Odyssey: Principles for enduring space exploration

As the USA, Europe and other nations embark on a new voyage of exploration to the Moon, Mars and beyond, they should lay the foundations and establish precedents that invite a host of participants and followers. We argue that international cooperation, driven by foreign-policy and cost-sharing considerations, has taken a prominent role but must be pragmatically and flexibly balanced with economic and strategic self-interest. Since exploration visions are likely to differ, the steps each country will pursue, the funding provided, and schedules followed will also differ. To support an enduring exploration vision, it will be important to remain flexible to changing priorities and amenable to the inclusion of new, non-traditional participants. Open-systems principles and metaprinciples should be employed at all levels—hardware, software, programmatic, political and cultural. Equally important, national leadership and decision makers should be mindful of the potential pitfalls that might undermine the venture. While the new vision inspires us all, it will take creativity, resourcefulness, hard work and cooperation to succeed.     

Stellar chromospheres

Observations indicating the presence of stellar chromospheres, that is hot envelopes around stars are summarized. Undisputed indicators (called type I) for hot stellar envelopes are spectral lines of highly ionized atoms, Fe ii emission lines and flares in late type stars and the presence of the He i10830 Å line. Whether indicators (called type II) like emission cores in the Ca ii H and K and Mg ii h and k lines or mass loss signify the presence of stellar chromospheres is still somewhat debated, although the discussion points in favour of the usefulness of these indicators. The combined evidence to date shows that all non degenerate type stars have chromospheres except possibly the A stars. There are however theoretical reasons for expecting chromospheres in A stars. Empirical chromosphere models for a rapidly growing sample of stars have recently been constructed on the basis of Ca ii and Mg ii line observations. A discussion of possible heating mechanisms is given and the relative importance of these mechanisms is evaluated. For the low and middle chromosphere the short period acoustic heating mechanism seems to be the dominant process although there are still uncertainties. Both steady state and time dependent theoretical models of stellar chromospheres, based on the short period acoustic heating theory, are discussed, and predictions of these models are compared with results from empirical models. This relatively favourable comparison shows that the explanation of the Wilson-Bappu effect might be at hand.     

Dominance in space — a new means of exercising global power?

Sustained criticism of the strategy of nuclear deterrence and technological developments in the military uses of space suggest that nuclear weapons may soon be replaced by control of outer space as the USA and USSR's primary instrument of global power. This article traces the change in perceptions of nuclear weapons policy and assesses the potential of outer space as a means of control, and the plans of the two superpowers for its exploitation, especially in the military sphere. The consequences for Western Europe of a shift from nuclear to space-based weapons as the primary guarantor of national security are also discussed.     

Can turbidity measurements be used for the estimation of aerosol parameters?

In a previous paper the authors showed that the aerosol size distribution can be estimated with reasonable accuracy from spectral extinction measurements in a limited spectral region (λ ≤ 1 μm) only. Using the same method it will be discussed if the anticipated WMO turbidity network with four spectral channels has the potential of estimating the aerosol size distribution.     

Covert Penetration Systems

This paper discusses past, present, and future strategic aircraft requirements for ingress and egress, then focuses on the technologies of the CO2 Laser Radar and the Automatic Target Recognizer. Present systems currently consist of a mix of various sensors which are not correlated until each is presented to the operator. Additionally, active sensors are highly detectable by threat warning systems, while passive sensors do not provide critical range information. CO2 Laser and ATR technologies will significantly contribute to the resolution of these issues.     

First results from the LUCID-Timepix spacecraft payload onboard the TechDemoSat-1 satellite in Low Earth Orbit

The Langton Ultimate Cosmic ray Intensity Detector (LUCID) is a payload onboard the satellite TechDemoSat-1, used to study the radiation environment in Low Earth Orbit ($～$635?km). LUCID operated from 2014 to 2017, collecting over 2.1 million frames of radiation data from its five Timepix detectors on board. LUCID is one of the first uses of the Timepix detector technology in open space, with the data providing useful insight into the performance of this technology in new environments. It provides high-sensitivity imaging measurements of the mixed radiation field, with a wide dynamic range in terms of spectral response, particle type and direction. The data has been analysed using computing resources provided by GridPP, with a new machine learning algorithm that uses the Tensorflow framework. This algorithm provides a new approach to processing Medipix data, using a training set of human labelled tracks, providing greater particle classification accuracy than other algorithms. For managing the LUCID data, we have developed an online platform called Timepix Analysis Platform at School (TAPAS). This provides a swift and simple way for users to analyse data that they collect using Timepix detectors from both LUCID and other experiments. We also present some possible future uses of the LUCID data and Medipix detectors in space.     

