Re-entry

If NASA faked the moon landings, does the agency have any credibility at all? Was the Space Shuttle program also a hoax? Is the International Space Station another one? Do not dismiss these hypotheses offhand. Check out our wider NASA research and make up your own mind about it all.
lux
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Re: Re-entry

Unread post by lux »

Quote from above linked article:
"[SpaceX Dragon] has a great return capability, it essentially replaces that capacity that we lost when the shuttle retired so that now we'll be able to bring home a wide variety of biological samples, physical sciences samples and we'll be able to bring home research equipment that we need to refurbish and then relaunch again."
Wide variety of biological samples? What biological samples are they talking about?
hoi.polloi
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Re: Re-entry

Unread post by hoi.polloi »

Oh, I see Fred54. Thanks! I must be getting old myself for not understanding the reference.
simonshack
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Re: Re-entry

Unread post by simonshack »

lux wrote:Quote from above linked article:
"[SpaceX Dragon] has a great return capability, it essentially replaces that capacity that we lost when the shuttle retired so that now we'll be able to bring home a wide variety of biological samples, physical sciences samples and we'll be able to bring home research equipment that we need to refurbish and then relaunch again."
Wide variety of biological samples? What biological samples are they talking about?
Bullcrap / horseshit - and derivatives? :P
lux
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Re: Re-entry

Unread post by lux »

:lol: That works for me!
Heiwa
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Re: Re-entry

Unread post by Heiwa »

You can, according NASA, both see (!) and hear (a double sonic boom!!) when a space ship is re-entering Earth atmosphere from space, e.g. a shuttle from the ISS:

http://www.nasa.gov/returntoflight/crew/photo_tips.html
Although it is possible to view a spacecraft reentry with the unaided eye, it is not possible to see the Shuttle reentry if the reentry flight path is in broad daylight since the plasma trail created as the Shuttle passes through the atmosphere is not bright enough to contrast with the sky. Naked eye viewing of the reentry itself is best when the observer's site has very clear skies, and the observer is in complete darkness or very close to local sunrise or sunset if you know precisely where to look.

Even if you know you cannot see the Shuttle reentry due to lighting or cloud problems, it is possible to hear the double sonic boom from the Shuttle if it is not too far away. It takes sounds about 1100 feet/sec (300m/s) to propagate to the ground; thus if the Shuttle is 200,000 feet (60,00m) away from you at its closest distance during reentry along your line of sight, it would nominally take around 96 seconds for the sound to reach your ears AFTER the shuttle passed that point. For the human ear to detect the boom(s) you should be far away from noises, especially traffic noise.
OK, a plasma trail, whatever it is, cannot be seen, and of course, clouds, rain and fog will make seeing difficult. But hearing? :rolleyes:

As noise cannot propagate in vacuum and propagates extremely slow in a thin atmosphere, e.g. 1 000 times slower than a landing space ship itself at 130 000 m altitude, how can noise from a shuttle propagate from space to ground? Anyone? :P
Heiwa
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Re: Re-entry

Unread post by Heiwa »

The next re-entry will take place October 28.
The SpaceX Dragon capsule will allegedly detach from the ISS that according NASA/JPL orbits the Earth every 90 minutes at tangential velocity 7 800 m/s at LEO about 300 000 m altitude and start the drop down to Earth.

At 130 000 m altitude the Dragon capsule starts to encounter Earth Atmosphere. The Dragon's total velocity has increased to about 9 000 m/s, i.e. the tangential velocity is about 8 800 m/s and the vertical velocity downwards is about 1 800 m/s. If Dragon continues to drop down at 1 800 m/s, it will hit or crash into ground (or the Pacific Ocean) after 72 seconds. :o

However, Dragon has some rocket engines that can change the course of events so it will take 30 minutes to stop the Dragon, so that parachutes can be deployed at 10 000 m altitude :rolleyes: and …
“… Dragon’s return is targeted for October 28, and the capsule will splash down about 250 miles southwest of Los Angeles.
Best,
Hannah
HANNAH POST | Communications |SpaceX
1 Rocket Road, Hawthorne, CA 90250
[email protected] 310.219.7840”
So it seems the Dragon capsule will enter Earth atmosphere say above New Guinea or so and then whizz by Hawaii at 70 000 m altitude and 4 500 m/s speed 15 minutes later direction LA! Or 250 miles southwest of LA. :blink:
Braking/deceleration is only due to friction against a magic PICA heat shield at the front of the Dragon and turbulence behind the capsule. And when velocity has come down to 50-100 m/s one magic way or another, parachutes are deployed and the Dragon descends intact into the Pacific 250 miles southwest of LA. :lol: You can be sure that some airplane will film the event!
And there the SpaceX armada of two small steel boats and two rubber boats will pick up the Dragon. :D
Fantastic! I wonder how people still can believe above rubbish. :P
Much easier is evidently to drop the Dragon from an airplane that took off from a nearby airport an hour earlier. :rolleyes:
Because the show must go on!
Heiwa
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Re: Re-entry

