Properties of the interstellar gas inside the heliosphere

Methods and results of investigations of the interstellar gas inside the heliosphere are summarized and discussed. Flow parameters of H and He and the relative abundances of H, He, N, O, and Ne in the distant heliosphere are given. Charge exchange processes in front of the heliosphere affect the flow of hydrogen and oxygen through the heliopause. The speed of hydrogen is reduced by 6 km/s, and screening leads to a reduction of the O/He and H/He ratios in the neutral gas entering the heliosphere. When the screening effect and the acceleration processes leading to the anomalous cosmic rays (ACR) are sufficiently understood, abundances in the LIC can be derived from measurements inside the heliosphere. Since isotopic ratios are virtually not changed by screening or by EUV and solar wind ionisation, relative abundances of isotopes in the gaseous phase of the LIC can be determined with no or minor correction from investigations of the neutral gas, pickup ions and ACR particles.     

Human exploration of near earth asteroids: Mission analysis for chemical and electric propulsion

This paper presents a mission analysis comparison of human missions to asteroids using two distinct architectures. The objective is to determine if either architecture can reduce launch mass with respect to the other, while not sacrificing other performance metrics such as mission duration. One architecture relies on chemical propulsion, the traditional workhorse of space exploration. The second combines chemical and electric propulsion into a hybrid architecture that attempts to utilize the strengths of each, namely the short flight times of chemical propulsion and the propellant efficiency of electric propulsion. The architectures are thoroughly detailed, and accessibility of the known asteroid population is determined for both. The most accessible asteroids are discussed in detail. Aspects such as mission abort scenarios and vehicle reusability are also discussed. Ultimately, it is determined that launch mass can be greatly reduced with the hybrid architecture, without a notable increase in mission duration. This demonstrates that significant performance improvements can be introduced to the next step of human space exploration with realistic electric propulsion system capabilities. This leads to immediate cost savings for human exploration and simultaneously opens a path of technology development that leads to technologies enabling access to even further destinations in the future.     

NaK release model for MASTER-2009

Sodium–potassium droplets from the primary coolant loop of Russian orbital reactors have been released into space. These droplets are called NaK droplets. Sixteen nuclear powered satellites of the type RORSAT launched between 1980 and 1988 activated a reactor core ejection system, mostly between 900 and 950 km altitude. The core ejection causes an opening of the primary coolant loop. The liquid coolant consists of eutectic sodium–potassium alloy and has been released into space during these core ejections. The NaK coolant has been forming droplets up to a diameter of 5.5 cm. NaK droplets have been modeled before in ESA's MASTER Debris and Meteoroid Environment Model. The approach is currently revised for the MASTER-2009 upgrade. A mathematical improvement is introduced by substituting the current size distribution function by the modified Rosin–Rammler equation. A bimodal size distribution is derived which is based on the modified mass based Rosin–Rammler equation. The equation is modified by truncating the size range and normalizing over the finite range between the size limits of the smallest and the biggest droplet. The parameters of the model are introduced and discussed. For the validation of the NaK release model, sixteen release events are simulated. The resulting size distribution is compared with radar measurement data. The size distribution model fits well with revised published measurement data of radar observations. Results of orbit propagation simulation runs are presented in terms of spatial density.     

Linking Primordial to Solar and Galactic Composition

Evolution and composition of baryonic matter is influenced by the evolution of other forms of matter and energy in the universe. At the time of primordial nucleosynthesis the universal expansion and thus the decrease of the density and temperature of baryonic matter were controlled by leptons and photons. Non-baryonic dark matter initiated the formation of clusters and galaxies, and to this day, dark matter largely determines the dynamics and geometries of these baryonic structures and indirectly influences their chemical evolution. Chemical analyses and isotopic abundance measurements in the solar system established the composition in the protosolar cloud (PSC). The abundances of nuclear species in the PSC led to the discovery of the magic numbers and the nuclear shell model, and they allowed the identification of nucleosynthetic sites and processes. To this day, we know the abundances of the ∼300 stable and long-lived nuclides infinitely better in the PSC than in any other sample of matter in the universe. Thus, we know the exact composition of a Galactic sample of intermediate age, allowing us to check on theories of Galactic evolution before and after the formation of the solar system. This paper specifically discusses the nucleosynthesis in the early universe and the Galactic evolution during the last 5 Gyr.     

