Mix the sugar and cornstarch, add the orange juice and bring to a boil stirring constantly. Boil for 2 minutes. Beat egg yolks slightly and add to the cooked mixture, boiling for another minute. Remove from heat and pour into baked pie shells. Beat the egg whites, add 1/2 cup sugar and continue to beat until stiff. Pile on top of pies and bake in a slow 325°F oven for 15 to 18 minutes or until brown.