I purchased the application from the MacUpdate website, downloaded it, unzipped it, and installed it. I found a bunch of old threads suggesting that I should copy the files to my desktop and back to remove the "quarrantine" but this did not work. I found another thread suggesting that I needed to move the files from the Applications folder to a (writable) User folder, but this did not work either. I found a log file from one of my earlier attempts:
[LOG 10:49:42.211] ******* Log Initiated for Kerbal Space Program - 1.5.1.0 (OSXPlayer) *******
Kerbal Space Program - 1.5.1.0 (OSXPlayer)
OS: Mac OS X 10.11.6
CPU: Intel(R) Core(TM) i5-5575R CPU @ 2.80GHz (4)
RAM: 8192
GPU: Intel(R) Iris(TM) Pro Graphics 6200 (1536MB)
SM: 46 (OpenGL 4.1 INTEL-10.14.74)
RT Formats: ARGB32, Depth, ARGBHalf, Shadowmap, RGB565, ARGB4444, ARGB1555, Default, ARGB2101010, DefaultHDR, ARGB64, ARGBFloat, RGFloat, RGHalf, RFloat, RHalf, R8, ARGBInt, RGInt, RInt, RGB111110Float, RG32, RGBAUShort, RG16
Log started: Wed, Oct 24, 2018 10:49:42
[LOG 10:49:42.297] Loading data opt-out preferences from PlayerPrefs
[LOG 10:49:42.330] Requesting data opt-out preferences from https://data-optout-service.uca.cloud.unity3d.com/player/opt_out?appid=39811e89-d29d-4faa-bb01-997f3cda24f0&userid=104558b8185194600ac5beb0a124ef5f&deviceid=DFE56116-CFDE-5F54-9F75-E9E5533B6E47
[LOG 10:49:42.356] ActionCanvas MASK: 3458764513820540928
[LOG 10:49:42.357] MainCanvas MASK: 3458764513820540928
[LOG 10:49:42.359] PhysicsGlobals: Loading database
[LOG 10:49:42.366] AppCanvas MASK: 3458764513820540928
[EXC 10:49:42.377] DirectoryNotFoundException: Directory '/Applications/GameData/Squad' not found.
System.IO.Directory.GetFileSystemEntries (System.String path, System.String searchPattern, FileAttributes mask, FileAttributes attrs)
System.IO.Directory.GetFiles (System.String path, System.String searchPattern)
System.IO.DirectoryInfo.GetFiles (System.String searchPattern)
System.IO.DirectoryInfo.GetFilesSubdirs (System.Collections.ArrayList l, System.String pattern)
System.IO.DirectoryInfo.GetFiles (System.String searchPattern, SearchOption searchOption)
(wrapper remoting-invoke-with-check) System.IO.DirectoryInfo:GetFiles (string,System.IO.SearchOption)
FontLoader.FindFonts ()
FontLoader+<LoadFonts>c__Iterator0.MoveNext ()
UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
FontLoader:StartLoad()
<LoadSystems>c__Iterator0:MoveNext()
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
LoadingScreen:Start()
[ERR 10:49:42.379] Couldn't open /Applications/KSP.app/Contents/Plugins/3DConnexionWrapperU5.bundle/Contents/MacOS/3DConnexionWrapperU5, error: dlopen(/Applications/KSP.app/Contents/Plugins/3DConnexionWrapperU5.bundle/Contents/MacOS/3DConnexionWrapperU5, 2): Library not loaded: /Library/Frameworks/3DconnexionClient.framework/Versions/A/3DconnexionClient
Referenced from: /Applications/KSP.app/Contents/Plugins/3DConnexionWrapperU5.bundle/Contents/MacOS/3DConnexionWrapperU5
Reason: image not found
[ERR 10:49:42.381] Couldn't open /Applications/KSP.app/Contents/Plugins/3DConnexionWrapperU5.bundle/Contents/MacOS/3DConnexionWrapperU5, error: dlopen(/Applications/KSP.app/Contents/Plugins/3DConnexionWrapperU5.bundle/Contents/MacOS/3DConnexionWrapperU5, 2): Library not loaded: /Library/Frameworks/3DconnexionClient.framework/Versions/A/3DconnexionClient
Referenced from: /Applications/KSP.app/Contents/Plugins/3DConnexionWrapperU5.bundle/Contents/MacOS/3DConnexionWrapperU5
Reason: image not found
[WRN 10:49:42.383] [SpaceNavigatorMac]: Could not initialize device.
3DConnexionWrapperU5
[LOG 10:49:42.668] Opt-out preferences successfully retrieved, applied and saved:
{"optOut":false,"analyticsEnabled":true,"deviceStatsEnabled":true,"limitUserTracking":false,"performanceReportingEnabled":true}