Docking Megaships, thoughts on how well KSP 2 will handle it?

[GoldForest]

I've been wondering about this for a few days. How well will KSP 2 deal with docking supersized ships such as two Daedalus ships docking together, kind of like in the movie Sunshine where Icarus II docked with Icarus I. 

I'd like to hear your thoughts on this subject. 

[darthgently]

It will involve more than a pair of Clamp-O-Tron Jr. ports I hope.  Like maybe some 20m giant ports with perhaps some additional supports deployed after hard mate, like big KIS telescoping joint type mechanism.  That would look great

[snkiz]

manual control of docking ports? you can use multiple ports to dock now, but it's very finicky. Often the secondary ports will just shut off once the primary port makes contact and the game considers it one vessel. A manual button to force a docking attempt would solve the issue. And just bigger more purpose built docking ports with structural properties in the node.

[The Aziz]

Docking port on one vessel, docking port on another and

Done.

[Pthigrivi]

The last dev video showed some pretty enormous thruster blocks, so in theory its all the same principles as docking other large vessels, just with bigger parts and more mass. There are also options for hall thrusters that run on xenon that might be a better option than monoprop later in the tech tree. Nate mentioned in an older video that a lot of the late-game engines have big radiation cones that would effect both departure and rendezvous. This might mean using secondary hydrogen engines on approach, or if you were leaving or arriving somewhere with an existing station you could use tugs to close that safe-distance. 

[GoldForest]

17 hours ago, Pthigrivi said:

The last dev video showed some pretty enormous thruster blocks, so in theory its all the same principles as docking other large vessels, just with bigger parts and more mass. There are also options for hall thrusters that run on xenon that might be a better option than monoprop later in the tech tree. Nate mentioned in an older video that a lot of the late-game engines have big radiation cones that would effect both departure and rendezvous. This might mean using secondary hydrogen engines on approach, or if you were leaving or arriving somewhere with an existing station you could use tugs to close that safe-distance. 

Less radioactive engines will definitely be needed for rendezvousing. I forgot about the radiation cone on engines. I wonder how big those comes will be though. Like could you use the Daedalus shield on craft 1 to protect you from the thrust from craft 2? If so, hydrogen engines wouldn't be needed, if you're a madman. 

Of course, that's if the docking ports even allow for two gigacrafts to be docked at all. Will the docking ports be weight restricted? Like if 120 ton craft B trying to connect to Craft A's 100 ton rated docking port, that the docking port won't engage at all. 

[kerbiloid]

1. Take two daedaluses.

2. Attach with nozzles.

3. Pump out the air.

Vacuum!

Spoiler

 

[Catto]

Big boy

[darthgently]

2 hours ago, GoldForest said:

Less radioactive engines will definitely be needed for rendezvousing. I forgot about the radiation cone on engines. I wonder how big those comes will be though. Like could you use the Daedalus shield on craft 1 to protect you from the thrust from craft 2? If so, hydrogen engines wouldn't be needed, if you're a madman. 

I don't think you want those engines firing at all when near other craft if one were to emulate NASA type protocols.  Probably thruster only within so N*L meters where N is some factor and L is max(length of craft 1, length of craft 2) or something like that.  I'm thinking for radiation danger purposes, N would be 5 to 10 at minimum for my game.  And no engine ignition at all if other craft is in the "thrust cone" with a greater safety distance that above probably

Edited April 19, 2022 by darthgently

[SciMan]

As far as docking two craft together goes, yeah we're gonna need MUCH bigger docking ports (rated for higher structural loads WITHOUT WOBBLING PLEASE!).

As far as the RCS goes, yeah monopropellant ain't gonna cut it for craft of that size.
Heck, even LF/Ox RCS like the Vernor (but with more RCS nozzles, and more thrust) still uses too much propellant (but hey at least the thrust is there).

Now, IMO the best way to create these massive RCS thrusters would be to have literally every (chemical) engine in the game be usable as RCS, by a "mode switch" you set in the VAB/SPH.
Additionally, you should also be able to use any (single-port) RCS thruster as an engine, again by a "mode switch" you set in the VAB (these ones just default to being controlled by the RCS controls instead of by the main engine throttle).
This works for any kind of hydrolox, LF/Ox, or Monopropellant engine.

And if you really want to, you should be able to use Ion engines (of various sizes) for similar purposes.

