3 ms·

I think we should be trying to do this kind of thing, but... it does make you wonder whether in 30 years, we'll have the infrastructure (fusion, much larger LE

I think we should be trying to do this kind of thing, but... it does make you wonder whether in 30 years, we'll have the infrastructure (fusion, much larger LEO refueling capacity, etc) to put it there in 10 years instead.

simonh 4y ago
5x faster is a spectacular improvement, the launch systems we have today are not much more capable than the ones we had 30 years ago. I don’t see any reason they will be all that much better again in 30 years, even with something like Starship. The problem is the rocket equation is brutal. The more propulsion system you add to increase the speed, the more of it you have to accelerate up to the original speed before you start getting any improvement. We do have some nice advances like hall thrusters, but they don’t actually help much for heavy duty payloads like this, and there are no huge multi-order of magnitude engine efficiency breakthroughs on the horizon.
feoren 4y ago
Are these probes micro-accelerating the whole time with ion engines? You'd need 4 times the average velocity to cover the same distance*, which means 8 times the final velocity, which means accelerating from 0 to 8 over 10 years instead of 0 to 1 over 40 years. That means 32x more acceleration over the whole period. No: we won't have that technology in 30 years, nor in 100 years. Maybe, maybe, maybe if you were able to refuel in orbit and strapped a ginormous multi-stage chemical rocket onto the thing in orbit. Maybe. But we're not going to be doing that in 30 years either. * Higher velocities can mean shorter distances though, because your trajectory is less warped by the curvature of space. The biggest time saver would be avoiding time-consuming gravity assists, if there are any (I assume there are, but I didn't download the 500-page PDF).

3 ms·

I think we should be trying to do this kind of thing, but... it does make you wonder whether in 30 years, we'll have the infrastructure (fusion, much larger LE

by bpodgursky 4y ago

simonh 4y ago
5x faster is a spectacular improvement, the launch systems we have today are not much more capable than the ones we had 30 years ago. I don’t see any reason they will be all that much better again in 30 years, even with something like Starship. The problem is the rocket equation is brutal. The more propulsion system you add to increase the speed, the more of it you have to accelerate up to the original speed before you start getting any improvement. We do have some nice advances like hall thrusters, but they don’t actually help much for heavy duty payloads like this, and there are no huge multi-order of magnitude engine efficiency breakthroughs on the horizon.
feoren 4y ago
Are these probes micro-accelerating the whole time with ion engines? You'd need 4 times the average velocity to cover the same distance*, which means 8 times the final velocity, which means accelerating from 0 to 8 over 10 years instead of 0 to 1 over 40 years. That means 32x more acceleration over the whole period. No: we won't have that technology in 30 years, nor in 100 years. Maybe, maybe, maybe if you were able to refuel in orbit and strapped a ginormous multi-stage chemical rocket onto the thing in orbit. Maybe. But we're not going to be doing that in 30 years either. * Higher velocities can mean shorter distances though, because your trajectory is less warped by the curvature of space. The biggest time saver would be avoiding time-consuming gravity assists, if there are any (I assume there are, but I didn't download the 500-page PDF).