FOR IMMEDIATE RELEASE
NASA Headquarters
Office of Space Science
Washington, DC 20546

                                                  September 9, 1994
Dear Colleague:

This letter is to advise you of the decision at NASA Headquarters to
restructure the Explorer program for astrophysics and space physics
missions.  The Explorer program is intended to provide these
communities with a continuing program of small, low-cost,
high-flight-rate, discipline-sustaining missions.  The Explorer
program currently includes the Small Explorers (SMEX), with launches
scheduled approximately once per year, and the Delta class Explorers,
for which launches had been planned for 1995 (X-ray Timing
Explorer-XTE), 1997 (Advanced Composition Explorer-ACE) and 2000 (Far
Ultraviolet Spectroscopic Explorer-FUSE).

Both the astrophysics and space physics communities have expressed the
need for more frequent flight opportunities.  The current plan for the
Explorer program including the large Delta class missions was
developed more than 3 years ago in a time of growth in space science
when it was anticipated that a lower cost Medium Explorers (MIDEX)
series of missions, which could be flown at a more frequent rate than
the larger Delta-class, could be started through anticipated
augmentations to the Explorer budget.  These anticipated augmentations
have not materialized and it now appears certain that funding for the
Explorer program will remain flat for the foreseeable future. As the
flight opportunities planned within the current baseline are
insufficient to meet the demands of the astrophysics and space physics
communities, the only remaining option for increasing the number of
missions is to restructure the program by eliminating one or more of
the large Delta class Explorers to release funds for more frequent,
smaller MIDEX class missions.

As a consequence of these constraints, we have reached the very
difficult decision to conclude the Delta class Explorers with the ACE
mission and not to start a Delta-class FUSE mission in FY95.  The
$250M anticipated cost for the FUSE mission is simply too large for
the current Explorer line budget. Terminating the Delta-class with ACE
will therefore make it possible to initiate the MIDEX series and allow
for more flight opportunities at lower cost, with the goal of one
flight per year.  It is now anticipated that an Announcement of
Opportunity for MIDEX will be available early in calendar 1995. With
the introduction of the MIDEX series, the Explorer program would be
able to provide one SMEX and one MIDEX flight each year.

This decision has been made with the intention of optimizing the
scientific return within the entire Explorer program. Nevertheless, it
is acknowledged that the science proposed for FUSE has been ranked
among the highest priorities in astrophysics and that many dedicated
scientists have devoted years to planning for this mission.
Consequently, we will give special effort to accomplishing far
ultraviolet spectroscopy within plans developed for the MIDEX
missions.

Sincerely, 
	Signed by
Wesley T. Huntress, Jr.
Associate Administrator for
  Space Science