Patent Number: 
Section: claims

1. A thermionic power cell, comprising:a housing including a lead layer and a vacuum insulation layer;a heat source within the housing;a first layer within the housing, the first layer comprising:a first collector; anda first emitter arranged such that the first emitter is disposed between the heat source and the first collector; andone or more additional layers within the housing, each additional layer comprising:an additional collector; andan additional emitter arranged such that the additional emitter of that additional layer is disposed between the heat source and the additional collector of that additional layer,wherein each additional layer is successively stacked upon the first layer and all layers are electrically insulated from one another,wherein the first emitter and each additional emitter each comprise an array of emitter points extending from a base,wherein a separation between the first emitter and the first collector is 10 nanometers or less and a separation between each additional emitter and its respective each additional collector is 10 nanometers or less, andwherein the first emitter and each additional emitter are comprised of copper (Cu), silicon (Si), silicon germanium (SiGe), or a lanthanide and the first collector and each additional collector are comprised of Cu. 2. The thermionic power cell of claim 1, wherein the heat source is comprised of plutonium 238 (Pu-238). 3. The thermionic power cell of claim 2, wherein the heat source is five grams of Pu-238. 4. The thermionic power cell of claim 2, wherein the first layer and each additional layer each include a respective spacer layer of oxide or nitrate between their respective emitters and collectors. 5. The thermionic power cell of claim 1, wherein the one or more additional layers are three additional layers. 6. The thermionic power cell of claim 1, wherein the first spacer layer is made of oxide or nitrate. 7. The thermionic power cell of claim 1, wherein the first emitter includes a first array of emitter spikes having first emitter tips, and wherein the first spacer layer is positioned on the first emitter. 8. The thermionic power cell of claim 7, wherein the first spacer layer does not cover the first emitter tips so that first open spaces are formed at the first emitter tips. 9. The thermionic power cell of claim 8, wherein the first open spaces extend between the first emitter tips and the first collector. 10. The thermionic power cell of claim 9, wherein the first spacer layer extends between and contacts the first emitter and the first collector, except for the first open spaces. 11. The thermionic power cell of claim 7, wherein the first spacer layer is made of oxide or nitrate. 12. The thermionic power cell of claim 7, wherein the first emitter includes a first base from which the first array of emitter spikes extend, and wherein the first spacer layer extends between the emitter spikes of the first array at the first base. 13. The thermionic power cell of claim 7, wherein a separation between the first emitter tips and the first collector is 10 nanometers or less. 14. A method of generating electrical current, comprising:providing a thermionic power cell; andconnecting the thermionic power cell to a load to generate an electrical current,wherein the thermionic power cell comprises:a housing including a vacuum layer for insulation surrounded by a lead layer for radiation shielding and;a heat source within the housing;a first layer within the housing, the first layer comprising:a first collector; anda first emitter arranged such that the first emitter is disposed between the heat source and the first collector; andone or more additional layers within the housing, each additional layer comprising:an additional collector; andan additional emitter arranged such that the additional emitter of that additional layer is disposed between the heat source and the additional collector of that additional layer;wherein each additional layer is successively stacked upon the first layer and all layers are electrically insulated from one another. 15. The method of claim 14, wherein the heat source is comprised of plutonium 238 (Pu-238). 16. The method of claim 15, wherein the heat source is five grams of Pu-238. 17. The method of claim 15, wherein the first layer and each additional layer each include a respective spacer layer of oxide or nitrate between their respective emitters and collectors.