When designing optical devices, the alignment of every element is integral to the proper functionality of the device. If
any of these elements is secured by means of a friction joint, it is important to understand the limitations of the joint
when vibrations (mainly during launch) occur; a phenomenon called "stick-slip" may happen and permanently displace
joints relying on friction and cause optical misalignments. There is little to no data documenting the characteristics of the
"stick-slip" phenomenon on friction joints under random vibratory motion. The test program was designed with the aim
of gathering data that would broaden the understanding of the "stick-slip" phenomenon and among other things provide
sufficient information to quantify the static coefficients of friction of several single-bolt friction joint material pairings.
This paper describes the test program in detail including test sample description, test procedures, and vibration test
results of multiple test samples. The material pairs used in the experiment were Aluminum-Aluminum, Aluminum-
Dicronite coated Aluminum, and Aluminum-Plasmadize coated Aluminum. Levels of vibration for each set of twelve
samples of each material pairing were gradually increased until all samples experienced substantial displacement. Data
was collected on 1) acceleration in all three axes, 2) relative static displacement between vibration runs utilizing
photogrammetry techniques, and 3) surface galling and contaminant generation. This data was used to estimate the
values of static friction during random vibratory motion when "stick-slip" occurs and compare these to static friction
coefficients measured before and after vibration testing.
This overview paper describes the system design of the structurally-connected interferometer (SCI) concept studied for the Terrestrial Planet Finder (TPF) project. This paper covers progress since August 2003 and serves as an update to a paper presented at that month's SPIE conference, "Techniques and Instrumentation for Detection of Exoplanets". SCI trade studies conducted since mid-2003 have focused on key factors driving overall flight segment mass and performance, including launch vehicle packaging, structural design, and instrument layout. This paper summarizes the results of the recent design trades, with discussion of the primary requirements that drive the baseline design concept.
This paper describes the basic structural design of the Terrestrial Planet Finder (TPF) Structurally Connected Interferometer concept developed within the Jet Propulsion Laboratory design team. Descriptions of the key structural components, optical elements, and basic load paths are included. Key structural requirements related to launch loads and on-orbit stability and alignment are identified. The analysis results for the baseline design are shown for both launch configuration and the deployed, on-orbit configuration. The finite element models are described with preliminary results shown. Excitation of the structure and the optical train caused by assumed external disturbances are shown for a preliminary analysis. Future work is identified.
This paper discusses the fabrication considerations and proposed testing concepts for a twelve meter, graphite-epoxy space truss that is being developed to provide structural support for the primary mirror system of the SpacE Laser ENErgy (SELENE) Beam Transmission Optical System (BTOS). A general description of the mirror support configuration is presented. Specific issues which are addressed include low-cost fabrication techniques utilized in the support structure. Later, a description of the dynamic testing program for the entire active primary mirror system is outlined.
This paper discusses the design issues and fabrication considerations specifically related to a large twelve meter, graphite-epoxy space truss that has been developed to provide support of the primary mirror system for the Space Laser Energy (SELENE) Beam Transmission Optical System (BTOS). Details of the optical system and wavefront corrector concepts have been discussed in prior papers. Specific issues which are addressed in this paper include optical performance needs, environmental requirements, and low-cost fabrication techniques.
The Articulating Fold Mirror (AFM) for the Wide Field/Planetary Camera-II (WF/PC-II) instrument is a very compact, complicated, highly precise mechanism. The AFM's basic function is to provide tip and tilt correction in the optical paths of the WF/PC-II instrument. Its necessity is brought about indirectly by the spherical aberration of the primary mirror in the Hubble Space Telescope (HST). Many challenges are created by the necessity of the new mechanism in the optical design. (1) The new mechanism must exhibit high precision in the placement of the mirror surface in two rotations (tip and tilt). (2) The available packaging volume for the AFM is very shallow and requires an innovative approach to achieve the necessary performance requirements. (3) The schedule for delivery of the flight certified AFM's is extremely tight, and as such does not allow for any failures during the qualification phase of the AFM project. Structural design and analysis plays a major role in meeting the stringent performance requirements within the schedule and fiscal constraints. The final result is a qualified mechanism which meets or surpasses all of its requirements.
An effort is currently being carried out by the Jet Propulsion Laboratory (JPL) to study mission feasibility and to define functional requirements for various subsystems of the Space Infrared Telescope Facility (SIRTF). As a major part of this effort, structural design requirements have been derived based on the stated mission objectives. Design concerns addressed by these requirements include the limits on mass and location of the center of gravity, launch stiffness and dynamic characteristics, design loads and analysis criteria, survivability of the TITAN IV/Centaur launch environment, thermal control for maintaining a near absolute-zero operating temperature, and helium cryogen volume and storage for a five-year mission. To illustrate how the structural design requirements can be met, a point design of the SIRTF flight hardware system was developed, modeled, and analyzed. A description of the key features of this point design, along with pertinent modeling and analysis results, are discussed in this Paper.
To assess the design feasibility of the Space Infrared Telescope Facility (SIRTF) and to identify parameters that might impose constraints on performance such as frequencies of vibration, structural concepts for both the telescope and spacecraft are developed and evaluated. Trade studies of key design features are carried out using FEM and analysis. In most cases, the margin of safety was greater than 0.50. An example of stress in the octagonal equipment bus panels is shown. The strap-supported mass is predicted to deflect 6 mm relative to the outer shell when subjected to 8.0 G in the X direction, and to deflect about 5 mm in the Y and Z directions when subjected to 10.0 G. Deflections for the top of the solar panel are predicted to be about 35 mm when subjected to the 10.0 G quasi-static load in the Z direction. The liquid helium tank, thermal isolation, and primary mirror and mount are discussed.