The Vikram Sarabhai Space Centre (VSSC) launched a total of 11 Rohini series indigenous sounding rockets from the Thumba Equatorial Rocket Launching Station here and the Satish Dhawan Space Centre in Sriharikotta to investigate the effects of the longest annular solar eclipse of this millennium, which occurred on Friday, on the earth’s atmosphere.
On Thursday, the VSSC launched two sounding rockets each of type RH 300 Mk II and RH 200, and on Friday, three sounding rockets of type RH 300 Mk II and two sounding rockets of RH 200 from Thumba. The RH 300 Mk II rockets can shoot to a peak altitude of 116 km above the earth and the RH 200 a peak altitude of 70 km above the earth.
Two larger Rohini rockets of the series RH 560 Mk II series were also launched by the VSSC from Sriharikotta, one each on Thursday and Friday. These rockets are capable of shooting up to a peak altitude of 548 km.
The eclipse assumed annular condition at 1.14 p.m. over Thumba. The maximum obscuration of 91 per cent of the sun occurred at 11.15 p.m. The annular phase of the eclipse lasted about 11 minutes and eight seconds over Thumba. The firing of the sounding rockets were scheduled in such a way as to collect relevant data on atmospheric structure and dynamics at different altitudes from the earth before, during and after the annular solar eclipse.
“Many scientifically interesting phenomena occur in the diurnal equatorial atmosphere [during an eclipse]. Equatorial electrojet, equatorial ionization anomaly and equatorial temperature and wind anomaly are examples of such phenomena. When solar eclipse occurs, there will be a sudden cut-off of solar radiation. This cut-off will affect the atmospheric structure and dynamics and there will be a large reduction in ionization and temperature. Today’s eclipse offered a unique opportunity to scientists to investigate the effects of fast varying solar flux on the photochemistry and electrodynamics of the different atmospheric regions, especially the equatorial mesopause and ionosphere-thermosphere regions,” the VSSC said.
The results of these experiments would be correlated with ground-based eclipse observations. The interpretation of the eclipse data together with the space data is expected to give new insights into earlier eclipse observations also, the VSSC said.
T.S.S. Subramanian reports from Chennai:
“Man is curious to understand nature,” declared an Indian Space Research Organisation (ISRO) scientist as the spectacular sight of the annular solar eclipse appeared in the sky and five sounding rockets sped into the atmosphere in a span of four hours from the beachfront at Thumba in Thiruvananthapuram on Friday afternoon.
An ISRO scientist said from Thumba: “It was a spectacular sight. It was an exhilarating experience. On the one hand, there was the awe-inspiring sight of the moon covering the disc of the afternoon sun, which could be safely seen only through a filter. On the other hand, there was the roar of five sounding rockets zooming into the sky one after another, complete with a countdown and commentary.”
Impact on electrojet
The scientist explained that when the eclipse occurred, the solar radiation was suddenly cut off. This impacted on the electrojet — an intense band of current system at an altitude of about 100 km and the structure and the dynamics of the upper atmosphere. The dynamics, that is, the various processes such as turbulence and eddies occurring in the atmosphere, had a bearing on the transmission of the global positioning system’s (GPS) signals.
“Hence the study of such rare phenomenon such as the annular solar eclipse is not only intellectually rewarding but has useful, long-term practical applications,” he added.
M.Y.S. Prasad, Associate Director, SDSC, said the RH-560 lifted off at 1.15 p.m. and reached an altitude of 523 km. “Everything went as per predictions. The rocket performance was good. The payload data will be collected and given to scientists,” Dr. Prasad said.
In connection with a report “Ten rockets fired to study solar eclipse” , there was a query on the life span of the RH series rockets.
A sounding rocket does not put anything into orbit. Instead, this type of rocket carries instruments in its nose that make measurements of the upper atmosphere as it ascends. This data is sent back via radio signals to the ground for scientists to analyse. Once the rocket’s fuel is exhausted, the rocket and its payload plummets to the ground. The ISRO website describes the various instruments carried by sounding rockets. In this case, sounding rockets were fired before, during and after the eclipse. This could have been done so that scientists could make appropriate comparisons and decide what changes had occurred in the upper atmosphere as a result of the eclipse.