If you've ever wondered what connection could there possibly be between chocolate and the space program, well, there is one. According to Colonel Chris Hadfield, the Canadian astronaut, it's the shape of a Hershey's Kiss.
On December 12, Hadfield posted on Facebook a picture of four spaceships, comparing the shape of the re-entry modules. All four have a similar shape. It's actually Hadfield's son Evan who manages most of Hadfield's social media posting, and he does so with grace and efficiency.
The Hadfields wrote a caption for the image:
The natural shape of spaceships. Apollo vs NASA's current fleet under construction. The Hershey's Kiss shape makes the spaceships inherently stable, and the broad flat bottom helps spread the blistering heat of re-entry. By moving the centre of gravity we can alter how the ships fly, and thus roll and steer them to both reduce g-load and land precisely.
It was Evan Hadfield who went on to add the following note:
All four of the modules shown have the same basic curved bottom, for the heat shield that protects the module while it returns to the Earth's surface. It is the shifting of the centre of gravity that allows it to creates lift – they shift it in the shaping of the capsule. Those two concepts are just different descriptions of the same thing.
One of the readers of Chris Hadfield’s Facebook page, Scott Corliss, had this to say about the curved bottoms of the re-entry modules:
The basic shape and curveture radius for the heat shields were worked out in the early 1960s by Harvey Allen, Max Faget and Caldwell Johnson (as noted in a book, Smithsonian Air & Space Collectors Edition, Fall 2013). Slide rule and engineering paper solutions still work today!
There's an adult discussion about the shape of the re-entry modules on the Space page on Reddit; for those who like to get a bit technical, click here.
And for those of any age who prefer a more hands-on approach to learning about space, there’s a link to a page here with instructions on how to make a spaceship-shaped treat for a space-themed party, complete with a Hershey's Kiss on top for a re-entry module. Now I know what to make for my brother's next birthday party -- he's been a spaceship fan since before the Apollo launches!