Space particle radiation is one of the main concerns in planning long-term human space missions. There are two main types of hazardous particle radiation: (a) solar energetic particles (SEP) originating from the Sun and (b) galactic cosmic rays (GCR) that come from the distant galaxies in space. Fluxes in particles of solar origin maximize during solar maximum when particles originating from the distant galaxies are more efficiently deflected from the solar system during times when the sun is active. Our calculations clearly demonstrate that the best time for launching a human space flight to Mars is during the solar maximum, as it is possible to shield from SEP particles. Our simulations show that an increase in shielding creates an increase in secondary radiation produced by the most energetic GCR, which results in a higher dose, introducing a limit to a mission duration. We estimate that a potential mission to Mars should not exceed approximately 4 years. This study shows that while space radiation imposes strict limitations and presents technological difficulties for the human mission to Mars, such a mission is still viable.

The severe space weather event of 13-16 May 1921 produced some spectacular technological impacts, in some cases causing destructive fires. It was characterized by extreme solar and geomagnetic variations, and spectacular aurora, recorded at many locations around the world. A wealth of information is available in scientific journals, newspapers, and other sources, enabling us to reconstruct the storm timeline. This shows that a series of major coronal mass ejections (CMEs) bombarded Earth in May 1921. The first pair may have prepared the way for latter intense activity, clearing density from the region between Sun and Earth, and energizing Earth's magnetosphere. Thus, a subsequent CME could travel more quickly and drive even more energy into the already active magnetosphere. This CME arrived late on 14 May, driving very intense activity early on 15 May, and leading to the spectacular technological effects. However, some effects, attributed at the time to space weather, were probably coincidental with the storm, and due to more prosaic faults. The timeline of the 1921 event, including the confusion caused by prosaic faults, can be used to construct scenarios for use today by those emergency managers planning how to reduce the adverse impacts of future space weather events.

In the last decade, machine learning has achieved unforeseen results in industrial applications. In particular, the combination of massive data sets and computing with specialized processors (graphics processing units, or GPUs) can perform as well or better than humans in tasks like image classification and game playing. Space weather is a discipline that lives between academia and industry, given the relevant physical effects on satellites and power grids in a variety of applications, and the field therefore stands to benefit from the advances made in industrial applications. Today, machine learning poses both a challenge and an opportunity for the space weather community. The challenge is that the current data science revolution has not been fully embraced, possibly because space physicists remain skeptical of the gains achievable with machine learning. If the community can master the relevant technical skills, they should be able to appreciate what is possible within a few years time and what is possible within a decade. The clearest opportunity lies in creating space weather forecasting models that can respond in real time and that are built on both physics predictions and on observed data.

Historical records of ground-level geomagnetic disturbance are analyzed for the magnetic superstorm of May 1921. This storm was almost certainly driven by a series of interplanetary coronal mass ejections of plasma from an active region on the Sun. The May 1921 storm was one of the most intense ever recorded by ground-level magnetometers. It exhibited violent levels of geomagnetic disturbance, caused widespread interference to telephone and telegraph systems in New York City and State, and brought spectacular aurorae to the nighttime sky. Results inform modern projects for assessing and mitigating the effects of magnetic storms that might occur in the future.