SOHO STATUS REPORT
Goddard Space Flight Center						Nov. 29, 1995
Greenbelt, Md.


     	At the Cape Canaveral Air Station in Florida, work continues to requalify the AC-121 
Atlas IIAS vehicle for the launch of the Solar and Heliospheric Observatory  (SOHO) spacecraft.  
Launch is anticipated to occur no earlier than Saturday, Dec. 2.  The launch window on that day 
extends from 2:34 a.m. to 3:25 a.m. EDT, a duration of 51 minutes.
	
	SOHO is a cooperative mission between ESA and NASA. SOHO is part of a larger effort 
known as the International Solar-Terrestrial Physics (ISTP) science initiative.  The ISTP program 
is managed by the Goddard Center. An Experiment Operations Facility located in Building 3/14 
will be used to coordinate and plan the scientific operations of the mission. 
	
	Engineers have found a generic problem with the Atlas booster precision regulator that 
malfunctioned Nov. 22 during a launch attempt.  This regulator provides reference pressures to 
control thrust of the booster engines.  The precision regulator will require removal and 
replacement and a failure analysis. 
	
	After the scrub which occurred at 10:45 p.m. on Nov. 22, engineers from Rocketdyne, 
manufacturers of the Atlas engines, located the problem with the booster engine s liquid oxygen 
precision regulator.  The diaphragm, or membrane of the regulator, was found to be made of 
polyvinylfloride instead of the correct mylar material.  A review is underway by NASA, Lockheed 
Martin and Rocketdyne as to how this occurred.  A similar regulator on the sustainer engine of the 
Atlas stage also has been identified with this problem and is being removed and replaced.  The 
Centaur stage, whose engines are manufactured by Pratt and Whitney, are not affected.  Both 
replacement regulators to be reinstalled in the AC-121 vehicle will be hot fired in 
California by Rocketdyne before being sent to Cape Canaveral for installation.
	
	A failure of the Atlas stage precision regulator in flight can mean reduced thrust which 
has the possibility for a  loss of mission.
	
	The SOHO spacecraft remains ready for flight atop the vehicle and no significant 
additional activity is required to meet a launch through early next week.