ISRO masters Multi-Burn Technology through PSLV-C35

ISRO has mastered the multi-burn technology by successfully placing satellites into two different orbits. The advanced version of the ISRO’s workhorse PSLV-C35 during the launch on September 26^th hoisted 8 satellites into multiple orbits.

About PSLV-35

PSLV made its debut in 1993, over the years earned a formidable reputation for its consistent performance. PSLV vehicles capitalizes on the unique advantage of using a combination of solid rocket motors and liquid-fuelled engines. PSLV known to be reliable and effective launch vehicle so far had delivered payloads in straight mission and never attempted to accommodate flexible missions where payloads are deployed into different orbits. Lifting satellites to different orbits invariably requires multiple restarts. The current PSLV mission was designed accommodate this feature. Consequently, engineers reworked the design of the L-2-5 engines in the upper stage of PSLV responsible for multiple start. This was achieved by developing new propellant handling techniques so that propellant would settle prior to engine start-up so that engines would take only liquid propellants and no gas bubbles. Moreover, additional power margins are included in PS4 (Upper stage) for extended coast periods so that PSLV can conduct missions for long hours. Initial tests for restarting of the upper stage were conducted in December 2015. After its successful performance in initial tests, a second round of tests set stage for final flight were completed in June 2016. After a green signal from the Launch Authorisation Board (LAB), the flight was conducted on Monday. Multi-burn technology involves switching on and off of rocket engines endowing the launch vehicle the ability to deliver satellites to two different orbits.

In its longest missions conducted so far that lasted for 2hrs 15 minutes and 33 seconds, PSLV-C35 weighing 320 tons and measuring 44.4mts lifted off from the first launch pad of the Satish Dhawan Space Centre, SHAR, Sriharikota, carrying eight satellites of total weight 675 kg. The major Indian weather satellite SCATSAT-1 weighing 371kg was deployed into a Sun Synchronous Orbit (SSO) at an inclination of 98.1 degrees over the equator.  While the two other Indian satellites PRATHAM (10 Kg) developed by IIT B students and PISAT (5.25kg) constructed by PES University, Bangalore and five other foreign satellites were placed in a 689 Km Polar Orbit at 98.21-degree inclination. PRATHAM was aimed at estimating the Total Electron Count (TEC) and PISAT Nanosatellite was constructed for remote sensing applications.

On its 37^th mission PSLV-C35, after a flight of around 17 minutes, SCATSAT-1 separated from the PSLV fourth stage. After separation solar panels were deployed automatically and ISRO’s Telemetry, Tracking and Command Network (ISTRAC) and Bangalore took over the control of the satellite. SCATSAT is a continuity to the Ocean SAT-II Scatterometer (popularly termed as Oscat) launched in September 2009 to provide wind vector data products for weather forecasting, cyclone detection and tracking services to users. This Earth observation satellite carries a ku-band Scatterometer similar to OceanSat-II and has mission life of 5 years.  OScat was the first microwave remote sensing satellite. It earned global repute for contributing the areas of wind-retreival, weather-forecasting, cyclone-tracking and prediction. It accurately predicted Cyclone Phalin that hit Odisha and avoided loss of human life. The 17 minutes’ ascent for deployment of SCATSAT involved standard patterns of flight and was relatively hassle-free. But the PSLV still had the task of placing the seven other satellites in a different orbit.

Post SCATSAT deployment

The PSLV began to coast over the South Polar region and then ascended towards the Northern Hemisphere. After a gap of one hour 22 minutes, when the PSLV is in North polar region, the two engines of the PS4 were reignited and fired for 20 seconds. As a result, it entered into an elliptical orbit which is 725km from one side of the earth and 685 km from other side. Again after 50 min, when PS4 was coasting in the South Polar region, engines were fired for another 20 seconds. This second firing propelled the rocket to enter the circular orbit of 669 km altitude with an inclination of 98.21 degree. Within the next three minutes the dual launcher adapter separated from PSLV fourth stage and the first satellite to separate was ALSAT-1N followed by NLS-19, PRATHAM, PISAT, ALSAT-1B, ALSAT-2B and PATHFINDER-1.

