Super-Earths in Need for Extremly Big Rockets (2018)

There&#x27;s a lot of loopholes you could plausibly escape through. For one: you could use hybrid atmosphere-breathing engines to get most of the way to low orbit. (Using ambient atmosphere as a reaction mass circumvents the rocket equation). From low orbit, you can switch to electric thrusters with Isp much higher than the engines considered here: it&#x27;s no longer necessary to have a thrust&#x2F;weight ratio greater than unity.<p>A hydrogen planet would be particularly easy, since the light molecules would maximize Isp for a (non-combustion) thermal engine. A nuclear scramjet on a Hycaean world would have some truly impressive performance.

Perhaps &quot;slow&quot; ascent would be a option, i.e. not reaching escape velocity but just steadily ascending until you are far enough away that gravity is lower. I know here on earth it is far more inefficient, which is why you always go for &quot;ballistic&quot; trajectories where you gain enough velocity that inertia carries you on.<p>Maybe there is something you could &quot;ratchet&quot; against? Thrust a bit upward and have something prevent you from falling back down. Maybe the denser atmosphere would provide an option. You could deploy large sails as intermediate launch pads in the atmosphere for example.

Read a sci-fi book recently with that being a central plot point. Reasonably advanced species unable to escape the gravity of its home world. There is also a dearth of fissile material in the solar system that prevent a &quot;nuclear option&quot;. Book was written as a bit of homage to &quot;The Mote in God&#x27;s Eye&quot; with wanting to leave to planet being seen as a &quot;Crazy Eddie&quot; idea.<p><a href="https:&#x2F;&#x2F;www.goodreads.com&#x2F;book&#x2F;show&#x2F;59554147-cold-eyes" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.goodreads.com&#x2F;book&#x2F;show&#x2F;59554147-cold-eyes</a>

Imagine non-super earth&#x27;s alien civilizations are probably writing up articles about how planets like ours are hard to escape.<p>You dealt the hand you&#x27;re given.

Bottom line: Chemical rockets are never going to take us any place interesting in the universe.

&gt; It should be noted that, while the subject of this paper is silly, the analysis actually does make sense. This paper, then, is a serious analysis of a ridiculous subject, which is of course the opposite of what is usual in astrophysics<p>From what I can tell, this was published in August of that year, though with the silliness toned down significantly [0]<p>[0] <a href="https:&#x2F;&#x2F;www.cambridge.org&#x2F;core&#x2F;services&#x2F;aop-cambridge-core&#x2F;content&#x2F;view&#x2F;90E8835704DB1C3449B38867D848AB74&#x2F;S1473550418000198a.pdf&#x2F;spaceflight-from-super-earths-is-difficult.pdf" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.cambridge.org&#x2F;core&#x2F;services&#x2F;aop-cambridge-core&#x2F;c...</a>

&gt; water (H2O) cannot become radioactive itself<p>This was interesting. I researched it a little and found this on <a href="https:&#x2F;&#x2F;www.quora.com&#x2F;Why-is-water-the-only-thing-on-Earth-that-cannot-become-radioactive" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.quora.com&#x2F;Why-is-water-the-only-thing-on-Earth-t...</a><p>When hit by neutrons &quot;hydrogen, move to another stable state and only become unstable when that particular atom gets hit twice&quot; &quot;Oxygen takes three absorptions to become radioactive&quot; and underwater neutrons &quot;activated mainly the sodium in the sea salt.&quot;

I&#x27;m curious how much harder it would be on these planets to launch 1) Sputnik like satellite 2) Hubble Space telescope

&gt; We find that chemical rockets still allow for escape velocities on Super-Earths up to 10x Earth mass. Much heavier rocky worlds, if they exist, will require using up most of the planet as chemical fuel for the (one) launch, a rather risky undertaking.<p>From the abstract. I love papers with a sense of humor.

I thought because gravity gets smaller by squared distance, large planets would not have crushing gravity on the surface because you are far away from the center of mass. Is that true? If so, how large would a super earth have to be to have an equivalent earth gravity on its surface?

One option that doesn&#x27;t seem to be mentioned is the used of beamed energy such as laser (visible or infra-red spectrum) which provide energy directly to a rocket.<p>This might be used in a secondary process (e.g., ion or plasma generators) or directly (heating atmosphere and&#x2F;or fuel) to generate thrust.<p>The advantage is that the power source is on the ground, and need not be lofted, which removes part of the rocket-equation limit. It&#x27;s still required to source or carry <i>reaction</i> mass, and I&#x27;d suggest that at least a fair portion of that be obtained within the atmosphere.<p>I don&#x27;t know what a launch trajectory would look like, though I suspect something which went relatively slowly vertical (to minimise low-elevation drag), then began a hybrid lifting-ballistic flight at the highest possible levels of the atmosphere, powered by a planet-ringing set of laser stations, and acquiring reaction mass from the atmosphere itself, <i>might</i> be within the realm of reason?<p>It also strikes me that a world with sufficient mass would tend to retain hydrogen gas itself (though that would still likely react with oxygen to form water vapour), but at higher elevations there might be a significant differential fraction of H2 to other atmospheric components. Root mean squared velocity of H2 at 27 C (300 K) is about 7,000 kph (~4,300 mph).[1]<p>That&#x27;s already less than Earth&#x27;s escape velocity, so the problem is the molecules which have <i>higher</i> velocity that &quot;boil off&quot; into space.[2] I don&#x27;t have the chops to compute this.<p>But a laser-pumped mesospheric hydrogen ramjet rocket might be able to take advantage of highly-energised (heated or ionised) hydrogen to gain escape velocity on even a significantly larger Super-Earth.<p>________________________________<p>Notes:<p>1. &lt;<a href="https:&#x2F;&#x2F;chem.libretexts.org&#x2F;Bookshelves&#x2F;General_Chemistry&#x2F;ChemPRIME_(Moore_et_al.)&#x2F;09%3A_Gases&#x2F;9.15%3A_Kinetic_Theory_of_Gases-_Molecular_Speeds" rel="nofollow noreferrer">https:&#x2F;&#x2F;chem.libretexts.org&#x2F;Bookshelves&#x2F;General_Chemistry&#x2F;Ch...</a>&gt;<p>2. Earth has lost roughly 25% of its primordial hydrogen (and water) by this mechanism. &lt;<a href="https:&#x2F;&#x2F;sciencenordic.com&#x2F;chemistry-climate-denmark&#x2F;the-earth-has-lost-a-quarter-of-its-water&#x2F;1462713" rel="nofollow noreferrer">https:&#x2F;&#x2F;sciencenordic.com&#x2F;chemistry-climate-denmark&#x2F;the-eart...</a>&gt;

Here&#x27;s the wiki page for ways around it. Of course, it&#x27;s all hypothetical and theoretical:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Non-rocket_spacelaunch" rel="nofollow noreferrer">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Non-rocket_spacelaunch</a>

I would assume that such planets have a very large surface area, larger than Earth and Mars combined? In this case, super-Earthlings have plenty of exploring to do, just in a different way from us. It can still be challenging and time consuming, for example air travel may not be practical, or may require balloons floating in denser atmosphere rather than jet engines. By the time we explored Mars and they explored their entire surface, or prospects for going further may not be so different. Either we have developed technology to travel much further, or we have to accept that that&#x27;s all the planetary surface we are going to see and we better take good care of it.

A super earth 2x the diameter of Earth but with the density of Mars would have the same surface gravity as Earth (according to my back of the envelope calculations).

just think of the countless civilizations of blind space whales living in subsurface oceans for whom merely getting to the surface of their planet is as difficult as it is for us to get to space

Extremly?!