Engineering topics
Publications and source records attributed to Mallik, Udayan.
The Goddard Modular Smallsat Architecture (GMSA) is developed at NASA Goddard Space Flight Center (GSFC) to address future reliability along with minimizing cost and schedule challenges for NASA Cubesat and Smallsat missions.
This paper discusses charge blooming and starlight saturation - two potential technical problems - when using an Electron Multiplying Charge Coupled Device (EMCCD) type detector in a high-contrast instrument for imaging exoplanets. These problems especially affect an interferometric type coronagraph - coronagraphs that do not use a mask to physically block starlight in the science channel of the instrument. These problems are presented using images taken with a commercial Princeton Instrument EMCCD camera in the Goddard Space Flight Center's (GSFC), Interferometric Coronagraph facility. In addition, this paper discusses techniques to overcome such problems. This paper also discusses the development and architecture of a Field Programmable Gate Array and Digital-to-Analog Converter based shaped clock controller for a photon-counting EMCCD camera. The discussion contained here will inform high-contrast imaging groups in their work with EMCCD detectors.
The key to broadband operation of the Visible Nulling Coronagraph (VNC) is achieving a condition of quasi- achromatic destructive interference between combined beams. Here we present efforts towards meeting this goal using Fresnel rhombs in each interferometric arm as orthogonally aligned half wave phase retarders. The milestone goal of the demonstration is to achieve 1 × 10−9 contrast at 2/D over a 40 nm bandpass centered at 633 nm. Rhombs have been designed and fabricated, and a multi-step approach to alignment using coarse positioners for each rhomb and pair has been developed to get within range of piezo stages used for fine positioning. The previously demonstrated narrowband VNC sensing and control approach that uses a segmented deformable mirror is being adapted to broadband to include fine positioning of the piezo-mounted rhombs, all demonstrated in a low-pressure environment.
Herein we report on our Visible Nulling Coronagraph high-contrast result of 109 contrast averaged over a focal planeregion extending from 14 D with the Vacuum Nuller Testbed (VNT) in a vibration isolated vacuum chamber. TheVNC is a hybrid interferometriccoronagraphic approach for exoplanet science. It operates with high Lyot stopefficiency for filled, segmented and sparse or diluted-aperture telescopes, thereby spanning the range of potential futureNASA flight telescopes. NASAGoddard Space Flight Center (GSFC) has a well-established effort to develop the VNCand its technologies, and has developed an incremental sequence of VNC testbeds to advance this approach and itsenabling technologies. These testbeds have enabled advancement of high-contrast, visible light, nulling interferometry tounprecedented levels. The VNC is based on a modified Mach-Zehnder nulling interferometer, with a W configurationto accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters.We give an overview of the VNT and discuss the high-contrast laboratory results, the optical configuration, criticaltechnologies and null sensing and control.
A significant and often overlooked path to advancing both science and technology for direct imaging and spectroscopic characterization of exosolar planets is to fly "near space" missions, i.e. balloon borne exosolar missions. A near space balloon mission with two or more telescopes, coherently combined, is capable of achieving a subset of the mission science goals of a single large space telescope at a small fraction of the cost. Additionally such an approach advances technologies toward flight readiness for space flight. Herein we discuss the feasibility of flying two 1.2 meter telescopes, with a baseline separation of 3.6 meters, operating in visible light, on a composite boom structure coupled to a modified visible nulling coronagraph operating to achieve an inner working angle of 60 milli-arcseconds. We discuss the potential science return, atmospheric residuals at 135,000 feet, pointing control and visible nulling and evaluate the state-or-art of these technologies with regards to balloon missions.
Herein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. Tbe VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. We discuss the development of the vacuum Visible Nulling Coronagraph testbed (VNT). The VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10(exp 8), 10(exp 9) and ideally 10(exp 10) at an inner working angle of 2*lambda/D. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the laboratory results, optical configuration, critical technologies and the null sensing and control approach.
An architecture for a Direct RF-digitization Type Digital Mode RADAR was developed at GSFC in 2008. Two variations of a basic architecture were developed for use on RADAR imaging missions using aircraft and spacecraft. Both systems can operate with a pulse repetition rate up to 10 MHz with 8 received RF samples per pulse repetition interval, or at up to 19 kHz with 4K received RF samples per pulse repetition interval. The first design describes a computer architecture for a Continuous Mode RADAR transceiver with a real-time signal processing and display architecture. The architecture can operate at a high pulse repetition rate without interruption for an infinite amount of time. The second design describes a smaller and less costly burst mode RADAR that can transceive high pulse repetition rate RF signals without interruption for up to 37 seconds. The burst-mode RADAR was designed to operate on an off-line signal processing paradigm. The temporal distribution of RF samples acquired and reported to the RADAR processor remains uniform and free of distortion in both proposed architectures. The majority of the RADAR's electronics is implemented in digital CMOS (complementary metal oxide semiconductor), and analog circuits are restricted to signal amplification operations and analog to digital conversion. An implementation of the proposed systems will create a 1-GHz, Direct RF-digitization Type, L-Band Digital RADAR--the highest band achievable for Nyquist Rate, Direct RF-digitization Systems that do not implement an electronic IF downsample stage (after the receiver signal amplification stage), using commercially available off-the-shelf integrated circuits.
Herein we report on the development. sensing and control and our first results with the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraph (VNC) for exoplanet coronagraphy. The VNC is one of the few approaches that works with filled. segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be Hown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center (GSFC) has a well-established effort to develop VNC technologies. and has developed an incremental sequence of VNC testbeds to advance this approach and the enabling technologies associated with it. We discuss the continued development of the vacuum Visible Nulling Coronagraph testbed (VNT). Tbe VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10(sup 8), 10(sup 9) and ideally 10(sup 10) at an inner working angle of 2*lambda/D. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the initial laboratory results, the optical configuration, critical technologies and the null sensing and control approach.