ISRO officials have declared the PSLV mission a total success in traditional post-launch speeches at the Satish Dhawan Space Center.

ISRO reports all six secondary payloads from Indonesia, Canada and the United States have separated as planned.

T+plus 22 minutes, 40 seconds. Astrosat separation confirmed in a very precise orbit 650 kilometers above Earth.

Six small secondary payloads will release from the fourth stage in the next few minutes.

T+plus 22 minutes. Fourth stage cut off confirmed. Standing by for Astrosat deployment.

T+plus 21 minutes. The fourth stage engines will shutdown in about one minute to set up for deployment of the Astrosat spacecraft, which is scheduled for T+plus 22 minutes, 32 seconds.

T+plus 20 minutes. The PSLV is now traveling at 6.87 kilometers per second and downrange distance is nearly 6,600 kilometers.

T+plus 17 minutes. The fourth stage engines are now firing, generating nearly 3,300 pounds of thrust.

T+plus 15 minutes. Standing by for ignition of the PSLV's fourth stage, which will fire for 4 minutes, 59 seconds. For this mission, engineers filled the fourth stage with 1.6 metric tons of hydrazine and nitrous oxide, short of the stage's 2.5-ton capacity.

The fuel load means the stage will burn for a shorter time than most PSLV flights.

T+plus 10 minutes. The PSLV's solid-fueled third stage has jettisoned, and the liquid-fueled fourth stage is set to ignite at T+plus 16 minutes, 57 seconds.

T+plus 7 minutes. The PSLV's third stage has consumed its solid propellant supply, beginning a more than 10-minute coast phase before ignition of the fourth stage.

T+plus 4 minutes, 45 seconds. The solid-fueled third stage has ignited after separation of the PSLV's second stage. This burn will last approximately 112 seconds.

T+plus 2 minutes, 55 seconds. The 10.5-foot-diameter aluminum payload fairing has jettisoned now that PSLV has reached the thin upper atmosphere.

The liquid-fueled Vikas second stage engine continues firing.

T+plus 2 minutes, 15 seconds. ISRO confirms separation of the PSLV first stage and ignition of the second stage for a burn of two-and-a-half minutes.

T+plus 90 seconds. The six ground-lit boosters have jettisoned.

T+plus 30 seconds. Two strap-on boosters have ignited to give the PSLV an extra boost as it climbs into the sky atop more than 2 million pounds of thrust.

Liftoff of a Polar Satellite Launch Vehicle with Astrosat, India's first dedicated astronomical satellite.

T-minus 90 seconds. In the final minute, computers will prepare the PSLV for launch by arming its solid-fueled motors.

T-minus 2 minutes and counting. When the countdown reaches zero, the PSLV's first stage, comprised of five solid-fueled segments, will ignite along with four of the launch vehicle's six ground-lit strap-on boosters.

The boosters will ignite in a staggered sequence two-tenths of a second apart. Two more boosters will ignite at T+plus 25 seconds after the PSLV clears the launch pad.

T-minus 3 minutes and counting. A check of the weather conditions show all parameters are acceptable for launch.

T-minus 5 minutes and counting.

T-minus 12 minutes. The automated launch sequence has been initiated.

T-minus 14 minutes. The PSLV's automated launch sequence has been authorized to begin at the countdown's T-minus 12 minute mark.

T-minus 15 minutes and counting. Everything is on schedule for launch at 0415 GMT (12:15 a.m. EDT).

The PSLV has received the final authorization to launch, and automated countdown sequence will oversee the final preparations to configure the 700,000-pound rocket for liftoff.

Today's launch will use the largest version of the Polar Satellite Launch Vehicle called the PSLV XL, with six strap-on motors with a length of 12 meters, or 39 feet.

The PSLV is a four-stage rocket with a solid-fueled first and third stages and liquid-fueled second and fourth stages.

We are now streaming live video from India's Satish Dhawan Space Center, where all launch preparations are on track for liftoff in 25 minutes.

The PSLV launch team reports the Sriharikota range and all weather conditions are "go" for an on-time launch.

