Lexicus
Deity
The short answer is 10,000 years ago.
The thread for space cadets!
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Berzerker
Deity
https://phys.org/news/2017-11-analysis-chicxulub-asteroid-struck-vulnerable.html
seems 'we' got very lucky... The asteroid that wiped out the dinosaurs had a roughly 1 in ~7.7 chance of hitting dense hydro-carbon deposits (which it did). The result was far more soot in the air, enough to make the world cold enough to doom larger land animals. So all that oil we're finding down there near the Yucatan was there before the impact.
Sorry, I understand this thread is more about space exploration and not earth sciences. I just dont want to start a thread for news items like this.
seems 'we' got very lucky... The asteroid that wiped out the dinosaurs had a roughly 1 in ~7.7 chance of hitting dense hydro-carbon deposits (which it did). The result was far more soot in the air, enough to make the world cold enough to doom larger land animals. So all that oil we're finding down there near the Yucatan was there before the impact.
Sorry, I understand this thread is more about space exploration and not earth sciences. I just dont want to start a thread for news items like this.
Tuesday 17th
The climate has always been changing, but anthropogenic (cause by humans) global warming stared with the large scale burning of fossil fuels during the industrial revolution. You can see from the graph below the impact this has on atmospheric CO2, but I think you could put the start sometime in the 1800s.
r16
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the issue is not earth getting warmer , that humans add too much to the equation and when the balance is found , it might be too untenable for humans .
the one on the previous page , involves some "response"
right on cue . Most , if not all , participants of this thread will know the Voyager carries a plate and recordings in case of an alien contact . In 55 different languages , according to the newspaper report on Sunday here . Everybody says "Hello" , the Turkish one is "Good Morning" . Mind you , that has put me off since like ı was 12 , buying a kids magazine , collecting parts of an encyclopedia on Space . Are we morons or something , losing so much in translation and all that ? Turns out it was done by a guy in the same university with Carl Sagan . A professor of Archeology today , he was teaching English at a college in Istanbul and one of his colleagues was a doyen of Turkish literature and he would greet the guy with that phrase . If this was good enough for the poet , why , it was good enough for the guy ... Mind you , the interview then goes onto hint Sagan was a fool or something who didn't know anything about the Turks living in the Balkans or the Caucaus . "Jeez, you are too smart to be a Turk, your ancestors were no doubt European slaves" was apparently a very fashionable thing back in the day , ı hear , especially if it involved coloured eyes . Back then , nobody would give a rat's backside about a conclusion that no American rocket would ever carry a Turkish satellite , now that NASA pointblank refused to accept the Republic was the true representative of Turks or the geographic location and chose as "Ottomanic" as possible or is it perhaps a joke that Aliens would immediately grasp that Turks didn't count as human ? After Friday , it becomes clear no American civilian rocket will either do it as well , we hear Sagan doesn't count for anything ? Don't know , maybe some cubesat was on some American rocket ? Husband of a cousin was involved in such a thing , maybe ı should inquire about that ... You know , their reward for being the first Turkish stuff in space or something was apparently getting all sacked with their office area being converted into a prayer room . And hiring as many as possible back , because it would be a rather good newspaper account when the son and son-in-laws of the Party come and declare they gloriously did some Space thing and the godless Republic never had anything to compare . It's of course the fault of the Congregation .
oh , why not go the way of saying it's a New Turkey satellite ? It happens a lot , Kurds prefer to run , like Americans would do , why the need to respect , you know , now ?
