How is celestial navigation done on a low-level?

Question

When we send a probe off to Jupiter or Saturn, or even Earth orbit, how are the rocket firings timed and coordinated?For instance, when I want to drive to another city I pull onto the highway and use the lines on the road to adjust my steering. I also use intuition to adjust my velocity, even though that won't make a difference _where_ I wind up (only _when_). However, spacecraft don't have lines on the road to line up with. Nor do they have a direct measurement to take for speed, which is critical in orbits and in planetary transfers.I suppose that some bright stars near opposition or off the ecliptic (Capella?) and GPS could be used for interplanetary navigation or LEO, but how was it done before GPS? Inertial navigation? How did the Soviets get the Vostok to enter a clean orbit (I understand that the Sputnik orbit was very elliptical)? How did early interplanetary probes orient themselves?

Answer 1

Getting into orbit is a matter of launching straight up to get above as much air friction as quickly as possible, then angling the rocket gradually more horizontal to gain enough speed to achieve orbit (about 5 miles per second) above the atmosphere. The horizontal direction you aim determines the orbit's inclination (relative to the equator). Newton's Laws dictate the design of the rocket stages using the weight of the stages and their fuel weight and the known thrust (force) of the rocket engines.

Interplanetary navigation involves precise alignment of the spacecraft by sighting on known stars. Then you fire the rocket engines (at a known thrust) for a precise length of time to change the spacecraft's speed by a very precise amount. You have defined your traffic lane, and now Newton does the driving! Your alignment will be close to the plane of the Earth's orbit and in the same direction as the Earth's motion around the Sun if you want to head to the outer planets, or opposite the Earth's motion to reach the inner planets. Then you just coast to your target with maybe a mid-course correction if observations show you are a little off target. Your fire the rocket again when you get to the target planet to slow down and get into orbit.