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Chimpy
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Reply #560 on: September 02, 2016, 12:34:23 PM

Since this test had not gotten near the point of ignition, the saying their plan to do this integrated to cut time off the window is moot anyway.

'Reality' is the only word in the language that should always be used in quotes.
Mandella
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Reply #561 on: September 02, 2016, 12:54:03 PM

The fact that they ever did vertical testing without the payload is the weird thing.

Pretty much all other horizontal integrators flip the rocket upright once when it reaches the pad and don't tilt it back down to avoid additional stress on the rocket. Also, it makes no sense to test the systems in a non integrated state and give it a green light for the launch as tilting it down and adding things changes the configuration/loading.


The 'entire rocket hotfire test' is an SpaceX speciality. Neither ULA, Arianespace nor the Russians do it.

For Ariane5 I know the main engine will be fired twice as part of acceptance testing before delivery, but that's before it's part of the rocket stack.



None of those guys are shooting for reusability and rapid turnaround either.

Unfortunately, Thursday's very loud and flashy anomaly shows that SpaceX hasn't quite reached that goal yet either.
Morat20
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Reply #562 on: September 02, 2016, 04:51:53 PM

From what I've heard, they decreased the temperature of the LOX fuel recently, which I'd consider a probable cause. Not just for the "because they changed something, then it exploded" but because material properties can vary over a thermal range, and it just takes missing a single part, weld, or stress to have it suddenly fail in colder conditions. (Admittedly, I'm biased -- my job is making software tools for materials properties, fracture control, and failure analysis, and the engineering department I work with does that sort of thing for spacecraft and airplanes for a living. So I'm reaching to what I'm familiar with).

There was an American automaker that had a raft of recalls back in the 70s or 80s because they made diesel engines by modding their gasoline ones, and the higher temps ate the engine fairly quickly.

In Other News:

Remember the EM/Cannae Drive? The reactionless one NASA was testing?

They're releasing a paper, and translated from Science to English, the synopsis reads something like: "It keeps producing thrust, and we don't know why. We've tested it and tested it, but it produces thrust outside our error bars." (30 to 50 pico-Newtons per kilowatt, I think. Would scale up to about ion-drive thrusts at half a megawatt) With an implied "Surely someone can find out how we messed up a year's worth of tests, because we can't figure it out and also we can't really believe this works".

NASA's only real explanation of thrust (virtual particle ion drive) is at odds with the inventor's own, and there's a few other weird theories floating around as well. Everyone's really loathe to believe it, because in terms of space holy grails, reactionless drives rate just below "working FTL" and "artificial gravity".
Torinak
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Reply #563 on: September 02, 2016, 05:18:41 PM

From what I've heard, they decreased the temperature of the LOX fuel recently, which I'd consider a probable cause. Not just for the "because they changed something, then it exploded" but because material properties can vary over a thermal range, and it just takes missing a single part, weld, or stress to have it suddenly fail in colder conditions. (Admittedly, I'm biased -- my job is making software tools for materials properties, fracture control, and failure analysis, and the engineering department I work with does that sort of thing for spacecraft and airplanes for a living. So I'm reaching to what I'm familiar with).

There was an American automaker that had a raft of recalls back in the 70s or 80s because they made diesel engines by modding their gasoline ones, and the higher temps ate the engine fairly quickly.

In Other News:

Remember the EM/Cannae Drive? The reactionless one NASA was testing?

They're releasing a paper, and translated from Science to English, the synopsis reads something like: "It keeps producing thrust, and we don't know why. We've tested it and tested it, but it produces thrust outside our error bars." (30 to 50 pico-Newtons per kilowatt, I think. Would scale up to about ion-drive thrusts at half a megawatt) With an implied "Surely someone can find out how we messed up a year's worth of tests, because we can't figure it out and also we can't really believe this works".

NASA's only real explanation of thrust (virtual particle ion drive) is at odds with the inventor's own, and there's a few other weird theories floating around as well. Everyone's really loathe to believe it, because in terms of space holy grails, reactionless drives rate just below "working FTL" and "artificial gravity".