However, to solve the problem of RCS on these mega-ships, I can think of only one option that combines the required thrust levels with the required low propellant consumption rate.
And that is an Arcjet thruster. An Arcjet thruster is a type of electrical thruster, however unlike an ion engine it does not rely on ionizing the gas to create thrust, and it is also able to generate much more thrust with much less power input, however the specific impulse is significantly lower.
The secret is that they're an electroTHERMAL thruster.
What that means is that they take the reaction mass and use electricity to heat it to high temperatures before shooting it out of a rocket nozzle to create thrust. Just like a nuclear thermal rocket, except in this case the heat comes from electricity and not nuclear reactions.
Arcjets use an electrical arc as the heating element.
Less sophisticated electrothermal thrusters are Resistojets, which basically run the reaction mass thru a chamber containing a higher power version of the heating element out of a blow dryer.
Arcjets have higher performance than Resistojets because they can heat the propellant to a higher temperature, due to the temperature of the propellant not not being limited by the melting temperature of the heating element, instead the maximum amount of power used is limited by the melting point of the material the arc electrodes are made of (both Carbon and Tungsten are good choices for this, due to high melting points and acceptable electrical characteristics).

Now to the incredibly great thing about Arcjet thrusters: They don't emit any ionizing radiation, which means they can be placed ANYWHERE that can withstand the loads imposed by the thrust they produce, and that has access to a sufficient source of electrical power.
This means that you could design a craft with a high-power nuclear reactor (perhaps the drive itself operating to generate electricity instead of thrust, perhaps an entirely separate reactor generating ONLY power), way out on a long truss (with a shadow shield) to keep the radiation down in the habitation sections of the craft, and yet still have the ability to place large, high performance high thrust RCS thrusters practically wherever you want to put the RCS translational CoT on top of (or near to) the craft's actual CoM, which would have the intended effect of the use of translational thrust creating a minimum of adverse change to the vessels attitude, while also maximizing the potential RCS Rotational torque that the thrusters can impart on the vehicle (basically, it lets you put the RCS where you need it, rather than where other constraints would have you put it).

[TheOrbitalMechanic]

On 4/26/2022 at 4:11 PM, SciMan said:

Now, IMO the best way to create these massive RCS thrusters would be to have literally every (chemical) engine in the game be usable as RCS, by a "mode switch" you set in the VAB/SPH.
Additionally, you should also be able to use any (single-port) RCS thruster as an engine, again by a "mode switch" you set in the VAB (these ones just default to being controlled by the RCS controls instead of by the main engine throttle).
This works for any kind of hydrolox, LF/Ox, or Monopropellant engine.

I believe this is already in KSP 1, but maybe only with the Advanced Tweakables setting enabled. You can set thrusters to respond to RCS controls or throttle controls, so the chances of getting something like this in KSP 2 seem high.

Additionally, having engines usable for RCS could be a cool way of driving home the scale of these giant ships--crazy to imagine something so big that you have to use Rhino engines to even turn it.

[t_v]

Just now, TheOrbitalMechanic said:

You can set thrusters to respond to RCS controls or throttle controls, so the chances of getting something like this in KSP 2 seem high.

This is new, thanks for the tips! I was using way too many vernier engines to turn my massive ships!

[shdwlrd]

3 minutes ago, TheOrbitalMechanic said:

Additionally, having engines usable for RCS could be a cool way of driving home the scale of these giant ships--crazy to imagine something so big that you have to use Rhino engines to even turn it.

That would be awesome to see.

[TheOrbitalMechanic]

1 hour ago, t_v said:

This is new, thanks for the tips! I was using way too many vernier engines to turn my massive ships!

On closer inspection, I seem to have been mistaken, although you may be able to rig something up with the KAL controller from Breaking Ground. There's a bunch of thrust direction customization available for your standard RCS thrusters (only fire in certain directions, fire forward under throttle input, etc.) so I must've gotten confused.

[Catto]

I'm not sure how they're gonna dock. It's definitely not going to make the kraken angry, though.

Edited April 29, 2022 by Catto

[mattinoz]

On 4/19/2022 at 2:33 AM, snkiz said:

manual control of docking ports? you can use multiple ports to dock now, but it's very finicky. Often the secondary ports will just shut off once the primary port makes contact and the game considers it one vessel. A manual button to force a docking attempt would solve the issue. And just bigger more purpose built docking ports with structural properties in the node.

The first question about docking we’d need an answer for is does the game with its new spacial graph, multiplayer and such consider the craft merged in to on craft when docked  or do they now remain 2 or more. 
 

requiring a explicit merging to allow space construction without merging with the construction platform. 
 

then all the construction clamps also come in the play as options.

[Snark]

I'd be curious how they'll handle the gameplay aspect, in terms of player patience. Angular moment of inertia goes up with the square of the linear dimensions; rotating a megaship is going to be sloooooow. (This would apply to all maneuvering, not just docking.)