the one on the previous page , involves some "response"
right on cue . Most , if not all , participants of this thread will know the Voyager carries a plate and recordings in case of an alien contact . In 55 different languages , according to the newspaper report on Sunday here . Everybody says "Hello" , the Turkish one is "Good Morning" . Mind you , that has put me off since like ı was 12 , buying a kids magazine , collecting parts of an encyclopedia on Space . Are we morons or something , losing so much in translation and all that ? Turns out it was done by a guy in the same university with Carl Sagan . A professor of Archeology today , he was teaching English at a college in Istanbul and one of his colleagues was a doyen of Turkish literature and he would greet the guy with that phrase . If this was good enough for the poet , why , it was good enough for the guy ... Mind you , the interview then goes onto hint Sagan was a fool or something who didn't know anything about the Turks living in the Balkans or the Caucaus . "Jeez, you are too smart to be a Turk, your ancestors were no doubt European slaves" was apparently a very fashionable thing back in the day , ı hear , especially if it involved coloured eyes . Back then , nobody would give a rat's backside about a conclusion that no American rocket would ever carry a Turkish satellite , now that NASA pointblank refused to accept the Republic was the true representative of Turks or the geographic location and chose as "Ottomanic" as possible or is it perhaps a joke that Aliens would immediately grasp that Turks didn't count as human ? After Friday , it becomes clear no American civilian rocket will either do it as well , we hear Sagan doesn't count for anything ? Don't know , maybe some cubesat was on some American rocket ? Husband of a cousin was involved in such a thing , maybe ı should inquire about that ... You know , their reward for being the first Turkish stuff in space or something was apparently getting all sacked with their office area being converted into a prayer room . And hiring as many as possible back , because it would be a rather good newspaper account when the son and son-in-laws of the Party come and declare they gloriously did some Space thing and the godless Republic never had anything to compare . It's of course the fault of the Congregation .
oh , why not go the way of saying it's a New Turkey satellite ? It happens a lot , Kurds prefer to run , like Americans would do , why the need to respect , you know , now ?
hobbsyoyo
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It's space related and interesting. No need to apologize.
So government auditors have found that neither SLS nor Orion have budget reserves adequate to cover expected cost overruns. In other words there will be more delays and these programs will end up eating the budget of other programs unless Congress appropriates more funding. I'd say the odds are good they will get more money from Congress - Congress did after all fund SLS and Orion well above requested limits in the past after all.
But you have to wonder about how badly these programs are run when they managed to spend through excess funds and still come up short....
Plus while NASA has officially put a placeholder on a Dec 2019 launch, there have been many reports and obvious signs that the launch will not happen until Spring 2020 at the earliest. Meanwhile Falcon Heavy hardware has been delivered and is just waiting for pad 40 to re-open so 39 can be temporarily deactivated and kitted out for the larger rocket. When it reaches operational cadence, a lot of the justification for the SLS will evaporate.
The fact that we're in this position is a testament to how dysfunctional the US government has become over the last decade. The SLS and Orion are the direct result of the Republican takeover of Congress in 2010. The entire Constellation program (already behind schedule and over budget) was axed by Obama, only to have Congress resurrect the heavy lift rocket and capsule from the dead for no other reasons than to jab at Obama and bolster government spending in southern states. This basically means the program exists as a job-creation mandate alone and doesn't have a technical rationale for existing. As heavy-lift commercial vehicles come online most of the potential use-cases for the SLS are becoming undermined.
Berzerker
Deity
thx Hobbs
The issue is complicated, the industrial revolution coincided with - followed - our departure from the little ice age. That doesn't mean we aren't making the world warmer with co2, but we were warming naturally in addition to polluting the air. Furthermore, our industry back then was dirty and that has a cooling effect countering somewhat increasing co2 levels. Ironically our more recent efforts to cut down on the dirt - well, China and India are choking on pollution - warms us even faster.
The issue is complicated, the industrial revolution coincided with - followed - our departure from the little ice age. That doesn't mean we aren't making the world warmer with co2, but we were warming naturally in addition to polluting the air. Furthermore, our industry back then was dirty and that has a cooling effect countering somewhat increasing co2 levels. Ironically our more recent efforts to cut down on the dirt - well, China and India are choking on pollution - warms us even faster.
I suspect that the costs of public projects with questionable benefits tend to be intentionally underestimated. A realistic guess of the project costs would increase the resistance to pushing it through. It seems to be easier to get a funding extension when billions have already been spent and you can promise success for just a bit more money. So the people tasked with the divination of the project costs prefer to err on the side of cheapness instead on the side of caution.
