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Dengan Hormat.

A Blue Sky Investigation
Finding out what happened to the Columbia is a unique challenge?and the answer 
may be lying in the Arizona desert
http://www.spectrum.ieee.org/WEBONLY/wonews/feb03/colinvest.html

As search parties recover wreckage and engineers sift through telemetry 
records, the harsh fact is that finding out how and why Space Shuttle Columbia 
broke up in clear blue skies during reentry on 1 February is likely to be one 
of the most difficult aerospace investigations ever, and certainly tougher than 
the 1986 Challenger investigation.

Although both disasters were equally fatal, the Challenger?s demise was still 
considerably less violent than Columbia?s: travelling at a relatively low 
velocity (Mach 1.5) and at a relatively low altitude (11 000 meters) at least 
some of the crew survived?albeit by a few seconds or minutes?the detonation of 
Challenger?s external fuel tank (ET). The 1986 debris search area was 1 650 
square kilometers off the coast of Kennedy Space Center, and many large 
sections were recovered, including most of the crew module. In addition, in 
1986 the explosion occurred within range of the phalanx of cameras used by NASA 
to record launches.

But Columbia was destroyed while travelling at Mach 18.3, some 63 100 meters 
up, visible only as a meteor streaking across the dawn sky. The debris field 
potentially stretches from Louisiana to the coast of California?an area of 
62,000 square kilometers of often rugged land. "There?s not a lot of experience 
[of this kind of search]. There?s few contingencies that you could compare this 
with," said Michael Kostelnik, NASA?s deputy associate administrator for the 
International Space Station and space shuttle. A few medium-sized pieces have 
been discovered so far, including a fuel cell, a section of fuselage, and a 
large portion of one or more of the space shuttle main engines, but most of the 
fragments have been small, hinting at the ferocity with which Columbia was 
destroyed. In any case, most of the fragments recovered to date come from 
Columbia?s final moments, and are likely to provide only limited insight into 
the cause of the disaster.


Three way investigation
The accident investigation has turned to pursuing three main lines of attack. 
The first is to unravel the stream of telemetry from Columbia, and it has been 
the most fruitful so far. A number of sensors monitoring the landing gear 
hydraulics detected a temperature rise of 16 to 22° in the left wheel well at 
7:53 Central Standard Time, minutes before the shuttle was destroyed. "This was 
the first occurrence that indicated a thermal event," was happening, explained 
Ron Dittemore, NASA?s manager of the space shuttle program. Then sensors 
monitoring the shuttle?s left elevons dropped out?the wiring for these sensors 
is routed close to the left wheel well. [For a detailed timeline of the 
Columbia disaster and investigation see 
http://www.spectrum.ieee.org/WEBONLY/wonews/feb03/coltline.html]

Although early speculation instantly focused on the wheel well as the location 
of the breach in Columbia?s thermal protection system (TPS), the data in fact 
rule this out. The relatively small temperature increase in the well, compared 
to the 1500° C temperature of the plasma buffeting Columbia at that time, means 
the wheel well is "not the point of a large thermal excursion," said Dittemore. 
"That?s reflecting something else?it does not seem logical that the wheel well 
would be the source" of the TPS failure. This view is supported by another 
sensor located along the top of the left wing, where it meets the main body of 
the orbiter, which also began to detect a similar rise in temperature around 
the same time?too soon for such a mild temperature increase originating in the 
wheel well to have been conducted to the upper wing.

Data sent from Columbia?s flight control system also indicate that it was 
trying to cope with an increasingly damaged left wing surface. At 7:58, the 
left elevons began to adjust the trim of the vehicle. "This is indicative of an 
increase in drag on the left hand side, [which in turn] is indicative of rough 
or missing tile," said Dittemore. The drag increased and the flight control 
system fired a number of rocket jets to help keep the shuttle on course. 
Although the amount of drag the shuttle was experiencing was within the 
capacity of the flight control system to handle, "we?re interested in the rate 
of change," of the increase in drag, said Dittemore. "We were losing ground." 

