3 ms·

I played enough KSP to know that this sort of thing is somewhere halfway up on the list of "things that you might think go to space but don't". Hitting the atm

by zaarn 9y ago

I played enough KSP to know that this sort of thing is somewhere halfway up on the list of "things that you might think go to space but don't". Hitting the atmosphere after accelerating will probably cause most materials outside of reentry heatshield to immediately melt, ignite and explode without particular order of these events. After turning into a molten blob of lava or a spent heatshield, it would still be nowhere close to orbital velocity and would have to fire an engine that somehow survived A) the heat and B) the intense G-forces involved. I'll probably file this under "solar freaking roadways" and hope they don't try to fire a human in this.

Cthulhu_ 9y ago
And yet, also in KSP, if you can find a cheap and efficient way to cross the first hundred meter upwards, you've already saved a load of fuel. I had a setup once where my first booster was a lot of plane engines; seemed to work all right.
- zaarn 9y ago
  The last half of the atmosphere is an easy flight; drag is reduced to the point that it barely matters and most of the bigger engines have reached almost peak efficiency. Due to lack of drag you will also barely loose any velocity anymore. The first half is hard because drag is so high but if you can sustain atleast 150m/s (or Mach 0.5) until you reach about 15km altitude and then sustain atleast 1.5G until 35km you can make it easily into space. If necessary you can try to gain some vertical velocity and abuse body-lift to drag you up higher despite not having sufficient lifting power in your boosters (if you have between 1.02 and 1.1 TWR) Most rockets burn 80% of their fuel to get out of the atmosphere, the remaining 20% are usually good enough to get into orbit, insert into any transfer orbit you like and fly off into empty space.
phire 9y ago
Eh, I'm going to give them the benefit of the doubt, mostly because they appear to be able to attract large amounts of VC funding. When it comes to orbital mechanics, the idea works. You just need to make your starting velocity high enough after it has decelerated though our atmosphere slows down to orbital velocity. Then you just design your ascent capsule to "deal" with the extreme declaration and heating, which isn't a huge problem: Heat shields exist, and so do g-force hardened electronics. Nobody should be under the impression that this will be used to launched anything other than small specially designed g-force hardened satellites. It's not like "solar freaking roadways" which has blearlying obvious economic and efficiency flaws, the designs for catapult based launchers have been well studied and there is nothing physically stopping them. It's more of a engineering problem. Honestly, I'm more concerned about the engineering practicalities of building an extremely large centrifuge spinning at some absurdly high RPM (presumably at the top of a mountain, so it bypasses some of our atmosphere)
- zaarn 9y ago
  >Eh, I'm going to give them the benefit of the doubt, mostly because they appear to be able to attract large amounts of VC funding. Just because someone is giving them money doesn't mean they can do it. >When it comes to orbital mechanics, the idea works. Of course it does, similar systems have been suggested for lunar transfers to earth (IIRC). Without atmosphere these systems are trivial to implement and use. (Comparatively) > Heat shields exist, and so do g-force hardened electronics. Heatshields are rather large and expensive. There is also a difference between heatshields for reentry and heatshields you'd need for leaving the atmosphere efficiently. At the moment, heatshields are basically ramming through the air and compressing it in front of the aircraft, this is most efficient in reducing velocity and can reduce the temperature at the shield somewhat. When you fire something through the atmosphere with the goal to get it into a suborbital trajectory you need a different solution; your aircraft becomes a spike/spear, generating friction with air instead of compression. Friction is harder to deal with if I recall correctly from various pages on the topic.

by zaarn 9y ago

Cthulhu_ 9y ago

And yet, also in KSP, if you can find a cheap and efficient way to cross the first hundred meter upwards, you've already saved a load of fuel. I had a setup once where my first booster was a lot of plane engines; seemed to work all right.

zaarn 9y ago
The last half of the atmosphere is an easy flight; drag is reduced to the point that it barely matters and most of the bigger engines have reached almost peak efficiency. Due to lack of drag you will also barely loose any velocity anymore. The first half is hard because drag is so high but if you can sustain atleast 150m/s (or Mach 0.5) until you reach about 15km altitude and then sustain atleast 1.5G until 35km you can make it easily into space. If necessary you can try to gain some vertical velocity and abuse body-lift to drag you up higher despite not having sufficient lifting power in your boosters (if you have between 1.02 and 1.1 TWR) Most rockets burn 80% of their fuel to get out of the atmosphere, the remaining 20% are usually good enough to get into orbit, insert into any transfer orbit you like and fly off into empty space.

phire 9y ago

Eh, I'm going to give them the benefit of the doubt, mostly because they appear to be able to attract large amounts of VC funding. When it comes to orbital mechanics, the idea works. You just need to make your starting velocity high enough after it has decelerated though our atmosphere slows down to orbital velocity. Then you just design your ascent capsule to "deal" with the extreme declaration and heating, which isn't a huge problem: Heat shields exist, and so do g-force hardened electronics. Nobody should be under the impression that this will be used to launched anything other than small specially designed g-force hardened satellites. It's not like "solar freaking roadways" which has blearlying obvious economic and efficiency flaws, the designs for catapult based launchers have been well studied and there is nothing physically stopping them. It's more of a engineering problem. Honestly, I'm more concerned about the engineering practicalities of building an extremely large centrifuge spinning at some absurdly high RPM (presumably at the top of a mountain, so it bypasses some of our atmosphere)

zaarn 9y ago
>Eh, I'm going to give them the benefit of the doubt, mostly because they appear to be able to attract large amounts of VC funding. Just because someone is giving them money doesn't mean they can do it. >When it comes to orbital mechanics, the idea works. Of course it does, similar systems have been suggested for lunar transfers to earth (IIRC). Without atmosphere these systems are trivial to implement and use. (Comparatively) > Heat shields exist, and so do g-force hardened electronics. Heatshields are rather large and expensive. There is also a difference between heatshields for reentry and heatshields you'd need for leaving the atmosphere efficiently. At the moment, heatshields are basically ramming through the air and compressing it in front of the aircraft, this is most efficient in reducing velocity and can reduce the temperature at the shield somewhat. When you fire something through the atmosphere with the goal to get it into a suborbital trajectory you need a different solution; your aircraft becomes a spike/spear, generating friction with air instead of compression. Friction is harder to deal with if I recall correctly from various pages on the topic.