This is a barred crossword with no specific grid symmetry.

Across:
1. One of two repeated words throughout a Beastie Boys song
2. Drones (abbr.) / Excite
3. Thine, in Turin / Brunch cocktail
4. Bury / Set of named constants
5. Joined together / Earth Day mon.
6. Antonio or Andreas / Type of penguin
7. Riyadh resident / Ladder foothold
8. Asian island about the size of Maryland / This precedes a switch
9. Missile abbr. / Fundamental particles
10. Ligotti’s Masquerade subtitle (2 wds.)
11. Brain recorder (abbr.) / On the same side of a molecular plane / It replaced WOV and LBW
12. Temple ___ Brith / Traveling workers
13. Even / Spread
14. Elderly / Part of the Old World
15. It administers the Clean Air Act / A general, in some parts / Radioactive, slangily
16. WMO program / Production
17. It connects heaven and earth (2 wds.)
18. Part of a tea brand name
Down:
A. Wadi Sura II (3 wds.) / Get ready for a spacewalk (2 wds.)
B. One of Corot or Kepler’s discoveries / Mini-stroke (abbr.) / Yearly
C. ESA mission to measure gravitational waves / An informative drawing / Standard of measure / Eggs
D. Obscure / Blood group system / Palm fruit / ISP with a butterfly logo
E. Site of Burke-Gaffney Observatory (abbr.) / Card drafting game themed around Japanese food (2 wds.) / Astronaut with four Stanford degrees / Excite
F. Private instructor / Biblical leader / Raised, say / Spew
G. “P as ___” (2 wds., Friends) / Having no chance for success (abbr.) / Russian ballerina Galina
H. Song in An American Tail (2 wds.) / Eragon author / Bite / ___ error
I. Leaves trash around / It was created at Yalta (2 wds.)