Info request about Space Shuttle controls

[Pedro Mira]

I'm looking for confirmation and info about a "technique" I've read about once, but that I can't find again for the life of me.

I don't remember the name exactly, but it had something to do with "positive energy". And it worked like this: during TAEM, the commander would always try to fly with the speedbrake half-deployed by default, and they made all the maneuvers towards the runway normally, as if the extra drag was inevitable and something they just had to account for. That made it so, if they realized they had too little energy, they could retract the speed brake making the shuttle glide better, as if they had engines. In fact, since the speed brake was controlled by the SSME throttle lever, the commander used this as a "pseudo-throttle", since removing drag is basically the same thing as adding thrust. This technique gave the shuttle pilots a more flexible and forgiving glide.

Does anyone know where I can find info about this technique? I remember reading about it once in a forum, probably this one. It's been so long since I read it that I can't remember who wrote it, so this could just be a hoax, but it does make a lot of sense and seem useful.

[gtae07]

Can't speak to the shuttle, but that's the technique I was taught during my glider training... I thought of it like having a limited throttle of sorts, given I was transitioning from powered aircraft.  Power (or speedbrake) for altitude, pitch for airspeed...

[laszlo]

First, you've got it backwards. The SSME thrust level could be controlled by the pilot's speedbrake handle. The commander's handle could only control the speedbrake. Second, the speedbrake logic changed several times over the life of the program finally ending up as the Smart Speedbrake after 1985. Whether it was used the way you describe probably depends on when in the program you look at it. In the first 4 Shuttle flights they experimented with manual speedbrake operation, though the 2nd and 3rd ones let it operate automatically for a fair bit of the approach and glideslope.

Looking at the descriptions in the attached documents, it seems very unlikely to me that once the Smart Speedbrake was implemented that it ever would be used to manually add deliberate drag to the system just so it could be thrown away again in an emergency. It's described starting on page 75 (real, not table of contents) of the JSC-23266 file. The algorithms are described in the other file.

The speedbrake's purpose was mostly to keep up with wind changes, not to provide a sudden burst of "thrust". The Shuttle was a 100-ton vehicle. It had a lot of inertia. Deleting speedbrake drag would not have suddenly accelerated it. It would have needed time to convert gravitational potential energy (altitude) into kinetic energy which would then become lift. On final approach the control system allowed 16 - 23 seconds for this.

The speedbrake was mostly useful for precisely trimming the airspeed to a specific value; to keep it within a specific range before velocity excursions could get out of hand. It was a partner to q-bar energy management that was controlled by vehicle attitude in the aerodynamic regime. Large corrections were made through attitude changes, smaller ones with the speedbrake.

Flying with partial brakes and popping them is something for slow, lightweight sport gliders, not trans-sonic 100-ton spacecraft.