Bill:
Am-241 is fissile, but it could never be used as a material "that, in concentrated
form, could be used as the primary ingredients of nuclear explosives."
Consequently, the NRC doesn't classify it as such, nor does the IAEA.
The bare sphere critical mass of AM-241 is 57.6 kg, which would produce ~5,760 W
thermal power. Pu-239, with ~> 55 times the half-life, lower decay energy, is
difficult enough to make work in a bomb - 10 kg bare sphere critical mass
generates 19.4 W thermal.
Best,
Mike
On March 1, 2021 at 7:45 PM, William Claybaugh <wclaybaugh2@xxxxxxxxx> wrote:
Mike:
Am 241 is a special nuclear material; if one has to use an RTG, one has to
deal with a government.
Bill
On Mon, Mar 1, 2021 at 5:04 PM Michael Kelly <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
Northrop Grumman makes a whole range of pulse-tube cryocoolers for space
applications, and have been developing them as electric generators when run in
reverse. They have no moving parts (well, no parts that move very far), and
last forever. https://rps.nasa.gov/internal_resources/160/
And, yes, Americium 241 is back in production (big time). It would provide a more
level power output in RTG applications, given a half-life ~> 5 times that of Pu
238.
On March 1, 2021 at 10:47 AM, William Claybaugh <wclaybaugh2@xxxxxxxxx> wrote:
Rand:
Yep, but that does not justify ignoring the best answers.
Bill
On Mon, Mar 1, 2021 at 8:24 AM Rand Simberg <simberg@xxxxxxxxxxxxxxx> wrote:
Bill, you're the one who started this topic as a "home-built space mission."
On 3/1/21 7:18 AM, William Claybaugh wrote:
Rand:
They don't last as long and NASA Gleen's Stirling power systems are (ground)
qualified for 20 years.
Bill
On Mon, Mar 1, 2021 at 8:02 AM Rand Simberg <simberg@xxxxxxxxxxxxxxx> wrote:
You could buy one from the UK. They've started making them out of Americium.
On 3/1/21 6:55 AM, William Claybaugh wrote:
Rand:
I think an efficient RTG is required and that will mean USG involvement in what
likely wants to otherwise be a privately funded activity.
Bill
On Mon, Mar 1, 2021 at 7:47 AM Rand Simberg <simberg@xxxxxxxxxxxxxxx> wrote:
That begs the question of why it would be either big budget, or done by
NASA. :-)
On 2/28/21 10:00 PM, Henry Spencer wrote:
On Sat, 27 Feb 2021, Robert Steinke wrote:
imparting about... 15km/s if the back of my envelope is
correct. That's a whole lot for a chemical rocket...
That close to the sun it should be easier to do high thrust solar
thermal.
Wikipedia says Isp up to 1000 seconds so the mass ratio would need to be
~4.5. Use a drop tank for boiloff so the burn starts out with a full
tank.
Unfortunately, that Isp requires LH2, and after circa a decade in
space (out to Jupiter and back), almost certainly it will all be gone.
There are ways of storing LH2 for years, in principle, e.g. active
refrigeration, but it's beyond today's state of the art, and I believe
Bill is hoping for a relatively low-cost mission.
(A big-budget planetary mission isn't going anywhere unless you can
convince a Decadal Review to make it their first priority, which isn't
going to happen for this. Smaller efforts can sometimes do end runs
around the traditional process, but ill-defined costs and risks from
techological pioneering are just what you don't want if you're trying
to convince people to stick their necks out in support.)
Henry