That does not mean I believe that the money is well spent, of course.
hobbsyoyo
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We get lucky all the time. IIRC, the Tunguska comet impacted at roughly the same latitude as several major cities. If it had arrived a few hours sooner it would have been a disaster of biblical proportions instead of just a curiosity. The same thing applies to the asteroid that exploded over Russia a few years back.
Every day we spend without a comprehensive and complete skymap and a method for dealing withthese threats is another roll of the dice.
I'm not sure. Public projects with massive cost overruns are just as likely (if not more so) to be axed altogether than have their funding re-upped which would defeat the purpose of purposefully under bidding the proposal in the first place.
I tend to think that NASA (and the government in general) are very bad at dealing with contractors. Contractors look at projects like this as cash cows. In fact, one of the biggest NASA criticisms of Boeing's new Starliner Capsule program is that Boeing is putting more effort into extracting maximum profit out of its development than into actually getting the project done.
It's also mind boggling that the SLS and Orion should cost so much to begin with. I understand it's a very big rocket but I think at this point we've spent more on it than on Saturn (inflation adjusted) which was actually a more capable vehicle and actually had a mission to achieve. The Falcon Heavy and New Glenn rockets won't cost anything close to this much money to develop and produce, for example, and they are both in the same payload class - particularly if you discount the upgraded SLS which doesn't exist and won't exist for another 5-10 years while FH and NG will both be flying in that time.
hobbsyoyo
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Carried over from here.
The shuttle, on the other hand, followed a gliding profile into the atmosphere. The flux into the heatsheild at any given moment was much lower than what a capsule heat shield sees. However, while the rate is lower, the amount of time spent in reentry is much higher for the shuttle, so the overall amount of energy its heat shield has to deal with is actually much higher - it just gets that energy in a more spread out time frame.
This drove the designers to move away from an ablative shield (which would need replacement with each mission) to absorptive tiles that just soak up the thermal energy and slowly release it again after landing. They don't shed any material because they don't have to do that in order to cope with the lower flux.
The big problem they faced with these was how delicate they are and how easily they fell off. They fell off constantly and NASA knew and monitored this to an extent but eventually the fact that they fell off become seen as a routine event not worthy of special investigation. This process is called 'Normalization of Deviation' and it's really bad for obvious reasons.
The shuttle got lucky in that until Columbia, all of the tiles shed were in non-critical areas or in non-critical amounts; in other words the Shuttle could deal with losing them. Columbia showed NASA how bad they miscalculated the risk they took on with every launch. Supposedly, the Russian Buran had a far superior heat shield that was much more durable though I haven't actually seen any data to back that up and half way assume they were talking out of their butts.
It was a design flaw because those seals should have never been designed that way and in fact they rectified the design post-Challenger.
It was user error because Thiokol (the manufacturer) knew all along that the boosters were not able to operate at that low of a temperature and their engineers warned of the danger literally right up until lift-off. The engineers were ignored by management at Thiokol and NASA and they launched it in an environment it was not designed for. This means that the cold actually wasn't the root cause, it was operator error.
A good way to think about this is if you tried to drive a car underwater. Sure the water will kill the car's engine but the real problem isn't the water, it's that you tried to drive it into water in the first place.
So the tiles on the space shuttle operated fundamentally different from what was on/is on capsules. Capsule re-entry profiles are basically ballistic (not really but for these purposes they are) and they experience brief, but extremely intense heating. The flux (rate of heat going into) those shields is incredibly high - so high that no known materials can withstand them. They cope with this by basically burning up - the act of burning off actually absorbs energy from the plasma front, thus protecting the capsule behind the shield. Also, the burning material ejected by the shield actually disrupts the plasma in front of the capsule enough that it actually deflects a ton of the energy away from the capsule altogether.
