Can I apply zero gravity on .urdf models?

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HI there.

I am trying to implement Gazebo simulation for space environment using International Space Station(ISS) urdf model.

I wants to ISS urdf model apply zero gravity but it doesn`t work.

Can I know my two questions?

1. Can I applying zero gravity for ISS urdf model? If that can`t, should I convert .urdf to .sdf?

2. Is there anyone who have experienced implementation about space environment using Gazebo??

Please let me know my questions, and any leave replies.

I am looking forward to your comments and feedbacks.

best regards