Space X - If at first you don't succeed...

GW Johnson · 2016-12-08 14:24:46

I agree, carbon of any kind in a LOX tank is a bad idea. If you coat it, that coating has to survive a variety of stimuli at harsh cryogenic temperatures. We're talking about a liquid helium tank here, not just LOX.

At temperatures like that, as I tried to indicate in post 69 above, everything is going to be brittle as hell. Anything that involves high strain rates will crack the coating. Such as loading the helium too fast, which raises the helium tank pressure rapidly.

Or vibrations in the vehicle, such as those always encountered when a rocket engine is firing.

They've been flying Falcon-9 for some years with a slower helium load. I suggest they just slow down again.

It's the big rocket that worries me about this issue. If the airframe is the tank, and it's carbon composite structure as indicated recently in Mexico, then the same problem returns, magnified by extreme size. More wetted area is just more opportunity for the coating to fail as a cold-embrittled material. That should have the effect of reducing effective carbon-LOX ignition delay, perhaps to the point where every little crack event inevitably causes a tank explosion.

This is just not the sort of thing youngsters reading reports and handbooks can effectively address. As I indicated before, there's engineering art here that was never written down. And probably not enough of that; most previous LOX items have been stainless steel, almost exclusively, and for very good reasons.

The "out" here is that LOX temperatures can be handled perhaps, with a reliable coating. Liquid helium temperatures, probably not. There should be a flourine-containing coating that will be reliable for the carbon composite LOX tank structure, but they'd better use stainless for the liquid helium tank, if they insist on mounting it inside the LOX tank.

GW

Last edited by GW Johnson (2016-12-08 14:33:33)

Oldfart1939 · 2016-12-08 16:05:38

The thought just occurred to me of making a bag made of a fluorocarbon polymer and "Shrink-wrap" it onto the tank? This could result in a multiplicity of layers, as well.

elderflower · 2016-12-09 04:56:45

You still need connections to it and this is where it will be weakest.

SpaceNut · 2016-12-09 20:41:30

http://www.snyderindustriestanks.com/Po … oly_2_.pdf

Fiber Reinforced Plastics Material Selection Guide

A bit dated NASA Tests Game Changing Composite Cryogenic Fuel Tank

Oldfart1939 · 2016-12-10 10:03:29

After giving this problem some thought, synthesis of a higher molecular weight fluorinated monomer is in order to allow a spray-on application , followed by an in-situ polymerization of a coating that's completely inert to LOX, and which alleviates the problem of oxygen crystallization within the carbon fiber overwrap? Robert: awaiting your thoughts on this. I've been exclusively a styrene guy in the past, doing suspension polymerization of my novel reactive monomers ---> reactive polymers.

Oldfart1939 · 2016-12-10 16:25:44

Just did some reading on Wikipedia re: Teflon or PTFE production. It strikes me as possible to Teflon coat the entire Helium pressure tank inside a large enough pressure chamber and initiate the polymerization which would coat EVERYTHING inside it. It would then even encapsulate the carbon fibers in a solid matrix including those exposed to the tetrafluoroethylene. Requires some "playing around" experimentally, but seems feasible to me... It's probably already been done, so we might be reinventing the wheel?

The concept of "shrink wrapping" is also described therein. No ability of LOX to permeate the carbon fiber overwrap = no disruption by freezing of oxygen.

Last edited by Oldfart1939 (2016-12-10 16:28:18)

SpaceNut · 2016-12-12 22:13:12

So we have been able to fix the tank that ruptured and can get the ship flying again but whats next for upgrades or new designs to get man beyond LEO....

Oldfart1939 · 2016-12-13 09:56:24

If a standard engineering approach is taken, then a switch to liquefied methane as the fuel will allow the new Raptor engines to replace the Merlins currently using RP-1 with a significant improvement in thrust generated with a higher ISP. The thus improved Falcon Heavy should be able to throw more and bigger chunks of hardware skyward. Maybe this is what Musk has in mind for his tentative 2018 Red Dragon to Mars launch? What about a Falcon Super Heavy with 4 detachable booster stages instead of 2? Maybe a bigger core stage with 4 Falcon 9 size boosters all using Methylox propulsion?

