Since the beginning of the space age, the number of orbital debris has skyrocketed to levels which seriously threaten the current and future use of space. It is estimated that -36,500 objects greater than 10 cm and orders of magnitude more smaller objects are currently in orbit, created predominantly by collisional events. The smaller objects, with characteristic size less than ~1 cm, are extremely hard to detect and cannot be tracked with existing technology but, with typical velocities of ~10 km/s, can create significant damage upon impact. Furthermore, with the ongoing commercialization of space and constellations of thousands of satellites envisioned in the near future, the orbital debris problem is expected to become much worse and methods for detection, tracking, characterization and possibly removal are much needed.

The geomagnetic storm that occurred on April 23-24, 2023 was the largest such event in nearly the last two decades. As the solar cycle begins to increase towards the maximum these events will increase with frequency and strength. The storm was observed by the FalconSEED sensor mounted on-board STPSat-6 in geosynchronous orbit (GEO). Observations were made of the injection of energetic electrons to the inner magnetosphere and enhancement of the electron population in GEO. The Falcon Solid-state Energetic Electron Detector (FalconSEED) is an energetic charged particle sensor that has been developed at the United States Air Force Academy to monitor electron flux across the energy range of 14 to 145 keV in GEO. This sensor has been developed to complement ongoing efforts by the Air Force Research Laboratory (AFRL) to advance a comprehensive space environment sensor suite, Compact Environmental Anomaly Sensor (CEASE3), for anomaly resolution. The FalconSEED instrument is designed with this in mind and is intended to demonstrate the ability to develop a CubeSat compatible, low size, weight, power, and cost (SWAP-C) energetic particle sensor, based on predominantly commercial off the shelf (COTS) components. The final flight payload fits within a volume of 10 cm x 10 cm x 20 cm, in a 4.3-kg, 3.4-Wpackage. The goal, already accomplished, is to fulfill a one-year mission lifetime in GEO thus demonstrating the low SWAP-C design can survive the harsh environment of space while still providing relevant science data. The electron flux data are used here to observe the energetic electron populations during the active storm event.

Reconnection in the magnetotail occurs along so‐called X‐lines, where magnetic field lines tear and detach from plasma on microscopic spatial scales (comparable to particle gyroradii). In 2017–2020, the Magnetospheric MultiScale (MMS) mission detected X‐lines in the magnetotail enabling their investigation on local scales. However, the global structure and evolution of these X‐lines, critical for understanding their formation and total energy conversion mechanisms, remained virtually unknown because of the intrinsically local nature of observations and the extreme sparsity of concurrent data. Here, we show that mining a multi‐mission archive of space magnetometer data collected over the last 26 yr and then fitting a magnetic field representation modeled using flexible basis‐functions faithfully reconstructs the global pattern of X‐lines; 24 of the 26 modeled X‐lines match ( B z = 0 isocontours are within ∼2 Earth radii or R E ) or nearly match ( B z = 2 nT isocontours are within ∼2 R E ) the locations of the MMS encountered reconnection sites. The obtained global reconnection picture is considered in the context of substorm activity, including conventional substorms and more complex events.

Thin current sheets (TCSs) have been postulated to be a necessary precondition for reconnection onset. Magnetic reconnection X‐lines in the magnetotail have been observed to be more common duskward of midnight. We take advantage of the MMS tetrahedral formation during the 2017–2020 MMS tail seasons to calculate the thickness of the cross‐tail neutral sheet relative to ion gyroradius. While a similar technique was applied to Cluster data, current sheet thickness over a broader range of radial distances has not been robustly explored before this study. We compare our analysis to recent theories regarding mechanisms of tail current sheet thinning and to recent simulations. We find MMS spent more than twice as long in ion‐scale TCSs in the pre‐midnight sector than post‐midnight, despite nearly even plasma sheet dwell time. The dawn‐dusk asymmetry in the distribution of Ion Diffusion Regions, as previously reported in relation to regions of TCSs, is also analyzed.