This feels like it has the potential to tax the player's patience somewhat. About the only way I could see to mitigate this (other than just telling the player "well, be patient, then") would be to substantially increase the maximum allowed physics warp. Which, in turn, would require careful programming. KSP1 tops out at 4x, and even that tends to get really unstable and kraken-prone for larger vessels.

It sounds as though megaships are intended as a pretty important part of KSP2 gameplay, so I assume they'll have some answer for all of this. I'm just curious to see what it will end up looking like.

[The Aziz]

I don't dock using physwarp. If I'm aligned and only need to push myself towards the target, normal warp is the way to go.

That said, how relevant is physwarp if we can apply timewarp while burning? If I have asymmetrical thrust, can I warp if my ship is doing circles?

[shdwlrd]

14 hours ago, Snark said:

I'd be curious how they'll handle the gameplay aspect, in terms of player patience. Angular moment of inertia goes up with the square of the linear dimensions; rotating a megaship is going to be sloooooow. (This would apply to all maneuvering, not just docking.)

This feels like it has the potential to tax the player's patience somewhat. About the only way I could see to mitigate this (other than just telling the player "well, be patient, then") would be to substantially increase the maximum allowed physics warp. Which, in turn, would require careful programming. KSP1 tops out at 4x, and even that tends to get really unstable and kraken-prone for larger vessels.

It sounds as though megaships are intended as a pretty important part of KSP2 gameplay, so I assume they'll have some answer for all of this. I'm just curious to see what it will end up looking like.

I would think of players would adopt a more reasonable design for huge motherships. Braking engines facing forward so you don't have to rotate the craft unnecessarily. Powerful RCS thrusters to help rotate/translate the craft when necessary. It would be reasonable to use smaller crafts to ferry crew and supplies back and forth just so you don't have to deal with the headache of docking all the time.

Edited May 20, 2022 by shdwlrd

[Bej Kerman]

14 hours ago, Snark said:

This feels like it has the potential to tax the player's patience somewhat. About the only way I could see to mitigate this (other than just telling the player "well, be patient, then") would be to substantially increase the maximum allowed physics warp. Which, in turn, would require careful programming. KSP1 tops out at 4x, and even that tends to get really unstable and kraken-prone for larger vessels.

We already know KSP 2 will have persistent thrust and I'm 99% confident that this extends to RCS and will also allow persistent rotation.

Edited May 20, 2022 by Bej Kerman

[SciMan]

I agree that truly gigantic craft would likely make use of smaller craft to transfer personnel and resources between each other, however even in just KSP 1 without using phyiscal time warp at all (staying on 1x speed!) I've been rather easily able to dock well-designed craft together with each massing significantly over 100 tons each. I've even been able to dock craft massing thousands of tons together in the past, tho that does require the use of high thrust RCS parts to make changing velocity and/or orientation not a painfully slow process.

(EDIT:)
The key thing I end up doing is using MORE THAN ONE RCS CLUSTER IN THE SAME SPOT. They all act as a unit in response to command input, so putting say 4 RCS thruster blocks next to each other might look a little ugly but hey it means you have 4 times the thrust you would otherwise have. I mean the Space Shuttle had many more than just a single thruster of each thrust level for a given control axis, just look at the nose RCS for evidence of that. Just like on the Shuttle, this also allows you to select just how much control authority you want when you input a command, say you're doing final docking and you're low on main engine fuel meaning you're quite a bit less massive than you would be fully fueled, you might turn off 3 of 4 of those RCS thruster blocks in my example to enable much finer control of your ship's pointing and trajectory, while still having the thrust of all 4 available (by enabling them all) when fully fueled and the thing might be otherwise starting to get a little hard to control.

You gotta remember, the monopropellant RCS thrusters you get in vanilla KSP are only capable of 1kn of thrust each. IRL that's a rather LARGE RCS thruster cluster (seeing as most satellite main apogee raising thrusters are about half as powerful, with the attitude control RCS thrusters on satellites being of the order of 10n or less each), but in KSP it can often end up falling short with the often gigantic vessels players are known to make. The Vernor thruster is an improvement at 12kn, and using LFO instead of Monopropellant can simplify the logistics of resupplying the vessel, but it's only 1 axis of thrust so you need a lot of them to fully control a craft, and even then 12kn can indeed still fall quite short on truly massive vessels (such as a vessel which uses multiple long 5m fuel tanks from MH with Rhino engines as the main propulsion for a Jool-5 mothership, yeah you're gonna need a LOT of Vernors to get that thing turning at a reasonably fast pace). At the same time, Vernors can be overkill, say on a orbital fuel transfer vessel built around a Rockomax Jumbo-64 fuel tank (the longest 2.5m tank). You might end up having a hard time docking that craft if the fuel is nearly depleted.
(END EDIT)