Unread post by Heiwa »

October 28:
Dragon then … conducting a de-orbit burn at 6:28 PM GMT. …
Entry Interface (EI) followed shortly thereafter, with Dragon making its fiery plunge through the atmosphere, protected by its PICA-X heat shield, which is designed to withstand off-nominal re-entries from Mars.
Following deployment of the three parachutes, Dragon was observed to have splashed down in the Pacific Ocean off the coast of California at 7:22 PM GMT.
Source: http://www.nasaspaceflight.com/2012/10/ ... cargo-iss/

You wonder who observed it? :P I mean, the heat shield managed to reduce the speed from 9 000 m/s to 100 m/s when parachutes were deployed. How is it done? :rolleyes:
Fred54
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Re: Re-entry

Unread post by Fred54 »

9000 m/s = 20,000 mph no wonder they are using the new and improved PICA-X heat shield the "X" must stand for XTRA high specific heat capacity maybe 500 times that of water? Or 2500 times that of your favorite heat shield material CONCRETE!! :lol:
lux
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Re: Re-entry

Unread post by lux »

An interesting side note:
SpaceX's CEO, Elon Musk, named the [Dragon] spacecraft after the 1963 song "Puff, the Magic Dragon" by Peter, Paul and Mary, reportedly as a response to critics who considered his spaceflight projects impossible.
source
:blink:
Heiwa
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Re: Re-entry

Unread post by Heiwa »

Fred54 wrote:9000 m/s = 20,000 mph no wonder they are using the new and improved PICA-X heat shield the "X" must stand for XTRA high specific heat capacity maybe 500 times that of water? Or 2500 times that of your favorite heat shield material CONCRETE!! :lol:
Water is very good to cool car engines as long as you keep it <100°C (and >0°C). Maybe the PICA-X heat shield was water cooled as extra safety? :lol:
According SpaceX the PICA-X heat shield design used on the Dragon is a trade secret but it cannot be better than the Apollo 11 heat shield 1969. The latter must have been 2-3 times more effective as Apollo 11 came dropping down much faster than Dragon.

There is no business like the space business as it is sky high and out of bounds for any audit. You just have to believe and march on. Heilelovyu.
lux
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Re: Re-entry

Unread post by lux »

Some questions have occurred to me lately about "heat shields" …

Now, I'm no rocket scientist but I do know something about aerodynamics and something seems fishy to me as regards the “heat shields” that these “space vehicles” are using.

Here are some photos of the “X-37B” and the shuttle showing their “heat shields” …

Image


Image


Image

Are we supposed to believe that the portions of these craft that are not covered by heat shield tiles do not experience any air friction? That the air flow separates from the craft at the heat shield leaving a vacuum along the rest of the craft's skin? So no heat shield is needed in those areas? That seems dubious to me.

What about the craft's tail section and other control surfaces? They appear to have little or no heat shielding but if they didn't receive any airflow then they would be useless as control surfaces, wouldn't they? And, if they did receive direct airflow then they would burn up, no? For example, look at the vertical fin & rudder on the above shuttle. What is protecting it from the heat of re-entry? And, the same with the V-tail section of the X-37B?

Now here is what the wiki (i.e., NASA) says about this:
Reentry heating differs from the normal atmospheric heating associated with jet aircraft, and this governs TPS design and characteristics. The skin of high-speed jet aircraft can also become hot, but this is from frictional heating due to atmospheric friction, similar to warming your hands by rubbing them together. The Orbiter [Space Shuttle] reenters the atmosphere as a blunt body by having a very high (40-degree) angle of attack, with its broad lower surface facing the direction of flight. Over 80% of the heating the Orbiter experiences during reentry is caused by compression of the air ahead of the hypersonic vehicle, in accordance with the basic thermodynamic relation between pressure and temperature. ...
OK, so the shuttle assumes a steep nose-up attitude which shields the tail section from the direct airflow but how is this attitude achieved and maintained? An aircraft's attitude is controlled by its control surfaces located in the tail section, wings, etc. If these control surfaces are not operating in a direct airflow then how can they be used to change or maintain a specific attitude?

