Why land at all?

You and I live on a planet. That's what we are used to.

But these colonists have lived for decades (centuries) in a finely-tuned space habitat. It seems temporary to us...but for them the habitat is 'home'.

They are in space, near a new star (source of energy), with plenty of asteroids and moons and comets at hand (resources). Everything they need to build new orbital habitats and maintain the life they are used to.

Some adventurous folks and scientists are likely to climb down the gravity well to the attractive earth-like planet. There might even be some outposts down there for various reasons. But civilization and the bulk of the population will be space-based, just like their ancestors.

Plan to land only what you need

Much of the colony ship has no reason to land.

• The stardrive and its fuel tanks


• Maneuvering thrusters and their fuel tanks


• The shielding


• Command and Engineering


• Air recycling (you might want water and waste recycling)

The list probably goes on for some considerable time. There'll be large amounts of empty space formerly taken up by stores for the journey that's just not needed any more. All of this extra mass and volume would need to be shielded for re-entry greatly increasing the amount of mass unnecessarily being hauled across space. So plan to leave it all in orbit and only take what you need. The rest of the ship can stay in orbit as your first communications satellite.

Eggs and baskets

Don't keep all of the former in one of the latter.

While you're sending three ships, entering an atmosphere is a very high risk activity, the fewer of your eggs you have in each basket the safer you're going to be. Break required parts of the ship down into separate re-entry modules, no more than one critical element in each pod. Make sure you don't lose too much if any one pod is lost.

This started as a comment on L.Dutchs answer

Bizzarely i actually built a similar ship to what you are referring to in Kerbal Space Program a year or so ago... i wouldn't recommend doing this as i had about 8 fps when leaving Kerbin Orbit... it took awhile.

You need to build you ship modularly with all the components you'd want to have on the landed colony. and then each module can be landed seperately, whether that be with parachutes and heat shields. You do this is for several reasons

1. Redundency: if there is a failure to land a module, that's all you lose


2. Efficiency, different modules will require different locations, you'll want water so being near a water source is required, but the best location to mine for metals extra might be miles away from the nearest water source, so being able to land the different modules in their different ideal locations and not have to move them later is a huge efficiency boost

So you could easily have an Ikea home flat packed with a descent module that would build the areas of housing, which would have the required modules positioned nearby, whereas the mining systems etc can be landed where those required materials are highest.

Once all the habitation and systems modules are landed, what about the rest of the ship... well there is a lot of valuable materials on board that ship, so landing them allows them to be recovered. There's no benefit to leaving it in orbit as its orbit will eventually degrade and reenter the atmosphere possible onto the colony... not ideal... and maintaining orbit will be costly in terms of remaining resources left on board. and that colony will not leave the planet to venture further for another world for a serious amount of time, by which time the systems would likely have degraded to beyond usefulness.

And don't forget that as you approach the planet you'll want to launch several satellites, for GPS, Weather and Communications.

In theory, yes it can.
But bringing such a giant ship in the athmosphere comes with some problems.

First you have to keep it from breaking apart. Usually the descend comes with lots of vibrations which might break the ship apart.

The next problem you might encounter is the giant heat shield such a big ship would need. (Also I don't know how much a descend like that would heat up the athmosphere)

So you could disassemble the ship in orbit and land small parts of it (I guess that is the way such an undertaking would actually be done) or

If your ship has plenty of fuel or whatever powersource it uses to power its engines and if the engines are strong enough, you could simply slow down the descend to a speed where the heating is no big deal. If you descend slow enough none of the problems would appear.

Using the athmosphere as a break is only done to save fuel. If you have plenty, then you don't need to do that.

Space Elevator

As a riff on the why land at all, consider parking the colony ship in geosynchronous orbit. Have it stocked with a set of GPS, weather and communication satellites which get dispersed around the planet, as well as some limited high tech foundries and a space elevator.

The colony ship serves as a support station ferrying hard to produce parts down as well as maintaining orbital assets until the colony is able to provide for itself.

Most of the colonial equipment will just makes a one way trip down the elevator. The empty space in the ship can then be converted into a university/museum of life back on Earth.

Okay, I know that other people have already said that you want to bring down the ship in sections, but I'm going to provide another reason to do so:

It's much easier to land things that aren't the size of skyscrapers.

Square-Cube

Take a really long piece of wood, and hold it horizontal. You'll notice it bends very easily, especially if you shake it. Now scale down the piece of wood, keeping the aspect ratios the same, and try shaking it. It won't bend. If your structure is bigger, it is relatively weaker than something scaled down. Square-Cube law again. If you have a structural failure, then your ship is now...

Aerodynamic Instability

There's also the matter of aerodynamic instability, a.k.a please don't spin out and fly apart in a massive explosion at 7km/s. This is going to involve reconfiguring the ship so that its center of mass is directly in front of the center of pressure. Rather than disassembling the ship and then reassembling it to get aerodynamic stability, just disassemble it and send the pieces down one at a time. It's safer that way. No need to worry about a poor job rebuilding the ship.

Ground Pressure

Finally, skyscrapers have foundations. Your ship does not. There is no infrastructure on the planet to build a suitable landing site for a skyscraper. A space-shuttle-sized module will be light enough to not immediately sink into the ground and/or fall over when landing.

You usually do not want to land large ships because it takes very large amount of energy to get them back to space, but if your ship is designed as a one way vehicle that's then to be used as habitat and will never fly again, then landing is not a problem.

There are a few things to consider though:

1. To slow down a massive ship like that enough to do an orbit insertion, you'll need massive amounts of energy / propellan . Assuming your ship has traveled to another star, at I'm guessing some significant fraction of the speed of light, we can safely assume you can hand wave this away.




2. You might want to look into using a skip-reentry (with multiple skips) instead of more traditional aerodynamic braking to reduce the high heating loads.

https://en.wikipedia.org/wiki/Boost-glide

Lay it down nice and slow.

Your colony ship will settle down very gradually and by doing so will sidestep heating in the atmosphere and also stresses on the ship.

It will not orbit, because orbit requires fast speeds that will then need to be shed as heat into the atmosphere. It will use its engines to counter the pull of gravity as it approaches from space, and ease its way into the atmosphere at subsonic speed.

In addition, once in the atmosphere the ship will deploy colossal hydrogen floats, making it neutrally buoyant.

https://en.wikipedia.org/wiki/Atmospheric_entry

An alternative low velocity method of controlled atmospheric entry is
buoyancy which is suitable for planetary entry where thick
atmospheres, strong gravity, or both factors complicate high-velocity
hyperbolic entry.

Here the hugeness of the ship complicates high velocity hyperbolic entry. Buoyancy will be adjusted with controlled release of hydrogen. This will allow the ship to turn its engines off while high above the planet, and gradually settle down like a giant balloon coming to rest.

This will minimize stresses on the ship, heating of the ship and the atmosphere, and impact on the ground below.

I forgot to mention that klaxons will sound as the ship nears touchdown, so local wildlife can clear the area.