Last edited by Oldfart1939 (2016-12-13 10:26:37)

GW Johnson · 2016-12-14 12:16:05

The easiest thing for Spacex to do with its Falcon rockets is either (1) slow down the helium load to what they have used before that didn't cause a problem, or (2) use a stainless steel helium tank in the LOX tank so they can load fast like they want to.

Neither solves the problem they have proposing carbon-fiber composite construction of LOX tanks for the MCT. My guess is there is a fluoropolymer coating that will be acceptable, but it will be restricted to slow load rates of both LOX and helium pressurant. It won't be thin coating either, but several layers for redundancy.

The blasting agent of choice at the Mesabi iron mines in Minnesota was LOX-charcoal, until they replaced it with ANFO for easier logistics. There is a VERY long history of fire and explosion violence with carbon in contact with liquid oxygen. It is just far wiser not to take that risk.

GW

SpaceNut · 2016-12-25 19:30:47

Soon the engineering issues will be resolved and Space X will restart launching rockets to the ISS soon and hopefully manned capsules to orbit in the near future.

The next step for Space x is the Falcon Heavy which looks similar to a Delta 4 Heavy, with a performance quite a bit higher and, simultaneously, its cost per launch is much lower. It can put 53 metric tons (117,000 lbs) in orbit compared to the Delta 4 Heavy’s 23 metric tons (or 50,600 lbs), a 230% improvement. At the same time, it only costs about $100 million per launch, while the Delta 4 Heavy launches cost $435 million each (calculated from an Air Force contract of $1.74 billion for 4 launches).

I got thinking about the strap on solid rocket boosters that Boeing and Lockheed use on there respective launch vehicles and wondered if you stuck a pair of Shuttle sized units on the first stage and changed it to be the EDS for a lunar launch whether it would work....

GW Johnson · 2016-12-26 15:57:51

You can get crude impulse kick control with well-designed solids, but not precision control. For that you need a throttleable liquid. You get less control precision out of multiple solids than a single. It's inherent. No two supposedly-identical motors will produce the exact same burn time (nearest millisecond) or average thrust (nearest pound of force out of thousands) to the needed precision.

If I understood the previous post correctly, Spacenut wants to use a couple of solids to help make the departure burns out of LEO. You can do that, but only with a liquid core that burns out with great precision, after the solids have already burned out. Get the bulk of the impulse from the solids, but adjust it for fine precision with the liquid.

Same as the ICBM CEP problem: the post-boost bus vehicle always had a liquid thruster for suitable precision. You didn't free up the warheads and decoys until you were in precisely the desired trajectory. But, the bulk of the delivered impulse came from the solids.

Used as singles, solids can be good enough, if the precision requirements are not too tight. The old "Scout" was a satellite launcher of 4 solid stages, with attitude control by little thrusters. The precision required to put one in LEO was low, so direct injection to final LEO orbit was fine with "Scout".

The final versions of "Scout" could put 100-200 lb into geosynch. But those precision requirements were much higher. The 4 stage solid put the payload into a suitable GTO. But, it was an on-board liquid thruster that circularized and adjusted the final satellite orbit, in every case.

Such is life.

GW

Last edited by GW Johnson (2016-12-26 16:04:18)

Oldfart1939 · 2017-01-01 21:17:24

GW-

If you recall, the original Ares I in the defunct Constellation program was relying on a solid propellant first stage? I actually thought it was a good concept, since SRBs are considerably less expensive than a LOX-RP-1 propellant booster; no enormous plumbing systems and turbo-pumps, not to mention the rocket motor itself. I had an online discussion with a friend who recently retired from NASA at the Ames Laboratory in California, and he commented that the cancellation would probably come later in the program anyway, since the manned vehicle had "gained weight" during the design process and the Ares I booster as designed would have been inadequate to place the overweight vehicle in LEO, even with some upgrades to the second stage.

