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Early evidence says shuttle tank foam performed well BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: August 30, 2009 
The shuttle Discovery's external tank appears to have performed well during the ship's launch overnight Friday. While engineers will not complete a detailed analysis for several more days, no major problems or foam loss have been seen so far in NASA's initial looks at ascent imagery and other data.
Shuttle commander Frederick "C.J." Sturckow will be flying the final approach to the station Sunday evening using the shuttle's big primary reaction control system thrusters, or PRCS jets, instead of less-powerful vernier jets. Two 24-pound-thrust vernier rocket engines are available in a nose-mounted rocket pod while four are available in the aft. But the right-firing forward vernier jet failed shortly after launch, forcing flight controllers to close a manifold and isolate both forward thrusters. As a result, Sturckow will be making NASA's first space station rendezvous and docking carried out with the larger 870-pound-thrust primary maneuvering rockets. "At this point, vernier thrusters are not available to us," Cain said. "We do have a couple of backup modes to the verniers and so it's really not a problem for us to use the other thrusters for attitude control and for maneuvers. ... The crew is very well trained for this particular failure mode, they've trained it numerous times. And so we don't have any concerns for that." Using what's known as the ALT-DAP, or alternate digital autopilot mode, the shuttle's flight computers will fire the primary jets as required to maintain Discovery's orientation in space while Sturckow, flying the shuttle from the aft flight deck, will use the big thrusters to move in for docking around 9:04 p.m. EDT. "I would characterize it as being slightly more challenging, simply because of the different autopilot modes the crew trains to and flies with," Cain sad. "They've certainly done more training where we have vernier autopilot mode available to us than cases where they don't have it." Once docked, the orientation of the combined shuttle-station "stack" will be maintained primarily by the station's control moment gyroscopes and Russian rocket thrusters. The shuttle's vernier jets normally are used to supplement the gyros, but that option is not available this time around. "It's a pretty sophisticated DAP mode where based on moments of inertia, the DAP can figure out which jets to fire individually to maintain attitude control and to do maneuvers," Cain said. "We have both of those modes for shuttle flying alone. Once we're docked, we do have the ability to use ALT-DAP for attitude hold (but) it's lower priority than some of the other modes for handling attitude for shuttle station combined." During the shuttle Endeavour's launching in July, an unusual amount of foam insulation fell away from the central intertank region of the ship's external tank. In addition, a piece of foam separated from an ice-frost ramp on the upper liquid oxygen section, the second flight in a row to experience that problem. Discovery's flight was delayed while engineers conducted extensive tests to make sure the next two tanks in the launch sequence were in good shape. Cain said based on a very preliminary look at the data, the intertank foam and the ice-frost ramps on Discovery's tank suffered no major losses. "From what I've been told, what we have seen is what we consider to be normal kind of erosion on a couple of the ice-frost ramps on the LOX tank," Cain said. "Don't see any losses, if you will, on the ice-frost ramps, nothing like on (the last two missions) where we had losses on the 718 IFR. So that looked really good to us." Likewise, "the intertank looked very good. As you know, we had several areas of losses from the interank on the previous mission and the intertank (on Discovery's tank) looked very good. We had one loss that I believe was in the intertank flange area, so the folks will be looking at that. ... But that would be very much in family with what we've been seeing on all these missions."
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