So now we just need some kind of space-worthy power system that puts out a half-MWe over a very long time. Too bad there aren't any--the closest the US has ever done was the SAFE-400 fission heatpipe system intended to deliver 100KW electricity for 10 years, and it was scrapped some number of years ago (2002?). There may be some comparable work done by a Russian company as recently as 2011 but even if it hasn't been cancelled it's still many years away, and that wasn't even a half-MW. Apparently there are serious materials considerations that make it hard to just scale up fission heatpipe designs.

Maybe NASA can get Pons and Fleischmann to revisit their rule-breaking power supply to match with the rule-breaking engine.  Oh ho ho ho. Reallllly?
Morat20
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Reply #564 on: September 02, 2016, 08:13:33 PM

So now we just need some kind of space-worthy power system that puts out a half-MWe over a very long time. Too bad there aren't any--the closest the US has ever done was the SAFE-400 fission heatpipe system intended to deliver 100KW electricity for 10 years, and it was scrapped some number of years ago (2002?). There may be some comparable work done by a Russian company as recently as 2011 but even if it hasn't been cancelled it's still many years away, and that wasn't even a half-MW. Apparently there are serious materials considerations that make it hard to just scale up fission heatpipe designs.

Maybe NASA can get Pons and Fleischmann to revisit their rule-breaking power supply to match with the rule-breaking engine.  Oh ho ho ho. Reallllly?
You don't really need a half newton of force. I mean the more the better, but it all adds up. That half-newton thrust is NASA's NEXT Ion engine, their 'strongest' yet.

ION engines generally measure thrust in mN. NSTAR ran at 20 to 92 mN. I think Dawn (using NSTAR) pushed it's delta v up to 10 km/s. Lacking reaction mass, an EM drive or equivilant would be more efficient -- 200kg of fuel can only be used once, but 200kg of solar panels or RTG can fire continuously. There's a reason NASA is putting so much money into ion drives for probe missions.

I'd also say that, if this thing actually works, that it's really unlikely that 1MW to 1N is anything resembling max efficiency, simply because nobody is entirely sure how it works -- much less have engineered for the most efficient mechanism.
MahrinSkel
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Reply #565 on: September 02, 2016, 08:21:22 PM

Latest WAG I heard for explaining it was essentially that it is generating Tesla waves (two matched and mutually inverted photons), which shows you how desperate they are a getting for an explanation that doesn't require junking the Standard Model.

--Dave

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Torinak
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Reply #566 on: September 02, 2016, 11:38:02 PM

So now we just need some kind of space-worthy power system that puts out a half-MWe over a very long time. Too bad there aren't any--the closest the US has ever done was the SAFE-400 fission heatpipe system intended to deliver 100KW electricity for 10 years, and it was scrapped some number of years ago (2002?). There may be some comparable work done by a Russian company as recently as 2011 but even if it hasn't been cancelled it's still many years away, and that wasn't even a half-MW. Apparently there are serious materials considerations that make it hard to just scale up fission heatpipe designs.

Maybe NASA can get Pons and Fleischmann to revisit their rule-breaking power supply to match with the rule-breaking engine.  Oh ho ho ho. Reallllly?
You don't really need a half newton of force. I mean the more the better, but it all adds up. That half-newton thrust is NASA's NEXT Ion engine, their 'strongest' yet.

ION engines generally measure thrust in mN. NSTAR ran at 20 to 92 mN. I think Dawn (using NSTAR) pushed it's delta v up to 10 km/s. Lacking reaction mass, an EM drive or equivilant would be more efficient -- 200kg of fuel can only be used once, but 200kg of solar panels or RTG can fire continuously. There's a reason NASA is putting so much money into ion drives for probe missions.

I'd also say that, if this thing actually works, that it's really unlikely that 1MW to 1N is anything resembling max efficiency, simply because nobody is entirely sure how it works -- much less have engineered for the most efficient mechanism.

