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> It's good to ask to learn. In that spirit, I have a question. How heavy are the solar panels? If their weight is comparable to 40kg then it makes RTG more at
by hrjet 12y ago
> It's good to ask to learn.
In that spirit, I have a question. How heavy are the solar panels? If their weight is comparable to 40kg then it makes RTG more attractive.
- gtirloni 12y agoI'm not sure about the exact weight but perhaps an estimation can be derived from the specifications available in the fact sheet [1] - Contractor: Galileo Avionica SpA - Cells Type: Si, Hi-ETA LILT - Cells Size: 3x3 cm2 - Power equiv. @ 3 AU: 32W - Total Size: 2.2m2 - Lifetime: 10 years [1] - http://www.dlr.de/rd/Portaldata/28/Resources/dokumente/rx/Philae_Lander_FactSheets.pdf http://www.dlr.de/rd/Portaldata/28/Resources/dokumente/rx/Ph...
- acqq 12y agoThe weight of solar cells used on the Earth comes from making them protected from the environment, the material that produces the power itself is very thin. http://sbir.gsfc.nasa.gov/SBIR/successes/ss/3-027text.html http://sbir.gsfc.nasa.gov/SBIR/successes/ss/3-027text.html Note "1 kW/kg" specification but it's probably in the Earth's orbit, using the inverse square law, it should be an order of magnitude less where Philae now is. Still, it appears it can remain quite light to have 2 m^2 of cells there. Anybody has more exact details for the weight of the cells on Philae?
- throwaway_yy2Di 12y ago1.7 kg, I think: TABLE I Mass breakdown of Rosetta Lander, including sub-units on the Orbiter. Unit Mass (kg) Thermal Control System 3.9 ...MLI ...2.7 ("multi-layer insulation") Power System 12.2 ...Electronics ...2.0 ...Batteries ...8.5 ...Solar Generator ...1.7 ***** Sum [Lander] 97.9 Sum [incl. Orbiter units] 111.0 Excerpt from table 1, page 208 of [paywall] http://link.springer.com/article/10.1007/s11214-006-9138-2 http://link.springer.com/article/10.1007/s11214-006-9138-2 [PDF mirror] http://www.researchgate.net/publication/257664668_The_Rosetta_Lander_(Philae)_Investigations/links/02bfe50e5ecb0f3078000000 http://www.researchgate.net/publication/257664668_The_Rosett...
- hrjet 12y agoThanks, but now I wonder. Mass is different from Weight (absolute and relative respectively). Are we comparing apples and oranges here?
- acqq 12y agoWe compare correctly: we measure everything on Earth (that means, under the same gravity) and the proportionality holds, so it's still more than 20 times less mass to carry for the power source with the given solar panels vs. the RTG. The mass doesn't go away, the amount of stuff remains, the weight is how much something pulls down the spring in the spring scale and that depends on gravity, but we conveniently measure on Earth.
- Rebelgecko 12y agoSince an RTG creates more "waste" heat than actual electricity, would that obviate the need for the thermal control system? Or at least reduce the amount of insulation needed?
- acqq 12y agoTypically it wouldn't "obviate the need for the thermal control system," see fbender's answer: https://news.ycombinator.com/item?id=8614514 https://news.ycombinator.com/item?id=8614514 "An RTG's primary objective is to produce electrical energy (at an abysmal efficiency). The excess heat generated by an RTG is seldomly used for thermal control since it can also not be regulated and it emits simply too much heat energy."