This entry is about Newtonian physics and making sense of it all.
If you launched a rocket directly east from Kennedy Space Center, Florida, (the white arrow) it would have an inclination of 28.6 degrees. The Hubble Space Telescope was launched nearly due east from KSC, and has an inclination of 28.5 degrees (not shown). If you launch due east from another latitude, the spacecraft will have the inclination of that launch pad. The inclination angle can be changed by changing the vector you launch at. If you decide to build the International Space Station (ISS), for example, and other countries are involved, you’ll want to have an inclination that the other countries can reach. The ISS has an inclination of 51.6 degrees (it goes to the northeast along the white path). Russia launches from the Baikonur Cosmodrome (the red Arrow) in Kazakhstan. Baikonur is located at 46 degrees latitude, so They’d would have to launch towards the east-north-east at the right time to get to the ISS. Are you with me so far?
In order for all of these angles to really make sense, the map provided (thanks to www.heavens-above.com!) is similar to the one shown frequently on NASA TV during manned spaceflight missions. The reason the path doesn’t line up with itself is because Earth rotates underneath the orbiting spacecraft. When the launch facility is “in-plane”, or directly underneath the orbit of the craft, you have a short period of time to launch. With regards to the ISS, that launch window is about 10 minutes. The opportunities to launch vary day to day, because the ascending node is when the US prefers to launch and land. NASA never launched toward the ISS when it’s in the descending node because it takes extra energy to make up for that extra 28.6 degrees above the equator. The ascending and descending nodes may seem a bit confusing, but looking at the map, the ascending node is the path going to the northeast, and the descending node is going southeast. If you’re still confused, remember that it is rocket science, but it’s not too hard to figure out with a little patience!
If you’re still with me, I’ll explain a little bit more. If you go to www.heavens-above.com, http://spaceweather.com/flybys/ or http://science.nasa.gov/RealTime/jtrack/you’ll be able to see some of the satellites that are constantly whizzing overhead at 5 miles/second! I’ve personally seen the ISS and space shuttle, hundreds of “Iridium flares” and even the Hubble Space Telescope once in a while from here in Philadelphia, PA, in the US. It’s quite a treat to see the ISS and shuttle following each other before docking or after separation!! To explain why NASA only prefers to land on the ascending node is to minimize risk to those of us here on terra firma. If something like the Columbia tragedy were to happen again, NASA doesn’t want the pieces of debris from the spacecraft falling on populated areas. There is some toxic things aboard that are best left untouched, but that’s a subject for a later date.
Outside looking up with a smile,
-Jeph