We analyze data returned by the Magnetospheric Multiscale mission (MMS) constellation during a rapid (∼1.5 s) traversal of a flapping and reconnecting current sheet (CS) in the near‐Earth magnetotail (X ∼−20 R E ). The CS was highly tilted, with its normal pointing strongly duskward. Its extreme thinness was confirmed by a curvature analysis of the magnetic field lines. The event was associated with a guide field of 8% of the reconnecting components. From the pitch angle distributions of low‐energy electrons we infer a crossing earthward of the X‐line. Traveling practically normal to the CS, MMS encountered an ion diffusion region (IDR) in which was embedded an electron diffusion region (EDR). IDR signatures included breaking of the ion frozen‐in condition in the presence of Hall B and E fields. EDR signatures included a strong out‐of‐plane current associated with a superAlfvénic electron jet, positive energy transfer, and a temperature anisotropy ( Te ∥ > Te ⊥ ) which disappeared at the field reversal. Derived scale sizes normal to the CS are: ∼6.9 d e (EDR) and ∼0.4 d i (IDR; 40 and 100 km). We estimate the average dimensionless reconnection rate as 0.077 ± 0.050. The observations and inferences are supported by particle‐in‐cell (PIC) numerical simulations. We find very good agreement in the reconnection rates. We also discuss the effects of asymmetries in the density, temperature and magnetic field strength on the Hall fields and length of the outflow jets. The event is associated with a substorm onset which began 7 min after the MMS observations.

We present a numerical algorithm to identify ion diffusion regions (IDRs) in the geomagnetic tail and test its applicability. We use five criteria applied in three stages. (i) correlated reversals (within 90 s) of V-x and B-z (at least 2 nT about 0; geocentric solar magnetospheric coordinates); (ii) detection of Hall electric and magnetic field signatures; and (iii) strong (>= 10 mV/m) electric fields. While no criterion alone is necessary and sufficient, the approach does provide a robust, if conservative, list of IDRs. We use data from the Magnetospheric Multiscale (MMS) mission spacecraft during a 5-month period (1 May to 30 September 2017) of near-tail orbits. We find 148 events satisfying Step 1, 37 satisfying Steps 1 and 2, and 17 satisfying all 3, of which 12 are confirmed as IDRs. All IDRs were within the X-range [-24, -15] R-E and the majority occurred during traversals of a tailward moving X-line. Eleven of 12 IDRs were on the duskside despite approximately equal residence time in the plasma sheet (56.5% dusk vs. 43.5% dawn). MMS could identify signatures of four quadrants of the Hall B-structure in three events and three quadrants in seven events. The events we report commonly display V-x reversals greater than 400 km/s in magnitude, normal magnetic field reversals often >10 nT in magnitude, maximum DC vertical bar(E) over right arrow vertical bar which are often well in excess of the threshold for Stage 3. Our results are then compared with the set of IDRs identified by visual examination from Cluster in the years 2000-2005.

In this paper we report on a sequence of large‐amplitude Alfvénic fluctuations terminating in a field and flow discontinuity and their effects on electromagnetic fields and plasmas in the near‐magnetopause magnetosheath. An arc‐polarized structure in the magnetic field was observed by the Time History of Events and Macroscale Interactions during Substorms‐C in the solar wind, indicative of nonlinear Alfvén waves. It ends with a combined tangential discontinuity/vortex sheet, which is strongly inclined to the ecliptic plane and at which there is a sharp rise in the density and a drop in temperature. Several effects resulting from this structure were observed by the Magnetospheric Multiscale spacecraft in the magnetosheath close to the subsolar point (11:30 magnetic local time) and somewhat south of the geomagnetic equator (−33° magnetic latitude): (i) kinetic Alfvén waves; (ii) a peaking of the electric and magnetic field strengths where E · J becomes strong and negative (−1 nW/m 3 ) just prior to an abrupt dropout of the fields; (iii) evolution in the pitch angle distribution of energetic (a few tens of kilo‐electron‐volts) ions (H + , He n + , and O n + ) and electrons inside a high‐density region, which we attribute to gyrosounding of the tangential discontinuity/vortex sheet structure passing by the spacecraft; (iv) field‐aligned acceleration of ions and electrons that could be associated with localized magnetosheath reconnection inside the high‐density region; and (v) variable and strong flow changes, which we argue to be unrelated to reconnection at partial magnetopause crossings and likely result from deflections of magnetosheath flow by a locally deformed, oscillating magnetopause.