GW Johnson · 2017-01-02 10:02:43

Oldfart1939:

I'm a believer in solids myself. Spent 16 years in a solid plant doing rocket and ramjet development. Also did a short stint with LTV working on "Scout" upgrades. Designed a one-off configuration they used for an ICBM chase mission.

It's like I said in post #86 just above, if the precision requirements are low, all you need is the solid. There is no more logistically-sane and inexpensive form of throwaway thrust. If delivery precision requirements are tough, then all you need is a little liquid thruster to do the fine adjustment once the solid puts you in the ballpark.

It's not all that hard to make a safe, man-rate-able solid, either. You pay attention to quality control by TQM instead of the government way, which means you far exceed their standards.

As for design development, you want the failures up front during development, while it's still cheap. That means running lots of tests to uncover all the unexpected problems. Once those rates dribble to zero, you've found them all. It does require valuing data above preferred belief, a characteristic woefully short anymore.

One thing to understand about solids: the smarts that support them lie within the contractors who build them, not the government labs. Those labs never actually built one from scratch. The contractors did. That's why the shuttle SRB joint seal designs were such a lethal botch-up: dictated by NASA. And made worse after Challenger. They STILL know next-to-nothing about how to REALLY build a solid.

It's just that as a contractor to the government, you build what they tell you to build, no matter how messed up it really is, or you don't get the contract. Fix THAT, and lot of these government project development problems ease. No one has ever fixed it, though.

Speaking of the SRB, remember the "thrust oscillations" encountered when they first went to the 5 segment design? I think they finally got those under control, but it was combustion instability at the longer length which had become more resonant. If you excite instability in an already-aluminized propellant, then only other geometry changes can fix it, you're already maxed-out on particulate damping.

Actually those supposedly-neutral burning grain segments are not as neutral as advertised. A keyhole-slot design can result in better neutrality, and a longer L/D, reducing the number of case segments and joints. We used that design with great success as the booster for ASALM-PTV. Its only side effect was enhanced erosion of the nozzle lip where the slot flow struck. You just use more ablative there.

One thing about the solid business to worry about: it's the tactical-size plants that do the better design analysis. The big motor guys tend to operate like the designers of the Titanic: just scale up your last design and try it to see if it works. The smart contracting officer should specify in the contract that the big motor guys get the full suite of design analyses done at a small-motor plant. But the casting has to be done at the big motor plant, where the facilities exist.

Of course, that strategy presumes that "smart contracting officer" is not an oxymoron.

GW

Last edited by GW Johnson (2017-01-02 10:14:47)

SpaceNut · 2017-01-02 13:44:39

Original falcon 9 with dragon cargo http://spaceflight101.com/spacerockets/ … -v1-1-f9r/
Upgraded http://spaceflight101.com/spacerockets/falcon-9-ft/

Made of aluminum honeycomb and carbon-composite materials, the four legs have a total mass of around 2,100 Kilograms consisting of a single-load bearing strut and aerodynamic fairing assembly. The central struts of the legs interface with the load-carrying structure of the first stage while the fairings have two structural interfaces at the base of the engine compartment heat shield and one interface on the lower portion of the leg.
During flight, the legs are stowed against the rocket body, covered by the fairings that ensure no additional aerodynamic disturbance is introduced by the legs. Deployment is accomplished by a pneumatic system using high-pressure helium. When deployed, the legs have a span of about 18 meters, capable of supporting the forces of landing and the mass of the nearly empty first stage.

The Red Dragon versus the Dragon does not seem to have much in the way of life support difference from what I can tell as the tonnage is very close. Other than the super Draco thruster with fuel tanks its about the same unit.

Still thinking we can do a single man short stay mission with what we ave with slight modification...

The second stage I am wondering if it was full on Mars Orbit and outfitted with the same blacket system for a mars entry firing the rocket engine then throttling them back until we get to the proper sonic level for a full up retro propulsion could it land if it had the legs scaled to size? Then would it have fuel remaining once all cargo has been off loaded for a return back to orbit or would it need to be topped off.

Oldfart1939 · 2017-01-02 17:28:23

In a press release dated 2 January, 2017 at 09:00 EST, SpaceX announced the results of the investigation of the September 2016 "anomaly," and announced a return to flight from Vandenburg AFB, launching the Iridium Next satellite constellation on 8 January 2017.