Now this next thing will improve the responsiveness of any craft, but it really becomes mandatory with these large craft:
Primarily, the vessel should be designed so that the "heavy bits are in the middle", meaning that only the things that are radioactive (power reactor if any, as well as likely the drive) should go on one end, and just the habitation on the other end (to maximize distance between the two), with both propellant reserves, other accessory equipment like batteries and reaction wheels, and non-crew-containing payloads (such as yet-to-be-landed colony modules) located as close to the center of mass as practical, followed by placing the RCS clusters as far apart on the craft as possible (so the ideal locations would be near the drive/reactor section and near the habitation section, but balanced around the average CoM).
The suggested placement of the most massive parts of the craft close to the center of mass minimizes rotational moment-of-inertia, which makes it easier to rotate the craft in the pitch/yaw axes. (as well as minimizing the distance by which the CoM shifts as propellant and/or other consumables are used).
The suggested placement of the RCS as distant from the CoM as possible (but balanced around it) still allows the RCS to be used in translation just as it would be if placed anywhere else on the vessel (so long as it's balanced) , but placing it distant from the CoM means that the RCS when commanded to rotate the craft in pitch/yaw will have a very long "lever arm" to do so with, thereby increasing the effective torque available to rotate the craft, which again makes it easier to rotate in the pitch/yaw axes.
Roll attitude control is generally not an issue with "long and skinny" craft, however if it does become an issue the solution is to simply put the RCS thrusters on girders to space them away from the long-axis of the craft (again, just like with pitch/yaw, this gives the thrusters a longer "lever arm" to act on when attempting to turn the craft in roll).

I already apply these principles in my craft design, and I've never really had any issues.

Like I believe I've stated before, the primary blocking issue is availability of high thrust RCS, and large docking ports capable of withstanding the force of a large ship's drive being used to push around another large ship (or being able to construct a large ship in parts and connect drive, truss, payload, propellant, and habitation sections with docking ports, without it wobbling excessively, but it's fine if you have to reinforce the connection after initial docking with EVA-attached struts or something like that, so long as they actually reinforce the joint unlike what most of the KSP 1 addons that add such things end up doing when designing such gigantic vessels).

(EDIT 2:)
Additionally, you don't end up needing forward-facing braking engines if you limit your approach velocity to something reasonable (depending on distance, I limit my docking approach velocity to between 2.5 and 5 meters per second), and fine-tune your rendezvous encounter to be "far enough away to not hit anything but close enough that you don't need to travel 2km just to target the docking port".
For optimal results this second factor will require planning and adjustment based on how large the vessels you are docking together end up being, with larger vessels resulting in a need to tune the rendezvous for a more distant encounter for orbital velocity matching.
Additionally, it may be advantageous to further tune the encounter to account for where on the two vessels the docking ports physically are.

Edited May 20, 2022 by SciMan

[darthgently]

1 hour ago, shdwlrd said:

Braking engines facing forward so you don't have to rotate the craft unnecessarily.

I like to have a pair of tugboats/workcraft that dock on the sides of the main craft and can align their main engines by way of orientation on their docking ports either to mothership fore or aft for this very purpose.  I use the little craft for contract rescues, contract science measurements, landings on low grav moons, etc

 

[darthgently]

1 hour ago, SciMan said:

MORE THAN ONE RCS CLUSTER IN THE SAME SPOT

This.  In a tweakscale game I will jack up the size, but even then, I'll use extra clusters also.  I really like the vernier linear thrusters for attitude adjustments at each end of the craft.  Often I'll put a ring of 12 each around each end just for yaw/pitch for large craft

[SpaceFace545]

2 hours ago, SciMan said:

-snip-

Nice edit 

[shdwlrd]

@SciMan what you described is completely possible with a 150m, several thousand tonne craft. I've run a craft with those type of specs on several occasions. But that is too small. I'm thinking of a 800m-1km, few hundred million tonne craft. (Aka, interstellar colony ships, orbital colonies.) So yes, you don't want to be flipping that around to dock. You only will want to flip that much mass when you absolutely have to.

@darthgently tugs is a good idea too. But the scale of the craft I've described above, you'll need a few more than a "couple" tugs. Maybe a couple dozen, possibly more. (Much like how in The Expanse dozens of maneuver drones are used to maneuver the Nauvoo/Behemoth.)