Security isn't really necessary in this colony, as there are no sentient beings or even hostile creatures. We could bring you along because the government demanded it for their funding, and then have pirates from the solar system follow us (or find out that they are already here), but other than a sheriff, I don't really think security would be necessary without something like that..
If your security force had technical skills (ex: army corp of engineers, air force scientists, etc.) then it could make sense too. Then their security role would be secondary, in case the pirates follow or we find hostile creatures/aliens.