Cometary habitats for primitive life.

Comet Halley studies indicate most of the nucleus is covered by an insulating crust, presumed of pyrolysed organic material. The subcrust is warmed and percolated by gases within 2AU, so provides one habitat for primitive replicating organisms. Cracks and crevices within contaminated ice in the craters provides a habitat for photosynthesising organisms. Subsurface lakes on the Europa model, though insulated by some metres of ice, would require a trigger (perhaps meteorite impact and energy source (chemical or metabolic energy) to initiate and maintain a suitable-habitat on short period comets. Constraints on transfer between comets and other planetary bodies implies that radiation-resistant species with lengthy hibernation potential would be expected.     

The implantation of life on Mars: feasibility and motivation.

Environmental conditions on Mars are extremely hostile, and would be destructive to any organisms which might arrive there unprotected to-day. However, it is a biocompatible planet. Its unalterable astrophysical parameters would allow the maintenance of a much thicker, warmer carbon dioxide atmosphere than that which currently exists. Though very cold (averaging about -60 degrees C), highly oxidizing and desiccated, Mars may possess substantial quantities of the materials needed to support life--in particular, water and carbon dioxide. A general scenario for implanting life on Mars would include three main phases: (1) robotic and human exploration to determine whether sufficiently large and accessible volatile inventories are available; (2) planetary engineering designed to warm the planet, release liquid water and produce a thick carbon dioxide atmosphere; and (3) if no indigenous Martian organisms emerge as liquid water becomes available, a program of biological engineering designed to construct and implant pioneering microbial communities able to proliferate in the newly clement, though still anaerobic, Martian environment. The process of establishing an ecosystem, or biosphere, on a lifeless planet is best termed 'ecopoiesis.' This new word, derived from Greek, means 'the making of an abode for life.' It is by no means clear whether ecopoiesis on Mars is scientifically possible or technologically achievable. Thus we urge that it be one of the objectives of space research during the next century to assess the feasibility of ecopoiesis on Mars.     

Design and operation of an algal photobioreactor system.

A photobioreactor system has been designed, constructed, and implemented to achieve efficient oxygen production for a closed ecological life support system (CELSS). The special features of this system are the optical transmission system, uniform light distribution, continuous cycling of cells, gravity-independent gas exchange, and an ultrafiltration unit. The fiber optic based optical transmission system illuminates the reactor internally and includes a light source which is external to the reactor, preventing heat generation problems. Uniform light distribution is achieved throughout the reactor without interfering with the turbulent regime inside. The ultrafiltration unit exchanges spent with fresh media and its use results in very high cell densities, up to 10(9) cells/ml for Chlorella vulgaris. The prototype photobioreactor system was operated in a batch and continuous mode for over two months. The oxygen production rate measured at 4-6 mmoles per liter of the culture per hour under continuous operation, is consistent with the expected performance of the unit for the provided light intensity.     

Modeling the time-intensity profile of solar flare generated particle fluxes in the inner heliosphere.

It is possible to model the time-intensity profile of solar particles expected in space after the occurrence of a significant solar flare on the sun. After the particles are accelerated in the flare process, if conditions are favorable, they may be released into the solar corona and then into space. The heliolongitudinal gradients observed in the inner heliosphere are extremely variable, reflecting the major magnetic structures in the solar corona which extend into space. These magnetic structures control the particle gradients in the inner heliosphere. The most extensive solar particle measurements are those observed by earth-orbiting spacecraft, and forecast and prediction procedures are best for the position of the earth. There is no consensus of how to extend the earth-based models to other locations in space. Local interplanetary conditions and structures exert considerable influence on the time-intensity profiles observed. The interplanetary shock may either reduce or enhance the particle intensity observed at a specific point in space and the observed effects are very dependent on energy.     

Advanced communications satellite technology

Technology drivers for commercial communications satellites are examined based on the efficient use of spacecraft mass which is to be accomplished by increasing the efficiency of the microwave power amplifiers and antenna feed systems used for communications satellites, such as the INTELSAT series. The history of the INTELSAT series of satellites, the late 1980s market and available technology, and future directions of development are considered. Emphasis is on multibeam solid-state antennas, microwave switch matrices, solid-state power amplifiers, and the use of several filter modes in one physical cavity. By using quasimonolithic solid state techniques in a class B amplification mode they have achieved 40-60% efficiencies, compared with 20% for the conventional travelling wavetube amplifiers. It is concluded that technology directed towards improving the economics of satellite communications will continue to be a major driver of future communications satellite payloads. Through their use and their extension, the authors foresee more than doubling the telephone channels per satellite from the current 80000 to perhaps 200000 by the turn of the century     

Ion signatures of reconnection at the magnetopause

For a rotational MHD discontinuity the bulk flow is Alfvénic in the de Hoffmann-Teller frame. Using AMPTE/IRM data, we present ion distribution functions during three crossings of the dayside low-latitude magnetopause. For these crossings a well defined de Hoffmann-Teller frame can be found, but the field-aligned bulk flow is always slower than the Alfvén speed. Nevertheless, we find signatures in the distribution functions that provide clear evidence for magnetic reconnection: solar wind ions reflected off the magnetopause, “D-shaped” solar wind ion distributions in the boundary layer, and counterstreaming of solar wind ions and ionospheric ions in the boundary layer.     

