Engineering topics
Nandi, S.
Publications and source records attributed to Nandi, S..
Dawn Maneuver Design Performance at Vesta
The Dawn spacecraft orbited the asteroid Vesta from July 16, 2011 to September 5, 2012, successfully accomplishing the four planned science orbits and two planned rotational characterization orbits. The lowest-altitude science orbit lasted four months, with 20 planned orbit maintenance maneuvers. Navigation results from Vesta demonstrate that the navigation plan was sufficient to achieve orbit delivery accuracy requirements. This paper compares the flown Dawn trajectory against the planned trajectory and expected maneuver dispersions. Understanding the effectiveness of the Vesta maneuver design plan is a key component of planning for operations at Ceres, the next destination for the Dawn mission.
The instrument on NASA's GRACE Mission: Augmentation of GPS to achieve unprecedented gravity field measurements
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GRACE: millimeters and microns in orbit
The Gravity Recovery and Climate Experiment launched March 17, 2002. The GPS data for this experiment are processed to contribute to the recover long wavelength gravity field; remove errors due to long term on-board oscillator drift; and align K/Ka-band measurments between the two spacecraft to 0.1 ns. This paper will concentrate on the use of GPS for these timing and calibration functions and will not address the recovery of the gravity field.
The instrument on NASA's GRACE Mission: Augmentation of GPS to achieve unprecedented gravity field measurements
This paper will describe the design and on-orbit performance of the GRACE Instrument Processing Unit (IPU) that integrates most of the critical science functions required by the GRACE mission to perform its gravity science and atmospheric radio occultation tasks.
Martian Geodesy with Netlander and Mars Infrastructure Constellation
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Netlander Positioning with the Mars Infrastructure Constellation and its Impact on Martian Geodesy
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Netlander Positioning with the Mars Infrastructure Constellation and its Impact on Martian Geodesy
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Ammonia Abundance at the Galileo Probe Site Derived from Absorption of its Radio Signal
The radio signal from the Galileo prove to the orbiter experienced attenuation due to ammonia in Jupiter's atmosphere during the probe descent.
Airborne Passive Remote Sensing of the Troposphere in Nashville/Middle Tennessee Area During the 1995 Southern Oxidants Study
In July of 1995 the Airborne Emission Spectrometer was deployed to Nashville, Tennessee to participate in the 1995 Ozone Study Intensive Campaign of the Southern Oxidants Study. AES is a high resolution mid-infrared interferometer that measures the spectrum of upwelling radiation in the 650-4250 cm-1 range.
Spatial and Temporal Distributions of Retrieved O(sub 3), CO, H(sub 2)O and Temperature from the Airborne Emission Spectrometer (AES)
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Spatial and Temporal Distributions of Retrieved O(sub 3), CO, H(sub 2)O and Temperature from the Airborne Emission Spectrometer (AES)
Ongoing Study to understand ground level ozone production and transport in the southeastern U.S.
The Mars Observer differential one-way range demonstration
Current methods of angular spacecraft positioning using station differenced range data require an additional observation of an extragalactic radio source (quasar) to estimate the timing offset between the reference clocks at the two Deep Space Stations. The quasar observation is also used to reduce the effects of instrumental and media delays on the radio metric observable by forming a difference with the spacecraft observation (delta differential one-way range, delta DOR). An experiment has been completed using data from the Global Positioning System satellites to estimate the station clock offset, eliminating the need for the quasar observation. The requirements for direct measurement of the instrumental delays that must be made in the absence of a quasar observation are assessed. Finally, the results of the 'quasar-free' differential one-way range, or DOR, measurements of the Mars Observer spacecraft are compared with those of simultaneous conventional delta DOR measurements.
New approaches for tracking earth orbiters using modified GPS ground receivers
A Global Positioning System (GPS) flight receiver provides a means to precisely determine orbits for satellites in low to moderate altitude orbits. Above a 5000-km altitude, however, relatively few GPS satellites are visible. New approaches to orbit determination for satellites at higher altitudes could reduce DSN antenna time needed to provide navigation and orbit determination support to future missions. Modification of GPS ground receivers enables a beacon from the orbiter to be tracked simultaneously with GPS data. The orbit accuracy expected from this GPS-like tracking (GLT) technique is expected to be in the range of a few meters or better for altitudes up to 100,000 km with a global ground network. For geosynchronous satellites, however, there are unique challenges due to geometrical limitations and to the lack of strong dynamical signature in tracking data. We examine two approaches for tracking the Tracking and Data Relay Satellite System (TDRSS) geostationary orbiters. One uses GLT with a global network; the other relies on a small 'connected element' ground network with a distributed clock for short-baseline differential carrier phase (SB Delta Phi). We describe an experiment planned for late 1993, which will combine aspects of both GLT and SB Delta Phi, to demonstrate a new approach for tracking the Tracking and Data Relay Satellites (TDRSs) that offers a number of operationally convenient and attractive features. The TDRS demonstration will be in effect a proof-of-concept experiment for a new approach to tracking spacecraft which could be applied more generally to deep-space as well as near-Earth regimes.
Tracking Galileo at Earth-2 Perigee Using The Tracking and Data Relay Satellite System
The Tracking and Data Relay Satellite System (TDRSS) was successfully used to track the Galileo spacecraft on December 8, 1992, during the Galileo Earth-2 Flyby. This flyby enabled Galileo to obtain a gravity-assisted energy increase as part of the Venus-Earth-Earth trajectory en route to the planet Jupiter.
Tracking Galileo at EArth-2 Perigee Using The Tracking and Data Relay Satellite System
The tracking and Data Relay Satellite System (TDRS) was successfully used to track the Galielo spacecraft on December 8, 1992, during the Galielo Earth-2 flyby. This flyby enabled Galielo to obtaina gravity assited energy increase as part of the Venus-Earth-Earth trajectory en route to the planet Jupiter.
Precise Tracking of the Magellan and Pioneer Venus Orbiters by Same-Beam Interferometry. Part 2: Orbit Determination Analysis
A new radio metric positioning technique has demonstrated improved orbit determination accuracy for the Magellan and Pioneer Venus Orbiter orbiters. The new technique, known as Same-Beam Interferometry (SBI), is applicable to the positioning of multiple planetary rovers, landers, and orbiters which may simultaneously be observed in the same beamwidth of Earth-based radio antennas. Measurements of carrier phase are differenced between spacecraft and between receiving stations to determine the plane-of-sky components of the separation vector(s) between the spacecraft. The SBI measurements complement the information contained in line-of-sight Doppler measurements, leading to improved orbit determination accuracy. Orbit determination solutions have been obtained for a number of 48-hour data arcs using combinations of Doppler, differenced-Doppler, and SBI data acquired in the spring of 1991. Orbit determination accuracy is assessed by comparing orbit solutions from adjacent data arcs. The orbit solution differences are shown to agree with expected orbit determination uncertainties. The results from this demonstration show that the orbit determination accuracy for Magellan obtained by using Doppler plus SBI data is better than the accuracy achieved using Doppler plus differenced-Doppler by a factor of four and better than the accuracy achieved using only Doppler by a factor of eighteen. The orbit determination accuracy for Pioneer Venus Orbiter using Doppler plus SBI data is better than the accuracy using only Doppler data by 30 percent.