Vertical staff spacing between song parts

[address@hidden]

Greetings,

I'm engraving an instrumental that has three parts; each part is two lines long.  How can I arrange them on the page so that there is vertical space between the parts. 

Here is a tiny example:

\version "2.18.2" \language "english"

\score {
     \new Staff 
     {
       a1^"part 1"  a a a \break
       a1 a a a \break
       a1^"part 2"  a a a \break
       a1 a a a \break
       a1^"part 3"  a a a
       a1 a a a \break
     }
}

Is there a way to create vertical space between the parts?

Thanks in advance for your assistance.

BruceP