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Columbia tragedy

Columbia tragedy

Columbia tragedy

(OP)
Dear all,

First of all I want to express my sincere condolences to the families of the brave crew of the columbia shuttle.I feel the space exploration should continue despite the setbacks at present simply because the sacrifice of the magnificient seven would go in vain if the project is stopped.
But as Engineers we have to discuss the possibilities & reasons of this disaster so that in future this should not happen again.
I am not a Aeronautical engineer but as a design engineer I feel something quite not right in the positioning of the shuttle w.r.t the booster rockets.
See,From the looks of the shuttle taking off I felt the positioning of the shuttle too low & too close to the booster rocket jets,It was almost as if the flames of the booster rockets were touching the orbiter during the take-off.I may be wrong but Is there a chance that the shuttle was getting over-heated due to this reason? Can the shuttle be shifted to the top of the arrangement without affecting the overall performance?
I have written the same to the CHICAGO TRIBUNE about my opinion,I am doing the same here hoping to get some answers from this community.
I would be glad to read other opinions as well.
bye!

RE: Columbia tragedy

Have you given any consideration at all about the overall stability and why that might require the Shuttle to be closer to the bottom?

TTFN

RE: Columbia tragedy

the rocket exhaust does not touch the shuttle. The space shuttle components are arranged in such a way that the solid rocket boosters, external fuel tank, and shuttle main engines balance each other out.
Also you don't want your center of gravity on a rocket in front of your center of pressure or you'll have an unstable platform. This is ok for an F-16, but on a spacecraft you can't afford to add extra drag by control surfaces that have to work overtime to compensate for unstability (Each control surface deflection = added drag).
just my 34 cents worth,
T

RE: Columbia tragedy

(OP)
Well!

I had this thought and I felt like getting it off my chest,That's all.No doubt that the NASA engineers must have tried out different arrangements & they must have decided on this setup to be safe.
Anyway,I only hope that they do find out the exact reasons for the tragedy.
Bye!Thanks for your replies.

RE: Columbia tragedy

My thoughts still go back to the foam insulation.  I think that there was a defect in the installation or weather checking of this insulation that allowed ice to form against the tank thus pushing off this insulation. I think that the peice seen hitting the wing was not just 2.3 pounds of insulation, but rather maybe 100 lbs of ice also.

Just my 2 cents.

RE: Columbia tragedy

Well, here's an amusing fact. The original concept was for the shuttle to sit on top of the stack, like the french Hermes destined for Ariane 5. The concept was rejected on cost grounds, hence the ride on the back of a firecracker concept that made it. Must admit I can't remember the exact reasoning, since I saw it documented on TV years ago.

It would have made more sence to me to have a reuseable lifter vehicle, piloted if necessary, to see the shuttle on it's way. In any case the whole thing really revolves around engine technology.

At the moment NASA is going back to it's pre-apollo route of a scram jet launched from a subsonic lifter. The costs of this will still only leave the route open to military/industry activities, and the technology is 20 or so years from being "commercial".

Graviman

RE: Columbia tragedy

Astroclone,

Your statement that a rocket should have its center of gravity (mass) behind its COP for stable flight is not correct.

RE: Columbia tragedy

I agree with Metalguy, in that you need to have your center of gravity forward of your center of dynamic pressure.

The reasons for that are similar to both the F16, and an arrow. When the shuttle goes through the atmosphere, and especially through MAX Q (the period of maximum dynamic pressure), it's important that the STS stack be able to make small corrections from the lower part of the launch stack.

The shuttle is positioned where it's at is a consideration early on, that the shuttle provide it's own engines, rather than just have the OMS (Orbital Maneuvering System) engines required to deorbit on the shuttle orbiter and the rest of the lifting power positioned on the main tank.
If the shuttle were on top of the main tanks, the SSME's (Space Shuttle Main Engines) would need to be on the main tank (possibly, if not probably, lost or damaged on each flight), along with requiring much larger SRB's (Solid Rocket Boosters) needed to compensate.

The placement of the shuttle Orbiter on the main tank is as close to the tank as possible to reduce the very high bending and compressive loads that the connective struts need to share.
larger in cross-section and weight, and every gram of weight counts.

RE: Columbia tragedy

Along this line of thought, I have always wondered why they don't place some type of protective shell over the heat tiles during launch.  In order to absorb the heat of re-entry these tiles have to be made of a rather brittle ceramic like material which leads to them loosing several on just about every launch.  Why not place a hardened plastic, kevlar, or whatever shell over the top of the tiles during lift off?  You wouldn't even need to have to eject it in orbit.  It would simply burn off during re-entry?  I realize it would add some weight to the shuttle, but perhaps by protecting the tiles on lift off you wouldn't need as many redundant layers to ensure safety on re-entry?  Even if it did add some weight, better that than loosing an occasional shuttle.

