Comparison of G force in space with G force on Earth I was reading another question on here where the general answer was that the G force would be the same on earth as it would be in space, this is the Q & A link:
Can a pilot in a small spaceship feel G force in space?
Now my question is, if the fastest speed of a fighter jet is around 1500 MPH, but the flight to the moon reached a point where Apollo 11 was travelling at 25,000 MPH, why was the G force bearable for the passengers of that ship?
Of course, the more we look at the possibilities of humans travelling through space, we have to think of the speed the orbiting spacecraft would need to leave Earths gravitational pull to get there, such as the Juno spacecraft that hit 165,000 MPH to generate enough speed to reach Jupiter. What would be the implications of human life being aboard a ship travelling at that speed?
 A: The main reason why high $g$ forces are generally not experienced in space as opposed to within the earth's atmosphere is modes of flight. Within the atmosphere, there is plenty of scope for high $g$ forces during fighter aircraft manoeuvres including aerobatics.
For fighter aircraft, which generally experience the highest $g$ forces for flight within the earth's atmosphere, the main causes of high $g$ forces are sharp turns, rapid acceleration/decceleration and upward acceleration. For a sharp turn at linear velocity $v$ and radius $r$, the $g$ force is acceleration $a$ in the equation:
$$a = {v^2\over r}$$
The larger $v$ is, the higher the $g$ force during the turn. Similarly, the sharper the turn, the smaller $r$ is, the greater the acceleration.
During the vertical ascent of a fighter aircraft, $g$ force is a sum of the earths gravitational force plus the acceleration of the fighter aircraft upwards:
$$g_{\small force} = g_{\small gravity} + a_{\small aircraft}$$
For space flight, up to about $3g$ are experienced in order to reach space. Once in space orbit, there are generally no manoeuvres that effect high $g$ forces. Low orbital vehicles like the ISS space station float around the earth at about 7.7 km/s. That is just enough to balance the earth's gravitational pull on the space station at its altitude ($408km$). The astronauts feel zero gravity inside this 'falling' vehicle. The thrusters on space vehicles are, unlike jet engine thrusters within the atmosphere, not used for aerobatics and steep manouvers, but to gently alter course at low $g$ forces.
If you intended to fly to a star outside our solar system very quickly (within months), then rapid acceleration causing high $g$ forces would be necessary.
A: Not only G- force, but any kind of force produces acceleration in a body, not speed. The magnitude of the force is proportional to acceleration. Moreover, speed is relative, that is different observers in different inertial frames of references can observe the same object to be at different speeds. Therefore there is no restriction on the speed at which humans can travel. The restriction is on acceleration. So, we can travel as fast as we want(less than the speed of light) if we increase our speed gradually enough.   
A: The absolute correct answer is depends on circumstance. 
Generally speaking, there is no felt zero G force in space because objects there are technically in free fall.  That does not mean that there is no g force at all. Again, it is about circumstances.
G force in atmosphere or closer to the earth is felt because the pilot is being pressed against the airplane seat or airplane itself. That force is proportional to the sheer force and of acceleration.
Now can a pilot in outer space feel g force via acceleration? yes. The force is calculated as F=ma or force= mass x acceleration. When mass is very low like pilot in space then the bulk of the g force is acceleration.  However, a body in free fall will not feel the acceleration unless they are being pressed against something in the ship.  Even then, it is less than on earth because of micro gravity where mass component on the pilot is only that of the acceleration which means the pilot in space feels less g force than on earth. This is one of those astrophysics questions that often trip up people.
