Why was the Apollo 14 radiation dosage so high?

[AstroBrant]

I've been revisiting Bob's outstanding article, Apollo and the Van Allen Belts:

http://www.braeunig.us/apollo/VABraddose.htm

In the dose chart at the very end of the article it's hard to miss how high Apollo 14 was, contrasted to the others -- more than twice as much as each of the last three missions, which lasted longer. Conversely, Apollo 15 was surprisingly low.

Why such unexpected variations? Solar activity?

[Noldi400]

I know this is an incomplete answer, but I seem to remember that one of the personal dosimeters failed on 14, so the CDR and LMP took the two functioning ones along on the landing; that probably skewed the figures somewhat.  I believe that 14 also (for some reason, perhaps related to the landing site?) took a more, um, equatorial trajectory at TLI, so the would have picked up more in the VAB.

As you know, Bob, they were still well below anything like dangerous levels.

[AstroBrant]

As you know, Bob, they were still well below anything like dangerous levels.

Oh sure, I know that. But it would be interesting to know why it was so comparatively high, and why A15 was so low.
(Brant)

[Bob B.]

Why such unexpected variations? Solar activity?

Good question.  Unfortunately I don't know the answer.

I believe that 14 also (for some reason, perhaps related to the landing site?) took a more, um, equatorial trajectory at TLI, so the would have picked up more in the VAB.

Apollo 14's TLI inclination was pretty typical.  It was Apollo 17 that actually had the lowest inclination.

TLI Inclination
Apollo 8 = 30.636^o
Apollo 10 = 31.698^o
Apollo 11 = 31.383^o
Apollo 12 = 30.555^o
Apollo 13 = 31.817^o
Apollo 14 = 30.834^o
Apollo 15 = 29.696^o
Apollo 16 = 32.511^o
Apollo 17 = 28.466^o

I don't know the inclinations of the return trajectories without doing a bunch of math that I don't want to do.  The only one I know for sure is Apollo 11, which was 39.925^o.

Also note that these inclinations are with respect to the geographic equator.  When dealing with the VAB, what matters is the inclination with respect to the geomagnetic equator.  Perhaps Apollo 14's geomagnetic inclination was less than the other missions, but it would again take quite a bit of math to figure that out.  Unfortunately that is something I really don't feel like taking the time to figure out (maybe someday but not today).

[AstroBrant]

Why such unexpected variations? Solar activity?

The only one I know for sure is Apollo 11, which was 39.925^o.

<chuckle>...give or take a few inches!

[VQ]

Why such unexpected variations? Solar activity?

One report says A14 travelled through the center of the inner belt, http://books.google.com/books?id=LGIrAAAAYAAJ&lpg=PA60&ots=O67m8RgKOa&dq=apollo%2014%20radiation&pg=PP1#v=onepage&q&f=false (page 60).

There was a significant solar flare on January 25, 1971, a week before Apollo 14 launched. Could there have been any additional proton levels in the belts as a result?

[Chew]

Was the higher dose received during the transit of the VAB? It was my understanding the CDR and LMP got higher doses because they landed in a high KREEP area.

[Dalhousie]

KREEP's not that radioactive. It's got about 1% K, 10 ppm Th and 4 ppm U.  Less than a typical granite.

[Noldi400]

Why such unexpected variations? Solar activity?

Good question.  Unfortunately I don't know the answer.

I believe that 14 also (for some reason, perhaps related to the landing site?) took a more, um, equatorial trajectory at TLI, so the would have picked up more in the VAB.

Apollo 14's TLI inclination was pretty typical.  It was Apollo 17 that actually had the lowest inclination.

TLI Inclination
Apollo 8 = 30.636^o
Apollo 10 = 31.698^o
Apollo 11 = 31.383^o
Apollo 12 = 30.555^o
Apollo 13 = 31.817^o
Apollo 14 = 30.834^o
Apollo 15 = 29.696^o
Apollo 16 = 32.511^o
Apollo 17 = 28.466^o

I don't know the inclinations of the return trajectories without doing a bunch of math that I don't want to do.  The only one I know for sure is Apollo 11, which was 39.925^o.

Also note that these inclinations are with respect to the geographic equator.  When dealing with the VAB, what matters is the inclination with respect to the geomagnetic equator.  Perhaps Apollo 14's geomagnetic inclination was less than the other missions, but it would again take quite a bit of math to figure that out.  Unfortunately that is something I really don't feel like taking the time to figure out (maybe someday but not today).

This is the only reference I've been able to find... there doesn't seem to be any further analysis anywhere, possibly because the dose was well under dangerous levels.

From the ALSJ, Apollo 14 Mission Report, Biomedical Section:

10.2.5 Radiation

The Lunar Module Pilot's personal radiation dosimeter failed to integrate the dosage properly after the first 24 hours of flight. To ensure that each lunar module crewman had a functional dosimeter while on the lunar surface, the Command Module Pilot transferred his unit to the Lunar Module Pilot on the fourth day of the mission. The final readings from the personal radiation dosimeters yielded net integrated (uncorrected) values of 640 and 630 millirads for the Commander and the Command Module Pilot, respectively. No value can be determined for the Lunar Module Pilot. The total radiation dose for each crewman was approximately 1.15 rads to the skin and 0.6 rad at a 5 centimeter tissue depth. These doses are the largest observed on any Apollo mission; however, they are well below the threshold of detectable medical effects. The magnitudes of the radiation doses were apparently the result of two factors: (1) The translunar injection trajectory lay closer to the plane of the geomagnetic equator than that of previous flights and, therefore, the spacecraft traveled through the heart of the trapped radiation belts. (2) The space radiation background was greater than previously experienced. Whole-body gamma spectroscopy was also performed postflight on the crew and indicated no cosmic ray induced radioactivity.


"Through the heart", I notice. Further evidence that the whole VAB radiation argument is nonsense.

A15's dosage was kind of low compared to the other J-missions, but it's a pretty small data group to draw many conclusions (layman's view, again), wouldn't you think?