The Lightning And Radio Emission Detector (LRD) instrument

The Lightning and Radio Emission Detector (LRD) instrument will be carried by the Galileo Probe into Jupiter's atmosphere. The LRD will verify the existence of lightning in the atmosphere and will determine the details of many of its basic characteristics. The instrument, operated in its magnetospheric mode at distances of about 5, 4, 3, and 2 planetary radii from Jupiter's center, will also measure the radio frequency (RF) noise spectrum in Jupiter's magnetosphere. The LRD instrument is composed of a ferritecore radio frequency antenna ( 100 Hz to 100 kHz) and two photodiodes mounted behind individual fisheye lenses. The output of the RF antenna is analyzed both separately and in coincidence with the optical signals from the photodiodes. The RF antenna provides data both in the frequency domain (with three narrow-band channels, primarily for deducing the physical properties of distant lightning) and in the time domain with a priority scheme (primarily for determining from individual RF waveforms the physical properties of closeby-lightning).     

Possible shock wave in the local interstellar plasma, very close to the heliosphere

We show, using the HST — GHRS data on velocity and temperature in the nearby interstellar medium, that the observed 3 – 4 km s^–1 relative velocity between the Local Interstellar Cloud (LIC) and the so-called G-cloud located in the Galactic Center hemisphere can be quite naturally explained assuming that the two clouds do interact with each other. In the proposed interpretation the two media are separated by a (quasiperpendicular) MHD shock front propagating from the LIC into the G-cloud. The LIC plasma is then nothing else but the shocked (compression 1.3 – 1.4) gas of the G-cloud. A 1-D single-fluid solution of the Rankine — Hugoniot equations can fit the most probable observed values of the relative velocity (3.75 km/s), LIC (6700 K) and G-cloud (5400 K) kinetic temperatures, if the plasma-beta of the LIC plasma is in the range 1.3 – 1.5 (Table 1). This corresponds to a super — fast magnetosonic motion of the heliosphere through the LIC, independently of LIC density. The LIC magnetic field strength is 1.9 (3.1) G for the LIC electron density n_e = 0.04 (0.10) cm^–3. In this case the shock is less than 30 000 AU away and moves at about 10 km s^–1 relative to the LIC plasma. The Sun is chasing the shock and should catch up with it in about 10⁴ years. If the heliospheric VLP emissions cutoff at 1.8 kHz is indicative of n_e (LIC) = 0.04 cm^–3 (Gurnett et al., 1993), the (pure plasma) bowshock ahead of the heliopause could be the source of quasi-continuous heliospheric 2-kHz emission band. We believe that with the expected increase in the performance of modern spectroscopic instrumentation the proposed method of magnetic field evaluation may in the future find wider application in the studies of the interstellar medium.     

Possible effects of protracted exposure on the additivity of risks from space radiations.

Conventional radiation risk assessments are presently based on the additivity assumption. This assumption states that risks from individual components of a complex radiation field involving many different types of radiation can be added to yield the total risk of the complex radiation field. If the assumption is not correct, the summations and integrations performed to obtain the presently quoted risk estimates are not appropriate. This problem is particularly important in the area of space radiation risk evaluation because of the many different types of high- and low-LET radiation present in the galactic cosmic ray environment. For both low- and high-LET radiations at low enough dose rates, the present convention is that the addivity assumption holds. Mathematically, the total risk, Rtot is assumed to be Rtot = summation (i) Ri where the summation runs over the different types of radiation present. If the total dose (or fluence) from each component is such that the interaction between biological lesions caused by separate single track traversals is negligible within a given cell, it is presently considered to be reasonable to accept the additivity assumption. However, when the exposure is protracted over many cell doubling times (as will be the case for extended missions to the moon or Mars), the possibility exists that radiation effects that depend on multiple cellular events over a long time period, such as is probably the case in radiation-induced carcinogenesis, may not be additive in the above sense and the exposure interval may have to be included in the evaluation procedure. It is shown, however, that "inverse" dose-rate effects are not expected from intermediate LET radiations arising from the galactic cosmic ray environment due to the "sensitive-window-in-the-cell-cycle" hypothesis.     

The Spacelab-Mir-1 "Greenhouse-2" experiment.

