WorkInProgress: Periapsis

Periapsis: the point of closest approach, or low point, in any orbit…

Anna has finished her EVA repair of the orbital shuttle, and now she, Laxmi, and Jaci are ready to try once again to return to their starship, Aniara. But is the long-abandoned alien space station ready yet to give up its grip on them? Will Anna’s repair withstand the rigors of engine ignition?

Will Jaci stop cracking jokes in the face of imminent demise? We all have our own way of dealing with stress, and this one is his. He really needs to find some little green aliens to talk to, but if that ever happens, you can be sure it will not go as expected.

Periapsis is an orbital component that you might be more familiar with as perigee, and it’s the opposite of apoapsis (or apogee). Perigee and apogee, of course, specifically refer to orbits around Earth (just as perihelion and aphelion refer to orbits around the Sun, and not just any sun, but specifically our Sun), whereas periapsis and apoapsis are “neutral” terms referring to orbit around any central body.

At the start of this scene, the shuttle is in an orbit matching that of the alien station, which is a circular orbit (periapsis = apoapsis) at geostationary altitude and zero inclination (i.e., directly above the planet’s equator). Anna intends to fly the shuttle up to their “parked” starship’s orbit, a hundred kilometers higher, by using a prograde burn to raise their apoapsis to match Aniara’s orbit. Along the way, however, something else happens…

If you want to get into geeky details about orbital mechanics, have a look at my earlier blog post Orbital Mechanics. If you just want to jump right in, however, join Anna and her crew in…

Periapsis


image credit: NASA/JPL-CalTech

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