Timeline for In retrospect, should they have provided more RTG fuel and a more powerful radio for Voyager?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Dec 10 at 8:30 | comment | added | Hobbes | An RTG produces energy using thermocouples. Those have to have one end exposed to the hot Pu-238, and the other and has to be as cold as possible. This limits how much fuel you can add to one RTG module. If you want more power, you have to add more RTG modules instead. | |
| Dec 7 at 21:15 | comment | added | Dewi Morgan | @jwenting Since the limitation on the system lifetime appears to be power (once it no longer has sufficient power to transmit, it is effectively "dead"), how would having more power NOT increase the lifetime of the system? | |
| Dec 7 at 4:58 | comment | added | jwenting | @DewiMorgan multiple RTGs would indeed produce more power but not increase the lifetime of the system. A larger RTG (past a certain limit) wouldn't produce more power, just add useless mass, and still not last longer. The ones installed on probes are of optimal size. And the size and mass of them dictates how many you can add before you exceed the capabilities of your launch vehicle. | |
| Dec 6 at 23:29 | comment | added | Dewi Morgan | @Mark Cunning! Thanks :) | |
| Dec 6 at 23:13 | comment | added | Mark | @DewiMorgan, no explicit reference for the half-life, I just computed it from the available power output numbers plus seeing a mention that thermocouple damage had a half-life-like behavior. Thermocouple degradation was expected and planned for, and the thermocouples on the Voyager spacecraft are actually failing slower than expected. | |
| Dec 6 at 23:13 | comment | added | Dewi Morgan | I mention because I wonder whether this thermocouple degradation may not have been known or predicted at launch, but rather was discovered over time. In which case, it'd be another answer to the OP: if they had expected the 89.7 year half-life to have applied, they wouldn't have expected the power to have dropped this far until the year 2100 or so, so they certainly wouldn't have felt the need to add more RTGs! | |
| Dec 6 at 23:07 | comment | added | Dewi Morgan | @Mark Do you have a ref for the 35 year halflife estimate? I find it entirely believable and logical, but annoyingly the wiki page only mentions the 87.7 years for the fuel, without mentioning the additional reduction due to degradation of the thermocouples. Google is also no help, or my Google-fu is weak today :( | |
| Dec 6 at 23:01 | comment | added | Dewi Morgan | @jwenting That's not my understanding, though I'm admittedly a naif. I think the power of each is added together, so more RTGs means more power. Every "half-life" just halves the power output of each one, it doesn't limit the "useful lifetime", as they still produce power, just less of it. Launch with 16 x en.wikipedia.org/wiki/MHW-RTG 1kW = 16 x 157 W = 2.5 kW. With a half-life of 35 years, then after 50 years you'd be down about 1 kW. | |
| Dec 6 at 8:20 | comment | added | jwenting | and even if it was, adding more RTG fuel wouldn't help as the fuel would all decay at the same rate and thus end up with a very similar useful lifetime of the radioactive core. | |
| Dec 5 at 23:02 | history | answered | Mark | CC BY-SA 4.0 |