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My aliens want to build the heaviest chemical rocket possible: They never were much into space travel, since their planets' gravity is about 1.5 of ours. They made lots of bad experiences fighting against gravity and 'decided' to keep their technology on the ground. Suddenly the world's biggest corporation decides that it's absolutely necessary and very urgent to send a few drives, a breeding station, and some robots into space. They don't care about everything they've built up or the rest of the world. They go with chemical engines because they don't have any experience with stronger ones. That would be about 100 tons of rocket for 1 gram of payload? Can we also use nanotubes and diamonds to make it hold together? Nice.

The best place for launch is the planets largest mountain, letting you skip a part of the atmosphere and also letting you abuse some of the planets rotation. Still, there's a good amount of distance to cover, because the atmosphere goes about 2 times further than earths. (50% hydrogen, 40% nitrogen and some heavy stuff that doesn't matter) If the air was warmer, it would be easier to pierce through, right? What could be better suited to warm up the atmosphere than a bunch of bombs? They'd shoot up a few rings of nuclear warheads that detonate at various heights, wait until pressure and wind are ok, uncover the rocket and launch it.

Of course air density is one of the less important factors when thinking about launching a rocket. I want it to be important, because I want to nuke the sky. I also know that there are better ways to escape a planets gravity than chemical engines, but that's what we're working with here. Try to work with a lunatic, please.

Two questions:

Is this way of heating up the atmosphere realistic?

If not, what would be the best way?

my last post with a similar topic

I'd also be thankful for comments that mention more variables to think about. What else would the aliens have to do to launch their monster of a rocket? It's not about solving a problem, but about creating new ones which the aliens can barely solve.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monty Wild Nov 8 at 5:20
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The main issue with this approach is that it's a largely pointless way of affecting the rocket power, as atmospheric drag is a very small part of the energy cost of launching a rocket. A much greater burden - especially on a high-g planet - is gravity drag: broadly speaking, the energy you have to expend maintaining the height you've already gained while you work to go higher/faster. As ever, the rocket equation is not your friend here.

The best approach is definitely to gain as much height and speed (remembering that gaining 'sideways' speed is what rockets spend most of their energy doing) before beginning the rocket phase. Putting the launch site on top of a mountain is a good start, but you need to do more.

An intelligent race on a high-g world would certainly have discovered both lighter-than- and heavier-than-air flight, and the idea of rocket-propelled flight won't be any more novel to them than the idea of rocket-propelled rocketry. From your mountain-top launch site, you should lift your launch platform as high as possible into the atmosphere using a balloon. Since the atmosphere is already 40% hydrogen this will consist of filling a zeppelin with pure hydrogen and then heating it like a hot air balloon - what could possibly go wrong?! This is a much less disruptive way of getting through the bulk of the dense atmosphere.

Once up there, you should launch your rocket more like a glider than anything else, using wings to generate as much aerodynamic lift as possible for as long as possible. Since the speed of sound in hydrogen is much higher than in terrestrial air you'll be able to get a lot of lateral speed up in this mode before it becomes more practical to jettison the wings (or lift up out of the atmosphere) rather than continue to strengthen them. Your chemical rockets can then switch into pure rocketry mode, with a good headstart in both altitude and lateral speed. Meanwhile, all that uranium can be put to good use powering the heaters that will keep that mountain-sized zeppelin launch pad aloft.

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    $\begingroup$ the balloon is surely interesting, almost cooler than my initial crap. It would have to be bigger than I can imagine rn. I really like it. $\endgroup$ – justthisonequestion Nov 6 at 13:18
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    $\begingroup$ Since this atmosphere has no oxygen, filling your absurdly massive zeppelin with superheated hydrogen would be much less dangerous than it would be on earth. Not that it's a good idea by any means, but at least it's less of a horrifically bad idea than it would be on earth. $\endgroup$ – Gryphon - Reinstate Monica Nov 6 at 14:20
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    $\begingroup$ "atmospheric drag is a very small part of the energy cost of launching a rocket. A much greater burden - especially on a high-g planet - is gravity drag" They are connected for this issue. More atmosphere => lower terminal velocity => lower energy-efficient travel velocity => longer travel time => longer time being affected by gravity drag. The question on whether the gravity drag costs you more than flying above terminal velocity is an interesting one, but since atmospheric pressure is effectively decided by gravitational force I suspect this is going to have a universally applicable answer $\endgroup$ – Flater Nov 6 at 21:30
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Is this way of heating up the atmosphere realistic?

