
Check out B. V. Larson's Swarm and Undying Mercenaries series, Dennis E. Taylor Bobiverse series, and Craig Alanson's Expeditionary Force.
Also what I mentioned to OP, what I'm doing my annual re-listen of https://www.goodreads.com/series/51166-troy-rising
They're not Heinlein by any means but they're fairly good hard science fiction. The audiobook versions all have fantastic narrators too if one has a commute.
- Hopscotch, by Kevin J. Anderson
- In Hero Years...I'm Dead, by Michael A. Stackpole
- On My Way to Paradise, by David Farland
- Santiago, by Mike Resnick
- Swarm, by B. V. Larson
- The Disappeared, by Kristine Kathryn Rusch
- (bonus) High-Opp, by Frank Herbert
- (bonus) The Stars in Shroud, by Gregory Benford