TEST REPORT

STEREO IMPACT SEP/SIT FM2 VIBRATION REPORT

Written by: Glenn Mason

Date: Aug 8, 2005

**1. OVERVIEW**

The STEREO SEP/SIT vibration test for the flight model 2 (FM2) unit was
conducted May 10-12, 2005, in the Bldg. 7 facilities at Goddard Space
Flight Center, Greenbelt, Maryland. Scott Lasley (UMd), Kristin Wortman
(GSFC), and Glenn Mason (UMd) supported instrument handling and testing
after each axis shake. Steve Wasserzug verified that the tests carried
out were in accordance with the test procedure. Test engineering support
was provided by Dan Worth and others on his staff (GSFC).

Tests were conducted in the X-, Y-, and Z- axes as defined in the Test
Plan.

After each axis, the instrument was removed from the shake cell, and
connected to its GSE for a functional test. The instrument passed all
the functional tests.

**2. REFERENCE DOCUMENTS:**

STEREO IMPACT SIT Acoustics and Vibration Test Plan, dated 17 Jan. 2005

**3. PASS / FAIL CRITERIA:**

Post-vibration CPT of the FM2 unit verified functionality was not lost
in testing. Inspection of the instrument revealed no notable degradation
mechanically or structurally.

On May 14, the telescope door was opened in preparation for the thermal
vacuum test. The door opening test on May 14 verified that the door
mechanism had not been significantly degraded.

At the time of the door opening on May 14 the outer foil was inspected
for any degradation. Two small holes or blemishes were observed in the
outer foil, but they did not show up well on photos. Since the telescope
design has provision for some damage to the foil (double foils; foils
mounted on \~1 mm square cells to prevent tears from spreading; aiming
of telescope so that sunlight never strikes the foil), this condition of
the foil was deemed acceptable.

The inner foil cannot be checked in this manner, so its status was not
determined. Inspection of the inner foil would require disassembly of
the telescope. However, since the outer foil showed only minor
degradation, and since the instrument was operating normally, it is
assumed that the inner foil was not significantly damaged in the
vibration test.

On July 8, 2005, the fm2 telescope was opened to replace the noisy solid
state detector. At this time the inner foil could be inspected, and it
was observed that 3 cells were broken on the inner foil. It is assumed
that these 3 broken cells on the inner foil, and the 2 broken cells on
the outer foil, were damaged during the vibration testing. The inner
foil broken cells were in different locations than those on the outer
foil, and so would not have been a significant problem if this had
occurred during flight. However, since the telescope was now open, and a
replacement pair of foils readily available, it was decided to install a
new set of foils.

The most likely time during the vibration when the foil damage occurred
was during the z-axis sine sweep. For this test, the telescope is moving
in a direction perpendicular to the foil surface. Because the telescope
door was closed during the test, in principle the air inside the
telescope will remain at rest, but pressure waves may set up in the
telescope resulting in small differential pressure across the foil. The
foil is extremely fragile to differential pressure. The telescope design
allows for rapid venting around the foil so that pressure does not build
up. This accommodates any systematic pressure changes during pump-down
or launch, but the sine sweep test is more dynamic and this may have
caused the problem.

Since there is no requirement for an additional sine sweep test of the
instrument, we believe that the risk of this damage occurring again
during I&T is very small.

During each axis test, the survival heater was powered, and the current
draw monitored visually on the power supply dial. There were no
variations observed in the survival heater current during the vibration
tests.