Sailing at the brink – The no-limits of near-/now-term-technology solar sails and SEP spacecraft in (multiple) NEO rendezvous

Near-Earth object (NEO) in-situ exploration can provide invaluable information for science, possible future deflection actions and resource utilisation. This is only possible with space missions which approach the asteroid from its vicinity, i.e. rendezvous. This paper explores the use of solar sailing as means of propulsion for NEO rendezvous missions. Given the current state of sail technology, we search for multiple rendezvous missions of up to ten years and characteristic acceleration of up to 0.10 mm/s². Using a tree-search technique and subsequent trajectory optimisation, we find numerous options of up to three NEO encounters in the launch window 2019–2027. In addition, we explore steerable and throttleable low-thrust (e.g. solar-electric) rendezvous to a particular group of NEOs, the Taurid swarm. We show that an acceleration of 0.23 mm/s² would suffice for a rendezvous in approximately 2000 days, while shorter transfers are available as the acceleration increases. Finally, we show low-thrust options (0.3 mm/s²) to the fictitious asteroid 2019 PDC, as part of an asteroid deflection exercise.     

Single ion actions: the induction of micronuclei in V79 cells exposed to individual protons.

Understanding the effects of single-particles from conventional radiation biology experiments is problematic due to the stochastics of particle tracks. This complicates the determinations of risk associated with low doses. We have developed a charged particle microbeam, which allows individually counted particles to be delivered to precise cellular locations. The system is capable of delivering a single charged particle with > 99% efficiency. Of these particles 90% are delivered with a resolution of +/- 2 micrometers and 96% with a resolution of +/- 5 micrometers. We have carried out preliminary studies in Chinese hamster V79 cells to monitor the effectiveness of low energy protons at inducing cytological damage. We have used the micronucleus assay as a measure of predominantly lethal chromosome damage. The effects of a single 3.2 MeV proton delivered individually to cells could be measured, with less than 2% of the exposed cells producing micronuclei 24 hours later. The yield of micronuclei formation was essentially linear up to the highest dose (30 particles per cell nucleus) delivered. Ultimately, the ability to target particles to different parts of the cell nucleus may start to impact on models available for chromosome aberration formation and chromosomal Organisation and mechanisms underlying genomic instability.     

On the practical exploitation of perturbative effects in low Earth orbit for space debris mitigation

This paper presents the results of a numerical evaluation of the natural lifetime reduction in low Earth orbit, due to dynamical perturbations. The study considers two values for the area-to-mass ratio, a nominal ratio which resembles a typical value of spacecraft in orbit today, and an enhanced ratio which covers the surface augmentation. The results were obtained with two orbit propagators, one of a semi-analytical nature and the second one using non-averaged equations of motion. The simulations for both propagators were set up similarly to allow comparison. They both use the solar radiation pressure and the secular terms of the geopotential ($J_2,J_4$ and $J_6$). The atmospheric drag was turned on and off in both propagators to alternatively study the eccentricity build up and the residual lifetime. The non-averaging case also covers a validation with the full 6?×?6 geopotential. The results confirm the findings in previous publications, that is, the possibility for de-orbiting from altitudes above the residual atmosphere if a solar sail is deployed at the end-of-life, due to the combined effect of solar radiation pressure and the oblateness of the Earth. At near polar inclinations, shadowing effects can be exploited to the same end. The results obtained with the full, non-averaging propagator revealed additional de-orbiting corridors associated with solar radiation pressure which were not found by previous work on space debris mitigation. The results of both tools are compared for specific initial conditions. For nominal values of area-to-mass ratio, instead, it is confirmed that this resonance effect is negligible.The paper then puts the findings in the perspective of the current satellite catalogue. It identifies space missions which are currently close to a resonance corridor and shows the orbit evolution within the resonances with a significantly shorter residual orbital lifetime. The paper finishes with a discussion on the exploitation of these effects with regards to the long-term simulation of the space debris environment and a flux and collision probability comparison.     

Investigating the cellular effects of isolated radiation tracks using microbeam techniques.

Studies of the effects of radiation at the cellular level have generally been carried out by exposing cells randomly to the charged-particle tracks of a radiation beam. Recently, a number of laboratories have developed techniques for microbeam irradiation of individual cells. These approaches are designed to remove much of the randomness of conventional methods and allow the nature of the targets and pathways involved in a range of radiation effects to be studied with greater selectivity. Another advantage is that the responses of individual cells can be followed in a time-lapse fashion and, for example, processes such as "bystander" effects can be studied clearly. The microbeam approach is of particular importance in mechanistic studies related to the risks associated with exposure to low fluences of charged particles. This is because it is now possible to determine the actions of strictly single particle tracks and thereby mimic, under in vitro conditions, exposures at low radiation dose that are significant for protection levels, especially those involving medium- to high-LET radiations. Overall, microbeam methods provide a new dimension in exploring mechanisms of radiation effect at the cellular level. Microbeam methods and their application to the study of the cellular effects of single charged-particle traversals are described.