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Spilker, T. R.

Publications and source records attributed to Spilker, T. R..

34 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Science Rationale for Jupiter Entry Probe as Part of JIMO

A Jupiter atmospheric entry probe as part of JIMO is a cost effective way to address fundamental science questions identified in the National Research Council Solar System Exploration Decadal Survey (SSEDS): New Frontiers in the Solar System, An Integrated Ex- ploration Strategy. Compared to either the cost of an entirely separate Jupiter mission, or the cost of JIMO itself, inclusion of such a probe on JIMO would be cost advantageous. The probe itself could be relatively simple, and could build on the Galileo Probe heritage. The SSEDS specifically identified the distribution of water across the Solar System as a Key Scientific Question. Correspondingly, knowing the water abun dance on Jupiter is fundamental to understanding almost every aspect of the evolution of the early solar nebula. The Galileo Probe obtained the abundance of several key elements in Jupiter's atmosphere, which data have already caused major rethinking of theories of how Jupiter formed and how the early solar nebula evolved. However, because of a combination of circumstances, the global abundance of the key element oxygen, in the form of water, was not obtained. Without knowledge of the jovian water abundance, further progress in understanding Solar System evolution and planet formation will be greatly inhibited. Therefore, quantifying jovian water abundance should be a goal of the very next mission to the jovian system. Such a measurement would be impossible via remote sensing from the JIMO orbiter because of the large distances the JIMO orbiter maintains from Jupiter. A Jupiter atmospheric entry probe as part of JIMO could achieve the fundamental water measurement. In order that a probe avoid repeating the Galileo probe's experience of failing to obtain the jovian water abundance, the probe should go deep, to at least 100 bars pressure. Probes to 100 bars have been accomplished many times in descending to the surface of Venus, and at 100 bars the temperature of the jovian atmosphere is 60-70 K less than the surface temperature of Venus.

Young, R. E.↗
NASA NTRS2001

Saturn Ring Observer

Answering fundamental questions about ring particle characteristics, and individual and group behavior, appears to require close-proximity (a few km) observations. Saturn's magnificent example of a ring system offers a full range of particle sizes, densities, and behaviors for study, so it is a natural choice for such detailed investigation. Missions implementing these observations require post-approach Delta(V) of approximately 10 km/s or more, so past mission concepts called upon Nuclear Electric Propulsion. The concept described here reduces the propulsive Delta(V) requirement to as little as 3.5 km/s, difficult but not impossible for high-performance chemical propulsion systems. Additional information is contained in the original extended abstract.

Spilker, T. R.↗
NASA NTRS2001

Saturn Deep Atmospheric Entry Probes Delivered by INSIDE Jupiter Derivative Spacecraft

In situ probes are the most reliable means for sampling composition and conditions deep in giant planet atmospheres. Deep constituent abundances at the giant planets offer clues to conditions in the solar systems protoplanetary disk and variations with heliocentric distance. Currently in situ atmospheric data are available from only one giant planet, Jupiter, and probes that penetrate deeper than the Galileo probe are needed there to measure the deep abundances of such important species as H2O and H2S. Deep probes at Saturn would extend the sampled heliocentric range to Saturn, providing important constraints on the conditions and variability of the protoplanetary disk, and would provide significant new information about Saturn and its evolutionary processes. Such a probe mission could be implemented using a derivative of the INSIDE Jupiter mission's spacecraft as the Carrier/Relay Spacecraft (CRSC), with probes per JPL/Team X and other design studies. Additional information is contained in the original extended abstract.

Spilker, T. R.↗
NASA NTRS2001

Flyby Delivers Multiple Deep Jupiter Probes

In situ probes are the most reliable means for sampling composition and conditions deep in giant planet atmospheres. While exceeding its baseline mission, the Galileo probe entered a distinctly non-representative region of Jupiter (a 'hot spot') and apparently did not measure the full deep abundances of such important species as H2O and H2S, whose measured abundances were still increasing at the deepest datum. Multiple deep (approx. 100 bar) in situ probes minimize the hot spot risk, and address spatial variations and deep constituent abundances. Additional information is contained in the original extended abstract.

