Last September, growing interest in a new generation of potential space experiments brought together 65 members of the active-experiments community for a workshop. Los Alamos National Laboratory’s Center for Nonlinear Studies and Center for Space and Earth Science sponsored this workshop, with the goal of assessing past accomplishments, reviewing lessons learned, and developing new ideas for future projects that conduct active experiments in space.
Discussions at the workshop focused on three questions:
- What have we learned from past active experiments in space?
- Why are active experiments not as popular anymore?
- What is the future of active experiments?
Active space experiments began early in the space age, when little was known about the near-Earth environment. Early experiments focused on very fundamental aspects of the space environment and its interaction with space vehicles. Over a span of several decades, active space-based experiments focused on such things as nuclear explosions, charged-particle beams, heaters, chemical releases, water dumps, plasma plumes, tethers, antennas, and voltage biases.
Attendees at the workshop discussed a number of important accomplishments from this period:
- Active experiments stimulated critical work in basic plasma physics (waves, instabilities, structuring, transport) and spacecraft charging.
- Barium and lithium releases elucidated the physics of plasma cloud dynamics, magnetic field modification, and auroral electric fields.
- Electron beam experiments demonstrated long-distance beam propagation, beam excitation of plasma waves, and the physics of beam-plasma discharges.
- Plasma jet experiments demonstrated plasma polarization effects and the propagation of plasma streams across magnetic fields.
- The Starfish Prime experiment demonstrated the long lifetime (years) of an artificially produced radiation belt.
- Ionospheric heater experiments stimulated the field of plasma turbulence and parametric instabilities research.
Since those early days, there has been a steep decline in space-based experiments, aside from ionospheric heating experiments. The workshop participants offered several reasons. First, prior experiments have collected most of the more easily obtained data. Second, in the early days of the space age, space flight was less bureaucratic. Third, as more became known about the space environment, exploration with experiments was less needed. Fourth, the community was not proactive enough in communicating their accomplishments. These aspects, combined with budgetary pressures, have restricted the interest in active experiments.
Workshop participants conveyed optimism for the future, however. Many maturing technologies (e.g., metamaterials, compact relativistic accelerators, antennas constructed of superparamagnetic nanoparticles, and cube satellites) could lead to a new era of active experiments. Diagnostics (which are always critical) have improved tremendously. Active experiments have identifiable strengths such as long-range coupling (low to high altitude, magnetosphere to ionosphere), and beam or wave propagation in the space environment can be addressed only with active experiments.
Most significantly, the workshop featured many exciting ideas for future experiments that are now under development. Some of these include Connections Explorer (CONNEX), Demonstration and Space Experiments (DSX), and Space Measurements of a Rocket-Released Turbulence (SMART) and superparamagnetic extremely low frequency/very low frequency (ELF/VLF) antennas.
Going forward, the community needs to identify the most compelling questions that can be answered only with active experiments, and they must demonstrate the relevance of these questions to other scientific areas and to national security. Future workshops, special sessions, and presentations are necessary to engage the broader scientific community and sponsors.
The abstracts and talks presented can be found on the workshop’s website.
—Gian Luca Delzanno (email: [email protected]), T-5 Applied Mathematics and Plasma Physics, Los Alamos National Laboratory, N.M.; and Joseph E. Borovsky, Space Science Institute, Center for Space Plasma Physics, Boulder, Colo.