Here's video of ISRO's recent test of the S200 solid rocket booster, at Satish Dhawan Space Centre. Meant for use in the upcoming GSLV-MkIII, the S200 is the world's 3rd largest booster of its kind, after the ones used by Ariane-5 and the Space Shuttle (well, since the Space Shuttle is now retired, I guess that would make this the 2nd-largest such booster). China and Russia use purely liquid-fuel technology. Solid rocket boosters offer superior thrust performance in comparison to liquid boosters, but cannot be throttled during flight.
4 comments:
Where did you get the information that solid boosters offer better performance? That is certainly not true. ISRO was foolish to have gone the solid way. Solids are more difficult to manage, offer lower performance and are heavier and as you pointed out cannot be throttled. But they are more reliable (few parts) and can be used to give a quick kick. They are also less suitable for manned spaceflight, the Shuttle and Ares I notwithstanding. France offered ISRO liquid tech but ISRO let that offer lapse many years ago. Now ISRO wants to develop low performance liquids for the GSLV-MkIII.
Solids offer better thrust-to-weight ratio. That's why they were chosen for Space Shuttle and also Ariane. They weren't just chosen on a roll of the dice. The issue with solids is that they're not throttlable, and of course they represent the burden of incorporating yet another technology into your system, and having to maintain distinct knowledge for it.
For Surface-to-Orbit, solids are fine, because to climb and escape the Earth's gravity well, you really need thrust more than you need efficiency. You can do ion engines, etc if you want to maximize efficiency, but those things will never lift you off the ground -- or even off the surface of the Moon.
Speaking as a rocket scientist(really), I'd say it's more complicated than that. Solids can provide high thrust but they don't last as long and their specific impulse (a measure of the momentum imparted to the rocket which is what really matters) is much lower than many commonly used liquids (Kerosene/Oxygen, Hydrogen/Oxygen etc.) Plus the entire rocket motor is the combustion chamber so the entire casing has to be strong enough to withstand pressure. That increases mass. So all solid rockets weigh more than liquid rockets that can carry the same payload to the same orbit i.e. the payload fraction of solids is much lower than liquids - compare the PSLV (two solid stages out of four) with early versions of the Ariane IV or Delta II of the U.S. The Indian rockets are heavy monsters for the same payload carried to orbit.
I think the ultimate metric is cost-per-pound to orbit, which is all that matters in the end. In that sense, solid rocket boosters are leveraging off the expenditure for other programs, like Agni IRBMs, etc.
Similarly, I think it's Morton-Thiokol in the US which manufactures the SRBs for the Space Shuttle, and also the solid motors for their ICBMs. They get a sweet contract on those Shuttle SRBs to ensure they stay in business to manufacture the ICBM motors for national defense.
Note that the new replacement Space Launch System just now announced by NASA for beyond Earth exploration, is also again using those solid rocket boosters. They're not going to go away any time soon.
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