Connect and share knowledge within a single location that is structured and easy to search. I want to understand the reasons why the shuttle did the rollover manoeuvre after launch. I would think better to do it earlier after launch while the air flow pressure is low.
Why not just adjust attitude when you reach orbit? Is the roll the same each time or set to where you want to end up? The first, performed throughout the Shuttle program, and known as the "roll program" or "Single Axis Rotation", was actually a multi axis maneuver that mainly served to set the launch azimuth.
Since the shuttle stack sat on the pad in a fixed orientation, it is clear that some sort of rotation must be done to point the vehicle in the desired direction. In the ISS era, most of the flights followed the same azimuth to that destination's orbital inclination. You state. In fact, the initiation of this roll program was a cue to the crew that guidance and control was working properly, and hence the call to the ground to acknowledge this "Roll Program, Houston.
It is also important to achieve the proper launch azimuth early in the trajectory because orbital plane changes are very costly in terms of propellant usage.
Because the Orbiter wings developed lift at zero angle of attack, the high dynamic pressure portion of ascent had to be flown at a negative angle of attack, close to the zero lift angle.
This could have been done heads-up or down, but the early crew members expressed a preference for having a horizon view. This led to the heads-down attitude. North on the nav ball is 0 degrees, while east is 90, South is and west is This does not line up with inclinations. A zero degree inclination is due east on the equator, while a polar orbit is inclined 90 degrees. And another side note, all prograde orbits or orbits following the rotation of the Earth are between 0 and 90 degrees inclination.
So of course, along with the command module, the rest of the vehicle had certain features. Such as the fuel and electrical umbilicals that connected the rocket to the launch umbilical tower, some external raceways which had some wiring and stuff, but most importantly when talking about the alignment of the rocket was a thing called the IMU.
This included a digital computer, ooh la la, an analog flight control computer, accelerometers and some gyroscopes. Now in the case of a Saturn V heading to the moon, the launch azimuth was 72 degrees which is 18 degrees north of due east.
So while on the launch pad, the flight path and the belly of the rocket were 18 degrees off from each other. Instead of moving the entire launch pad to just face the belly of the rocket at that 18 degree angle, the rocket could simply perform a roll to align its belly with its flight path and simply pitch over.
Now all the rocket has to do is pitch over! This made it so the computer really only had to calculate one set of numbers instead of two, making the math and the calculations much much easier. Keep it simple. Another physical consideration is gimbal lock.
Gimbals can freely rotate on all three dimensions and align themselves to a fixed position in space which can tell the guidance computers where the vehicle is pointing. And gimbal lock can be a very, very bad thing. So to head out on an equatorial, 90 degree inclination orbit, you need to only press a single key the right amount.
In this example, that key is the D key which will yaw you over due east. One finger flying, nice and easy! Now this can still be easily done, using just two keys this time, but it is noticeably harder to do. Why not keep it simple?
This is a map of downtown Waterloo, Iowa. It makes navigating a lot easier than thinking about NE and SW.
We take the navigation from a 3 dimension equation to a 2 dimension equation. But this meant that when the rocket pitched over, the commander could look out the small port window in the blast protective cover and get visual references of their orientation.
By zeroing out the roll, the horizon would always appear across the window, which made it easy to use as a reference. This also made it so that if the commander saw the ground suddenly coming up or the horizon spinning, they may have considered aborting, or at least had a good visual reference on if that would be necessary.
Although most rockets look relatively symmetrical, they almost always have some kind of protruding feature. Take a look at the Saturn V. The solution was, thus, pretty simple: roll the rocket so its orientation lined up with the launch azimuth, then start a simple pitch program. This gimbal-mounted guidance platform used three nested gyroscopes to hold a preprogrammed orientation, in this case the launch azimuth.
This alignment was held using a theodolite about feet due south of the launch pad; it shined a light through a window on the IU that helped it keep steady.
And this had a very interesting effect. Before the IU was held to the launch azimuth by the theodolite, it was free, so if you could stand by the launch pad and watch a Saturn V for a full day, you would see the Instrument Unit appear to make a full turn when, really, it was the rest of the rocket turning with the Earth.
At T-minus 17 seconds — 17 seconds before launch — the guidance platform was released from the theodolite. About one second after launch, the Saturn V made its first flight manoeuvre.
The yaw program was the disconcerting-looking tilt of the rocket away from the launch tower, a move designed to protect it from any swing arms that failed to move away or a strong gust of wind. About 12 seconds after launch came the second manoeuvre, the roll program.
This had the rocket roll to align itself with the launch azimuth as prescribed by the guidance computer, which was usually at a bearing of 72 degrees. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day.
The Complete Star Atlas. First, a shuttle must launch to achieve the desired orbit orientation. Because the launch pad can't pivot to the needed angle before liftoff, a shuttle must rotate after launch to adjust. Then the vehicle, which initially moves slightly faster than ISS because it starts off in a lower orbit, can "catch up" to the station and dock with it. Second, about a minute after liftoff, all atmospheric forces on the vehicle reach their peaks.
Rotating a shuttle right after launch puts the vehicle into a position that helps reduce stress on the orbiter, especially on the wings and tail. Finally, the roll maneuver enables a shuttle's pilot to see the horizon. This provides an important reference in the event controllers need to abort a mission during launch.
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