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At least 73 records · Page 4

Silicon Photonic Transceiver for Spacecraft Navigational Lidar

NASA is developing an entry, descent, and landing (EDL) lidar system, the Navigation Doppler Lidar (NDL), for high-precision landing on the Moon, Mars, and beyond. The current flight NDL systems use 1550 nm fiber-optic components for frequency-modulated continuous wave (FMCW) ranging beyond 5 km, but have reduced performance under vibrational and thermal stresses during EDL. Here we describe recent efforts to develop a breadboard silicon photonic optical transceiver for integration into NDL to reduce instrument size and improve robustness to environment and demonstrate the optical balanced receiver performance during testing with the breadboard NDL unit. Initial testing shows improved suppression of common mode noise by 25 dB over the current receiver, but a 10 dB reduction in signal to noise ratio (SNR) resulting from coupling losses from fiber to the on-chip waveguides. Future work will target reduced coupling loss, hermetic packaging, and co-integration of a single sideband suppressed carrier modulator into the same chip.

Photonic Integrated Circuits↗

Results of a demonstration of the use of Differential Very Long Baseline Interferometry data for precise navigation of interplanetary spacecraft

A set of experiments in the use of Differential Very Long Baseline Interferometry for spacecraft navigation have been completed. Data using both Voyager spacecraft and a single quasar were acquired during the Jupiter encounter time period. The data were processed and analyzed in order to assess the navigation accuracy of Differential Very Long Baseline Interferometry. The paper focuses on the data reduction and techniques for assessing data quality and consistency.

Christensen, C. S.↗

Innovations in Spacecraft Proximity & Navigation Lighting

New spacecraft bound for the Moon and Mars should be exploring lighting technologies that can reduce safety risks while increasing capability. The operational lighting environment for these new missions will not have the forgiving 90 minute orbit of the International Space Station. Advances in solid state lighting and optics design are yielding new form factors for lamps that have the potential to reduce operational risk for both humans and imaging systems that are impacted by high contrast lighting environments. This project evaluated light source form factors and control innovations for spacecraft exterior proximity and navigation lighting by building a demonstration test rig and testing the effectiveness of the light sources and their controls to increase visibility and usability.

Clark, Toni A.↗

Autonomous Navigation of the SSTI/Lewis Spacecraft Using the Global Positioning System (GPS)

The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) is pursuing the application of Global Positioning System (GPS) technology to improve the accuracy and economy of spacecraft navigation. High-accuracy autonomous navigation algorithms are being flight qualified in conjunction with GSFC's GPS Attitude Determination Flyer (GADFLY) experiment on the Small Satellite Technology Initiative (SSTI) Lewis spacecraft, which is scheduled for launch in 1997. Preflight performance assessments indicate that these algorithms can provide a real-time total position accuracy of better than 10 meters (1 sigma) and velocity accuracy of better than 0.01 meter per second (1 sigma), with selective availability at typical levels. This accuracy is projected to improve to the 2-meter level if corrections to be provided by the GPS Wide Area Augmentation System (WAAS) are included.

Hart, R. C.↗

CCD sensors for spacecraft optical navigation

The optical navigation process uses spaceborne measurements of the apparent direction vector from the spacecraft to a target body, (planet, satellite, star, etc.) to improve estimates of the spacecraft trajectory. Ground-based controllers assimilate the optical measurements, together with spacecraft radio-tracking data and target ephemeris data, to generate a best estimate of the trajectory relative to the target. The present paper deals with a development program supporting the use of (solid state) CCD (Charged Coupled Device) imagers for spacecraft navigation. It is shown that stars can be detected that are two to three magnitudes fainter than with an equivalent vidicon based instrument, that effects of global response nonuniformity and dark current spikes can be essentially eliminated from the data as a result of the reproducibility of both effects, and that charge trailing during readout of star image data can lead to position measurement errors.

Eisenman, A. R.↗

Navigation of spacecraft on deep space missions

The control of deep mission spacecraft by computing and signaling to the spacecraft a series of propulsive, velocity correction commands which maneuver the craft to its desired course is examined. The technical elements of the global navigation system (measurement, communications, computation, and propulsion) are described. The ground-computing facilities used to navigate spacecraft on deep space missions consist of computer and software systems used to compute orbits from radio tracking and on-board optical image data (radio, Doppler, and VLBI measurements). The accuracy of these measurements is evaluated, and the modeling of the data is discussed. Examples concerned with the navigation of Voyager and Galileo are presented.

Jordan, James F.↗