Here is a scale from which to measure science-fiction and science-fiction fan fictions by

 1=Softest 10=Hardest

0= This is fantasy-like urban fantasy. Examples: Harry Potter

1= This is sci-fi/fantasy (fits in both genres but is not a Space Opera). Examples: Artemis Fowl 

2= Extremely soft sci-fi, yet not Space Opera. Examples: Futurama

3= These are space operas (the softer variety) Examples:  30s-50s pulp magazines

4= These are space operas (the harder variety) People still consider this to be space opera, yet it is more plausible than normal space operas Examples: Star Wars

5= These are borderline. They are barely used. Probably are comedic modern-day scifi, so no explaining need be done. Examples: Men In Black

6= These are on the hard side. Very few things explained, but they have roots in reality, except for many devices left unexplained. Examples: War of the Worlds, Doctor Who (Star Trek is up ahead, see 7 and 8)

7= These are pretty hard. Most everything is explained, but some of it is unexplained, and others are complicated.  Examples: Star Trek TOS, Star Trek VOY

8= Super-Hard. Still is pretty complicated, though, and sometimes overlook the fact that space is silent. Examples : Star Trek TNG, Star Trek DS9, Star Trek ENT, and The Matrix

9= Cyberpunks, or very limited space sci-fi that is so grounded in reality, no explaining is needed. However, these sometimes limit the imagination. If you want to be hard, but imaginative, head for 8 and 7. Examples: 2001: A Space Oddessy (Could be around 8.5, though)

10= Real-life science. Examples: NOVA