64441284 A description fig1 is a schematic diagram illustrating a preferred embodiment of the invention fig1 illustrates at the top left half of the figure the invention in its initial position and at the bottom half of the figure the invention as the components appear when the miv is fully expanded the figure shows an extendible section of nozzle 10 telescoped around the outside of a fixed section of nozzle 12 of a rocket engine 13 the extendible nozzle 10 is fixed in place centered and locked by at least three spaced locking arms 14 each locking arm 14 is formed with a notch 16 into which the rearward end of the fixed nozzle is inserted the radially outer end of the arm 14 is formed with a hook 20 and the outer end of the rear of the extendible nozzle 10 is formed with a circular flange 22 see fig2 the flange 22 fitting inside the hook 20 whereby the rear end of the extendible nozzle 10 is held in place and centered the forward end of the extendible nozzle 10 is centered by a set of at least three spaced centering rods 24 each of which has a finger 25 at its outer end to hold the nozzle end in place a plate with a rearwardly extending circular flange may be used in place of the centering rods 24 a main inflation vessel miv comprising a doughnut shaped nozzle extending inflatable pressure vessel or bag 26 is placed inside the fixed nozzle 12 near its rear end the miv 26 is preferably formed in sections separated by partitions 27 each separating partition 27 having a gas passage valve 31 therein to allow gas to pass from the front.