DOCUMENT:
XRT-OAB-PR-002
ISSUE:
2
SUBJECT:
Post TVAC test XRT Mirror Inspection
DATE:
8th July 2004
PREPARED BY:
G. Tagliaferri
CHECKED BY:
O. Citterio
APPROVED BY:
G. Chincarini
SIGNED BY:
XRT Mirror Module
Osservatorio
Astronomico di Brera
XRT FPCA
Tony Abbey
University of Leicester
XRT Lead
David Burrows
Penn State University
Observatory I and T
Manager
Mark Edison
Spectrum Astro
Quality Assurance
Terry Fletcher
Spectrum Astro
Instrument Module
I and T Manager
Joanne Baker
GSFC
Contamination Control
Diane Day
Swales
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CHANGE RECORD
ISSUE
0
1
2
3
4
5
DATE
25 May 2004
31 May 2004
8 July 2004
CHANGE
Draft
Issue 1
Issue 2
DISTRIBUTION
University of Leicester
Space Research Centre
Penn State University
Physics and Astronomy
Osservatorio Astronomico di Brera
Tony Abbey, Tim Stevenson, Alan Wells
Swales Aerospace
Diane Day, Brian Kittle
Spectrum Astro
Mark Edison, Terry Fletcher
NASA Goddard Space Flight Center
Renan Borelli, Oren Sheinman, Joanne Baker,
Pat Izzo
Dave Burrows, Joe Hill
Sergio Campana, Guido Chincarini, Oberto
Citterio, Gianpiero Tagliaferri
APPLICABLE DOCUMENTS
XRT Requirements Document, XRT-PSU-015
NFI Door Deployment Test Procedure, 1143-ET-M42685
XRT Contamination Control Plan, XRT-PSU-030
1.0 SCOPE OF DOCUMENT
This document specifies the steps to be carried out for the XRT Mirror inspection after
Swift has completed its Environmental Tests including TVAC and Acoustics. The
inspection will be performed while Swift is mounted on the Ransome table and after the
XRT Door Deployment on the primary side. It is assumed this procedure will only be run
from the NFI Door Deployment Test Procedure.
1.1 Motivation to Inspect the Mirrors
It has been recognised that, after the Acoustic Test is performed on the Swift satellite, it is
necessary to check the glued connections that are fixing the 12 mirror shells inside the
grooves on the spider arms. According to the qualification test performed on the X-ray
optics at the unit level, we do not expect that these connections will have been damaged
by the Observatory Environmental Tests. However, we know that very strong vibrations
can damage them (from the development tests carried out for the Jet-X project). In this
case, the quality of the X-ray image could be altered and the on-ground calibration will no
longer be valid. In the worst case, the glue may be completely removed and the HEW
could degrade from ~18 to ~30 arcsec at 1.5 keV while the effective area could be
reduced by 30-50% due to the mirror contamination from the debris.
Thus, although the glued connections have been qualified to a much higher level of stress
and we do not expect them to be damaged, it is nevertheless important for the complete
control of the hardware and of the mission to re-evaluate their status post environmental
testing and before launch.
1.2 How the Inspection will be performed
For a full evaluation of the mirror status it would be necessary to perform a new X-ray
calibration campaign. To this end we would need to take the Swift satellite to an X-ray
calibration facility, send X-ray photons through the X-ray mirrors and evaluate their
performance again. Clearly this is not possible. Thus, we will evaluate the status of the
glued connections via a visual inspection. In this way we will assess the status only of the
glued connections on the front spider, because the rear spider will not be visible. Given
that the connections are the same and that the stresses transmitted to the two spiders will
be very similar (the Mirror Module is fixed to the Spacer at its centre at an equal distance
from the two spiders), it is reasonable to assume that the connections on the rear spider
will be in the same state as those on the front spider.
Figure 1: This schematic shows the set-up for the mirror inspection. The satellite distance from the
ground and its orientation are only indicative, in order to give an idea how the test will be carried
out.
1.2 Inspection Requirements
To perform the mirror inspection we need a digital camera (optical zoom 8 or better, or
lens with ~200 mm focal length, and 5 to 8 Megapixels), a tripod and a lamp to illuminate
the spider arms and the glued connections (see the set-up sketched in Figure 1). We also
need a lap-top or desk computer to transfer the images to properly evaluate them. The
lamp must be adjusted to have a uniform illumination without shadows on the spoke side
to be photographed. The flash of the camera must be kept off to protect the Solar Cells on
the front of the Inner Baffle. The lamp must be placed about 5º-10º out of the optical axis
to avoid photons passing through the optics by two reflections on the active surface of the
mirrors. A UV-blocking filter, blocking wavelengths below 350 nm, should also be put in
front of the lamp to avoid fixing any particulates on the mirror surface.
Figure 2 shows how the pictures are expected to look for a good evaluation of the glued
connections. This picture was taken with a Nikon camera Coolpix 5700 at optical zoom
8x. The connections, made with a blue, coloured glue, are clearly visible and from
zooming in on the various parts it is possible to evaluate their status. In this picture only
one side of a spider arm is shown, clearly we need to take a pictures on both sides. This
will then need to be repeated for all 12 arms of the front spider. Moreover, in order to
make sure that all 12 arms are checked, we need to fix a zero point on a reference arm
(e.g. the one nearer to the Star Tracker or any other reference point that can be used for
this purpose).
