Monitoring and understanding the Earth’s magnetic field and the ionospheric environment is key for both fundamental science and multiple applications. The Earth’s magnetic field protects our planet from incoming energetic charged particles and organizes the way the near outer space (the magnetosphere) and the ionized upper layers of the atmosphere (the ionosphere) respond to solar activity. This response can produce strong magnetic signals that can affect ground technology such as power transmission networks, radiation hazards that can affect satellites in the near outer space, and multiple ionospheric perturbations that can severely affect radio transmissions, radars and GNSS systems (hazards collectively known as space weather hazards). Monitoring Earth’s magnetic field and ionospheric environment is crucial for investigating all these phenomena. Identifying and understanding Earth’s magnetic field multiple sources is also crucial to aid precise navigation, reveal properties of the shallow and deep Earth, and provide key information for geophysical surveying for minerals.
The very successful on-going ESA Earth Explorer Swarm constellation revealed the considerable science value of using a well-conceived satellite constellation for such investigations. Building on Swarm’s achievements, NanoMagSat has been designed to demonstrate the ability of New Space technology to bring such studies to the next level of success.
The constellation will consist of an innovative low-Earth orbit (LEO) constellation of three 16 U nanosatellites, with a current baseline of two 60° inclined and one polar orbits, allowing much faster local time coverage of all geographic locations up to 60° North and South latitudes than is currently possible with Swarm. This constellation would also allow even better coverage, should NanoMagSat be launched while Swarm is still in operation. Each satellite will carry an identical payload consisting of an advanced Miniaturized Absolute scalar and self-calibrated vector Magnetometer (MAM) combined with a set of precise star trackers (STR), a compact High-frequency Field Magnetometer (HFM), a multi-needle Langmuir Probe (m-NLP) and dual frequency GNSS receivers. This payload will allow the production of absolute vector magnetic data at 1Hz sampling, scalar and vector magnetic data at 2 kHz sampling, electron density data at 2 kHz sampling, electron temperature data at 1 Hz sampling, as well as TEC and ionospheric radio-occultation data.
As already demonstrated in the context of the NanoMagSat Scout consolidation phase carried out in 2020, this combination of data, particularly those acquired at higher rates than on Swarm, and the proposed new constellation configuration, will allow improvement of the type of monitoring and investigations Swarm (and previous missions such as Oersted and CHAMP) achieved, also bringing entirely new science opportunities.
Science primary objectives begin with the precise recovery of the field produced by the geodynamo within the Earth’s core. This field, also known as the Earth’s main field, is critical to characterize and understand the way the Earth reacts to the incoming flux of energetic charged particles (the solar wind). Its precise knowledge is also used for many practical applications, both ground-based and space-borne. Recovering its fast dynamics is a top priority, as our still-limited knowledge of this dynamics severely hampers present efforts, relying on data assimilation and advanced numerical dynamo models, to predict main field evolution at the level requested by users. Twenty years of space-born observations by Oersted, CHAMP and Swarm, combined with ground observation data, has allowed great progress, making it possible to study inter-annual changes as well as abrupt changes known as geomagnetic jerks. Thanks to recent progress in numerical dynamo simulations, we now know that further observations are needed to fully characterize and understand these phenomena, since much faster changes can occur. It has not been possible to study such rapid variations with the existing satellite constellations. NanoMagSat will have the ability to considerably improve the situation by capturing core field signals with periods of as short as three months.
A second set of primary objectives will be to also improve our ability to recover fast changing planetary scale ionospheric and magnetospheric fields. These also need to be better monitored and understood. The mid and low latitude ionospheric field typically varies on a daily and seasonal basis, but significant day-to-day variability occurs in response to solar activity. In contrast to Swarm, NanoMagSat will have the ability to recover such variability. The magnetospheric field shows even stronger and faster dynamics. The ability of the NanoMagSat constellation to cover all local time scales at mid-latitudes over its orbital period will also make its recovery much easier. Characterizing both these fields, and the companion fields produced by the electrical currents they induce in the solid Earth, will not only help understand the way the Earth responds to solar activity, but also help reconstruct the still poorly known conductivity structure of the solid Earth.