The above reference further states ...
...A hot shock wave is created in front of the vehicle, which deflects most of the heat and prevents the orbiter's surface from directly contacting the peak heat. Therefore reentry heating is largely convective heat transfer between the shock wave and the orbiter's skin through superheated plasma.
Huh? Could you repeat that? A hot shock wave is created in front of the vehicle which deflects most of the heat and prevents the shuttle's surface from directly contacting the peak heat? How is this hot shock wave created? Why doesn't every high speed object create such a hot shock wave that prevents it from contacting the “peak heat”? Why don't meteorites “create a hot shock wave” that protects them from burning up? Or falling space junk? What property or device does the shuttle have that creates this protective hot shock wave that other re-entry objects lack?

But wait! There's more …
Some high temperature metal alloys can withstand reentry heat; they simply get hot and re-radiate the absorbed heat.
Oh, OK. The shuttle's skin must be made from this metal that can withstand the heat of reentry, right?
However, the amount of high-temperature metal required to protect a large vehicle like the Space Shuttle Orbiter would have been very heavy and entailed a severe penalty to the vehicle's performance. Similarly, ablative TPS [thermal protection system] would be heavy, possibly disturb vehicle aerodynamics as it burned off during reentry, and require significant maintenance to reapply after each mission.
Oh, never mind. I guess they can't use that special heat resistant metal because it's too heavy. They have to use good old aluminum.

So then how do they protect the shuttle exactly?
Much of the shuttle is covered with LI-900 silica tiles, made from essentially very pure quartz sand.[1] The insulation prevents heat transfer to the underlying orbiter aluminum skin and structure. These tiles are such poor heat conductors that one can hold one while it is still red hot. There are about 24,300 unique tiles individually fitted on the vehicle, for which the Orbiter has been called "the flying brickyard".

The tiles are not mechanically fastened to the vehicle, but glued. Since the brittle tiles cannot flex with the underlying vehicle skin, they are glued to Nomex felt Strain Isolation Pads (SIPs) with RTV silicone adhesive, which are in turn glued to the orbiter skin. These isolate the tiles from the orbiter's structural deflections and expansions.
Wow! The tiles are glued to felt pads which are then glued to the craft's skin. Must be some glue! Wish I had some of that stuff! It would be really useful around the house.

OK, now down to specifics:
HRSI tiles (black in color) provide protection against temperatures up to 1,260 °C (2,300 °F). There are 20,548 HRSI tiles which cover the landing gear doors, external tank umbilical connection doors, and the rest of the orbiter's under surfaces. They are used in areas on the upper forward fuselage, parts of the orbital maneuvering system pods, vertical stabilizer leading edge, elevon trailing edges, and upper body flap surface as well.
So these other heat shielding tiles are used on the control surface leading and trailing edges. But, not on the rest of the control surfaces themselves evidently. So, do the control surfaces also create this "hot shock wave" ahead of them which protects them from the heat so the rest of their surfaces need no further protection? What happens when a control surface is used, i.e., turned into the airflow? Wouldn't its "flat" surface now be subject to the intense heat of reentry? But, that part of the control surface doesn't have any heat shield tiles so why doesn't it burn up?

According to this reference the SR-71 Blackbird spy plane develops skin temperatures up to about 800°F at its Mach 3 top speed. Mach 3 is about 2300 mph. But this reference says the shuttle entered the atmosphere at about 17,500 mph – about 7.5 times faster so I would think the skin temperature of the shuttle would be lots higher than 800°F and since the shuttle is mostly made of aluminum and aluminum melts at about 1200°F I would think the unprotected parts of the control surfaces would be in big trouble on reentry with only their leading and trailing edges protected.

But, even if if were true that the unshielded portions of the fuselage skin did not experience the high heat of reentry, what would happen if the craft, say, pitched or yawed due to air turbulence while mid re-entry? Such that the unshielded portions of the fuselage skin or tail section were directly exposed to the air flow? Wouldn't the unprotected portions of the craft immediately burn?

Now, with a “space capsule” shaped like this Apollo thing …

Image

... I can see that the non-heat shielded portions of the craft might be more protected from air friction but, again, if the thing pitched or yawed out of a perfect state of trim (and it has no control surfaces to correct for this) it would expose the unshielded portion of the skin to thousands of degrees of air friction, would it not?