The shuttle, on the other hand, followed a gliding profile into the atmosphere. The flux into the heatsheild at any given moment was much lower than what a capsule heat shield sees. However, while the rate is lower, the amount of time spent in reentry is much higher for the shuttle, so the overall amount of energy its heat shield has to deal with is actually much higher - it just gets that energy in a more spread out time frame.
This drove the designers to move away from an ablative shield (which would need replacement with each mission) to absorptive tiles that just soak up the thermal energy and slowly release it again after landing. They don't shed any material because they don't have to do that in order to cope with the lower flux.
The big problem they faced with these was how delicate they are and how easily they fell off. They fell off constantly and NASA knew and monitored this to an extent but eventually the fact that they fell off become seen as a routine event not worthy of special investigation. This process is called 'Normalization of Deviation' and it's really bad for obvious reasons.
The shuttle got lucky in that until Columbia, all of the tiles shed were in non-critical areas or in non-critical amounts; in other words the Shuttle could deal with losing them. Columbia showed NASA how bad they miscalculated the risk they took on with every launch. Supposedly, the Russian Buran had a far superior heat shield that was much more durable though I haven't actually seen any data to back that up and half way assume they were talking out of their butts.
Root cause was not actually the cold temperatures, it was a combination of design flaw and operator error.
It was a design flaw because those seals should have never been designed that way and in fact they rectified the design post-Challenger.
It was user error because Thiokol (the manufacturer) knew all along that the boosters were not able to operate at that low of a temperature and their engineers warned of the danger literally right up until lift-off. The engineers were ignored by management at Thiokol and NASA and they launched it in an environment it was not designed for. This means that the cold actually wasn't the root cause, it was operator error.
A good way to think about this is if you tried to drive a car underwater. Sure the water will kill the car's engine but the real problem isn't the water, it's that you tried to drive it into water in the first place.
As far as I understand it, the main job of the tiles was not to absorb the heat (their heat capacity was not particularly good), but to act as thermal insulator due to their low heat conductance. The result was, that the heat stayed closed to the surface, where it could be quickly radiated away. Only a small part of the heat was actually stored, more as a side effect than actual design.
I wonder what the design process for these tiles was. Did anyone ever think that it was a good idea to glue (with space-compatible glue, no less) 20000 tiles to the frame of the orbiter? Or were they just desperate, because they had no better idea?
Berzerker
Deity
when I saw the Challenger blow up I later heard the thing had icecycles hanging on it the morning of its launch and that the launch was sped up or scheduled for the morning because Reagan wanted to have his photo-op speaking to the crew during the day... Dont know if all thats true, but I still believe an icecycle fell onto the fuel lines below connecting the shuttle to the main tank and that when they went full throttle the fireball originated at that crossover line... They said a seal gave out. But I still remember watching the slo-mo of the fireball and it looked to me like it was where the fuel lines connected the two about a 1/3 of the way up from the engines.
r16
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it's a dangerous trait to dismiss every Russian claim , however it might be routine in daily life to discover they come up short in this or that . They took the Shuttle as a surprise bomber , they got theirs , no issues .
uhm , Lockmart . You are never allowed to have a better idea .
uhm , Lockmart . You are never allowed to have a better idea .
hobbsyoyo
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Thank you for the correction!
There probably was not a better way to attach those tiles due to material limitations. As with many 'super-materials', the tiles are probably really good at one thing and terrible at everything else. It is very likely that adding holes for fasteners to go through them would cause untenable stress concentrations and result in fractures, so you couldn't bolt them to the vehicle. Trying to add bracketing to them wouldn't work either because any bracketing exposed would have melted during re-entry. The tiles probably don't machine well either so it was probably too difficult to make them into complex shapes to allow them to be bracketed on the back side in a clever way that shields the brackets.
That's just my guess but I assume that anything other than glue would not work for these tiles.
