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starship-design: FW: SSRT: X-33 Tank Delivered, Strength Questioned

-----Original Message-----
From: listserv@ds.cc.utexas.edu [mailto:listserv@ds.cc.utexas.edu] On
Behalf Of Chris W. Johnson
Sent: Tuesday, May 25, 1999 10:42 PM
To: Single Stage Rocket Technology News
Subject: SSRT: X-33 Tank Delivered, Strength Questioned

Summary of "X-33 Tank Delivered, Strength Questioned" by Michael A. Dornheim
in Aviation Week & Space Technology, May 10, 1999, pp 68-69:

"Lockheed Martin has delivered [the right-hand] X-33 composite liquid
hydrogen tank to NASA's Marshall Space Flight Center for testing, showing
that the experimental rocket program is beginning to recover form a large
structural failure of a tank in December."

* Tests indicate that the right-hand "tank is weaker than expected, and
engineers are trying to calculate what, if any, strength margin remains."

* The left-hand liquid hydrogen tank was more extensively damaged during
the Dec. 23, 1998, autoclave cycle than previously thought. "Besides the
massive delamination of one of the four graphite/epoxy honeycomb tank
walls, another wall (lobe skin No. 4) sprung loose from the graphite/epoxy
frame that holds the walls and end domes together."

* Subsequent tests have shown that the bond between the tank wall's
honeycomb core and its face sheets is 25% weaker than expected under
tension. Shear strength is what's really important, however, and engineers
are still trying to reach useful conclusions about it. Directly testing it
would be destructive. It is believed that the minimum 1.25 safety factor
is still met, though.

* The tank (left-hand) "should be delivered to Marshall for tests by July
or August."

* Questions are being raised about X-33 performance. Intended to fly to
Mach 15, its ability to reach that speed is in doubt. T. Cleon Lacefield,
LockMart X-33 program manager, states that it should reach Mach 13,
at a minimum. That is still sufficient to test the vehicle's thermal
protection system. However, some engineers are reporting that X-33's top
speed will really be Mach 10, and that this has been known within the
project for some time. "Weight is the culprit. The weight at main engine
cutoff has risen to 83,900 lb. from the initial specification of 69,000
lb., a 20% growth. But Lacefield says people may be confused by an upper
limit of Mach 11 to stay within Michael AAF."

Chris W. Johnson                  | "Do we realize that industry,
                                  |  which has been our good servant,
chrisj@mail.utexas.edu            |  might make a poor master?"
http://gargravarr.cc.utexas.edu/  |             --Aldo Leopold, 1925