How to skip challenge mode. Edit the "moonbase.ini" file in the game folder. Locate the "[Challenge]" heading towards the end of the file. The entries in this section look like "0-3=3". The number after the dash is the challenge mode level number. The number after the equals sign is the medal you have on the level. Use the following hint for the values:
0: Not completed
1: Gold
2: Silver
3: Bronze