SRIHARIKOTA: India’s workhorse PSLV has helped the national space agency to conquer yet another complex “multi-burn technology” that gives the luxury to enter different orbits in single mission. Indian Space Research Organisation (ISRO) on Monday has lobbed eight satellites, including 371 kg SCATSAT-1 that detects and track cyclones, into two different orbits.
This was ISRO’s first commercial project using multi-burn technology, where five international customer satellites from Algeria, USA and Canada were launched. The technology was earlier successfully demonstrated in last December and January missions. With this capability, ISRO now stands to be able to reduce its launch costs further as well as launch more satellites faster. Only few days ago, European Space Agency’s Vega rocket has achieved a similar feat.
Just one minute before the separation of SCATSAT-1, the fourth stage or rocket’s engine was cut-off and restarted after one hour and 22 minutes into its flight. The same exercise was repeated again after one hour interval.
In its longest journey till date, PSLV-C35 travelled for two hours and 15 minutes clocking top velocity of 7,527.63 metre per second. While country’s weather satellite SCATSAT-1 was released first into a 730 km Polar Sunsynchronous Orbit (SSO) after about 17 minutes, the rest were injected into a lower orbit of 689 km after around two hours.
At 9.12 am, the vehicle measuring 44.4 m and lift-off mass of 320 tonne blasted-off from the First Launch Pad at Satish Dhawan Space Centre (SDSC-SHAR), which is about 100 km north of Chennai, on a beautiful morning. This was PSLV’s 37 flight and 15 in ‘XL’ configuration using solid strap-on motors.
Besides SCATSAT-1, there were two student satellites PRATHAM developed by IIT-Bombay and PISAT from PES University and consortium from Bengaluru. The remaining five were of foreign origin. Three satellites - ALSAT-1B, ALSAT-2B and ALSAT-1N – were from Algeria, and Pathfinder-1 and NLS-19 from USA and Canada, respectively. The combined weight of all the eight satellites was about 675 kg.
How it is done?
| Event | Time after lift-off |
| First stage ignition | 0 |
| First stage separation | 1 min 52.74 sec |
| Second stage ignition | 1 min 52.94 sec |
| Second stage separation | 4 min 25.40 sec |
| Third stage ignition | 4 min 25.40 sec |
| Third stage separation | 9 min 47.80 sec |
| Fourth stage ignition | 12 min 26.52 sec |
| Fourth stage cut-off (injection) | 16 min 55.84 sec |
| SCATSAT-1 separation | 17 min 32.84 sec |
| Fourth stage engine restart-1 | 1 hr 22 min 38.02 sec |
| Fourth stage restart-1 cut-off | 1 hr 22 58.56 sec |
| PS-4 engine restart-2 | 2 hr 11 min 46.52 sec |
| PS-4 engine restart-2 cut-off | 2 hr 12 min 5.96 sec |
Complexity
Starting and shutting off the engines only sounds simple. Such a description glosses over the fact that the fourth stage is equipped with two liquid-fuel engines that have to be operated in sync. The engines also heat up considerably while in operation, so if they have to be restarted, they need to be cooled down rapidly in the interim period. Additionally, because the maneuvers are being performed in space, gravity is extremely weak and the flow of fuel to the engines would not be as efficient as it is on Earth’s surface, when the PSLV takes-off.
SCATSAT-1 utility
1. The mission objective of SCATSAT-1 is to provide weather forecasting services to the user communities through the generation of weather vector products for weather forecasting, cyclone detection and tracking.
2. It is a continuity mission for Scatterometer payload carried by the earlier Oceansat-2 satellite (September, 2009 to March, 2014), which was ISRO’s first microwave remote sensing sensor.
3. Compared to Oscat, significant improvements have been incorporated in the hardware configuration in order to achieve higher data quality for Climate Data Records.
4. In its lifetime, Oscat has appreciated by global community for its quality and accuracy. Landfall of Phailin Cyclone in the Odisha coast I 2013 was accurately predicted. Typhoon Kabayan in Phillippines in 2011, Hurricane Irene in US in 2011 and Hurricane Sandy in US in 2012 were some of the extreme weather events captured by Oscat.
5. SCATSAT-1 data will be shared with international agencies like EUMETSAT, KNML, NASA, NOAA and ECMWF apart from Indian users.
International customer satellites:
ALSAT-1B (Algeria)
Mass: 103 kg
Objective: Earth observation satellite for monitoring agriculture, environment and disasters.
ALSAT-2B (Algeria)
Mass: 117 kg
Objective: High resolution remote sensing satellite with panchromatic and multispectral imaging capability.
ALSAT-1N (Algeria)
Mass: 7 kg
Objective: Technology demonstration nanosatellite built by Algerian students.
Pathfinder-1 (USA)
Mass: 44 kg
Objective: Commercial high resolution imaging microsatellite
NLS-19 (Cannada)
Mass: 8 kg
Objective: Technology demonstration nanosatellite built to reduce space debris and for tracking commercial aircraft.
Student stat:
PRATHAM
Mass: 10 kg
Objective: To estimate Total Electron Count (TEC) with a resolution of 1 km x 1 km location grid.
PISAT
Mass: 5.25 kg
Objective: Design and develop a nanosatellite for remote sensing applications.