The Apllo program on a Super Earth

[Richter]

Would the Apollo program have been a success if it took place on a planet 5 to 10 times the mass of earth?

I read this article on the main space.com page today, well yesterday now, and it really got me thinking about how much more technologically advanced a civilization would need to be in order to get out of a so-called super earth planet's gravity well. Would it be impossible to get to GEO with chemical propulsion if you're already experiencing 5Gs before you start accelerating? Is it possible to do but would take much more advanced chemical propulsion than the Apollo era had at it's disposal? Would such a civilization be stuck on it's planet until the next best, still unknown to us, propulsion technology is invented?

So, here's the scenario question I'm proposing for this thread:

It's May 25th, 1961. Kennedy has just announced the intention for NASA to attempt to go to the moon.

Everything about this is exactly as you remember it except for one thing: Kennedy weighs about 850 pounds, and not because he ate too many cheeseburgers, because he's standing on a planet exactly 5 times the mass of Earth.

You're the head engineer of Aeronautics at NASA that's been charged with coming up for a plan to take our existing know-how of chemical propulsion and make a rocket that will propel us out of our planet's orbit.

Since I've been chewing on this question all day, I'll list some things here that stood out to me as potential challenges for you all to address other than the obvious question about the actual power and fuel needs for the rocket:

-More weight means more stress on the materials used to build structures, how much of a limiting factor is this?
-A larger planet means more atmospheric pressure at sea level. I don't know the calculations on this but it will certainly be higher than ours (135.3 kPa per Wikipedia). This should have implications on maintaining a similar cabin pressure for the organisms. Would we need new technology to make space suits that simulate these pressures? What implications will this have on drag?
-Since you start out at 5Gs, how many Gs will the astronauts need to sustain to reach escape velocity? I believe it was about 11Gs on Apollo missions, someone please correct me if I'm wrong.

Final note - I'm very much a novice when it comes to physics calculations and technical rocketry so part of me is hoping that I'm not missing something painfully obvious that makes this question moot (I'm a bio major). I started just wanting to know how much of a disadvantage civs on super earths would be at but this post is more than that, I hope to see some interesting responses to the scenario!

 

[Shpaget]

Hi and welcome.

It's a complex question.
Let's start from the end of your post.

Since you start out at 5Gs, how many Gs will the astronauts need to sustain to reach escape velocity? I believe it was about 11Gs on Apollo missions, someone please correct me if I'm wrong.

You don't need to reach the escape velocity to get away from the planet. As long as you have propulsion that can overcome current gravity, it doesn't really matter how fast you go. Achieving high speed is only important to reduce fuel consumption.

You can't say "Everything about this is exactly as you remember". It can't be.

Since the gravity is significantly stronger on this planet, life would have developed differently and humans (lets call them that) would probably be much shorter and smaller creatures, so entire capsule could be smaller, affecting the design.

Also, the planet's composition, or at least the top layer important to us, would be different, offering different elements in different ratios, so technology would probably need to find other ways to construct rocket engines, if rocket engine would be invented at all.

Since the gravity is stronger, it would mean that the atmosphere density, which isn't affected only by gravity but by it's mass as well, would decrease more rapidly with altitude, meaning that the air resistance might actually be significantly lower if you launch from a mountain.

Hope this helps.

 

[silylene]

Hi and welcome.

It's a complex question.
Let's start from the end of your post.

Since you start out at 5Gs, how many Gs will the astronauts need to sustain to reach escape velocity? I believe it was about 11Gs on Apollo missions, someone please correct me if I'm wrong.

You don't need to reach the escape velocity to get away from the planet. As long as you have propulsion that can overcome current gravity, it doesn't really matter how fast you go. Achieving high speed is only important to reduce fuel consumption.......

You do need to get a very high speed in the horizontal direction once above the atmosphere in order to achieve a stable orbit. Assuming a circular orbit, v = SQRT(G * M / r) where M = mass of planet and r = orbital radius above the center of the planet (I know, actually the barycenter). In near earth orbit, the required speed is about 7 km/sec, which is very fast. Otherwise, you will fall back down as soon as the fuel is exhausted.

I also want to point out that soft landing into a strong gravity well without extreme deceleration g-forces is also more challenging. Need very good heat shields !

 

[Richter]

"Everything about this is exactly as you remember"

Thanks for the reply Shpaget. To clarify, the purpose of making this statement was to keep the question simple and avoid details that would stifle this exercise.

I recognize that many more factors would come in to play than can be considered here so I'm asking those of you interested in answering to try to suspend considering factors for which we cannot reasonably predict the outcome. Keep it simple - 5xMass earth, thicker and heavier atmosphere, materials and elemental composition available similar to Earth.

Regarding the biology of the organisms, though, I think the most relevant factor to consider is the atmospheric pressure that will need to be simulated in the vacuum of space. Of course, this isn't really worth talking about until you can get a rocket up there.

 

[Shpaget]

You do need to get a very high speed in the horizontal direction once above the atmosphere in order to achieve a stable orbit.

No one mentioned orbits. Richter asked about moon shot.
And I did say "As long as you have propulsion that can overcome current gravity".

Anyway, all you need is more power.
For example Space Shuttle uses two solid rocket boosters and three engines on the Shuttle itself. So, If you need more thrust, you could just add more engines and/or SRBs.