Across:
   1. see 24 down
   6. Vessels around southern fringes (5)
   9. Old nine act play (7)
  10. One-vehicle weeding device - novel! (7)
  11. One with fear of no energy? Not even close! (4)
  12. Great traveller's excitement reaches peculiar nadir around start of landing (4 6)
  14. see 2 down
  15. Agreement by the boss as I plan big finales (7)
  17. Near the destination, but partially grounded (7)
  20. State where I'd be lost in vegetation (7)
  22. Turned shy at pricy treatment! (10)
  23. Marks correct but backward, with no colour intially in sketch (4)
  25. Recreation relies on travelling around University (7)
  26. Instrument of British union alternating between the right and left (7)
  27. Exciting and great lander, establishing firsts (5)
  28. As pets, llamas making a comeback, but missing a little bit of the process (5 4)
Down:
   1. Have canal rebuilt for mounting danger (9)
   2,14ac. Great traveller in hell's comical disarray (7 7)
   3. Voyage some might rekindle? (4)
   4. Gets away from crazy sour nut (7)
   5. Large beast sounds unhappy (7)
   6. Map working to protect the French in upbeat activity (10)
   7. Thus finally pop star gets introduction to Zappa and his essentially light-hearted pieces of music (7)
   8. Vessel back without levity (5)
  13. Might it save vessels to commit act of arson? (10)
  16. Two soldiers plea to be relocated, as a 28 may be (when expanded upon?) (5 4)
  18. Right before religious music embraces one God with similar final sounds (7)
  19. Where to store things like underwear (7)
  20. Recipe for KAl(SO4)2-12H2O coming up? (7)
  21. Terrible stink around that is most dark! (7)
  22. Sign of living healthy food (5)
  24,1ac. Great traveller returning (not the first one) ignores title "Alien" after making "E.T." (4 9)