50 pico Newton is nine orders of magnitude lower than what NSTAR puts out, so if the Cannae drive scales linearly and is at 50 pN per KW now, it'd need on the order of terawatts of power to match what Dawn's ion engine does now.

I would be more than slightly surprised if it turns out that optimizing something involving unknown principles results in a billion-fold increase in performance.

But the proof of the pudding is in the eating, as they say--a Cannae drive-equipped cubesat is going to be launched in the near future, if they can get funding.

If it works, and generates more thrust than, say, a laser pointing into vacuum, not only do we have a nifty propulsion system, but we also have a working perpetual motion machine!
Morat20
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Reply #567 on: September 03, 2016, 08:26:44 AM

50 pico Newton is nine orders of magnitude lower than what NSTAR puts out, so if the Cannae drive scales linearly and is at 50 pN per KW now, it'd need on the order of terawatts of power to match what Dawn's ion engine does now.
I have no idea how they derived their scale factor, since as Mahrin points out, everyone's really confused over the mechanism with multiple competing theories. (Mahrin: I read one that had some sort of weird modified concept of inertia and Unruh radiation, which I've never even heard of).

What NASA tested was made by an American based on the rough EM drive specs by the inventor, and that the Chinese have reported different thrust numbers and nobody understands how this stupid thing produces momentum. People aren't testing the exact same engine and not with the same power inputs. Nobody knows what's causing it --  Tesla waves, virtual particles, whatever that inertia thing is, whatever the inventor claims it is). So I have no idea the scaling factor, I have no idea how the few sources I got rated it at about 1N per MW, but I do really suspect that whatever design they've got is not optimal.

Because nobody knows what's going on, only NASA finally got annoyed enough to shove it in a vacuum chamber and it still works and it shouldn't at all. I think the best description is "It's like standing in a box, pushing on both sides of the box, and having the stupid thing move".

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Reply #568 on: September 03, 2016, 01:39:43 PM

From what I've heard, they decreased the temperature of the LOX fuel recently, which I'd consider a probable cause. Not just for the "because they changed something, then it exploded" but because material properties can vary over a thermal range, and it just takes missing a single part, weld, or stress to have it suddenly fail in colder conditions. (Admittedly, I'm biased -- my job is making software tools for materials properties, fracture control, and failure analysis, and the engineering department I work with does that sort of thing for spacecraft and airplanes for a living. So I'm reaching to what I'm familiar with).

Yes, propellant densifcation, used in the latest iteration of the rocket.

- 207° C for the LOX. I don't have numbers on the what temperature they used before, but logic dictates it must have been below boiling point, so < -183° C.

- 7° C for the Kerosin, compared to (I am guessing) ambient temperature beforehand.

Another source for issues could be the Helium COPVs which that are used to pressurize the other tanks. The CRS-7 accident was caused by one of those bottles breaking free and in 2014 a launch had to scrubbed due to a helium leak.

They used to be a supplier manufactured item, but SpaceX (possibly as response to the 2014 issue?) now produces them in-house. Overall not a trivial component, even NASA had worries regarding the Shuttle COPVs, although there there issues were mostly due to age and degradation over time.


I guess we'll know more in a few weeks.  smiley
« Last Edit: September 03, 2016, 01:55:25 PM by calapine »

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Morat20
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Reply #569 on: September 03, 2016, 02:25:26 PM

Rocket science is harder. Rocket engineering is quite possibly harder. :)
Ghambit
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Reply #570 on: September 03, 2016, 03:17:16 PM

There was talk it was possibly the payload's fault for the mishap.  Given where it seemed the flash originated from, that's a tough sell.  Sadly, this will set a bunch of projects behind schedule (including my division's).  We were supposed to fly on a falcon-heavy.   swamp poop   If it turns out to be the upper-stage's improved fuel system, they'll potentially lose 30% thrust and the ability to backburn during  a geosync insertion.

Work on Tuesday should be interesting at the water cooler.

