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"Super-Earth" planets are giant-size versions of Earth, and some research has suggested that they're more likely to be habitable than Earth-size worlds. But a new study reveals how difficult it would be for any aliens on these exoplanets to explore space.
To launch the equivalent of an Apollo moon mission, a rocket on a super-Earth would need to have a mass of about 440,000 tons (400,000 metric tons), due to fuel requirements, the study said. That's on the order of the mass of the Great Pyramid of Giza in Egypt.
"On more-massive planets, spaceflight would be exponentially more expensive," said study author Michael Hippke, an independent researcher affiliated with the Sonneberg Observatory in Germany. "Such civilizations would not have satellite TV, a moon mission or a Hubble Space Telescope."
https://www.space.com/40375-super-earth-exoplanets-hard-aliens-launch.html
[Also Covered By]: GIZMODO
[Paper]: Spaceflight from Super-Earths is difficult
[Related]: 10 Exoplanets That Could Host Alien Life
(Score: 2) by zocalo on Tuesday April 24 2018, @07:06AM (10 children)
UNIX? They're not even circumcised! Savages!
(Score: 5, Insightful) by frojack on Tuesday April 24 2018, @08:32AM (9 children)
Wrong. It makes those methods MORE viable. A denser atmosphere (virtually a given on a high gravity planet) provides just as much (if not more) lift capability for a balloon. Helium is still lighter than nitrogen and oxygen. A bag of helium will still rise.
Wings work better in dense air than they do in thin air. And combustion engines produce more power in dense air than thin air.
Basically we've settled on vehicles that work on earth. Then we try out those formulas on what we imagine another planet might present, and make pronouncements about impossibility.
Don't you suppose an intelligent life form on a high gravity planet would try different solutions than ours?
Is ours box the only box within which all alien life forms have to think?
No, you are mistaken. I've always had this sig.
(Score: 3, Funny) by Anonymous Coward on Tuesday April 24 2018, @09:11AM
Getting altitude is only half the battle. the real trick is to be going fast enough so you can get a stable orbit.
Source: Kerbal Space Program.
(Score: 2) by zocalo on Tuesday April 24 2018, @10:04AM (5 children)
And no, I'm definitely not assuming terrestrial conditions/tech - see my other post below - but the problem with hypothetical alien tech is in the name; we have no way of knowing what it is or how it might work making it kind of hard to second guess, so all we can really do is extrapolate from what we do know. Even if aircraft would work on a given heavy Earth, I'd expect that you'd see either a radically different approach to deal with the specific conditions, or at the very least some fairly obvious changes in the relative size of the lifting surfaces and weight ratios.
UNIX? They're not even circumcised! Savages!
(Score: 4, Interesting) by Immerman on Tuesday April 24 2018, @02:24PM (4 children)
No need to burn fuel getting off the ground, balloons will do the job far more efficiently. All you need to do is contain enough helium or hydrogen to reduce your balloon + payload density below that of the surrounding atmosphere. Gravity is irrelevant, and the denser the atmosphere, the less lift-gas you need to accomplish the task, since your payload is more buoyant to begin with.
Once you're above the vast bulk of the atmosphere, you can then worry about getting up to orbital speeds. If you try to do that with a traditional rocket then yes, you'll still have to spend enough energy to keep it from falling while it accelerates, and you're back to directly fighting a much greater gravity. However, an airship-to-orbit (http://www.jpaerospace.com/) giant high-altitude delta-wing -rocket propelled airship could still be feasible - aerodynamic enough that lift keeps it rising through the increasingly vacuous atmosphere as it accelerates. It might take you several weeks to accelerate to orbit, but lift and buoyancy are doing most of the work of keeping you up while you do so.
Plus, since you're not relying on raw thrust to keep you in the air, you can use less powerful, more efficient rockets - even current ion drives typically have around 10x the specific impulse of chemical rockets.
