Primary Scientific Objective Research Articles

Jupiter After the Galileo Probe

The Galileo Mission to Jupiter, which arrived in December of 1995, provided the first study by an orbiter, and the first in-situ sampling via an entry probe, of an outer planet atmosphere. The rationale for an entry probe is that, even from an orbiter, remote sensing of the Jovian atmosphere could not adequately retrieve the information desired. This talk provides a current summary of the most significant aspects of the data returned from the Galileo entry probe. As a result of the probe measurements, there has been a reassessment of our understanding of outer planet formation and evolution of the solar system. The primary scientific objective of the Galileo probe was to determine the composition of the Jovian atmosphere, which from remote sensing remained either very uncertain, or completely unknown, with respect to several key elements. For example, the O abundance, in the form H2O, was uncertain by two orders of magnitude. Only a highly depleted upper abundance limit obtained near the 1 bar pressure level was known for S, and abundances of noble gases heavier than He were unknown. The probe found that the global He mass fraction is significantly above the value reported from the Voyager Jupiter flybys but is slightly below the protosolar value, implying that there has been some settling of He to the deep Jovian interior. The probe He measurements have also led to a reevaluation of the Voyager He mass fraction for Saturn, which is now determined to be much closer to that of Jupiter. The elements C, N, S, Ar, Kr, Xe were all found to have global abundances approximately 3 times their respective solar abundances. This result has raised a number of fundamental issues with regard to properties of planetesimals and the solar nebula at the time of giant planet formation. The global abundance of O was not obtained by the probe because of the influence of local processes at the probe entry site (PES), processes which depleted condensible species, in this case H2O, well below condensation levels. Other condensible species, namely NH3 and H2S, were similarly affected but attained their deep equilibrium mixing ratios before the maximum depth sampled by the probe. Processes that might be capable of producing such effects on the condensibles are still under investigation. Measured isotopic ratios of noble gases and other heavy elements are solar, and (D + 3He)/H is the same to within measurement uncertainties as in the local interstellar medium. No thick clouds were detected, and in particular no significant water cloud, but the PES location clearly affected the probe measurements of clouds. In fact, the probe data must be understood in the context of the location of the PES, which was within what is termed a 5 μm hot spot, a local clearing in the clouds that is bright near the 5 μm spectral region. The thermal structure at the PES was determined from approximately 1000 km above the 1 bar pressure level (10−9 bars) to 132 km below 1 bar (22 bars). Probe measurements showed the atmosphere to be generally stably stratified as deep as the probe made measurements, with a typical static stability of ~0.1 K km−1 at and below visible cloud levels. In the upper atmosphere the probe derived a maximum positive vertical temperature gradient of approximately 5 K km−1, and maximum temperature of ~900 K. The energy sources producing the warm upper atmosphere have yet to be completely identified. At first glance, Doppler tracking of the probe indicates that the long observed cloud level zonal winds extend to levels at least as deep as the probe made measurements. Zonal wind increases from ~80 m s−1 at pressures less than a bar to about 180 m s−1 near 5 bars, and remains approximately constant with depth thereafter. However, there is a question as to whether the winds measured from probe tracking are representative of the general wind field, or are considerably influenced by localized winds associated with the PES.

High-resolution continental water storage recovery from low–low satellite-to-satellite tracking

Abstract The low–low satellite-to-satellite (SST) tracking mission, Gravity Recovery and Climate Experiment (GRACE), has the primary science objective of measuring climate-sensitive signals generated by mass redistributions on Earth at spatial scales greater than several hundred km and temporal scales longer than 30 days. Its science data products include 30-day time-series of geopotential models in spherical harmonic coefficients, and the changes in the geopotentials represent observations of the time-variation of the Earth's gravity field. In this contemporary technique, the spectral components representing signals are limited up to a certain degree and order, while the ill-determined higher frequency signals are usually filtered. In this study, we use an alternative method to compute the in situ disturbing potential observations at satellite altitude assuming energy conservation and to determine continental water mass variations with an objective to enhance regional spatial resolution of the signals. In a simulation study using GRACE observable, NCEP daily mean terrestrial water storage data, and realistic atmosphere and ocean tide modeling errors and temporal aliasing, we estimated monthly mean water storage variations for 1 year over South America using both this method and the contemporary global analysis method. We conclude that our method provides more accurate estimates for regional hydrology and with higher spatial resolutions than the contemporary Stokes’ approach using global spherical harmonics.