The Digital camera and lamp will be moved to the position to which pictures of the
reference arm can be taken, from there on pictures of the next arm will be taken moving
always in the same direction (either clockwise or counter-clockwise) in order to take
pictures of all 12 spider arms. The pictures will be numbered from 1 to 12, altogether
2x12 pictures need to be taken for each side of the spider arms.
Figure 2: This photograph, taken in the same configuration foreseen for the inspection after
TVAC and Acoustic Tests, shows the blue glued connections on one side of a spider arm (2 spider
arms are visible).
1.2 Inspection Procedure
Minimum 30 minutes photo set up time will be required prior to beginning test. The XRT
Door will be taped shut while the set-up is performed.
One hour is planned for the photography with the XRT Door open.
1. Mount a single 250 watt quartz lamp above and as close as possible to the barrel
of a 200mm lens. The front of the lamp should be approximately ¾ inch forward
of the lens first surface.
TC ____________
2. Set up camera on tripod approximately 7 ft above floor in front of XRT.
TC ____________
3. Align the optical axis of the lens with the optical axis of the XRT as a starting
position.
4. Position the front of the lens 36.5 inches from the front of the telescope. Front of
lens to glue joint will be 64 inches.
TC ____________
5. Perform steps 6 and 7 if a lamp intensity less than 250 Watts is necessary. If not
continue at step 8. 250 Watts?_________
TC ____________
6. Plug the lamp into a Variac
7. Adjust the Variac to lower the lamp wattage.
TC ____________
TC ____________
8. Attach a 2B ultra violet cut off filter to the front of the lamp. Insure lamp and
filter have adequate ventilation.
QA ___________TC ____________
9. Set up a lap top PC close to the camera position.
TC ____________
10. Attach a flashcard reader to the computer USB port. The computer will have a
version of Adobe Photoshop or software capable of viewing TIFF images.
TC ____________
11. Place a 512 megabyte image card into the camera. 2 image cards will be used.
Labelled A and B
TC ____________
12. Adjust camera as follows:
a. ISO = 125
b. exposure control = manual
c. metering = spot
d. white balance = tungsten
e. format = TIFF
f. timer = 5 sec
g. anti-mirror = on
h. aperture = f 22
TC ____________
13. Verify no more than four people total are in the SCA and only two people with in
the vicinity of the Observatory (Door Technician and Photographer)
TC ____________
14. Establish the reference spider arm. See Figure 3 and mark (use TAM Baffle as a
reference point)
TC ____________
15. Make test exposures
a. turn on lamp
b. focus lens on a spider arm
c. adjust shutter speed
d. make three exposures at different shutter speeds.
e. turn off lamp
16. Give image card to test director for evaluation on the PC.
17. Adjust exposure and camera position as directed by the test director.
TC ____________
18. Make additional exposures as required for approval by the test director.
19. Begin photography of both sides of 12 spider arms, moving in a clockwise
direction. Mark up Figure 3 with a number corresponding to the position of the
photograph and record in Table 1 with the number corresponding to the exposure.
TC ____________
20. Photograph 3 spider arms on the card A.
21. Give image card to test director for inspection and saving images to the computer.
22. Continue photography with second image card B.
23. Repeat steps 19 through 22 until all spider arms have been photographed.
TC ____________
24. Tape XRT Door Closed
TC ____________
25. Verify photographs of all Glued connections are adequate for Glued Connection
evaluation
QA _________TC ____________
26. Secure from test and break down equipment when directed by the test director.
TC ____________
Figure 3 provides a drawing of the mirror with the TAM baffle as a reference point. This
drawing will be used to mark up with numbers correlating to each picture and
documented in Table 1.
Figure 3: This Drawing shows the mirrors mounted on the spacer and the TAM baffle to be used as a
reference point. This drawing is to be marked up to correlate with the image numbers documented in
Table1.
1.3 Evaluation of the results
If from the inspection of the pictures taken on both side of the 12 spider arms, no cracks
or evidence of damage is seen on the glued connections and no blue particulate is seen
spread on the surfaces around the connections, then we will declare that the optics glued
connections have passed the Observatory Level Environmental Test without visible
damage.
Instead, if from the picture inspection, we find that there damage evident to the glued
connections, the implication will be that there is a high probability that during the launch
the glued connections will get loose and blue glue debris will probably be spread on the
various surfaces of XRT (including the mirrors). As a result the XRT image quality could
be much worse (HEW~30 arcsec or worse) and the effective area reduced (up to a factor
of 2). In any case, given that the mirror shells are constrained inside the grooves carved
on the spider arms, there will be no damage to the hardware and XRT will still be fully
functional although at a lower efficiency and quality (however, one should consider the
possibility that some pieces of glue fall down on the Focal Plane Camera Door). Of
course, the on-ground calibrations will not be valid any more and one will have to rely
only on in-flight calibrations. At this point the Swift PI (and Executive) will have to
decide if the mission will go ahead in any case.
The same considerations will apply if, from the pictures inspection, we find that the glued
connections have completely come apart.
It must be stressed, however, that the results obtained during the Qualification Test
performed on the X-ray optics give us strong confidence that no problems should have
arisen IF the level of the Acoustic Test were kept at the expected limits.
Position Number as Marked Card A or B
in Figure 3
Image Name/ Number