Jim Sahli
Goddard Space Flight Center
Greenbelt, Md.

XTE Status Report #1
Jan.  17, 1996
10 a.m.

	NASA's X-Ray Timing Explorer (XTE) has concluded its engineering
checkout and the science team is now conducting a calibration of its science 
instruments before commissioning the spacecraft for full-time science research at 
the end of this month.

	"We are checking out the spacecraft instruments and mapping out the 
particular space environment of our orbit under current conditions. The densities 
of energetic electrons and protons determine when our instruments can safely 
operate and obtain good data," said Dr. Jean Swank, XTE project scientist. 

	"We are doing that while observing selected X-ray sources that allow us to 
calibrate the instrument parameters and determine that the whole system for 
interpreting the data is working correctly," said Swank.

	With the pointed instruments, the Proportional Counter Array (PCA) and 
High Energy X-ray Timing Experiment (HEXTE), "we first looked at a supernova 
remnant containing a spinning neutron star called PSR 1509-58, with a 150-
millisecond period. The PCA obtained about 120 good X-ray counts and clearly 
detected the neutron star's periodic flashes.  Results from this "first light" X-ray 
observation, an observation of the Crab nebula and pulsar and a short look at a 
quasiperiodic oscillator, can be found on the internet at the URL 
http://heasarc.gsfc.nasa.gov/docs/xte/SOF/First_Results.html.  

	“The first of many expected observations of the binary X-ray source Cygnus 
X-2 (the second X-ray source found in the constellation Cygnus) found 
oscillations of a few percent at a frequency of 20 Hz (a period of 50 milliseconds).  
The excellent signal to noise ratio promises us exciting sensitivity to oscillation 
changes. These give rise to the smearing of the frequency in the not-quite periodic 
oscillations and will change the frequency greatly in additional observations,” 
said Swank.

	After initial observations, the spacecraft’s All Sky Monitor (ASM) 
experienced problems with internal high-voltage breakdown in 2 of 3 detectors. 
The instrument has been turned off while the data is analyzed to determine 
possible recoveries. 

	"In the next couple of weeks, we will do some observations of special targets 
being observed at the same time with other satellites, while we continue to work 
on our calibrations.  We hope the system will then be ready for the proposed 
science program. We hope the ASM can be on-line then too," said Swank. 

	"We concluded our engineering checkout Friday (Jan. 5). We have checked 
all of  the spacecraft subsystems and have determined that they are operating as 
required. The bottom line is that NASA's new X-ray satellite is on orbit and 
working," said Dale Schulz, XTE project manager.  

	"During that first week on orbit the XTE operations team also turned on 
the three instruments.  At this point we are fine tuning and calibrating the 
spacecraft," said Schulz.  The XTE mission is being managed by the Goddard 
Space Flight Center in Greenbelt, Md. 

	The satellite was launched Dec. 30 at 8:48 a.m. EST from the Cape 
Canaveral Air Station in Florida.  The satellite was placed into a circular 360 
statute mile (580 kilometer) orbit with an inclination of 23 degrees by
a Delta II launch vehicle.

	Among the objects to be studied by NASA'S XTE mission are stellar black 
holes, neutron stars and quasars.  Stellar blackholes and neutron stars 
represent the end stages of the lives of stars several times heavier than the 
Sun.  Quasars are thought to be super-massive black holes about the size of
the solar system, containing the mass of billions of stars.
   
	Spacecraft officials have indicated that they are monitoring a loss of
solar array power which is stable at this time.  Engineers say that science
objectives can be met with the existing power generation capability. 

	The XTE Science Operations Facility home page can be found at http://
heasarc.gsfc.nasa.gov/docs/xte/SOF/XTESOF.html. It has links to other
information about the schedule and progress of the spacecraft checkout.

	Subsequent XTE status reports will be issued as further information 
becomes available. 
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