The Spacelab-Mir-1 (SLM-1) mission is the first docking of the Space Shuttle Atlantis (STS-71) with the Orbital Station Mir in June 1995. The SLM-1 "Greenhouse-2" experiment will utilize the Russian-Bulgarian-developed plant growth unit (Svet). "Greenhouse-2" will include two plantings (1) designed to test the capability of Svet to grow a crop of Superdwarf wheat from seed to seed, and (2) to provide green plant material for post-flight analysis. Protocols, procedures, and equipment for the experiment have been developed by the US-Russian science team. "Greenhouse-2" will also provide the first orbital test of a new Svet Instrumentation System (SIS) developed by Utah State University to provide near real time data on plant environmental parameters and gas-exchange rates. SIS supplements the Svet control and monitoring system with additional sensors for substrate moisture, air temperature, IR leaf temperature, light, oxygen, pressure, humidity, and carbon-dioxide. SIS provides the capability to monitor canopy transpiration and net assimilation of the plants growing in each vegetation unit (root zone) by enclosing the canopy in separate, retractable, ventilated leaf chambers. Six times during the seed-to-seed experiment, plant samples will be collected, leaf area measured, and plant parts fixed and/or dried for ground analysis. A second planting initiated 30 days before the arrival of a U.S. Shuttle [originally planned to be STS-71] is designed to provide green material at the vegetative development stage for ground analysis. [As this paper is being edited, the experiment has been delayed until after the arrival of STS-71.]     

3D nonlinear wave heating of coronal loops

The heating of solar coronal loops by the resonant absorption or phase-mixing of incident wave energy is investigated in the framework of 3D nonlinear magnetohydrodynamics (MHD) by means of numerical simulations.     

Induction of high grade astrocytoma (HGA) by protons: molecular mechanisms and RBE considerations.

Protons of a specific energy, 55 MeV, have been found to induce primary high grade astrocytomas (HGA) in the Rhesus monkey (Macaca mulatta). Brain tumors of this type were not induced by protons of other energies (32-2,300 MeV). Induction of HGA has been identified in human patients who have had radiation therapy to the head. We believe that the induction of HGA in the monkey is a consequence of dose distribution, not some unique "toxic" property of protons. Comparison of the human experience with the monkey data indicates the RBE for induction of brain tumors to be about one. It is unlikely that protons cause an unusual change in oncogenic expression, as compared to conventional electromagnetic radiation.     

Microgravity effects on "postural" muscle activity patterns.

Changes in neuromuscular activation patterns associated with movements made in microgravity can contribute to muscular atrophy. Using EMG to monitor "postural" muscles, it was found that free floating arm flexions made in microgravity were not always preceded by neuromuscular activation patterns normally observed during movements made in unit gravity. Additionally, manipulation of foot sensory input during microgravity arm flexion impacted upon anticipatory postural muscle activation.     

Development of plant protoplasts during the IML-1 mission.

During the 8 day IML-1 mission, regeneration of cell walls and cell divisions in rapeseed protoplasts were studied using the Biorack microscope onboard the Space Shuttle "Discovery". Samples from microgravity and 1g protoplast cultures were loaded on microscope slides. Visual microscopic observations were reported by the payload specialist Roberta Bondar, by down-link video transmission and by use of a microscope camera. Protoplasts grown under microgravity conditions do regenerate cell walls but to a lesser extent than under 1g. Cell divisions are delayed under microgravity. Few cell aggregates with maximum 4-6 cells per aggregate are formed under microgravity conditions, indicating that microgravity may have a profound influence on plant cell differentiation.     

The complex Hα profile of the hypergiant HR 8752 during 1970–1992

The profiles of H observed during the 1970–1992 period in the binary hypergiant HR 8752 (G0 Ia) are presented. We distinguish five typical H profiles designated as A, B, C, D and E types according to the number of emission and absorption features. The profiles of H are complex and contain several emission and absorption components, with: –130 km/s in emission or absorption, –84 km/s in absorption, –49 km/s in emission and about +6 km/s in emission. All of them are rather stable in radial velocities except of the main absorption component in the P Cygni profile with –84 km/s. The frequency of appearance and the periods of duration of the occurrence of the components is discussed. The duration times range between about 3 to 10 months for various components. The red emission component E₂ is particularly interesting. Possible explanations of its origin are discussed.A long-term acceleration of the absorption component in the P Cygni profile is found; it can be interpreted as monotonous acceleration of the stellar wind.