2 upvotes, 2 direct replies (showing 2)
View submission: Ask Anything Wednesday - Engineering, Mathematics, Computer Science
Why are magnetic catapults just now being researched in launching satellites into space and not decades ago?
Comment by bluesbrother21 at 26/07/2024 at 01:27 UTC
2 upvotes, 0 direct replies
There's two reasons, one economic and one technical. Economically, there wasn't really room for small startup style companies in the space sector until fairly recently - the barrier to entry was extremely high, and there wasn't much of a commercial market. This is changing now, but meant that there was generally not much funding to pursue this kind of idea.
Technically, there's some major hurdles that limit the applicability of any kind of "catapult" launch system. Orbits are fundamentally periodic, meaning that if you put something on a ballistic arc starting at the Earth's surface, it will come back to that same altitude. This means that any satellite launched with a catapult system will need to perform a large maneuver within tens of minutes of launch to raise it's perigee enough to not immediately re-enter, which is a very very tall ask. Thats a lot of propulsion the vehicle now needs to bring on-board that it can't otherwise use for mission. Additionally, doing *anything* that soon after launch is difficult. There's also the structural issues caused by the acceleration of launch itself, which are much higher than with a rocket.
Frankly, the reason it hasn't seen more investment or research is because it's impractical. Not for the magnetic launcher itself, but for all the issues that come with using it.
Comment by subnautus at 25/07/2024 at 13:36 UTC
2 upvotes, 0 direct replies
It's mostly because of the amount of energy involved. Let's say you're at the equator, where the rotational speed of the ground is highest. From outside Earth, you're moving a little less than 0.5 km/s. LEO orbits are typically around 7 km/s. Assuming there's no atmosphere, you're talking about going from 125 kJ to 24.5 MJ in kinetic energy minimum to launch a 1 kg satellite.
Now consider that you lose 1.6-1.9 km/s worth of orbital speed pushing through Earth's atmosphere. Now we're up to 37 MJ of energy for that 1 kg satellite.
Now consider: what is energy? Force applied through distance, right? Which is going to require less force, a magnetic catapult that's, say, 1-2 km long, or a rocket that's burning the entire time it's under the 100 km "ceiling" of Earth's atmosphere?
So, with all that in mind, you can see why--from a technological level--we just haven't been able to even *consider* a magnetic catapult. The amount of energy involved has been too much to deal with.