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8.4. FLYING THE SPACE SHUTTLE 91
The first rule of flying a glider—quite unlike flying a powered plane—is this: Never come up
short. When bringing a powered plane in for landing, if the pilot thinks the craft will not quite
make it to the runway, it is no big deal. She or he just adds a bit more power to cover the extra
distance. If a little more speed is needed, it is again no problem—just add power.
Gliders play by a different set of rules, though. There is no engine to provide power, so when
setting up a landing, a pilot must be sure to have enough altitude and speed to be able to coast
to the airport, because if s/he guesses low by even one foot, the craft will hit the ground short
of the runway, crashing. Gliders must never be low on speed or altitude, because if they ever are,
there is no way of getting it back—a crash is assured. (Thermals, or rising currents of air, provide
the exception to this rule. These can give efficient gliders enough boost to get the job done, but
thermals will typically provide less than 500 feet per minute of vertical speed—not enough to keep
even a lightweight Cessna in the air!)
Now, with the Space Shuttle, it is certainly true that the aircraft has engines—three liquidfuel
rockets putting out 375,000 pounds of thrust each, to be exact. (To put this in perspective, a
fully-loaded Boeing 737 tips that scales around 130,000 pounds, so each engine of the orbiter could
punch the Boeing straight up at 3 Gs indefinitely. That is not even considering the solid rocket
boosters attached to the Shuttle’s fuel tank that provide millions of pounds of thrust!)
So, the Space Shuttle has engines; the problem is fuel. The orbiter exhausts everything it’s
carrying getting up into orbit, so there is nothing left for the trip down. Thus, the ship is a glider
all the way from orbit to its touch-down on Earth. With the final bit of fuel that is left after the
mission, the orbiter fires its smaller de-orbit engines to slow it down to a bit over 15,000 miles per
hour and begins its descent into the atmosphere.
So, if you want to fly the Space Shuttle, and the Space Shuttle is a glider from the time it leaves
orbit to the time it touches down on Earth, you must bear in mind the cardinal rule of gliding:
Always aim long (past the landing point), not short, because if ever you aim short, you are dead,
because you cannot make up lost speed or altitude without engines. Aim long since the extra speed
and altitude can always be dissipated with turns or speedbrakes if the craft winds up being too
high, but nothing can be done if it comes up short.
In observance of this rule, the Orbiter intentionally flies its glide from orbit extra high to be on
the safe side. But there is one problem. It would appear that if the Orbiter flies its entire approach
too high, it will glide right past Edwards. In reality, this doesn’t happen for one reason. For most
of the re-entry, the Shuttle flies with the nose way up for extra drag, and it makes steep turns to
intentionally dissipate the extra energy. The nose-up attitude and steep turns are very inefficient,
causing the Shuttle to slow down and come down to Earth at a steeper glide angle. If it ever looks
like the Orbiter might not quite be able to make it to the landing zone, the crew simply lowers
the nose to be more efficient and level it out in roll to quit flying the steep turns. This makes the
Orbiter then glide more efficiently, so the crew can stretch the glide to Edwards for sure. The extra
speed and altitude is the ace up their sleeve, but the drawback is they have to constantly bleed the
energy off through steep turns (with up to 70 ◦ bank angle!) and drag the nose up (as high as 40 ◦ !)
to keep from overshooting the field.
We will now walk through the re-entry process from the beginning as it is done both in the real
Shuttle and in X-Plane.
After de-orbit burn, the shuttle heads for the atmosphere at 400,000 feet high with a speed of
17,000 miles per hour and a distance of 5,300 miles from Edwards (equivalent to landing in the
Mojave Desert after starting a landing approach west of Hawaii—not a bad pattern entry!). In
reality, the autopilot flies the entire 30-minute re-entry, and the astronauts do not take over the
controls of the shuttle until the final 2 minutes of the glide. The astronauts could fly the entire
re-entry by hand, but it is officially discouraged by NASA, for obvious reasons. These speeds and