India has deployed its EMISAT intelligence-gathering satellite Monday via a PSLV launch from the Satish Dhawan Space Centre. The launch – which was also carry twenty-eight small satellites and demonstrate operation of the vehicle’s fourth stage as an orbiting experimental platform – lifted off at 09:27 local time (03:57 UTC).



Monday’s launch, the second of the year for India’s Polar Satellite Launch Vehicle (PSLV), was tasked with a series of maneuvers for the rocket’s upper stage to insert twenty-nine deployable payloads into their pre-planned orbits over the first two hours of its flight.

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.

The primary payload, EMISAT, is a 436-kilogram (961-pound) satellite to be operated by India’s Defence Research and Development Organisation (DRDO).

Constructed by the Indian Space Research Organisation (ISRO), also responsible for conducting Monday’s launch, EMISAT is based around the Indian Mini Satellite 2 (IMS-2) bus with solar panels providing 800 watts of power for the spacecraft.

Its mission is officially stated as “electromagnetic spectrum measurement”. 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.

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 – as indicated in the mission’s official description – and then using these to determine the nature and location of the transmission’s source.

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.

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.

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) – with larger satellites’ 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.

Twenty of the CubeSats aboard Monday’s 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.

Each satellite, known individually as a Dove, carries an imager that can capture pictures of the Earth’s 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.

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 – inferring atmospheric conditions such as temperature, pressure and humidity from how GPS signals are affected by passing through atmosphere.

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 – while AirSafe performs a similar function for the Automatic Dependent Surveillance Broadcast (ADS-B) transmitters carried aboard aircraft.

Two satellites launched for Texas-based AST&Science, through its Lithuanian subsidiary NanoAvionics. Both are six-unit CubeSats – measuring 10 by 20 by 30 centimeters (3.9 by 7.9 by 11.8 inches) – based around the M6P platform that NanoAvionics have been developing for future customer missions.

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 – which will validate the use of satellites to relay data for internet of things (IoT) devices.

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’s 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.

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.

After deploying all of its payloads, PSLV’s 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’s own batteries.

The test that began with Monday’s 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’s launch will test the upper stage for a longer duration.

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’s ionosphere.

Monday’s launch was the forty-seventh flight for India’s 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 – including sub-geosynchronous transfer trajectories – 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’s most successful and reliable rocket.



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’s smallest configuration, and those that require its most powerful form.

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 “Core Alone”.

The PSLV-G configuration was the original version of PSLV – 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.

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.

Across all of these configurations, the PSLV’s four core stages remain common.

Monday’s 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.

ISRO has two Vehicle Assembly Buildings, the first was used to assemble PSLV C45 for Monday’s launch, while the second – newly completed – 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.

PSLV’s first stage, or PS1, is solid-fuelled and powered by an S-138 motor. The PS0M or PS0M-XL boosters – four PS0M-XLs in the case of Monday’s launch – are clustered around the base of the first stage. At the zero mark in Tuesday’s countdown, PSLV’s first stage ignited followed 0.42 seconds later by one pair of boosters.

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 – with the first pair separating 69.9 seconds after liftoff and the second pair following two-tenths of a second later.

PSLV’s first stage burned for another 38.7 seconds after booster separation – 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 – used on earlier members of the Ariane family or rockets – and is built under license in India.

Vikas consumes UH25 propellant, a mixture of unsymmetrical dimethylhydrazine and hydrazine hydrate, oxidized by dinitrogen tetroxide.

After the second stage burned out and separated, PSLV’s third stage – HPS3 – 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.

PSLV’s fourth stage – PS4 – 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’s 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.

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 – about 504 kilometers (313 miles, 272 nautical miles), and the slightly lower inclination of 97.5 degrees. The first of PSLV’s 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.

The PS4’s final two maneuvers were made using its reaction control system (RCS) maneuvering thrusters. The first, beginning 16 minutes and 42.5 seconds after the final payload had been deployed, lasted 63 seconds and lowered the perigee further to 485 kilometers (301 miles, 262 nautical miles). Forty-six minutes and 11.5 seconds later, another 116.5-second firing circularized the orbit again. Once it reached this orbit the launch wascomplete, and the upper stage began its own experimental mission.

Monday’s launch was India’s second of the year, following on from January’s PSLV mission which deployed the Microsat-R satellite and the Kalamsat v2 experimental platform built around the rocket’s upper stage. At the time Microsat-R was understood to be an imaging satellite, however subsequent events have revealed that it was instead a target for India’s development of an anti-satellite (ASAT) weapons system.

The PSLV launch comes five days after India conducted the first successful test of its ASAT system, using a PDV Mk.II missile launched from Kalam Island to destroy Microsat-R in orbit.

India is the fourth country to demonstrate such a weapon by destroying a satellite: both the Soviet Union and United States tested anti-satellite weapons during the Cold War, while the People’s Republic of China conducted an ASAT test against a decommissioned weather satellite in 2007.

In 2008, the United States used a modified Standard Missile 3 (SM-3) – designed as an anti-ballistic missile system – to destroy the crippled USA-193 reconnaissance satellite which had failed immediately after launch in late 2006.

While the US operation was billed as necessary to mitigate the danger of a fully-fuelled satellite falling to Earth, it was widely seen as a response to the Chinese test.

India’s test has raised concerns internationally about the creation of unnecessary debris in orbit around the Earth. For as long as they remain in orbit, fragments of the destroyed satellite pose a danger to other spacecraft, which may have to maneuver to avoid collisions or sustain damage if they are unable to maneuver or are hit by debris too small to track.

A simulation of India's anti-satellite test from @AGItweets estimates the demonstration created 6500 pieces of debris (larger than 0.5 cm). https://t.co/tFxfQVvlyB (video courtesy of Analytics Graphics) pic.twitter.com/jk9NjXR3tB — Michael Sheetz (@thesheetztweetz) March 29, 2019

Planet Labs – one of the customers for Monday’s launch – put out a statement condemning the test on the grounds that “space should be used for peaceful purposes, and destroying satellites on orbit severely threatens the long term stability of the space environment”.

It is too early to see if the test will have any impact on the companies flying their payloads aboard Indian rockets, which have proven popular for launching small satellites at low cost.

India’s next launch is currently scheduled to fly later in April, with another PSLV deploying the Cartosat-3 Earth observation spacecraft. A mission for the larger GSLV Mk.III rocket, carrying the Chandrayaan-2 spacecraft bound for the Moon, is also slated for liftoff at the end of the month.