More clues may be found in telemetry that never reached flight controllers? 
screens. To avoid flight controllers reacting to a non-existent reading, 
telemetry must pass through a quality control filter before being displayed. 
NASA estimates some 32 seconds of additional data after voice contact was lost 
with Columbia at 8:00 am may by sitting in the bowels of NASA?s computers and, 
when examined manually, may yield information. But retrieving the partially 
corrupted data has proved "not as easy as originally thought," said Dittemore. 
A team has been sent to see if more data can be extracted from the White Sands, 
New Mexico, shuttle downlink receiving station, which passes telemetry on to 
Houston


Tiles are the key
The second line of inquiry is focusing on searching for material from as far up 
the trail of debris as possible, including in California and Arizona. "If it 
exists, it?s extremely important?it could be the key in the puzzle," said 
Dittemore. The further up the trail, the closer the origin of the material will 
be to the location of the shuttle-destroying event.

Observers in California have reported seeing debris separating from Columbia as 
it passed over head. NASA is taking the reports seriously, as it could indicate 
that tiles were peeling away from the skin of the shuttle much earlier than 
originally thought. Kostelnik confirmed that investigation teams have been 
dispatched to possible debris sites in California and Arizona, but cautioned 
against presuming the material was from the shuttle, as suspected debris was 
recovered close to the main debris field in west Texas, which turned out to 
have "nothing at all," to do with the shuttle.

Finding an intact tile from far upstream could also greatly speed pinpointing 
the origin of the Columbia?s failure for another reason: each tile is 
individually labeled with a serial number, painted in a yellow paint designed 
to survive re-entry temperatures. If the number is legible, finding out where a 
tile came from will not require a lengthy reconstruction of the orbiter, but a 
simple database search.


Second Guessing
The third main line of investigation is replaying NASA?s analysis of the 
collision of a piece of ET (external fuel tank) foam insulation with Columbia 
about 80 seconds after liftoff on 16 January. The collision with the foam was 
detected when engineers reviewed film of the launch the following day. The 
resulting analysis concluded unequivocally that the collision did not 
constitute a threat to the orbiter, although in a worst case situation some 
localized damage could be expected. But this would only be a repair issue when 
preparing Columbia for its next flight.

The analysis was based on the launch film, a computer software program that was 
strongly biased in favor of overestimating damage, and evidence gleaned from 
earlier flights that had sustained collisions with debris from the ET without 
suffering significant damage. However, the size of the foam fragment was 
estimated at 51 cm x 41 cm x 6 cm and Kostelnik admitted that "if the 
dimensions are accurate, this is the largest piece we?ve [ever] had."

The analysis estimated the mass of the fragment to be a mere 1.21 kg, but 
questions have been asked as to how that estimate was reached. Ice frequently 
forms on the supercooled ET, and if the foam fragment was saturated with water 
and it subsequently froze, that would increase the mass of the fragment 
significantly?a block of ice of the same size as the fragment would weigh 11.3 
kg. And that would increase the likelihood of serious damage.


Putting it all together
While it is certain that there are surprises ahead and that the cause of the 
Columbia disaster may be found on a completely separate line of inquiry from 
the ones outlined above, it?s clear that some kind of failure of the thermal 
protection system occurred, virtually ruling out problems with Columbia?s 
payload, maneuvering engines or flight control computer. Whether this thermal 
failure was the cause, or result of, Columbia?s structural failure is as yet 
unknown. Right now "we have pieces of info, but it?s all around the edges," 
warned Dittemore. "We may never know the exact root cause because there?s not 
enough data, and we may just have to just use our best judgement." 

Whether or not the US will accept NASA?s best judgement in the wake of two 
fatal shuttle accidents is an open question, but it is clear that until some 
conclusion is reached about the cause of Columbia?s demise, the entire shuttle 
fleet will stay on the ground. If the cause is discovered relatively quickly to 
be the result of a one-off sequence of events, the shuttle fleet may escape the 
almost three year halt in flights that followed the Challenger disaster. If the 
cause is found to be inherent to the shuttle?s design or operation, or never 
determined with any confidence, Columbia may have the bitter irony of being the 
first and last shuttle to fly with humans onboard. 

With any possible US replacement vehicle at least a decade away from flight, 
and an incomplete, but occupied, International Space Station (ISS) orbiting 
overhead, the ability of the Russian, European?and even Chinese?space programs 
to meet the challenges of human space flight now take center stage. In 
particular, Russian Soyuz and Progress vehicles will be critical to the ISS, 
and for an analysis of Russia?s readiness to step up to the plate, see 
Anatoly?s Zak?s IEEE Spectrum Online article at 
http://www.spectrum.ieee.org/WEBONLY/wonews/feb03/colrussia.html.


Terima Kasih.
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