Characteristics of the equatorial F-region vertical plasma drift observed during post-sunset and pre-sunrise hours

Post-sunset and pre-sunrise vertical plasma drifts at the equatorial F-region have been investigated using the HF Doppler radar and ionosonde observations. Observed vertical plasma drift features during the sunrise are found to complement that observed during the evening. The post-sunset vertical plasma drift is characterized by an upward enhancement, a pre-reversal enhancement and a reversal in the drift direction. Similarly, the pre-sunrise plasma drift is characterized by a sudden downward excursion followed by an upward turning. The wavelet analysis of the plasma drift shows the presence of fluctuations in the period range 4–32 min and the short period fluctuations are attributed to the atmospheric gravity waves.     

Observations on the evolution of satellite launch volume and cyclicality in the space industry

Satellites have been rightly described as the lifeblood of the entire space industry and the number of satellites ordered or launched per year is an important defining metric of the industry's level of activity, such that trends and variability in this volume have significant strategic impact on the space industry. Over the past 40+ years, hundreds of satellites have been launched every year. Thus an important dataset is available for time series analysis and identification of trends and cycles in the various markets of the space industry. This article reports findings of a study for which we collected data on over 6000 satellites launched since 1960 on a yearly basis. We grouped the satellites into three broad categories – defense and intelligence, science, and commercial satellites – and identified and discussed the main trends and cyclical patterns for each of these. Institutional customers (defense and intelligence, and science) accounted for over two-thirds of all satellites launched within our time period (1960–2008), and, in the 1960s and 1970s, they accounted for 90% and 73.5%, respectively. A fair conclusion from this data is that the space industry was enabled by, and grew because of the institutional customers, not commercial market forces. However, when the launch data is examined more closely, a growing influence of the commercial sector is noticeable. Over the past two decades communication satellites accounted for roughly half of all launches, thus reflecting an important shift in the space industry in which the commercial sector is playing an equal role (on a launch volume basis) to that of the institutional market. Cyclical patterns in the satellite launch volume over the past decade are separately discussed before we sum up with a conclusion.     

Planning the unplannable: Scenarios on the future of space

This article explores the use of scenario analysis as a methodology to rigorously analyze potential space futures, particularly with respect to space security challenges, in the context of rapid and uncertain change across several dimensions of human space activities. The successful use of scenario analysis in other (e.g. corporate and military) sectors is described and results of an initial scenario analysis workshop are presented. Scenario analysis is recommended as a promising approach to evaluating the long-term consequences of various policy choices in the context of uncertainty, and as a process well-suited to fostering communication and building consensual knowledge among diverse stakeholders.     

A direct fusion drive for rocket propulsion

The Direct Fusion Drive (DFD), a compact, anuetronic fusion engine, will enable more challenging exploration missions in the solar system. The engine proposed here uses a deuterium–helium-3 reaction to produce fusion energy by employing a novel field-reversed configuration (FRC) for magnetic confinement. The FRC has a simple linear solenoid coil geometry yet generates higher plasma pressure, hence higher fusion power density, for a given magnetic field strength than other magnetic-confinement plasma devices. Waste heat generated from the plasma?s Bremsstrahlung and synchrotron radiation is recycled to maintain the fusion temperature. The charged reaction products, augmented by additional propellant, are exhausted through a magnetic nozzle. A 1 MW DFD is presented in the context of a mission to deploy the James Webb Space Telescope (6200 kg) from GPS orbit to a Sun–Earth L2 halo orbit in 37 days using just 353 kg of propellant and about half a kilogram of ³He. The engine is designed to produce 40 N of thrust with an exhaust velocity of 56.5 km/s and has a specific power of 0.18 kW/kg.     