Palliative care: a supportive adjunct to pediatric phase I clinical trials for anticancer agents?

Hampering enrollment of children to phase I oncology research would dramatically impair the ability of investigators to develop new treatments to improve medical care for the pediatric cancer population. The variability in pediatric tumor response indicates a need for the development of new anticancer agents that specifically target varying histologies of malignancies.1 Aleska and Koren argue that “clinical trials may be the only way to determine the appropriate types of treatments for pediatric cancer.”2 The primary scientific objectives of a phase I trial are to assess the safety and tolerability of tested agents, to identify the maximum-tolerated dose of the drug, and characterize the drug's pharmacokinetics.1,3–8 Secondarily, preliminary antitumor efficacy data are sought.1,3–8 However, enrolling children with cancer in phase I trials raises important ethical concerns. Although pediatric clinical investigators hope that participation in the phase I trials will help subjects, they are not meant to cure or even improve the condition of the child. Usually, however, they offer the only remaining treatment option for children with advanced cancer and thereby provide an important source of hope at a difficult time. Similar to adult phase I trials, pediatric phase I trials generally have a 5% to 8% response rate.1,3–8 Thus, it may be questionably unreasonable to offer enrollment in pediatric phase I trials because the likelihood of risk and discomfort are disproportionate to the marginal benefit. These trials may raise unrealistic hopes of a cure, burden already sick children with potentially invasive procedures, compound suffering through chemotherapeutic and other associated drug side effects, and limit the opportunity for palliation. On the other hand, families may perceive even a low likelihood of benefit favorably, and ethically we ought to respect the family's prima facie … Reprint requests to (C.M.U.) School of Nursing and Center for Bioethics, Room 357 NEB, 420 Guardian Dr, Philadelphia, PA 19104-6096. E-mail: culrich{at}nursing.upenn.edu

New Results from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) Mission

The primary scientific objective of RHESSI Small Explorer mission is to investigate the physics of particle acceleration and energy release in solar flares, through imaging and spectroscopy of X-ray/gamma-ray continuum and gamma-ray lines emitted by accelerated electrons and ions, respectively. Here we briefly describe the mission and summarize the new solar observations, including the first hard X-ray imaging spectroscopy, the first high resolution spectroscopy of solar gamma-ray lines, and the first imaging of solar gamma-ray lines and continuum.

Performance and surface scattering models for the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS)

The primary scientific objective of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), which will be on board Mars Express mission scheduled for launch in 2003, is to map the distribution and depth of the liquid water/ice interface in the upper kilometres of the crust of Mars. MARSIS will also provide unique information to help us understand the recent crustal evolution of the planet. In addition an ionosphere sounding experiment will measure the electron density and structure of the upper atmosphere during day-time operations. We describe the design approach and expected performance by focusing on a model of the surface scattering, which is critical to obtaining a good quality radar response. We characterize the surface in terms of large-scale morphology upon which small-scale geometric variation is superposed. Moreover, MOLA data have been processed using a fractals model to better describe the surface roughness of Mars. We used three categories of rock material with different dielectric properties to assess the performance of the Radar Sounder and detect the depth of the ice/water and dry/ice interface. This paper will focus on studying the effect of Mars surface roughness on the penetration performance of MARSIS as a subsurface sounding instrument. The impact of ionosphere on MARSIS operation and performance is significant and will be discussed in a future paper by other authors.

SAC-C mission and the international am constellation for earth observation

The primary mission of SAC-C is to provide multispectral imaging of terrestrial and coastal environments, measurement of the Earth’s geomagnetic field, and studies of the structure and dynamics of the Earth’s atmosphere and ionosphere. The primary scientific objectives are to monitor the condition and dynamics of the terrestrial and marine biosphere and environment, better understand the Earth’s geomagnetic field and related Sun -Earth interactions, and to develop and utilize new GPS based techniques to globally measure atmospheric phenomena for the study of weather, seasonal, interannual and long term climate change.

International Genetic Epidemiology Society: commentary on Darkness in El Dorado by Patrick Tierney.