That said, I'd rather have a SpaceX induced delay than a NASA or JPL one.  And this kind of thing is why a lot of tech. is moving away from the ginormous, expensive space platforms.  Cheap nanosat swarms get more and more en vogue every year (blow em up all you want).  The tracking is the problem (so the AirForce hates em for obvious reasons).
« Last Edit: September 05, 2016, 12:25:09 PM by Ghambit »

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Mandella
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Reply #571 on: September 03, 2016, 06:41:15 PM

Latest WAG I heard for explaining it was essentially that it is generating Tesla waves (two matched and mutually inverted photons), which shows you how desperate they are a getting for an explanation that doesn't require junking the Standard Model.

--Dave

Honestly, most physicists I read would be happy to junk the Standard Model -- they'd just rather it be cracked by something like the 9 billion dollar LHC than somebody rattling an old tin box!

There are standards to be kept, no pun intended....
Morat20
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Reply #572 on: September 03, 2016, 07:40:34 PM

Latest WAG I heard for explaining it was essentially that it is generating Tesla waves (two matched and mutually inverted photons), which shows you how desperate they are a getting for an explanation that doesn't require junking the Standard Model.

--Dave

Honestly, most physicists I read would be happy to junk the Standard Model -- they'd just rather it be cracked by something like the 9 billion dollar LHC than somebody rattling an old tin box!

There are standards to be kept, no pun intended....
Well, there are SM explanations. Some barely even stretch it a little (the QM stuff). I think everyone would be simultaneously pleased and annoyed. Pleased that we found a crack, a place where weird stuff happens so we can poke at it and find more interesting stuff. Annoyed that it was a guy with a tin box, and not focused research. I think the physicists, at least, felt they were pretty far past someone accidentally discovering something weird.

I keep suspecting there's a magnetic or thermal component, but some weird magnetic interaction (say with the Earth's field) is easy enough to test for (you know, you point it different directions, for one. Also, magnetic shielding) and thermal stuff is also generally possible to account for. (Thermal radiation was what was boosting Voyager's speed -- took them a long time to figure that out). Plus, I think Eagleworks did break down and do some vacuum chamber tests (not sure if they had it running a vacuum, but I know they dropped the temp really low) -- which means they can generally measure that.

Ghambit:

NASA's problem has always been Congress and public opinion. They're simply not allowed failures, and trying to design anything when Congress randomly changes your budgets and goals is a PITA. Don't even get me started on the weird way they've budgeted Orion and the new heavy lift vehicle. it's killing in-house tool development, and it ain't because the directorate chiefs don't see the problem.

ISS was a nightmare. They kept changing designs over and over and over, and yanking in and out partners. It's a freaking miracle it's up there. At this point. I'm willing to bet half the total cost -- minimum -- of ISS was because of endless redesign cycles. Someone in Congress would get a bug up their ass, declare they wanted 6 people instead of 4, and then NASA would have to chunk hundreds of millions in designs, prototypes, and the like, and start mostly over. Then three years later, it'd be 5 people.

Honestly, I think NASA would work a heck of a lot better if Congress would basically say "We'll assess programs and large project budgets every 5 years". Heck, NASA's on what -- the third or fourth attempt to replace the Shuttle, because Congress keeps cancelling the program then restarting it again a year later, when they realize magic hasn't created rockets? Do you know how many billions were tossed down that rathole? NASA's reused what it could, and finally just started claiming that whatever Congress wanted, they  needed a new manned rocket and a new heavy lift vehicle to do it. (Want to go to Mars? We need a new manned rocket and a new heavy lift vehicle. The moon? Same? The underwater city of Atlantis? We'll need those rockets to launch the magic Atlantis finding stuff and man it)  and got away with (as best I can tell) just renaming it. It still involved rebidding congrats and some more tear-down and redesign, but they've at least kept some forward momentum.

