As useful as the NERVA nuclear rocket engine would have been (and may yet be), you wouldn’t want to spend too much time too near it when it fired up. Below is an image from an Aerojet report from late 1964, showing locations of test instruments overlaid atop a graph showing fast neutron and gamma ray flux for an engine at power. Sadly, the graph is pretty damned vague about the absolute magnitude of the units. There are numerous steps in the order of magnitude, at which point the units reset.. so what, on the right, might look like 1.5 ergs/gm/hr, is probably 1.5 time ten to the power of X ergs/gm/hr, with X being an unknown. My copy of the report is sadly incomplete, and is missing out on little details like what “X” is.
UPDATE: the magnitude of the neutron and gama ray flux can be seen in the form of the faint larger numerals in the background. See comments for more.
Somewhere around here I have another report that shows similar radiation levels for a NERVA engine; I’ll look for that until some shiny object passes by and distracts me.
7 Responses to “NERVA rads”
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That would be an interes… Look! A cat video!
Looking at the image, the caption to the bottom left states :-
“Bold dashed lines separate regions with different orders of magnitude.
Orders of magnitude specified by large underlying numerals.”
Now if you look _very_closely, in the background, you will see large faint numbers, either side of the image, coloured to match the contour lines.
On the left, I see 11, 12, 13, 13, 12, reading from top to bottom, and on the right, 8, 9, 11, then 12 to the right, then 9, again reading from top to bottom.
HTH.
Ah. Ayup. One of those forest-for-the-trees things… I’d mised the Large Underlying Numerals. So, the gamma ray doses are on the order of 10 to the 10th ergs/gram/hr, or 1,000,000 gray per hour. According to Wiki, a 5-gray whole body dose will typically lead to death within 14 days.
And then there’s the neutrons…
So, don’t stand too close.
So what sort of shielding would you need on a manned vehicle…?
A lot of the shielding would come from the hydrogen tank and a bioshield. The Beyond Apollo blog had a post once that said that NERVA could be a danger to satellites around it from the radiation. Also the ability to reuse it might be overstated.
after Harry O. Ruppe book “Grenzenlose Dimension Raumfahrt. Vol one”
is minimum safety margin for unshielding Nerva is 14 km, (so 9 miles)
wat remind me of a Idea by Krafft Ehricke: Helios (first Version)
a two stage rocket first chemical second NERVA like
in mid a crewcomparment “spiked” by Nerva engine
the Rocket blast off up to high of 80 km then fist stage seperate and fly back
the crewcomparment roped down from Nerva engine by 4 steel cabels
on 300 meter (1000 foot) down, then NERVA running up…
the version 2 of Helios is like a Atlas rocket 1/2 stage but with a NERVA enigne as sustainer
VASIMR (and NEP in general) gets way to much air time. NTR is the way to go.