4 ms·

You can't fire anything into Earth orbit. Once propulsion is complete, you are in an orbit. Orbits repeat. So if your orbit starts from the ground, your orbit

You can't fire anything into Earth orbit. Once propulsion is complete, you are in an orbit. Orbits repeat. So if your orbit starts from the ground, your orbit will intersect the ground which is... undesirable. Instead, you have to fire a rocket motor to alter the initial orbit into one that doesn't intersect the ground. Now you have a new problem: you have to design a rocket motor which can withstand the launch. A solid rocket almost certainly will spontaneously RUD when heavy acceleration is applied. A liquid rocket has pumps and pipes which are likely can't survive the acceleration. This is the reason spin launch is nonsense: you've traded a solved problem (make big rocket motor) for an unsolvable problem: make a rocket motor which can withstand absurd acceleration. The other red flag with spin launch is that genuinely new approaches to problems do not come from unqualified randos thinking about a problem. For example, if a company has a crazy new idea for blood testing, it's really bad if the crazy new idea came from someone with zero experience and zero domain knowledge.

01100011 4y ago
> https://www.freethink.com/space/low-earth-orbit-satellite https://www.freethink.com/space/low-earth-orbit-satellite Seems like there is already a mechanism, sans moving parts, of generating force post-launch. Not saying it is sufficient to correct a ground-launched, ballistic projectile though. > A solid rocket almost certainly will spontaneously RUD when heavy acceleration is applied I am skeptical that there is no chemical propellant capable of resisting the initial acceleration. That seems like a bold claim. What about gas-based thrusters(i.e. ion drive with xenon or even just nitrogen gas)?
- cjensen 4y ago
  The LEO post-launch force you link to is for minor orbital changes. Or large changes over a large amount of time. The problem with an orbit that begins at the ground is that you have exactly one orbit's worth of time in which to convert it into a real orbit. Magnetic or ion propulsion won't cut it. My comment about solid rockets is due to the fact that they include fully combustable fuel in a ready-to-use mix. Solid rockets don't require much input to get them to combust. I assume no one is considering solid rockets for this application; I only mention it as part of assuming they would need a liquid rocket so I could explain the problem with liquid rockets which rely on pumps and pipes.
  - 01100011 4y ago
    Fill a tank with nitrogen and cap it with something akin to an explosive bolt. When attitude is favorable, blow the bolt and let nature take its course. Sorry it's late here and I'm just spitballing. Seems feasible though.
    - amanaplanacanal 4y ago
      I guess the problem then becomes designing an explosive bolt that can survive the 10,000G launch without exploding.
jklp 4y ago
I had to google this myself but for others who may be unfamiliar RUD = Rapid Unscheduled Disassembly Seems to be popularised by Elon Musk [1] but I managed to find a page which links to evidence [2] going back as far as the 70s. [1] https://www.theguardian.com/technology/2015/jan/16/elon-musk-falcon-9-rapid-unscheduled-disassembly https://www.theguardian.com/technology/2015/jan/16/elon-musk... [2] https://space.stackexchange.com/questions/10022/who-coined-the-phrase-rapid-unscheduled-disassembly https://space.stackexchange.com/questions/10022/who-coined-t...
jasonwatkinspdx 4y ago
Rocket assistance is common among artillery rounds, and several militaries have been trailing next generations of these rounds that may reach performance ranges similar to intermediate ballistic ranges. So it's not that out there of a concept. I share the skepticism about a high performance liquid engine however.
misnome 4y ago
Doesn’t this ignore the fact that earth has an atmosphere? Couldn’t you fire something that would have an escape trajectory but then decays though air resistance into an orbit?
- cjensen 4y ago
  Suppose you have an object that has just left the atmosphere, and suppose it is in an orbit. You have the same problem again: every orbit repeats, so the object's orbit, having just left the atmosphere, will repeat into the atmosphere. Let's put this another way: every orbit is an ellipse. If you do not alter your orbit, you will only travel on the ellipse. The moment you stop interacting with the atmosphere, you are on a fixed ellipse. The problem is just behind you on the ellipse is the atmosphere, and if you continue forward on the ellipse you will inevitably come back to the part of the ellipse that is still in the atmosphere.
  - misnome 4y ago
    I know how orbital dynamics work with the absence of non-gravitational forces. But it's not a point that you suddenly stop interacting with the atmosphere, it's a gradient, with asymmetric forces on the forwards and down directions from gravity/air resistance that are smeared over time, a bit like a non-instantaneous burn around the fast end of the ellipse; I'm not sure how well the "free motion in a vacuum" intuition holds in this case; but especially when your delta-v from the atmosphere is smeared nonlinearly over your ascent period. Yes, you end up at the same height or lower the next time round, and will incur drag from that, but shrug, that's just regular orbital dynamics.
naasking 4y ago
You keep using "likely" and "almost certainly", suggesting uncertainty, but then somehow arrive at a strong conclusion that such a rocket is an "unsolvable problem". The latter does not follow from the former.

