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Backdrop

In the ending of my book, the closing scene is the control room of the mangled and torn-up starship diving into the atmosphere (maybe not so dramatic) on its fusion engines, slowing down and sliding with a sizzle into the ocean, with a view of the capital city, Elysium, and a convoy of choppers with military and first response crews closing in.

I was actually more concerned with the closing words of the book, to set the backdrop for the probable sequel, but I realized that I didn't actually know if a starship can even survive propulsive reentry, let alone slamming into the ocean.

Sure, I can hand-wave a little of the last part because the laidenfrost effect should keep the water off the ship until the inside floods, but I don't actually know what would or would not let such a ship survive reentry.

The Question

Could any cargo ship survive slow, propulsive reentry? Assuming that its drives can deliver 1+ Gs of acceleration and won't collapse on impact with the launchpad / space-x-chopstick-arms / ocean.

Do note: I am talking about a starship built like the typical sort-of-combat-rated spaceship in the expanse. I would give details about the ships systems but let's just use the expanse because it's simple and the differences are negligible. It has shield panels, engines, maneuvering thrusters, all there usual.

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If not, then what is the minimum a ship needs to survive reentering? Intuitively, I'd assume that the only issues would be atmospheric heating and maybe possible issues with a vaccum-tuned fusion engine, but theres also maneuvering engines or strap-on SRBs.

Also note: I am talking about a habitable, earth-like planet with a 1 ATM pressure atmosphere, with earth like mass.

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  • $\begingroup$ What do you mean by the cockpit of starship? Starships ae not commanded from cockpits but from control rooms, usually buried deep inside the ship for protection. $\endgroup$
    – M. A. Golding
    Jan 30 at 6:47
  • $\begingroup$ @M.A.Golding If were being accurate, it would be called the C.I.C. or the bridge, if you're using naval terms. I was still in the the space-plane vernacular when writing it and used the wrong term. $\endgroup$
    – Sam Kitsune
    Jan 30 at 17:18
  • $\begingroup$ Is the fusion drive a torch drive (a drive that has both high thrust and good gas mileage, I.E. The Epstein drive)? $\endgroup$
    – redfrogcrab
    Jan 30 at 17:27
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    $\begingroup$ @redfrogcrab Yes, I basically copy-pasted the spec-sheet of the drive into the equations which I used to calculate the orbits, speeds and trajectories. $\endgroup$
    – Sam Kitsune
    Jan 30 at 17:40
  • $\begingroup$ There's potentially a difference between surviving reentry in a ship and a ship surviving reentry. The ship could plausibly be designed to bring its crew to the surface alive and relatively unharmed in an emergency, even if this effectively destroys it as a spacecraft. $\endgroup$
    – Christopher James Huff
    Feb 2 at 17:11

4 Answers 4

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Fortunately, there is in real life a space transportation services provider named SpaceX who routinely and frequently posts on YouTube complete videos of their missions, which in recent years have almost always involved the safe re-entry and landing of (the first stage of) their rockets.

If you look at any of those missions, you will notice that the trick is to fire-up the engines just before entering the atmosphere to slow the vehicle down to a convenient speed; they call this the entry burn. For SpaceX's Falcon-9 boosters, that convenient speed is about 3800 km/h (1 km/s, 2400 mph). After the entry burn, they let the vehicle fall freely, and be slowed down by air resistance to its terminal velocity.

For your unspecified spacecraft, the entry burn will probably have to slow the vehicle down to some other convenient speed, to be calculated by the engineers who designed it.

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  • $\begingroup$ Well... yes, I have watched them, but my concern is atmospheric friction or other unforeseen issues a spaceship might have, if it was built to run in vacuum but forced to dive into the atmosphere. $\endgroup$
    – Sam Kitsune
    Jan 28 at 23:26
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    $\begingroup$ If it was not built to fly at high speed through the atmosphere then it was not built to fly at high speed through the atmosphere. They will have to slow down to the maximum speed their ship allows. Again, only the engineers know what that speed is. It might be 1000 mph, it might be 100 mph, it might be 10 mph. If the ship was not actually designed to fly at high speed through the atmosphere, chances are that the engines are nowhere near powerful enough to bring it down in one piece. $\endgroup$
    – AlexP
    Jan 28 at 23:49
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    $\begingroup$ @SamKitsune: Typical commercial aircraft are built to handle emergency water landings, even though they never plan to use them. Similarly, cars are built with crumple zones as an emergency safety feature. Equipment just for emergency re-entries would reasonably explain why your ship can survive it but only barely, or else (if things go a little worse) nearly survive it but not quite. $\endgroup$
    – Peter LeFanu Lumsdaine
    Jan 29 at 12:53
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If you have engines that can exceed 1g and you have enough delta-v then your ship has no problem surviving a propulsive entry--you can slow it as much as you need to, the engineers who built it can tell you the maximum indicated air speed (yeah, that's from the world of airplanes but it still is what matters for figuring what the air will do to your ship) it can take without damage and the maximum it can take without destruction (if it's an emergency measure you might not care if a bunch of fragile stuff on the surface gets destroyed.)

The bigger issue is surviving your own engines. You say it's fusion engines but you don't specify how they work. What happens when the exhaust from the engines hits the atmosphere (or, even worse, the ocean as you land on it) and some of the energy is reflected back at your ship. Even with our chemically powered rockets this becomes an issue--launch pads have sound suppression systems to keep from damaging the rocket and you're talking about something far bigger and more powerful. I would actually be surprised if any such ship could survive the touchdown.

