M. C. Kochte

UMBRAS: a matched occulter and telescope for imaging extrasolar planets

We describe a 1-meter space telescope plus free-flying occulter craft mission that would provide direct imaging and spectroscopic observations of Jovian and Uranus-sized planets about nearby stars not detectable by Doppler techniques. The Doppler technique is most sensitive for the detection of massive, close-in extrasolar planets while the use of a free-flying occulter would make it possible to image and study stellar systems with planets comparable to our own Solar System. Such a mission with a larger telescope has the potential to detect earth-like planets. Previous studies of free-flying occulters reported advantages in having the occulting spot outside the telescope compared to a classical coronagraph onboard a space telescope. Using an external occulter means light scatter within the telescope is reduced due to fewer internal obstructions and less light entering the telescope and the polishing tolerances of the primary mirror and the supporting optics can be less stringent, thereby providing higher contrast and fainter detection limits. In this concept, the occulting spot is positioned over the star by translating the occulter craft, at distances of 1,000 to 15,000 kms from the telescope, on the sky instead of by moving the telescope. Any source within the telescope field-of-view can be occulted without moving the telescope. In this paper, we present our current concept for a 1-m space telescope matched to a free-flying occulter, the Umbral Missions Blocking Radiating Astronomical Sources (UMBRAS) space mission. An UMBRAS space mission consists of a Solar Powered Ion Driven Eclipsing Rover (SPIDER) occulter craft and a matched (apodized) telescope. The occulter spacecraft would be semi-autonomous, with its own propulsion systems, internal power (solar cells), communications, and navigation capability. Spacecraft rendezvous and formation flying would be achieved with the aid of telescope imaging, RF or laser ranging, celestial navigation inputs, and formation control algorithms.

Imaging planets about other stars with UMBRAS II

In this paper we discuss operational considerations for the free-flying occulter. Operations consist of maneuvering the Solar-Powered Ion-Driven Eclipsing Rover (SPIDER) between targets, alignment with the space-based telescope line of sight to the target, and stationkeeping target-to-target maneuvers need to be optimized to conserve propellant. A reasonable balance needs to be determined between target observation rate and the number of targets that are observable during mission lifetime. Velocity matching of the SPIDER with the telescope is essential to mission performance. An appropriate combination of solar electric and cold-gas thrusters provides the ability to match velocities using positional information derived from comminution and ranging between telescope, occulter and any metrology stations. Desirable features of using an external coronagraphic vehicle include the ability to obtain coronagraphic data with any instrument on the telescope-- imaging, spectroscopic, or interferometric.

Apodized Square Aperture Plus Occulter Concept for TPF

The standard approach to achieving TPF-level starlight suppression has been to couple a few techniques together. Deployment of a low- or medium-performance external occulter as the first stage of starlight suppression reduces manufacturing challenges, mitigates under-performance risks, lowers development costs, and hastens launch date for TPF. This paper describes the important aspects of a conceptual 4-metre apodized square aperture telescope system utilizing a low-performance external occulter. Adding an external occulter to such a standard TPF design provides a benefit that no other technique offers: scattered and diffracted on-axis starlight is suppressed by orders of magnitude before reaching the telescope. This translates directly into relaxed requirements on the remainder of the optical system.

HST/FGS Photometry of Planetary Transits of HD 209458

We present the data, and modeling and analysis results from the photometric monitoring of five planetary transits of HD 209458 using the Fine Guidance Sensors (FGS) onboard the Hubble Space Telescope (HST). We have now included the output from all four FGS photometers in our data reduction and analysis increasing our S/N over our previous results. We have modeled the transits as an opaque spherical planet in a circular orbit about a limb darkened spherical star and simultaneously fit the model to the FGS data and published STIS transit data. The measured light curves show small features, a fraction of the transit depth. Some of these faint bumps and ripples appear to be real. We present an analysis of the FGS transit light curves, showing the results of the model fitting and a search for a possible planetary satellite.

The Advantages of Multiple Coronagraphic Vehicles in Occulter Missions

Free-flying external coronagraphs for space telescopes have been studied since the 1960s, but cost/ benefit analysis has not proved convincing for skeptics. A single space vehicle carrying an occulting screen can increase the contrast between a star and its orbiting extrasolar planets for a suitably designed space telescope. However, a number of advantages ensue when replacing the single occulter with a fleet of lighter-mass occulters. Target observation rates can increase in proportion to the number of coronagraphic free flying vehicles devoted to a mission. At the same time, mass requirements for individual vehicles is dramatically reduced. Mission lifetimes can at the same time potentially increase, and the risk of independent catastrophic failures onboard an occulting vehicle eliminating all science productivity for the mission are effectively vanish. Perunit vehicle costs are substantially lower than for production of a single unique craft.

Imaging Terrestrial Planets

We present optical simulations of a new approach to directly image terrestrial planets. Terrestrial planets typically are 10 orders of magnitude fainter than the central star, a difficult challenge for any optical system. Our studies show that the combination of an external occulter and an apodizer yields the required contrast, with significantly reduced requirements on stray light and diffraction. This mitigates the very high mirror tolerances required of other coronagraphic methods and makes exo‐planet detection feasible with current technology.

Evolution of science data processing for the Hubble Space Telescope: a user's perspective

Upgrades of the science instrument complement on the Hubble Space Telescope (HST) and observing strategy innovations have combined to greatly increase the number of observations and the volume of data during the first decade of HST operations. At the same time, the data processing component of HST operations has undergone a parallel evolution in strategy and implementation, partly in response to the increased volume of data from HST while reducing staffing requirements, and partly due to the phasing out of old technologies and the exploring of new ones. This paper describes the original HST data processing strategy and implementation, how it has evolved to the current design today, and where it may be going for future space telescope missions (HST, NGST, et al.).

Feedback loops from the Hubble Space Telescope data processing system

This paper presents an overview of the history and technology by which tools placed in the Hubble Space Telescope (HST) data processing pipeline were used to feedback information on observation execution to the scheduling system and observers. Because the HST is in a relatively low orbit, which imposes a number of constraints upon its observations, it operates in a carefully planned, fully automated mode. To substitute for direct observer involvement available at most ground-based observatories and to provide rapid feedback on failures that might affect future visits, the Space Telescope Science Institute (STScI) gradually evolved a system for screening science and engineering products during pipeline processing. The highly flexible HST data processing system (OPUS) allows tools to be introduced to use the content of FITS keywords to alert production staff to potential telescope and instrument performance failures. Staff members review the flagged data and, if appropriate, notify the observer and the scheduling staff so that they can resolve the problems and possibly repeat the failed observations. This kind of feedback loop represents a case study for other automated data collection systems where rapid response to certain quantifiable events in the data is required. Observatory operations staff can install processes to look for these events either in the production pipeline or in an associated pipeline into which the appropriate data are piped. That process can then be used to notify scientists to evaluate the data and decide upon a response or to automatically initiate a response.