-higher stresses just shortens the number of cycles to failure. And some exposures will deform the craft or structure, if yield stress is exceeded. Only a rank amateur would ever try to size a structure using its material's ultimate strength! (I see a lot of rank amateurs do exactly that, though! In all sorts of venues, not just this forum.)
We have gotten about 3 decades of service life out of the ISS so far, and likely nearing 4 decades by the time they deorbit it. The concern is that a cracked weld is leaking, and the leak rate is increasing. That means the crack is growing, and they still do not know where it is, despite 2-4 years of looking for it. The risk of a fatal explosive decompression is getting rather large now! It may no longer be wise to continue trying to use the structure without trying to make an effective repair (which so far they have been unable to do).
Structures that rotate should not see cyclic stresses, unless they are out of balance and wobbling. But the things I called out regarding staying below the stress for infinite fatigue life still apply, as all space structures will see thermal cycling due to day/night exposures. My best recommendation is you NEVER obscure access to the pressure shell from inside the pressurized spaces. That way is much easier to trace a leak and find the crack. Once found, you drill out its ends with small bit to relieve the stress concentrations there by radiusing the sharp ends of the crack, and then you can patch over it (which is WAY easier from the inside pressurized space).
Few spacecraft designers follow my advice, though, which is why in 3-something years they have not found the leaking cracked weld in the ISS module, nor could they find the leaking holes in at least two Soyuz spacecraft docked to it.
GW
PS -- don't tell me that composite materials do not experience fatigue. They do accumulate damage over time, but the mechanism is not usually a crack, so they don't use the word "fatigue". It's most commonly delaminating de-bond between fiber and matrix. But the material life is limited, regardless of what you call this effect. There are NO materials that last "forever". Not even wood: there is cumulative damage for wood under cyclic loads, plus there are two different types of rot. And strength depends very strongly on moisture content. It is extremely unlikely that there ever will be any material with an unlimited life under cyclic stresses.
PPS -- no, I am not a materials engineer, nor am I a professional stress analyst. I trained in aerodynamics, thermodynamics, heat transfer, and propulsion. But I had to learn a whale of a lot about the other disciplines, enough to be competent in them, in order to be effective on the job in the kind of defense work we did. My usual role was tying together the other 1-or-2-specialty specialists into a team,
by acting as a "chief engineering scientist", as well as a specialist in some other things my colleagues couldn't cover, such as inlet characteristics and fuel-air combustion aerodynamics.
From today’s AIAA “Daily Launch”, regarding risks of an aging ISS:
ARS TECHNICA
NASA confirms space station cracking a “highest” risk and consequence problem
US space officials do not like to talk about the perils of flying astronauts on the aging International Space Station, elements of which are now more than a quarter of a century old. However, a new report confirms that NASA managers responsible for operating the space station are seriously concerned about a small Russian part of the station, essentially a tunnel that connects a larger module to a docking port, which is leaking. Russian and US officials have known that this small PrK module, which lies between a Progress spacecraft airlock and the Zvezda module, has been leaking since September 2019. A new report, published Thursday by NASA's inspector general, provides details not previously released by the space agency that underline the severity of the problem.
My take on it:
They seem to have focused on a leaking weld, which is a weld that has cracked. They do not seem to be worried about a crack in the pressure shell. Weld cracking is a serious issue, because it risks a sudden decompression blowout, if it comes apart. This usually is a known metallurgical problem, probably with an aluminum alloy (“duralumin”, aluminum with a dollop of copper in it) or maybe a titanium or steel item.
This WILL get worse as time goes by, because the stresses in the metal cycle with day/night temperature changes every 90 minutes, and that cycling causes fatigue. With aluminum, there is a stress level below which fatigue does not occur, but it is quite low (down near 5-10 ksi). To reduce weight, you go for higher design stresses, and accept the limited fatigue life. That is very likely EXACTLY what you are looking at here.
Steel is similar, but the no-fatigue stress level is much higher (a majority fraction of yield, near 30 ksi). Similar for titanium, although I would hesitate to do any welding on 6-4V (alpha phase) titanium! Fasteners are far more reliable for it. Alpha phase is not formable: you literally carve your parts from ingots. There are a couple of beta-phase alloys that are formable into sheet metal, but they age at only room temperature, and do not respond well to welding. One of them was used for SR-71/YF-12/A-11 skins, and cracked somewhere after nearly every flight.
