First a couple of points further comparing SR-71 to Atlas rocket:

The liftoff weight of the Atlas being 200,000 lbs with a thrust of 300,000 lbs gives 200,000 lbs to maintain status quo flight (hover) with 100,000 lbs thrust to effect acceleration. With 200,000 lbs mass accelerated with 100,000 lbs of thrust yields a 1/2 g acceleration at launch. As the tank empties the same thrust is applied to a lighter vehicle resuling in in increase of acceleration to (reportedly) 6 g at staging.

The SR71 maintains status quo flight by being supported by the air through which it passes so most of its thrust can be used for acceleration with altitude maintained as a side effect of its speed through the air. With a reported weight of 140,000 lbs and a (reported) thrust of apx. 65,000 lbs also yields an acceleration of just slightly less than 1/2 g. Like the Atlas, as its fuel burns it also gets lighter for the same thrust and so its acceleration also increases.

Additionally the SR-71 "launches" from 30,000ft at 600 mph above 75% of the aptmosphere after midair refueling whereas the Atlas launches from sea level at zero mph. Atlas has to burn an enormous amount of fuel just to get to where the SR-71 starts fully fueled with nearly 3 times the effective fuel load and nitrogen reaction mass on its side.

As to the question of lack of control rockets you are mistaken. All of those ultra high altitude aircraft do have control rockets as there is not enough air for the airfoil control surfaces to work at those altitudes. I guess you didn't see them because you weren't looking for them or they didn't have those compartments open when you looked.

Regarding ramjets as used for orbital flight the principle works like this: The SR-71 has a bypass duct to take the ram air past the turbofan at high speed. as the speed increases more air is ramed into the engine without the turbofan getting in the way. The more air the engine has the more fuel it can burn, the more fuel it burns the more thrust it has and the faster it goes, the faster it goes The more air the engine has the more fuel it can burn, the more fuel it burns the more thrust it has and the faster it goes etc... to the limit you can pump fuel into the combustion chamber. The idea of the hypresonic air breather is to achieve most of its orbital speed and burn most of its fuel while it is still in the aptmosphere in one big spurt and then to coast on the rest of the way out of the aptmosphere into orbit. Surely some early designs did contemplate using airbreather/rocket combinations but the ideal and the current designs are pure airbreathers.

Finally, as I couldn't find the performance envelope of the SR-71 only the speed of quoted of 2200 mph is not quoted using the standard nomenclature ASL (at sea level) If we assume that its speed as reported is 2200mph ASL then at performance altitude of 85,000 ft it is above 90% of the aptmosphere so its ground speed would be ten times more than its air speed thus 22,000 mph which is orbital speed.

Additionally its range at 2200mph ASL for (stated) endurance of one hour gives a range of only 2200 miles. The range as stated from various sources I have seen has been anywhere from 2200 (official) to 10,000 (unofficial but reliable) miles. If 10,000 miles is true then it is certainly suborbital.

<font size=-1>[ This Message was edited by: SAMU on 2002-08-21 21:41 ]</font>