(Fun random space fact: You know how capsules use parachutes when coming down from orbit? Like multiple sets? You know how they make sure the are severed at the right time? EXPLOSIVES. Yeah, when you need a parachute cord cut, you use two chunks of metal and wad of explosives o slam the sharp chunk of metal into the flat one at high speeds, with the cable in between. Simple is sometimes best. And also awesome. That mechanism dates back to Mercury, IIRC. I know Apollo used it).
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Reply #573 on: September 05, 2016, 07:51:14 AM

Phliae has been found!  smiley







Labeled close up, spoilered for size:

Quote
The images were taken on 2 September by the OSIRIS narrow-angle camera as the orbiter came within 2.7 km of the surface and clearly show the main body of the lander, along with two of its three legs.

The images also provide proof of Philae’s orientation, making it clear why establishing communications was so difficult following its landing on 12 November 2014.
---
The discovery comes less than a month before Rosetta descends to the comet’s surface. On 30 September, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in the Ma’at region, where it is hoped that critical observations will help to reveal secrets of the body’s interior structure.
http://www.esa.int/Our_Activities/Space_Science/Rosetta/Philae_found


Edit: If one considers how bright the surrounding area is Philae was really unlucky to get stuck at that one particular spot...
« Last Edit: September 05, 2016, 08:50:21 AM by calapine »

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pxib
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Reply #574 on: September 05, 2016, 08:55:16 AM

Well, sort of. It's very likely that big outcropping is the thing that stopped it from bouncing. Otherwise who knows where it might have ended up.

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calapine
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Reply #575 on: September 05, 2016, 09:43:15 AM

Well, sort of. It's very likely that big outcropping is the thing that stopped it from bouncing. Otherwise who knows where it might have ended up.


True, good point...



Guessing game:

Which one of those potential locations turned out to be the real Philae?






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Viin
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Reply #576 on: September 06, 2016, 09:40:23 AM

Wow that really shows how rugged that rock is in that area.

- Viin
calapine
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Reply #577 on: September 12, 2016, 09:58:23 AM



Jeff Bezos announced his new rocket "New Glenn". Conveniently 2 weeks before Elon Musk's presention of BFR on the next International Aeronautical Congress.


This is starting to be a dick waving context...

Edit: Just look at that:

Stage diameter: 7 Meter
Height New Glenn 2: 82.3 Meter
Height New Glenn 3: 95.4 Meter
Thrust first stage: 17,125 kN
Engines First Stage: 7x BE-4 CH4/LOX
Engines Second Stage: 1x BE-4 Vac.
Engine Third Stage: 1x BE-3 Vac LH2/LOX

First launch: Before 2020.  ACK!

« Last Edit: September 12, 2016, 10:05:07 AM by calapine »

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01101010
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Reply #578 on: September 12, 2016, 10:17:59 AM

Musk is building BFRs now? Holy shit! That is what really fucked up Planetside.  why so serious?


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Mandella
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Reply #579 on: September 12, 2016, 10:19:28 AM

AND he's teasing out info on the next size up planned that would be able to make lunar orbit, the New Armstrong!

Bezos' slow and steady might just end up winning the space(X) race.

As a humorous point, some poster on another site got a spit take from me by mentioning in reply to the question what would Bezos name a conjectured Mars capable rocket, --"Anything but New Musk."
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Reply #580 on: September 12, 2016, 10:58:25 AM

I think the Mars rocket would be "New Watney".

'Reality' is the only word in the language that should always be used in quotes.
calapine
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Reply #581 on: September 12, 2016, 12:01:41 PM

As a note, size is a bit deceptive here as Methan is a less dense fuel compared to Kerosin. Performance wise the rocket seems to be 20-30% above Falcon Heavy for Low Earth Orbit and ~ 50% above for Mars injection (in the 3 stage version).

I am sort of skeptical regarding the development timeline: first launch before 2020. Again taking Falcon Heavy as comparison, Musk initially talked about first launch in 2013. And see where he is now...

Second issue is the business case.

Bezos "New Glenn is designed to launch commercial satellites and to fly humans into space".