As for the aging ISS, the risks grow daily (a cycle every 90 minutes) that a weld or a panel somewhere is going to blow out and cause an explosive decompression. That will kill the crew, all of them! They have no place to shelter, and no way to get into a p-suit!
Now do you understand why this thing needs to be decommissioned and replaced by something else, and fairly soon, too? It will “look fine” right up to the point where it fails and kills everyone on board, just like the old Dehavilland Comet jet airliner did back in the 1950’s.
GW
Also from today’s Daily Launch:
SPACEFLIGHT NOW
SpaceX grounds its Falcon rocket fleet after upper stage misfire
SpaceX's Falcon rocket fleet was grounded for the third time in three months after a second stage problem occurred Saturday following the successful launch...
My take:
This was the deorbit burn for the second stage of the Falcon-9 that took Crew-9 to the ISS. It did the burn, but underperformed for reasons not yet understood. That delayed entry out of the area designated for it. That is technically a violation of the launch license, but that is not the real problem here.
The real problem is some sort of occasional restart-in-space problem with the long-performing Merlin engine. That needs to be found and rooted out, because this is a man-rated vehicle! Whatever has been going on with Raptor restarts is likely related, and that needs to be fixed, too.
GW
Any sort of mass driver or mass slinger on the moon is inherently a weapon of mass destruction aimed at the Earth. Any sort of solid rock slung from the moon would hit the Earth's atmosphere at something near 11 km/s. It would enter very steeply, very nearly vertically, but being a solid rock, would survive the entry heating and gees, and hit the surface at a speed near 10 km/s. At that speed, it doesn't take much rock mass for the kinetic energy to equal that of a hydrogen bomb.
Doesn't matter who builds such a thing there; us, China, Russia, or anybody else. It's all the same threat to Earth, and should be outlawed under treaty. This was described in Heinlein's "The Moon is a Harsh Mistress", which I read over half a century ago. Nothing has changed, and there is still little or no defense. This is uniquely a lunar problem. It is really hard to use a mass driver or mass slinger to hit the Earth from any other celestial body. Because the moon orbits Earth, the other bodies do not.
As for our troubles with Russia, I have to disagree with Kbd512. The real problem is the extremist dictator Putin. We did NOT have problems with Russia under his two elected Russian Federation predecessors, and under the last Soviet Premier, Mr. Gorbachev. The trouble began again when Boris Yeltsin made the fatal error of designating Putin as his successor. History clearly says so. Putin is THE Russia problem! Not its people. And it is not our fault, either!
Similar obtains with Xi's China. The two worst extremist dictators there are today's Xi and Mao Tse Tung many years ago. Under Xi, China's aggressions have ballooned completely out of sight all over world, but especially in the western Pacific. We actually fought a war with Mao's China in Korea 1950-1953. If we need to, we could again, although today there are more consequences, should we be required to do that. The consequences of NOT resisting bullying are worse, as history clearly shows. So, again, I disagree with Kbd512 on China. It's simple bullying, little different than 5 year olds on the playground. Give the bully a bloody nose, and he will back down (meaning simply and summarily sink the Chinese boats that ram other's boats). We've seen it before.
GW
Well, at this stage, all is speculation.
As far as I am concerned, they (the Chinese) can "race" all they want, there is no need for NASA to race. We've been there, and we're (finally) going back. I'm actually more encouraged and impressed by the commercial landers than I am Artemis.
As we already know, anything useful in space can also be a weapon. Such as rockets. Mass drivers are not just useful, they are also weapons (yeah, I read Heinlein's "The Moon Is a Harsh Mistress" half a century ago). Perhaps they should be considered as such under the Outer Space Treaty.
The reverse is true, too. Atom bombs are not just explosives, they can also be used for propulsion.
The "trick" here is when any given technology is used as a weapon instead of for a peaceful, useful purpose. All swords are double-edged and double-ended in space.
GW
I think they did a good job, and the right job, too.