A third set of primary objectives will take advantage of the innovative payload combination of NanoMagSat to investigate the ionospheric environment. As demonstrated by the experimental “burst mode” of the absolute magnetometers (ASM) on board the Swarm satellites (scalar data acquired at 250 Hz), whistlers produced by lightning strikes in the neutral atmosphere can be detected at LEO altitude and used to sound the state of the ionosphere below the satellites. NanoMagSat will have an extensive ability to even better do so, thanks to the 2 kHz sampling rate of its vector magnetometers. Such information, together with the TEC data, ionospheric occultation data (which Swarm lacks), and local electron density data will provide a powerful means to monitor the state of the ionosphere, to both investigate its dynamics and improve ionospheric models, such as the International Reference Ionosphere (IRI) model. Investigation of the local smaller scale dynamics of the ionosphere will also be made possible thanks to the joint use of 2kHz sampling vector magnetic and electron density data. This will provide access to ionospheric meter-scale plasma density structures and allow monitoring of the electrical currents testifying for the energy input that feeds them from the magnetosphere.
Additional secondary, but equally important, science objectives have also been identified. Some are already addressed by Swarm, but would considerably benefit from both longer (ideally permanent) satellite observations and could also greatly benefit from the joint use of NanoMagSat and Swarm data, should NanoMagsat be launched while Swarm is still in operation. This is the case for the magnetic signals produced by oceanic lunar tides. NanoMagSat would allow these minute signals to be recovered faster and more accurately. As already demonstrated, these signals can be used to sense the electrical conductivity of the uppermost regions of the solid Earth. On the long term, they could also potentially be used to assess the evolution of the temperature of the oceans (the magnitude of the tidal signals being sensitive to ocean temperature), thus contributing to monitoring one key parameter of climate global change. Additional signals produced by the global ocean circulation and its variability could also potentially be investigated, at time (month to interannual) and length scales expected to be accessible with NanoMagSat.
Another important secondary science objective that could benefit from NanoMagSat, especially if operated jointly with the Swarm constellation, is the recovery of the magnetic field signals produced by magnetized rocks within the lithosphere. Maps of these provide invaluable information about the nature and thermal state of the lithosphere and its deep- seated rocks, as well as about their tectonic history. This objective requires making the best of all missions, as it benefits from the accumulation of data over long periods. The Swarm constellation (with two satellites side-by-side) was optimally designed for that purpose. However, the much better local time coverage provided by NanoMagSat could be taken advantage of in order to better remove signals produced by all other sources and assist in better isolating this lithospheric signal.
Many additional possible secondary objectives are also now under study, thanks to the support of the science community, following a dedicated NanoMagSat brainstorming session organized in Athens in October 2021, as a follow-up of the 11th Swarm Data Quality Workshop. In particular, exciting ideas have emerged that could take advantage of the ability of the NanoMagSat payload to study ionospheric-magnetospheric dynamics, as a stand-alone mission or in conjunction with other missions.
In this invited talk, we will strive to illustrate all the numerous science objectives NanoMagSat could achieve, also reporting on E2E simulations that will have been run by the time of the meeting. Since we just learned that following successful negotiations with ESA, the NanoMagSat project will soon (January 10, 2022) kick off a new technical phase of Risk Retirement Activities for a period of 18 months, we will also report on how we have started backing up this phase with appropriate science preparation activities. All scientists willing to contribute to this effort to further enhance the science return of the NanoMagSat mission and demonstrate the potential of New Space for such science are warmly welcome to join. Beyond this initial mission, NanoMagSat could indeed be used as a stepping-stone for permanent low-cost monitoring of the Earth’s magnetic field and ionospheric environment.