Flying the Shuttle - Final Approach

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Note  This article refers to the SpaceShuttle in the FGAddon repository.

This mission phase can directly be started using --aircraft=SpaceShuttle-approach on the command line.

What are we trying to do?

In the very last part of its flight, the Space Shuttle flies like an airplane. Yet, its design is a compromise between a small launch weight, a body that is suitable for hypersonic aerobraking and can withstand the heat generated by atmospheric entry and aerodynamical flight. As a result, it's aerodynamics is more similar to a brick than to a glider. Even at its best, the glide ratio is about 4.5, much less during supersonic flight.

As a result, the glidepath is fairly steep (about 17 degrees, more than five times of what a commercial airliner flies on approach) and the touchdown speed is unusually high (about 200 kt). Yet, the landing gear of the shuttle is as fragile as a normal landing gear, thus touchdown has to be gentle. And since the Shuttle is a glider, there is just one chance.

The tasks during final approach are

  • bring the Shuttle safely to the runway, allowing for a variation of different energies
  • perform a soft touchdown on all three wheels
  • bring the Shuttle to a stop on the runway

How it feels in FG

The aerodynamics of the Space Shuttle in FG is taken from a large body of wind tunnel data, i.e. both basic capabilities like L/D and details such as the response to airfoils is fairly realistic.

As in reality, the rudder of the spacecraft is controlled by guidance logic to minimize sideslip, i.e. the rudder pedals should normally not be needed unless side slip is explicitly desired. At subsonic velocities, the Shuttle is dynamically stable which makes it fairly easy to fly.

The final approach starts at an altitude of about 10.000 ft, some eight miles from touchdown. The runway seems very far below at this point.

Final approach of the Space Shuttle into Vandenberg, cockpit view

Push the shuttle down to a 17 - 20 degree glideslope from here. This is steeper than it's optimum glidepath, so use speedbrake to control the approach speed to about 340 - 350 kt. The aim point for the nose is a little before the runway. Make sure you have good visibility to do this, in reality the Shuttle is just re-routed to a different landing site if the weather is bad, there are no provisions for an IFR approach.

The speedbrake is a fairly powerful drag device, so you can accomodate quite a variation in energy at this point. If the speedbrake is not operational, the landing gear works almost equally well, but note that the maximum gear extension speed is 312 kt.

At an altitude of about 2000 ft, pull the Shuttle gently into pre-flare, i.e. onto a shallower glideslope aiming at the threshold.

Pre-flare of the Space Shuttle

At this point, airspeed should decay rapidly. If you started preflare with 340 kt, this is fine, but if your airspeed was much lower, you may have to retract speedbrakes to avoid early touchdown.

Pre-flare of the Space Shuttle, cockpit view

Inner glideslope of the Space Shuttle

Before preflare, vertical speed is about 190 ft/sec, after preflare this should be reduced to 12 ft/sec. With airspeed continuously dropping, you should reach the runway threshold. Deploy the landing gear at an altitude of 300-400 ft (i.e. only a few seconds before touchdown). The gear is a poweful drag device and will slow you down quite a bit. Pull further up into a final flare. The nose at this point should be some 12-14 degrees above the horizon and the airspeed should approch 210 kt. The nominal touchdown point is some 2500 ft behind the threshold.

Preparing to flare, Space Shuttle Cockpit view

The orbiter creates a powerful ground effect, so you can let that cushion your sinkrate. At touchdown, vertical speed should be 3-6 ft/sec and may not exceed 9 ft/sec without damaging the gear. To avoid tire damage, speed over ground at touchdown may not exceed 230 kt. The pitch angle at touchdown can not exceed 15 degrees without causing a tailscrape.

Don't relax as touchdown is called out, your work is only halfway done. With the nose gear still up, make sure airspeed is below 230 kt and deploy the drag chute ('c'-key). This is deployed in two stages, so hit the key twice for full effect.

Touchdown of the Space Shuttle and drag chute deployed

Wait for airspeed to reduce to 185 kt, then begin derotation to bring the nose wheel onto the ground. Do it gently - the derotation speed may not exceed 2 deg/s without damaging the nose gear.

If you manage to come in too hard, prepare to deal with asymmetric friction caused by blown tires and / or damaged gear struts. Use ailerons to perform load relief for the damaged side.

Once the nose wheel is on the ground, hit the brakes and use nose wheel steering to stay on the runway. The drag chute will be jettisoned once the Shuttle is slower than 40 kt. Wait for a final call of 'Wheels stop!'

Congratulations - you're home.