GW
Water's triple point is listed as 6.1173 mbar (.0060373 atm) at 0.01 C. Any pressure lower than that, and ice sublimes. Lowering the temperature of the ice slows its sublimation rate. Any pressure higher than that, and you can have liquid melt present. Raising the temperature requires more pressure for stability.
The Viking average pressure was just about 6-7 mbar. There are low places with higher pressures, perhaps over 8 mbar. But any of the highlands would be under 6 mbar.
GW
I was taught something similar in 6th grade English long ago: tell 'em what you're going to tell them, then tell it to them, and finish by telling them what you just told them. The first and last pieces are short forms, the middle piece is the long form.
I like adding the relevance to the reader from the SQ3R thing. It was implied to be in the middle part of the 6th grade English thing. Putting it overtly is a reminder to get that job done.
My 6th grade teacher was the school's football coach (yes there was grade school football in those days). He was the only male grade school teacher I had. I think his name was Charles Brown. He used to make jokes about himself vs the "Peanuts" cartoon strip character of the same name.
GW
I don't know what the new "sustainable jet fuels" really are.
About 25 years ago I worked with biodiesel, which is more viscous than kerosene, physical properties resembling #2 diesel, which is too thick for gas turbines as currently built. It also freezes at about 29 F, when commercial Jet-A typically freezes near -58 F.
We could only blend it with kerosene. Typically 20 to 30% by volume biodiesel in Jet-A, which would then freeze somewhere around -10 to -15 F. I did make one blend with 30% biodiesel and about 0.5% ethyl tetra butyl ether (ETBE). That did not freeze even at -68 F, despite the plain Jet-A freezing at -58 F in tests I ran.
But that's not a fully sustainable fuel, only a fuel extender. It did not reduce emissions of NOx, but it did reduce carbon sooting quite a bit. You could smell the source of the biodiesel in the jet blast.
GW
Very sorry to hear that, Harold. Anything I can do?
GW
I second Oldfart1939's motion.
See how bad "not invented here" attitude is? It's worse at government agencies than in the contractors, and it's bad enough in the contractors.
Innovation comes from the smaller outfits, who are not so consumed with bureaucracy and "not invented here".
GW
By now, everybody on these forums (and anywhere else) should know better than to believe an Elon Musk schedule prediction. Those are what he wants, not what SpaceX can do.
Most of the delays getting launch licenses have to do with SpaceX violating the terms of their launch licenses (usually at Elon's bidding), or by wanting to do a test outside what was previously approved (as with the next test flight, because of the attempt to catch the returning booster).
Elon's disdain of regulations is quite clear and no surprise to anyone anymore. And yet those regulations are quite necessary. If that returning booster goes off course and cannot be destroyed, it represents a rather severe crash risk for the city of Brownville, only 5 miles away from SpaceX's site, a risk comparable to a large bomber with its bomb load still aboard.
Yeah, that issue needs to be addressed thoroughly, and the FAA is quite right to consult with other agencies, as this is a bit unique. Not like the usual big aircraft crash risk. Even only a few tons of remaining propellant is still a rather large bomb waiting to go off on impact.
GW
I've seen arguments for estimating Isp with other working fluids, but I haven't seen good reason to believe them, because there are no test data. So, the answer is, I cannot give you a reliable figure for a water NERVA. I do not know.
GW
There's other discussions in other threads about the actual result from smacking into Didymoon. Yes, they changed its orbit, and by more than they expected. I've heard that a lot.
What no one wants to talk about in public is the amount of debris flung free into space from Didymoon, and that it almost came completely apart, despite the very small size of the impacting craft. The extra debris spalled into space is EXACTLY why they got more orbit change than they expected. They did NOT expect to nearly break up the asteroid the way they very nearly did.
But they SHOULD have expected this!
Didymoon was C-type, not S-type, and certainly not M-type. Everything we have visited that was classifiable as C-type has been dry fragments held together by NOTHING but vanishingly-weak gravity. Why on Earth anyone would be surprised that a suddenly-applied force threatens disruption is totally beyond my understanding.
How can you push on a cloud of particles when the forces binding them together are weaker than your slightest possible touch? How can you attach anything to a cloud like that?
If one can go find those other threads with the impact mission discussions, you will see that I have been predicting that very outcome for some years now. I learned about this disruption problem when I went to the asteroid defense conference in Granada, back in 2009. This stuff is not a secret.
