Place sugar, 1/2 cup water, and orange peel in small saucepan. Bring to simmer over high heat, stirring to dissolve sugar. Reduce heat to medium. Simmer 1 minute.
Pour into 8x8x2-inch metal pan and cool.
Puree melon in processor until smooth but some texture remains. Measure scant 2 cups melon puree and add to syrup in pan.
Whisk to blend. Freeze mixture until thoroughly frozen, about 4 hours, stirring with fork every 1 1/2 hours. Cover and keep frozen.
Using electric mixer, beat cream and sugar in medium bowl until peaks form. Using fork, scrape granita into icy flakes. Spoon 2 rounded tablespoons granita into each of 6 glasses. Top granita with 1 rounded tablespoon whipped cream. Repeat layering with granita and whipped cream.
Garnish with mint sprigs, if desired, and serve immediately.