# (rev. 1) {#rev.-1 .unnumbered}

# Introduction 

Constellation-X is NASA\'s next major X-ray observatory. It consists of
4 identical satellites. Each satellite in turn consists of, among other
instruments, a spectroscopic telescope. The telescope mirror assembly is
1.6 meters in diameter and has a focal length of 10 meters (for more
information on the Constellation-X mission, go to
http://constellation-x.gsfc.nasa.gov). The mirror assembly consists of
nested Wolter-I (i.e., parabola and hyperbola two-reflection) mirror
segments (outer segments are 30°, inner are 60°). In order to reduce
both mass and cost, the mirror segments will be made of accurately
figured thin (400 microns) glass substrates onto which a smooth metallic
surface is replicated from an accurately figured and polished mandrel.
The thin glass substrate is obtained by slumping a commercially
available flat glass sheet onto a forming mandrel at approximately 600
degrees centigrade as shown in Figure 1. ![](media/image1.wmf)

Figure 1 Illustration of the glass slumping process. Here the forming
mandrel is depicted as a complete revolution of a cone, but it does not
have to. It only needs to be a conical section as large as 75 degrees in
the azimuth.

This document describes the requirements for the forming mandrels and
seeks information from industry about capabilities in fabricating these
forming mandrels. The number of mandrels required is subject to changes
based on progress, but a minimum number is 140 conical mandrels which
will be required for delivery over a period spanning several years.
Prior to the procurement of the mandrels needed for actual fabrication
of the flight x-ray optics, GSFC may elect to procure a small number of
mandrel prototypes to further test the feasibility of its approach and
the capability of industry sources. GSFC would like to stress that the
requirements list below are subject to discussion and negotiation. We
seek to maximize cost effectiveness and efficiency. Therefore, we
strongly encourage interested parties to identify possible cost-saving
alternatives to the baseline requirements identified herein. Parties are
welcome to contact the GSFC technical representative by sending emails
to **mandrels@milkyway.gsfc.nasa.gov** to discuss the feasibility of
alternative approaches prior to submission of its response to this
request for information.

# Material requirements 

As examples, GSFC recommends one or more of the following materials:
fused silica, titanium, graphite, etc. In general, the material should
meet the following requirements:

## Uniformity 

The forming mandrel material must be of sufficient uniformity so as to
preserve its figure over the temperature range of 0 to 750 degrees
centigrade. It can expand and contract, but it must maintain its
geometrical figure. It does not have to conduct heat well, but good
thermal conductivity is a desirable property.

## Stability 

The material has to be stable and totally solid or rigid (i.e., does not
sag or change its geometrical figure under its own gravity) over the 0
to 750 degrees centigrade temperature range. It should not oxidize nor
undergo any other chemical or physical change in the same temperature
range.

## Thermal Expansion Characteristics 

We do not place formal requirements on the size of the thermal expansion
coefficients (CTE) as long as it is known and stable over the
temperature range of 0 to 750 degrees centigrade.

# Mathematical Description 

The geometrical shape of the forming mandrel should be conical. The
diameter at the mid-point of the cone ranges from 50 to 160 centimeters,
with the cone angle ranging from 0.3 to 3.6 degrees and the height at 60
centimeters. It is the outer surface of the cone that is of interest. As
such, we place no requirements on any other part of the cone. For
example, the cone could be hollow or could be a solid piece. If it is
hollow, the wall thickness should be determined by mechanical and
structural properties so that the outer surface maintains its figure in
different configurations under gravity and across the range of
temperatures. In particular, the forming mandrels do not have to be
whole-shell cones. They can be part of cones, or conical segments. The
size in the azimuth direction should be 80+/-5 degrees.

# Tolerances 

Mid-point Diameter: +/- 100 microns

Cone Angle: +/- 20 seconds of arc

Waviness: P-V \< 2 microns (wave lengths between 1mm and 600mm)

Height: +/- 5000 microns or 5 millimeters

Circularity: +/- 5 microns

Surface Roughness: \<20 Angstroms (wave lengths below 0.3 mm)

# Response Required

The written response to this RFI shall consist of:

1.  Identification of the respondent, including the name of the
    representative, his/her contact information (phone number, fax
    number, and/or email address),

2.  A brief description of the responding firm's experience in making
    related parts,

3.  A brief description of the technical approach, including the
    proposed material, fabrication technique, expected accuracy in
    meeting the requirements, any known/perceived advantages and/or
    disadvantages,

4.  Non-binding estimates of cost for fixed setup costs and recurring
    costs, as well the amount of time required for fabricating the 140
    mandrels.