New evidence of solar variation in temperature proxies from Northern Fennoscandia

A new summer temperature proxy was built for northern Fennoscandia in AD 1000–2004 using parameters of tree growth from a large region, extending from the Swedish Scandes to the Kola Peninsula. It was found that century-scale (55–140 year) cyclicity is present in this series during the entire time interval. This periodicity is highly significant and has a bi-modal structure, i.e. it consists of two oscillation modes, 55–100 year and 100–140 year variations. A comparison of the century-long variation in the northern Fennoscandian temperature proxy with the corresponding variations in Wolf numbers and concentration of cosmogenic ¹⁰Be in glacial ice shows that a probable cause of this periodicity is the modulation of regional climate by the secular solar cycle of Gleissberg. This is in line with the results obtained previously for a more limited part of the region (Finnish Lapland: 68–70° N, 20–30° E). Thus the reality of a link between long-term changes in solar activity and climate in Fennoscandia has been confirmed. Possible mechanisms of solar influence on the lower troposphere are discussed.     

Removing orbital debris with lasers

Orbital debris in low Earth orbit (LEO) are now sufficiently dense that the use of LEO space is threatened by runaway collision cascading. A problem predicted more than thirty years ago, the threat from debris larger than about 1 cm demands serious attention. A promising proposed solution uses a high power pulsed laser system on the Earth to make plasma jets on the objects, slowing them slightly, and causing them to re-enter and burn up in the atmosphere. In this paper, we reassess this approach in light of recent advances in low-cost, light-weight modular design for large mirrors, calculations of laser-induced orbit changes and in design of repetitive, multi-kilojoules lasers, that build on inertial fusion research. These advances now suggest that laser orbital debris removal (LODR) is the most cost-effective way to mitigate the debris problem. No other solutions have been proposed that address the whole problem of large and small debris. A LODR system will have multiple uses beyond debris removal. International cooperation will be essential for building and operating such a system.     

Origin of planetary atmospheres

The near absence of noble gases on earth, other than those of radioactive origin, indicates that the earth was formed by the accumulation of planetesimals; this process systematically excluded all constituents that did not enter into the solid phase. The atmosphere and the ocean with many of its dissolved salts have arisen from gases emitted from the earth's interior, a process that continues today. The oxygen in the earth's atmosphere plus a greater quantity that has been removed from the atmosphere to oxidize geologic materials, has arisen mainly from a small excess of photosynthesis over decay of organic material. The atmospheres of Mars and Venus have probably arisen in a manner similar to the atmosphere on earth, by emission from the planetary interiors. However, they have not received any oxygen from photosynthesis and so are nearly oxygen free. Mars has very little water in its atmosphere, and this can be explained by its lower than freezing average surface temperature. Venus also has very little water, and this requires an ad hoc explanation; one possibility is that Venus was formed from much drier planetesimals than was the earth. Mercury and the moon are virtually without atmospheres. Although some gases may be emitted from their interiors, they are presumably rapidly lost by escape. Whatever atmosphere they possess is probably due to the neutralized solar wind that impinges upon them. The outer planets retained volatiles, including hydrogen and helium, to a much greater extent than did the terrestrial planets.     

Leveling of Analytic Platforms

Use of an analytic platform or strapdown system requires that the system em be initially leveled just as a conventional multigimbaled platform must be leveled. The process of leveling involves the determination of the orientation between the local vertical and an instrumented reference nce frame. With a conventional platform it is quite common to use a pair of servo loops to precess the inner gimbal until gravity signals are nulled on two orthogonally mounted accelerometers. The input axes of these two accelerometers thus define the horizontal plane and the platform is said to be leveled. A strapdown system, however, lacks the physical entity of the inner gimbal and consequently cannot be physically precessed into verticality. The method of leveling is nonetheless analogous if we consider the computational reference frame of the analytic platform to be the "alter ego" or counterpart of a physical inner gimbal. In general, strapdown leveling techniques can be divided into two categories: closed-loop leveling and open-loop leveling. These two techniques are quantitatively developed and discussed in this paper.     

Pseudorandom Frequency Modulation in Range-Doppler Radar

In many radar systems, efficient use of transmitter power requires the transmission of a constant-amplitude signal for a substantial fraction of time; for a monotonic transmission, however, the range resolution is restricted by the length of the transmitted pulse. Linear frequency modulation removes this constraint for targets with negligible, or known, radial velocities; it is not suitable, however, for simultaneous observations of range and radial velocity (Doppler shift). This paper describes a class of waveforms suitable for simultaneous measurement of range and Doppler shift. These waveforms are characterized by a uniform distribution in frequency and by pseudorandom frequency changes. Uniform frequency distribution is attained by a uniform spacing of frequencies with each frequency present for an identical length of time. Frequency changes are effected by sequencing the frequencies with a pseudorandom number generator. Ambiguity functions are computed for pseudorandom frequencymodulated waveforms designed for ionospheric backscatter studies. By suitable choice of parameters, the ambiguity function becomes a narrow central peak surrounded by a plateau whose height varies randomly between zero and approximately twice its average. Waveform generation by means of a digital frequency synthesizer and data reconstruction considerations are described.     

Italy's contribution, from a medical standpoint, to the space safety of payload scientists, and perspectives for the future

In Italy, the selection of the Italian payload scientists has been performed according to the Spacelab Program of ESA. Twenty-four subjects underwent a screening performed by the Health Service of Italian Air Force. They were requested to pass an exercise test on treadmill and another ten-minute test on centrifuge, subject to the effect of +3 Gz. The authors briefly describe the results of the test. Noteworthy is the determination of Central Flicker Fusion Frequency. This parameter makes it possible to assess the endurance level of the subject, much earlier than other techniques (e.g. EKG). The importance of an accurate preliminary screening is emphasized as well as of successive training periods. Future studies will be undertaken to compare evoked cortical potentials with behaviour parameters of space safety, with a view to setting up a subtle tool of evaluation for both future candidates and payload scientists.     

Thrust modulation of solid propellant rockets by a fluidic vortex valve with secondary combustion

An analytical model for calculation of the thrust and pressure modulation of a solid propellant rocket by means of a fluidic vortex valve with secondary combustion has been developed. Thrust control by the vortex valve method was found superior to the axial injection of control flow. Addition of oxygen in the injected flow improves the energetic performance of the system as well as the thrust modulation capability. Experiments have been conducted using a mixture of nitrogen and oxygen as the injection gas. The two main parameters investigated in a series of experiments were the oxygen percentage in the injection gas and the ratio between the mass flow rates of the control gas and the solid propellant combustion products. The results show an increase of thrust by a factor of 2 for a 25% addition in mass flow rate by secondary injection at optimal conditions.     

Structural and functional changes in man accompanying the weightlessness in "Skylab" flights: a mathematical approach

The present paper reports a kinetic analysis of changes of some physiological parameters, obtained from international literature, after changes in gravitational environment. The overall phenomenology of the adaptation to weightlessness is characterized by a rapid process followed by a slow one. The two processes show half time values differing by about five times. Also in the case of readaptation to gravity, after recovery on the Earth, two well resolved processes, showing different half time values, are observed. It is of interest to notice that the rate of response to weightlessness is lower than that to gravity. Of course, the half time values observed depend on the different physiological parameters considered. In any case, the experimental data suggest a general trend of many adaptive changes, that may all be described by a simple mathematical model.