Engineering topics

Chassefiere, E.

Publications and source records attributed to Chassefiere, E..

10 records

NASA NTRS2000

The DYNAMO Orbiter Project: High Resolution Mapping of Gravity/Magnetic Fields and In Situ Investigation of Mars Atmospheric Escape

Dynamo is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for Dynamo of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere, and water, from the planet. There is much room for debate on the importance of current atmosphere escape processes in the evolution of the Martian atmosphere, as early "exotic" processes including hydrodynamic escape and impact erosion are traditionally invoked to explain the apparent sparse inventory of present-day volatiles. Yet, the combination of low surface gravity and the absence of a substantial internally generated magnetic field have undeniable effects on what we observe today. In addition to the current losses in the forms of Jeans and photochemical escape of neutrals, there are solar wind interaction-related erosion mechanisms because the upper atmosphere is directly exposed to the solar wind. The solar wind related loss rates, while now comparable to those of a modest comet, nonetheless occur continuously, with the intriguing possibility of important cumulative and/or enhanced effects over the several billion years of the solar system's life. If the detailed history of the Martian internal field could be traced back, and the current escape processes could be understood well enough to model the expected stronger losses under early Sun conditions, one could go a long way toward constraining this part of the mysterious history of Mars' atmosphere.

Smrekar, S.↗

NASA NTRS2000

The Pascal Discovery Mission: A Mars Climate Network Mission

The climate of Mars is a major focus of Mars exploration. With the loss of MCO, however, it remains uncertain how it will be achieved. We argue that a truly dedicated climate mission to Mars should have both orbital and landed components, and that these should operate simultaneously for at least 1 Mars year if not longer. Pascal is a Discovery mission that emphasizes the landed component. Its principal goal is to establish a network of 24 small weather stations on the surface of Mars that will operate for 2 Mars years, with an extended mission option for an additional 8 Mars years bringing the total mission lifetime up to 10 Mars years. The stations will collect hourly measurements of pressure, temperature, and optical depth. After delivering the probes to Mars, Pascal's carrier spacecraft will go into an elliptical orbit which will serve as a relay for the landers, and a platform for synoptic imaging. These simultaneous measurements from the surface and from orbit will allow us to characterize the planet's general circulation and its interaction with the dust, water, and CO2 cycles. During entry, descent, and landing, each of Pascal's 24 probes will also measure the temperature structure of the atmosphere and acquire images of the surface. These data will allow us to determine the global structure of the atmosphere between 15 and 130 km, and characterize the local terrain to help interpret the landed data. The descent images are part of Pascal's outreach program, as the probe camera system will be developed by faculty-supervised student project. The intent is to generate enthusiasm for the Pascal mission by directly involving students. Pascal will be launched on a Delta II-7925 in August of 2005. A type I trajectory will deliver Pascal to Mars in January of 2006. On approach, the three-axis stabilized carrier spacecraft will spring deploy the Pascal probes in 4 separate salvo's of 6 each. Global coverage is achieved with small time-of-arrival adjustments in between each salvo. Pascal's probes utilize an aeroshell, parachute, and crushable material for entry, descent and landing. On the surface, their long life and global coverage is enabled by a Micro Thermal Power Source with demonstrated heritage. After all probes are released, the carrier spacecraft will execute a small burn for insertion into an elliptical orbit. The long lifetime of the Pascal network was chosen in part to maximize the chances that orbital sounding, like that planned with MCO, would occur at some point during the mission. If Pascal is selected for launch in '05, this could occur if MCO-like science is reflown in the '05 opportunity or, if it is reflown in '03, the mission is extended to overlap with Pascal. The combination of temperature sounding from orbit, and surface pressure mapping from the surface will allow a direct determination of the full 3-D wind field for the first time.

