Potentially fatal rudder flaw revealed in shuttle

NewScientist ^ | March 23, 2004 | Jeff Hecht

[NCjim]

A potentially disastrous problem with a space shuttle rudder went undetected for two decades, NASA has revealed. However, the problem can be fixed in time for the shuttle's planned return to flight in March 2005.

When a shuttle returns to Earth, the rudder brakes the craft to a speed that is safe for landing. Shuttle program manager Bill Parsons told a press conference on Monday that a gear in one of four actuators that move the two-part rudder was installed backwards on Discovery.

By good fortune, the defective actuator was installed in the top position on the tail-mounted rudder, where it was subject to the least force. However, the faulty actuator could not have handled the most extreme forces during landing if it had been in the bottom position.

That could have disabling the rudder by jamming it open or closed. "Loss of the rudder speed brake would mean loss of vehicle and loss of crew," said Parsons.

Slightly asymmetric

The mistake dates back to the actuator's assembly at Hamilton Sundstrand in Rockford, Illinois, and is not easy to spot. The gear fits into the assembly both ways, but is slightly asymmetric so the teeth do not fit exactly if the gear is reversed.

Discovery flew safely 30 times with the defective actuator since its first launch August 30, 1984, and no one suspected a problem until the actuator was taken apart to check for corrosion.

NASA had spotted rust on similar body-flap actuators and was planning to test the rudder actuators before the Columbia disaster. During return-to-flight checks, engineers removed Discovery's four rudder actuators, and inspections revealed corrosion and microcracks - and the reversed gear.

NASA then went back and removed the four spare actuators it had installed into Discovery when the original four were removed. They found that the one next to the bottom also had a reversed gear. "It's a process mistake that shouldn't have happened," Parsons said.

Rescue mission

Discovery's original actuators are being scrapped, because the course of corrosion is hard to predict, and a small chip falling off could jam a gear. The replacement actuators will be repaired and returned to Discovery.

There had been concern that actuators would not be available for Atlantis, which must be ready for a possible rescue mission when Discovery launches.

However, NASA has found two spare actuators, and has 94 per cent of the parts needed to build two more, Parsons said. He says the remaining parts could come from actuators being removed from the least-flown shuttle, Endeavour. That leaves Parsons "feeling pretty comfortable" about meeting the timetables needed for a return-to-flight launch of Discovery in March 2005.

A lot more progress than expected has been made on repair techniques for the reinforced carbon composite panels on the leading edge of the wings, a hole in which doomed Columbia. Parsons also cited progress on upgrading the shuttle arm so it could check the shuttle for damage, as recommended by the Columbia Accident Investigation Board.

[NCjim]

Thank goodness they found this before we lost another shuttle...

[jmcclain19]

Nothing like using 30 year old technology to go to space.

Imagine using a car for that long, let along an object subject to that amount of stress each flight.

Safety isn't exactly priority one with Nasa.

[Oztrich Boy]

Just Damn. When are they going to get around to repealing Murphy's Law?

[mwyounce]

I'd say they did.... if Murphy's law were in effect, Discovery would've been the first shuttle disaster on it's initial landing.

[Damagro]

Just the fact that this part was possible to install backwards is idiocy. What kind of engineer would design a part this critical without at least a locator to prevent this from being possible?

[Oztrich Boy]

No they didn't. they mamaged to install the actuator backwards, and were just lucky that it was the non-critical one.

[Oztrich Boy]

Imagine using a car for that long,

I don't have to imagine.

[mwyounce]

Not to argue semantics, but isn't Murphy's law "EVERYTHING that can go wrong will go wrong." I'm just saying that not EVERYTHING went wrong.... if everything had gone wrong, the Discovery wouldn't be here today either.

[First_Salute]

Bump.

[Oztrich Boy]

Not to argue semantics, but isn't Murphy's law "EVERYTHING that can go wrong will go wrong."

That may be the Family Feud understanding, but the Original Murphy's Law as formulated by Commander (later Admiral) Joseph M Murphy was
"If the design allows some part to be installed incorrectly, sooner or later some idiot will do so".

In other words it's not a fatalistic "we're doomed" idea, but a design it right originally maxim.

[tubebender]

Do you have the ping list for the Columbia thread...

[XBob]

thanks for the ping.

There never was a real ping list, just sort of a group of us who tried to ping each other. I am probably the last of the group. Bonesmccoy got into some sort of a religious/corruption argument and got banned, (for a while at least) and left (though I think he may check in occassionally). Snopercod got bored and left. The others I dont know, but it would be nice to get together a ping list and get back together for the next launch, if we ever have one.

[XBob]

note - if I were still working on the shuttle, this is where I would be involved, making sure all the problem parts were there at the right time and in the right place for the guys to do their jobs. The missing 6% could be a real bitch:

"However, NASA has found two spare actuators, and has 94 per cent of the parts needed to build two more, Parsons said. He says the remaining parts could come from actuators being removed from the least-flown shuttle, Endeavour. That leaves Parsons "feeling pretty comfortable" about meeting the timetables needed for a return-to-flight launch of Discovery in March 2005."

Apparently they can't find them, and are going to cannibalize them and make another orbiter unflyable, and then the race is on to get somebody to gear up the manufacturing to build them by the time that shuttle is due to fly. (that's if they don't break the old parts taking them off or reinstalling them).

I wonder if this problem impacted the colombia? The way the problem is worded in the story, it possibly could have.

[tubebender]

I wonder if this problem impacted the colombia? The way the problem is worded in the story, it possibly could have.

That was my thought and why I pinged you. Sorry to hear about Snopercod...

[XBob]

Yes. Polling my memory, and I may be wrong, but I seem to remember some report of rudder anomalies not long before breakup. I would have to research it, but it would be on our long thread. And as the control became more and more tenuous, if the rudder froze or the break deployed. I know the OMS/RCS motors were busting their butts to keep it flying straight (unusual activity), and the elevons were moving to maximum. I don't think the rudder was supposed to activate yet. But these thoughts are just working from memory.

[XBob]

from story - "That could have disabling the rudder by jamming it open or closed. "Loss of the rudder speed brake would mean loss of vehicle and loss of crew," said Parsons."

The 'rudder' on the orbiter is rather strange in that it is multipart, and has a speed brake incorporated into it which opens sort of like a clam, hinge side forward, to act as a speed brake. In addition to the left/right movement of the major part of it (generally used only near the end for aerodynamic steering).

Ah sorry if any inaccuracies. This particular thing was not my area, and I am sure one of the others from our thread would have a better knowledge of its operations.

[mwyounce]

The United States Air Force seems to agree with my "Family Feud" understanding... although they also attribute it to a different Murphy than you did:

http://www.edwards.af.mil/history/docs_html/tidbits/murphy's_law.html