It'll heat up the atmosphere fine, but the low-pressure, low-density region left behind won't persist for very long. Certainly not long enough to fire a rocket through it. Or at least, not a rocket that needed to survive.

If not, what would be the best way?

The best way is not to use a chemical rocket. I'm not sure that you'd have much luck even if you built some kind of evacuated launch tube, Star Tram style, and shot your rocket out of that.

If you're so willing to nuke your world, why not just implement Project Orion instead? Lots of thrust, high Isp, everyone's happy. Apart from those who develop cancer as a result of the launches. It'll be easier than the launch tube, and it is more likely to work given your apparent tech level, too.

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  • $\begingroup$ The aliens would surely love to use more advanced technologies, but it was a corporate decision that they would only use what they already know. They also don't have much time for testing. -I'm not sold. Back to the low-density region: If they had access to a few thousand warheads, maybe even causing lasting wind into a certain direction, do you think they had enough time to pass through. $\endgroup$ – justthisonequestion Nov 6 at 12:37
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    $\begingroup$ @justthisonequestion "not much time for testing" that's either a lame excuse (it took only a few short decades between the first V2 launch and man landing on the moon, a timespan which encompassed the development of thermonuclear weapons, the Orion project and solid core nuclear rockets) and a foreshadowing of total, inevitable and pointless failure. You can't just wing it, here, regardless of what management would like. As a wise man once observed, "For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." $\endgroup$ – Starfish Prime Nov 6 at 12:40
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    $\begingroup$ @justthisonequestion no, they will not be able to pass through, because they will be cooked, or smashed, or irradiated to death, or a combination of all of the above. $\endgroup$ – Starfish Prime Nov 6 at 12:42
  • $\begingroup$ too bad. Thanks for your time. starts furiously ketching a giant flamethrower $\endgroup$ – justthisonequestion Nov 6 at 12:46
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    $\begingroup$ Ah Project Orion, what's the best way into space? Well you stick a wok over a nuke, sit on the wok and detonate the nuke. What could possibly go wrong? $\endgroup$ – Separatrix Nov 7 at 9:05
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Just use the nukes as propellant instead.

Back in the 1960s, some NASA scientists investigated the possibility of spacecraft propelled by relatively small nuclear bombs; they called it "Project Orion". The idea is that the spacecraft would launch the nuclear bombs out of a hole on the bottom of the ship, where they would detonate; the bombs would be designed to be "shaped charge" explosives so that most of the bomb's energy would be focused back up towards the spacecraft, where it would hit a 20m steel plate. That plate would be connected to a massive set of shock absorbers, which in turn would be connected to the rest of the spacecraft.

The numbers they calculated for it would be that such a rocket would be capable of carrying 6000 tons of cargo (the weight of an entire Saturn 5 rocket) to the moon and back on one tank of fuel. While I'm not a rocket scientist, so I'm not certain how much delta-V a rocket would have left when launching from your alien planet, I'm sure that they'd be able to do so.

Unfortunately, international politics and Cold War tensions rendered the construction of nuclear pulse propulsion rockets infeasible, but this might not be the case for your aliens.

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  • $\begingroup$ en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion), if you really want to screw everything that you leave behind. Just the megalomania of it... $\endgroup$ – Flummox - don't be evil SE Nov 7 at 8:45
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    $\begingroup$ @Flummox-don'tbeevilSE Actually, you can minimize nuclear fallout with a correctly-designed launchpad, since fallout is caused by items being sucked into the nuclear fireball and burned into tiny particles; it's why airbursts produce much less fallout that groundburst nuclear explosions. IIRC the engineers of Project Orion calculated that the optimal launchpad was a giant iron plate covered with a thin layer of graphite. $\endgroup$ – nick012000 Nov 7 at 9:23
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Mount your nuke on the pointed spike on your rocket.