Haberle, R. M.↗

NASA NTRS2000

The Pascal Discovery Mission: A Mars Climate Network Mission

The climate of Mars is a major focus of Mars exploration. With the loss of MCO, however, it remains uncertain how it will be achieved. We argue that a truly dedicated climate mission to Mars should have both orbital and landed components, and that these should operate simultaneously for at least I Mars year if not longer. Pascal is Discovery mission that emphasizes the landed component. Its principal goal is to establish a network of 24 small weather stations on the surface of Mars that will operate for 2 Mars years, with an extended mission option for an additional 8 Mars years bringing the total mission lifetime up to 10 Mars years. The stations will collect hourly measurements of pressure, temperature, and optical depth. After delivering the probes to Mars, Pascal's carrier spacecraft will go into an elliptical orbit which will serve as a relay for the landers, and a platform for synoptic imaging. These simultaneous measurements from the surface and from orbit will allow us to characterize the planet's general circulation and its interaction with the dust, water, and CO2 cycles. During entry, descent, and landing, each of Pascal's 24 probes will also measure the temperature structure of the atmosphere and acquire images of the surface. These data will allow us to determine the global structure of the atmosphere between 15 and 130 km, and characterize the local terrain to help interpret the landed data. The descent images are part of Pascal's outreach program, as the probe camera system will be developed by faculty-supervised student project. The intent is to generate enthusiasm for the Pascal mission by directly involving students. Pascal will be launched on a Delta 11-7925 in August of 2005. A type I trajectory will deliver Pascal to Mars in January of 2006. On approach, the three-axis stabilized carrier spacecraft will spring deploy the Pascal probes in 4 separate salvo's of 6 each. Global coverage is achieved with small time-of-arrival adjustments in between each salvo. Pascal's probes utilize an aeroshell, parachute, and crushable material for entry, descent and landing. On the surface, their long life and global coverage is enabled by a Micro Thermal Power Source with demonstrated heritage. After all probes are released, the carrier spacecraft will execute a small bum for insertion into an elliptical orbit. The long lifetime of the Pascal network was chosen in part to maximize the chances that orbital sounding, like that planned with MCO, would occur at some point during the mission. If Pascal is selected for launch in -05, this could occur if MCO-like science is reflown in the '05 opportunity or, if it is reflown in '03, the mission is extended to overlap with Pascal. The combination of temperature sounding from orbit, and surface pressure mapping from the surface will allow a direct determination of the full 3-D wind field for the first time.

Haberle, Robert M.↗

NASA NTRS1994

GOMOS: Gobal Ozone Monitoring by Occultation of Stars

In this paper we report on the progress and status of the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument, and imaging spectrometer under development for flight on the European Space Agency's Polar Orbiting Earth Mission (POEM-1) mission in 1998. Employing occultation of stars as a light probe of the Earth's atmosphere from a sun-sychronous polar orbit, the instrument will monitor ozone and other atmospheric trace gases over the entire globe. Atmospheric transmission resolution of approximately 1.7 km. When data are combined regionally, it will be possible to detect ozone concentration trends as small as 0.05 percent/year, depending on the degree of combination.

Leppelmeier, G. W.↗

NASA NTRS1993

Cloud, dust, and ozone vertical profiles from solar occultation measurements: Implications for dynamics

An instrument was designed for solar occultation measurements of the martian atmosphere from the Phobos spacecraft. It was composed of three different dispersive systems working in the ultraviolet (UV: 0.22-0.32 microns) for the measurement of O3 and aerosols, in the near infrared (NIR: 0.76 microns, 0.94 microns) for the detection of O2 and H2O, and in the infrared (IR: 1.9 microns, 3.7 microns) where CO2 and H2O were measured. A detailed description of the instrument may be found in the special issue of Nature. Its principle objective is to measure from the Phobos orbit the spectrum of the Sun, modified by atmospheric extinction, during sunset. The UV-NIR spot has an angular diameter of 1 arcmin, or approximately 3 km vertical resolution, and is located near the center of the solar disk. The IR field is about twice as large and its line of sight is shifted by 8.5 arcmin, or approximately 20 km, relative to the previous one. It is therefore located near the edge of the solar disk. Sampling times are generally 0.5, 1, and 2 s for IR, UV, and NIR channels respectively, corresponding to vertical excursions of the line of sight of 1, 2, and 4 km respectively under nominal conditions. The instrument operated from February 8 to March 26 (the martian equinox occurred on February 17). The latitude of the intersection of the Sun-spacecraft axis with the surface of Mars varied from -11 to +20, the seasonal date L(sub s) being in the range 0 - 20. All measurements were therefore made near northern spring equinox in equatorial regions. Due to an error in the pointing system, only partial results were obtained, the region below approximately equals 30 km altitude being never sounded by the UV-NIR spectrometer. On the contrary, nine complete occultations were obtained in the IR channels, whose line of sight was fortunately approximately equals 20 km below the UV-NIR axis.

