What they talk about when they talk about the GSLV?

The GSLV-F10/EOS-03 mission failed on August 12, 2021. The vehicle faced an issue in it’s third cryogenic stage.

What does ISRO mean when they say GSLV? There is a lot of confusion between the GSLV Mk I and the GSLV Mk II. The YouTuber Gareeb Scientist raised this question in a video he posted on August 8, 2021. He provides the reasons for this confusion.

I believed the first version of the story shared in Gareeb Scientist’s video. I believed that the Mk I was a reference to the GSLVs which flew with the Russian cryogenic engine, KVD-1. And, thought that the Mk II referred to the GSLV which flew with the Indian cryogenic engine, CE-7.5.

This version was shared by ISRO in the brochure of the GSLV-D3 which flew on April 15, 2010. ISRO has removed this brochure from it’s website. But, there is an archived version online as well as on the VSSC website [PDF]. Page two of this brochure carries this explanation.

The Wikipedia page for GSLV still references this explanation and describes variants in this manner. I think that this has contributed to this confusion.

ISRO seems to have changed this version of the story in 2015 in an e-book published on its website, Fishing Hamlet to Red Planet. You need an epub reader to read the book. In an essay by R V Perumal titled, Evolution of the Geosynchronous Satellite Launch Vehicle, he mentions that the GSLV Mk I was actually a modified version of the PSLV with a cryogenic upper stage. However, since the Cryogenic Stage did not work out for the PSLV, hence the idea of the GSLV Mk I was dropped. Perumal was the Project Director for the PSLV and GSLV and later the Director, Liquid Propulsion Systems Center (LPSC). I think I would trust this version.

Since there is no Mk I and all the flights of the GSLV are what ISRO called the Mk II project, it seems ISRO just dropped the Mk II and began calling the launch vehicle GSLV in 2017. This change is also seen on the ISRO website on the GSLV page from 2017.

The GSLV Mk III is a totally different project. I think the GSLV tag got attached to it only because it primarily delivers its payload to a geostationary transfer orbit.


Addendum – August 17, 2021

In response to this blog post @zingaroo replied on Twitter stating that ISRO had always called the GSLVs with the Russian cryogenic engines as the Mk-I and the ones with the Indian cryogenic engines as the Mk-II. He provided two examples of the same from the past.

He presents evidence from the magazine, SPACE-India April-June 2003, Page 11. Also from Gopal Raj’s book Reach for the Stars published in 2000.

It seems ISRO is also re-writing history in a way. It seems that the project started somewhere after 2010.