Yes, they might need need to be more technologically advanced before they could actually pull it off, but what's another century or two of technological development in the face of the thousands it took to reach the point where they could even start dreaming up solutions?
(Score: 2) by zocalo on Tuesday April 24 2018, @02:44PM (3 children)
UNIX? They're not even circumcised! Savages!
(Score: 2) by Immerman on Tuesday April 24 2018, @07:47PM (2 children)
Why use helium? Hydrogen is a LOT more plentiful, slightly more potent, and not dramatically more dangerous as long as you treat it with due respect (LOTS of airships used hydrogen safely for years, the Hindenburg was never designed to do so - it was designed to use helium). There's also no particular reason to "use it up" - it's quite possible to have both a balloon and pressure tank, and pump your lift gas between them to control buoyancy.
And building a large enough balloon is a safe assumption for a species even 100 years more technologically advanced than us, we could probably do it today - heck, we've figured out how to mass-produce graphene, which is probably as good as it gets for balloons. If you want to lift a 1000kg point mass (to sidestep payload buoyancy considerations) on Earth you need a balloon large enough to hold a bit more than 1000kg of air - at 1.225 kg/m^3 that's 816 cubic meters, or a sphere roughly 12m across. On Venus air density is 67 kg/m^3, so to get the same lift you'd only need about 15m^3, or only 3m across. Of course you need a bigger balloon as you get closer to vacuum, but that's why the Airship-to-orbit folks plan a transfer from their "deep atmosphere" to their orbital one.
And again - it doesn't matter what the gravity is, your balloon just has to displace a greater than-payload mass of air, buoyancy does all the work. The only place the force of gravity factors in is the necessary strength of the balloon to support your payload - which if you're using graphene might have to be dozens of atoms thick.
(Score: 0) by Anonymous Coward on Wednesday April 25 2018, @07:47AM (1 child)
The hydrogen wasn't the problem with the Hindenburg anyway. Hydrogen burns with a faint blue flame, not the large yellow-orange flames the Hindenburg burned with.
The Hindenburg was covered in a conductive paint due to problems with static discharges. That paint was basically thermite, which just happens to burn with huge yellow-orange flames.
(Score: 2) by Immerman on Thursday April 26 2018, @02:48AM
True, but the Hindenburg is pretty much why hydrogen, and airships for that matter, went out of style. Facts are irrelevant once the media adopts a narrative.
(Score: 2) by fadrian on Tuesday April 24 2018, @02:28PM
There are a lot of other ways to lift weight than rockets. A launch loop [wikipedia.org] would be feasible, for instance. Though, to be fair, having worked next to its inventor for a couple years, I do have a bit of an unfair advantage in thinking of this solution for our poor, gravity-bound aliens.
That is all.
(Score: 2) by HiThere on Tuesday April 24 2018, @04:50PM
I'm not sure that it makes those methods more viable, but it sure doesn't make them less viable.
The problem is, once you get high enough, you still need to lift off against a greater gravitational pull. Orbital velocities are higher, escape velocity is higher, etc. You get this "higher velocity requirement" for free with a stronger gravity.
OTOH, if the atmosphere were dense further out (lots further out) like that of Venus, then balloons might actually be a better first stage. But I'm having a hard time thinking of that kind of a planet as a Super-Earth. It would be more like a Hypo-Jupiter (except for having a necessary rocky core...but most of my life we didn't know that Jupiter didn't have one, and we're still not sure).
With an atmosphere that reaches far enough from ground a nuclear powered plane might be a reasonable "one stage to orbit" vehicle. But that's not a SuperEarth.
Still, with a SuperEarth I expect that you could get to orbit with a nuclear powered spaceplane. It just wouldn't be any trivial exercise. You'd basically need to get above orbital velocity while still in the atmosphere, where you could use the atmosphere as working material for your nuclear powered jet. I'm rather sure that no chemical fuel would be energetic enough to make this work.
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