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Uploaded:2020-05-22
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Some satellites orbit in the same direction the planet rotates, which means they get a boost for their launch, but most have orbits where that isn’t ideal, and that creates some challenges for engineers.

Hosted by: Caitlin Hofmeister

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Sources:
https://maps.esri.com/rc/sat2/index.html#
https://image.gsfc.nasa.gov/poetry/ask/a10840.html
http://www.digitaljournal.com/tech-and-science/science/herd-shot-around-the-world-the-last-east-coast-polar-launch/article/567614
https://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html
https://earthobservatory.nasa.gov/features/OrbitsCatalog
https://www.oxfordreference.com/view/10.1093/oi/authority.20110803095935986
http://www.satobs.org/faq/Chapter-04.txt
https://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits#SSO
http://www.eurockot.com/wp-content/uploads/2012/10/Ch3UsersGuideIss5Rev0.pdf [PDF]
https://acadpubl.eu/jsi/2018-118-16-17/articles/17/18.pdf [PDF]
https://www.planetary.org/blogs/guest-blogs/jason-davis/3450.html
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http://www.aerospaceweb.org/question/spacecraft/q0089.shtml

Images:
https://svs.gsfc.nasa.gov/2971
https://svs.gsfc.nasa.gov/3117
https://svs.gsfc.nasa.gov/4772
https://worldview.earthdata.nasa.gov/
https://svs.gsfc.nasa.gov/4745
https://www.nasa.gov/content/astronaut-alexander-gerst-checks-out-station-cupola
https://svs.gsfc.nasa.gov/30763
https://commons.wikimedia.org/wiki/File:Astra_Rocket_3.0_flight_1_launch_campaign_97.jpg
https://www.nasa.gov/centers/marshall/history/this-week-in-nasa-history-first-crewed-saturn-v-mission-launches-dec-21-1968.html
https://en.wikipedia.org/wiki/File:Enterprise_at_Vandenberg_AFB_SLC-6_-_DF-ST-86-09420.jpg
https://commons.wikimedia.org/wiki/File:Lift_Off_120403-F-CY114-094.jpg
[♪ INTRO].

Launching a satellite is not as simple as pointing the rocket up and counting to zero. I wish it was.

Because Earth doesn’t sit still. It’s constantly spinning. And like we’ve talked about before, rockets get a boost from that spin if they launch in the direction of Earth’s rotation.

But Earth’s rotation might help some launches, but it doesn’t help all of them. Like, over half of satellites have orbits that are harder to reach because of Earth’s spin. So, what are we supposed to do about those?!

Well, at least in the U. S., part of the answer is simple: You move your rocket to California. Obviously the ground and everything on it is constantly moving around Earth’s axis, including us, launch pads, and the rockets sitting on top of them, so when a rocket launches, it starts out with that horizontal motion.

Up near the poles, this doesn’t mean a lot, since the ground is moving more slowly there. But at low latitudes, closer to the equator, like, say, at NASA’s Kennedy Space Center in Florida, ground is really truckin. Since Earth spins west-to-east, if you launch your rocket eastward, you can get an extra speed boost without burning any fuel.

This can be great if you’re launching a satellite that orbits Earth in the same direction the planet rotates. Because to orbit, you need to be going fast. The thing is, though, the vast majority of satellites have orbits where a low-latitude, eastbound launch isn’t ideal.

Including the International Space Station. That is thanks to the inclination of their orbits. Inclination is the angle between an orbit and a reference plane, like Earth’s equator.

A satellite that travels directly above the equator and is moving west to east, the same direction as Earth's rotation, has an inclination of zero degrees. And a satellite that travels from north to south is in a polar orbit, with an inclination of around 90 degrees. So a satellite that travels from east to west, the opposite direction of the Earth's rotation, is in a retrograde orbit, with an inclination higher than 90 degrees.

The ISS has an inclination of about 51 degrees, which is considered high, and just over half of all satellites have polar ones. So, why would you fly a more complicated orbit like this, and how does that even work? Well, the why is actually pretty easy.

One big reason is that, when a satellite is in a highly inclined orbit, it passes over more of the planet. Like, as the ISS moves, the Earth is still rotating underneath it. So it gets to see huge parts of Earth’s surface a couple of times a day.

Meanwhile, in a truly polar orbit, a satellite might get to see the whole planet. Which is great for communication, photos, taking measurements, staring longingly out the Space Station’s window, you know, that kind of thing. The problem with reaching these orbits is that the satellites in them don’t go east relative to the Earth’s surface, so they’re not helped by the boost from the planet’s spin.

Instead, at some point, their rockets need to cancel out that purely eastward motion of the launch pad. And if they’re launching from a place closer to the equator like in Florida, they have to cancel a lot of eastward motion. On the up side, doing that is pretty straightforward:.

You just point your rocket a little bit to the west. But like lots of things in engineering, that’s easier said than done. For one, it takes more fuel, since these rockets can’t devote all their energy to flying north and getting into orbit; they have to use more of it to fly west as well.

This is one reason Florida is kind of a crummy place to launch a polar satellite. Somewhere farther north would be more efficient, like the launch pad in Alaska. That said though, the boost from Earth’s spin is nice when you can use it, but it’s not a mission-killer to fight against it.

I mean, if you started from the equator and wanted a polar or retrograde orbit, it would definitely take more fuel. And to keep more fuel on board, you’d have to reduce the number of scientific instruments on your mission. You might even have to upgrade to a bigger, more expensive rocket.

For some missions, those are big sacrifices. But for a whole space program, those costs are still a lot less than the cost of building and maintaining a whole new facility at a snowy, windy location closer to the poles. So, the real problem is that pointing your rocket west, well, it requires a bunch of empty space to the west.

Otherwise, if something goes wrong, you run the risk of hitting people and buildings and cows with debris. It’s true. We’ve hit cows before.

Today, this is mainly why the U. S. doesn’t typically launch satellites with polar orbits from Florida. Instead, they launch at Vandenberg Air Force Base, way up north in… southern California.

It’s not that much farther north, but its big advantage is that the ocean is to the west. So rockets don’t have to go over populated areas, and as a nice bonus, they save a little fuel, too. At the end of the day, spaceflight is complicated, but hey:.

When you get to put people in space, or launch a satellite that helps us understand our home and the universe; it’s all worth it. Thanks for watching this episode of SciShow Space! And a huge shoutout to our patrons on Patreon for making this episode and everything we do possible.

If you want to learn about supporting more episodes like this, you can find the details at patreon.com/scishow. [♪ OUTRO].