The International Genetic Epidemiology Society (IGES) has examined the charges against James V. Neel and his colleagues contained in the recently published book by Patrick Tierney entitled Darkness in El Dorado: How Scientists and Journalists Devastated the Amazon (W.W. Norton, 2000). The book implicates Neel in causing or promoting an epidemic of measles among the Yanomamö Indians of Venezuela in 1968 leading to "hundreds if not thousands" of deaths by using a "dinosaur" vaccine (Edmonston B) as a deliberate "experiment" to test his "eugenic" theories. Tierney also attempts to link this research, funded by the Atomic Energy Commission (AEC), with a broader tapestry of human radiation experiments. To investigate these serious charges, the IGES undertook a thorough examination of most source documents referenced in Tierney's book, Neel's field logs, notes, first-hand reports, contemporary writings, film sound tracks, etc., and conducted interviews with many relevant persons. The IGES finds that these allegations are false. Neel was not a eugenicist and was in fact highly critical of both the scientific basis of eugenics and its coercive social policies. In this regard, Tierney has grossly misrepresented Neel's views on a wide range of social implications of modern civilization for the long-term health of the gene pool. Far from causing an epidemic of measles, Neel did his utmost to protect the Yanomamö from the ravages of the impending epidemic by a vaccination program using a vaccine that was widely used at the time and administered in an appropriate manner. There was nothing experimental about the vaccination program, which in fact severely hindered the primary scientific objectives of the expedition. Although the research was funded in large part by the AEC, there was no element of radiation research and the work had no connection with the ethical abuses that have been reported from AEC-sponsored radiation research, such as studies of heavy isotopes. Neel's seminal contributions to a broad range of topics in human genetics have been extensively chronicled elsewhere. His research on the Yanomamö in particular has provided unique insights into the evolutionary biology of our species, the role of sociocultural practices, such as kinship relationships and selective pressures in shaping the genetic diversity of primitive population isolates, as well as the general picture of health in such populations. The IGES decries the damage done to the reputation of one of its founders and its first President and the misperception this book may have caused about the conduct of research in genetic epidemiology. Ethical issues about scientific research in primitive populations deserve serious and wide discussion, but the IGES condemns the gross misrepresentation of the facts and demonization of the principal characters in this book.

Mars Color Imager (MARCI) on the Mars Climate Orbiter

The Mars Color Imager, or MARCI, experiment on the Mars Climate Orbiter (MCO) consists of two cameras with unique optics and identical focal plane assemblies (FPAs), Data Acquisition System (DAS) electronics, and power supplies. Each camera is characterized by small physical size and mass (∼6×6×12 cm, including baffle; <500 g), low power requirements (<2.5 W, including power supply losses), and high science performance (1000×1000 pixel, low noise). The Wide Angle (WA) camera will have the capability to map Mars in five visible and two ultraviolet spectral bands at a resolution of better than 8 km/pixel under the worst case downlink data rate. Under better downlink conditions the WA will provide kilometer‐scale global maps of atmospheric phenomena such as clouds, hazes, dust storms, and the polar hood. Limb observations will provide additional detail on atmospheric structure at 1/3 scale‐height resolution. The Medium Angle (MA) camera is designed to study selected areas of Mars at regional scale. From 400 km altitude its 6° FOV, which covers ∼40 km at 40 m/pixel, will permit all locations on the planet except the poles to be accessible for image acquisitions every two mapping cycles (roughly 52 sols). Eight spectral channels between 425 and 1000 nm provide the ability to discriminate both atmospheric and surface features on the basis of composition. The primary science objectives of MARCI are to (1) observe Martian atmospheric processes at synoptic scales and mesoscales, (2) study details of the interaction of the atmosphere with the surface at a variety of scales in both space and time, and (3) examine surface features characteristic of the evolution of the Martian climate over time. MARCI will directly address two of the three high‐level goals of the Mars Surveyor Program: Climate and Resources. Life, the third goal, will be addressed indirectly through the environmental factors associated with the other two goals.

