GW Johnson Postings and @Exrocketman1 YouTube videos

tahanson43206 · 2024-09-12 13:23:56

This post may be of interest to a few NewMars members.

The link below points to an animation that GW Johnson was trying to explain with words and fixed drawings.

https://www.youtube.com/watch?v=XLjnTgXXgXk

It turns out that I had made the same mistake made by millions of others in expecting that an ellipse that is the path of a planet would be skinny at the end near the Sun, and fat far from the Sun. The proof of the equivalence of the shape at both ends is provided in the video.

The specific problem I was having is accepting that the ellipse that results from the cut of a cone by a plane delivers the same result regardless of the angle of eccentricity.

This video deserves a place as a reference for the book project.

(th)

tahanson43206 · 2024-09-20 17:35:22

For GW Johnson...
https://newmars.com/forums/viewtopic.ph … 02#p226702
News from SpaceNut...
(th)

tahanson43206 · 2024-09-22 12:42:52

For GW Johnson....

Tried and true method of study ,.... I recognize elements that apply to the book project...

https://lifehacker.com/use-the-sq3r-met … wtab-en-us

(th)

GW Johnson · 2024-09-23 09:46:56

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

GW Johnson · 2024-09-30 10:02:50

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

tahanson43206 · 2024-09-30 10:13:11

For GW Johnson re #405 and RobertDyck's Large Ship

The deterioration of the ISS, detailed in your post, is happening to a vehicle that is NOT rotating once every 20 seconds, as ships designed along the lines of RobertDyck's Large Ship will be doing.

RobertDyck put development on the back burner, but he could return to the project at any time.

What advice do you have for folks who are now or will be designed large rotating vessels and stations?

Is there a way to design so that some components can be replaced quickly and easily?

Could the ISS have been so designed?

I understand the ISS is a special case because it was driven in large part by the urgent need to try to capture Russian good will when there was an opportunity.

(th)

GW Johnson · 2024-09-30 13:26:24

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.

Last edited by GW Johnson (2024-09-30 13:44:30)

tahanson43206 · 2024-09-30 14:33:12

For GW Johnson ....

Thanks for that long post #407, with details and examples of various kinds of stress loads on metal.

Bearing in mind that you are not an expert in the field, but instead are doing the best you can to explain a complex behavior of materials, I think that the question of how to deal with metal fatigue in a vehicle in flight needs attention.

Because we have at least three members with US Navy experience (military or civilian) I am guessing that metal fatigue of large structures that must endure all the stresses that the open ocean provides has received a ** lot ** of attention over centuries. A requirement for RoberDyck's Large Ship is that it must be as light as possible. At the same time it must be resilient in the face of all that challenges that come from flight in open vacuum.

Where I'm headed with this is a concept of self-healing structures.... I've read that some work has been attempted along these lines, but I think the work has been with Carbon, which is such a versatile atom.

(th)

GW Johnson · 2024-09-30 15:58:35

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

GW Johnson · 2024-10-01 09:58:22

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

tahanson43206 · 2024-10-01 11:41:28

For GW Johnson re #410, but also an interesting post in the Asteroid deflection topic ...

Re #410

I haven't read any reports about this ongoing problem, other than yours, so am hoping you might be willing to consider a couple of questions.

1) Have there been any attempts to use tracer atoms (ie, radioactive) to show where air drifts as the leak does it's thing?

2) Related.... what does "looking for the leak" mean in this context?

3) Risk question: It is possible to pressurize the module to try to create more visible evidence of the leak activity. Does that increase risk of blowout?

****
Regarding the asteroid deflection post ....

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 know you meant that quotes around "push" would be read by a sophisticated reader as "pull", but why not just say pull in the first place?

The machine you're describing sounds like a gravity tractor.

There is no "push" involved with a gravity tractor, except the "push" on the tractor, which is vanishingly small, because it needs to be small enough not to escape the tiny gravity of the object to be manipulated.

Upon reflection, it occurs to me that the greater the mass of the tractor, the more effective it will be, so if our hypothetical deep space defense force has enough resources to put a tractor near a rubble pile, it might as well put the largest (most massive) tractor in position that it can.

(th)

GW Johnson · 2024-10-01 13:03:58

I cannot answer most of your questions because those answers are not in any of the reports I have seen.

All of the ISS is pressurized to about 1 atm of synthetic air (21% O2, 79% N2). That would include the leaking tunnel module, except when that hatch is closed. Then only that module (and presumably the docking adapter it connects to) leaks down, without leaking down the pressure in the rest of the ISS. Nobody says, but I presume they have to equalize by bleeding air (somehow) into the leaky module before they can re-open the hatch and use the docking adapter.

I have seen absolutely nothing describing how they have been searching for the leak.

Any impactor to an asteroid is a "push", meaning compression in the material underneath the impact point. The gravity tractor is actually a "pull", because the force on the asteroid is directed toward the spacecraft, and the force on the spacecraft directed toward the asteroid. The spacecraft thrusts to keep from being pulled onto the asteroid. That thrust has to be canted at rather strong angles, so that the expelled mass streams DO NOT strike the asteroid, but instead just pass it by. Ion, other, makes NO difference.

Most people think you use a nuclear device as a direct surface impact, or even exploded within the asteroid, but that IS NOT correct! There is no blast wave in a vacuum. You explode the thing alongside very close by, and use the radiant energy to overheat and vaporize the adjacent asteroid surface materials. Those vaporized materials "explode" into space quite violently, causing a big "rocket reaction" force in the opposite direction. The spalled material from an impactor works exactly the same way. Neither approach can be used on a dry C-type (excepting the very smallest, rather inconsequential impactors), because the asteroid will disrupt into a cloud of debris instead of accelerating in the "push" direction.

And yes, the larger the mass of the gravity tractor craft, the more effective it will be. And the larger your thrust requirement, the more expensive your construction, and the more demanding your launch problem. It's a very complex trade-off. Nobody yet knows the right answers, because it has yet to be attempted in any form.

GW

Last edited by GW Johnson (2024-10-01 13:07:02)

tahanson43206 · 2024-10-01 22:08:30

For GW Johnson....

This post by kbd512 is in a topic you might miss if you are limited in time, which seems likely...

https://newmars.com/forums/viewtopic.ph … 09#p226909

The post is a follow up to a post by Calliban about stronger concrete.

I bring this up because you had indicated you are not familiar with 'self-healing' metal, and what kbd512 is talking about is not "self healing" so much as it is tear resistant. What I'm wondering is if the metal used to make space craft might have some feature like this, to help to prevent massive blowout due to the incessant stress cycles of space travel.

(th)

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Re: GW Johnson Postings and @Exrocketman1 YouTube videos

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#407 2024-09-30 13:26:24

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#408 2024-09-30 14:33:12

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#409 2024-09-30 15:58:35

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#410 2024-10-01 09:58:22

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#412 2024-10-01 13:03:58

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