Microsatellite missions to conduct midlatitude studies of equatorial ionospheric plasma bubbles

Two missions presently under development by the United States Air Force Academy (USAFA), FalconSAT-2 and FalconSAT-3, include mission scientific objectives targeting the study of ionospheric F region plasma density depletions and topside bubbles associated with the so-called Equatorial Spread F (ESF) phenomena. The Miniature Electrostatic Analyzer (MESA), a USAFA-designed patch sensor that measures differential energy fluxes of electrons from 0.05 to 13 eV in six channels, is the primary experiment aboard FalconSAT-2, a 25-kg microsatellite intended for launch into an International Space Station (ISS) orbit via the Space Shuttle. Because the orbit will be approximately 360 km in altitude and of 52° inclination, FalconSAT-2 observations will complement those of low latitude missions (e.g., C/NOFS) and polar latitude, higher altitude missions (e.g., DMSP). Realistic internal magnetic field models demonstrate that field lines with apex heights of 1500 km (representing the upper altitude limit of equatorial plasma bubbles) may intersect the orbit plane at dip latitudes greater than 35°. Thus, FalconSAT-2 will be able to observe plasma depletions that have propagated poleward along the field lines and lower in altitude, depletions that may not be observed with the high altitude DMSP and the low latitude C/NOFS. Additionally, there may be opportunities for FalconSAT-2 to make simultaneous multipoint in situ measurements of large-scale plasma bubbles with other low altitude satellites, such as C/NOFS and DMSP. We will present a statistical analysis of the probability of making such measurements using nominal orbital parameters of the relevant spacecraft. Finally, a description of the FalconSAT-3 follow-on mission, including scientific objectives associated with seeking kinetic effects, is presented.