Initial experimental results from the Laboratory Biosphere closed ecological system facility.

An initial experiment in the Laboratory Biosphere facility, Santa Fe, New Mexico, was conducted May-August 2002 using a soil-based system with light levels (at 12 h per day) of 58-mol m-2 d-1. The crop tested was soybean, cultivar Hoyt, which produced an aboveground biomass of 2510 grams. Dynamics of a number of trace gases showed that methane, nitrous oxide, carbon monoxide, and hydrogen gas had initial increases that were substantially reduced in concentration by the end of the experiment. Methane was reduced from 209 ppm to 11 ppm, and nitrous oxide from 5 ppm to 1.4 ppm in the last 40 days of the closure experiment. Ethylene was at elevated levels compared to ambient during the flowering/fruiting phase of the crop. Soil respiration from the 5.37 m2 (1.46 m3) soil component was estimated at 23.4 ppm h-1 or 1.28 g CO2 h-1 or 5.7 g CO2 m-2 d-1. Phytorespiration peaked near the time of fruiting at about 160 ppm h-1. At the height of plant growth, photosynthesis CO2 draw down was as high as 3950 ppm d-1, and averaged 265 ppm h-1 (whole day averages) during lighted hours with a range of 156-390 ppm h-1. During this period, the chamber required injections of CO2 to continue plant growth. Oxygen levels rose along with the injections of carbon dioxide. Upon several occasions, CO2 was allowed to be drawn down to severely limiting levels, bottoming at around 150 ppm. A strong positive correlation (about 0.05 ppm h-1 ppm-1 with r2 about 0.9 for the range 1000-5000 ppm) was observed between atmospheric CO2 concentration and the rate of fixation up to concentrations of around 8800 ppm CO2.     

Titan aerosol analogues: analysis of the nonvolatile tholins

Laboratory experiments that produced tholins in a simulated Titan atmosphere were conducted. We report the first systematic analyses of these compounds using Fourier-transform ion cyclotron resonance mass spectrometry. The findings suggest surprising simplicity and nonrandomness in the mass distribution and regularity in species clusters. The degree of unsaturation generally increased with increasing molecular weight in a predictable fashion, and nitrogen is proposed as the dominant carrier of unsaturation. In detected compounds with a general formula of C(x)H(y)N(z), the carbon to nitrogen ratio (x/z) varied only slightly within a narrow limit, and decreased with increasing molecular weights. These compounds are of potential prebiotic interest since they sediment to the surface of Titan, and would dissolve readily in transient aqueous pools that might be generated from time to time by impacts and volcanic     

Collision Probabilities for Keplerian Orbits

We present a new derivation of the probability of collisions between spherical satellites occupying Keplerian orbits. The equations follow from the central concept of the instantaneous collision rate, an expression that describes the occurrence of collisions by using a Dirac -function. The derivation proceeds by showing how this instantaneous collision rate can be averaged over orbital mean anomaly angles and, additionally, over orbital precession angles to generate expressions appropriate for intermediate and long time scales. Collision rates averaged over mean anomalies tend to be non-zero during relatively brief collision seasons, when the peak collision probability may exceed the long-term average by several orders of magnitude. Derived precession-angle averages have a functional form similar but not identical to the collision probability expression derived using the spatial density approach of Kessler (Icarus, 48: 39–48, 1981), and the two methods have been found to yield numerical results to within 1% for all cases examined.     

The Mercury Dual Imaging System on the MESSENGER Spacecraft

The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin and evolution. MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC). The NAC is a 1.5° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 10.5° FOV and 12-color filter wheel. The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled device detector. Only one camera operates at a time, allowing them to share a common set of control electronics. The NAC and the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments. Onboard data compression provides capabilities for pixel binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression. MDIS will acquire four main data sets at Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor images at low incidence angles, and targeted high-resolution images of key surface features. These data will be used to construct a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips. Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement history of volcanic materials, and the thickness distribution and compositional variations of crustal materials. This paper summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated from MDIS data.     

The Radio Frequency Subsystem and Radio Science on the MESSENGER Mission

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Radio Frequency (RF) Telecommunications Subsystem is used to send commands to the spacecraft, transmit information on the state of the spacecraft and science-related observations, and assist in navigating the spacecraft to and in orbit about Mercury by providing precise observations of the spacecraft’s Doppler velocity and range in the line of sight to Earth. The RF signal is transmitted and received at X-band frequencies (7.2 GHz uplink, 8.4 GHz downlink) by the NASA Deep Space Network. The tracking data from MESSENGER will contribute significantly to achieving the mission’s geophysics objectives. The RF subsystem, as the radio science instrument, will help determine Mercury’s gravitational field and, in conjunction with the Mercury Laser Altimeter instrument, help determine the topography of the planet. Further analysis of the data will improve the knowledge of the planet’s orbital ephemeris and rotation state. The rotational state determination includes refined measurements of the obliquity and forced physical libration, which are necessary to characterize Mercury’s core state.     

