rigidbody.useGravity doesnt work?

I have a problem here. I made a balloon that is affected by gravity, I want it to go straight up when I hold the up arrow key, therefore, I need to turn off the gravity when the key is pressed, or else, the balloon will lose speed and fall down. The thing is: when I type “rigidbody.” or “rigidbody2d.”, useGravity doesn’t appear. What’s happening?

Try unity monodevelop for script editor.