New answers tagged physics
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The answer is that the two telescopes have different focal lengths and that focal length and mirror size are parameters that can be independently adjusted (there are obviously other tradeoffs to do with resolution and focal ratio).
Here's a description of why.
Here is a rather terrible diagram of a simplified Newtonian reflector – I've simplified it just by ...
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It's the tiny payload that matters--the rocket is lighter than normal so the same thrust causes it to move faster. This is because it's heading to Mars instead of to orbit, they are trading payload capacity for the speed needed to get there.
It's not going to make a big effect in the liftoff speed, though, the weight of the payload is quite small compared ...
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2kW is not that much on Earth
You've mentioned radiation and convection in your answer (you forgot conduction). Turns out the properties of Earth's atmosphere make conduction and convection way better than radiation for moving heat around.
For an illustration, consider the size of a portable, 2kW, oil-filled radiator: this one lists the size as ...
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There are a lot of ions in space already, adding a few from the thruster is not really that big of a deal. They are moving so fast that it won't really make a huge difference being neutral or not, they are going away from the spacecraft, and at the point where electrons are typically injected they are far enough away that it doesn't matter much.
All that ...
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