# What is the difference between escape velocity and orbital speed?

if for instance i was to send a satellite into mars, firstly the rocket with the satellite would need to get into earth's orbit right?

so for this to occur, does it have to go upwards at orbital speed or escape velocity?

i know this question probably sounds really really stupid but i am totally uneducated in this field and i have an assignment about sending a satellite to mars so i need to understand this

thanks !

Orbital speed is the speed you need to obtain orbit. Note that by definition, since you are in orbit, you still have not 'escaped' Earth. You need an even higher velocity to get beyond Earth orbit.

A good example of the difference between orbital speed and escape velocity is when Apollo went to the moon.

First the Saturn V rocket boosted the astronauts into near Earth orbit which required a speed of about 18,000 mph. Then once everything checked out, they re-lit the third stage of the Saturn V to gain speed to break out of Earth orbit and head towards the Moon. This required a higher speed of about 25,000 mph.

Upon reaching the Moon, they would fire the spacecraft's engine to 'slow down' to orbit the Moon. Without this 'braking' maneuver, they would have too much speed and been swung around the Moon and flung back to Earth (too fast for orbit).

Upon leaving Lunar orbit, they had to again fire their spacecraft's engine to gain speed and break out of their lunar orbit (escape the Moon's gravity) to return to Earth.

This is why the speed of the Apollo spacecraft returning to Earth was higher than say, the Space Shuttle. The Shuttle only has to bleed off it's orbital speed. Apollo had to bleed off its significantly higher escape speed!

#1

escape velocity is needed to get out.

Orbit speed depends on the height of the orbit the speed has to be fast enough to create enough centrifugal force outward to counter the earth's gravity. with an equal force between to hold orbit.

#2

The first step in your Mars trip would be to get the satellite in orbit, say at 200 km. At that height it needs to have enough speed so that it falls *around* the Earth, rather than back to Earth. See here: http://img.sparknotes.com/content/testpr…

Getting into Earth orbit, means you have to do two things: 1) to take your spaceship from sea level to 200 km height 2) go from 0 to 8 km/s. On take off the rocket first goes vertically up to pass as quickly as possible through the densest layers of the atmosphere. Next it slowly changes direction, until it arrives in orbit, at the correct speed.

Escape velocity is higher than orbital velocity. When you switch on the motor again in orbit, the orbit changes from on circle into a more and more elongated ellipse. When you reach the escape velocity, this ellipse no longer closes on itself. See here: http://www.physast.uga.edu/~jss/1010/ch4…

#3

escape velocity is how fast you have to go to leave earth's atmosphere.

Orbital speed is how fast something needs to travel to maintain orbit.

For example, if the moon was static and didn't go around the earth, it would fall into earth via gravity. The speed holds it up.

#4

Escape velocity is the speed that you need to leave the planet so that without any more push you keep moving away forever. Orbital speed is the speed needed to circle the planet at the same altitude without getting farther or closer. From any circular orbit you need to speed up by a factor of the square root of 2 to get to escape velocity. For Low Earth orbit, orbital speed is 17,500 MPH, and escape velocity is the square root of two (about 1.414) times as fast, or a little less than 25,000 MPH. The Apollo missions entered Earth orbit at 17,500 MPH and then restarted the third stage engine to increase speed to almost 25,000 MPH and go to the Moon.

#5

If you were to send an object to Mars there would be no need to put it into orbit first. Technically. They usually do go into orbit first just because it makes it simpler. Especially when dealing with different rocket stages and getting the timing right to actually get to Mars instead of missing it altogether. Technically you could go to Mars at 1 mph. If you had constant propulsion. But rockets burn so much fuel they run out quickly. Escape velocity is just the speed you have to reach so that once you run out of fuel and start coasting you'll have enough momentum to make it out of the Earth's gravity pull and just basically fall the rest of the way to Mars or wherever you're going. You can escape the atmosphere at any speed. But since an airplane's wings are useless out of the atmosphere you would just fall back into the atmosphere if you weren't at orbital speed. There isn't just 1 orbital speed. It depends on the gravity of the object you're orbiting, and the altitude. The closer to the object the faster you have to be going. Also just reaching that speed isn't enough. If you go straight up at "orbital velocity", but don't reach escape velocity, then once your momentum runs out you'll just fall straight back down to the Earth. You have to be at orbital velocity, and actually IN orbit, to maintain an orbit.

#6

The escape velocity is the speed required for an orbiter to escape Earth's atmosphere.

The orbital speed is the speed of the orbiter while in orbit (in space).

#7