I have a question
Hello
I have a question about this.
The biggest physical challenges facing people in space are ~
is people correct?
Thank u for advice

Question

I have a question
Hello 
I have a question about this.
The biggest physical challenges facing people in space are ~
is  people correct?
Thank u for advice

Answer

That would work, but I might suggest changing it to

The biggest physical challenges people face in space are...