RE: Columbia tragedy

Agree.  I wonder how they are going to launch another shuttle without some drastic improvements like that.  They'll also have to develop an inspection and repair scheme while in orbit.

I am still amazed that alum. was used for the skin under the tiles in the high-heat areas.  While alum. is a far better conductor of heat than Ti, it's melting temp. is over 3,000 deg. F (IIRC) vs. alum. at 1200+.  Ti also retains its yield strength at high temps. far better than  Al alloys.

RE: Columbia tragedy

Are there experts in this forum who might care to comment on the servicability of the shuttle heat shield design? Since the future of the shuttles will become a subject of public debate, and maybe even a vote in Congress, those of us who are not as well informed should try to get educated.

It appears, from reading risk assessments available on NASA web pages, that the current shuttle heat shield is a major weak link in the system. Changes in operating procedures and provisions for repairs may allow existing shuttles to fly some more but ultimately, it seems to me, they should be phased out in favour of space craft with more robust (and forgiving?) skin technology.  

Would you agree that the risk of shuttle skin failure is sufficient enough to make a design change the appropriate action?



RE: Columbia tragedy

I would agree that the risk of shuttle skin failure is sufficient enough to make a design change the appropriate action?
One wonders if one could not dispense altogether with the ablative tiles and introduce a new skin design wherein the core is ventable and coolants (liquid hydrogen?) are pumped through the core during re-entry to serve as a heat sink.The weight saving of the tiles should allow for the weight of the coolant.The nozzles of the rocket engines are
regenerativly cooled so why not extend this concept to the nose cone.

RE: Columbia tragedy

Good idea.  Makes me wonder if an internal water spray system might work.  It would spray water on the internal skin surfaces of the critical areas, but only if detectors sensed above-normal temps.  Shouldn't be too hard to do some tests to find out how much water would be required to save the present alum. skin and a possible future Ti one.

Water has a very high latent heat of evap., so a "moderate" amount sprayed in the right places might be able to "save the day".

RE: Columbia tragedy

The water spray system is a cool idea.I worry about how one might contain the steam that would be generated.
Does the shuttle carry any reserve amount of liquid hydrogen upon its re-entry or is it jettisoned? Seems that it could be circulated through a metal foam sandwich panel that is brazed together rather than glued.Maybe three plies.
Are there titanium open metal foams available with say a 40 pores per inch in order to maximise the brazing area of core to the titanium skins to make a nose cone sandwich panel a true monocoque assembly that is fully ventable.Ideas on coolants would be welcomed as I personally don't trust the use of cryogenics after the cryo-pumping episodes of the x33
Perhaps the water may do the job as well as any other coolant.Superheated espresso coffee will be served upon landing.

RE: Columbia tragedy

Have you done the analysis already?

There's a heat load of 20 kW/m^2 for probably over 600 sec.  On a 50 ft square area, that's about 3 billion joules.

TTFN

RE: Columbia tragedy

How many gallons of freon 16 does it take to quench 3 billion joules?
Serious answers only please!

RE: Columbia tragedy

To make this more realistic, I think we have to assume a small area of skin exposure-say 0.1 sq. meter.  So at worse all we have to do is absorb 2,000 watts for 10 min.-should be easy if the spray system is designed with some thought.

Since we could tolerate quite a bit of temp. rise, we might only have to absorb half of that.

RE: Columbia tragedy

Running the coolant through the core would allow the skin to which the ablative tiles are affixed to be directly cooled.That's where we need the chill factor.


The core would need to have major ventability and with the metal foam cell size at 10ppi I wonder whether that would allow a sufficient flow rate. The increase in cell size unfortunately diminishes the strength of the skin to core bond.
If lateral vent channels were  discretely cut into the titanium metal foam core a higher density foam could be used.Back to high strength.!!
The original thought was that this was to be a replacement for the use of ablative tiles but if it couldnt handle that job it would still be a fine back-up or an in-tandem system.
It may also be a stand alone system.
With a three layered system with each layer having say 3/8th" square cross sectioned ventways cut into a 1/2' thick titanium foam metal core at a spacing of say 1" would that allow a sufficient flow rate of coolant through the panel. That depends on the coolant I guess. I wonder how freon would do.