Selection of the Mars Science Laboratory Landing Site

The selection of Gale crater as the Mars Science Laboratory landing site took over five years, involved broad participation of the science community via five open workshops, and narrowed an initial >50 sites (25 by 20?km) to four finalists (Eberswalde, Gale, Holden and Mawrth) based on science and safety. Engineering constraints important to the selection included: (1)?latitude (±30°) for thermal management of the rover and instruments, (2)?elevation (<?1?km) for sufficient atmosphere to slow the spacecraft, (3)?relief of <100–130?m at baselines of 1–1000?m for control authority and sufficient fuel during powered descent, (4)?slopes of <30° at baselines of 2–5?m for rover stability at touchdown, (5)?moderate rock abundance to avoid impacting the belly pan during touchdown, and (6)?a?radar-reflective, load-bearing, and trafficable surface that is safe for landing and roving and not dominated by fine-grained dust. Science criteria important for the selection include the ability to assess past habitable environments, which include diversity, context, and biosignature (including organics) preservation. Sites were evaluated in detail using targeted data from instruments on all active orbiters, and especially Mars Reconnaissance Orbiter. All of the final four sites have layered sedimentary rocks with spectral evidence for phyllosilicates that clearly address the science objectives of the mission. Sophisticated entry, descent and landing simulations that include detailed information on all of the engineering constraints indicate all of the final four sites are safe for landing. Evaluation of the traversabilty of the landing sites and target “go to” areas outside of the ellipse using slope and material properties information indicates that all are trafficable and “go to” sites can be accessed within the lifetime of the mission. In the final selection, Gale crater was favored over Eberswalde based on its greater diversity and potential habitability.     

Diffuse cosmic X- and gamma radiation: The isotropic component

SummaryA. Spectral features The ability of the various theories to explain the three main spectral features at 1/4 keV, 60 keV and 1 MeV is summarized in Tables II and III.Clearly, confirmation of the reality of these features, especially the soft X-ray and -ray excesses, is one of the key elements in enabling us to decide between the competing theoretical interpretations.B. Energy requirements None of the proposed interpretations are easily explained in terms of the available energy in cosmic rays (except perhaps the Seyfert galaxy proposal, and this runs into difficulties). It seems that one either has to regard normal galaxies at the present epoch as prolific sources of cosmic rays ( 10⁶⁰ erg/galaxy in protons), as is required by the Brecher-Morrison model, or to argue that at early stages in their evolution far more energy is available than at present. One ends up with much the same energy requirement in this approach.One could conceivably identify such an early phase with the radio galaxy or QSO phenomena: in any event, cosmological evolution plays a major role. Cosmology does ease the energy requirements, but only for the inefficient mechanisms, such as nonthermal bremsstrahlung or ° -production.It seems that one still needs the metagalactic cosmic ray flux to be 10^-2 of the galactic flux in the diffuse inverse Compton models, and 10^-2–10^-4 in the nonthermal bremsstrahlung models.Faced with problems of energetics, one is tempted to turn to the most energetic objects in the Universe, namely Seyfert nuclei and QSO's, to provide the basic energy source, whether directly or indirectly, for the diffuse X-ray background. A direct connection could be more readily investigated when X-ray observations are available of more extra-galactic sources.C. Angular variations Another approach, complementary to that of looking for remote discrete sources, is to seek angular fluctuations, or limits on such fluctuations in the diffuse X-ray background.The best results presently available are those from the X-ray experiment on board OSO 3. Schwartz (1970) reports a limit of I/Ifour percent on small-scale (10°) fluctuations over 10–100 keV over about one-quarter of the sky. If one assumes a astrophysics, namely the origin of cosmic rays, is intimately linked to the origin of the X-ray background.It may well be that no single mechanism suffices to account for the entire spectrum of isotropic X- and -radiation. Nature is sufficiently perverse for there to be a reasonable probability that several different processes are contributing, and considerable ingenuity will be required to ascertain which mechanism, if any, is assigned the dominant role in a given spectral region.This review is based on an invited paper presented at the joint meeting of the A. A. S. Division of High Energy Astrophysics, and the A. P. S. Division of Cosmic Physics, Washington, D. C., 28 April–1 May, 1970     

The Mercury Laser Altimeter Instrument for the MESSENGER Mission

The Mercury Laser Altimeter (MLA) is one of the payload science instruments on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, which launched on August 3, 2004. The altimeter will measure the round-trip time of flight of transmitted laser pulses reflected from the surface of the planet that, in combination with the spacecraft orbit position and pointing data, gives a high-precision measurement of surface topography referenced to Mercury’s center of mass. MLA will sample the planet’s surface to within a 1-m range error when the line-of-sight range to Mercury is less than 1,200 km under spacecraft nadir pointing or the slant range is less than 800 km. The altimeter measurements will be used to determine the planet’s forced physical librations by tracking the motion of large-scale topographic features as a function of time. MLA’s laser pulse energy monitor and the echo pulse energy estimate will provide an active measurement of the surface reflectivity at 1,064 nm. This paper describes the instrument design, prelaunch testing, calibration, and results of postlaunch testing.     

