Columbia tragedy 1

[cranekiran]

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!

 

[IRstuff]

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

 

[astroclone]

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

 

[cranekiran]

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.

 

[dpaulson]

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.

 

[GraviMan]

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

 

[Metalguy]

Astroclone,

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

 

[rocketdoc]

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.

 

[jsalls]

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.

 

[Metalguy]

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.

 

[krd]

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?

 

[bobhexa]

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.

 

[Metalguy]

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".

 

[bobhexa]

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.

 

[IRstuff]

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

 

[bobhexa]

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

 

[Metalguy]

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.

 

[bobhexa]

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.

 

[Metalguy]

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.

 

[valhalla]

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/