-my $satname = uc shift @f;
-my $numhours = shift @f; # the number of hours ahead to print
-my $step = shift @f; # tracking table resolution in minutes
+my $satname = uc shift @f if @f;
+my $numhours = shift @f if @f; # the number of hours ahead to print
+my $step = shift @f if @f; # tracking table resolution in minutes