Re: [Starlink] lumen orbit

[David Lang <david@lang.hm>]

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 :-)

David Lang