# What is the big hole next to the 2mm hole that caused the 2018-08-30 Soyuz MS-09 / ISS leak?

The small hole in this picture is being reported as the cause of the ISS leak. What is the large hole next to it on the perpendicular surface? The one that appears to have been drilled by an amatuer with a hole saw? Does it have a purpose?

• @Uwe You think these holes were cut to save weight? That seems very unlikely. Also, there are lots of reasons to deburr holes e.g. keeps debris from breaking off later, rounds off sharp edges that could snag or cut something. – foobarbecue Sep 12 '18 at 23:28
• Weight-saving holes are common in aerospace vehicle structures. Like the ones in the ribs of this airplane wing. cfinotebook.net/graphics/aerodynamics-and-performance/… – Organic Marble Sep 13 '18 at 2:02
• That said, I agree with you about the apparent low quality of this work. – Organic Marble Sep 13 '18 at 2:04
• Looks like the big holes are painted, but the small hole is not. That may be a clue to when they were made. – DrSheldon Sep 13 '18 at 7:21
• @OrganicMarble oh my word, I've been looking at it wrong this whole time! I've been seeing the larger hole as more distant than the smaller, damn you schroeder stairs! – Jack Sep 13 '18 at 13:27

It's a lightening hole.

The structure you see on the upper right of the image is a ring frame with a flanged C-channel cross-section that goes around the circumference of the Soyuz orbital module pressure shell. Below is a crude text diagram of what you're looking at:

            __________
|          |
|          | <-- lightening holes here
|          |    leak here
|          |   /
_______|          |__v____
------------------------- --------
^
Pressure wall here


The leak hole is in the flange of the C-channel, and the lightening hole (one of many, regularly spaced along the channel) is in the "vertical" wall of the C-channel. The "ragged" appearance of the lightening hole is actually residue from some tape that was covering the ring frame. You can see some of that tape at the bottom center of the image.

• Very good graphic to explain where is the pressure wall and where the ring frame. Also where are the lightening holes and the leak. If the leak would be covered by the ring frame, fixing it would be difficult to impossible. – Uwe Sep 13 '18 at 18:10