An astronaut riddle is:
 
Q: When does an astronaut eat?
A: At launch time.
 
“Launch” sounds a little bit like “lunch.” The joke has been cited in print since at least 1965 and 1966.
 
 
10 June 1965, The Rockland County Journal-News (Nyack, NY), “Noah Numskull” cartoon, pg. 42, col. 6:
DEAR NOAH—HOW CAN AN ASTRONAUT EAT BEFORE “LAUNCH TIME”?
VERA LEWIS
HOLLAND, MICH.
     
14 May 1966, The Globe and Mail (Toronto, ON), pg. 34, col. 7 ad:
Q: When does an astronaut eat?
A: At launch time.
(Thorncrest Ford.—ed.)
       
10 July 1976, Battle Creek (MI) Enquirer and News, “Mini Jokes,” The Mini Page, pg. 3, col. 1:
Q. Why did the astronaut eat a sandwich?
A. It was launch time!
—Sandy Oliver, Battle Creek
 
22 October 1978, Newsday (Long Island, NY), “Smiles,” Kidsday sec., pg. K13, col. 3:
When do the astronauts eat?
At launch time.
—Bobby Mulcahy, Shoreham
 
Google Books
July 1993, Boys’ Life, “Think & Grin,” pg. 88, col. 2:
Telly: At what time does an astronaut eat?
Nelly: I haven’t a clue. When?
Telly: At launch time. — Mark Ferisin, Irvington, N.Y.
   
Google Books
Kids’ Funniest Jokes
Edited by Sheila Anne Barry
New York, NY: Sterling Publishing Company, Inc.
1993
Pg. 77:
When do astronauts eat?
At launch time.
SAMANTHA THOMSON, 7
 
10 August 1996, Morning Advocate (Baton Rouge, LA), “Jumble” word game by Henri Arnold and Mike Argirion, pg. 8C, col. 3:
When did the astronauts eat their meal?—AT LAUNCH TIME
 
26 January 2001, Los Angeles (CA) Times, “The Kids’ Reading Room; Jokes & Riddles,” pg. E8, col. 4:
When does an astronaut eat? At launch time. (Carlos, 9, Chavez Elementary, Norwalk)
   
Google Books
696 Silly School Jokes & Riddles
By Joseph Rosenbloom\
New York, NY: Sterling Publishing Company, Inc.
2003 (1986)
Pg. 63:
TEACHER: When do astronauts eat?
SCOTT: At launch time.
   
Google Books
The Super, Epic, Mega Joke Book for Kids
By Whee Winn
Grand Rapids, MI: Zonderkidz
2016
Pg. ?:
When do astronauts eat?
At launch time.
   
Google Books
Laugh-Out-Loud Jokes to Tell Your Friends
By Michael Dahl
North Mankato, MN: Capstone Press
2018
Pg. 29:
When do astronauts eat?
Launch time
 
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@dadtellsjokes
When does an astronaut eat?
At Launch time!!
6:15 PM - 6 Mar 2018