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efreysson
01-15-2017, 11:57 PM
My WIP has two spacefaring cultures. One has mastered it and can blast off into space in a moment, with the crew feeling no effects. The other one isn't that much more advanced than 21st century Earth, and I'm wondering how to depict a takeoff from inside the ship. I know that real-life astronauts experience immense g-forces, but is there a minimum speed that needs to be reached, and therefore a maximum amount of time that an orbit-breaking blast can take?

King Neptune
01-16-2017, 12:31 AM
There is escape velocity, which is the velocity at which something would have to be propelled to break free of gravity; this is a one-time surge of energy. One can also get out of a gravity well by applying a longer term continuous impulse that is slower than the escape velocity but would impart as much energy to the spaceship. What would you want to show?

efreysson
01-16-2017, 01:46 AM
There is escape velocity, which is the velocity at which something would have to be propelled to break free of gravity; this is a one-time surge of energy. One can also get out of a gravity well by applying a longer term continuous impulse that is slower than the escape velocity but would impart as much energy to the spaceship. What would you want to show?

Well, I suppose that depends on how long either one takes.

King Neptune
01-16-2017, 02:18 AM
Well, I suppose that depends on how long either one takes.

When a rockets accelerates very quickly, it will hit escape velocity in a couple of minutes, and everyone suffers from high g forces. This is the lower tech way to do it, so this probably is what would be going on. Or you could have the crew chat about football; it would fill the space, and it might reflect more confidence with the ship.

Mark HJ
01-16-2017, 07:37 PM
If I remember correctly, the relatively short duration high-g launch of our rocket technology is a balance between what the crew can endure, how much fuel is packed into the rocket and the 'energy density' of the fuel. In principle you can launch with a much longer duration burn at lower accelerations, but that means carrying more fuel, and the extra fuel is extra mass that means more fuel... Very crudely, the more gently you want to launch the more fuel is needed, and the quantity rises rapidly as you take the launch more gently. The only way around it, so far as I am aware, is to find a fuel which delivers more energy per unit mass, without turning into a bomb just waiting to go off.

blacbird
01-16-2017, 11:30 PM
Just for context info: The minimum velocity required to reach a stable orbit from the Earth is about 17,000 miles per hour (about 27,000 kph); the velocity required to overcome the planet's gravitational force altogether, and travel freely into space, is about 25,000 mph (about 40,000 kph).

caw

Techs Walker
01-25-2017, 02:04 AM
Well, I suppose that depends on how long either one takes.

Howdy efreysson,

Nice tech-y question you got there, but here's an approximate method to break your impasse between time taken and acceleration experienced. Blacbird has supplied the escape velocity, and others have explained the issues involved in the trade-off. One gravity is 9.8 meters per second-squared. You pick the acceleration you want (one-half extra gravity should allow you to sit comfortably for quite some time and still lift the TV remote), then calculate the time needed to get up to blacbird's escape velocity. Repeat if necessary.

Techs