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Comment by johnwalkr | Hacker News Reader

The convention for orbital spacecraft is that the local coordinate system has +z facing whatever it is orbiting and +x facing travel direction. Then you can refer to directions relative to the spacecraft such as "+x", "-y", etc.

The space shuttle normally orbited with it's payload bay, opposite of the landing gear facing Earth. The payload bay was +z direction. From the layperson's point of view, the shuttle orbited upside down, but from an aerospace engineer's point of view it orbited right side up and landed upside down.

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>> The space shuttle normally orbited with it's payload bay, opposite of the landing gear facing Earth

That wasn't a choice. The doors had to remain open and pointing away from the earth so that the radiators could properly dissipate heat. It also, in theory, kept the most important thermal tiles pointing away from incoming space rocks.

> The doors had to remain open and pointing away from the earth

It's the opposite. The orbiter usually kept it doors pointed toward Earth and the "bottom" tiles pointed away from Earth, and orbited with its engines pointed prograde. (Upside-down and backward relative to the atmospheric flight people are familiar with)

https://space.stackexchange.com/questions/12321/why-did-the-...

That's a convention, but hardly the convention.

I used to work satellite navigation for NOAA. For the GOES sats we often used Intrack (Prograde/Retrograde), Crosstrack (Normal/Anti-normal), and Radial (Towards planet/away from). I don't think anyone really referred to any directions as "plus x" or "minus y"

There are different conventions, yes. Even for the shuttle I've seen +z point in the opposite direction in some documents. I work in systems engineering so I'm less exposed to terms used in operations and more in discussions about which part of the spacecraft things are located.

Actually I work on rovers and it's a perennial debate whether to follow spacecraft convention (+z is down) or automotive convention (+z is up). Then mechanical engineers will usually follow what is intuitive on the screen (+z is forward). This is because computer graphics convention is +z facing out of the screen.

Yeah, operations is kind of where engineering's best practices go out the window for practicality haha.

We used to tilt the spacecraft when doing inclination burns so that we could get a little bit of intrack delta-v to even out our orbit. I always thought that was delightfully janky.

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