Finding a contract vehicle that balances the concerns of the customer and the contractor in a development project can be difficult. The customer wants a low price and an early delivery, with as few surprises as possible as the project progresses. The contractor wants sufficient cost and schedule to cover risk. Both want to clearly define what each party will provide. Many program offices do not want to award cost plus contracts because their funding sources will not allow it, their boards do not want an open ended commitment, and they feel like they lose financial control of the project. A fixed price incentive contract, with a mutually agreed upon target cost, provides the owner with visibility into the project and input into the execution of the project, encourages both parties to save costs, and stimulates a collaborative atmosphere by aligning the respective interests of customers and contractors.
The Discovery Channel Telescope (DCT) is a 4.3-meter astronomical research telescope being built in northern Arizona
as a partnership between Discovery Communications and Lowell Observatory. The telescope will be able to support
substantial instrument payloads at Cassegrain, Nasmyth, and prime foci, and high observing cadences. The first-light
configuration will be as an f/6.1 Ritchey-Chrétien at Cassegrain with a 30 arc-minute field-of-view. Major facility work
is complete, and the telescope is currently in the integration phase with first-light anticipated in 2011. We present an
overview of the design and progress to date, and include plans for final integration, commissioning, and early science.
The Discovery Channel Telescope is a 4.2-meter clear aperture telescope undertaken by the Lowell Observatory in
Flagstaff, Arizona. It will feature an interchangeable secondary assembly to allow the use of either a prime focus
instrument or a secondary mirror. In addition, it will have an active optical system and provisions for a wide range of
instruments. This paper describes the design of the telescope mount and drive systems. Particular challenges associated
with the design include: consideration for the weight of the 3500 lb Prime Focus Assembly (PFA) instrument;
interchangeable secondary assemblies; and providing thermal and mechanical stability in between updates to maintain
alignment between optical elements.
The Cornell Caltech Atacama Telescope (CCAT) is a 25m far infrared telescope in the conceptual design phase. Its primary mirror is composed of a set of panels supported by a space truss. The primary and secondary mirror arrangement resembles the reflector and quadrapod arrangement seen in many radio telescopes, but with shallower primary mirror geometry. In addition, the optical layout calls for a close spacing between the tertiary mirror and the Nasmyth and bent Cassegrain instruments. The mount design is driven by the spacing of the optical elements, the presence of the Nasmyth and bent Cassegrain ports, and the size of the primary mirror truss. This paper examines the mechanical and control system design solutions provided in response to the challenges posed by the optical requirements. These solutions include tradeoffs in structure, drive, and control system design.
Developments in computer hardware and software have made analysis techniques that were formerly too expensive within the reach of most project budgets. Foremost among these has been seismic response spectrum analysis. This method yields much more accurate results than the equivalent static approach. The problem with using response spectrum analysis exclusively in the design of deflection controlled structures, such as astronomical telescopes, is that the nature of the structure minimizes the benefits of the approach. A typical response spectrum from Eurocode 8 deals with a range of natural periods between 0.1 and 5 seconds. These correspond to a frequency range of 0.2 to 10 Hz. The typical telescope structure has a minimum frequency of around 10 Hz. or greater. The result is that the response spectrum analysis involves only a narrow band of frequencies and accelerations. This result could be reliably obtained using an equivalent static analysis approach.
The 4.2 m Discovery Channel Telescope requirements create interesting challenges for the Mount mechanical and control system design. The wide field of view survey telescope incorporates two operational foci: prime focus and cassegrain, either one must be available during any night's observing. The mission for observing requires fast slewing / offsets between each exposure with fast settling times to maintain the mission requirements. The prime focus arrangement includes a dedicated camera on the spider assembly and the cassegrain configuration includes a secondary mirror at the spider assembly with a dedicated instrument located at the cassegrain focus. This requirement challenges the design team to incorporate a prime focus / secondary mirror flipping mechanism within the secondary spider. The configuration requires a substantial prime focus and cassegrain payload with long focal distances creating a large inertia on the altitude axis. These are a few of the interesting challenges that are presented in this paper along with the design, trade-offs of different solutions, and the recommended design for the telescope Mount.
The telescope mount is an important component for the success of the Southern Observatory for Astronomical Research (SOAR) scientific mission. The SOAR telescope structure must have the best combination of extremely high structural stiffness, low torque bearings, sophisticated encoder pick-offs and smooth drive trains so that the servo system can achieve closed loop control in the sub-arc second regime. While challenging, these parameters are achievable. Once assembled, this mount will enable the telescope to have superior image viewing quality and large payload capacities. This paper will address the telescope mount structure, drive system performance, structural analysis and thermal design.
The Extreme Ultraviolet Explorer (EUVE), launched on June 7, 1992, is an extremely successful NASA astrophysics mission that contains three extreme ultraviolet (EUV) spectrometers designed to be used in pointed spectroscopic observations of astrophysical sources in the 70-760 angstrom wavelength region. The spectrometers utilize a slitless design based on grazing- incidence optics and variable line-space gratings. Detailed wavelength scales determined from ground-based calibrations and refined with in-orbit data are used to assign wavelengths for each detected photon to within half a resolution element (less that 0.8 angstrom in all cases). Spectral resolving power (FWHM of non-Gaussian profiles) varies in the range R approximately 150-450. Spectrometer throughputs were determined from an extensive laboratory calibration and then were adjusted slightly based on in-flight calibration spectra of known astrophysical continuum sources (hot DA white dwarf stars). We also have measured count rates from the detector and the geocoronal and distributed backgrounds, parameters critical to assessment of accurate flux levels from the astrophysical sources.
The paper describes the main features and selected results of the calibration of the scientific instruments to be flown on the Extreme Ultraviolet Explorer in 1991. The instrument payload includes three grazing incidence scanning telescopes and an EUV spectrometer/deep survey instrument covering the spectral region 70-800 A. The measured imaging characteristics, the effective areas, and the details of spectral responses of the instruments are presented. Diagrams of the cross-sectional views of the scanning telescope and the deep-survey/spectrometer telescope are included.