Spilker, T. R.↗
NASA NTRS2000

Saturn Ring Observer

This paper outlines a mission design for a Saturn Ring Observer (SRO) mission that has Saturn itself provide the bulk of the delta V necessary for orbit insertion, with the remainder within chemical propulsion capability.

Saturn↗
NASA NTRS1998

Avanced Jupiter Probe

This paper describes the results of new analyses and mission/system designs for low cost Advanced Jupiter Probes. Science and mesurement objectives, instrumentation, entry probe design, and mission/system design options are described and reflect an aggressive approach to the application of new advance technologies expected to be both available and developed over the next ten years.

Jupiter probes cost Jupiter composition Jupiter zo↗
NASA NTRS1998

A Neptune Orbiter Mission

This paper describes the results of new analyses and mission/system designs for a low cost Neptune Orbiter mission. Science and measurement objectives, instrumentation, and mission/system design options are described and reflect an aggressive approach to the application of new advanced technologies expected to be available and developed over the next five to ten years.

Neptune Orbiter↗
NASA NTRS1994

(abstract) Neptune: CO and HCN Distributions from Observations at the CSO

We used the Caltech Submillimeter Observatory (CSO ) to make spatially unresolved observations of the 230.538 GHz 2-1 transition of CO and the 265.886 GHz 3-2 transition of HCN at Neptune. All observations used the 10.4 meter antenna with a double sideband SIS junction heterodyne receiver. Spectra were observed with parallel acousto-optic spectrometers simultaneously providing 580 MHz bandwidth at 0.57 MHz resolution and 50 MHz bandwidth at 0.049 MHz resolution. Observed line shapes agree with prior observations by Rosenqvist et al and Marten et al. Analysis of the line shapes and intensities will yield information about the distributions of CO and HCN in the stratosphere of Neptune, and these results will be compared with previous results. The data imply that the mixing ratios of CO and HCN must decrease with altitude somewhere within the pressure range from 1 to 0.001 mbar. HCN data will also address the sharp saturation-induced decrease in the HCN mixing ratio at the lower levels in the stratosphere.

Caltech Submillimeter Observatory SRO CO carbon mo↗
NASA NTRS1991

Refraction effects on the Galileo probe telemetry carrier frequency

As the Galileo probe relay radio link (RRL) signal propagates outward through the Jovian atmosphere, the atmosphere will manifest itself in two ways. First, the geometric path length of the signal is increased, resulting in a small change of the RRL signal departure angle from the proble (transmitter). Secondly, the velocity of the signal is decreased. For a spherical, static atmosphere with a known profile of refractivity versus altitude the effects of refraction on the RRL frequency can be found using a variation of standard ray-tracing techniques, whereby the ray departure angle is found by an iterative process. From the dispersive characteristics of a mixture of hydrogen and helium with trace amounts of methane and ammonia a simple model of the Jovian atmosphere is constructed assuming spherical symmetry and uniform mixing. The contribution to the RRL Doppler frequency arising from refraction is calculated, and its effect on the Doppler wind measurements is discussed.

Atkinson, D. H.↗
NASA NTRS1990

Laboratory measurements and modeling of microwave absorption by ammonia in gas mixtures applicable to giant planet atmospheres

Accurate knowledge of the microwave absorption behavior of ammonia is critical to the correct interpretation of radio astronomical and radio occultation data from the giant planets. New cavity resonator techniques developed at the Stanford Center for Radar Astronomy have allowed accurate laboratory measurements of the microwave absorptivity and refractivity spectra of gas mixtures containing trace amounts of ammonia. A parameterized version of the modified Ben-Reuven formalism of Berge and Bulkis was optimized to fit the new data. The new formalism produced by this method predicts ammonia absorptivity much more accurately than previous formalism over a significant range of conditions.

Spilker, T. R.↗