Foreign Satellites

Other than PRATHAM and PISAT which are of Indian origin, rest of them belonged to international customers. ALSAT series satellites are from Algeria. The 103 kg, ALSAT 1B earth observation satellite aids in environment and disaster monitoring, ALSAT-2B weighing 117 kg is a high resolution remote sensing satellite with panchromatic and multispectral imaging capability and the 7kg ALSAT-1N is a Nanosatellite built by students for technology demonstration. NLS-19 is 8kg Canadian Nanosatellite used to perform experiments for reducing the space debris and tracking commercial aircraft. Finally, the PATHFINDER-1 of Black Sky Global of Seattle, is a 44kg American microsatellite used for commercial high resolution imaging. With this PSLV-C35 launch, ISRO has so far delivered 42 Indian payloads and 79 foreign satellites. As a precedent ISRO conducts four PSLV launch missions. This launch was fifth PSLV launch, a record for this year and seems to be in line with ISRO’s long term goals for PSLV of carrying out 6 to 8 launches a year to gradually shift the vehicle’s satellite services for commercial purposes. Europe’s Vega rocket clocking seven successful launches this year emerged as stiff competitor for PSLV. Vega operators are aiming to increase their launches to 10 per a year. Similarly, Khurinchev Space Centre of Moscow and its commercial wing, International Launch Services of Reston, Virginia with the announcement of two variant Proton Launch Vehicles for small satellites is also offering tough competition to ISRO. While ISRO undoubtedly has immense cost benefit ratio over the rest, they must indeed work really hard to stay ahead in the commercial satellite launching market.

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Splendid Success of GSLV operational launch

With the successful operational launch of GSLV F-05 rocket that hoisted the meteorological satellite INSAT-3DR into the geostationary transfer orbit (GTO), ISRO has entered into a new phase of self-reliance. Till now, PSLV (Polar Satellite Launch Vehicles), the trusted workhorse adorned the prestigious crown of ISRO with over consecutive 30 successful launches. PSLV could hoist satellites weighing few kilograms to less than 1400kg limiting ISRO’s capability of launching heavy satellites. PSLV are capable of carrying remote sensing satellites which are lighter and are placed in polar orbits. These satellites weigh from few hundred kilograms to about a tonne. Polar orbits are orbits in which satellites don’t move in tandem with the rotation of the earth and hence they are not suitable for communication. The cost efficiency and the reliability of PSLV has been established in the segment of the smaller satellites. India already boasts of 30 to 35% cheaper launches than other countries. Whereas Communication satellites are heavier, weigh 2 to 5 tons and need big boosters. GSLV series of vehicles are designed to hoist heavy satellites into the geosynchronous orbits 36,000km above the equator, where the satellite moves in tandem to earth’s rotation and hence service of satellite is available to the user all the time. GSLV (Geosynchronous Launch Vehicle) can carry satellites weighing over 1.5 tonnes to 4 tonnes. For heavier satellites of over 4 tonnes India employs Ariane-6 rocket of European Space Agency. Satellite launching services of foreign providers are very high. ISRO with three consecutive successful launches can now induct GSLVs for launch of heavy commercial satellites. Previous successful launches with the indigenous cryogenic engines were GSLV-D5 of January 2014 and GSLV-D6 August 2015 that launched GSAT-14 and GSAT-6 satellites into the designated orbits.

About the Launch & Satellite

The 49 meter- long, GSLV MkII, weighing 450 tons, powered by an indigenous cryogenic engine CE-7.5, lifted off from the second launch pad of Satish Dhawan Space Centre, Sriharikota delivered the satellite with remarkable precision. Launch was delayed by 40 minutes due to gas leak in a ground circuit. INSAT-3DR weighed 2211 kg of which 1225 kg is propellant. The propellant helps in satellite to fire up from the GTO to geostationary orbit and to maintain the satellite in the orbit slot during its life time. It is an advanced satellite with an imaging system, an atmospheric Sounder, Data-Relay Transponder & Satellite-aided search and Rescue Transponder. Imaging system with infrared and color camera can provide better night time pictures, images storms. Camera will take images every 26 minutes and its life span is 10 years.  Sounder would collect data on humidity, temperature and ozone data from different layers of atmosphere. The satellite has solar arrays, generating power. This satellite will track storms and tropical cyclones, will relay data from remote weather stations and ocean buoys to weather forecast centers, precisely indicate distress signals from ships and planes, aiding in search and rescue operations. INSAT-3DR will supplement the services of INSAT-3D launched in 2013.  INSAT-3DR now joins the conglomerate of meteorological satellites operated by ISRO- KALPANA, INSAT-3A and INSAT-3D.

