Confident that GSLV will launch NASA-ISRO satellite NISAR next year: ISRO on GSLV-F12 success

Springing back with a successful launch of the GSLV rocket, after a failed launch of the same rocket nearly 22months ago(GSLV-F10 on August 12th, 2021), ISRO officials expressed confidence that the GSLV rocket will launch the NASA-ISRO joint mission NISAR in 2024. Launched from the second launchpad at Satish Dhawan Space Centre, Sriharikota at 10:42 am, the 51.7meter tall vehicle carried the 2,232kg NVS-01 next-generation navigation satellite into a Geosynchronous Transfer Orbit(GTO).

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In the coming days, the satellite will be using its onboard propulsion systems to loft the satellite into the intended final orbit. The NVS-01 satellite has both civilian and military applications. It is notable that Indian Air Force Chief Air Chief Marshal VR Chaudhari and top Indian Navy officials witnessed the launch from the Mission Control Centre at Sriharikota.

"The NVS-01 Satellite has been placed in the precise orbit by the GSLV-F12 vehicle today, after the debacle we had faced in the GSLV-F10 mission(in August 2021) and the Cryogenic(third stage) did not ignite" Chairman ISRO, Dr. S.Somanath said.

He added that several corrections and modifications had been made to ensure the increased reliability of the GSLV rocket. He added that the GSLV rocket would be used in the coming months to place in orbit a weather satellite and a NASA-ISRO joint satellite.

NP Giri, Mission Director, GSLV-F12/NVS-01 said that the use of a 4-meter Ogive-shaped payload fairing(nose cone) in this mission has ensured that the rocket can accommodate and launch larger-sized satellites. Further, he expressed confidence that the NASA-ISRO Synthetic Aperture Radar Satellite(NISAR) would be launched by the same vehicle, next year.

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NASA-ISRO SAR (NISAR) is a Low Earth Orbit (LEO) observatory being jointly developed by the American and Indian Space agencies. It is meant to carry L and S dual-band Synthetic Aperture Radar (SAR), a highly powerful, all-weather, day and night mean of imaging from space, that can help researchers and scientists observe changes in Earth’s land and ice surfaces down to fractions of an inch. The NISAR satellite is undergoing testing at integration at ISRO's UR Rao Satellite Centre, Bengaluru. 

KVS Bhaskar, the Satellite Director for this mission said that this was a satellite launch that everyone in the domain of navigation was looking forward to, as it also operates in L1 band frequency, which is interoperable with International operators (GPS, Glonass, Galileo, and BeiDou) and also contains an indigenously developed atomic clock. 

NVS-01 is the first in the series of second-generation navigation satellites built by ISRO's UR Rao Satellite Centre in Bengaluru. At present, India uses its Navigation with Indian Constellation(NavIC) series of satellites for civilian and defence navigation, positioning, and timing services in the Indian mainland and even 1500 km beyond India's borders.

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"NVS series of satellites will sustain and augment the NavIC with enhanced features. This series incorporates L1 band signals additionally to widen the services. For the first time, an indigenous atomic clock will be flown in NVS-01" ISRO said. 

Atomic clocks are highly precise timekeeping instruments that are placed within satellites. They offer measurements of time that are precise down to a billionth of a second(nanosecond). Such precision is crucial because they help in offering accurate positioning services. While using satellite-based positioning and navigation services, our position(of the GPS receiver) is determined with respect to its distance from multiple satellites.

When such a calculation happens, the distance value is obtained by multiplying the time(taken for a signal to travel) and the speed of the signal(almost similar to the speed of light). In such cases, (when large values are being multiplied) even a variation of a billionth of a second can lead to an inaccurate distance value(by a few meters or tens of meters). Hence it is necessary to have atomic clocks that can work for several years without even nanosecond-level errors in timekeeping. 

Earlier, the NavIC series of satellites were known as IRNSS(Indian Regional Navigation Satellite System). It provides two types of services- Standard Positioning Service (SPS) which is provided to all the users and Restricted Service (RS), which is an encrypted service provided only to the authorised users.

According to ISRO, some of the applications of the IRNSS/NavIC system are Terrestrial, Aerial, and Marine Navigation, Disaster Management, Vehicle tracking, and fleet management, Precise Timing, etc. According to ISRO, NavIC SPS signals are interoperable with other global navigation satellite system (GNSS) signals such as - GPS, Glonass, Galileo, and BeiDou. 

ISRO's current series of NavIC satellites were placed in orbit in a phased manner between the years 2013 and 2018 using PSLV rockets. All satellites in the first-generation NavIC series weighed 1,425kg and carried foreign-origin atomic clocks. All IRNSS/NavIC series satellites carried two types of payloads – navigation payload and ranging payload.

The navigation payload of transmits signals for the determination of position, velocity, and time. Rubidium atomic clocks are part of the navigation payload of the satellite. The ranging payload of these satellites consists of a C-band transponder which facilitates accurate determination of the range of the satellite.

Speaking to reporters prior to the launch day, Chairman ISRO, Dr.S. Somanath said that only four of the existing fleet of seven NavIC satellites were operational now. Instead of replacing the three defunct satellites of the old generation, ISRO is launching a fleet of five next-gen NavIC satellites, of which NVS-01 would be the first, he added.

The rationale behind launching a new fleet of five satellites is the fact that the existing constellation would be defunct in a few years(owing to the completion of mission life). Hence, it would not be prudent to replace the old fleet. It is expected that two next-gen NavIC satellites will be launched every year.