The Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) Mission

Abstract

The overarching science goal of the Tandem Reconnection And Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission is to connect the cusp to the magnetosphere by discovering how spatial or temporal variations in magnetic reconnection drive cusp dynamics. This goal will be achieved with a simple mission design comprising two identical small spacecraft in identical low-Earth orbits in a follow-the-leader configuration. TRACERS will make repeated measurements in the cusp for a twelve-month primary mission using plasma and field instruments. These data will be analyzed using established dual-spacecraft techniques and supported by modeling that ensures science closure on the objectives. The TRACERS team leverages hardware collaborations from the University of Iowa, Southwest Research Institute, University of California Los Angeles, University of California Berkeley, and Millennium Space Systems. The larger science team consists of experts in reconnection, cusp physics, and modeling. TRACERS is dedicated to its proposer, and original Principal Investigator, Professor Craig Kletzing.

Keywords: Cusp; Heliophysics; Magnetic reconnection; NASA; TRACERS.

Fig. 1

Magnetic reconnection modifies the magnetic field lines that thread the cusp. TRACERS takes advantage of multiple passes of two spacecraft through the cusp to observe these modifications and achieve its overarching science goal

Fig. 2

TRACERS is dedicated to Prof. Craig Kletzing who died peacefully at home on August 10, 2023. The instrument suite main electronics box on each spacecraft includes one of Craig’s guitar picks (purple). TRACERS will carry Craig’s curiosity into space one last time

Fig. 3

The Earth’s magnetospheric cusps concentrate magnetic reconnection effects into a small, low altitude region. TRACERS flies through this region, separating temporal and spatial effects

Fig. 4

(top) Schematic of magnetopause reconnection for southward IMF. Dashed line shows faster ions while dashed-dot line shows slower ions. (middle) Modeled resulting cusp ion energy-latitude dispersion. (bottom) Equivalent observations from a low-altitude cusp crossing

Fig. 5

Science Objective 1 - Determine whether magnetopause reconnection is primarily spatially or temporally variable for a range of solar wind conditions

Fig. 6

Fortuitous cusp conjunction between the Fast Auroral SnapshoT (FAST) and Polar spacecraft. The black overlaid line represents the average location of the maximum flux in the cusp ion energy dispersion. Although the spacecraft encountered the cusp at very different times and latitudes, the structure of the cusp dispersions is similar. While this suggests a spatial interpretation of the cusp ion dispersions, the results are ambiguous due to the large time separation between the spacecraft. Within individual cusp ion steps, there are more rapid ion dispersions suggesting that there is temporal variability within cusp ion steps. With superior time resolution and close spacecraft separations at low altitude, TRACERS will determine if ion dispersions within cusp ion steps are truly temporal variations in reconnection at timescales of seconds. (From Trattner et al. 2002b)

Fig. 7

Science Objective 2 - For temporally varying reconnection, determine how the reconnection rate evolves

Fig. 8

The same spatial and/or temporal reconnection variability and velocity dispersion effects that create structure in the ion precipitation should theoretically produce similar structure in the electron precipitation. Previous missions such as DMSP F12 (Lockwood et al. 2005) did not resolve structure in the electron edge; however, TRACERS’ enhanced time resolution and two spacecraft will enable discovery science targeting the electron edge of the Cusp

Fig. 9

In-situ FAST measurements adapted from Chaston et al. (2007). Panel (a) occurrence frequency of Alfvén waves and panel (b) fraction of energetic electrons driven by the waves. If this statistical picture is consistent with individual cusp crossings, TRACERS should observe Alfvén waves nearly 100% of the time in the cusp. Where they occur relative to cusp ion steps determines if they are associated with temporal or spatial reconnection

Fig. 10

Energy-time spectrogram of precipitation cusp electrons adapted from Tanaka et al. (2005a). Time-dispersed electrons often associated with Alfvén waves are indicated by the red arrows. TRACERS ACE has the time resolution necessary to measure these time-dispersed electrons

Fig. 11

Science Objective 3 - determine to what extent dynamic structures in the cusp are associated with temporal versus spatial reconnection

Fig. 12

Results of a global hybrid simulation of the cusp (Tan et al. 2012). (Upper panels) The global reconnecting field lines at the magnetopause and particle tracing. (Lower panel) the resulting cusp ion dispersion predicted from the particle tracing. These simulations are conducted for a select number of TRACERS cusp encounters to determine how the 3-D structure of the reconnecting magnetic field in the top panel relates to the modeled cusp ion dispersion in the bottom panel. The bottom panel is compared to the ion dispersion observed by TRACERS

Fig. 13

The TRACERS Instrument Suite is identical on both spacecraft

Fig. 14

Instrument orientation during the Region of Interest (ROI). Note that the 2D electric field measurement is perpendicular to the background field and both ACI and ACE can instantaneously resolve complete pitch angle distributions

Fig. 15

Main Electronics Box (MEB) flight hardware

Fig. 16

Central Data Processing Unit (CDPU) lock diagram

Fig. 17

Orbit-in-the-life Design Reference Mission Scenario

Fig. 18

TRACERS launch configuration with the two-spacecraft stacked