For this the rocket is way overized, typical GTO satellites weight 3 - 5.5 tons, with the heaviest topping out somewhere at 6.7 tons.  Of course some of the nominal performance will be spent/wasted for re-usability, but even factoring in that it's still too big.
« Last Edit: September 12, 2016, 12:03:17 PM by calapine »

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Chimpy
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Reply #582 on: September 12, 2016, 12:19:41 PM

The large fairing diameter is going to be his big selling point.

One of the reasons commercial launches are all in the same weight range is that they are all limited in physical dimensions in the same way. Allow them to build a bigger box that they can fill with more electronics and bigger/better inertia wheels and the weight will go up as a consequence.

'Reality' is the only word in the language that should always be used in quotes.
calapine
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Reply #583 on: September 12, 2016, 12:31:03 PM

The large fairing diameter is going to be his big selling point.

One of the reasons commercial launches are all in the same weight range is that they are all limited in physical dimensions in the same way. Allow them to build a bigger box that they can fill with more electronics and bigger/better inertia wheels and the weight will go up as a consequence.

Not, really no. Current satellites don't even use the width offered by widest flying now:

Ariane 5 uses a 5,4m diameter fairing (same as stage width). Aerodynamically it would have been easily possible to increase to 7 meter, (same as the New Glenn), if there was customer desire, but there was no pressure by the market.

Ariane 6 will receive a longer fairing, but diameter stays the same.

Falcon 9 uses a 5,2m diameter fairing and apparently SpaceX doesn't see this as a drawback.

Proton uses a 4,35 m fairing.

Edit: I queried about GTO performance, the answer was ~ 30 tons, according to Dr. Zubrin.


Edit 2: I did not mean to sound rude, just tired.
« Last Edit: September 12, 2016, 01:04:57 PM by calapine »

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Reply #584 on: September 20, 2016, 09:58:30 AM

Sitxy Symbols does a pretty good job talking about Lisa Pathfinder:

Golden Cubes and Gravitational Waves - Sixty Symbols

6m39 sec video.


NASA is very likley to rejoin für eLISA btw:

Quote
This week, at the 11th LISA symposium in Zürich, Switzerland, a NASA official said he was ready to rejoin the LISA mission, which the agency left in 2011. Meanwhile, ESA says it is trying to move the launch of the mission up several years from 2034. “This is a very important meeting,” says David Shoemaker, a gravitational wave physicist at the Massachusetts Institute of Technology in Cambridge. “It feels like a turning point.”

[...]

Originally, LISA was conceived as a joint ESA-NASA mission. Both partners would pay 50% of the mission cost, estimated at some $2 billion. But in April 2011, NASA dropped out of the collaboration because of budgetary problems, and the program was almost killed. “The next year, the LISA symposium felt like a funeral,” recalls astrophysicist Paul McNamara of ESA’s space research and technology center ESTEC in Noordwijk, the Netherlands.

Then, in 2013, a trimmed-down, €1 billion version of LISA was selected by ESA as its L3 mission—the third large mission in its Cosmic Vision 2020 program. Called eLISA (where the “e” euphemistically stands for “evolved”), it would have less capability and sensitivity than the original design. Launch was foreseen for 2034. NASA expressed interest to become a minor partner, providing technological support.

But things have changed a lot in the past few years. ESA’s technology demonstrator LISA Pathfinder, launched in December 2015, has performed flawlessly, says McNamara, who is the mission’s project scientist. Then, in February, the ground-based Laser Interferometer Gravitational-Wave Observatory experiment announced that it had bagged its first direct detections.

NASA moves to rejoin sped-up gravitational wave mission

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Reply #585 on: September 23, 2016, 10:56:07 AM

SpaceX just posted an anomly updated regarding the Falcon 9 explosion:



http://www.spacex.com/news/2016/09/01/anomaly-updates


Which ties in to something I posted earlier:
Another source for issues could be the Helium COPVs which that are used to pressurize the other tanks. The CRS-7 accident was caused by one of those bottles breaking free and in 2014 a launch had to scrubbed due to a helium leak.