SpaceNut · 2017-01-02 18:33:23

Yes they are using a heated helium gas to pressurise the fuel and oxydizer tanks rather than pumps. So filling them to fast does not allow for the internal gas pressure to settle and since its exposed to the rockets external climate it can get over pressured and explode. Via embrittlement due to how cold the liquid helium is...

SpaceNut · 2017-01-02 20:37:30

Better than the words I just said but simular to GW's
In words from the horses mouth SpaceX Explains September Explosion, Says It'll Try Again Sunday

The "anomaly" — SpaceX's word — was caused when supercold helium led carbon fibers and aluminum to cool at different rates on the second of the rocket's two stages, the company said. That opened gaps between two layers of overwrap, where liquid oxygen escaped and got trapped, it said.
That, in turn, caused one of the protective layers to "buckle," or fail. Static ignited the trapped oxygen, setting off a chain of catastrophic explosions, SpaceX said.
Monday that its engineers have managed to rejigger the configuration of the rocket's helium containers, moderating the temperature of the helium and presumably eliminating buckling in the overwrap layer.

GW Johnson · 2017-01-03 11:39:02

Well, it's hard to parse the words of a press release that seems to obscure the technical details in doubletalk. Probably deliberately.

It seems that "friction ignition" of oxygen trapped in contact with carbon is the problem. It also seems they are going back to slower load rates and warmer conditions that worked before. The long-term solution seems to be a redesign that eliminates the voids in which oxygen could get trapped next to carbon.

I saw no words at all to suggest there is a barrier film to isolate the LOX from the carbon in the overwrap. That worries me, for LOX directly on carbon was the explosive of choice at the Mesabi iron ore range before they found out about ANFO. All it needs is an ignition agent to go high-order detonation. The miners used porous charcoal, with the oxygen absorbing into the porosity. (Oops, that ought to sound familiar, in spite of the doubletalk!)

The guy who did the fastest-charcoal-lightoff stunt at Purdue a few years ago (winning an Ig Nobel for it) was very aware of the explosion risk. He put the light cigar on the charcoal before pouring LOX on it. He said it would detonate if you poured the LOX and then put the lit cigar on it.

LOX in direct contact with any form of carbon is just a REALLY BAD idea! There is just no way around that ugly little fact of life.

GW

Last edited by GW Johnson (2017-01-03 11:41:19)

Oldfart1939 · 2017-01-03 15:44:19

GW-

I agree that there's a significant materials incompatability in the system. Elsewhere on either this thread or one closely related, I suggested a shrink-wrap of a PTFE-type polymer bag around the outside of the Helium pressure vessel. That, or do a Teflon-type coating in a polymerization vessel which would impregnate/seal all the possible voids with solid PTFE.

GW Johnson · 2017-01-04 10:36:14

Well, such coatings could work if the load rates and temperature excursions are very slow. They want to load fast to cut costs. They want to extremize the low temperatures to densify the LOX as much as possible. All these goals may simply be incompatible with that design approach.

The problem is two-fold: (1) extreme thermal shrinkage going to liquid helium temperatures from ambient (the differential strain incompatibility from the bi-material design compounds this greatly), and (2) liquid helium temperatures are far below the glass transition temperature of all known polymers and plastics. Extreme thermal strain is involved, so with materials that badly embrittled by cold, strain rates with time must be very slow, or you will get fracture.

Frankly, I'm surprised the carbon composite overwrap doesn't fracture instead of just buckling. And I don't understand how the overwrap can contribute to hoop stress strength in that locally-buckled condition.

What I suspect happened here is the same sort of inappropriate-assumption design analysis mistake that NASA made analyzing the resilience of cold-soaked joint O-rings under sudden-loading conditions at ignition for Challenger's SRB's. That sort of thing gets too far along when there's no old guys on the staff who know better.

GW

Last edited by GW Johnson (2017-01-04 10:56:46)

GW Johnson · 2017-01-14 13:27:32

Congrats to Spacex!

