Starship electrical system

Since Starship will have Tesla batteries there are many possible uses of the available power and energy storage.

Any spacecraft needs batteries to provide continuous operation during eclipse periods. For low Earth orbit, that can last for 45 minutes over a 90 minute orbital period. Therefore it is necessary to power all electrical systems during such insolation outages, which will easily reach several kW for such a large spacecraft. For large human rated Starships, much higher cooling and heating requirements may be needed, since the total internal volume exceeds that of ISS.

But that is not all. Starship flaps/wings will also require high power during the deceleration phase of the flight providing control authority during descent. 

I have argued in previous post that SpaceX will most likely use electric powered pump similar to Rocket Lab Rutherford engine, as it provides an ideal combination of high trust, fast ignition and very precise power control. But these engines have a use much broader than just lunar landing and ascent.

During Earth landing we have the flip maneuver which is tricky since it has to be performed in very short period of time to minimize fuel consumption in the terminal phase of he flight. Reliable ignition and trust control of Raptors were critical in four consecutive landing failures. Using auxiliary lunar landing engines could reduce the flip time considerably. Not only that. The same engines could be used during the actual landing to provide more precise positioning (providing horizontal movement capability) and even provide smoother landing during touchdown simply because the reaction/response time of electric pump engines is much faster than for Raptor turbo pumps. That would significantly reduce transient forces on the landing legs during touch down. 

Is that all? No. Rockets are very sensitive to winds and especially wind gusts. That is a major reason for weather related launch scrubs. But capability to provide rapid counterforce in response to wind (gust) would enable Starship to launch and land in harsher weather conditions. The same lunar landing engines could be used for Mars landing too (with reduced payload or with additional engines installed to counter higher gravity). 

But there is more. What if Raptors fail during the terminal landing? Would human crew be doomed? In the current Starship design, that would be almost certain. But having auxiliary landing engines enables interesting capabilities. Note that main tanks will be empty. What if there would be explosives that would detach Raptors and main tanks from the payload section? That would reduce weight at least by half and provide enough power to crash land on auxiliary engines alone. But if that can be done during landing...why not during ascent too? Such engines beefed up could provide a launch escape system too. Not with 6g acceleration like with Dragon/SuperDraco, but 1g acceleration would be possible to achieve.

In addition, Starship would not require or any large solar panels for each mission. To charge the batteries in the shorter flights (for example in quick LEO missions) it could rely on auxiliary metholox power unit (APU), similar to units found in commercial airplanes from Boeing and Airbus. It is small and lightweight solution.

But lets get back to the Moon. Once there, Starship should in the long run be capable of surviving through the lunar night. That is 14 days of extreme cold. But it will need to keep its electronics and batteries warm plus the human living space. Being in vacuum will help due to excellent isolation. One solution is radioisotopes and kilopower nuclear reactors. But the combination of batteries and APU (that would consume available propellant) would enable longer stays too without nuclear material issues. 

The great thing about electrical batteries and auxiliary electric powered engines is that their capacity can be easily scaled to mission requirements, which the number of Raptors or tank sizes cannot be easily changed. That is important because space missions are very sensitive to mass budgets due to rocket equation. It should be relatively easy to add four instead of two Tesla batteries. Or double the number of APUs. Or even double the number auxiliary rocket engines (provided that piping has been designed for the start for such additional propellant flow).