As I understand it the initial motion of the rocket launch is the most energy intensive. Why is there not some propulsion method (electromagnetic or old skool motors) that assist with pushing the spacecraft up. This would also reduce the fuel load?
Basically, why do we not slingshot the craft up and let the onboard fuel take it the rest of the way once it’s got some momentum, even if it’s the first 100 meters?
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They can and do…that’s the entire reason for air-launched rockets like Virgin Orbit or Pegasus or Stratolaunch. In that case, the “rocket launch structure” is an airplane and you get a free hundred mph and a few miles of altitude for “free” from the rocket’s point of view.
For larger terrestrial rockets, the short answer is that launch towers aren’t much taller than the rocket itself and, at launch, rockets are *really* heavy and their structures are (relatively) not very strong…they can’t handle much more force…if you pushed them with something on the launch tower you’d have to reduce the engine thrust to match so that the total load on the rocket wasn’t too high. So you’d only gain the altitude of the launch tower (a few hundred feet) and you wouldn’t be going meaningfully faster when you cleared the tower. It would help, but not enough to be worth it for the extra complexity.
You’d have to have the engines up and running before launch just so you know that they *will* be running when you clear the tower.
There is another more sutble version though…if you move the entire rocket launch structure somewhere that the entire structure is going fast…like the equator…then you get a free boost. This is why most launch facilities are as far south as their respective countries can get them and why it’s preferred to launch in the direction of earth’s rotation. The gain from doing this is *far* higher than anything you could get from pushing the rocket up the tower.
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