Paul B. Brugarolas

ACCESS – A Concept Study for the Direct Imaging and Spectroscopy of Exoplanetary Systems

ACCESS is one of four medium-class mission concepts selected for study in 2008-9 by NASAs Astrophysics Strategic Mission Concepts Study program. ACCESS evaluates a space observatory designed for extreme high-contrast imaging and spectroscopy of exoplanetary systems. An actively-corrected coronagraph is used to suppress the glare of diffracted and scattered starlight to contrast levels required for exoplanet imaging. The ACCESS study considered the relative merits and readiness of four major coronagraph types, and modeled their performance with a NASA medium-class space telescope. The ACCESS study asks: What is the most capable medium-class coronagraphic mission that is possible with telescope, instrument, and spacecraft technologies available today? Using demonstrated high-TRL technologies, the ACCESS science program surveys the nearest 120+ AFGK stars for exoplanet systems, and surveys the majority of those for exozodiacal dust to the level of 1 zodi at 3 AU. Coronagraph technology developments in the coming year are expected to further enhance the science reach of the ACCESS mission concept.

On-board vision-based spacecraft estimation algorithm for small body exploration

A methodology is summarized for designing on-board state estimators in support of spacecraft exploration of small bodies such as asteroids and comets. This paper focuses on an estimation algorithm that incorporates two basic computer-vision measurement types: a landmark table (LMT) and a paired feature table (PFT). Several innovations are developed to incorporate these measurement types into the on-board state estimation algorithm. Simulations are provided to demonstrate the feasibility of the approach.

Exo-C: a Probe-Scale Space Mission to Directly Image and Spectroscopically Characterize Exoplanetary Systems Using an Internal Coronagraph

“Exo-C” is NASA’s first community study of a modest aperture space telescope designed for high contrast observations of exoplanetary systems. The mission will be capable of taking optical spectra of nearby exoplanets in reflected light, discover previously undetected planets, and imaging structure in a large sample of circumstellar disks. It will obtain unique science results on planets down to super-Earth sizes and serve as a technology pathfinder toward an eventual flagship-class mission to find and characterize habitable exoplanets. We present the mission/payload design and highlight steps to reduce mission cost/risk relative to previous mission concepts. At the study conclusion in 2015, NASA will evaluate it for potential development at the end of this decade.

ACCESS Pointing Control System

ACCESS (Actively-Corrected Coronagraph for Exoplanet System Studies) was one of four medium-class exoplanet concepts selected for the NASA Astrophysics Strategic Mission Concept Study (ASMCS) program in 2008/2009 [14, 15]. The ACCESS study evaluated four major coronagraph concepts under a common space observatory. This paper describes the high precision pointing control system (PCS) baselined for this observatory.

Zodiac II: Debris Disk Science from a Balloon

Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity. The Zodiac II instrument is a 1.1-m diameter SiC telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visiblewavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights within the United States followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescopes Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

An integrated optimal estimation approach to Spitzer Space Telescope focal plane survey

This paper discusses an accurate and efficient method for focal plane survey that was used for the Spitzer Space Telescope. The approach is based on using a high-order 37-state Instrument Pointing Frame (IPF) Kalman filter that combines both engineering parameters and science parameters into a single filter formulation. In this approach, engineering parameters such as pointing alignments, thermomechanical drift and gyro drifts are estimated along with science parameters such as plate scales and optical distortions. This integrated approach has many advantages compared to estimating the engineering and science parameters separately. The resulting focal plane survey approach is applicable to a diverse range of science instruments such as imaging cameras, spectroscopy slits, and scanning-type arrays alike. The paper will summarize results from applying the IPF Kalman filter to calibrating the Spitzer Space Telescope focal plane, containing the MIPS, IRAC, and the IRS science instrument arrays.