Teething Problems with GSLV                                                     

India’s tryst with GSLV which began in 1986 was beset with many obstacles. When India announced its decision to start the project, several countries stepped forward to help and train personnel. Indeed, US and French companies had put forth their proposals. But India declined them because of high costs. Eventually India clinched an agreement with Russian company Glavkosmos by 1990 for supply of seven cryogenic engines of 7.5 tons thrust along with the transfer of cryogenic technology. But in 1993 irked by the Indo-Russian deal, US severely objected Russia selling cryogenic technology to India as this would be a violation under the Missile Technology Control regime (MTCR).  As per MTCR guidelines, members established a “no undercut” policy means if a member denies sale of technology to another country, then the policy has to be strictly adhered by all other members. Further developed countries felt that their business interests would be severely threatened by India’s entry into the heavy satellite-launch business. Under pressure Russian company backed off from transferring technology, but supplied cryogenic engines and an additional mock-up engine. As a result, ISRO had to single-handedly sweat out to the technology which was zealously protected by all nations. Indigenous engines were eventually built at Liquid Propulsion Systems Centre, Thiruvananthapuram.

GSLV Variants

GSLV is a three stage launcher and ISRO has three variants- MkI, MkII, MkIII. All these variants have the solid-fuel first stage and a liquid fuel second stage powered by Vikas engine. The third stage of MkI uses the Russian cryogenic engines while the third stage CUS (Cryogenic Upper Stage) of MkII and MkIII have the indigenously developed engines CE-7.5 and CE-2- respectively. MkIII developmental flight is scheduled for launch by December 2016 is capable of carrying much heavier payloads. It will piggy-back GSAT-19 communication satellite. Once MkIII also establishes its reliability India will be become self-sufficient in terms of launching capacities. GSLV F-05 is an MkII variant capable of carrying payloads of around 2.5 tons. MkII has assured ISRO of its reliability during its two developmental flights. Unlike in developmental flight, during operational flight (the current launch) flight parameters (like altitude, relative velocity, time etc) or flight routes will not be tested.

Cryogenic Technology

Cryotechnology is incredibly difficult. In general, three types of rocket fuels are used- Solid, Liquid and gaseous. Solid fuels despite releasing more amount of energy than liquids are not preferred because of their high density. Liquid fuels flow and release more energy than gaseous fuels. It is established that when hydrogen gas burns in presence of oxygen, the combustion reaction generates 30% more thrust than other rocket fuels. In cryogenic technology, both hydrogen and oxygen are cooled to such a low temperature that they become liquids, occupy less space and start flowing. Hydrogen and Oxygen are liquefied under very low temperatures. Hydrogen is cooled to -253°C and Oxygen to -183°C and stored in pressurized chambers with extreme care as they are brittle, explosive in nature and can evaporate quickly. These propellants can’t be pumped into combustion chambers using normal pumps, special turbo pumps are to be employed. All operations must be condensation free. Presence of moisture can be disastrous for a launch. The magnitude of the extreme complexity is truly onerous.

So far ISRO conducted 10 launches with GSLV starting with GSLV-D1 (Mk1) in April 2001. Of which four launches have failed, one was a partial success and with the latest meticulous launch India seems to have tamed the “naughty boy” (GSLV fondly recalled by Indian scientists) GSLV. With this success, ISRO is now geared to launch second robotic mission to Moon Chandrayaan-2 in 2018 with a GSLV MkII variant. Moreover, with Space X’s Falcon 9 exploding ahead of its scheduled flight, global markets are experiencing the crunch of reliable launch vehicles for heavy satellites. GSLV F-05 successful launch boosted and substantially improved ISRO’s chances of making a mark in satellite launching services as a reliable player. ISRO’s reliability with MkIII would further establish its stature as trusted player facilitating its entry into the $300 billion global satellite-launching industry.

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