The management of the geostationary environment

The population in the geostationary orbit is increasing at the rate of about 25 spacecraft a year and operating lifetimes are increasing. The size of the spacecraft is increasing, as is the power level. The only way to protect the operational arc is to reboost spacecraft at end of life to a burial orbit. While most operators do some reboost maneuver at end of mission there has been no agreed upon criterion for the maneuver. The ITU-R S. 1003¹ recommends reboost of not less than 300 km with the apogee as high as possible. The Interagency Debris Coordination Working Group (IADC) has recently achieved a consensus on a recommendation that the minimum maneuver be 235 km + Cr 1000 A/M. The concept is that this accommodates the ± 3 7.5 km variance in normal radial positioning and a 167.5 km corridor above the arc for repositioning or supersynchronous delivery and establishes a criterion by which the dispositioned spacecraft will never enter that zone after its completion of the maneuver. It also deals with the fact the area mass ratio of spacecraft has been evolving to higher values. Earlier spacecraft had characteristic values of 0.03 but the average now is closer to 0.05 and there are some as great as 0.10.

Disposition of the upper stage should be the same as the spacecraft if it is delivered to GSO. It is preferable to have the stage deliver the spacecraft supersynchronous and then have the spacecraft maneuver down to the GSO.     

Searching for biosignatures using electron paramagnetic resonance (EPR) analysis of manganese oxides

Manganese oxide (Mn oxide) minerals from bacterial sources produce electron paramagnetic resonance (EPR) spectral signatures that are mostly distinct from those of synthetic simulants and abiogenic mineral Mn oxides. Biogenic Mn oxides exhibit only narrow EPR spectral linewidths (～500 G), whereas abiogenic Mn oxides produce spectral linewidths that are 2-6 times broader and range from 1200 to 3000 G. This distinction is consistent with X-ray structural observations that biogenic Mn oxides have abundant layer site vacancies and edge terminations and are mostly of single ionic species [i.e., Mn(IV)], all of which favor narrow EPR linewidths. In contrast, abiogenic Mn oxides have fewer lattice vacancies, larger particle sizes, and mixed ionic species [Mn(III) and Mn(IV)], which lead to the broader linewidths. These properties could be utilized in the search for extraterrestrial physicochemical biosignatures, for example, on Mars missions that include a miniature version of an EPR spectrometer.     

The Genesis Solar Wind Concentrator

The primary goal of the Genesis Mission is to collect solar wind ions and, from their analysis, establish key isotopic ratios that will help constrain models of solar nebula formation and evolution. The ratios of primary interest include ¹⁷O/¹⁶O and ¹⁸O/¹⁶O to ±0.1%, ¹⁵N/¹⁴N to ±1%, and the Li, Be, and B elemental and isotopic abundances. The required accuracies in N and O ratios cannot be achieved without concentrating the solar wind and implanting it into low-background target materials that are returned to Earth for analysis. The Genesis Concentrator is designed to concentrate the heavy ion flux from the solar wind by an average factor of at least 20 and implant it into a target of ultra-pure, well-characterized materials. High-transparency grids held at high voltages are used near the aperture to reject >90% of the protons, avoiding damage to the target. Another set of grids and applied voltages are used to accelerate and focus the remaining ions to implant into the target. The design uses an energy-independent parabolic ion mirror to focus ions onto a 6.2 cm diameter target of materials selected to contain levels of O and other elements of interest established and documented to be below 10% of the levels expected from the concentrated solar wind. To optimize the concentration of the ions, voltages are constantly adjusted based on real-time solar wind speed and temperature measurements from the Genesis ion monitor. Construction of the Concentrator required new developments in ion optics; materials; and instrument testing and handling. This revised version was published online in August 2006 with corrections to the Cover Date.