They used to be a supplier manufactured item, but SpaceX (possibly as response to the 2014 issue?) now produces them in-house. Overall not a trivial component, even NASA had worries regarding the Shuttle COPVs, although there there issues were mostly due to age and degradation over time.


I guess we'll know more in a few weeks.  smiley

First thought: So it's Helium again. Either a) they didn't find the root cause in CRS-7 and it happend again or b) their revised Quality Assurance and production changes post-accident weren't enough to avoid or catch another critical manufactuing error just 10 flights after the last disaster. Edit: or c) there is another unconnected design flaw in the same sub-system.

Both is bad.
« Last Edit: September 23, 2016, 11:27:43 AM by calapine »

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Reply #586 on: September 24, 2016, 09:28:25 AM

Don't forget, they swapped to deeper cryo for this launch. There's also the possibility of failure due to change in the thermal regime -- someone's safety factor on a part or inspections procedure might not have been properly adjusted to fit the new temperature profiles.

SpaceX wouldn't be the first company to have a fuck-up due to changing operating temperatures.

It's amazing the little shit that can break something. I watched a breakdown analysis at work -- someone had subbed in kevlar straps for nylon to add additional margin for a test. It didn't go well, because there was an initial force on the straps that the nylon cords stretched on (so the force was handled over a longer time span) and the kevlar...did not. I watched a video of metal bending like putty then snapping back as the kevlar layers broke.

They'd been doing that test for years with nylon, never realized the forces at the moment of initiation were that high. Not until they changed test parameters and wanted additional margin, and then that was months of analysis to figure out why it broke, to be able to model and test the break reliably, then put in a real fix that the test people would accept. (That test, the way it broke -- could have been really, really bad. Like fatalities bad. I don't blame the folks who own the equipment for saying "Not until you can explain this, model it, show physical tests, and basically make me certain it's not gonna happen again")
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Reply #587 on: September 24, 2016, 10:53:30 AM

Tank weld QA/QC procedures were the thing I heard quite a bit of rumors about being pretty terrible at Space-X years ago. Which means I am not really surprised to hear that tank integrity might have been a cause, especially if it is true that they had recently re-insourced the production of the tanks. Welding pressure vessels properly is no joke, even with common materials like steel. When you use the crazy light-weight alloys that are used in rockets it is even more difficult to do correctly.

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Reply #588 on: September 24, 2016, 11:18:45 AM

Tank weld QA/QC procedures were the thing I heard quite a bit of rumors about being pretty terrible at Space-X years ago. Which means I am not really surprised to hear that tank integrity might have been a cause, especially if it is true that they had recently re-insourced the production of the tanks. Welding pressure vessels properly is no joke, even with common materials like steel. When you use the crazy light-weight alloys that are used in rockets it is even more difficult to do correctly.
I've heard the same thing from some guys in the materials section -- they did some analysis work on tank welds, and the gist was "NASA wouldn't fly with that". (It was, I admit, a bit up in the air as to whether NASA was being too cautious or SpaceX too risky).

I know the guys that do weld analysis go bonkers doing lifetime calcs because welding itself can add in a lot of stresses, depending on a complex stew of variables (material welded, material used in the weld, weld technique, how good the welder was, dimensions of weld) that can be hard to factor in. That's before you get things like cracks in the weld, or impacting the weld....or god help you, thermal expansion of the weld and base material aren't the same....
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Reply #589 on: September 24, 2016, 11:26:17 AM

This was not "being too cautious" kind of rumors. It was "the welds looked bad enough that a person welding like that on a certification exam would probably not pass" kind of rumors. And the fact that Space-X was (at least at the time) full of young fresh out of engineering school know-it-alls who scoffed at anything told to them by a guy with grey hair made it likely that they ignored advice because "it was strong enough in the tests we ran".

