void propulsionForm_FormClosed(object sender, FormClosedEventArgs e)
 {
     if (propulsionForm != null)
     {
         propulsionForm.Dispose();
         propulsionForm = null;
     }
 }
 private void buttonPropulsion_Click(object sender, EventArgs e)
 {
     if ((propulsionForm == null) && (modelControl != null))
     {
         propulsionForm = new PropulsionForm();
         propulsionForm.ModelControl = modelControl;
         propulsionForm.FormClosed  += new FormClosedEventHandler(propulsionForm_FormClosed);
     }
     if (propulsionForm != null)
     {
         propulsionForm.Show();
         propulsionForm.BringToFront();
     }
 }