VLBI observations to the APOD satellite

The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10?cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1?s integration time of the correlator output is on the level of 0.1?ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.     

Psychology and culture during long-duration space missions

The objective of this paper is twofold: (a) to review the current knowledge of cultural, psychological, psychiatric, cognitive, interpersonal, and organizational issues that are relevant to the behavior and performance of astronaut crews and ground support personnel and (b) to make recommendations for future human space missions, including both transit and planetary surface operations involving the Moon or Mars. The focus will be on long-duration missions lasting at least six weeks, when important psychological and interpersonal factors begin to take their toll on crewmembers. This information is designed to provide guidelines for astronaut selection and training, in-flight monitoring and support, and post-flight recovery and re-adaptation.     

SSETO—Small Satellite for Exoplanetary Transit Observation

SSETO is the result of a phase-A study in context of the small satellite program of the University of Stuttgart that demonstrates the capability of a university institute to build a small satellite with a budget of 5 million Euro. The satellite will be capable of observing exoplanets in a Neptune–Earth scale and obtaining data of interstellar dust. Due to a system failure of NASA?s Kepler mission, there is currently (October 2013) a lack of satellites searching for exoplanets. This paper details the design of subsystems and payload, as well as the required test tasks in accordance with the mission profile at a conceptional level. The costs for standard spacecraft testing and integration tasks are included, but not those of launch, ground support, operations and engineer working hours.     

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

Recent advances in the study of geomagnetic field reversals are reviewed. These include studies of the transitional field during the last geomagnetic reversal and the last geomagnetic excursion based on paleomagnetic observations, and analysis of reversals in self-consistent 3D numerical dynamo simulations. Field models inferred from observations estimate reversal duration in the range of 1–10 kyr (depending on site location). The transitional fields during both the Matuyama/Brunhes reversal and the Laschamp excursion are characterized by low-latitude reversed flux formation and subsequent poleward migration. During both events the dipole as well as the non-dipole field energies decrease. However, while the non-dipole energy dominates the dipole energy for a period of 2 kyr in the reversal, the non-dipole energy merely exceeds the dipole energy for a very brief period during the excursion. Numerical dynamo simulations show that stronger convection, slower rotation, and lower electrical conductivity provide more favorable conditions for reversals. A non-dimensional number that depends on the typical length scale of the flow and represents the relative importance of inertial effects, termed the local Rossby number, seems to determine whether a dynamo will reverse or not. Stable polarity periods in numerical dynamos may last about 1 Myr, whereas reversals may last about 10 kyr. Numerical dynamo reversals often involve prolonged dipole collapse followed by shorter directional instability of the dipole axis, with advective processes governing the field variation. Magnetic upwellings from the equatorial inner-core boundary that produce reversed flux patches at low-latitudes of the core-mantle boundary could be significant in triggering reversals. Inferences from the observational and modeling sides are compared. We summarize with an outlook on some open questions and future prospects.     

Isotopic Composition of H,HE and NE in the Protosolar Cloud

Observations and measurements in the solar wind, the Jovian atmosphere and the gases trapped in lunar surface material provide the main evidence from which the isotopic composition of H, He and Ne in the Protosolar Cloud (PSC) is derived. These measurements and observations are reviewed and the corrections are discussed that are needed for obtaining from them the PSC isotopic ratios. The D/H, ³He/⁴He (D+³He)/H, ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios adopted for the PSC are presented. Protosolar abundances provide the basis for the interpretation of isotopic ratios measured in the various solar system objects. In this article we discuss constraints derived from the PSC abundances on solar mixing, the origin of atmospheric neon, and the nature of the “SEP” component of neon trapped at the lunar surface. We also discuss constraints on the galactic evolution provided by the isotopic abundances of H and He in the PSC. This revised version was published online in August 2006 with corrections to the Cover Date.