In-situ observations of rocket burn induced modulations of the top side ionosphere using the IDEA payload on-board the unique orbiting experimental platform (PS4) of the Indian Polar Orbiting Satellite Launch Vehicle mission
The fourth stage (PS4) of the Polar Satellite Launch Vehicle (PS4-PSLV) C-38 mission, was used for the first time as an orbiting platform to carry out measurements of ionospheric parameters, on June 23, 2017. The measurements were made in two phases. i) During the initial launch phase wherein the launch vehicle traversed from the launch pad to an altitude of 500 km. ii) During the 10 orbits at an altitude of 350 km (after the PS4 stage was brought down in a controlled manner).
Space Physics Laboratory (SPL), VSSCindigenouslydeveloped the Ionization Density and Electric-field Analyzer (IDEA) payload which was flown on board the PS4 stage providing electron density (Ne) and electric field (EF) information at F region altitudes. The first observational results from the IDEA-Langmuir probe during the initial launch phase
of PSLV-C38 has been published in the Journal of Atmospheric and Solar Terrestrial Physics (JASTP) https://doi.org/10.1016/j.jastp.2020.105203.
The objective of the IDEA flight was to study the Equatorial Ionization Anomaly (EIA) which is an important large scale process in the equatorial and low latitude region. The equatorial ionosphere is the region between ±30◦ geomagnetic latitudes covering an altitude range of 60–1000 km. The EIA refers to the anomalous latitudinal distribution of ionospheric F region (180–1000 km) ionization with two crests on either side of the magnetic equator and a trough right over the magnetic equator during day time. The EIA region is characterized by large electron density gradients and the variabilities associated with the electron density distribution are still not fully understood and modelled.
Electron density and electric field are the two most important parameters in the ionospheric F region which play a key role in modulating all the major physical processes in the equatorial and low latitude ionosphere. Measurements of the top side ionosphere are sparse compared to those at the bottom side due to its inaccessibility to ground based radio sounding.The PS4 orbital platform of PSLV was perceived to be extremely useful in probing both the bottom and top side ionospheres as well as to make systematic measurements on the EIA. In the context of the strong coupling between ionosphere and thermosphere, the availability of a probe which can simultaneously give measurements of multiple ionosphere-thermosphere parameters is very valuable. The Electron Density and Neutral Wind and Langmuir probe (ENWi_LP) experiment had been flown in sounding rockets, in a campaign mode, during the solar eclipse event of January 2010 and later as part of the SOUREX Phase 1 experiment from Trivandrum. During the present PS4 mission, the ENWi - LP experiment was operated in the electron density and electric field analyzer mode as the IDEA experiment.
The IDEA payload (Fig.1a) during its initial launch phase took an altitude-latitude cut through the ionosphere that encompassed the bottom and top side ionospheres, over a range of latitudes (Fig.1b). Fig. 1c shows the calibrated in-situ electron density values from the IDEA-LP (thick black curve) along with the International Reference Ionosphere (IRI) model and Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations. The interesting aspect to be noted is that the IDEA observations reveal a clear double peaked structure whereas, the model simulationsreveal a single peak which coincides with the first peak seen ~5 Deg. by the IDEA payload. This indicates that the background conditions prevalent on 23 June 2017 do not favour the manifestation of a top side enhancement as seen in the observations (second peak).In such a scenario, the role of the rocket burn or exhaust in producing such a top side enhancement is examined, in terms of the different events during the rocket launch phase, from first stage ignition to last customer satellite separation (Fig.2). The IDEA payload was stationed on the PS4 orbital platform and is hencesensitive to any events occurring in the vicinity of the platform.Examining the sequence of operations, it is evident that PS4 ignition happens around 501s and the activity persists till the fourth stage cut off ~959 s.Remarkably, that the dramatic Ne increase(second peak) happened as soon as the PS4 ignition commenced around 501 s and it persisted up to the cut off stage. Thus, the IDEA PS4 experiment provided first of their kind in-situ observations of top side electron density enhancement concurrent with the operation of the PS4 stage of PSLV demonstrating the plausible role of rocket burn and exhaust gases in modulatingthe ionosphere in the vicinity. The results indicate that the unique trajectory of the PS4 orbiting station serves as an ideal one to investigate top side electron density enhancements. Further, the experiment underlines the fact that the novel orbiting platform, will be useful for carrying out measurements of multiple parameters in the near-Earth space.
Fig.1a) Photograph of IDEA payload b) The IDEA payload trajectory during the initial launch phase. c) Comparison of the IDEA LP electron density observations with the IRI model output and TIEGCM model simulation.