01100011 4y ago

> https://www.freethink.com/space/low-earth-orbit-satellite https://www.freethink.com/space/low-earth-orbit-satellite Seems like there is already a mechanism, sans moving parts, of generating force post-launch. Not saying it is sufficient to correct a ground-launched, ballistic projectile though. > A solid rocket almost certainly will spontaneously RUD when heavy acceleration is applied I am skeptical that there is no chemical propellant capable of resisting the initial acceleration. That seems like a bold claim. What about gas-based thrusters(i.e. ion drive with xenon or even just nitrogen gas)?

cjensen 4y ago
The LEO post-launch force you link to is for minor orbital changes. Or large changes over a large amount of time. The problem with an orbit that begins at the ground is that you have exactly one orbit's worth of time in which to convert it into a real orbit. Magnetic or ion propulsion won't cut it. My comment about solid rockets is due to the fact that they include fully combustable fuel in a ready-to-use mix. Solid rockets don't require much input to get them to combust. I assume no one is considering solid rockets for this application; I only mention it as part of assuming they would need a liquid rocket so I could explain the problem with liquid rockets which rely on pumps and pipes.
- 01100011 4y ago
  Fill a tank with nitrogen and cap it with something akin to an explosive bolt. When attitude is favorable, blow the bolt and let nature take its course. Sorry it's late here and I'm just spitballing. Seems feasible though.
  - amanaplanacanal 4y ago
    I guess the problem then becomes designing an explosive bolt that can survive the 10,000G launch without exploding.

jklp 4y ago

I had to google this myself but for others who may be unfamiliar RUD = Rapid Unscheduled Disassembly Seems to be popularised by Elon Musk [1] but I managed to find a page which links to evidence [2] going back as far as the 70s. [1] https://www.theguardian.com/technology/2015/jan/16/elon-musk-falcon-9-rapid-unscheduled-disassembly https://www.theguardian.com/technology/2015/jan/16/elon-musk... [2] https://space.stackexchange.com/questions/10022/who-coined-the-phrase-rapid-unscheduled-disassembly https://space.stackexchange.com/questions/10022/who-coined-t...

jasonwatkinspdx 4y ago

Rocket assistance is common among artillery rounds, and several militaries have been trailing next generations of these rounds that may reach performance ranges similar to intermediate ballistic ranges. So it's not that out there of a concept. I share the skepticism about a high performance liquid engine however.

misnome 4y ago

Doesn’t this ignore the fact that earth has an atmosphere? Couldn’t you fire something that would have an escape trajectory but then decays though air resistance into an orbit?

cjensen 4y ago
Suppose you have an object that has just left the atmosphere, and suppose it is in an orbit. You have the same problem again: every orbit repeats, so the object's orbit, having just left the atmosphere, will repeat into the atmosphere. Let's put this another way: every orbit is an ellipse. If you do not alter your orbit, you will only travel on the ellipse. The moment you stop interacting with the atmosphere, you are on a fixed ellipse. The problem is just behind you on the ellipse is the atmosphere, and if you continue forward on the ellipse you will inevitably come back to the part of the ellipse that is still in the atmosphere.
- misnome 4y ago
  I know how orbital dynamics work with the absence of non-gravitational forces. But it's not a point that you suddenly stop interacting with the atmosphere, it's a gradient, with asymmetric forces on the forwards and down directions from gravity/air resistance that are smeared over time, a bit like a non-instantaneous burn around the fast end of the ellipse; I'm not sure how well the "free motion in a vacuum" intuition holds in this case; but especially when your delta-v from the atmosphere is smeared nonlinearly over your ascent period. Yes, you end up at the same height or lower the next time round, and will incur drag from that, but shrug, that's just regular orbital dynamics.

naasking 4y ago

You keep using "likely" and "almost certainly", suggesting uncertainty, but then somehow arrive at a strong conclusion that such a rocket is an "unsolvable problem". The latter does not follow from the former.