Heat reduces drag. If you are going to make heat, make it where you need it - right in front of your rocket. This works to reduce air resistance.

https://www.researchgate.net/publication/268555192_Drag_Reduction_of_Spiked_Missile_by_Heat_Addition

Experiments conducted in Germany 45 years ago and later repeated in the USA in the early 1980s indicate a drag reduction of approximately 50% for a spiked missile due to burning of hydrogen gas in the separated flow. This paper investigates through computational fluid dynamics (CFD) means the role of heat addition, by burning of hydrogen gas, in reducing drag... Addition of heat into the turbulent separated flow virtually eliminates the shear layer reattachment shock wave and also modifies base drag. Injection of hydrogen into the separated flow region without burning did not eliminate the reattachment shock wave, indicating that heat addition is a necessary condition for eliminating shear layer reattachment shock wave and drag reduction, as observed in both the German and the USA experiments.

If you have the fixings for a nuclear bomb you can probably make a fission reactor. Mount one on the tip of your rocket and use it to heat the tip to very hot. From the linked article - the longer the spike the better this works and so your rocket should have a very long glowing hot spike on the tip. Aerospikes are already in use but I could not find a picture of a glowing hot one.

Once you are out of the atmosphere you might want to dump the fission reactor. As there is less passing air it will not be cooled as well and it will get hotter and hotter.

- Note - the large percentage of hydrogen in your atmosphere will also reduce air resistance as compared to Earth. Also people might talk in squeaky voices.

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    $\begingroup$ Would the reduced drag be enough to offset mounting a fission reactor to your rocket? $\endgroup$ – Michael Richardson Nov 6 at 20:26
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    $\begingroup$ @MichaelRichardson - It is small. No carbon rods. No cooling tower. But the term "Reactor" is less scary than "Runaway Fission Reaction Welded to a Giant Metal Spear". As regards ways to make metal hot, it is probably one of the less practical methods. $\endgroup$ – Willk Nov 6 at 20:38
  • $\begingroup$ nice. thank you very much $\endgroup$ – justthisonequestion Nov 7 at 7:22
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What about lightning?

Note: all the other answers about air resistance being totally negligible part of the rocket launch are 100% correct. But since this isn't tagged hard science, the rule of cool prevails.

Nukes are inefficient at rarefying a column of air, because much of their heat is spread over a an area much larger than your rocket. Lightning however does very good at heating a very localized column extending from ground to the cloud layer.

Lightning "bolts" naturally follow a column of air ionized by the the strong static field built up in the clouds. Another way to ionize the air is with a high intensity laser. So, mount an array of high-power lasers around your launchpad, wait for a stormy, overcast day, fire off the whole laser array at once, and take off as soon as the turbulence from the awesome giant column of lightning has dissipated.

If you really wanted to stick with the "nuke the skies" concept, nukes definitely ionize the air pretty well, too. Rather than big clusters of megaton strategic nukes, you'd want a small vertical string of kiloton tactical nukes. You could combine that with the lasers to get could column containment. So a slow-motion video capture of your launch would show

1) A sequence of small nuclear blasts starting 2) Immediately followed by high powered lasers stabbing up into the sky 3) Immediately followed by a huge lightning blast 4) Followed a short time later by your scorched and wind-buffeted rocket lurching into the sky

Bonus:

In addition to the chemical rockets, harvest the lightning strike to give your craft some initial kick with a rail-gun type launcher.

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A few years ago I looked at a proposal to speed aircraft by using a laser to ionise the air in front of them. This is an extreme form of plasma aerodynamics, which is mainly being tested with gentler approaches, but it would have the effect you desire.

The trick is using an ultra-short pulse laser which is essentially self-focusing to achieve the required intensity with a relatively modest laser.

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