The Relationship between Precipitation and Lightning in Tropical Island Convection: A C-Band Polarimetric Radar Study

One of the primary scientific objectives of the Maritime Continent Thunderstorm Experiment was to study cloud electrification processes in tropical island convection, in particular, the coupling between ice phase precipitation and lightning production. To accomplish this goal, a C-band polarimetric radar was deployed in the Tropics (11.68S, 130.88E) for the first time, accompanied by a suite of lightning measurements. Using observations of the propagation-corrected horizontal reflectivity and differential reflectivity, along with specific differential phase, rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex (known locally as Hector) over the Tiwi Islands on 28 November 1995. Hector’s precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field, cloud-to-ground (CG) and total lightning flash rates, and ground strike locations. During Hector’s developing stage, precipitating convective cells along island sea breezes were dominated by warm rain processes. No significant electric fields or lightning were associated with this stage of Hector, despite substantial rainfall rates. Aided by gust front forcing, a cumulus merger process resulted in larger, taller, and more intense convective complexes that were dominated by mixed-phase precipitation processes. During the mature phase of Hector, lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall. Merged convective complexes produced 97% of the rainfall and mixed-phase ice mass and 100% of the CG lightning. As Hector dissipated, lightning activity rapidly ceased. As evidenced from the multiparameter radar observations, the multicell nature of Hector resulted in the continuous lofting of supercooled drops to temperatures between 2108 and 2208C in discrete updraft cores during both the early and mature phases. The freezing of these drops provided instantaneous precipitation-sized ice particles that may have subsequently rimed and participated in thunderstorm electrification via the noninductive charging mechanism.

The Infrared Imaging Surveyor (IRIS) project: Astro-F

IRIS (Infrared Imaging Surveyor) is the first Japanese satellite dedicated solely to infrared astronomy. The telescope has 70-cm aperture, and is cooled down to 6 K with super-fluid helium assisted by two-stage Stirling cycle coolers. On the focal plane, the two instruments, the InfraRed Camera (IRC) and the Far-Infrared Surveyor (FIS), are mounted. IRC is a near- and mid-infrared camera for deep imaging-surveys in the wavelength region from 2 to 25 microns. FIS is a far-infrared instrument for a whole sky survey in the wavelength region from 50 to 200 microns. The diffraction-limited spatial resolution is achieved except in the shortest waveband. The point source sensitivity and the survey coverage are significantly improved compared to previous missions. The primary scientific objective is to investigate birth and evolution of galaxies in the early universe by surveys of young normal galaxies and starburst galaxies. IRIS is thrown by a Japanese M-V rocket into a sun-synchronous orbit, in which the cooled telescope can avoid huge emissions from the Sun and the Earth. The expected holding time of the super-fluid helium is more than one year. After consumption of the helium, the near-infrared observation can be continued by the mechanical coolers.

Radio and optical detection of Martian dust storm discharges

Given the known physical attributes of Martian dust storms, we derive their electromagnetic signatures as they would be perceived both remotely and in situ. We also describe a radiowave and optical experiment (REDD), suitable for deployment on the Mars Surveyor 2001 Lander, whose primary scientific objective is to establish the electrical nature of dust storms in the Martian atmosphere. This experiment would be capable of the remote tracking of dust storms across the Martian surface while estimating electrical properties of dust, dust densities, and surface conductivities. The experiment sensors consist of two orthogonal magnetic search coil antennas, an electric field antenna, and a horizon-looking photodetector. The sensors drive a waveform capture system and a set of multichannel analyzers that span the radio spectrum from 1 kHz to 100 MHz. The data sampling strategy incorporates a low-resolution survey mode and a high time-resolution direction-finding mode. Intelligent use of an event-trigger system, circular buffer storage, and data compression minimize the instrument data rate and the impact on spacecraft resources.

Overview of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a research facility instrument provided by the Ministry of International Trade and Industry (MITI), Tokyo, Japan to be launched on NASA's Earth Observing System morning (EOS-AM1) platform in 1998. ASTER has three spectral hands in the visible near-infrared (VNIR), six bands in the shortwave infrared (SWIR), and five bands in the thermal infrared (TIR) regions, with 15-, 30-, and 90-m ground resolution, respectively. The VNIR subsystem has one backward-viewing band for stereoscopic observation in the along-track direction. Because the data will have wide spectral coverage and relatively high spatial resolution, it will be possible to discriminate a variety of surface materials and reduce problems in some lower resolution data resulting from mixed pixels. ASTER will, for the first time, provide high-spatial resolution multispectral thermal infrared data from orbit and the highest spatial resolution surface spectral reflectance temperature and emissivity data of all of the EOS-AM1 instruments. The primary science objective of the ASTER mission is to improve understanding of the local- and regional-scale processes occurring on or near the Earth's surface and lower atmosphere, including surface-atmosphere interactions. Specific areas of the science investigation include the following: (1) land surface climatology; (2) vegetation and ecosystem dynamics; (3) volcano monitoring; (4) hazard monitoring; (5) aerosols and clouds; (6) carbon cycling in the marine ecosystem; (7) hydrology; (8) geology and soil; and (9) land surface and land cover change. There are three categories of ASTER data: a global map, regional monitoring data sets, and local data sets to be obtained for requests from individual investigators.

