High-Sensitivity Quartz Accelerometer for Measurements of Small Accelerations of Spacecraft

A quartz sensor of small accelerations with a capacitive transducer is designed and produced, allowing one to measure spacecraft accelerations with a resolution of 10^–7 m/s² in the range ±10^–1 m/s². The results of calibration of the sensor by the method of inclinations are presented.     

Research priorities and plans for the International Space Station-results of the 'REMAP' Task Force

Recent events in the International Space Station (ISS) Program have resulted in the necessity to re-examine the research priorities and research plans for future years. Due to both technical and fiscal resource constraints expected on the International Space Station, it is imperative that research priorities be carefully reviewed and clearly articulated. In consultation with OSTP and the Office of Management and budget (OMB), NASA's Office of Biological and Physical Research (OBPR) assembled an ad-hoc external advisory committee, the Biological and Physical Research Maximization and Prioritization (REMAP) Task Force. This paper describes the outcome of the Task Force and how it is being used to define a roadmap for near and long-term Biological and Physical Research objectives that supports NASA's Vision and Mission. Additionally, the paper discusses further prioritizations that were necessitated by budget and ISS resource constraints in order to maximize utilization of the International Space Station. Finally, a process has been developed to integrate the requirements for this prioritized research with other agency requirements to develop an integrated ISS assembly and utilization plan that maximizes scientific output.     

Surface characteristics of spacecraft components affect the aggregation of microorganisms and may lead to different survival rates of bacteria on Mars landers

Layers of dormant endospores of Bacillus subtilis HA101 were applied to eight different spacecraft materials and exposed to martian conditions of low pressure (8.5 mbar), low temperature (-10 degrees C), and high CO(2) gas composition and irradiated with a Mars-normal ultraviolet (UV-visible- near-infrared spectrum. Bacterial layers were exposed to either 1 min or 1 h of Mars-normal UV irradiation, which simulated clear-sky conditions on equatorial Mars (0.1 tau). When exposed to 1 min of Mars UV irradiation, the numbers of viable endospores of B. subtilis were reduced three to four orders of magnitude for two brands of aluminum (Al), stainless steel, chemfilm-treated Al, clear-anodized Al, and black-anodized Al coupons. In contrast, bacterial survival was reduced only one to two orders of magnitude for endospores on the non-metal materials astroquartz and graphite composite when bacterial endospores were exposed to 1 min of Mars UV irradiation. When bacterial monolayers were exposed to 1 h of Mars UV irradiation, no viable bacteria were recovered from the six metal coupons listed above. In contrast, bacterial survival was reduced only two to three orders of magnitude for spore layers on astroquartz and graphite composite exposed to 1 h of Mars UV irradiation. Scanning electron microscopy images of the bacterial monolayers on all eight spacecraft materials revealed that endospores of B. subtilis formed large aggregates of multilayered spores on astroquartz and graphite composite, but not on the other six spacecraft materials. It is likely that the formation of multilayered aggregates of endospores on astroquartz and graphite composite is responsible for the enhanced survival of bacterial cells on these materials.     

Microgravity effects on water supply and substrate properties in porous matrix root support systems.

The control of water content and water movement in granular substrate-based plant root systems in microgravity is a complex problem. Improper water and oxygen delivery to plant roots has delayed studies of the effects of microgravity on plant development and the use of plants in physical and mental life support systems. Our international effort (USA, Russia and Bulgaria) has upgraded the plant growth facilities on the Mir Orbital Station (OS) and used them to study the full life cycle of plants. The Bulgarian-Russian-developed Svet Space Greenhouse (SG) system was upgraded on the Mir OS in 1996. The US developed Gas Exchange Measurement System (GEMS) greatly extends the range of environmental parameters monitored. The Svet-GEMS complex was used to grow a fully developed wheat crop during 1996. The growth rate and development of these plants compared well with earth grown plants indicating that the root zone water and oxygen stresses that have limited plant development in previous long-duration experiments have been overcome. However, management of the root environment during this experiment involved several significant changes in control settings as the relationship between the water delivery system, water status sensors, and the substrate changed during the growth cycles.     

