India has deployed its EMISAT intelligence-gathering satellite Monday via a PSLV launch from the Satish Dhawan Space Centre. The launch \u2013 which was also carry twenty-eight small satellites and demonstrate operation of the vehicle\u2019s fourth stage as an orbiting experimental platform \u2013 lifted off at 09:27 local time (03:57 UTC).<\/p>\n
Monday\u2019s launch, the second of the year for India\u2019s Polar Satellite Launch Vehicle (PSLV), was tasked with a series of maneuvers for the rocket\u2019s upper stage to insert twenty-nine deployable payloads into their pre-planned orbits over the first two hours of its flight.<\/p>\n
Following separation of the last payload, the upper stage will maneuver to a final orbit where it will operate as a research platform, hosting three attached payloads to demonstrate this capability for future missions. The launch also tests out a new configuration for the PSLV, a further intermediate between the lightest and heaviest versions of the rocket.<\/p>\n
The primary payload, EMISAT, is a 436-kilogram (961-pound) satellite to be operated by India\u2019s Defence Research and Development Organisation (DRDO).<\/p>\n
Constructed by the Indian Space Research Organisation (ISRO), also responsible for conducting Monday\u2019s launch, EMISAT is based around the Indian Mini Satellite 2 (IMS-2) bus with solar panels providing 800 watts of power for the spacecraft.
\n![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/03\/2019-03-31-221027.jpg\")
Its mission is officially stated as \u201celectromagnetic spectrum measurement\u201d. It is understood that EMISAT will be used for electronic signals intelligence (ELINT). The satellite likely carries Kautilya, an ELINT package that India has been developing since at least 2014.<\/p>\n
ELINT capabilities are among the most highly-classified and closely-guarded aspects of operation for military satellites with the countries that already operate such spacecraft, and India appears to have taken a similar approach with EMISAT as few details of the satellite or its planned operations have been made public. ELINT missions typically involve monitoring radio signals \u2013 as indicated in the mission\u2019s official description \u2013 and then using these to determine the nature and location of the transmission\u2019s source.<\/p>\n
EMISAT will operate in a circular sun-synchronous polar orbit, at an altitude of 749 kilometers (465 miles, 404 nautical miles) and an inclination of 98.4 degrees.<\/p>\n
Joining EMISAT for the ride into orbit were twenty-eight smaller satellites. These have all been built to CubeSat specifications, a set of standards for small satellites based around common form factors and deployment mechanisms so that each spacecraft does not need custom hardware to carry it aboard a rocket.<\/p>\n
The CubeSat standard has become ubiquitous for small satellites and has played a significant role in their increased popularity in recent years. A single-unit CubeSat has a cubic shape with sides of ten centimeters (3.9 inches) \u2013 with larger satellites\u2019 sizes based around multiples of this unit: for example, a three-unit CubeSat measures ten centimeters along two axes and 30 centimeters (11.8 inches) along the third.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/03\/2019-03-31-214959.jpg\")
<\/p>\n
One of the Spire satellites in the cleanroom.<\/p>\n
Twenty of the CubeSats aboard Monday\u2019s launch are three-unit spacecraft for US company Planet Labs. These Flock-4a satellites represent the next generation of spacecraft in a large Earth imaging constellation that Planet has deployed over the last five years.<\/p>\n
Each satellite, known individually as a Dove, carries an imager that can capture pictures of the Earth\u2019s surface at resolutions of up to three meters. Designed to be low-cost and short-lived, over three hundred of these spacecraft have already been deployed allowing Planet to image each location many times per day so customers to monitor changes in near-real-time.<\/p>\n