GW
This is from the Wikipedia article on liquid CO2. I think the triple point may be too high for Mars, unless you keep the pressure vessel warm. We get into trouble with its critical point here on Earth at 88 F.
GW
Liquid carbon dioxide is the liquid state of carbon dioxide (CO
2), which cannot occur under atmospheric pressure. It can only exist at a pressure above 5.1 atm (5.2 bar; 75 psi), under 31.1 °C (88.0 °F) (temperature of critical point) and above −56.6 °C (−69.9 °F) (temperature of triple point).[1] Low-temperature carbon dioxide is commercially used in its solid form, commonly known as "dry ice". Solid CO
2 sublimes at 194.65 K (−78.5 °C; −109.3 °F) at Earth atmospheric pressure — that is, it transitions directly from solid to gas without an intermediate liquid stage. The uses and applications of liquid carbon dioxide include decaffeinating coffee,[2] extracting virgin olive oil from olive paste, in fire extinguishers, and as a coolant.
La Rinconada is the town evaluated in the AAAS "Science" article I used to set my long-term hypoxia criteria. Nearly all its residents suffer from chronic mountain sickness symptoms, and there is an elevated rate of childbirth difficulties.
GW
Spacenut:
Don't feel too bad. My college training was in Fortran-II and what I used in industry was Fortran-IV. I sort of just picked up BASIC as I went to industry, using a version of it on my desktop, once those came out. Never learned anything newer.
GW
Under these assumptions: rate = constant * Cox^1 * Cfuel^1 * exponential-in-temperature, then the reaction rate depends upon the mass concentrations of both fuel and oxygen, both to the 1st power.
At 21% by volume oxygen in air, the mass fraction of oxygen is about 25%. At 1 atm pressure, that's 0.25 kg oxygen per kg of air.
At 7% by volume oxygen, the mass fraction would be about 9%. At 3 atm pressure, that's about 0.27 kg oxygen per kg of "air". Which is about the same.
That's just the oxygen, there are also the fuel concentrations. Fuels burn with oxygen in a narrow range of fuel/oxygen ratios, some narrower, some wider. Assuming those concentrations work out similar, then the reaction rates will be similar. If not, they won't.
It's one thing to be ignitable at all. It's quite another to burn at a similar rate. What you want in a habitat atmosphere is reaction rates no faster than in sea level warm-day air. A faster rate is a flash fire verging into an explosion.
GW
The reason leaded avgas has persisted as long as it has is twofold: (1) it is the only way known to create 100 motor octane gasoline, and (1) the threat from piston aviation was minimal.
Piston aviation is a tiny source compared to motor transportation on the roads. The lead in avgas can only be just barely detected near the very busiest airports, and only almost on the airport site itself. The "newer" 100LL (for "low lead") avgas has at 2cc per gallon half the tetraethyl lead content of the older 100/130 grade it replaced (long ago).
Folks have been trying to create a lead-free 100 motor octane gasoline for at least 3 decades now. There might now be one "in the wings", but it's not out there yet. Not every airplane needs 100 MON, but most of the modern ones do. A stiff gasohol blend might serve, something around E-20 or E-25, but the aviation manufacturers never transitioned to ethanol-tolerant materials. Methanol is even worse for material incompatibilities. They'll have to do it without either of those alcohols.
Just to "calibrate" this, the unleaded regular in your car has about 82 motor octane and about 92 research octane. The average of those is the "pump octane number" or PON they can legally advertise on the pumps and signs. For unleaded regular, that's 87 PON. Mid grade is about 89 PON, and premium is about 91 or 92 PON. It's pretty easy to create lead-free gasolines down in that octane range. These days, it's done with ethanol additions up to about 10% (for an E-10). A few years ago when I was experimenting actively with these materials, unleaded regular as I tested it with the water separation test was usually an E-8 material.
Piston aviation just isn't much of a threat for poisoning the air with lead. Road transportation very definitely was. Size of an industry really does matter. But I'll also say this: the reason to get the lead out of motor gasoline was more about oxygen sensors for fuel injection than it was about protecting the public health. Lead poisons those sensors. They had to remove the lead to use the technology. Money talks.
GW