Re: [Starlink] lumen orbit

[David Lang <david@lang.hm>]

David Lang via Starlink wrote:

> On Wed, 4 Sep 2024, Brandon Butterworth via Starlink wrote:
>
>> On 04/09/2024 15:48:51, "Dave Taht via Starlink" 
>> <starlink@lists.bufferbloat.net> wrote:
>>> They plan to build a 5GW 4k solar square for data centers in orbit,
>>> launched on starship:
>>>
>>> https://www.lumenorbit.com/
>>
>> Maintenance call outs are going to be interesting
>>
>>> How are they going to cool this thing?
>>
>> With some big radiators. From
>> 
> https://www.nasa.gov/wp-content/uploads/2021/02/473486main_iss_atcs_overview.pdf
>>
>> it seems that the ISS units take about 23 * 3.5m area for 35kW so
>> about 440 W/m^2, if they are about the same then 5GW will need
>> around 11 million sq metres.
>>
>> That seems a totally unfeasible number so either I messed up the
>> calculation, or they have way more efficient radiators than NASA,
>> or this is wishful thinking/investor grift.
>
> the efficiency of radiators goes up drastically as the temperature of the 
> radiator goes up (there is a T^4 factor in the equasion, T in kelvin) so if 
> they 
> can get the coolant hot enough, they can shrink the radiator area by 
> increasing 
> the temp.
>
> but since 0c = ~273K, running the temp up to just over the melting 
> point of aluminum would let you get to about 1000x efficiency for the 
> radiators 
> (@1255c) but would still need a massive radiator. 11k sq meters is still a 
> lot. 
> the ISS radiators are a little of 6Kg/sq meter, so you are up to around 70T 
> worth of radiators (possible with a starship, but still massive)
>
> designing a heat pump that can pump heat from chips into molten aluminum is 
> left 
> as an excercise for the reader :-)

correction, sloppy reading (F vs C), molten aluminum is only 660c, to get the 
1000x efficiency, you would be up to the temp of molten iron.

just don't let if freeze in the pipes :-)

David Lang