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In the near-to-mid future when ISRU and manufacturing in space is large enough to have an export industry back to Earth, there may be not only a significant volume of raw materials heading back to earth, but also a sizeable quantity of delicate finished goods (e.g. electronics).

While getting things back down may be orders of magnitude easier than bringing them up, doing it on scale poses its own problems. For small quantities of goods, I can imagine them easily being brought back down on a Starship. But once Tonnage to Earth exceeds Tonnage to Space, you have to come up with a different way of getting things down.

There are several challenges:

  • The craft must survive re-entry
  • The craft needs a mechanism to slow down
  • The craft must be steerable to a certain designated crash point on Earth's surface.
  • This crash point needs to be a decent distance away from people or animals.
  • The craft needs to decelerate at a rate low enough to ensure the survival of the cargo.
  • The craft needs to be as light as possible, because it is either being transported up from Earth or it is being manufactured in space, meaning the raw materials are at least a handful of km/s of delta-V away.

For the transport of raw materials like metals, some of these requirements may be less stringent. The craft containing raw iron could come in quite fast, providing the end collision isn't at such a high velocity as to scatter the material everywhere. For such purposes, a craft would obviously be single use.

For more delicate imports that have a maximum G-force a human would relate to, its landing craft would probably be partly reusable. with engines and parachutes manufactured and refurbished on earth and sent up into space in bulk, and a single use ablative carbon frame manufactured in space.

Have there been any proposals or other work done on this front? How do you transport goods down to Earth's surface at a scale larger than your ability to get tonnage to orbit?

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    $\begingroup$ It seems to me the most of the goods made in space will be for use in space, not on earth. I can't see mining minerals in space being financially viable when they are plentiful on earth. For anything that is destined for Earth it will probably be the old fashioned way, i.e. a thermal protection system and parachutes. $\endgroup$
    – GdD
    Aug 5 at 10:08
  • $\begingroup$ This would be much better asked at Worldbuilding.SE. I'm voting to close this here as opinion-based. $\endgroup$ Aug 7 at 12:13
  • $\begingroup$ @DavidHammen This question is best asked at Space.SE. It is dealing with an actual problem, not a fantasy problem, and is asking if any real-life proposals have been made to that effect. $\endgroup$
    – Ingolifs
    yesterday

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This answer is from a worldbuilding perspective, so take this answer with a grain of salt.

Given that ISRU and production of various objects is decently advanced, the export industry should be able to build their own reentry vehicles without much incident, so there isn't really a problem with transportation. The main problem is the design of them.

TL;DR

Essentially an engine-less, expendable Starship with maximized payload volume. Landing would be done with parachutes and an ablative heat shield, with deep-space propulsion done by a VASIMR/NERVA tug and its own RCS thrusters.

The Basics

The first idea I came up with was a Starship with no engines with maximum payload space (taking up pretty much the entire volume). It would be steerable with RCS thrusters powered by some byproduct from mining, landing with parachutes (not sure if this is really viable given that payload would weigh up to 500 tons, 5 times heavier than the Space Shuttle SRB (which as far as I know is the heaviest object landed by parachute), so chute stresses would be immense). Normally this would have to land via splashdown to the spacecraft intact upon impact, but the deceleration could break fragile parts, which would have to be strapped to the walls.

However, the problem with fragile parts breaking could be completely mitigated by having the raw materials shipped to Earth for processing instead.

Production

As the OP did not provide locations of ISRU sites, I'll assume that there are production facilities on the Moon, Mars, and in the asteroid belt. For the Moon, the RCS thrusters would use LH2/LOX from water extraction and electrolysis, which would be boosted into space either by mass driver, spinlauncher, or a reusable booster with about 3-4 km/s of delta-v. The last option would have the booster fly to LLO or up to an eccentric orbit, detach the payload, and return to the launch site for reuse. The payload, once in orbit, would use its RCS or a VASIMR/NERVA tug to escape orbit (about 1-2 km/s of delta-v). Note that the LH2/LOX combination is probably a bad idea because it doesn't provide enough energy to lift heavy payloads.

For a Mars-based launch site, the same would work as the Moon but orbital assembly may be needed due to transfer window issues as well as more delta-v needed to get to orbit and escape. Here, perhaps 100-200 tons could be lifted to orbit via hydrolox engines, assembled into a large cargo ship, then would depart via a nuclear engine or VASIMR for a 2-3 year transfer time. Upon arrival at Earth, the ship would split into its individual parts, orient themselves for reentry, and land. The VASIMR tug would miss the atmosphere and skip off into space on a slingshot back to Mars, or use maneuvering to return.

An asteroid-based plant would have the easy way out as it wouldn't need assistance during ascent, but would face the challenge of long transfer times and high entry velocities. Perhaps 1000 tons of materials could be returned at once via VASIMR, then the same thing would occur as the Mars entry vehicle. However, due to long travel times, shipments of resources probably would arrive once a year, making it inefficient compared to today's production rates. However, with more expansion of the ISRU plants onto larger asteroids, production may be matched.

Other stupid answer

Pack payloads into ablative balls, 10-100 tons at a time and launch them at the Earth like meteors. The general public will enjoy scheduled meteor showers but recovery may be an issue as they are completely unguided like regular meteoroids are. Beware of unscheduled property damage.

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    $\begingroup$ 100 tons in an ablative ball. One way or another, that's going to be spectacular! Brilliant and scary aIl in one Mega Nerf Ball package. I vote we try this first! 😄 $\endgroup$ Aug 4 at 15:18
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    $\begingroup$ If you're exporting from the asteroid belt you may be able to use ice as an ablative material, which is nice for the environment. And if you're flinging stuff at Earth, giant snowballs from space sound less scary than some of the other options. ;) $\endgroup$
    – PM 2Ring
    Aug 5 at 2:30
  • $\begingroup$ @PM2Ring I'm not sure if ice would be a valid heat shield material because of its relatively low melting point, as well as there being better uses for it (cooling agent, drinking water, rocket fuel). Maybe if there was extra LH2/LOX after the coasting phase water ice could be produced for extra shielding, but I doubt it would be of much use. $\endgroup$ Aug 5 at 16:30
  • $\begingroup$ Sure, ice has a low melting point, so you need lots of it. OTOH, per unit mass, water has a very high heat capacity. And water / ice is an easy material to work & polish (and a lot easier to handle than LH2/LOX, and much denser than LH2). Also, loosely packed snow is a great insulator (which is important in igloo construction). Of course, I'm assuming you have access to plenty of ice. $\endgroup$
    – PM 2Ring
    Aug 5 at 16:54
  • $\begingroup$ Water ice is far too valuable to ablate away. But most manufacturing processes produce slag or other unusable byproducts. They might make good ablative shields for a small payload that comes down by parachute once slowed down. It also has the benefit of removing the slag from space. It really depends on what you are making. $\endgroup$
    – Dan Hanson
    Aug 5 at 18:57

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