Wet dress rehearsal

File:COTS 2 Falcon 9 - WDR.1.cropped.jpg

A Falcon 9 rocket during a Wet Dress Rehearsal on 1 March 2012

A Wet Dress Rehearsal (WDR), or a more extensive Static Fire, are system tests of a fully integrated space launch vehicle and its associated ground support equipment (GSE) prior to launch. The spacecraft or payload may or may not be attached to the launch vehicle during the WDR or static fire, but sufficient elements of the rocket are in place to help verify that the rocket is ready for flight, allowing problems to be seen prior to the actual launch.

A wet dress rehearsal is called “wet” because the liquid propellant components (such as liquid oxygen, liquid hydrogen, etc.) are loaded into the rocket during the test.

Static fire

A static fire test takes a wet dress rehearsal and goes one step farther: actually firing the engines at full thrust. The engine (or engines) is fired, while the launch vehicle is held firmly attached to the launch mount, for a few seconds so as to test engine startup while measuring pressure, temperature and propellant-flow gradients. The data gathered in such tests may be used to form a basis, upon analysis, for a unique (rocket- and engine-specific) set of criteria that will form a part of the go/nogo decision tree in the automated launch software that is used on the actual launch day, typically a few days later. Some static fire tests have fired the engines for up to seven seconds, although shorter firings are more typical.

External links

• SpaceX Systems Engineering presentation from CASE 2012, 28 September 2012. Includes description of SpaceX approach to fifth-level hardware-software integration testing during their wet dress rehearsal and/or static fire testing.