Kasei and H3 Boosters (KSP-Sol)

Added: 2026-05-25

[00:00:01]Hello everyone, and welcome to Realism Overhaul Sandbox in Kerbal Space Program 1.12, where I was shocked to discover that I had not yet tested my Kasei rocket with H3 boosters. The H3 is the primary rocket from Japan, from JAXA, and these are boosters using the first stage from that rocket.

[00:00:21]And the reason why it would make sense to use the H3 boosters is because in my future history, in the lore behind my space program here, the Japanese are major part of TIPA, the organization, the NASA equivalent organization, which encompasses many countries. Of the TIPA countries, the Japanese are the furthest ahead as far as developing space things.

[00:00:42]And also, the character that designs the Kasei rocket is Japanese and formerly worked for Mitsubishi Heavy Industries, the people who build the H3 rocket. So, that would all make sense. So, it was a surprise that I had never uh tested this out. Well, except for the part where the H3 boosters actually last longer than the core of the Kasei rocket. That's a little bit inconvenient, but we can sort of work around that by temporarily throttling down the engines on the Kasei. And I decided that eventually we would probably just not have the boosters decouple. They are about the same efficiency as the core engines anyway. They're also hydrogen oxygen burning. So, it just saves us some pyrotechnics to not have them decouple, and for the whole thing to go out at once. The benefit of using the boosters is it makes it more modular, meaning that we can increase our payload capacity easier.

[00:01:38]So, right there, Ascent Guidance managed to make orbit with 130 tons, and I decided to try out kOS. I have a kOS script for the Kasei rocket, and also try out the throttling down bit, and see if that'll work out for us.

[00:01:56]So, here it goes again with the two boosters. The fact that the two boosters are certainly not colored in a way really compatible with the body of this thing is a bit of a downside. I might have to make my own version of the H-III rocket.

[00:02:09]This version of the H-III rocket comes from the Japanese launcher pack or Japanese launch vehicles, which is a very old mod for Kerbal Space Program and hasn't been updated in a long time.

[00:02:21]The shading on the parts is sometimes awkward.

[00:02:25]But anyway, here we go. We're getting close to when the stage is going to complete here and we'll see what happens. There's the throttle down that the script is going to do.

[00:02:37]Is that the most efficient thing to do at this point? Well, it probably isn't make too much of a difference, not as much as the trajectory of the KOS script.

[00:02:47]And then the boosters go out is what happens next there and then the core goes out.

[00:02:53]And then everything needs to go.

[00:02:57]And I just decoupled the fairings at the same time since I swear it's just more convenient that way.

[00:03:03]So, this time we are carrying the same payload as the previous time, but I was going to see how KOS did compared to ascent guidance and it turns out that ascent guidance is better in this case.

[00:03:17]The KOS script needs a little bit more tweaking.

[00:03:22]So, we're going to actually fall a little bit short here.

[00:03:26]So, maybe call it 125 tons capability with the KOS script as opposed to the 130 that we get with the ascent guidance.

[00:03:36]The core alone Kasei rocket gets 35 tons and it can lift off on its own without any boosters. Here, I decided to put three boosters.

[00:03:48]And that's largely because of how the gaps in the pad are actually shaped. So, putting four is a little bit dodgy or putting three is a clear capability of the plate at the bottom of the launch pad.

[00:04:07]Unfortunately, it rolled the wrong way.

[00:04:09]I wanted the booster to be on top, not on the bottom. It's mildly cooler that way.

[00:04:16]But, here we are.

[00:04:18]I replaced my old Raezer Space logo with the Teipa logo on the rocket. So, now it's lore correct.

[00:04:27]Technically, Raezer Space does not design the Ksay rocket. Raezer Space is a competitor to the organization that does this, which is Hayashi Aerospace.

[00:04:41]So, we probably should have a Hayashi Aerospace logo as well, but I'm not going to do that. I have no idea what that looks like.

[00:04:48]This time we're trying for 150 tons, but we're not going to quite make that.

[00:04:53]We're going to fall short about the same as we did with the previous one. So, probably ascent guidance would be able to bring this to orbit with the 150 tons, maybe.

[00:05:04]We have tested reusability with the first stage, and of course that would cut into the capabilities a bit, but not too much.

[00:05:12]And it's only the first stage that is capable of reusability here.

[00:05:17]Pekka has been making a rocket that can reuse both its stages and that'll be a competitor to this. Anyway, that was the testing. I figure that we can do 135 tons to orbit with this configuration with the KOS script, and I'll leave it at that for now. With that, thank you for watching. Hope you enjoyed this video. If you did, please do press like.

[00:05:36]If you have any comments or suggestions, please leave them in the comment section below, and I'll see you next time.

[00:05:51]>> Mhm.