Opinion

ISRO’s GISAT-1 is a first for India

Photo: ISRO’s GISAT–1 onboard the GSLV-F10.

By Kartik Bommakanti

The Indian Space Research Organisation (ISRO) announced that it would be indefinitely postponing the launch of its GISAT-1 Earth Observation (EO) weather satellite. The launch, which was originally scheduled for Mar. 5. 2020 has now been indefinitely postponed by the ISRO. Although the ISRO did state the precise technical reasons behind the postponement, in addition, one possible development preventing the scheduled launch was due to the outbreak and spread of the COVID-19 pandemic. Regardless, the spread of the disease has potentially and conceivably induced a precautionary delay.

Beyond the uncertain reschedule, we need to survey why ISRO has decided to launch a Meteorological Satellite (METSAT) or Earth Observation into Geostationary Orbit (GEO). Compared to other countries, where does India stand in the launch of this category of satellites? If the launch is successful, India will join an exclusive club. The first country to launch a MET EO satellite into GEO was the United States (US). The latter launched the world’s first METSAT in 1974, dubbed the Synchronous Meteorological Satellite 1, followed by Japan’s Himawari satellite and Europe’s Meteosat in 1977. Russia followed 17 years later in 1994 with the launch of its METSAT or EO satellite Elektro. China became the sixth country to launch this type of satellite in 2004 called the Feng Yun 2 (FY-2) in 2004. In the event ISRO is successful, India will thus become only the seventh country to launch and operate a satellite of this kind. The ISRO otherwise has generally operated weather satellites in polar orbits. Nevertheless, among all these states, let us compare where India stands vis-Ă -vis China.

Beijing’s geostationary meteorological satellite programme started in the 1980s. Before the launch of dedicated operational METSATs as part of the Feng Yun (“winds and clouds” in Chinese Mandarin) series, the Chinese launched the Feng Yun 2A and Feng Yun 2B in 1997 and 2000 respectively into geostationary orbit. These were, however, experimental satellites, and the first operational METSAT that China launched and placed in GEO in Oct. 2004 was the FY-2C. A back up spacecraft FY-2D was launched in Dec. 2006. Thereafter, they launched three additional METSATs as part of the series Feng Yun series called FY-2E (2008), the FY-2F (2012) and the FY-2G (2014). As of today, the only operational Chinese Geostationary METSAT in the Fengyun-2 series is the Fengyun-2H launched in 2018. Evidently, China has far greater experience and a longer history than India does in operating METSATs in geostationary orbit.

India is for the first time using a four-diameter Ogive-shaped Payload Fairing (PLF) or heat shield for the upper of the GSLV. There are several reasons why the ISRO has proceeded with an Ogive upper stage, which literally means tapered or curved front end of a rocket or missile. Scientists and technologists from the ISRO had already conducted several research studies on developing and using an Ogive PLF. Indeed, the Vikram Sarabhai Satellite Centre (VSSC), as well the National Aerospace Laboratories (NAL), both located in Bengaluru, did demonstrate through technical analysis that an Ogive shaped PLF has advantages over other types of heat shields, namely, Bulbous Heat Shield (BHS) and BiCone Heat Shield (BiHS).

Following intensive tests, it became evident that the Ogive Heat Shield (OHS) was the most advantageous because it reduced aerodynamic stress on the satellite payload and potentially manned crew module at Transonic Mach speed (approximately the speed of sound). Regardless of the angle of attack, the Ogive shaped PLF produces the least amount of aerodynamic load, aerothermal load and gives optimum drag allowing the front end of the PLF to withstand the stress of transonic flight as opposed to the other two PLFs.

Indeed, it is precisely for this reason that as two rocket technologists from the US observed many years ago that the Ogive shape is an evolution from the cylindrical and conal shaped PLF. Since the PLF experiences great in-flight instability at the boat-tail region when detaching from the main joints of the vehicle without affecting its trajectory at transonic speed, the Ogive shape helps withstand acoustic loads or sound pressure by reducing drag and also allows heat to be to be deposited more gently on the surface of the OHS. If the GISAT-1 launch is successful, India’s manned mission to space will also benefit, as the crew module is likely to be at the front-end of the rocket. Now it stands evident why ISRO is going to use an Ogive shaped heat shield for its forthcoming launch.

What are the other advantages and disadvantages to launching MET satellite? Let us start with the latter. Geosynchronous MET satellites are very costly. They require a large launcher, as is already evident from the fact that GSLV F-10 is going to launch the GISAT-1. Further, its spatial resolution at 42 metres will be low because of its high orbit at 36,000 km above the equator.

On the other hand, the GISAT-1 type EO satellites advantage lies in providing high quality 24-hour atmospheric, hydrological, weather coverage of substantial land and ocean area. Thus, the temporal resolution of the GISAT-1 will be high, which a Low Earth Orbit (LEO) polar satellite cannot provide. In addition, the likely beneficiaries of the GISAT-1 will be the Indian armed services from this launch, which will provide round the clock observation across the entire Indian subcontinent. Regardless of these qualifications, GISAT-1 will be an important milestone completed by the ISRO.

(The article was first published online by New Delhi-based Observer Research Foundation. The writer is an Associate Fellow at ORF’s Strategic Studies Programme.)

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