The Mars thermosphere-ionosphere: Predictions for the arrival of Planet-B

The primary science objective of the Planet-B mission to Mars is to study the Martian upper atmosphere-ionosphere system and its interaction with the solar wind. An improved knowledge of the Martian magnetic field (whether it is induced or intrinsic) is needed, and will be provided by Planet-B. In addition, a proper characterization of the neutral thermosphere structure is essential to place the various plasma observations in context. The Neutral Mass Spectrometer (NMS) onboard Planet-B will provide the required neutral density information over the altitude range of 150–500 km. Much can be learned in advance of Planet-B data taking as multi-dimensional thermosphere-ionosphere and MHD models are exercised to predict the Mars near-space environment that might be expected during the solar maximum conditions of Cycle 23 (1999–2001). Global model simulations of the Mars thermosphere-ionosphere system are presented and analyzed in this paper. These Mars predictions pertain to the time of Planet-B arrival in October 1999 (F10.7∼200; Ls∼220). In particular, the National Center for Atmospheric Research (NCAR) Mars Thermosphere General Circulation Model (MTGCM) is exercised to calculate thermospheric neutral densities (CO2, CO, N2, O, Ar, O2), photochemical ions (CO+2, O+2, O+ below 200 km), neutral temperatures, and 3-components winds over 70–300 km. Cases are run with and without dust loading of the lower atmosphere in order to examine the potential impacts of dust storms on the thermosphere-ionosphere structure. Significant dust-driven impacts are predicted in the lower thermosphere (100–120 km), but are less pronounced above 150 km. The ionospheric peak height changes greatly with the passage of a Mars global dust storm event. In addition, Martian dayside exobase temperatures are generally warmer during dusty periods, in accord with Mariner 9 UVS data (Stewart et al., 1972). During the Planet-B mission, the NMS team intends to use the MTGCM as a facility tool whose simulated output can be utilized to aid various investigations.

Nuclear instrumentation for a soft X-ray detection system on a small satellite, CATSAT

Nuclear instrumentation has been designed and tested for a large field of view soft X-ray sensor utilizing Si avalanche photodiodes (APDs). The instrument will be launched on a low cost satellite mission in mid 1998. The mission's primary scientific objective is to determine the distance scale to the sources of cosmic gamma ray bursts by utilizing interstellar absorption effects observable in their X-ray emission at energies below 2 keV. The soft X-ray (SXR) sensor incorporates 7 identical panels, each with 16 APDs collectively collimated to a 1 steradian field of view. The SXR panels are radiatively cooled to -35 degrees C, and taken together, view a full hemisphere. The instrumentation for each of the sensors in the SXR detector includes a low noise, charge sensitive preamplifier/shaping amplifier and an analog electronics unit (AEU) containing a voltage amplifier, peak track and hold circuit, and threshold-timing logic. Each panel has an analog to digital interface (ADI) based on a field programmable gate array (FPGA), which controls the digitization of the event amplitudes, implements the in-flight calibration (IFC) for each APD, and coordinates the data output to and command input from the instrument CPU.

THE ELECTRIC FIELD AND WAVE EXPERIMENT FOR THE CLUSTER MISSION

The electric-field and wave experiment (EFW) on Cluster is designed to measure the electric-field and density fluctuations with sampling rates up to 36000 samples s-1. Langmuir probe sweeps can also be made to determine the electron density and temperature. The instrument has several important capabilities. These include (1) measurements of quasi-static electric fields of amplitudes up to 700 mV m-1 with high amplitude and time resolution, (2) measurements over short periods of time of up to five simualtaneous waveforms (two electric signals and three magnetic signals from the seach coil magnetometer sensors) of a bandwidth of 4 kHz with high time resolution, (3) measurements of density fluctuations in four points with high time resolution. Among the more interesting scientific objectives of the experiment are studies of nonlinear wave phenomena that result in acceleration of plasma as well as large- and small-scale interferometric measurements. By using four spacecraft for large-scale differential measurements and several Langmuir probes on one spacecraft for small-scale interferometry, it will be possible to study motion and shape of plasma structures on a wide range of spatial and temporal scales. This paper describes the primary scientific objectives of the EFW experiment and the technical capabilities of the instrument.

