Morning Guys....is it really morning? My last few days have been so mixed up I really have no idea.....
TAEM = Terminal Area Energy Management. This is a fancy term for making sure that you always have a positive margin of energy to make the runway. Since the shuttle is a glider, you can only take away excess total energy, you can't add any. TAEM is a software module in the Shuttle that kicks in about 2.5 Mach. It is designed to guide the shuttle to the runway environment with excess energy, so that we are absolutely sure that we won't land short. to do this with a safety margin, you will always get there with an excess.
The result is an approach with a built in "circle to land". When you come into the airport environment, you are aiming not for the start of the final approach, but at a "Heading Alignment Cylinder" (OK, it's actually a cone, but the acronym has been used both ways...), or HAC. The HAC is a circle of decreasing radius off the end of the runway which lines you up on centerline, and you use it to modulate your energy so that you always arrive on final at the same energy state (distance and altitude from the runway at 295 knots IAS).
If you are approaching from the west for a landing on 33, and you have plenty of energy, you fly OVER the field, and turn right onto the hack that is southeast of the threshold, turning 270 degrees to get rid of the energy. That would be Plan A. But let's say that the winds weren't as expected, and as you are approaching the field from out over the gulf, the TAEM software says you are running low on energy. In that case, you can downmode to the HAC on the southwest side of the threshold, which means you make a LEFT turn, and only turn 90 degrees. See how it works?
(RV Content - you can do this same kind of planning in your head for a dead-stick emergency landing to make sure you make your field!)
Once the HAC dumps you out on final, you are doing 295 knots, on a 19 degree glideslope for the runway, passing through about 14,000'. At this point, you still have some excess energy, and the speed brake is used to dump that. Usually, you leave it in auto, letting it maintain speed and fly to the glideslope using pitch. The aim-point at this time is actually short of the runway. You say on this glideslope until about 2,000', where you fly a constant-G pull-out that we call the "Preflare" to attain a 0.5 degree glideslope, changing your aim point to a spot about 2500 feet down the runway. You hold that shallow glideslope until touchdown at about 195 knots (205 heavy). Piece of cake....except the Orbiter, being a delta wing, has negative glideslope response, so if you increase pitch, the instantaneous response is an increase in sink, not a decrease.....but that is a whole 'nuther article. The bottom line is that you bets be set up for touchdown at the end of the pre-flare, because if you work too hard to sweeten the landing, you just make things worse....
And Doug is pretty much right on the big fan on the runway - it is used IN CASE there are any toxic gasses escaping form the vehicle. They deploy that first, then send out guys in suits with sniffers to make sure the jets aren't leaking (rocket fuel is REALLY nasty stuff!). Once they have cleared the vehicle, then it is safe to approach in regular clothes - but they keep the fan running anyways - I think maybe they think it keeps the 'skeeters away?
OK, that qualifies as my work for today....gotta run out to Ellington to welcome the crew back to Houston at noon - if you're in the area, come join us! But first, I'm headed to the airport to give the Valkyrie a Dynamic Prop Balancing I've been promising her all along.....just now getting around to it.