Timeline of last flight of space shuttle Columbia

AP | 2/02/03

[kattracks]

A timeline of events in the last flight of space shuttle Columbia. All times EST.

-- Jan. 16, 10:39 a.m.: Columbia rockets into orbit from Kennedy Space Center.

-- Feb. 1, 8:15 a.m.: Columbia fires braking rockets, streaks toward touchdown.

-- 8:53 a.m.: NASA loses temperature measurements for shuttle's left hydraulic system.

-- 8:58 a.m.: NASA loses measurements from three temperature sensors on shuttle's left side.

-- 8:59 a.m.: NASA loses eight more temperature measures and pressure measures for left inboard and outboard tires. One of the measurements remains visible to crew on a display panel; which crew acknowledges.

-- 8:59 a.m.: Final transmission. Mission Control radios: "Columbia, Houston, we see your tire pressure messages and we did not copy your last." Columbia replies: "Roger, uh, ..."

-- 9 a.m.: NASA loses all data and contact with Columbia at 207,135 feet.

-- 9 a.m.: Residents of Texas, Arkansas and Louisiana report hearing "a big bang" and seeing flames in the sky.

-- 9:16 a.m.: Columbia's scheduled landing time.

-- 9:29 a.m.: NASA declares an emergency.

-- 9:44 a.m.: NASA warns residents to stay away from possibly hazardous debris.

-- 11 a.m.: Kennedy Space Center lowers flag to half-staff.

-- 2:05 p.m.: President Bush announces: "Columbia is lost; there are no survivors."

[Bad~Rodeo]

-- 8:53 a.m.: NASA loses temperature measurements for shuttle's left hydraulic system.

-- 8:58 a.m.: NASA loses measurements from three temperature sensors on shuttle's left side.

-- 8:59 a.m.: NASA loses eight more temperature measures and pressure measures for left inboard

Anyone have pics of the lift-off?

[leadpenny]

Try here.

[Samurai_Jack]

What we have here is fairly obvious, a structural burn through that began at 8:53 and took 6 minutes to burn through successive systems till it became catastrophic.

[Bad~Rodeo]

No it's NOT obvious. Initial Reports show a piece of foam breaking away on Lift-Off. Ground Control reported that it was no big deal.

[Pikachu_Dad]

You both have a point.

One of you is talking about the immediate failure on that day. The other is talking about the causes leading up to why that failure occured.

Both views are correct.

[mikegi]

There were five minutes between losing the temps on the left hydraulic system and losing the rest of the left side measurements. The crew was alive and well during this time. If there was a burn through, wouldn't they have noticed the temps spiking up on the sensors that survived longest? I haven't read anything about what the sensors' were reading just before failure or if there was a trend. Of course, the burn could have been isolated to the wiring.

Maybe there was a mechanical failure where the left wing connects to the fuselage. It would be interesting to see a diagram of where the sensors were located and where their wires ran.

[Pikachu_Dad]

Next step would be for them to look at the physical location of each of the sensors and associated wiring along with the the final say ten minutes of sensor history.

From that, they should be able to pinpoint the area where the heat breakthrough and the speed of the breaktrhough occured.

[EternalVigilance]

The final voyage of Columbia

[RadioAstronomer]

This indicator here is the word "lose".

First what is telemetry?: Telemetry is the process of conveying information by transmitting information from one point to another. The Merriam-Webster dictionary term for telemeter is “transmit (as the measurement of a quantity) by telemeter”. In other words it is a process of conveying information, such as voltages and temperatures, from a remote location to another for subsequent data analysis or interpretation.

On the average satellite there are hundreds, possibly even thousands of individual items (including mission data) that need to be transmitted from the vehicle to a ground station for analysis such as a voltage, temperature, attitude and the like.

It is impractical if not downright impossible to simultaneously transmit all of this data to a ground station. So the data is ”injected” into a serial telemetry stream that only requires one (or possibly a few) links between the vehicle and the ground. This process of inserting all of this data in a specific pre-determined pattern is called commutation.

To do this, the data must be digitized (i.e. converted to ones (1_s) and zeros (0_s). Due to fidelity reasons, link margin, and communications bandwidth, many of these parameters are sent down as an 8 bit (8 serial 1_s and 0_s) "word". Without going into the math here, this converts into 0 thru 255 decimal or the number 0 thru FF in hex. Usually these values are called Engineering Units (EU_s).

