New Horizons Arrives At Ksc Options

[Redstone]

NASA Press Release
APL press release
Space.com Article

Coming up...
October: communications checks
November: hydrazine loading and Atlas V countdown rehearsal
December: integration with Atlas V
January: LAUNCH!

No pictures on the KSC webcams yet.

But still pictures here.


Is that the flight RTG attached to the spacecraft? Or just a dummy?

[SigurRosFan]

But how many RTGs are actually on board?

Earlier ...

--- Half of the plutonium for New Horizons was on hand when DoE stopped work at the nuclear weapons plant in July 2004. A total of 36 of the 72 fuel units ordered had been left over from a spare RTG built earlier for NASA's Galileo and Cassini missions. When the lab shut down, it had 18 more units in the works. The 2006 launch will go ahead with as few as 61 fuel units.

Los Alamos scientists could convert plutonium bought from Russia into pellets packaged in hockey-puck-sized containers. Then the Argonne National Laboratory at Idaho Falls would put those RTG containers into the RTG.

An RTG with a full load of 72 fuel units can deliver 200 watts of electricity. With only half of its fuel, 36 fuel units, it could deliver about 100 watts. With a minimum of 61 fuel units, the RTG could provide 170 watts of electrical power. The electricity would be used to power seven science instruments and spacecraft systems aboard New Horizons. ---

[helvick]

But how many RTGs are actually on board?
.....
An RTG with a full load of 72 fuel units can deliver 200 watts of electricity. With only half of its fuel, 36 fuel units, it could deliver about 100 watts. With a minimum of 61 fuel units, the RTG could provide 170 watts of electrical power. The electricity would be used to power seven science instruments and spacecraft systems aboard New Horizons.  ---

Not sure but Alan Stern's message here on Feb 19th says:

The RTG and the necessary fuel are both in good shape. Previous problems resolved.
All needed fuel is now ready. We expect 190 W or a tad more at Pluto in mid-2015.
The s/c requires ~165W, so there is a healthy margin. The launch approval process
has begun, and will take the remainder of the year to complete.

These RTG's degrade at around 0.79% per annum so 190W at Pluto (mid 2015) works back to around 205W now and should still be >165Watts in 2031.

Alan commented later:

This depends on when we launch in the 2006 window or the backup 2007
window because the exit velocity varies with launch date. The basic answer
is that predicts show that we have sufficient power to run out to 2025, which
corresponds to ~50-60 AU if all goes well.

So basically, no worries, loadsa juice. Let's just all do our bit to make sure that we don't let woowoo panic merchants hamper the launch.

Actually I've just been re-reading the whole thred - it's well worth it.

[SigurRosFan]

... degrade at around 0.79% per annum ...

0.79%? I thought the spacecrafts RTG generally loses 3 to 5 watts of power-generating capacity a year.

What is correct?

[helvick]

0.79%? I thought the spacecrafts RTG generally loses 3 to 5 watts of power-generating capacity a year.

What is correct?

The loss is exponential not linear - it follows the half life of Pu-238 (more or less) which is around 87.7 years. So after 87.7 years you would have 50% of the power you have right now.

[Guest_Richard Trigaux_*]

The loss is exponential not linear - it follows the half life of Pu-238 (more or less) which is around 87.7 years. So after 87.7 years you would have 50% of the power you have right now.

Add to this the degradation of the thermocouple junctions by the neutron flux. Semiconductors are used to build thermocouples to convert the heat into electricity, and these semiconductors crystals must be perfect and very pure, and thus they are very sensitive to impurities and crystal defects. The neutrons emanating from the RTG heat sources are not very numerous, but they can transmute some of the semiconductor atoms, forming impurities. Or most probably the atom recoil and secondary beta/alpha emissions will disrupt the crystal lattice. I am sure of what I say, having worked in the domain. But I cannot give figures about the degradation rate. It is slow enough to allow Cassini (and Pioneer and Voyager) to work, but Cassini will be very probably out of power before being out of nuclear fuel.

Add to this that the thermodynamic efficiency of the convertion of heat into electricity may decrease with the temperature of the heat sources.

[helvick]

It is slow enough to allow Cassini (and Pioneer and Voyager) to work, but Cassini will be very probably out of power before being out of nuclear fuel.

You're quite right - even though these are solid state devices there is some level lof degradation over time which is why I said that it follows the half of Pu-238 more or less.

Its a long time since I did any nuclear physics but I don't recall that there are any Neutrons emitted as part of the Pu-238 decay cycle. (Pu238->U235+Alpha and all subsequent decays are "Nasty Radioactive Isotope"+Alpha|Beta|Gamma ... Lead). It's still a stressful environment for the thermocouple but the dominant component of the loss of power should be the fuel's half life.

[Guest_Richard Trigaux_*]

Its a long time since I did any nuclear physics but I don't recall that there are any Neutrons emitted as part of the Pu-238 decay cycle. (Pu238->U235+Alpha and all subsequent decays are "Nasty Radioactive Isotope"+Alpha|Beta|Gamma ... Lead). It's still a stressful environment for the thermocouple but the dominant component of the loss of power should be the fuel's half life.

There is not only Pu238 in the RTGs. Pu238 is not produced from isotopic separation from other Pu isotopes. This process would be very difficult and anyway not complete, lefting an amount of Pu239 and even Pu240. It fact it seems that they start from Neptunium. There are only two "stable" isotopes of Np: 236 and 237, and they are much easier to extract from ordinary nuclear wastes of electricity reactors. Then they irradiate this neptunium into a special nuclear reactor, where it absorbs neutrons until it forms Np238 which quickly beta decays into Pu 238. But the time this pu238 remains in the reactor, it can in turn transmute into Pu239 and even Pu240. So whatever the method, there is a percentage of Pu239 in the Pu238. They certainly try to minimize it, as it does not produce heat, but it cannot be completelly avoided. It is like that, in nuclear physics even a theoretically "clean" reaction often has parasitic minority paths which can be very harmful.

So the presence of Pu239 is enough to explain that the RTGs emit neutrons. The other rays (alpha or beta) are damped by the casing before reaching the thermocouples.

Another consequence of this is that the RTGs are not just recycled nuclear wastes, they require the production of other nuclear wastes to be manufactured, so they arise the same issues than the nuclear reactors. The only white point is that the RTGs fuel cannot be used to make bombs, in case it falls into bad hands.