Control design for momentum-compensated fast steering mirror for WFIRST-AFTA coronagraph instrument

This paper presents results of the feedback control design for JPLs Fast Steering Mirror (FSM) for the WFIRST- AFTA coronagraph instrument. The objective of this controller is to cancel jitter disturbances in the beam from the spacecraft to a pointing stability of 0.4 masec over the duration of the observation using a momentum- compensated FSM. The plant model for the FSM was characterized experimentally, and the sensor model is based on simulated modeling. The control approach is divided between feedback compensation of low frequency attitude control system (ACS) drift, and feedforward cancellation of high frequency tonal disturbances originating from reaction wheel excitation of the telescope structure. This paper will present various aspects of the controller design, plant characterization, sensor modeling, disturbance estimation, performance simulation, and preliminary experimental testing results.

The Debris Disk Explorer: A Balloon-Borne Coronagraph for Observing Debris Disks

The Debris Disk Explorer (DDX) is a proposed balloon-borne investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. DDX will measure the size, shape, brightness, and color of tens of disks. These measurements will enable us to place the Solar System in context. By imaging debris disks around nearby stars, DDX will reveal the presence of perturbing planets via their influence on disk structure, and explore the physics and history of debris disks by characterizing the size and composition of disk dust. The DDX instrument is a 0.75-m diameter off-axis telescope and a coronagraph carried by a stratospheric balloon. DDX will take high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Two flights are planned; an overnight test flight within the United States followed by a month-long science flight launched from New Zealand. The long flight will fully explore the set of known debris disks accessible only to DDX. It will achieve a raw contrast of 10−7, with a processed contrast of 10−8. A technology benefit of DDX is that operation in the near-space environment will raise the Technology Readiness Level of internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

Focal plane calibration of the Spitzer space telescope

The Spitzer space telescope (Spitzer) is currently NASAs largest and most sensitive infrared (IR) telescope in space. Spitzers focal plane carries detectors from three science instruments, namely, the infrared array camera (IRAC), the infrared spectrograph (IRS), and the multiband imaging photometer for Spitzer (MIPS). In this article we discuss the instrument pointing frame (IPF) Kalman filter, which is used to calibrate Spitzers telescope focal plane. The IPF filter is a high-order square-root iterated linearized Kalman filter that carries 37 states to estimate frame misalignments, while correcting for systematic errors due to optical distortions, scan-mirror errors, thermomechanically induced drift variations, and gyro bias and drift in all axes. The Spitzer application demonstrates that the integrated approach offers significant advantages with respect to optimality, time-efficiency, anomaly detection, and health monitoring compared to existing telescope-calibration approaches, where the parameters are artificially broken into subsets that are estimated by separate teams of analysts. Performance results for the IPF Kalman filter indicate that all Spitzer calibration requirements are satisfied, and are consistent with margins predicted by preflight error analysis. On a final note, after more than five-and-a-half years of probing the cool cosmos, Spitzer entered standby mode on May 15, 2009, as a result of running out of the liquid helium coolant that kept its infrared instruments chilled. This event marks the successful completion of the Spitzers cold mission as originally commissioned by NASA. However, even though the telescope is warming up, the IRAC arrays continue to operate and provide useful scientific data. A new follow-on warm mission based on the IRAC arrays has been defined and initiated, so that Spitzer will remain in commission for several years to come.

Pointing control system for the Eclipse mission

This paper describes the high precision pointing control system for the Eclipse telescope. Eclipse is a mission under study at the Jet propulsion Laboratory. Eclipse is a space telescope that uses a coronagraph for high-contrast optical astronomy to study planets around nearby stars. Eclipse observations require very precise pointing, 0.01 arcseconds (3- σ) during the exposure periods that could be as long as 1000 seconds. This study shows a two layer pointing approach for achieving these requirements. In the first layer, the spacecraft ACS stabilizes the line-of-sight to 0.15 arcseconds (3- σ). In the second layer, a Fine Steering Mirror centers the star in the occulting mask to the 0.01 arcseconds (3-σ). The knowledge needed to achieve the desired pointing accuracy is provided by a Fine Guidance Camera. In addition, structural and thermal induced jitter is minimized by design, and through the use of reaction wheel isolators and operational constraints.