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Lesson 8 Archive Notes: May 19, 2010

Posted by drspaceshow in Uncategorized.

Space Show Classroom Lesson 8:  Human Factors, Part Two

 Tuesday, May 18, 2010

 Archive Notes and Program Information

 The Space Show Classroom Lesson 8 can be downloaded or heard at:


Guests:  CLASSROOM:  Dr. Jim Logan, Dr. John Jurist.  Topics:  Lesson 8, Human Factors Part Two.  Drs. Logan and Jurist returned for this Classroom program which focused on long duration human spaceflight.  As we started our first segment, I asked our guests what constituted long duration spaceflight. The working definition centered around spaceflight more than six months to a year in duration and any human spaceflight going beyond LEO.  Both our guests said there were no show stoppers regarding Life Science in short term space flight but that it was very different in the long duration flight with the two major issues being radiation and microgravity effects, specifically bone issues.  During this first segment, we focused on the bone loss issues.  Our discussion with Dr. Logan and Dr. Jurist was comprehensive and detailed, explaining the problems, the facts about exercise (you will probably be surprised at what you hear on this topic), and counter measures such as artificial gravity, centrifuges, bisphosphonate usage, and more.  Because of the bone loss issues, Dr. Logan said that some destinations in space would probably be classified as a civilization destination while others would be typed as a sortie destination.  We talked about the lack of knowledge for the gravity prescription and what that really means for human spaceflight.  In discussing artificial gravity which was typed as pseudo gravity by our guests, we learned that it was not the same as natural gravity on Earth and the lack of knowledge about it was a problem.  You will certainly want to hear this comprehensive discussion on this and the other topics in this segment.  Our second segment focused on space radiation issues.  The two major types of radiation were identified as cosmic rays and the solar wind.  Dr. Logan gave us some interesting facts for comparison in shielding on Earth versus shielding in a spacecraft, a space habitat, and a spacesuit.  You will want to pay particular attention to the percentages Dr. Logan provided as this information was used throughout this segment.  Our guests brought up the solar cycle, solar modulation from all directions, the LRO mission and its data findings, and the geometric issue for radiation shielding.  We also talked about magnetic shielding and noted that when the spacecraft size decreases, the radiation field needed to deflect particles increases.  Don’t miss this discussion and explanation.  Dr. Rowe asked about radiation and the early Apollo missions.  Joe asked as question about the atmospheric particles and could they be used for shielding.  Don’t miss the answer to these questions.  Much of our discussion centered on possible mitigation techniques.  We went over many of those suggested but Dr. Logan suggested that the ultimate answer would not be in the form of a silver bullet but more likely a multiple faceted solution, a type of sandwich of solutions mixed together.  Near the end of the program, our guests responded to a medical treatment question for a long duration spaceflight crew member with a heart attack.  Pharmaceutical usage in space was talked about and our guests brought up the fact that humans were the weak link in the spaceflight chain.  Fly By Wire was used as an example.  Please remember to visit The Space Show Classroom Blog at https://spaceshowclassroom.wordpress.com.  Post all your comments and questions there.  Any comments or questions sent to me will be posted to the blog under the name of the sender. 


1. Jim Davis - May 21, 2010

This was a great show as is the Classroom series as a whole.

I’m curious if the standard science fiction cliche of some form of “hibernation” (as depicted in 2001: A Space Odyssey, for example) is a practical proposition. If so, would such a procedure alleviate bone loss on long duration missions?

Thanks and I look forward to future shows.

2. jmj - May 21, 2010

Interesting questions. The short answers are “no” and “probably not.” Current technology allows human body temperatures to be reduced somewhat in order to cut metabolic rate but cellular activity continues at a reduced rate. Thus, bone loss would most likely continue. If our technology allowed freezing and (successful) thawing of people, which it does not, bone loss might be stopped. Remember the frost on the crew pod windows in 2001 before HAL turned off the freezers? We are not even close to that kind of capability.

3. Jim Logan - May 21, 2010

Thank you for your feedback. We appreciate your comments. Glad you are enjoying the Classroom.

Excellent question about the possibility of hibernation!

Black bears hibernate for up to seven months without bone loss. They maintain bone mass and strength during this prolonged period of inactivity.
In space, astronauts immediately go into a negative calcium balance. Bone resorption (by osteoclast cells) proceeds unchecked by new bone formation (by osteoblasts) resulting in substantial bone loss over time. Even more troubling, this ‘bone demineralization’ does not apprear to reach a new ‘micro-g’ set point. It may go on for as long as the astronaut remains in space.
Disuse (prolonged bed rest, weightlessness, etc) results in decreased rates of bone formation but in bears the rate of resorption is also decreased, balancing the two – – leading to an overall reduction in bone turnover. Bear parathyroid hormone differs from human parathyroid hormone by nine amino acids BUT other studies have suggested bear Parathyroid hormone isn’t the whole story. Other factors are also in play.
Whether ‘hibernation’ would work for humans on long duration flights is mere speculation at present. But it remains an intriguing possibility.

4. Dr Space - May 21, 2010

Jim, you mentioned black bears. What about other bears that hibernate. Also other mammals hibernate and there are non-mammals that hibernate. Have there been any applicable studies on others that hibernate re bone loss issues? Are black bears the best model to study relative to humans?

Thanks for the info.

David Livingston

5. Andy Hill - May 25, 2010

Instead of shielding an area of the crew cabin against radiation would it be possible/feasible for astronauts to wear extra shielding sewn into their flight suits?

