To Mars or Bust - Weakened Immune Systems
A new study by Bigley et al. (2018) has revealed prolonged spaceflight weakens astronauts’ immune systems. This should be taken very seriously by the likes of those eager to send humans to Mars within the next few years. The study monitored 8 crewmembers of the International Space Station (ISS) by taking their blood samples before, several times during, and after their missions. When compared to healthy humans on Earth, it revealed impaired immunity.
More specifically, the blood tests taken during their study showed impaired function of what are called natural killer cells (NK cells). These are cells in our bodies that are a type of cytotoxic lymphocyte critical to our bodies’ innate immune system. In addition to their collective critical role in our bodies’ innate immune system, they also play an important role in our adaptive immune response (Murillo et al., 2007).
NK cells have a rapid response to virus-infected cells, as well as tumor formation; tumors, as in cancer. Unlike other immune cells (e.g. T lymphocyte cells), NK cells can detect harmful cells even in the absense of a certain marker (MHC I). In simpler terms, this means they are capable of recognizing stressed cells in the absense of antibodies—something other immune cells must first recognize before jumping into action—thus allowing for a much faster immune reaction. This is critical here on Earth, and only more so in a hermetically-sealed spacecraft bound for Mars.
NK cells’ collective role in both our innate and adaptive immune responses has made their activity a primary focus as a potential cancer therapy. That alone should speak volumes of how critical their proper function is to our survival.
Every step conceivable is taken to ensure spacecraft bound for Mars (or anywhere for that matter) are sterile. Absolute sterilization is not foolproof, but even if we were to assume a crewed spacecraft were perfectly sterile, we must remember that the bodies of its crew will invariably host dormant viruses from previous infections.
Viruses responsible for shingles, mononucleosis, cold sores, and other infectious illnesses remain in the body for a person’s entire life. Such viruses reactivate when the body is stressed, as I presume would be the case when in spaceflight. I can think of few things more stressful to an organism’s physiology than to take it out of the environment in which it evolved, and place it in one that is completely foreign to it. In this case, humans would be taken from the planet on which they evolved, crammed into a metal cylinder, launched into a high-radiation environment with no gravity, and given no guarantees of a safe return.
NK cells supress dormant viruses from reactivating… on Earth. Yet as the Bigley et al. (2018) study has shown, NK function is impaired under conditions of prolonged spaceflight, which suggests dormant viruses in the body can reactivate unhindered. In fact, NK function impairment is evident by day 90, when NK-cell cytotoxic activity against leukemia cells in vitro decreases by about 50% (Ibid.).
And while the study showed slightly less NK function impairment in veteran astronauts as compared to rookies, the impairment exists nonetheless. Also, there are no veteran astronauts when it comes to Mars.
No human has ever experienced spaceflight beyond Earth’s protective magnetic field, much less attempted to land on another planet. The only veterans who have experienced landing a spacecraft on a foreign celestial body are either deceased, or too old to physically participate in future Mars missions.
So I suspect even “veteran” astronauts, should they be bound for Mars, will experience a tremendous amount of stress. The track record for successful landings on Mars by uncrewed landers is not what I would call reassuring. Unlike our moon, Mars has just enough gravity to make things considerably difficult for would be landers.
While tedious emotional stress takes its toll, Mars-bound astronauts will be subject to the realities of cosmic radiation beyond Earth’s protective magnetic field. An experience no human has ever known. Sadly, some popular vloggers on YouTube seem to think the fact our Sun is in a prolonged inactive period (solar minimum), that radiation levels for a Mars-bound crew will be less. And they’re naive followers believe them without question.
Solar minimum does not equate to less radiation. This belief is simply not true, precisely because its folly is to assume the Sun is the only source of radiation in our solar system. While the solar wind is weaker during solar minimum, and the likelihood of coronal mass ejections (CMEs) during solar minimum are decreased, those weaker solar winds are unfortunately less effective at deflecting ionizing cosmic radiation. There are more stars out there spewing ionizing radiation than just our Sun, and their cell-destroying radiation will wreak havoc on the biology of unprotected crews bound for the red planet. I’ve seen nothing done in the way of outfitting spacecraft with protective shields of one sort or another (e.g. magnetic shielding) to mitigate or prevent this danger.