Media reaction to a SETI success

Consideration of the reaction to a SETI detection by the media, and the effect this will have on the public, is more than mere sociological speculation. An accurate forecast of the media's interest can lead to actions that will help ensure that correct and comprehensible information reaches the public. This is most critical in the first few weeks following a discovery. While a widely accepted protocol for dealing with a detection exists in the "Declaration of Principles Following the Detection of Extraterrestrial Intelligence," it gives scant consideration to the fact that the actual situation will be chaotic and not subject to easy control. The 1996 story about the possible discovery of martian microfossils has provided a useful precedent for what will happen if astronomers uncover the existence of alien intelligence.     

A parametric study of space transfer/upper propulsion stages

For Space Transportation System (i.e. Space Shuttle) launched satellites destined for a Geosynchronous Earth Orbit (GEO), there is a need for cost-effective, versatile propulsion systems to provide the perigee burn, i.e. to boost the satellite from Low Earth Orbit (LEO) to Geosynchronous Transfer Orbit (GTO). Surveys of commercial spacecraft activities and future GEO satellite requirements indicate that a spacecraft propulsion system that will provide the perigee burn for a broad range of future commercial satellites would have an excellent market potential.Parametric studies to investigate and define attractive perigee-burn upper propulsion systems (i.e. an Upper Propulsion Stage, or a UPS) are presented. The feasibility and payload capacilities that could be provided by a UPS assembled from essentially off-the-shelf components and subsystems, and the benefits that could be achieved by using major subsystems specifically tailored for the application are presented. The results indicate that attractive UPS configurations can be defined using either off-the-shelf or optimized major subsystems.     

Modal control of the planar motion of a long flexible beam in orbit

Attitude control techniques for the pointing and stabilization of very large, inherently flexible spacecraft systems are investigated. The attitude dynamics and control of a long, homogeneous flexible beam whose center of mass is assumed to follow a circular orbit is analyzed. In this study, first order effects of gravity-gradient are included, whereas external perturbations and related orbital station keeping maneuvers are neglected. A mathematical model which describes the system deflections within the orbital plane has been developed by treating the beam as having a maximum of three discretized mass particles connected by massless, elastic structural elements. The uncontrolled dynamics of this system are simulated and, in addition, the effects of the control devices are considered. The concept of distributed modal control, which provides a means for controlling a system mode independently of all other modes, is examined. The effect of varying the number of modes in the model as well as the number and location of the control devices are also considered.     

The Solution of Some Problems of Optimizing the Processes of a Flexible Correction of Motion of Satellite Systems: I

The first of a series of problems of the optimization of correction of satellite systems, moving over near-circular orbits, is considered. The correction is accomplished by means of low-thrust engines and is supposed to be flexible, where only the parameters of the relative motion of satellites must be corrected. The problem has a large dimension, but is invariant with respect to renumbering of satellites. This allows us to decompose the problem, i.e., to find new variables, linearly dependent on old ones, in which the problem breaks down into a series of independent subproblems of low dimension. The decomposition is accomplished by means of the technique [1] based on the theory of linear representations of groups.     

Influence of Trapped Plasma on the Structure of Collisionless Thin Current Sheets

Using both analytical and numerical models of the collisionless anisotropic current sheet generated by the impinging flows of transient ions, we have studied the self-consistent solutions taking the plasma trapped in the sheet into account. It is demonstrated that there exists a limited window in the space of system parameters where self-consistent solutions can exist. When the density of the quasi-trapped plasma is sufficiently large, a redistribution of the total current can be a cause of the sheet decay, when the local current of the trapped particles compensate (totally or in part) the main current in the center and at the edges of the sheet, while the total current generated by ions on the trapped trajectories vanishes.     

Bubble detector characterization for space radiation

In light of the importance of the neutron contribution to the dose equivalent received by space workers in the near-Earth radiation environment, there is an increasing need for a personal dosimeter that is passive in nature and able to respond to this neutron field in real time. Recent Canadian technology has led to the development of a bubble detector, which is sensitive to neutrons, but insensitive to low linear energy transfer (LET) radiation. By changing the composition of the bubble detector fluid (or “superheat”), the detectors can be fabricated to respond to different types of radiation. This paper describes a preliminary ground-based research effort to better characterize the bubble detectors of different compositions at various charged-particle accelerator facilities, which are capable of simulating the space radiation field.