If all data is lost, the number either reverts to 0 or 255, which usually is an out-of-limit condition.

AT THIS POINT I AM SPECULATING: If for some reason the connection to those sensors was severed, the data on the ground may just have shown an out-of-limit maxed one way or the other depending on how the bit stream was designed for that particular parameter.

[Aracelis]

Interesting post, RA. Thanks!

[VadeRetro]

So the data is ”injected” into a serial telemetry stream that only requires one (or possibly a few) links between the vehicle and the ground. This process of inserting all of this data in a specific pre-determined pattern is called commutation.

A more basic word is "multiplexing." If a bunch of separate data channels share a physical link, each coming across as if it had a link unto itself, you're typically either carving up the one physical link's frequency spectrum into channels (frequency-division multiplexing, FDM) or thinly time-slicing it (time-division multiplexing, TDM). I would suspect it's FDM in this case.

[RadioAstronomer]

Not quite. All the telemetry monitors are "gathered" as digital words and injected into the telemetry stream one at a time. The problem is figuring out how to pull that stream of ones and zeros back apart on the ground. So every so often a known set of bits, specific pattern such as "fdc0f1_hex" (nonsense number I just made up)is inserted into the stream so the ground decommutator can "pull" the data back apart and "read" the individual words. This known "word" is what is synced up on and is called the frame sync.

We can further sub-divide this telemetry stream into sub frames with a counter or a sub-frame sync to allow greater flexibility in how the parameters will be downlinked. Lets say we are doing something special, like running the robotic arm on the Shuttle. The telemetry stream has a finite space, so using a different set of sub-frames, we can downlink more data at that moment on the arm than our normal State-of-Health (SOH) telemetry monitors.

Often this link is QPSK modulated allowing for a large data rate. I have seen data rates over 300 million (yes three hundred) bits per second.

[RadioAstronomer]

Rememer, there may be more than five thousand (5000) individual monitors that can be sent to the ground. The trick is, which ones and at what time during the mission should they be sent.

[RadioAstronomer]

Sorry for the multiple posts.

Note: before the radio frequency (RF) link is modulated with this digital bit stream, the commutation has already occurred. So all the RF link "sees" (and is modulated with) is a stream of continuous ones and zeros.

[VadeRetro]

You're clearly up on the telemetry details. In any seeming conflict, I'm the outsider and wrong.

Anyway, it might be worth mentioning to the lurkers that modern communications protocols nest inside each other rather neatly. The way the Internet is put together is an example. Application programs on different machines (say, the browser on your computer and the server software on FR) talk to each other through "network sockets," which are a software analog of the old phone company socket connector panel from the days when operators physically plugged you into the line of the person you're calling. Your browser program doesn't know or care what kind of modem you have, or whether your connection is broadband or dialup. Lower levels handle that. Your traffic stream goes down to levels which talk to each other, each not knowing or caring much about how other layers work. A lower layer breaks your data stream into packets. Another layer manages merging different packets coming from different programs running on your machine at the same time. (That is, you can be checking your email while your browser downloads a new page. The routing info in the packets keeps them from getting confused.) A lower-yet layer layer handles talking back and forth with your modem. This layer, and only this one, has to know the dirty details of what kind of modem you have.

On FR's server, it's the same kind of thing in reverse. A layer handles the physical link. A layer decodes and sorts the incoming packet stream (all kinds of stuff coming in from various people all over, in jumbled order). A layer breaks the packets open and translates them into data records that the network server applications recognize. The server applications recognize things like, "Here's another goddam 'My comments' request from VadeRetro."

But the shuttle is older than the Internet, so I'm not sure if there's as much commo layering there as I've been assuming. It sounds almost as if they wrote a primitive multiplexed network in the late 70s just to do telemetry.

[VadeRetro]

Note: before the radio frequency (RF) link is modulated with this digital bit stream, the commutation has already occurred. So all the RF link "sees" (and is modulated with) is a stream of continuous ones and zeros.

Didn't see this before I posted my last. Clearly, there's some nesting of protocols.