The hype around new rocket tech seems stuck on how reusable they are, or how much cargo they can carry, or how cool their names are (e.g. BFR). While these are important factors (save for rocket names), they pale in comparison to the importance of how well a spacecraft can protect its crew for missions that would be as long as those intended for Mars. Certainly not a genuine priority at SpaceX whose launch window for a crewed mission is just over 5 years away at the time of this writing.
One can only imagine the inherent dangers posed by a crewmember harboring dormant viruses in a sealed spacecraft unable to return to the safety of Earth for years due to facts only advanced differential calculations could reveal with regard to planetary orbits and rocket trajectories. Under stress, and other factors not yet understood, her or his dormant viruses could reactivate, causing illness to the host as well as likely infect the rest of the crew. It’s like those cruise ships that make the news every year, where everyone on board gets diarhea. When you’re stuck in a confined space, even a cruise ship, and forced to eat the same food, use the same facilities, breath the same air, you become a target for whatever illness is on the loose.
If a human can make mistakes while healthy, then consider the likelihood of there being critical ones by those who are battling some sort of sickness in flight. And if they get sick, they will have to contend with it on their own. There is no turning back to Earth for help.
Missions to Mars are unlikely to be less than 850 days in duration; from time of launch from Earth, to time of landing back on Earth. It will take 9 months just to get to Mars, and while many have touted faster flight times to Mars, they haven’t explained how faster spacecraft will slow down and land on Mars without flying right by it, or killing the crew by crushing their vital organs during acceleration. I’d imagine anyone from the Mercury missions could attest that G-force on the human body is often more intense during the acceleration of slowing down, than speeding up.
The New Horizons spacecraft traveled through our solar system at an impressive 36,000 mph… and it flew right by its target (Pluto), unable to slow down enough to position itself in orbit, much less make a landing… and so on it goes into oblivion. That’s obviously not the fate we have in mind for future crewed missions to Mars.
The energy needed for a transfer between planetary orbits (called “Delta V”) is lowest at intervals fixed by the synodic period; the time between successive conjunctions of a planet with the Sun. Insofar as I’m aware, the lowest energy transfer to Mars is a Hohmann transfer orbit, which for a crewed spaceflight unwilling to endure 15 Gs of acceleration, would take about 9 months. It takes 26 months between launch windows when Mars is closest to Earth (an opposition). So a crew that actually makes it onto the red planet without crashing will have to endure another 500 days or so on the planet’s surface in wait for the next transfer window to Earth, then another Hohmann transfer of about 9 months to get back. That’s 18 months of spaceflight, and well over a year on a hostile planet nearly devoid of a protective atmosphere, or magnetic field.
Perhaps engineers could design a spacecraft capable of shaving off a couple months from the roundtrip journey to/from Mars, but the crew would still be exposed to elevated levels of radiation whilst suffering from compromised NK function.
While I’ve suggested crewed missions to Mars are needed to truly investigate the planet’s geomorphilogical past, I realize it isn’t entirely necessary. Robotic missions are showing their worth, and can be done at considerably less cost than sending humans to Mars. In fact, I now see the only reason to send humans to Mars as little more than hyperbolic delusions of grandeur of national, institutional, corporate, and individual pride.
Apollo 8 astronaut, Bill Anders agrees. And while I’m committing a host of logical fallacies by name dropping, I see no other reason for the push to go to Mars other than perhaps the benefits highly-publicized missions have on funding for certain organizations. I can understand this, as I feel funding for certain organizations has always been paultry. But there are many other missions of greater benefit to humankind than trying to set foot on Mars, when we can send more robotic rovers instead.
Mars entire population right now is robots, and they’ve taught us a tremendous amount about that fascinating planet(ary embryo). To send an NK-function impaired, sickly, stressed, border-line-lord-of-the-flies crew there seems unnecessarily naive. But what do I know?