ISRO's eighth navigation satellite launch: Things to know about the IRNSS constellation

New Delhi: The Indian Space Research Organisation (ISRO) has been setting benchmarks for its global counterparts and has gained a solid foothold in the space race.

After its last big launch of the Cartosat-2 series and 30 co-passenger satellites last month, ISRO has won the appreciation and admiration of people from around the world.

With its commendable space program, ISRO is being lauded across the globe as one of the pioneers in space, along with exemplaries like NASA, ESA, JAXA and Roscosmos.

Considered the new kid on the block in the multi-billion dollar world launcher market, ISRO aims to set an enviable benchmark for the space-faring nations.

Today, the Indian space agency is all set to launch its eighth navigation satellite – the IRNSS-1H – as a spare or back-up for its constellation in the geo-orbit.

The 1.4 tonne satellite will join the Indian Regional Navigation Satellite System (IRNSS) constellation and will serve as a replacement to the IRNSS-1A, all three of whose atomic clocks have failed.

In order to understand the dynamics behind the constellation, we first need to understand what the IRNSS program entails.

As per ISRO, IRNSS is an independent regional navigation satellite system being developed by India and is designed to provide accurate position information service to users in India as well as the region extending up to 1500 km from its boundary, which is its primary service area.

IRNSS will provide two types of services, namely, 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.

The IRNSS System is expected to provide a position accuracy of better than 20 m in the primary service area.

Some applications of IRNSS are:

• Terrestrial, Aerial and Marine Navigation
• Disaster Management
• Vehicle tracking and fleet management
• Integration with mobile phones
• Precise Timing
• Mapping and Geodetic data capture
• Terrestrial navigation aid for hikers and travellers
• Visual and voice navigation for drivers

Below is the list of navigation satellites in the IRNSS constellation in order of their launch timelines along with a brief description:

IRNSS-1A:

Launched in 2013, it was the first navigation satellite in the constellation to be sent into orbit. IRNSS-1A carries two types of payloads navigation payload and ranging payload. The navigation payload of IRNSS-1A transmits navigation service signals to the users and the ranging payload of IRNSS-1A consists of a C-band transponder which facilitates accurate determination of the range of the satellite.

IRNSS-1B:

The second navigation satellite, IRNSS-1B was launched in 2014. With a lift-off mass of 1432 kg, it carries two types of payloads – navigation payload and ranging payload. The navigation payload of IRNSS-1B transmits navigation service signals to the users. The ranging payload of IRNSS-1B consists of a C-band transponder which facilitates accurate determination of the range of the satellite.

IRNSS-1C:

The third navigation satellite of the seven satellites constituting the IRNSS space segment, the IRNSS-1C was also launched in 2014, within 7 months of IRNSS-1B. The satellite is powered by two solar arrays, which generate power up to 1,660 watts, and has a life-time of ten years. IRNSS-1C carries two types of payloads – navigation payload and ranging payload.

IRNSS-1D:

This is the fourth navigation satellite in the IRNSS constellation. The two solar panels of IRNSS-1D consisting of Ultra Triple Junction solar cells generate about 1660 Watts of electrical power. Sun and Star sensors as well as gyroscopes provide orientation reference for the satellite.

IRNSS-1E:

Launched in January 2016, the IRNSS-1E has a lift-off mass of 1425 kg. Its two payloads – the navigation payload and ranging payload - transmit navigation service signals to the users and facilitates accurate determination of the range of the satellite respectively.

IRNSS-1F:

The sixth of the seven IRNSS satellites was launched in March 2016 and has a configuration that is similar to that of IRNSS-1A, 1B, 1C, 1D and 1E.

IRNSS-1G:

The final satellite in the IRNSS space segment was launched in April 2016 into a sub Geosynchronous Transfer Orbit (sub GTO). Like its other IRNSS predecessors, IRNSS-1G also carries two types of payloads – navigation payload and ranging payload.

IRNSS-1H:

The eighth satellite in the IRNSS segment is being launched on Thursday, August 31 at 7:00 pm. While IRNSS-1H joins the constellation for providing navigation services, IRNSS-1A will be used for messaging services. IRNSS 1H comes with more flexibility in service and it is compatible with the satellites, which are in orbit.