# How did the Space Shuttles manage to find their respective landing sites?

The space shuttle was an unpowered falling wedge. It entered the atmosphere at some 17 thousand miles per hour.

Yet after some enormous atmospheric breaking somehow manged to twist and turn and find it’s way to a small speck of a runway thousands of kilometers away: and this was before GPS technology, as far as I know.

It seems inconceivable to me how an unpowered craft could just do this, and do it perfectly, each and every time. (Yes, please discount Columbia.)

How did that work, exactly?

Thomas guides?

Seriously though, it’s called rocket science. They had a team of rocket scientists to do the math. And well trained pilots knowledgeable in geography and navigation.

Not really. I believe the ship is on autopilot mode.

Pilot McCool is on record for turning off autopilot just prior to Columbia’s disintegration.

The onboard computers defiantly helped

Also, they did land on some pretty big runways and I am sure the pilots had practiced in a smaller glider beforehand but it is still an impressive feat.

Even more impressive is Space X (I think)

The actual re-entry course and slowdown maneuvers are calculated by the shuttle’s computer system and largely automated. Once the shuttle gets down to a reasonable cruising speed, it is flown manually by the shuttle commander, who intercepts the TACAN beacon on the landing site. TACAN is basically just the military version of the radio localizers used by commercial pilots at civilian airports. (The shuttle did later get an upgrade for GPS capability, but most of the landings were done with the old-skool radio beacons.)

That’s pretty much the answer right there. Ballistics.

You have an object flying at A miles per hour. Starting at point and altitude X, you begin to reduce speed at a pre-determined rate. The object slows and falls predictably until it eventually ends up on the ground at point Y.

Naturally, there are a lot of calculations involved and the margin for error is pretty much nonexistent, but it’s really just gravity and math.

And if you think the Shuttle was impressive, consider that Apollo lunar missions were plotted on a “free return” which meant they could go around the Moon and return to Earth without any kind of mid-course correction.

Personally, I’d prefer subservient help from computers. But I’m sure that defiant help is better than no help at all.

Definitely

Got to love auto correcting

If you want to play around and get an approximate idea of how easy or difficult it is, try downloading this freeware video game. You can pick a real or fictional spacecraft (including a Space Shuttle), put in orbit, and try landing at your chosen destination. You can try it with and without the computer, and compare.

The Space Shuttles had three IMUs, three TACANs, and later, three GPS units.

The IMUs are inertial reference units. They measure acceleration and, by applying those accelerations to a known starting position and velocity, allow the calculation of subsequent positions. They are used in the orbital phase. Known / anticipated errors are corrected by software while additional errors are identified by star tracking and an optical sight and corrected manually.

During the entry phase, TACAN is used. This is a military version of a VOR/DME and measures bearing and distance from a ground based station.

So that’s how it knew where it was. As far as knowing where it had to be and how to get it there, that comes down to the rocket surgery and, once in the atmosphere, old fashioned piloting. They were a big heavy glider with a steep glide profile during an approach and could be flown like any other airplane.

I came across this on Youtube. It has a pretty good explanation.

I would suggest that the Apollo spacecraft reentry and splashdown was a rather greater triumph. They regularly hit the water within a mile or so of the mark. Given they started the journey from the moon, and not LEO, and had to hit an entry corridor a few miles high, and had no wings, just a lifting body and reaction jets, the accuracy is silly.

I’ve often wondered about the Apollo command modules too, but they didn’t really need to hit a specific target, just an area.

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(Yes, I also did realize that I typed “breaking” in the OP instead of braking. D’oh!)

[quote=“caligulathegod, post:12, topic:788406”]

I came across this on Youtube. It has a pretty good explanation.

[/QUOTE]

That’s a really nicely done talk.

Apollo and Mercury missions:

Winds that could lead to course changes that exceeded the correctional capability kept the Shuttle from being a simple bullet headed towards a very wide target (Apollo bullet headed towards, oh I don’t know… an OCEAN, etc).

Shuttle gliding/flying: Much more maths! That’s as technical as I need to be to point out the difference.

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I always assumed that they used the Force.

This is tangent from the OP, but since you brought it up and I think it’s really interesting…

The free-return trajectory was used on the early lunar flights as a safety measure. Starting on, IIRC, Apollo 12, they began using a hybrid trajectory. After achieving Earth orbit they performed the TLI burn (trans lunar injection) to send them toward the moon. This was on the free-return trajectory. But a few hours later they performed another burn that took them off the-free return, on a more direct path to the moon to save time.

The logic behind this was elegant - by executing the second burn, you demonstrated that the engine on the command / service module was working properly, and could be counted on if an abort burn was needed later. This worked great on Apollo 12, not so great on 13. Their emergency happened after departing the free-return trajectory, which complicated their situation and necessitated using the LM’s engine to get back on the return trajectory.

I’ve noticed that the runway extending into a dry lakebed at Edwards AFB in California is obviously visible through a commercial airplane window at cruising altitude. As long as the shuttle arrived in the right general area, the pilot would have no trouble finding the runway.