It seems to me that if you're going to use a "heat shield" it would have to cover 100% of the craft or you would surely lose at least some, if not all, of them on re-entry. All you'd need is some turbulence to upset the attitude a bit so that unprotected surfaces were directly exposed to the leading airflow and ... poof!

We're told that the "Space Shuttle Columbia disaster" was caused by a small piece of the craft's wing heat shield being damaged, causing the entire craft to break apart and burn up. So, what would happen then if the craft simply yawed to one side exposing a large percentage of its unshielded skin? Is there something preventing this from happening?

Or, is this whole concept of "heat shields" just one of NASA's little jokes?
agraposo
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Re: Re-entry

Unread post by agraposo »

lux wrote:Image
What are those workers doing? They stand like the workers in Austin Powers movies, doing nothing :D

Image
lux wrote:Or, is this whole concept of "heat shields" just one of NASA's little jokes?
One of the astronauts in the Columbia disaster you mention was called William McCool. Is this another joke? :D

Apart from that, your logic is conclusive!
simonshack
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Re: Re-entry

Unread post by simonshack »

lux wrote:
Or, is this whole concept of "heat shields" just one of NASA's little jokes?
Apollo 12 module : (1969) An almost pristine, re-usable spacecraft?
Image
https://www.astronautinews.it/2019/11/a ... -pacifico/

Soyuz module (2003): A brutally charred / barbecued spacecraft ready for the junk yard !
Image
http://ru.wikipedia.org/wiki/%D0%A4%D0% ... anding.jpg


It looks to me like that this heat shield technology is going backwards ! :lol: :lol: :lol:

Yes, Lux - I vote for "it's just one of NASA's little jokes".


****************************************************************************

And here's the story of an alarming/ dramatic 2008 Soyuz landing which almost killed the asstronots on board due to the harsh re-entry angle which "caused unusual burn damage" - yet that Soyuz white paint coating looks pretty o-ok to me!! :huh: ???

"
Russian news agencies quoted unidentified sources as saying that the astronauts were in serious danger during the descent and that the capsule suffered unusual burn damage during its fiery re-entry to the atmosphere."
http://www.nytimes.com/2008/04/23/scien ... .html?_r=0
Image
Geez...whatever... :rolleyes: (Don't you love the guy in the foreground pointing his index finger at ... something?

*******************************************************************************


Oh - and by the way: here's my valiant attempt at fitting three adult men into the Soyuz spacecraft which is, of course (now that NASA's Space Shuttle has gone into early retirement) the one-and-only spacecraft serving the International Space Station with human cargo ... Do you still dream of becoming an astronaut? Seriously? ^_^

Image
icarusinbound
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Re: Re-entry

Unread post by icarusinbound »

simonshack wrote:
lux wrote:

"
Russian news agencies quoted unidentified sources as saying that the astronauts were in serious danger during the descent
http://graphics8.nytimes.com/images/200 ... an-600.jpg
Or perhaps in even more danger from sustaining a colllision and bounce when hitting the earth faster than a train-wreck
simonshack wrote:Geez...whatever... :rolleyes: (Don't you love the guy in the foreground pointing his index at ... something?)
He's maybe pointing at the impossible empty (and elastic) impact crater. How many more 100g would they have sustained??

Do whistleblowers ever really blow that whistle? Maybe only if their keepers (or matte artist) lets them...

Edit- split the upper quoted section so that my inserted comment was separated from the text above and below
Last edited by icarusinbound on Wed Nov 14, 2012 6:25 am, edited 1 time in total.
icarusinbound
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Re: Re-entry

Unread post by icarusinbound »

Simon, I've often tried to visualise how this would work out for spacing, and for me your composite shows the impractical cramped squeeze the cosmonuts would suffer so clearly.

To me, whether it's the classic Apollo LEM with those suited/booted/backpacked footballer jocks implausibly jammed inside a tiny tin, or this bonfired Russian doll's house, where is the practical reality? The inhabitants of any such capsule would receive physical impact forces (irrespective of parachute deceleration) that should justify much-larger capsule sizes- the lack of internal separation to protect the inhabitants from g-forces on hitting (and bouncing) just adds to the unrealism of all of this.

Here's a thought- on the basis that Americans and Russians spacemen are fundamentally the same species, can we make a composite picture showing the (presumably larger) Apollo capsule overlaid with this tiny Russian barbecued salt-shaker? I know that we're almost comparing unicorns to griffons here, but it might be informative. The Americans claimed to have their intrepid explorers on their backs for exit from and entry to Planet Earth...that looks even less likely for these Russian oven-fried travellers when we see their body sizes.
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