Biosphere 2: a prototype project for a permanent and evolving life system for Mars base.

As part of the ground-based preparation for creating long-term life systems needed for space habitation and settlement, Space Biospheres Ventures (SBV) is undertaking the Biosphere 2 project near Oracle, Arizona. Biosphere 2, currently under construction, is scheduled to commence its operations in 1991 with a two-year closure period with a crew of eight people. Biosphere 2 is a facility which will be essentialy materially-closed to exchange with the outside environment. It is open to information and energy flow. Biosphere 2 is designed to achieve a complex life-support system by the integration of seven areas or "biomes"--rainforest, savannah, desert, marsh, ocean, intensive agriculture and human habitat. Unique bioregenerative technologies, such as soil bed reactors for air purification, aquatic waste processing systems, real-time analytic systems and complex computer monitoring and control systems are being developed for the Biosphere 2 project. Its operation should afford valuable insight into the functioning of complex life systems necessary for long-term habitation in space. It will serve as an experimental ground-based prototype and testbed for the stable, permanent life systems needed for human exploration of Mars.     

Rapid impactor sample return (RISR) mission scenario

Due to the long lead time and great expense of traditional sample return mission plans to Mars or other astronomical bodies, there is a need for a new and innovative way to return materials, potentially at a lower cost. The Rapid Impactor Sample Return (RISR) mission is one such proposal. The general mission scenario involves a single pass of Mars, a Martian moon or an asteroid at high speeds (7 km/s), with the sample return vehicle skimming just 1 or 2 m above a high point (such as a top ridge on Olympus Mons on Mars) and releasing an impactor. The impactor strikes the ground, throwing up debris. The debris with roughly the same forward velocity will be captured by the sample return vehicle and returned to Earth. There is no delay or orbit in the vicinity of Mars or the asteroid: RISR is a one-pass mission. This paper discusses some of the details of the proposal. Calculations are presented that address the question of how much material can be recovered with this technique. There are concerns about the effect of Mars tenuous atmosphere. However, it will be noted that such issues do not occur for RISR style missions to Phobos, Deimos, or asteroids and Near Earth Objects (NEOs). Recent test results in the missile defense community (IFTs 6–8 in 2001, 2002) have scored direct hits at better than 1 m accuracy with closing velocities of 7.6 km/s, giving the belief that accuracy and sensing issues are developed to a point that the RISR mission scenario is feasible.     

Controlled Ecological Life Support Systems (CELSS) flight experimentation.

The NASA CELSS program has the goal of developing life support systems for humans in space based on the use of higher plants. The program has supported research at universities with a primary focus of increasing the productivity of candidate crop plants. To understand the effects of the space environment on plant productivity, the CELSS Test Facility (CTF) has been been conceived as an instrument that will permit the evaluation of plant productivity on Space Station Freedom. The CTF will maintain specific environmental conditions and collect data on gas exchange rates and biomass accumulation over the growth period of several crop plants grown sequentially from seed to harvest. The science requirements of the CTF will be described, as will current design concepts and specific technology requirements for operation in micro-gravity.     

"Living off the land": resource efficiency of wetland wastewater treatment.

Bioregenerative life support technologies for space application are advantageous if they can be constructed using locally available materials, and rely on renewable energy resources, lessening the need for launch and resupply of materials. These same characteristics are desirable in the global Earth environment because such technologies are more affordable by developing countries, and are more sustainable long-term since they utilize less non-renewable, imported resources. Subsurface flow wetlands (wastewater gardens(TM)) were developed and evaluated for wastewater recycling along the coast of Yucatan. Emergy evaluations, a measure of the environmental and human economic resource utilization, showed that compared to conventional sewage treatment, wetland wastewater treatment systems use far less imported and purchased materials. Wetland systems are also less energy-dependent, lessening dependence on electrical infrastructure, and require simpler maintenance since the system largely relies on the ecological action of microbes and plants for their efficacy. Detailed emergy evaluations showed that wetland systems use only about 15% the purchased emergy of conventional sewage systems, and that renewable resources contribute 60% of total emergy used (excluding the sewage itself) compared to less than 1% use of renewable resources in the high-tech systems. Applied on a larger scale for development in third world countries, wetland systems would require the electrical energy of conventional sewage treatment (package plants), and save of total capital and operating expenses over a 20-year timeframe. In addition, there are numerous secondary benefits from wetland systems including fiber/fodder/food from the wetland plants, creation of ecosystems of high biodiversity with animal habitat value, and aesthestic/landscape enhancement of the community. Wetland wastewater treatment is an exemplar of ecological engineering in that it creates an interface ecosystem to handle byproducts of the human economy, maximizing performance of the both the natural economy and natural ecosystems. Wetland systems accomplish this with far greater resource economy than other sewage treatment approaches, and thus offer benefits for both space and Earth applications.