T-minus 60 minutes. Today's launch will mark the:

31st PSLV launch since 1993

49th Indian orbital launch attempt since 1979

10th PSLV XL launch since 2008

3rd PSLV launch of 2015

1st dedicated Indian astronomical satellite

54th global space launch attempt in 2015

All launch preparations are on schedule for liftoff of the Polar Satellite Launch Vehicle on Monday at 0430 GMT (12:30 a.m. EDT).

The mobile service tower at the PSLV launch pad has been retracted to the launch position 150 meters away from the rocket, and no problems are reported in the countdown.

The first activity after the countdown began Saturday morning, Indian time, was the filling of the PSLV's liquid-fueled fourth stage with hydrazine and nitrogen tetroxide propellants.

The fourth stage will inject the Astrosat spacecraft into an circular orbit with about 404 miles (650 kilometers) above Earth at an inclination of 6 degrees to the equator. The twin-engine fourth stage, named the PS4 or L2.5, will fire for nearly 5 minutes in the last phase of the launch.

The mobile gantry at the launch complex, located on Sriharikota Island on India's east coast, was retracted more than 150 feet from the rocket early Monday, local time, to prepare for fueling of the PSLV's second stage with liquid propellant.

The PSLV's first and third stages, along with the six strap-on boosters, burn solid propellant already packed inside the motor casings.

Live video of the final countdown will begin about 30 minutes prior to launch, according to ISRO. The webcast will be seen on this page.

India's first dedicated astronomical observatory is awaiting liftoff Monday aboard a Polar Satellite Launch Vehicle, which will loft the satellite into a 400-mile-high orbit to begin a five-year mission studying the births and deaths of stars.

The Astrosat mission, estimated in Indian news reports to cost $27 million, will peer into the cosmos with a suite of X-ray and ultraviolet instruments, looking at collapsed stars, haze-enshrouded stellar factories and black holes.

Liftoff is set for 0430 GMT (12:30 a.m. EDT) Monday from a launch pad at the Satish Dhawan Space Center on India's east coast, or 10 a.m. local time in India.

The 3,335-pound (1,513-kilogram) Astrosat spacecraft hosts four X-ray science instruments and an ultraviolet telescope.

"Astrosat's five payloads are chosen to facilitate a deeper insight into the various astrophysical processes occurring in the various types of astronomical objects constituting our universe," officials wrote in a press kit released by the Indian Space Research Organization.

Astronomers in India plan to use Astrosat to survey the galaxy for black holes and measure the intense magnetic fields generated by neutron stars, the collapsed ultra-dense remnant left behind after supernovas.

Astrosat will also observe X-ray binaries -- systems where a black hole or neutron star can suck matter away from a nearby star, emitting powerful signals visible to X-ray telescopes.

The observatory's ultraviolet imaging telescope will scan the sky in visible, ultraviolet and far ultraviolet light, focusing on star-forming clouds throughout the nearby universe and infant solar systems closer to home.

Scientists will also coordinate observations between Astrosat's ultraviolet and X-ray sensors, which were developed by Indian scientific institutions and the University of Leicester in Britain.

The 145-foot-tall (44.4-meter) Polar Satellite Launch Vehicle will deploy Astrosat into a 404-mile-high (650-kilometer) orbit inclined 6 degrees to the equator about 22 minutes after liftoff.

Fitted with four enlarged strap-on solid rocket boosters, the PSLV will also deliver six commercial secondary payloads to orbit.

Four satellites owned by Spire Global, a San Francisco startup aiming to develop spacecraft for commercial weather applications, are fastened aboard the PSLV for Monday's launch. The Lemur 2 CubeSats, each about the size of a toaster oven, carry maritime tracking and GPS radio occultation payloads.

The exactView 9 ship-monitoring satellite built by the University of Toronto Institute for Aerospace Studies Space Flight Laboratory is also packaged as a secondary passenger on Monday's launch. About the size of a small briefcase, exactView 9 is owned by exactEarth Ltd. of Canada, which specializes in vessel tracking services.

Indonesia's Lapan A2 microsatellite carries video and digital cameras to image Earth from orbit, plus a ship-tracking payload and amateur radio equipment.

Monday's launch marks the 10th flight of the PSLV XL configuration, and the PSLV's 31st flight overall since 1993.