The impact of the Apollo space program runs deep. Aside from the vast technological and scientific advancements it brought to life, footsteps on the moon left a legacy of hope, wonder, inspiration, and unity. The Apollo astronauts took humanity on a crazy journey of discovery. Now it seems that, even in death, Apollo astronauts are helping us prepare for future journeys that involve deep space travel.
|The emblem of the Apollo program.
Image Credit: NASA
Project Apollo lasted for 11 years (1961-1972), and manned missions took place during the last four of those. Nine of these missions involved astronauts flying into deep space. All other human spaceflights have stayed within or below low Earth orbit, which tops out at around 1,200 miles above the Earth. The moon, on the other hand, is about 200 times as far from the Earth as this. The International Space Station is just 160 miles from the Earth. Apollo astronauts are the only humans to have traveled so far into space.
According to research published yesterday in the journal Scientific Reports, astronauts who flew on Apollo missions have a significantly higher mortality rate due to cardiovascular problems than other astronauts. This may be the result of their exposure to deep space radiation say the authors, a theory supported by experiments the team performed on mice.
In a detailed analysis of the cause of death of astronauts that included cardiovascular disease, cancer, accidents, and all other causes of death, Michael Delp from Florida State University and his co-authors* found that Apollo astronauts that traveled into deep space had a 43% mortality rate from cardiovascular problems, a rate 4-5 times higher than astronauts that didn’t travel into space and astronauts that flew in low Earth orbit.
The researchers readily admit that they are working with small numbers. Only 24 men and no women have traveled into deep space, and eight of them have since died. Seven were included in the study, the eighth passed away after the analysis was complete. This Apollo group was compared to two control groups: one included 35 astronauts that flew in low Earth orbit, and the other consisted of 35 astronauts that were trained but never flew. The average age at which they were selected to become astronauts, age at time of death, and total days spent in space were the same for all three groups.
Astronauts experience physical conditions that differ from life here on Earth—most notably they spend extended periods of time in microgravity. Astronauts are also exposed to harmful space radiation, which is ordinarily blocked by Earth’s atmosphere and magnetosphere—the magnetic “shield” generated by the planet’s molten, spinning core. To explore whether the increase in cardiovascular-related deaths could be related to either of these factors, the researchers studied the effect of both on mice. Their findings showed that six months after treatment (the equivalent to about 20 years for a human in terms of average lifespan), mice that were irradiated sustained a kind of damage known in humans to lead to plaque buildup in the arteries. Mice that experienced only simulated weightlessness didn’t show any cardiovascular effect, nor did a control group.
Although astronauts in low Earth orbit are outside of the Earth’s atmosphere, they are still inside of the Earth’s magnetosphere, which deflects away less energetic, lighter radiation particles from galactic cosmic rays and solar flares. Astronauts in deep space don’t have this protection. In fact, they have to travel through the magnetosphere, which contains trapped radiation. This could mean increased exposure and increased health risks. Although some recent studies have demonstrated that ionizing radiation may be associated with increased risk for cardiovascular disease, this hasn’t really been explored for space radiation.
In addition to the small numbers, the authors point out two additional limitations of their study. First, it’s still not clear exactly what specific factors may be responsible for the cardiovascular damage. It’s a challenge to reliably estimate the radiation dose on an astronaut, but it’s not clear that Apollo astronauts experienced significantly more total radiation from galactic cosmic rays than those in low Earth orbit. It could be that the energy distribution of the radiation makes a difference, but this is still unclear. Second, the mice received higher doses of radiations than astronauts, and over a shorter period of time. Nevertheless, the results indicate a connection between this type of radiation and long-term cardiovascular damage.
As we look forward to sending astronauts to Mars and back to the moon, it’s clear that a number of health concerns need to be more thoroughly explored. In fact, a 2015 audit report by NASA highlighted several health hazards that must be addressed before humans blast off for Mars. Minimizing the risks of these thrilling missions means first identifying the risks, really understanding them, and then determining an appropriate course of action. This work is an important step in that direction, and gives us one more reason to look back and honor the brave astronauts that first set foot in deep space.
*Delp’s co-authors include Jacqueline Charvat from Wyle Science, Technology and Engineering Group, Charles Limoli from the University of California Irvine, Ruth K. Globus from NASA Ames Research Center, and Payal Ghosh from Florida State University.