Lift Off Time
(Subject to change)
August 12, 2021 – 00:13 UTC | 05:43 IST
Mission Name
Launch Provider
(What rocket company is launching it?)
Indian Space Research Organization (ISRO)
(Who’s paying for this?)
Indian Space Research Organization (ISRO)
Launch Location
Second Launch Pad, Satish Dhawan Space Centre, India
Payload mass
2,268 kg (5,000 lb)
Where is the satellite going?
Geostationary Transfer Orbit (GTO)
Will they be attempting to recover the first stage?
No, this is not a capability of ISRO
Where will the first stage land?
It will crash off the coast of India in the Bay of Bengal
Will they be attempting to recover the fairings?
No, this is not a capability of ISRO
Are these fairings new?
How’s the weather looking?
No weather information is available yet
This will be the:
– 79th mission for ISRO
– 14th launch of a GSLV Mk I or Mk II rocket
– 1st launch of a GSLV Mk II rocket since 2018
– 77th orbital launch attempt of 2021
Where to watch
Official livestream

What’s all this mean?

The Indian Space Research Organization (ISRO) will be attempting to launch an Earth observation satellite for India. Geo Imaging Satellite (GISAT)-1 will arrive in a geostationary orbit and will hover over the longitude line of 85.5 degrees east. The satellite will be launched on a Geosynchronous Satellite Launch Vehicle Mk II (GSLV Mk II) rocket, which has the capability to lift up to 2,700 kg (6,000 lb) into a geostationary transfer orbit (GTO).

What is EOS-03 (GISAT-1)?

EOS-03, more commonly referred to as GISAT-1, will be the first satellite in at least a pair that will be outfitted with instruments to conduct Earth observation tasks. The second satellite, EOS-05 (GISAT-2) is expected to launch sometime in 2022. The main goal of GISAT-1 is to provide near real time, high resolution images of Earth.

gisat-1, eos-03, isro, gslv mk ii
The GISAT-1 satellite just before encapsulation into the payload fairings. (Credit: ISRO)

Once both satellites are in orbit and are fully operational, they will be able to provide images with resolution ranging from 42 meters per pixel to 318 meters be pixel. Images will be taken in intervals of five minutes for selected field regions and 30 minutes for the entire Indian land mass at 42 meters per pixel.


To acquire these images, GISAT-1 is equipped with a Ritchey–Chrétien telescope (RCT), which is a variant of a Cassegrain telescope. It uses a primary hyperbolic mirror and a secondary hyperbolic mirror. The use of two mirrors in this case eliminates any spherical aberration typically caused by the use of one mirror. An example of a design that uses one mirror would be a Newtonian telescope. Therefore the RCT also allows for a larger use of the entire field of view since the edges generally are not disturbed by spherical aberration. Some other examples of RCT telescopes used in space are the Hubble Space Telescope (HST) and the Subaru telescope at Mauna Kea Observatory, United States.

ritchey chretien, telesopes, diagram
A diagram of the Ritchey Chretien telescope. The large mirror to the right is the primary mirror, while the small one to the left is the secondary mirror. (Credit: TPO Telescopes)

The specific RCT telescope in use on the GISAT-1 satellite has a focal length of 700 mm. For comparison, the Hubble Space Telescope, which has a primary mirror with a diameter of 2.4 m, has a focal length of 57,600 mm. So GISAT-1 is equipped with a rather small telescope when compared to HST.

Imaging Capabilites

GISAT-1 can image in multispectral and hyperspectral at various resolutions. Multispectral means that the images taken can be viewed in multiple bands, usually ranging from three to ten bands, which are all wide, and encapsulate various wavelengths. Hyperspectral means shortening the bands and introducing a larger number of them. There could be hundreds or thousands of bands which include small number of wavelengths.

For GISAT-1 in particular, the multispectral imaging uses six channel, or bands, and ranges in wavelengths from 0.45 to 0.875 micrometers (μm). This is in the visible to near-inferred range. The first hyperspectral imaging uses 158 channels and has a resolution of 318 meters per pixel. These channels range from 0.375 – 1.0 μm, which is just on the edge of the ultraviolet, but also within the visible to near-infrared part of the electromagnetic spectrum. Finally, the other hyperspectral imaging contains 256 channels and ranges from 0.9 – 2.5 μm, which is almost entirely in the infrared part of the spectrum.

