"Impactful" is a very modern academic adjective. Usually it refers to publishing paper in journals with high impact factors (calculated by some formula) and receiving big number of citation. I tried to find out how impactful Gary Arnold Flandro's research is by searching Google Scholar. Not many papers were found, and most of them were published in journals that I am not familiar with. On that, he doesn't sound a very impactful scientist, right? So who is he?
In 1965, Flandro was a graduate student of Caltech. He used the summer to work as an intern in NASA's Jet Propulsion Laboratory, which locates only 13-min driving distance from Caltech campus. There he was given the job of looking at various possible missions to the outer planets (those outside the orbit of Mars). Since space crafts could not carry big amount of fuel, they relies on speed of inertness for reaching to the planet targets. Therefore, the exploring mission usually target one planet.
However, one day Flandro noticed that, in the year 1976, the outer planets would align in the formation, allowing Jupiter to accelerate fly-by space craft by its gravity toward Saturn, which in turn accelerated it toward Uranus, and then Neptune. It's like Tarzan trying to make long-distance travel by swing between trees, one by one. The particular alignment occurs once every 175 years.
Flandro reported his finding and it excited NASA immediately. A space needed to be built in 9 years for launching in 1977. In fact, NASA built two spacecrafts, Voyager 1 and 2, which was launched in September 5 and August 20 in 1977, respectively. This project was named appropriately as "The Grand Tour". The two space crafts would become the man-made objects that travel the farthest distance in human history. They have sent back so many valuable data and are still working, while leaving the solar system to enter the interstellar space.
After graduation, Flandro has been a very successful aerospace engineer and professor for decades. However, his concept and works to build the project of the Grand Tour impact the history of human civilization- and he has accomplished it as a summer intern! As biomedical researchers, we count number of publications, citations, and impact factors. When we reach to the later stage of our career, maybe we should look back and ask ourselves: what our impact really is.