Why can’t the space shuttle just go slow enough to not be heated up by friction with earths atmosphere on re-entry?
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A space shuttle absolutely could slow down so that it doesn’t heat up on re-entry. However, this would require a huge amount of energy to do, which would require a lot of fuel.
In order to get into orbit, a spacecraft has to accelerate to at least around 18000 mph. That’s how orbits work, if you went any slower, you’d fall back to Earth. Look at how much energy (and fuel) it took for the space shuttle to go from 0 to 18000 mph. It required giant fuel tanks and a huge fireball shooting out the bottom for like 10-15 minutes straight. If you wanted to slow down from 18000 mph to 0 mph without using friction, you’d need to use the same amount of energy.
You might think that it would cost 2x the fuel to do a powered deorbit. The real problem is that if you wanted to use your engines to slow down, you’d have to carry all that fuel up into space. And fuel is heavy. So, now in order to launch the space shuttle along with all that extra fuel, you need even more fuel for the initial launch.
I haven’t done the math, but I wouldn’t be surprised if it would require 5-10x as much fuel to launch a spacecraft+fuel that is capable of a powered descent. The launch cost would be significantly higher. Even with the most efficient spacecraft, it still costs well over $1000 to lift a pound of payload into orbit. Imagine the extra cost of bringing 20000 pounds of fuel into orbit just to avoid a traditional re-entry.
Basically, we use atmospheric friction as a “free” energy source to slow the spacecraft down from 18000 mph to 0 mph, so that we don’t have to haul up tons of extra fuel for that purpose.
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