What is a cryogenic engine

GSLV MK2 versus Falcon 9 - reasons for big differences in performance

There are many factors that affect the mass a launcher can put into orbit. In this case we need to consider not only the thrust of the first stage, but also its efficiency, measured in rocket science as a specific impulse (I. sp ), which indicates the energy that an engine can extract from a certain mass of propellants.

According to Wikipedia, the first stage of the GSLV MkII has a very low I due to the use of a solid fuel motor sp (237 s), while the boosters have a slightly higher I. sp (262) which is still quite low for liquid motors. For comparison: the Merlin 1D motors of the Falcon 9 Full Thrust reach a speed of 282 seconds.

In addition, the side of the GSLV MkII indicates that the first stage burns for 100 seconds, while the strap-on boosters burn for 160 seconds. This means that for the last 60 seconds of their combustion, the four liquid boosters carry the housing of the first stage, which has become a sheer dead weight.

A look at the take-off mass of both vehicles gives us another reason: Falcon 9 The full thrust takes off at 549 tons, while the GSLV MkII weighs 414 tons. We don't know the exact fuel mass fraction either, but most rockets have around 90 mass% fuel at launch - the GSLV just carries a lot less fuel than the Falcon 9 FT


Jithin Jose

But is that enough to get a 5-fold increase in performance?

Amyine orbit

See the added paragraph on mass. If you combine less efficient motors, less efficient staging (which means you carry dead mass for a minute, far from negligible), and nearly 25% less lift-off mass, that wouldn't surprise me. Keep in mind that we also don't have access to a lot of important numbers: the fuel mass fraction of each vehicle (very important for orbit), trajectory optimizations (I can't find a map but I'm pretty sure I can take off from the ISRO launch complex Getting to LEO requires a dogleg bend during the ascent.


@cesarparent Another very important element is that the thrust difference becomes very large. After 100 seconds, the total thrust of the GSLV MKII is only 3040 kN, since the full core stage has been completed. The Falcon's 9FT thrust continues to increase, in a vacuum it is 8227 kN. This makes a huge difference in payload. Another thing is that the 2nd through 3rd stages of the GSLV are small. The 2nd stage has a low Isp 295s and burns for 150s compared to Falcon 9 348s which burn for 397s. The 3rd stage is very small and is used to generate a little more payload, but still cannot compensate for large losses in the 1st and 2nd stages. You can edit your answer.

Jithin Jose

@ Mark777 but the level 3 specific impulse is much higher (454) and burns for 720 seconds. Doesn't that have enough impact?


We should combine all elements together here, not just one, the 3rd level ISP. It really has the Isp 454, but also a very low thrust of 75 kN. And those kind of upper steps come in handy when you're putting a large payload in a high orbit where you're not dealing much with gravity. In this case, gravity-fighting stages have very little performance. At the moment the 3rd stage is ignited the payload would be very small because it lost a lot of power in the 1st stage mostly and 2nd Combine all the downsides of cesarean section and what I wrote this power will be for Giving GSLV.