Some Good News for the Human Exploration of Mars
NASA FISO Presentation: New Estimates of Space Radiation Risks are Favorable for Human Exploration of Mars
“Dr. Cucinotta developed the astronaut exposure data base of organ doses and cancer risk estimates for all human missions from Mercury to the International Space Station (ISS), and developed risk models for acute, cancer and circulatory disease.”
Note: The audio file and presentation are available online and to download.
Thanks for posting this Marc. Good, relevant, new information.
It’s remarkable how little the estimate of the radiation hazard has really changed in the last 30 years. The conclusion today is the same as it was then. The risk of radiation induced cancer is significant, but it is almost certainly lower than the risk the astronauts already accept of death due to destruction or failure of the spacecraft.
In my opinion the crew should know exactly what risks they face. But I am not sure we should be telling the astronauts they cannot accept a risk greater than 3%. This is not a profession that attracts people who are risk-averse. If they can choose to accept the risk of death in a spacecraft mishap, they should be given the same right to accept the radiation hazard and fly the mission, if they choose to do so.
That said, the whole analysis assumes a single mission to Mars and back with a small crew. If we really want to colonize Mars or the Moon, people will make multiple trips, be there for years or lifetimes, and the number of people will be much greater, as will both the individual and aggregate exposure. So we are back to square one. We still need much more effective radiation shielding.
Lightweight radiation and gravity mitigation DNE. Over the decades, NASA has shifted to operations (3B/yr SLS/Orion *2-4* g/cm2) and *abandoned* its Challenges, and the balance between R&D/Ops lost:3B/yr for a HLV + 2-4 g/cm2 capsule.
Of many, there are a few key sentences in the presentation.
o “Major Unanswered Questions in Cancer Risk Estimates– Lack of Data for Heavy Ion quality factors–will NASA *ever* fund such studies” (pg 35)
o “The current risk for a Mars mission is nearly 3-fold above acceptable risk levels” “Spacecraft have areas with at least 20 g/cm2 shielding” “Storm shelters with ~40 g/cm2 are practical” So 10X more mass required and is still 3 fold above the acceptable levels…..yet no funding… go figure.
o “Note: Leadership is finding solutions to space radiation problem, while waiving radiation limits is not leadership.”
Simply head to the moon for 6 day lunar sorties like Apollo, add 2-4 g/cm2 for SPE, ignore R&D, focus on engines.
It is *essential* that the architecture have a balance of R&D and Ops. One of the best balanced solutions is to use EP to preposition supplies and propellant with a direct shot 3 month trip to minimize crew health issues. At the same time, build and place prototypes that mitigate or study the health issues as L2, The perfect staging point to Mars. This balance approach develops the low cost infrastructure while at the same time performs *real* R&D. One can always take the more efficient 6 month trip too.
It seems to me one big solar flare and it’s all over. Though these studies are interesting I regard not much practical value until BEO travel becomes routine. Heck it’s years and years until we can do a single mission like a Apollo 8 repeat.
Depends on how sturdy your equipment is. The crew can be protected – flares usually don’t last long, and you can put your crew in a sheltered area behind packed water/etc for the duration. But that won’t do any good if it screws up the ship.
Radiation damage to the ship isn’t really a problem. Well, it’s a problem, but a solved one. I fatal dose for a person is around 500 rad (to use archaic units), while electronics which can survive 20,000 rad are common and parts which can take over a megarad are available. As far as the hardware is concerned, we can build a spacecraft that goes to Mars without radiation failures the same way we currently, well, build spacecraft that go to Mars without radiation failures.
That’s why I don’t think flares are a show-stopper for crewed missions to Mars. I was more worried about the other-than-cancer health effects of cosmic rays (because the cancer risk is probably tolerable as well, as long as you don’t do more than one mission as part of the crew – colonies or long-term outposts are another matter).
This presentation raised two interesting points about that 3% risk level.
First, it was adopted in 1989 because it was to career risk for people working in “less-safe” industries. But, since then, occupational safety has improved, and that same standard would, today, imply 1% or 1.5%. Does the fact that life in the United States has become safer imply that the acceptable risks from exploration have also dropped? I don’t think so, but that’s where the logic behind that 3% number would take us.
Second, the presentation states that, “Leadership is finding solutions to space radiation problem, while waiving radiation limits is not leadership.” I disagree with the first clause and also with the implication of the second. Solving the problem is a technical and engineering exercise, not policy making (which is what I would consider “leadership”.) While waiving a requirement might not be leadership, setting that limit (what level of risk is acceptable) certainly is. Whether it’s 3%, a floating limit (equal to current career risk in “less-safe” industries) or “leave it up to the astronaut” (as Woodard suggests), this is setting a high-level policy. When that’s done well, it’s called either leadership; when done poorly, it’s called a lack thereof.
At the same time, the study is a little positive. The standard is 3% at 95% confidence, and that’s much lower than a dose corresponding to the best estimate of a 3% risk. As the presentation notes, we can reduce the uncertainty in the estimates, so the 95% confidence level corresponds to a higher does, even if the 3% dose level hasn’t changed.
It’s not an easy area to study. What would you suggest?
As much as it makes me grimace, this is why we need an EML station. In the end, we will only be able to reliably estimate the prolonged radiation exposure risk for primates in exo-magnetosphere space if we actually ask (volunteer) astronauts to experience prolonged exposure. A space lab 5-10 days away in cis-Lunar space would be ideal for this.
The extremely long latency periods for radiation induced cancer and the low and sporadic incidence would mean that any method utilizing large animals, whether humans or primates, would take decades and cost billions. And how would we send people to take care of the primates if we do not know if it is safe?
I think Dr. Cuchinotta’s analysis is sound; he has a lot of data we did not have 30 years ago. However a large part of the presentation is devoted to the question of “How much risk should the astronauts be forced to accept?” I think there’s a simple answer to that. Ask the people who will be going. I don’t know any of them who would turn down the flight.
We’re not trying to give the astronauts cancer. We’re trying to carry out biomedical monitoring for long durations in exo-Magnetosphere space.
I am not sure that long-term monitoring is needed. To predict effect of spaceflight we need 1) ground-based biological experiments with artificial sources to refine the model of biological effects and 2) instrumented probes to assess the natural radiation environment at various locations in space. The radiation risk can already be predicted accurately enough for potential crewmembers to make a reasonable decision as to whether to go.
Actually, your second point is covered in some of the presentation. There is a comparison of model radiation flux and dose to the actual measurements by the RAD instrument on Curiosity. The model is pretty good.
In the back-up material. Where it summarizes past recommendations, a 2010 external review is quoted as saying, ”The Panel believes that, at this time, the accuracy of predicting particle fluxes in space (of the order of ±15%) is sufficient for risk prediction and could not be significantly improved without a major investment in resources better utilized in addressing other gaps.”
I agree. The NASA standards of adding a 95% confidence limit on top of the “acceptable” 3% risk and of including non-ocupational exposure (i.e. medical tests) in the career limit are inconsistent with the approach followed in other industries under the direction of the Nuclear Regulatory Commission, in which medical treatment is not included because the goal of regulation is to provide a safe workplace and the guiding principle is not to achieve a specific level of risk, but rather to keep exposure as low as reasonably achievable.
What is your point about the age of the data?
The Subtitle of the talk is: “However major scientific questions remain”…so after decades no new data or methods to approach the problem.
Gathering data for decades will be costly, hence the need to have a balance between operations and R&D. A crew tended deep space voyager position at L2 is step in that direction, where it receives full GCR at the proper dose rate.