With a large variety of light imaging capabilities, GISAT-1 will be able to provide a plethora of views in various types of light. This can be advantageous, as different objects on the ground appear differently depending on weather and atmosphere conditions

What is GSLV?

The Geosynchronous Satellite Launch Vehicle (GSLV) rocket, which first flew in 2010, is the Indian Space Research Organization’s (ISRO) heavy lift launcher for placing satellites in high, geostationary orbits around the Earth. The Mk II variant has the capability to carry up to 2,700 kg (6,000 lb) into a geostationary transfer orbit (GTO). This specific variant also features three total stages. Each stage actually uses a different type of fuel. The first stage uses solid fuel, the second stage uses liquid fuel, and the third stage uses cryogenic fuel.

gslv mk II, isro
GSLV Mk II poised on the launch pad ahead of the launch of the INSAT-3DR satellite. (Credit: ISRO)

Stage 1 and Strap Ons

The first stage of the GSLV Mk II vehicle consists of a 139 ton solid rocket motor, which has a nominal burn time of 100 seconds. Contrary to other rockets such as SLS and the Atlas V, GSLV Mk II has a center core which uses solid fuel and four strap on boosters, which are all powered by liquid propellant. Specifically, the solid fuel used in the center core is Hydroxyl-terminated polybutadiene (HTPB) and can produce 4,700 kN of thrust. As for the liquid strap-ons, they use unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide (N2O4) and have the capability to produce 680 kN of thrust each for about 160 seconds. Each strap on booster uses one Vikas engine.

Stage 2

GSLV Mk II features a liquid propellant powered second stage, which uses the same hypergolic propellants and engine as the strap-on boosters. The unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide (N2O4) propellants feed into a more vacuum optimized Vikas engine, which has the capability to produce 800 kN of thrust for about 150 seconds.

Stage 3

The third and final stage uses cryogenically cooled liquid propellants. These propellants are liquid oxygen (LOx) and liquid hydrogen (LH2). Known as the Cryogenic Upper Stage (CUS), ISRO developed an engine specifically for this stage. It is known as the CE-7.5 and uses a staged combustion system cycle. For more information on the staged combustion system and how different engines work, check out Everyday Astronaut’s video and article on the topic. The CE-7.5 has the capability of producing 75 kN of thrust in a vacuum and can burn for up to 720 seconds.

ce-7.5, isro
The CE-7.5 engine mounted to the cryogenic third stage. (Credit: ISRO)
  1. Actually the first stage SRB is of 139 tons and not 125 tons. Earlier it used to be 125 but was updated since

  2. In your tour with musk,I heard using a hypergolic upper stage is inefficient,but this rocket is having its 1st stage strap on motors and 2nd stage power by costly hypergolics. This is absurd. If wish to know if there is any valuable reason for having such vast usage of hypergolics in many stages. Thank you.

    1. Hypergolic fuel are easily combustible as they start burning just by coming in contact hence protecting us from stage failure. I see this to be the only valid point. But yeah they are hard to handle as they are toxic to humans.

    2. The reason ISRO has 1st and 2nd Stages of GSLV (and 2nd and 4th of PSLV) using Hypergolic Fuels is mainly historical and complexity of rocket engine development.

      It’s way easier to develop and build engines that use Hypergolic propellents that can stored at “room temperatures” and burns without the need for igniters. Cryogenic propellents (LOX/LH2 or LOX/ Liquid CH4) or Semi-Cryogenic propellents (LOX/RP-1) given they have to be stored and used at Cryogenic temperatures and have more complex Combustion Cycles.
      This is true for most Space Entities.

      But ISRO did crack that tech about a decade ago and now does have the CE-7.5 and CE-20 LOX/LH2 Upper Stage engines. It has plans to replace the Hypergolic Stages of GSLVs to LOX/RP-1 ones (SCE-200 is in development).

      Eventually ISRO plans to replace GSLVs and PSLVs with ULV (Unified Launch Vehicle) and RLV (Reusable Launch Vehicle) and do away with Solid and Hypergolic stages completely. I plan to make a video about in in my youtube channel Mars2Eris (hopefully soon)!

      Besides SpaceX, I find ISRO the other interesting Space Entity to follow!

    3. This stage runs on dimethyl hydrazine and nitrogen tetroxide. Not momnomethyl hydrazine.

  3. the satellite is destined to GEO (geostationary earth orbit). but article showing GTO (geostationary transfer orbit)

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