They actually launched in frigid weather because H.W. Bush (VP at the time) was in town for that day only and they wanted to show off to him. He was a big space proponent and they wanted to put on a good show to make sure he would push for more funding with Congress. This was a critical time for the Space Shuttle as it was just ramping up into operational cadence. The shuttle was meant to replace all other boosters in the US fleet and to do this it had to launch a lot. Because each launch was about an order of magnitude more expensive than cheap non-reusable boosters, NASA really counted on Congress keeping money flowing to offset the red ink the program operated under.
Icicles were not the problem. The problem was that the boosters were made in barrel-shaped segments that were joined together and sealed with an o-ring. The way these joints were constructed meant that the o-rings were providing all of the sealing force in the joint - the metal parts of the joint provided mechanical strength to the whole booster but did very little to physically block the hot gas from squirting out the side.
As long as the o-rings worked correctly, the booster was supposed to be fine. However, it was later shown that the o-rings were barely functional under the best of conditions. Every time the boosters were ignited, hot gas shot into the o-rings and melted them. The melted byproducts and hot gas then filled the gap left by the o-rings, solidified and sealed the booster. This worked for several launches but was not a design feature - every Shuttle before Challenger just got lucky that this happened and the ersatz plug held during the launch. Engineers had seen on recovered boosters that the o-rings were vaporizing but the design wasn't fixed.
During Challenger's launch, the cold temperatures meant the o-rings were very stiff and even less useful than normal. The same blow-out/self-sealing action happened on Challenger as with all other launches but was more dramatic. Challenger then hit a high-altitude, high-shear wind stream that knocked the plug in the joint loose. This allowed SRB exhaust to dump directly into the ET and the support struts, breaching the former and breaking the latter. Then the booster broke loose entirely and the ET ripped apart.
The astronauts died a few minutes later when the cabin impacted the water. At least some of them survived the explosion and trip down to the water.
The Shuttle was Rockwell's product (and Rockwell was bought by Boeing). I don't think Lockheed had anything to do with the Orbiter itself though I wouldn't be surprised if they provided components.
I don't dismiss every Russian claim, it's just that this one is one of those things that Russian engineers throw out there whenever they are interviewed on the Buran/Shuttle and I have never seen anything to back up the claim.
I agree that glue is probably unavoidable as long as you stick with the many-small-tiles approach. They probably would have had to go for larger (form-fitting) tiles, but they could either not make those, or they would have been to brittle. I was just wondering, whether there would have been a less optimized-for-one-purpose material that might have resulted in a slightly heavier, but safer shuttle.
Berzerker
Deity
Jesus, what a way to go... And I cant even spell icicles
Samez
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Afaik the heat shield of the shuttle was segmented intentionally to compensate for thermal expansion.
The tiles were made of a complexe composite material of porouse sintered silica coated with the iconical black borosilicate layer. The processes for production of such materials was quite new in the 80s /90s and i am not sure they were even able to produce larger parts even if they would have liked to do so.
For ceramics there is also a engineering concept which advises to use more smaller parts if possible due to the fact that ceramics fail/crack catastrophically when they fail and the risk of failure increases with size. This can be limited by fiber enforced materials but the fibres have to be optimized for this ( pull out strength, crack ablation potential aso) and it would have contradicted the thermal properties.
Space faring is usually in the edge of many engineering fields aplyed which can sometimes lead to great dissaster but the challange makes it even more interesting for those involved (... not because it is easy but because it is hard...)
The tiles were made of a complexe composite material of porouse sintered silica coated with the iconical black borosilicate layer. The processes for production of such materials was quite new in the 80s /90s and i am not sure they were even able to produce larger parts even if they would have liked to do so.
For ceramics there is also a engineering concept which advises to use more smaller parts if possible due to the fact that ceramics fail/crack catastrophically when they fail and the risk of failure increases with size. This can be limited by fiber enforced materials but the fibres have to be optimized for this ( pull out strength, crack ablation potential aso) and it would have contradicted the thermal properties.
Space faring is usually in the edge of many engineering fields aplyed which can sometimes lead to great dissaster but the challange makes it even more interesting for those involved (... not because it is easy but because it is hard...)