The electrolytical processes in dirty ices: implications for origin and chemistry of minor bodies and related objects.

Many moonlike bodies (M approximately or = 1 Moon) beyond the Martian orbit contain large amounts of dirty ice (approximately 50%) forming thick mantle with the solid phase thermal convection. When a body moves through the inter- or nearplanetary magnetized plasma, electric current is generated in the body and its environment. The current passing through a dirty ice containing up to 10% of organic admixtures produces a lot of electrochemical effects which have a profound impact on its composition. At this stage one can hardly say something definite concerning changes experienced by organics. The changes must occur inevitably and can be of a rather unexpected and far-reaching nature, so deserving a close study. Another obvious effect is a volumetric electrolysis of ice containing alien inclusions. The electrolysis products accumulate in ice in the form of a solid solution which is capable of detonation at 15-20 wt.% of 2H2 + O2. If M > or = 1 Moon (Galilean satellites, Titan), the body loses in explosion a part of its mass in the form of vapor and ice fragments (=short-period comet nuclei), whereas if M < or = 0.2 Moon, the body breaks up totally (the Main Belt asteroids origin approximately 3.9 Byr ago). 2H2 + O2 containing cometary nuclei are capable of burning or suffer new explosions when receiving an additional energy. The combustion in the sublimation products containing also light organics and 2H2 + O2 explains unexpected energetics and nearnuclear chemistry of Comet P/Halley (e.g. great abundances of negative and positive ions, atomic carbon, CO over CO2, origin of CHON particles etc) and its distant outbursts correlated, possibly, with the Solar activity. Thus the electrochemical processes in the dirty ice with organics, along with its subsequent thermal, radiative etc. processing, open up new potentials for explanation and prediction of quite unexpected discoveries.     

Evaluation of JGM 2 geopotential errors from Geosat, TOPEX/Poseidon and ERS-1 crossover altimetry

World-ocean distribution of the crossover altimetry data from Geosat, TOPEX/Poseidon (T/P) and the ERS 1 missions have provided strong independent evidence that NASA's/CSR's JGM 2 geopotential model (70 × 70 in spherical harmonics) yields accurate radial ephemerides for these satellites. In testing the sea height crossover differences found from altimetry and JGM 2 orbits for these satellites, we have used the sea height differences themselves (of ascending minus descending passes averaged at each location over many exact repeat cycles) and the Lumped Latitude Coefficients (LLC) derived from them. For Geosat we find the geopotential-induced LLC errors (exclusive of non-gravitational and initial state discrepancies) mostly below 6 cm, for TOPEX the corresponding errors are usually below 2 cm, and for ERS 1 (35-day cycle) they are generally below 5 cm. In addition, we have found that these observations agree well overall with predictions of accuracy derived from the JGM 2 variance-covariance matrix; the corresponding projected LLC errors for Geosat, T/P, and ERS 1 are usually between 1 and 4 cm, 1 – 2 cm, and 1 – 4 cm, respectively (they depend on the filtering of long-periodic perturbations and on the order of the LLC). This agreement is especially impressive for ERS 1 since no data of any kind from this mission was used in forming JGM 2.

The observed crossover differences for Geosat, T/P and ERS 1 are 8, 3, and 11 cm (rms), respectively. These observations also agree well with prediction of accuracy derived from the JGM 2 variance-covariance matrix; the corresponding projected crossover errors for Geosat and T/P are 8 cm and 2.3 cm, respectively. The precision of our mean difference observations is about 3 cm for Geosat (approx. 24,000 observations), 1.5 cm for T/P (approx. 6,000 observations) and 5 cm for ERS 1 (approx. 44,000 observations). Thus, these “global” independent data should provide a valuable new source for improving geopotential models. Our results show the need for further correction of the low order JGM 2 geopotential as well as certain resonant orders for all 3 satellites.     

Negative body potential as result of modulated electron beam emission into ambient plasma

Two different processes play an important role during emission of pulsed electron beam from a satellite: the positive charging of the spacecraft by emitted electron current and the body neutralization by ambient plasma electrons (mainly in pauses between electron pulses).

The injection of modulated electron beam (pulses of 2μs duration, E=8keV, I=0.1A and 25μs repetition) was carried on in the APEX Project. A simple computer model of this process for APEX scenario was performed.

The results show that after primary positive charging (during gun operation) a significant negative charging (in pauses between pulses) caused by neutralization process by ambient plasma with fp>2MHz takes place.