msnbc (boyle): Launch outlook brightens as shuttle is fueled

Alan tells it all:


1. Fuel gauge 'glitch' does NOT reappear.

2. Weather is perfect.

3. No sign of any other hardware problems.


http://www.msnbc.msn.com/id/8706454/

Launch outlook brightens as shuttle is fueled
No sign of fuel-gauge glitch; weather forecast improves as liftoff nears
By Alan Boyle
Science editor
MSNBC
Updated: 4:13 a.m. ET July 26, 2005

CAPE CANAVERAL, Fla. - During Tuesday's final preparations for the first
space shuttle mission in two years, NASA kept close watch on the shuttle
Discovery's fuel-gauge system as well as on the weather. On both fronts,
there was good news.

Discovery is due to lift off at 10:39 a.m. ET, beginning a 12-day mission to
resupply the international space station and test safety procedures that
were developed in the wake of the shuttle Columbia's catastrophic breakup in
February 2003.

Among the VIPs expected to watch the liftoff are first lady Laura Bush and
her brother-in-law, Florida Gov. Jeb Bush, as well as families of the fallen
Columbia astronauts. Thousands lined viewing areas on Florida's Space Coast.
Overnight, weather forecasters upgraded their outlook for the launch, from a
60 percent chance of acceptable conditions to 80 percent.

The first major task for launch day was to fill Discovery's fuel tank with
526,000 gallons (2 million liters) of cryogenically cooled liquid hydrogen
and oxygen - a task that took three hours. As the tank was filled,
controllers watched for a reappearance of the mysterious fuel-gauge glitch
that forced a halt to Discovery's first launch attempt, back on July 13. But
the gauges were working just as expected, NASA reported.

For days, hundreds of engineers tried to find out why one of the liquid
hydrogen tank's four low-level sensors registered bad readings - a problem
that went away after the tank was emptied.

The low-level sensors work roughly like a fuel gauge in an automobile,
alerting the shuttle's computers when propellants are close to running out.
If the system reads "empty," the computers would start shutting down the
main engines.

Failure of the system could shut off the engines too early or keep them
running on empty, risking serious damage. The sensor system is designed to
work even if two of the four low-level sensors go bad, but since the
Challenger explosion in 1986, NASA has required all four to be in working
order before launch.

Engineers narrowed down the causes of the glitch to electromagnetic
interference or grounding problems that have since been fixed.

But the only way to make sure the glitch had disappeared was to check the
sensor system under cryogenic conditions, mission managers said. So during
Tuesday's tanking, the launch team set up the same situation that resulted
in the bad readings during the earlier countdown. They also switched the
connections between the questionable sensor and a good sensor.

No sign of glitch
During Tuesday morning's tests, the system was set artificially to give an
"empty" or "dry" reading. If one of the two sensors involved in the switch
didn't show the right reading, that would help engineers narrow down the
root of the problem - and mission managers would be willing to go ahead with
the countdown as long as they feel the glitch is well-understood.

But if any other problem arose - for example, if both sensors go bad, or if
other sensors show questionable readings - the countdown would be called
off, "because that says we really need to do more testing," deputy shuttle
program manager Wayne Hale told reporters.

All the sensors were "performing as expected" as fueling ended, NASA
spokeswoman Jessica Rye reported. The tank will continue to be topped off
with propellants, and the sensor system will be monitored all the way
through the countdown, with two extra tests scheduled at T minus 3 hours and
T minus 9 minutes.

Meanwhile, an inspection crew went to the launch pad to check the tank for
any signs of excessive ice buildup.

Safety first
The main focus of this shuttle mission is to test new safety procedures in
the wake of the Columbia tragedy in 2003, which investigators traced to
damage done to the shuttle by a piece of foam insulation flying off the
external fuel tank shortly after launch. The breakup of the shuttle during
its re-entry killed all seven astronauts aboard and led to the grounding of
the rest of the shuttle fleet.

Since then, NASA has made dozens of upgrades in the shuttle and the fuel
tank, and has also taken measures to reform its "safety culture." More than
100 cameras will record Discovery's launch, and engineers have developed a
new extension boom for inspecting the shuttle in orbit. During the first of
three spacewalks, astronauts will test techniques that could eventually be
used to repair damage to the shuttle during this mission.

However, a task force monitoring the return to flight determined that NASA
has not yet met three of the Columbia Accident Investigation Board's
recommendations for heading off potential damage from ice or foam flying
from the fuel tank, or for repairing such damage.

The idea that NASA would consider launching the shuttle with an unresolved
glitch raised additional questions about the agency's commitment to safety.
When asked about the controversy over the fuel-gauge glitch, NASA
Administrator Mike Griffin said that he felt comfortable with the process
mission managers went through, and that he was more concerned about "doing
what's right, not what necessarily is obvious or popular."

Looking ahead
If the countdown is halted Tuesday, due to weather or an unacceptable
glitch, mission managers could try again Wednesday. In all, four launch
attempts could be made between now and the end of the month - with a
possible extension of the launch window several days into August. After that
point, NASA would have to wait until September, due to the lighting
conditions and the position of the international space station.

Discovery's crew is due to take up tons of supplies to the station - and
bring back tons of trash from orbit. In between, spacewalkers are to install
a replacement guidance gyroscope on the station, as well as a storage
platform for future construction jobs.

Jim Oberg wrote:
Alan tells it all:
[...]
During Tuesday morning's tests, the system was set artificially to give an
"empty" or "dry" reading. If one of the two sensors involved in the switch
didn't show the right reading, that would help engineers narrow down the
root of the problem
[...]

I'm still wondering how they do this...obviously, during this portion
of testing, they do not empty the tank and refill it to watch the
sensor change.

It also sounds like more than just enabling/disabling an inverter.

/dps

snidely wrote:
Jim Oberg wrote:
Alan tells it all:
[...]
During Tuesday morning's tests, the system was set artificially to give an
"empty" or "dry" reading. If one of the two sensors involved in the switch
didn't show the right reading, that would help engineers narrow down the
root of the problem
[...]

I'm still wondering how they do this...obviously, during this portion
of testing, they do not empty the tank and refill it to watch the
sensor change.

It also sounds like more than just enabling/disabling an inverter.



I was wondering if JimO, TimK, or Jorge had found some info to share
about this "toggling".

I believe on Sunday, Wayne Hale showed a sensor during the press
conference, and we've seen pictures of the ceramic frame with the
platinum wire woven on it, but what else is in the sensor (as opposed
to in the box in the Orbiter), and how is it toggled?

/dps