ExoMars 2016 Schiaparelli Module Trajectory and Atmospheric Profiles Reconstruction

On 19^th October 2016 Schiaparelli module of the ExoMars 2016 mission flew through the Mars atmosphere. After successful entry and descent under parachute, the module failed the last part of the descent and crashed on the Mars surface. Nevertheless the data transmitted in real-time by Schiaparelli during the entry and descent, together with the entry state vector as initial condition, have been used to reconstruct both the trajectory and the profiles of atmospheric density, pressure and temperature along the traversed path.The available data-set is only a small sub-set of the whole data acquired by Schiaparelli, with a limited data rate (8 kbps) and a large gap during the entry because of the plasma blackout on the communications.This paper presents the work done by the AMELIA (Atmospheric Mars Entry and Landing Investigations and Analysis) team in the exploitation of the available inertial and radar data. First a reference trajectory is derived by direct integration of the inertial measurements and a strategy to overcome the entry data gap is proposed. First-order covariance analysis is used to estimate the uncertainties on all the derived parameters. Then a refined trajectory is computed incorporating the measurements provided by the on-board radar altimeter.The derived trajectory is consistent with the events reported in the telemetry and also with the impact point identified on the high-resolution images of the landing site.Finally, atmospheric profiles are computed tacking into account the aerodynamic properties of the module. Derived profiles result in good agreement with both atmospheric models and available remote sensing observations.     

The Delivery of Water During Terrestrial Planet Formation

The planetary building blocks that formed in the terrestrial planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the terrestrial planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local planetesimals in the terrestrial planet region or into the planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the terrestrial planet region as the planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant planets begin roughly in their final locations and the disk of planetesimals and embryos in the terrestrial planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant planets implants material from beyond the snow line into the asteroid belt and terrestrial planet region, where it can be accreted by the growing planets. Sufficient water is delivered to the terrestrial planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the terrestrial planets.     

The Solar Isotope Spectrometer for the Advanced Composition Explorer

The Solar Isotope Spectrometer (SIS), one of nine instruments on the Advanced Composition Explorer (ACE), is designed to provide high- resolution measurements of the isotopic composition of energetic nuclei from He to Zn (Z=2 to 30) over the energy range from ∼10 to ∼100 MeV nucl−1. During large solar events SIS will measure the isotopic abundances of solar energetic particles to determine directly the composition of the solar corona and to study particle acceleration processes. During solar quiet times SIS will measure the isotopes of low-energy cosmic rays from the Galaxy and isotopes of the anomalous cosmic-ray component, which originates in the nearby interstellar medium. SIS has two telescopes composed of silicon solid-state detectors that provide measurements of the nuclear charge, mass, and kinetic energy of incident nuclei. Within each telescope, particle trajectories are measured with a pair of two-dimensional silicon-strip detectors instrumented with custom, very large-scale integrated (VLSI) electronics to provide both position and energy-loss measurements. SIS was especially designed to achieve excellent mass resolution under the extreme, high flux conditions encountered in large solar particle events. It provides a geometry factor of ∼40 cm2 sr, significantly greater than earlier solar particle isotope spectrometers. A microprocessor controls the instrument operation, sorts events into prioritized buffers on the basis of their charge, range, angle of incidence, and quality of trajectory determination, and formats data for readout by the spacecraft. This paper describes the design and operation of SIS and the scientific objectives that the instrument will address. This revised version was published online in June 2006 with corrections to the Cover Date.     

Observation of a 27-day solar signature in noctilucent cloud altitude

Previous studies have identified solar 27-day signatures in several parameters in the Mesosphere/Lower thermosphere region, including temperature and Noctilucent cloud (NLC) occurrence frequency. In this study we report on a solar 27-day signature in NLC altitude with peak-to-peak variations of about 400?m. We use SCIAMACHY limb-scatter observations from 2002 to 2012 to detect NLCs. The superposed epoch analysis method is applied to extract solar 27-day signatures. A 27-day signature in NLC altitude can be identified in both hemispheres in the SCIAMACHY dataset, but the signature is more pronounced in the northern hemisphere. The solar signature in NLC altitude is found to be in phase with solar activity and temperature for latitudes $?70°$N. We provide a qualitative explanation for the positive correlation between solar activity and NLC altitude based on published model simulations.