Nickolaos Mastrodemos

Invited Article: Deep Impact instrument calibration

Calibration of NASAs Deep Impact spacecraft instruments allows reliable scientific interpretation of the images and spectra returned from comet Tempel 1. Calibrations of the four onboard remote sensing imaging instruments have been performed in the areas of geometric calibration, spatial resolution, spectral resolution, and radiometric response. Error sources such as noise (random, coherent, encoding, data compression), detector readout artifacts, scattered light, and radiation interactions have been quantified. The point spread functions (PSFs) of the medium resolution instrument and its twin impactor targeting sensor are near the theoretical minimum [ approximately 1.7 pixels full width at half maximum (FWHM)]. However, the high resolution instrument camera was found to be out of focus with a PSF FWHM of approximately 9 pixels. The charge coupled device (CCD) read noise is approximately 1 DN. Electrical cross-talk between the CCD detector quadrants is correctable to <2 DN. The IR spectrometer response nonlinearity is correctable to approximately 1%. Spectrometer read noise is approximately 2 DN. The variation in zero-exposure signal level with time and spectrometer temperature is not fully characterized; currently corrections are good to approximately 10 DN at best. Wavelength mapping onto the detector is known within 1 pixel; spectral lines have a FWHM of approximately 2 pixels. About 1% of the IR detector pixels behave badly and remain uncalibrated. The spectrometer exhibits a faint ghost image from reflection off a beamsplitter. Instrument absolute radiometric calibration accuracies were determined generally to <10% using star imaging. Flat-field calibration reduces pixel-to-pixel response differences to approximately 0.5% for the cameras and <2% for the spectrometer. A standard calibration image processing pipeline is used to produce archival image files for analysis by researchers.

Configuring the Deep Impact AutoNav System for Lunar, Comet and Mars Landing

JPL’s autonomous onboard optical navigation system – AutoNav which has been responsible for obtaining all of NASA’s close-up images of comet nuclei, is being expanded in capability to accomplish a host of much more advanced missions than even the spectacular impact with comet Tempel-1 on July 4, 2005 (Figure 1). Among the most important of these mission scenarios are those that require precision landing on the Moon, a comet, and Mars. Lunar missions, in particular, are high on NASA’s agenda; both manned and unmanned. AutoNav is being utilized at this stage as a platform for evaluating lunar landing navigation strategies, and for testing algorithms, and indeed is being extended to become an onboard AutoGNC (Guidance Navigation and Control) system, that is an integrated inertial position and attitude determination function. At the core of these strategies is the nature and form of the optical navigation techniques to be used. AutoNav is being integrated with a comprehensive system for surface modeling and landmark tracking called OBIRON (OnBoard Image Registration for Optical Navigation). OBIRON provides both the means of simulation and onboard processing for purposes of estimating spacecraft position and attitude. This paper will describe the system architecture of the AutoGNC landing configuration, and also the simulation platform that provides simulated sensor inputs to the AutoGNC system. During the landing, performance of the system was excellent, with meter-level knowledge and control achieved. This paper will provide an evaluation of these results, and the associated system and process, from trial simulated operation of the system during landings at the Moon and on a small body.

Optical Navigation Plan and Strategy for the Lunar Lander Altair; OpNav for Lunar and other Crewed and Robotic Exploration Applications

This paper reviews the currently planned Altair Optical Navigation (OpNav) system. The discussion includes description of the OpNav camera manifest. The Altair OpNav plan envisions one, OpNav camera assembly, with perhaps a functional backup that includes a wide angle-imager (of 40 deg to 60 deg field of view - FOV), and a narrow angle imager (of 1 to 3 deg FOV) co-mounted on a 2-degree-of-freedom gimbal. Both imagers are assumed to be relatively wide aperture and large dynamic range to provide excellent short-exposure images at mid-latitudes, and adequate images of longer-exposure near the poles. Landmark modeling and tracking methodology is discussed, including the stereophotoclinometry method assumed to be used to obtain high-accuracy terrain maps at lunar landing sites of 1 - 2 m, and 50 - 100 m elsewhere, using the images expected to be obtained from the Lunar Reconnaissance Orbiter (LRO). Characteristics of the OpNav navigation system are discussed and architecture and results from landing simulations presented, showing expected landing accuracies of better than 10m.

AutoNav Mark3 : engineering the next generation of autonomous onboard navigation and guidance

The success of JPLs AutoNav system at comet Tempel-1 on July 4, 2005, demonstrated the power of autonomous navigation technology for the Deep Impact Mission. This software is being planned for use as the onboard navigation, tracking and rendezvous system for a Mars Sample Return Mission technology demonstration, and several mission proposals are evaluating its use for rendezvous with, and landing on asteroids. Before this however, extensive re-engineering of AutoNav will take place. This paper describes the AutoNav systems-engineering effort in several areas: extending the capabilities, improving operability, utilizing new hardware elements, and demonstrating the new possibilities of AutoNav in simulations.

The challenges of deep impact autonomous navigation

On July 4, 2005 at 05:44:34 UTC the Impactor spacecraft (s/c) impacted comet 9P/Tempel 1 with a relative speed of more than 10 km/s. The Flyby s/c captured the impact event, using both the medium resolution imager and the high resolution imager, and tracked the impact site for the entire observing period following impact. The objective of the Impactor s/c was to impact in an illuminated area viewable from the Flyby s/c and telemeter high-resolution context images of the impact site prior to impact. The Flyby s/c had two primary objectives: (1) capture the impact event in order to observe the ejecta plume expansion dynamics and (2) track the impact site for at least 800 s to observe the crater formation and capture high-resolution images of the fully developed crater. All of these objectives were met by estimating the trajectory of each spacecraft relative to 9P/Tempel 1 using the autonomous navigation system, precise attitude information from the attitude determination and control subsystem, and allowing each spacecraft to independently select the same impact site. This paper describes the challenges of targeting and tracking comet 9P/Tempel 1.

Dawn Navigation and Mission Design at Dwarf Planet Ceres

Dawn, one of NASA’s Discovery Program missions, was launched on September 27, 2007, to explore two residents of the main asteroid belt in order to yield insights into important science questions about the formation and evolution of the solar system [1]. Its main objective is to acquire data from orbit around two complementary bodies, Vesta and Ceres, the two most massive objects in the main belt. From July of 2011 to September of 2012, the Dawn spacecraft orbited Vesta and returned much valuable science data, collected during the six planned mapping orbits at the protoplanet. Figure 1 depicts the Dawn’s interplanetary trajectory and timeline.