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For background, read my question.

What would be scientifically the best way to get the lander out of the atmosphere?

  • It is 12ft high and 15 ft long.

  • It's about 11,000 pounds of dry weight (tell me if this doesn't make sense).

  • The technology should be as close to our current level.

Best meaning either light enough to bring enough for a two-way journey, or be able to find on an Earth-like planet without animals, as seen in this question.

If you have any questions, please ask. I'm in middle school, so bear with me and my understanding of science.

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  • $\begingroup$ You half-answer this in your other question but it's good to have it here too: how futuristic of technology are you allowing? Without limitations, my quick answer is "antimatter" because its annihilation will be nearly optimally energetic $\endgroup$ – Punintended Oct 27 '20 at 22:52
  • $\begingroup$ Don't know what a "lander" is, or why it needs to get out of the atmosphere, or where it is supposed to go, but in April 2019 a SpaceX Falcon Heavy rocket put a 14,000 pound satellite on a geosynchronous transfer orbit. All three first-stage cores returned to Earth. Falcon rockets use Merlin engines, which burn kerosene. A Falcon Heavy rocket can lift a payload of 63,800 kg (140,655 pounds) to low Earth orbit. $\endgroup$ – AlexP Oct 27 '20 at 23:03
  • $\begingroup$ Most of those answers are in my other question: worldbuilding.stackexchange.com/questions/188802/… $\endgroup$ – Anderson Oct 27 '20 at 23:04
  • $\begingroup$ The point is that we routinely lift such payloads onto orbit. $\endgroup$ – AlexP Oct 27 '20 at 23:06
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    $\begingroup$ You might need to define what you mean by "best", liquid hydrogen + liquid oxygen (LH2/LOX) has very a good energy/weight ratio but LH2 requires some pretty expensive materials to keep it, well... liquid. Kerosene/LOX is much cheaper but has a lower energy density so more of your rocket needs to be fuel instead of payload. You could probably get away with a solid rocket booster if you stuck it on a jumbo jet and flew it to the edge of the atmosphere ala Virgin Galactic style, the rocket would be very cheap and simple compared with the others, but now you need a custom built plane so... $\endgroup$ – Samwise Oct 27 '20 at 23:26
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This has no answer, under the stipulation of "The technology should be as close to our current level."

Your requirement is for a SSTO, fully reuseable orbit-to-surface-to-orbit vessel.

There is NO possible chemical fuel propulsion that can achieve this, at anything like the sort of mass fractions we can achieve. You would need to make your 11000 pound lander be capable of fuelling up 300000 pounds of fuel (mass fraction 99.5%) to achieve this. And it would need to be able to land at about 90% of that mass!

SO scratch chemical fuel.

Advanced nuclear thermal might do the job, but there is no ways you could shoehorn a strong enough reactor AND the shielding for pilots AND reentry and landing gear into a 11 000 pound package. Nor even in one 50 times that mass. Multi-gigawatt reactors are heavy, and that is what you would need to launch SSTO from Earth surface.

So you need a miracle. Take the Skylon concept, make its engines (which don't exist yet) another 50% better/stronger/lighter, invent some miraculum for the landing gear, and you might be able to make this work.

So finally, your fuel. Whether Nuclear Thermal or SABRE engine derived, will be mostly liquid hydrogen, and some liquid oxygen for part of the flight regime.

Realistically, you will need to advance the technology 50-100 years or so. Allow semi-compact, low-radiation, fusion reactor that can be used as power source, hydrogen as reaction mass, and nuclear-powered plasma-accelerated hydrogen for your thrust.

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  • $\begingroup$ Ok. Thank you a lot. $\endgroup$ – Anderson Oct 28 '20 at 2:33
  • $\begingroup$ /NO possible/ Weren't the moon landers surface to surface 2 way vessels? How does the pride of 1969 not qualify? $\endgroup$ – Willk Oct 28 '20 at 19:13
  • $\begingroup$ @Willk no, they were separate low-lunar-orbit to lunar-surface and lunar-surface to low-lunar-orbit vehicles, the latter being part of the payload of the former, and both being launched from Earth and delivered to LLO by three Saturn V stages and the Apollo service module. And even going to orbit from the surface in a single stage was only possible because of the moon's smaller gravity well. $\endgroup$ – Christopher James Huff Oct 29 '20 at 6:41
  • $\begingroup$ Actually SpaceX is working on a single stage lunar lander for NASA that would go from lunar orbit to the lunar surface and back again. So it should be possible. The difference with Earth is indeed the much lower lunar gravity, and no atmosphere. $\endgroup$ – JanKanis Oct 30 '20 at 22:34
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    $\begingroup$ Guys, READ THE OP's foundational question. It contains the part "Imagine a world very similar to Earth". EARTH, not moon. $\endgroup$ – user79911 Oct 31 '20 at 5:27
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As noted above you cant have a lander that size for an Earth sized world the Apollo Lunar Landers weighed in dry at something like 9,500 pounds.

Best I can see you doing with that sized platform is a one way lander with a rover package. The rover deploys, collects some samples (maybe a few kilos) then returns to the lander and offloads it.

Once the samples are on-board the probe deploys and inflates a high altitude balloon with a transponder that should take the sample module up to about 60-70 thousand feet (assuming Earth like atmospheric pressure) with the payload suspended on the end of a long line.

Then? You'd need a 2nd craft, with some kind of 'air' breathing engine to descend 'hook' onto and collect the payload, winch it in and then use rockets to get into LEO. For all I know probably a third rocket to recover the payload from LEO.

You would really want the those samples to be worth it though.

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  • $\begingroup$ Ok, thank you a lot. $\endgroup$ – Anderson Oct 29 '20 at 12:54
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If you want a freeflying vehicle, as MarvinKitfox said no chemical fuel is going to get you down and back up again in a single stage with today's technology, Earth's gravity is just too strong. But depending on what you want to do you could look at Project Orion, which was a proposed concept of propelling a spacecraft by detonating small nuclear bombs behind it. Amazingly, in theory that should work. Obviously it was never developed in full, but it should be able to lift off to orbit from Earth's surface, and I guess given its performance it would also be able to land from space and then lift off again. Obviously there are some issues with radiation, so don't land near inhabited area's. And I don't know if the principle can be scaled down to your size lander, you may need a much bigger ship. But apparently it could have been developed with today's technology. (Though as nobody did, we can't be 100% sure.)

As for future fuels, one theoretical candidate you could have a look at could be metallic hydrogen.

Another more realistic option if you want to look beyond a freeflying vehicle would be a space elevator. That is almost possible with today's technology, we just need to be able to make much longer carbon nanotubes and do so economically. Or you could have a look at other non-rocket space launch systems that may fit your need.

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