Defining hard science fiction seems pretty darn central to a thread asking for hard science fiction.
Hardness in fiction is a tool to make problem-solving interesting and realistic. It distracts from character and plot. In real life, the usual reward for solving a problem is another harder problem. So in SF, hardness naturally goes with frustration and despair.
No, not really.
Look, he asked for good hard SF that isnt depressing.
So, suggest what- in your opinion- is good hard sf that isnt depressing. Easy.
And if it doesn’t fit the OP’s definition of hard SF then it is a useless suggestion.
Oh boy. You know what’s even better than arguing over what’s hard SF? Arguing over whether we should argue over hard SF.
Do what you gotta do.
I read the title of this thread and immediately thought of Dragon’s Egg. I should have guessed I wouldn’t be the first to recommend it. 
I first read it back in college a few decades back. It’s one of the best novels I’ve ever read – definitely not depressing and a very interesting premise. My paperback copy is in in a box somewhere in the basement, so I bought it on Kindle a couple of years ago so that I could read it again whenever I wanted.
Not really a spoiler (just a technical point about fictional future technology in the story):
It’s not a major plot point, but the author spends some time discussing the fictional “HoloMem” crystals used for data storage in the story, which is set in 2050 (with even more detail provided in a technical appendix). Per the appendix, each HoloMem holds about 0.4 trillion bits, and the crystals are cubes 5 cm on a side. Since 0.4 trillion bits equates to 50 GB, and you can now get a microSD card with a capacity as great as 512 GB, it appears that in the real world we have surpassed the data density of the HoloMem crystals by several orders of magnitude several decades early. However, the novel was written in 1980.
Also not really a spoiler:
On the other hand, the very next technical appendix discusses the spaceship used in the novel, which is a “primitive monopole-catalyst fusion rocket”. We don’t seem to be anywhere near to developing anything like this.
The sequel was OK, I thought, but it didn’t grab me like the first book did. Maybe I should try reading it again.
Glad to hear that there is another Analog reader here! I got a subscription for my 13th birthday, and have maintained it continuously since then.
Anyway, I agree that it was a good editorial that questioned whether the apparently increasing prevalence of dystopias in SF is a good thing. As Mr. Lerner writes: “Fiction, like life, will always involve people confronting challenges. How about, a bit more often, we have plots show people surmounting those challenges?”
He goes on to give examples like addressing and solving environmental issues, and providing clean and abundant energy, as opposed to presenting failed societies set in a dystopian future with their “weird gladiatorial contests.”
Very fair summary, LHOD. The ansible is an example of “ftl technology”. Some people will immediately dismiss it as not “hard sf”. I just think that doing so creates an arbitrarily narrow boundary on the concept behind “hard” science fiction. And I only bring it up because several posts in the thread have debated whether or not individual suggestions met the OPs qualifying limits of “hard” SF.