I'm a graphic designer and recently started a space themed etsy store. Please feel free to comment / critique / or suggest ideas for future designs.
The first one looks really amazing and is my favorite. The chosen font looks amazing and the little icons look really good. The only thing I'd suggest for making it better is possibly making the whole thing colored, like making the background a dark blue, making the letters white, and changing up the colors of each icon.
The second one looks pretty good and is my second favorite. I like the cleverness of the phrase used. I like the red circle behind the rocket and the rocket and smoke look very well made. One thing I would suggest is making the rocket a different color from the smoke, this is because it blends in a bit too much with the smoke, making it look slightly unattractive. This would make the rocket pop out more, since that's the subject of the piece. Another little thing would be to maybe adding white or gray dots in the background to resemble stars, but that might be a little too much.
The third one looks alright but is my least favorite. The typography looks really nice and it fits well with the piece. The color choice is nice and the white background looks well made. Unfortunately, Carl Sagan (I'm assuming) doesn't look that good. His face looks really unappealing and a lot more detail could have put have been put into his body. The lips just look really bad. But overall it's pretty good.
You're a very good artist and I like the work you made, keep it up :)