ＡＳＴＥＲによる地球観測

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a multi-spectral imaging radiometer to be launched on NASA's Earth Observing System AM-1 (EOS AM-1) platform in 1998. ASTER has 3 spectral bands in the VNIR, 6 bands in the SWIR, and 5 bands in the TIR regions with 15, 30, and 90 m ground resolution respectively. The primary science objective of the ASTER mission is to improve understanding of the local- and regional-scale processes occurring on or near the Earth's surface and lower atmosphere, including surface-atmosphere interactions.

Current‐voltage characteristics of the TSS 1 satellite

One of the primary science objectives of the TSS 1 project was that of studying the current‐voltage (I‐V) characteristics of a highly charged body in the ionosphere. In this paper, using data from experiments of the TSS 1 mission for an event of high satellite charging, we derive points of the I‐V characteristics of the TSS satellite. These are then compared with different theoretical models. The comparison shows that the measured currents, for given potentials, are well above the predictions of the Parker and Murphy model. The results obtained appear, in fact, to support a model which computes an enhancement of the collected current due to the rapid motion of the collector across the geomagnetic field.

Konus-W gamma-ray burst experiment for the GGS Wind spacecraft

The Konus-W experiment to be flown on board the GGS-Wind spacecraft is designed to observe gamma-ray bursts and solar flares with moderate spectral and high time resolution. Two large scintillators are used to provide omnidirectional sensitivity. The primary scientific objectives are the study of the continuum energy spectra and spectral features of these events in the energy range of 10 keV to 10 MeV, as well as their time histories in soft, medium, and hard energy bands, with a time resolution to 2 ms.

The visible imaging system (VIS) for the polar spacecraft

The Visible Imaging System (VIS) is a set of three low-light-level cameras to be flown on the POLAR spacecraft of the Global Geospace Science (GGS) program which is an element of the International Solar-Terrestrial Physics (ISTP) campaign. Two of these cameras share primary and some secondary optics and are designed to provide images of the nighttime auroral oval at visible wavelengths. A third camera is used to monitor the directions of the fields-of-view of these sensitive auroral cameras with respect to sunlit Earth. The auroral emissions of interest include those from N+2 at 391.4 nm, 0 I at 557.7 and 630.0 nm, H I at 656.3 nm, and 0 II at 732.0 nm. The two auroral cameras have different spatial resolutions. These resolutions are about 10 and 20 km from a spacecraft altitude of 8 R(sub e). The time to acquire and telemeter a 256 x 256-pixel image is about 12 s. The primary scientific objectives of this imaging instrumentation, together with the in-situ observations from the ensemble of ISTP spacecraft, are (1) quantitative assessment of the dissipation of magnetospheric energy into the auroral ionosphere, (2) an instantaneous reference system for the in-situ measurements, (3) development of a substantial model for energy flow within the magnetosphere, (4) investigation of the topology of the magnetosphere, and (5) delineation of the responses of the magnetosphere to substorms and variable solar wind conditions.

A low cost Mercury orbiter mission

Due to Mercury's small mass and position deep within the solar gravitational well, an orbiter mission poses difficult performance requirements (i.e. ΔV, thermal extremes). However, Yen (JPL) showed that with extended trip times, substantial Mercury missions are feasible. Low cost, quick concept-to-launch, high quality, and reliability are balanced in constraining a small spacecraft mission to Mercury. The primary science objective is high quality multispectral imagery and altimetry. The spacecraft is based on the Clementine spacecraft and sensors. UV/Visual/infrared cameras, star trackers, and a laser altimeter are proposed to determine mineralogical composition, surface structure/morphology, spectral/compositional mapping, and topography. Clementine sensors would require upgrades to enhance thermal dissipation and to increase radiation protection. The first available launch opportunity is in August 1996 and the target orbit is a 300 km polar Mercury orbit. Launch vehicle options are discussed. Options for companion or follow-on spacecraft are presented.