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Engineers Find Cracks in Shuttle Fuel Tank Foam



COPIED FROM AMSAT & SPACE.COM NEWS

SUBMITTED BY ARTHUR N1ORC - AMSAT A/C# 31468

*Engineers Find Cracks in Shuttle Fuel Tank Foam *
*By Tariq Malik <http://www.space.com/php/contactus/feedback.php?r=tm>*
Staff Writer
posted: 22 November 2005
4:43 p.m. ET

/This story was updated at 5:41 p.m. EST. /

Engineers investigating a debris shedding problem with NASA’s shuttle 
fuel tanks have found a series of hairline cracks in the same area where 
foam popped free during the July launch 
<http://www.space.com/missionlaunches/050726_sts114_launchsuccess.html> 
of the Discovery orbiter, agency officials said Tuesday.

A total of nine cracks – only two of them visible on the surface – were 
detected along a protective foam ramp on NASA’s External Tank 120 
<http://www.space.com/missionlaunches/rtf_tank_041228.html> (ET-120), 
one of several under scrutiny at the agency’s Michoud Assembly Facility 
in New Orleans, tank officials said during a briefing at the agency’s 
Johnson Space Center in Houston.

“We’re still trying to figure out what this means,” said NASA’s John 
Chapman, external tank project manager at Marshall Space Flight Center 
in Huntsville, Alabama. “I wouldn’t consider that a Eureka [moment] or 
smoking gun at all.”

Originally tapped 
<http://www.space.com/missionlaunches/rtf_tankupdate_050106.html> to 
fuel Discovery’s STS-114 <http://www.space.com/returntoflight/> liftoff 
but later replaced 
<http://www.space.com/missionlaunches/050519_rtf_tankswap.html>, ET-120 
was one of three tanks sent back to Michoud from NASA’s Kennedy Space 
Center in Florida and the only one of them to hold the supercooled 
liquid fuel used during shuttle launches.

Shuttle program manager Wayne Hale added that, while the engineering 
assessment of the cracks is still pending, it appears that the thermal 
and pressurization changes involved in fueling the tank during two tests 
<http://www.space.com/missionlaunches/ft_050520_sts114_tankupdate.html> 
may be one potential cause.

“It does appear that that’s a factor,” he told reporters.

Hale said that if everything proceeds as expected, NASA could be ready 
to launch Discovery on STS-121, the agency’s second return to flight 
mission, in May 2006 
<http://www.space.com/missionlaunches/051014_rtf_shuttle_update.html>, 
but stressed that the external tank work – not a schedule – comes first.

*Safeguarding shuttles*

Preventing the loss of potentially harmful chunks of external tank foam 
during a shuttle launch has been a major focus of NASA since the loss of 
the Columbia orbiter <http://www.space.com/columbiatragedy/> and its 
seven-astronaut crew during reentry Feb. 1, 2003.

A 1.37-pound chunk of foam critically damaged Columbia’s heat shield at 
launch leaving it vulnerable to the searing hot atmospheric gases during 
its descent, investigators later found.

NASA spent two and a half years and some $200 million to reduce the 
amount of large foam debris during shuttle launches, but was surprised 
when an onboard camera caught 
<http://www.space.com/missionlaunches/050727_rtf_sts114_shuttle_grounded.html> 
a one-pound chunk fall from a protective ramp thought to be safe.

The cracks on ET-120 were found on the same ramp – known as a 
Protuberance Air Load (PAL) ramp – designed to protect fuel length 
cabling from the aerodynamic pressures of launch.

Hale said that while initial shuttle fuel tanks designed in the late 
1970s required PAL ramps, newer containers have been improved and 
strengthened over time. Plans are underway to streamline foam 
applications on the PAL ramp – which consists of 22 pounds of insulation 
foam – as well as strip it from future tanks altogether, he added.

“It is possible that we may get there for the first flight,” Hale said, 
referring to STS-121. “It is more likely that it may take us until the 
fall to complete that work.”

*Orbiter work*

While engineers continue their work on shuttle fuel tanks, other workers 
are preparing the orbiters themselves for flight.

Steve Poulos, head of NASA’s orbiter project office, said that engineers 
have determined that faulty stitching caused a nose-mounted thermal 
blanket 
<http://www.space.com/missionlaunches/080503_sts114_blanketupdt.html> to 
balloon outward during Discovery’s STS-114 flight.

“We’ve inspected 486 blankets on both Discovery and Atlantis,” Poulos 
said, adding that 40 blankets will be replaced aboard Discovery and 60 
on Atlantis.”

Shuttle workers have also pored over Discovery’s heat-resistant 
reinforced carbon carbon (RCC) panels that its nose and wing leading 
edges to determine which need replacement or repair.

Poulos added that new adhesion processes are also in hand to glue 
ceramic cloth gap fillers 
<http://www.space.com/missionlaunches/050731_sts114_gapfillers.html> 
between the heat tiles that line a shuttle’s underside.

During Discovery’s STS-114 flight, orbital photographs 
<http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=h_exp11_sts114_gapfiller_02.jpg&cap=In+this+view+of+Discovery+seen+from+the+International+Space+Station%2C+one+of+two+protruding+gap+fillers+can+be+seen+jutting+out+from+between+the+shutt> 
showed two gap fillers jutting out of the orbiter’s tile-lined belly, 
raising concern that they may lead to hotter reentry temperatures along 
the shuttle’s aft. STS-114 astronaut Stephen Robinson plucked the 
offending gap fillers from Discovery’s hull during the flight’s third 
spacewalk. 
<http://www.space.com/missionlaunches/080503_eva3_gapfiller.html>

“At the end of the day, we will have checked every gap filler on the 
vehicle,” Poulos said
----
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