There are a few articles about technical parameters of Buran heat shield. I cannot compare them myself, since I'm not a specialist in this field, I can only conclude that a bit different approach and separately designed materials were used. Claims about superiority are most likely from TV-shows, so I wouldn't pay too much attention to them unless they were made by engineers who worked on the project.
hobbsyoyo
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Some interesting articles:
A commercial imagery provider is now able to take images of every point on the Earth once a day. They downlink 6 TB of data daily as well which to me is almost as big a feat as getting the constellation up in the first place. Most of their constellation is in the form of 3U CubeSats that caught rides as secondary payloads though they have bought at least one dedicated rocket launch (a Minotaur-C). Their per-satellite cost is low enough that they can afford losses from launch vehicle failures (which have afflicted them with both Antares and Falcon and probably more) and in-orbit failures (which they don't talk about).
This is the future of commercial and civil space applications. To a large extent we are going to be moving away from very large, expensive satellites in the next decade.
This guy claims that China is going to build 'space militias'. I find this notion laughable for a bunch of reasons. It also reeks of paranoia - it seems like every other day I read an opinion piece about how the Russians and Chinese are somehow racing ahead of the US with very little to back that up. For one, Russia's space efforts are moribund (and I say that with a heavy heart, not as an attack on Russia's space program). For another, while the Chinese definitely have the capability to plan and execute big, long-term space projects, they have been trying to internationalize their own projects. They have announced plans to open up their forthcoming space station to foreigners and have tried to become part of the ISS but are blocked by the US. And in the end, I haven't seen many revolutionary efforts by the Chinese in space; at this point they are just trying to catch up and do the things that the US and Russia did decades ago.
The head of US military space efforts says that huge, expensive satellites are on the way out for military projects as well. I'm not sure I believe that he can really pull this change off given how intertwined the military and most satellite builders are. Plus there are decades of bureaucratic inertia to overcome to switch to small- and nano-satellites. But I hope he is successful because he is right that big satellites are an easy target, even if he does display a lot of the paranoia I just mentioned.
A commercial imagery provider is now able to take images of every point on the Earth once a day. They downlink 6 TB of data daily as well which to me is almost as big a feat as getting the constellation up in the first place. Most of their constellation is in the form of 3U CubeSats that caught rides as secondary payloads though they have bought at least one dedicated rocket launch (a Minotaur-C). Their per-satellite cost is low enough that they can afford losses from launch vehicle failures (which have afflicted them with both Antares and Falcon and probably more) and in-orbit failures (which they don't talk about).
This is the future of commercial and civil space applications. To a large extent we are going to be moving away from very large, expensive satellites in the next decade.
This guy claims that China is going to build 'space militias'. I find this notion laughable for a bunch of reasons. It also reeks of paranoia - it seems like every other day I read an opinion piece about how the Russians and Chinese are somehow racing ahead of the US with very little to back that up. For one, Russia's space efforts are moribund (and I say that with a heavy heart, not as an attack on Russia's space program). For another, while the Chinese definitely have the capability to plan and execute big, long-term space projects, they have been trying to internationalize their own projects. They have announced plans to open up their forthcoming space station to foreigners and have tried to become part of the ISS but are blocked by the US. And in the end, I haven't seen many revolutionary efforts by the Chinese in space; at this point they are just trying to catch up and do the things that the US and Russia did decades ago.
The head of US military space efforts says that huge, expensive satellites are on the way out for military projects as well. I'm not sure I believe that he can really pull this change off given how intertwined the military and most satellite builders are. Plus there are decades of bureaucratic inertia to overcome to switch to small- and nano-satellites. But I hope he is successful because he is right that big satellites are an easy target, even if he does display a lot of the paranoia I just mentioned.
Broken_Erika
Play with me.
Sure, Laugh now; But one day those Chinese Space Militia's will be the only thing standing between us and total domination by the Moon Nazi's!
