Velocity and leaving earth's atmosphere

[tamousfleck]

I have a basic understanding of the escape velocity principles when it comes to an object lacking propulsion such as a bullet or a baseball. If the projectiles speed is not equal to 11.2km/s (or whatever EV equals with atmosphere), then the projectile will return toward Earth's center of mass, etc...

My question is what about a system with propulsion? Would it be possible to have a rocket travel into outer space if it were programmed to accelerate to a velocity lower than 11.2km/s (say 50-500m/s) and then merely maintain that speed until it reached outer space.

It seems simple enough that as long as force A is greater than force B, then the object would continue to move in direction A, but does the atmosphere get in the way or something practical like fuel limitations make it close to impossible? or is it merely that simple?

I also realize another possibility is that I'm just getting confused with the way orbit might differ from just going to outer space. 99% of the time when leaving Earth's atmosphere is discussed, sending an object into orbit is the reason and so that may be why escape velocity seems to be so important in all things space program related. But to just send something in the direction of the moon, Mars or Mercury... velocity may not be important at all, just force.

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Where's the math that says ∞! is bigger than God's nose hair?

 

[pallidin]

Indeed. As you know, a common helium balloon will continue to rise towards space until it overly expands and bursts in our atmosphere well before reaching space.
Of course, even if it did not "overly expand" it still would not reach space, as helium is heavier than "vacuum", as well as the balloon material itself.

So, some additional propulsion is required to go into space.

However, you are right. It is not necessary for the propulsion to be at "escape velocity"
As long as there is "some force" continuing propelling it upwards it will continue upwards.

That's my understanding. MODS or anyone else please feel free to correct me.

 

[russ_watters]

It's correct. You could rise out of the atmosphere and keep going at 1 m/s if you want. But consider this: What do you think uses less fuel, applying a force of 1.0015g for 10 hours or applying a force of 3g for 10 minutes?

 

[Lsos]

The usual published escape velocity (11.2km/s) is at the surface of the earth. As you get further away, the escape velocity drops. You could very well crawl veeeeeeeeeeery slowly far away from the earth, and then fire some cheap booster and leave the Earth forever.

As has been mentioned though, nowadays this is only a good theory. Perhaps when we start building space elevators, taking advantage of this will become practical.

 

[BruceW]

The escape velocity of 11.2km/s assumes zero friction with the Earth's atmosphere (you can do the calculation yourself). Therefore the initial speed you need to give the rocket would actually need to be far greater than the escape velocity.
This is why in real life, they have to use propulsion on rockets. When propulsion is involved, the rocket doesn't need to be sent off at the escape velocity.