3 ms·
> In order to produce thrust, it has to exit the back of the satellite at a significantly higher speed. Why? It can exit at 1 m/s and still be thrust. And as l
by deepsun 2y ago
> In order to produce thrust, it has to exit the back of the satellite at a significantly higher speed.
Why? It can exit at 1 m/s and still be thrust. And as long as momentum from engine pushing is larger than momentum of stopping atmosphere -- it will accelerate.
In other words -- chemical engines have exit speeds way lower than 8 km/s, but are able to accelerate spaceships to and above 8 km/s.
- perihelions 2y agoYou're overlooking the conservation of mass constraint.
- deleted 2y ago[deleted]
- starspangled 2y agoI suppose because they are catching them when they are at ~0m/s in the atmosphere so they're worth -8km/s worth of momentum to begin with. So you would have to fire them out a >8km/s to get a net +ve change in momentum.
- SideburnsOfDoom 2y ago> It can exit at 1 m/s and still be thrust But it won't be enough thrust to counterbalance the force of scooping up air that collides at 8 km/s In order to produce net thrust, it has to be more than that.
- jcarrano 2y agoThe mass of propellant being expelled is many times higher than the mass of air colliding with the rocket.
- deepsun 2y agoIf that is the case then yes, agree, but there was no indication that is the case. The air is very thin out there. In fact, it's linearly proportional, because momentum us m*v, so for 20 km/s propellant exhaust seed and 8 km/s air it needs to spend exactly 8/20=0.4 times the propellant to not slow down.
- jcarrano 2y agoI understood that they want to used scoop up air to use as propellant. Only a fraction of the air it encounters will be able to be sucked in by the rocket.
- deleted 2y ago[deleted]