Congratulations to Spacex on a successful return to flight and launch from Vandenburg AFB of the first 10 of the new Iridium satellite constellation. The corrections to the problem experienced last September worked fine. Launch was on-time into a window only 1 second long.

The first stage successfully turned around, re-entered, and landed on the drone ship just off Vandenburg. Video from the first stage was maintained all the way through touchdown. It was spectacular.

The second stage successfully placed itself and the payload into the transfer orbit. After reaching the right point about 40 minutes later, the second stage relighted briefly and finalized the orbit. All 10 satellites were successfully released in sequence as planned.

Well done, Spacex!

Upcoming things to watch for this year: more satellite launches, more cargo deliveries to the International Space Station, and the first flight of the new Falcon-Heavy rocket.

GW

SpaceNut · 2017-01-14 19:36:40

Yes a good thing but as I said before every stand down hurts the efforts to get man beyond LEO in this next decade and onto mars..

louis · 2017-01-14 19:45:42

Great start to the New Year for SpaceX!

GW Johnson wrote:

Congrats to Spacex!
Congratulations to Spacex on a successful return to flight and launch from Vandenburg AFB of the first 10 of the new Iridium satellite constellation. The corrections to the problem experienced last September worked fine. Launch was on-time into a window only 1 second long.
The first stage successfully turned around, re-entered, and landed on the drone ship just off Vandenburg. Video from the first stage was maintained all the way through touchdown. It was spectacular.
The second stage successfully placed itself and the payload into the transfer orbit. After reaching the right point about 40 minutes later, the second stage relighted briefly and finalized the orbit. All 10 satellites were successfully released in sequence as planned.
Well done, Spacex!
Upcoming things to watch for this year: more satellite launches, more cargo deliveries to the International Space Station, and the first flight of the new Falcon-Heavy rocket.
GW

SpaceNut · 2017-02-18 17:49:41

err'ing on the side of caution this time from Kennedy Space Center's Launch Complex 39A Last-second launch delay for SpaceX at historic moon pad

SpaceX halted the countdown with just 13 seconds remaining. The second-stage steering issue actually cropped up several minutes earlier. Of course engineers want to make certain the "slightly odd" position of an engine piston isn't representative of bigger trouble. The question that Saturday's problem is somehow related to the minor upper-stage helium leak detected the day before.
The next launch attempt — provided everything can be fixed quickly — would be Sunday morning.
French astronaut Thomas Pesquet had a light-hearted take on the delay.
"Looks like I'll have to wait one more day to get my French cheese " Pesquet wrote via Twitter.
Russia, meanwhile, plans to launch a supply ship to the International Space Station on Wednesday. If the SpaceX mission doesn't get going soon, it would likely have to get in line behind the Russian delivery.

GW Johnson · 2017-02-19 11:55:59

Congrats to Spacex for Sunday's successful CRS-10 launch to ISS. No troubles out of the rocket, capsule sent to correct orbit (should arrive at ISS in 2 days), and the first stage returned to Canaveral and landed successfully. Well done.

GW

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#76 2016-12-08 14:24:46

Re: Space X - If at first you don't succeed...

#77 2016-12-08 16:05:38

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#78 2016-12-09 04:56:45

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#79 2016-12-09 20:41:30

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#80 2016-12-10 10:03:29

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#81 2016-12-10 16:25:44

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#82 2016-12-12 22:13:12

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#83 2016-12-13 09:56:24

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#84 2016-12-14 12:16:05

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#85 2016-12-25 19:30:47

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#86 2016-12-26 15:57:51

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#87 2017-01-01 21:17:24

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#88 2017-01-02 10:02:43

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#89 2017-01-02 13:44:39

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#90 2017-01-02 17:28:23

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#91 2017-01-02 18:33:23

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#92 2017-01-02 20:37:30

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#93 2017-01-03 11:39:02

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#94 2017-01-03 15:44:19

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#95 2017-01-04 10:36:14

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#96 2017-01-14 13:27:32

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#97 2017-01-14 19:36:40

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#98 2017-01-14 19:45:42

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#99 2017-02-18 17:49:41

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