putnanja wrote:From the
GSLV-D5 documenton ISRO site
ok, noobie question, so please don't laugh
The first stage which is solid provides altitude gain of almost 70kms, and that is while trying to escape the earth's gravity. However, the CUS provides altitude gain of around 73kms in outer space where the earth's pull will be less. How exactly is the cryogenic stage providing better capability? does it have to do with the size/propellants required for cryogenic stage as compared to the solid stage?
A cryogenic engine is needed after a certain amount of time (rather payload weight and insertion needs) because we need to move a certain amount of fuel and oxidizer at a sufficiently fast rate to impart a sufficient increase in velocity(deltaV). To do that - solid and liquid traditional fuel cannot do that rapidly enough as the rate of pumping versus fuel efficiency is not possible to be achieved with current traditional solid and liquid noncryogenic fuels.(solids are not pumped but burn as is where is and the rate is determined by altering the surface area of the burning solid fuel to put it simply) For oxygen and hydrogen in gaseous form the problem is the holding tanks for these in gaseous form would be just too large offsetting fuel transmission needs (good) to tank weight (bad).So we need to hold the fuel in as efficient form in smaller tanks . Verner Von Braun found out that this could be overcome by holding the gaseous fuel as cryogenic liquids (LOX - liquid oxygen) and Liquid hydrogen (LH2) and this allows compact storage in weight saving smaller tanks and the gas can now be "vaporized" at the time of injection into the ignition chamber but be held cryogenically till then during pumping so we can now throw a huge amount of efficient fuel rapidly allowing a bigger "bang for buck" though the bang is a controlled one
The problems we face are one of handling that cryogenic fuel - holding pumping and efficiently igniting in a controlled manner this fuel. Not so easy as metals etc behave differently at such low temperatures so the holding containers, pumps etc must work properly both at cryogenic temperatures as well as in the vacuum of space.
Just to indicate how complex this is the rocket cone gets heated so much that it should melt so part of the cryogenic fuel actually circulates around the engine nozzle (the inverted aluminium bucket
) to cool it and simultaneously gets converted to gaseous form to enter the ignition chamber.
If I am right there is some photo showing the external temperature of the cryogenic rocket engine nozzle which is technically cool enough to put a hand on it but for the fact we cannot stand near the rocket when it is firing !! I cannot seem to get hold of that picture.
Hoe this helps
If you want to read some more see
http://www.slideshare.net/pandu_sravs/c ... nes-report