Four Lemur-2 spacecraft for another American company, Spire Global, also flew with the PSLV. Each Lemur is a three-unit CubeSat equipped with three payloads: STRATOS instrument measures occultation of signals from GPS satellites \u2013 inferring atmospheric conditions such as temperature, pressure and humidity from how GPS signals are affected by passing through atmosphere.<\/p>\n
SENSE is a receiver for the Automated Identification System (AIS) used by ships, collecting and relaying tracking data from vessels out of range of the shore \u2013 while AirSafe performs a similar function for the Automatic Dependent Surveillance Broadcast (ADS-B) transmitters carried aboard aircraft.<\/p>\n
Two satellites launched for Texas-based AST&Science, through its Lithuanian subsidiary NanoAvionics. Both are six-unit CubeSats \u2013 measuring 10 by 20 by 30 centimeters (3.9 by 7.9 by 11.8 inches) \u2013 based around the M6P platform that NanoAvionics have been developing for future customer missions.<\/p>\n
Named BlueWalker1 and M6P, these are designed to test the platform in orbit for the first time and will validate its three-axis control, communications and propulsion systems. M6P also carries two separate prototype communications payloads for SpaceWorks Orbital and Lacuna Space \u2013 which will validate the use of satellites to relay data for internet of things (IoT) devices.<\/p>\n
The Swiss Astrocast 0.2 satellite will also test communications for IoT devices. It is a three-unit CubeSat to be operated by Astrocast SA, joining the Astrocast 0.1 satellite that was launched aboard SpaceX\u2019s Falcon 9 rocket in December. Astrocast 0.2 is a prototype for a larger L-band communications constellation, allowing the spacecraft and ground terminals to be tested and for its operators to develop an understanding of the characteristics of the radio signals transmitted between the two.<\/p>\n
AISTECHSAT-3, for AISTech of Spain, is a two-unit CubeSat pathfinder for a constellation of ship and aircraft-tracking satellites which AISTech aims to deploy in the near future. Like the Lemur satellites, it is equipped with AIS and ADS-B receivers. The satellite is also known as Danu Pathfinder, as the final constellation will be named Danu.<\/p>\n
After deploying all of its payloads, PSLV\u2019s PS4 upper stage will begin its own demonstration mission which is aimed at proving that the spent stage can host attached payloads in orbit for up to six months after launch. To facilitate this, the PS4 will fly with solar panels for the first time, providing power beyond the limitations of the upper stage\u2019s own batteries.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/03\/2019-03-31-215120.jpg\")
<\/p>\n
The fourth stage with arrays \u2013 via ISRO<\/p>\n
The test that began with Monday\u2019s launch builds on the Kalamsat v2 experiment that was flown on the previous PSLV launch. Kalamsat was battery-powered and designed to operate for about fifteen hours, while Monday\u2019s launch will test the upper stage for a longer duration.<\/p>\n
Three payloads have been attached to the upper stage for this experimental phase of its mission. These are an AIS receiver, the Automatic Packet Repeating System (APRS) amateur radio payload furnished by AMSAT India and Advanced Retarding Potential Analyser for Ionospheric Studies (ARIS), which will be used by the Indian Institute of Space Science and Technology (IIST) to study Earth\u2019s ionosphere.<\/p>\n
Monday\u2019s launch was the forty-seventh flight for India\u2019s Polar Satellite Launch Vehicle (PSLV), a workhorse rocket that ISRO developed in the 1990s to provide access to low Earth orbit, but which has also proved adaptable enough to send small satellites into higher orbits \u2013 including sub-geosynchronous transfer trajectories \u2013 and to deploy missions to the Moon and Mars. PSLV first flew in September 1993, and although the maiden flight failed to reach orbit PSLV has gone on to prove itself India\u2019s most successful and reliable rocket.
