The problem is not the energy ... but the weight you need to lift to get that energy airborne. We don't send astronauts in paper aircraft although they are light - we put layer. There are some things that you need - you need them and you get them. If you need 3 x everything = you put them in. It is you engineering duty to make them best, lightest, coolest etc ... but you cannot cut corners.

If it was up to me though I would just create some of the external parts of the vehicle as a thermocouple and use the fact that one sight is frying on the syn briefly and the other is exposed into the almost absolute zero. That should create some juice. But I suppose there are good reasons they don't do it.