'Reality' is the only word in the language that should always be used in quotes.
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Reply #590 on: September 25, 2016, 06:57:21 AM

This was not "being too cautious" kind of rumors. It was "the welds looked bad enough that a person welding like that on a certification exam would probably not pass" kind of rumors. And the fact that Space-X was (at least at the time) full of young fresh out of engineering school know-it-alls who scoffed at anything told to them by a guy with grey hair made it likely that they ignored advice because "it was strong enough in the tests we ran".
The bolded bit is a false assumption; for any given welding procedure certification, the weld is judged much more harshly for acceptance than a production weld because weld tests are welded under ideal conditions.

I know the guys that do weld analysis go bonkers doing lifetime calcs because welding itself can add in a lot of stresses, depending on a complex stew of variables (material welded, material used in the weld, weld technique, how good the welder was, dimensions of weld) that can be hard to factor in. That's before you get things like cracks in the weld, or impacting the weld....or god help you, thermal expansion of the weld and base material aren't the same....
No weld going into space would ever be accepted with a crack in it.

"i can't be a star citizen. they won't even give me a star green card"
Morat20
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Reply #591 on: September 25, 2016, 05:27:35 PM

No weld going into space would ever be accepted with a crack in it.
A crack that you know is there. You can't go over every inch of a vehicle with the highest resolution scanners. It'd take forever and cost a fortune. And it's unnecessary.

Analysts (everything from guys doing lifetime analysis or setting inspection schedules to design work) basically take your material (and the shape of it), take the stresses into account, and work to find the critical crack size. That is, the size of the crack where stuff goes pear shape and it grows to failure.

In this case, you've got a guy who looks at the PV and the weld and works out the critical size --- it might be, say, any crack over 0.1mm in the weld will grow to failure in a single launch. So that'll determine inspection -- they'll use the tools and techniques to find cracks that small or larger (there's usually knockdown factor, so they'll really search for anything over 0.05mm). This is true whether it's a single-use item or a reusable one.

Airframe folks do the same thing -- that's how they determine flight hours between inspections and recerts.

(This is actually what I do for a living -- we provide tools to people doing this sort of thing).

So yeah, they won't fly with a noticeable crack. But if their inspection regime was looking for, say, 0.5mm (1mm being the "oh shit" crack size with a high chance to grow to failure with, so a safety factor of 2) and bigger on the weld but the change in thermal regime meant that the critical size was really 0.6mm or so, and suddenly their safety margins are jack shit. So some weird residual stresses from a weld or from fabrication might be enough to cause failure.

Fun fact: NASA trains inspectors to do this crap -- take a part and find all cracks, notches, or flaws of a given size or bigger. You don't get your cert if you miss even one, and the people that do them like to be sneaky. I work with a guy that was fabbing some test articles for the latest batch of inspectors -- it's apparently a massive PITA to make realistic looking cracks, notches, and flaws that have to be an exact size (where the smallest ones are REALLY small) without damaging the surroundings and making them more obvious than they'd be on a real part. It's not a good test if you have tool marks pointing to suspicious areas. He spent a lot of time working his ass off on those.
« Last Edit: September 25, 2016, 05:29:50 PM by Morat20 »
calapine
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Reply #592 on: September 27, 2016, 11:01:13 AM

Full Steam ahead for Elon:

SpaceX released a Youtubeclip of it's Interplanetary Transport System

42 Raptor engines in the first stage, 127 800 kN thrust. Or just shy about 4x Saturn-Vs, refueling in Orbit, humans on Mars, the whole enchilada:

https://www.youtube.com/watch?v=0qo78R_yYFAx


« Last Edit: September 27, 2016, 11:11:16 AM by calapine »

Restoration is a perfectly valid school of magic!
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Reply #593 on: September 27, 2016, 03:31:43 PM

Here is an Imgur album with all the slides from his presentation




Dick measuring contest
« Last Edit: September 27, 2016, 03:39:32 PM by calapine »

Restoration is a perfectly valid school of magic!
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Reply #594 on: September 28, 2016, 10:27:51 AM


"I have more qualifications than Jesus and earn more than this whole board put together.  My ego is huge and my modesty non-existant." -Ironwood
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