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  • $\begingroup$ I mean, technically you could just turn off the engines a couple hundred meters off the surface and use maneuvering thrusters or just plain nothing until you hit the surface. Sure, the ship will be mangled after, but it is already scrap for the sake of my story. +1 $\endgroup$
    – Sam Kitsune
    Jan 29 at 0:23
  • $\begingroup$ Ah! And about the working principle of my particular spaceship, its basically a copy-paste of the Epstein Drive spec-sheets. Sure, its just called a [generic fusion engine], but it does basically everything it does in the books. $\endgroup$
    – Sam Kitsune
    Jan 29 at 0:25
  • $\begingroup$ And... when I said surface, I mean the ocean, not the side of a mountain, or else you'd be better off in a car crash, without an airbag. $\endgroup$
    – Sam Kitsune
    Jan 29 at 0:28
  • $\begingroup$ @SamKitsune I was assuming ocean and still expecting the destruction of the ship by reflected energy. Maneuvering thrusters--not powerful enough, if they were it would be the same situation anyway. Turning off the drive 200m up--you're going to get quite a splat (see how you fare jumping off a skyscraper.) You might have survivors if it's a warship. $\endgroup$
    – Loren Pechtel
    Jan 29 at 0:41
  • $\begingroup$ Hmmm... Well I guess I need to figure out some solution to that... or maybe just let the entire drive section slag itself, its just three people left aboard a massive ship, and they can huddle near the bow and probably be fine, or maybe figure some way for them to jump ship beforehand, and get to some arbitrary safe distance from the drive plume. $\endgroup$
    – Sam Kitsune
    Jan 29 at 2:12
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possible, but very hard to do if you want your ship in one, not-crumpled piece

Early in the space race, both Nasa and Roscosmos used Lithobreaking (a fancy space flight term for crashing into the surface of a body) for early moon landers.

But since you are working with fusion torch drives, you would probably have enough thrust and fuel to pull off a propulsive re-entry, maybe even a soft landing if you're lucky/bold enough to do it.

first, de-orbit, slow down to a few hundred meters a second, if your crew has time to, rig up some air brakes from some spare hull plates or the doors on a cargo container. then strap in everyone to crash couches, preferably at the highest point in the craft, keep the drive going but at an acceleration that's only enough to keep you below supersonic speeds, if you run out of fuel for the fusion drive, go max power on the forward RCS thrusters, if those runout, pray to god that the lower decks will crumple enough to slow you down to a halt while also not crushing every living thing aboard.

If you have a back-up propulsion system that's not an Ion thruster, save it for a few thousand meters above the ground/sea level to perform a suicide burn, this is the most optimal outcome, ignite it and keep the thrust steady.

If you somehow survived all that, great! salvage what you can from the ship's supplies, call for help if you can, and wait for rescue, or starve to death.

DO NOT LAND IN THE SEA, water at that speed for any object is just as hard as concrete, at least on land the guys who manage to survive can retrieve supplies and call for help from the remains of the ship.

I'd also make a make-shift parachute deployer+parachutes for added deceleration in atmosphere

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  • $\begingroup$ Fantastic answer! Do note, the engines are like the Epstein Drives in the expanse, even your missiles have enough fuel to run laps around the solar system and not break a sweat. You can burn all the way down, but the only problem would be slowing to a standstill, and then cutting the drives before the reflected heat off the water/ground melts the engines, and plummet the rest of the way down. $\endgroup$
    – Sam Kitsune
    Jan 30 at 18:31
  • $\begingroup$ @SamKitsune thanks! you could probably keep the main drive from melting by either installing side-mounted retro-rockets (preferably liquid fuel, purely so you can adjust thrust) or performing the planetary lithobraking speedrun any %, either way your drive cone is getting destroyed. maybe also do a "stone skip" maneuver on a large body of water. also love this story idea $\endgroup$
    – redfrogcrab
    Jan 30 at 22:01
  • $\begingroup$ I need you to clarify something, are you a frog, or are you a crab? (I don't need sleep, I need answers!) $\endgroup$
    – Sam Kitsune
    Jan 30 at 23:28
  • $\begingroup$ @SamKitsune I am the species Rania Rania, or the Red Frog crab, a species of pacific crab typically fished for Asian seafood, any further discussion of my origins can be conducted in chat $\endgroup$
    – redfrogcrab
    Jan 30 at 23:34
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With a drive able to accelerate the ship with 1+ G, the ship could decelerate before touching the atmosphere to come to a relative stop and descend at a snail's pace, limiting stress due to landing to a minimum. Since it (hopefully) is build to withstand it's own drive's acceleration the ship should be strong/sturdy enough to not break apart under it's own weight, as long as it is correctly oriented (the main drive pointing towards the planet).

The main issues I see would be

  • is there enough fuel to land that slowly?
  • keeping the ship at the right angle - presumably a ship that is not supposed to land on planets might have no computer aided program for that.

But for a story those "issues" are probably more productive then problematic - not having enough fuel to do it quite the easy and safe way sounds a lot more exciting. And the words "The computer can't do this, we'll have to fly it manually" are practically mandatory for every story involving cool space ships. ;)

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