Not a lead suit of armour but possibly plates covering areas that would reduce the overall radiation dose to the body to mitigate the problem. Is such an approach a non-starter that would make the garment to clumsy to wear or are their materials that could at least provide partial protection to reduce the risk to crew? Have any trials been done using this approach?

jmj - May 25, 2010

I know of no trials and suspect the idea is a non-starter. The tradeoff would be additional mass for shielding the vehicle versus shielding each individual crew member. Remember the atmospheric half value layer for cosmic radiation is something like 7 psi or the equivalent of something like 5 meters of water. Trying to get that kind of mass per unit area on a suit sounds extremely problematic to me.

jmj - May 25, 2010

David, bone metabolism in bears differs from that in humans as Jim has so deftly pointed out. They don’t lose bone mass during hibernation but humans can’t hibernate and humans do lose bone mass through inactivity. Yo-yo dieting in humans is a no-no, but bear hibernation requires them to put on an enormous amount of body fat before each winter. Also, vitamin D metabolism is intimately related to fat metabolism and also to parathyroid hormone metabolism. The short answer is we really don’t know much about the details of how we work at the molecular level although we learn more every day.

jmj - May 25, 2010

Andy, my reply to you was posted under David Livingston’s comment (#4, above) in error. Sorry.

Jim Logan - May 26, 2010

Good thought about protecting the crew from radiation by wearing a special suit rather than having to use additional weight and volume to protect the entire vehicle (this same reasoning was why the famed aviator Wiley Post, the GREATEST aviator of all time in my opinion, decided to ‘pressurize the pilot rather than the airplane’ by designing the world’s first pressure suit – – his aging plywood Lockheed Vega could not be pressurized unlike the brand new all-metal aircraft of the day).
BUT….unfortunately….this would require the most popular element of space exploration: UNOBTAINIUM. We have no material whatsoever that would even begin to provide the radiation protection required. Plus, what about the head, face and eyes (maybe we could just make our UNOBTAINIUM transparent)?
Also, don’t forget sensitive spacecraft electronics – – they’ll need protection too. So will the food stores (which will degrade until the constant bombardment of radiation) and the onboard pharmacy (that’s already a problem with the medical kit on ISS).
Unfortunately our only real option TODAY is to ‘radiation harden’ the critical areas of the spacecraft (sleep stations, ward room, command & control, medications, electronics, servers, food storage, etc.).
Don’t misunderstand – – It’s not that your Vision is wrong, it’s just many decades beyond current technology.
Reality can indeed bite!!

Andy Hill - May 28, 2010

Damn that Unobtainium, its lack is holding us back! Just think of all those powerpoint rockets that would be flying now.

Does the body concentrate radiation its subjected to in specific parts of the body or does it disperse equally throughout?

6. jmj - June 2, 2010

Radiation exposure takes place in several ways. The first comes from eating, inhaling, or injection of radioactive materials. They can be concentrated in specific parts of the body such as radioactive iodine concentrating in the thyroid or radioactive glucose concentrating in tissues with high metabolic activity. The second is radiation from outside the body (either particles such as helium nuclei, electrons, etc. or photons — gamma rays or x-rays). Another mechanism is neutron activation in which a neutron is absorbed by an atomic nucleus and converts it into a radioactive material.

7. Jared - June 4, 2010

I may have missed the boat on this lesson, but if the Drs. are still taking questions, I have another question about sci-fi and gravity:

Most hard science fiction seems to go with the idea that people could be born in weaker gravity than Earth’s just fine, but would then be unable to ever walk around freely on Earth. Or that long-duration colonists would eventually suffer muscle deterioration that would prevent them from returning home. Was there ever any scientific basis/consensus behind this idea, or was it always just convenient, agreed-upon speculation? (Clarke generally knew what he was talking about, which is why I ask).

Dr. Logan, what problems do you suspect would crop up in long-duration or life-cycle human stays in lower gravity? I know you said there’s no real data to go by, but where would you guess gravity needs to be for long-term human health? .6 g? .8? Impossible to even guess? What about gravity slightly greater than Earth’s?

8. Tom Hill - August 6, 2010

Wrapping up this show. Excellent discussion. I agree that there are lots of unknowns related to gravity and radiation, but need to pose this question:

Wouldn’t a crewed engineering test of a future Mars-bound (or return) spacecraft answer most of these questions? I understand that the sample size would be small, but large problems should make themselves apparent. In my scenario, the craft would:

1. Generate artificial gravity (.38g) by using its upper stage as a counterweight
2. Hover at Earth/Moon L1 for a period of time to validate its mechanical functionality for the eventual Mars mission (A Mars Direct habitat would need to function for on the order of 2 Earth years, an Earth Return Vehicle for on the order of 8 Earth months)
3. Answer part of another human factors question by releasing Martian dust simulant into the environment after a simulated travel time to Mars.

With a mission so close to Earth, any big problems that crop up would allow the crew to return to Earth in a matter of days.

It’s my understanding that the two year test would actually give travelers a greater radiation exposure than a Mars mission, because a crew on the surface of Mars has 1/2 of its cosmic ray dose blocked by the planet itself. Is that correct?

Tom Hill - August 7, 2010

Should have waited until the end of the lesson before commenting. Just got to the part where Jim said (and I agree) that while the cosmic ray dose is about 1/2, the complicating factors of scattering make the “1/2 argument” too simplistic.

My earlier question about the engineering tests of Mars hardware remains.

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