Chassefiere, E.↗

NASA NTRS1993

Eddy mixing coefficient upper limit derived from the photochemical balance of O2

This work is based on the study of the photochemical balance of molecular oxygen in the martian atmosphere by using a one-dimensional model of photochemical reactions involving species derived from CO2 and H2O. The model is basically similar to one used previously for the study of the regulation of CO on a global scale, but the chemical rates are taken from another source. In the present scheme, the regulation of molecular oxygen is studied over timescales of the order of its photochemical lifetime (approximately equals 30 yr), which is much shorter than typical escape timescales. Thus, the escape fluxes are fixed to the values given by 3 and 4. We examine the calculated equilibrium abundances of O2 for given thermal, eddy diffusion coefficients and H2O profiles. The thermal profile is taken from in the lower atmosphere. At higher levels, in order to include the diurnal and seasonal thermal profile variability, we have also used the IRTM data. In order to study the influence of both temperature and pressure profiles on the O2 mixing ratio, we have made several tests corresponding to different martian seasons. The results show that the influence of pressure and temperature is quantitatively weak compared to the one of K and of the water vapor density (H2O). Thus, in the following we have fixed the pressure at the surface to a value of 7 mbar and we have used unique standard thermal profile corresponding to a profile roughly averaged over the year, the season, and the day: T equal 205 K at 0 km altitude, 175 K at 25 km, and 145 K at 50 km.

Rosenqvist, J.↗

NASA NTRS1993

Two-dimensional modeling of thermal inversion layers in the middle atmosphere of Mars

There is some evidence that the thermal structure of the martian middle atmosphere may be altered in a significant way by the general circulation motions. Indeed, while it is well known that the circulation in the meridional plane is responsible for the reversal of the latitudinal thermal gradient at the solstice through the adiabatic heating due to sinking motions above the winter pole, here we want to emphasize that a likely by-product effect could be the formation of warm layers, mainly located in the winter hemisphere, and exhibiting an inversion of the vertical thermal gradient.

Theodore, B.↗

NASA NTRS1992

Vertical structure and size distributions of Martian aerosols from solar occultation measurements

Phobos 2 spectrometer measurements of solar occultations close to the evening terminator have furnished data on the vertical structure of the Martian aerosols near the northern spring equinox. Since the thermal structure derived from saturated IR profiles of water vapor does not allow the reaching of the CO2 frost point at cloud altitudes, said clouds' particles may be formed by H2O ice. Dust was also monitored at two wavelengths; it is assumed that the dust particles are levitated by eddy mixing. A parallel is drawn between these thin clouds and the polar mesospheric clouds observed on earth.

Chassefiere, E.↗

NASA NTRS1992

Huygens/ACP: An instrument for aerosols chemical composition measurements

The Aerosol Collector Pyrolyzer (ACP) which will be used aboard the Huygens probe is introduced. The scientific objectives, scientific rationale, and a technical description of the ACP are given. The ACP will sample the aerosols of the Titan's atmosphere in two regions, 160 to 60 and 60 to 25 km, respectively. In the first region, it will collect aerosol particles absorbed by a complex core (organic polymers) coated with absorbed or condensed molecules. The second collect will sample larger aerosols and the N2-CH4 droplets. In each sampling, the particles are collected on a metallic filter through which the atmospheric gas is pumped. The filter is then inserted into an oven connected to the Gas Chromatograph Mass Spectrometer (GCMS) Experiment which analyzes the gases produced during the heating of the samples. For each sample it will be possible to bring information on the nature and abundance of the volatile components contained in the particles and/or the composition of the photochemical core.

Israel, Guy↗

NASA NTRS1991

Interplanetary Lyman-alpha observations with UVS on Voyager - Data, first analysis, implications for the ionization lifetime

A fraction of the measurements of the interplanetary Lyman-alpha background collected by the Ultraviolet Spectrometer during the cruise of Voyager 1 and 2 between 1977 and 1983 is presented and compared with results from current models of the interaction between the sun and the neutral interstellar gas. An analysis of two sets of data indicates that the same H atom lifetime cannot fit all the data. The actual ionization rate is inferred from the intensity gradient in the maximum emissivity region observed from a sidewind Voyager position at 6 AU, yielding a lifetime of about 1 exp 6 s at 1 AU, whereas the upwind/downwind intensity ratio in the inner solar system favors 2 x 10 exp 6 s, as measured by Voyager, Prognoz, and Pioneer Venus instruments. It is proposed that there is an excess of Ly-alpha emission in the downwind region which forces the model toward excessively high values of the lifetime. Possible explanations are discussed, like incorrect modeling or an additional source of H atoms.

Lallement, R.↗