Mk16G = 12" / 50 mark 8 naval gun or 8"/55 RF Mark 16

Dilandu wrote:I give up. It is impossible to teach this child anything.

Actually, the radar power needed to detect an object with a given radar cross section is proportional to the range raised to the fourth power.

Solar panels work great in space when the satellite is in sunlight. They suck in the dark.

Relax wrote:Not sure what is worse, someone who thinks 3kW is a lot of power or someone who doesn't know that average Solar energy(irradiance) on the face of the earth at ground level is around 1KW per square meter Currently efficiency of collected said solar energy into power is 15% at ground level, but in space its efficiency is 40% and the panels weigh a tiny fraction as there is no protective glass and no frame to speak of. Solar power per square meter in space is 1.4kW/m^2. So, for 3kW, continuous, you need roughly (3/1.4/0.4) = You need 5.5 square meters of panel... Oh the horrors, you need 4 small panels at roughly 5kg/panel + rotation equipment and a fold mech, call it 2kg more at most. So maybe a little over 25kg instead of 500kg. Who knew? 1960s tech sucks compared to the 21st century. Who knew?

I've got a dumb question. If that's correct then 120 kW would require just over 214 square meters. So why does the ISS have a solar array of 2,500 square meters (over 11 times as large) to produce its stated "84 to 120 kilowatts of electricity"?

Did NASA go for far less efficient cells for some reason? (cost, durability, time of design/procurement leading to obsolescence, etc) Or is there some other factor that causes the ISS's 8 solar panels to produce so much less power than the simple calculation shows they should?


(And of course with its orbit, like most low earth orbits, its in the dark much of the time so the ISS needs hefty batteries and in sunlight up to 60% of its generated power goes into those. So a RORSAT that wasn't able to stick to something like a Sun-synchronous orbit would presumable need similar levels of batteries and excess peak consumption. Instead of 3 kW peak you might need 7.5 kW)

Jonathan_S wrote:I've got a dumb question. If that's correct then 120 kW would require just over 214 square meters. So why does the ISS have a solar array of 2,500 square meters (over 11 times as large) to produce its stated "84 to 120 kilowatts of electricity"?

Average house uses maximum of 50 amps at 240V on a given day if say you are cooking, heating hot water, heating the house, and watching TV with all the lights on. Why do most homes have 150 or 200Amp service? Future considerations. Peak loads. Safety. Solar Panels are the ISS "service".

ISS was designed when? 80's 90's and was built to last effectively indefinetly. How often do you want to orient your panels to the sun? This leads to dynamics problems that must be dampened and parts that wear out. What were their Solar Panels initially? 20% efficient when PV were 10% on the ground(Not true later modules). Radiation also kills the panels so you need overkill to begin with. Did they know how long those panels would last? No. How bad was the die off of their initial panels? BAD. Thermal cycling cracked the wafers/wiring. Radiation killed their panels. Half way in building ISS they upgraded to MUCH superior panel technology if I recall correctly with higher solar conversion efficiencies(37% and the newer 40++%. Later versions have Carbon heat exchangers on their backsides which improved life endurance drastically as well if I remember correctly. You learn over 30 years of operations.

On top of this, when launching satellites etc, if you have spare tonnage left over and volume available inside the fairing, one keeps throwing more dirt cheap Solar Panels in until it is full or until you have to increase the sizing of the solar panel structural dynamic dampeners.

Now add the simple requirement for FOD damage redundancy. This has been used twice if I recall correctly and an array had to be fixed. I do not recall if they could fix it. Now add extra redundancy because this is space and humans are supposed to live on it full time.

Now add Day/Night reality.

If you see a picture of the ISS, quite often you will see half of its arrays completely turned away from the sun or not even deployed(extended) at all.

Ta Da, you have 10X more surface area than required.

Relax wrote:[snip]
Ta Da, you have 10X more surface area than required.

Thank you for answering my, admittedly dumb, question.

TFLYTSNBN wrote:

Dilandu wrote:I give up. It is impossible to teach this child anything.

Actually, the radar power needed to detect an object with a given radar cross section is proportional to the range raised to the fourth power.

Solar panels work great in space when the satellite is in sunlight. They suck in the dark.

A 737/A320 can be seen by a fighter from ~200nm away. Its side cross section is a whopping 3.5m x 40 = ~ 140m^2

Aircraft Carrier or Cargo ship from space is 300m x 70m or 2100m^2 or almost 10X the cross section.

Now you want to play make believe you cannot see it from HALF the distance as a 737 with a satellite in LEO with LESS atmosphere/clouds/rain in the way???

Come on... Pull the other leg guys.

Now this really is my last post on this topic.

PS> You might want to look up what Synthetic Aperture RADAR is used for today.... from space satellites.... in LEO: I had forgotten about RADARSAT-1 which I can actually discuss...