\n![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/03\/2019-03-31-221132.jpg\")
<\/p>\n
The EMISAT launch, designated PSLV C45, is the first to use a new version of the rocket, PSLV-QL. Like the PSLV-DL which was first flown in January, the PSLV-QL is designed to accommodate payloads in between those that can be carried by the rocket\u2019s smallest configuration, and those that require its most powerful form.<\/p>\n
The PSLV-QL has four solid rocket motors attached to its first stage to provide additional thrust, as opposed to the six that are used on the heavier PSLV-XL, two on the DL or zero on the smallest PSLV-CA, or \u201cCore Alone\u201d.<\/p>\n
The PSLV-G configuration was the original version of PSLV \u2013 like the PSLV-XL it uses six solid rocket motors, but it has smaller PS0M boosters with S-9 motors instead of the PS0M-XL boosters (with S-12 motors) that are used across the rest of the family.<\/p>\n
The introduction of the PSLV-DL and PSLV-QL configurations allows ISRO to standardize on a single type of booster, so it is unlikely that the PSLV-G will be used for future launches.<\/p>\n
Across all of these configurations, the PSLV\u2019s four core stages remain common.<\/p>\n
Monday\u2019s launch used the Second Launch Pad at the Satish Dhawan Space Centre. Built in the early 2000s to support launches of the PSLV and the larger GSLV, this launch complex uses a vertical assembly building away from the pad to prepare rockets, before they are transported into position atop a mobile launch platform.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/03\/2019-03-31-215949.jpg\")
<\/p>\n
The Satish Dhawan Space Centre \u2013 via ISRO<\/p>\n
ISRO has two Vehicle Assembly Buildings, the first was used to assemble PSLV C45 for Monday\u2019s launch, while the second \u2013 newly completed \u2013 is being used for a GSLV Mk.III rocket that will carry the Chandrayaan-2 spacecraft towards the Moon at the end of this month.<\/p>\n
PSLV\u2019s first stage, or PS1, is solid-fuelled and powered by an S-138 motor. The PS0M or PS0M-XL boosters \u2013 four PS0M-XLs in the case of Monday\u2019s launch \u2013 are clustered around the base of the first stage. At the zero mark in Tuesday\u2019s countdown, PSLV\u2019s first stage ignited followed 0.42 seconds later by one pair of boosters.<\/p>\n
The second pair ignited two tenths of a second after the first, and PSLV C45 began to climb away from Sriharikota. The boosters provided thrust for just under seventy seconds \u2013 with the first pair separating 69.9 seconds after liftoff and the second pair following two-tenths of a second later.<\/p>\n
PSLV\u2019s first stage burned for another 38.7 seconds after booster separation \u2013 before it, too, was jettisoned. The second stage ignited its Vikas engine two tenths of a second after staging, beginning a 152.3-second burn. The second stage, or PS2, uses a single Vikas engine which is derived from the French Viking \u2013 used on earlier members of the Ariane family or rockets \u2013 and is built under license in India.<\/p>\n
Vikas consumes UH25 propellant, a mixture of unsymmetrical dimethylhydrazine and hydrazine hydrate, oxidized by dinitrogen tetroxide.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/03\/2019-03-31-215223.jpg\")
<\/p>\n
C45 during processing \u2013 via ISRO<\/p>\n
After the second stage burned out and separated, PSLV\u2019s third stage \u2013 HPS3 \u2013 took over. This is another solid-fuelled stage with an S-7 motor, which ignited 1.2 seconds after stage separation and burned for about 70 seconds. Once the third stage is all-burnt, PSLV coasted to the highest point, or apogee, of its trajectory. The third and fourth stages separated at 509.7 seconds mission elapsed time, with the fourth stage igniting 18.4 seconds later for its first burn.<\/p>\n
PSLV\u2019s fourth stage \u2013 PS4 \u2013 uses liquid propulsion with two engines burning monomethylhydrazine and mixed oxides of nitrogen. The fourth stage can be restarted for multiple burns, a capability which used during Monday\u2019s launch. The first burn lasted 455.1 seconds, inserting EMISAT into its planned orbit. Spacecraft separation came 45 seconds after the end of the burn.<\/p>\n
One hour and 11.5 seconds after liftoff, the PS4 restarted for a 10.1-second burn, lowering the perigee of its orbit. Forty-eight minutes and 28.9 seconds later a 10.5-second burn circularized the orbit at this lower altitude \u2013 about 504 kilometers (313 miles, 272 nautical miles), and the slightly lower inclination of 97.5 degrees. The first of PSLV\u2019s secondary payloads separated one minute and 25 seconds after the end of this burn, with the remaining deployments occurring over the next four minutes and 45 seconds.<\/p>\n<\/p>\n