RE: Columbia tragedy

I see selective-area water cooling as a last-ditch effort for saving only a small tile-damaged area on the 3 remaining shuttles.  I don't think it possible to completely redesign them.  New ones would probably have all kinds of improvements.

RE: Columbia tragedy

This is in regard to the reasons why the shuttle is positioned farther up on the solid boosters during launch.  If you watch film of a launch, the main Shuttle engines are ignited a few seconds before the solids are ignited.  The delay was introduced because the main engines are powerful enough to significantly flex the solid motors and waiting allows the Shuttle to rebound to vertical.  I'm not sure but it is possible that the Shuttle is not positioned higher because this would increase the stress on the solid boosters during the flexing.  Increasing the height would mean that stronger boosters with higher mass would be needed.  Maybe the position was chosen as a compromise between heating issues and the amount of aluminum that would be necssary to reinforce the solid boosters for launch.

Brian Lewis
The Aerospace Corporation
http://www.aero.org/

RE: Columbia tragedy

..."amount of Aluminum"...

AFIK, the solids have steel casings!

Just like great, big chunks of water pipe with very expensive machining at each end...

cheers
Jay

Jay Maechtlen

RE: Columbia tragedy

How interesting.  Maybe they'll throw me a red star. <g>

RE: Columbia tragedy

Just for giggles, let's figure out how much water we'd need to carry based on that description:
10 liters water -- 1.6 m^2 surface area of DART

shuttle minimum surface area = 100 ft*50 ft = 464 m^2

==> shuttle would need to carry about 290 times more water or 2900 kg of water or about 6400 lbs of water.

Oh, the DART description implies approximately equal amounts of air volume as water volume, so we'd also need about 5.8 m^3 of volume, not counting the plumbing and material need to contain superheated steam at 5 atmospheres of pressure.

TTFN

RE: Columbia tragedy

I'd guess they only intend to cool the hot bits (ie leading edge of wing, front lower panel on nose), so I'd expect more like 40 m^2, so they'd only need 300 kg of water by your figures. 5 atmosphere is a trivial pressure for plumbing, shop air is about that.

 

Cheers

Greg Locock

RE: Columbia tragedy

The problem is that on the Shuttle, there's only hot and hotter.  

The leading edges and nose run above 1260°C, while the remainder of the fuselage and wings are simply somewhat below 1260°C.  These are the black parts of the Shuttle.

Parts of white parts are still hot, running up to 650°C.

TTFN

RE: Columbia tragedy

   The "260 Inch" Solids blew out windows 20+ miles away
   Every Titan or even Delta (despite its 2% loss rate) has failed when built large enough to carry a Shuttle's cargo.
   The unpredicatable explosions "for no reason" are called "combustion Instability".
   To reduce the Problem, Physicist Fletcher suggested 1/20th size Solids, stacked 4 on each side (only 8/20ths, so the Liquids are run 8.5 minutes not the original 3 -- that is why they have to be off to one side.
   Be happy though -- because the thrust goes at an angle they put the heaviest part, the "Lox" atop so the LH2 underneath has its ullage-- a 3 foot layer of Helium -- on top & so BETWEEN the fuel & oxidiser.  The reason cameras were removed from Shuttle was the Moon rockets blew up too fast to take pictures -- but the Shuttle doesn't!
   Note the Farming out of the Foam question to Boeing 'caus all the Rocket Scientists at NASA got fired.
  Notice their total lack on the Panels.
   It would be easy to make Escape systems that work, NOW, but I -- or anyone else -- can't get a Scientist to change the rulings made in the 1960s  -- because they DON'T EXIST.
   Engineers are not really trained to anyalyze from basic principles ... but it disgusts me that I have proposed methods that would have save BOTH crews we lost, BEFORE the losses, and ones that (a) were mostly designed already, they just had "show stoppers" that I can evade, PLUS the false impression ALL accidents would vaporize the astronauts instantly (obviously, if we can recover live Worms , or Pieces of our crews, we can recover them intact).  Yet the official Dictum is still that of the next 1000 accidents, 1000 will be too quick for sensible response.
   
  I am so tired of recovering PIECES of Astronauts !

RE: Columbia tragedy

Wish NASA would throw me a line. I'm pretty darn sure I could find a way to stop crews taking risks with high speeds and temps.

I sympathise with the rocket Scientists though, since I've seen too many bungling attempts at management in the auto industry. You'd have thought the wheel would be about right by now.

Still if I document my ideas, and bung 'em in a time capsule, future generations could dig 'em out and say "hell they figured that out then!"...

Maybe I'm jus' gettin' cynical.

Mart

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