function launch, dsince=dsince
;
;+
;   Name: launch 
;
;   Purpose: return yohkoh launch day (default) or days since 
;
;   Optional Keyword Parameter:
;      dsince - if set,  returns number of days since launch
;
;   History: slf, 25-Mar-92
;
;-
launch='10:30:00 30-Aug-91'
;
retval=launch
if keyword_set(dsince) then $
   retval=fix(addtime(syst2ex(),diff=anytim2ex(launch))/(24*60))
;
return,retval
end