John Glenn's first flight ushered in the modern era of space exploration for America. His landmark return to space represented the final chapter of space exploration in the 20th century. John Glenn's first flight ushered in the modern era of space exploration for America. His landmark return to space represented the final chapter of space exploration in the 20th century. John Glenn's first flight ushered in the modern era of space exploration for America. His landmark return to space represented the final chapter of space exploration in the 20th century. John Glenn's first flight ushered in the modern era of space exploration for America. His landmark return to space represented the final chapter of space exploration in the 20th century.