XKM-1-C "Crichton" Mk.2 (Heavy SSTO, Cargo Vessel)

[Umami]

After some very appreciated feedback I now finished Mk.2

XKM-1-C Mk.2 "Crichton"

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XKM-1-C (Mk.2) (stock)

STATS:

Cargo Size: Dual bays (CRG50+CRG25)

Cargo Capacity: (2 x 18.5 tons)

Crew Capacity: Unmanned

Engine Cluster: 2 x (S3 KS25x4), 4 x (NERVA)

Parts: 158

Launch Weight: 507,000 tons (no cargo)

Range: Mun

Launch Cost: ~300,000

Return Value: launch cost -fuel

INFORMATION:

The vessel that I normally use is a mechjeb version. It functions perfectly well without it but landing is a bit tricky (slept through flight school). Just slap a MechJeb module if you are like me.

Liftoff: The NERVAs have a tendency to explode a little bit if run at 100%. Around 95% seams to be OK (MechJeb usually sorts that out for me). So no maxing throttle otherwise it goes boom. This is now fixed in Mk2, just punch it.

Reaching Orbit: Much closer to the limits than Mk1. Use the main engines as little as possible. Not enough dV to get to RV point otherwise. This is tested and I RVed with my station at 200km orbit with maximum load and got safely back on Kerbin.

Landing: It has a whole bunch of radial chutes, and two four drogue chutes. That brings the speed down to 13.5m/s 24m/s. The rest is up to the engines. Make sure that you switched on the big engines before this. They can easily take care of the rest. Don't land too hard. The two main engines is also the landing gear.

Action Groups: Well, I built this in my career mode. I dont have a fully upgraded VAB yet so the only Action Group I use is "Breaks" which toggles the main engines and "Gears" that opens the cargo bays. Feel free to make your own.

Mk.2 Updates: It now has lights and a bigger docking port. The weight of the vessel caused minor issues when docked and the bigger port gives a little more stability. Mk1 had some fuel flow issues which is solved on Mk2. It also have 50% larger cargo bays than Mk1, a redesigned engine cluster and mostly Mk3 fuel storage.

SUMMARY:

A big SSTO (no space plane) that brings modules and stuff all the way to the Mun LKO at an end cost of ~30,000 Kredits. Don't know the cost yet, but the fuel cost anyway.

/I have created another version of this that brings fuel to my Station. I have not used that enough to suss out the little undesired quirks yet but it is on my little yellow notes of things to do.

Edited February 5, 2015 by Umami
Updated to Mk.2

[Rune]

Funny, I was just testing up this X-33 replica with also a ~20mT payload. I think the runway landing is easier, unless you have chutes, and I think my mass ratio is considerably lower than yours, since mine is 340mT on the pad and 77mT empty:

Rune. May I suggest you are losing a lot of fuel real soon due to low atmospheric isp?

[polan]

Rune, do you have a download link for that X-33? It looks gorgeous.

[Umami]

Rune. May I suggest you are losing a lot of fuel real soon due to low atmospheric isp?

Thanks for the tip. I might try the 4 x Engine Cluster. Same as you got, right? Would require some redesign.

I did a quick test by just switching my KR-2L with the 2 sets of engine clusters and that almost worked. With a more optimal trajectory I think that would do it. The reason it didn't was that I increased the cargo weight to 20T each, so double. Requires a little more tweaking and instead of making it lighter it will lift more stuff. With the extra power from the clusters it might be worthwhile looking into upgrading the cargo hold to full size.

[Rune]

Rune, do you have a download link for that X-33? It looks gorgeous.

Working on it, this one will be released for sure. Might even be tonight, though the plan was to release the wheel station I said I would release like two weeks ago... I might sit on this one a while to see if I can figure out a way of landing it with the payload bay full. Or figuring out the maximum payload that can be landed right now... it's tantalizingly close to being able to land right now, I have managed to survive the rear wheels touching the ground (had to do it powered to get the sink rate below 5m/s), but so far the fall due to the "high" angle of attack is enough to break it in two when the forward wheels hit. That is, of course, trying to land the maximum payload, empty it glides like a feather. But I might try to make both doable, so Soonâ„¢.

Thanks for the tip. I might try the 4 x Engine Cluster. Same as you got, right? Would require some redesign.

I did a quick test by just switching my KR-2L with the 2 sets of engine clusters and that almost worked. With a more optimal trajectory I think that would do it. The reason it didn't was that I increased the cargo weight to 20T each, so double. Requires a little more tweaking and instead of making it lighter it will lift more stuff. With the extra power from the clusters it might be worthwhile looking into upgrading the cargo hold to full size.

You are welcome, and yeah, with a higher thrust and the same isp curve you should be able to lift more obviously. But note that there are eight aerospikes in there too, not too awesome in the TWR department, but their isp at sea level is second to none. That, and keep TWR at about 1.4, and you should be set to get the same payload fraction. Though considering that aerospikes have that low TWR, you might even improve on it using two of the big NASA clusters: decent sea level isp, and awesome TWR (I think I have too many aerospikes for too little high-TWR-with-almost-the-same-isp A.K.A. NASA cluster, and I shut the spikes too early instead of exploiting their higher isp as much as I can, but you know, the coolness factor also influences builds).

In the middle I would put something with very high isp, like spikes or a Poodle, but I wouldn't go for the NERVAs. They may have awesome isp, but their thrust is tiny, and their weight is more than considerable (you lug 10mT on nuclear rockets to orbit to get 240kN out of them for five minutes...). You just don't use them for long enough to justify their low TWR during a climb to orbit. If you are going further than there, sure, very efficient (but then you only need the one), but the climb to orbit is ideally sized for chemical engines. You have it easier to add more fuel too!

Oh and before I go... Teasers galore!

(You still can't see the aerospikes there. But I wanted to show it off anyway)

Rune. Me, I would screw with CoM/CoL too much if I increased fuel load.

Edited February 2, 2015 by Rune

[Mesklin]

Try to use in construction only Mk3 rocket tanks and Mk3 adapters. There are best tanks in game for current time, on the contrary, S3 tanks have less efficiency then standard tanks. For rocket SSTO mass efficiency of tanks are playing key role.

[Umami]

Try to use in construction only Mk3 rocket tanks and Mk3 adapters. There are best tanks in game for current time, on the contrary, S3 tanks have less efficiency then standard tanks. For rocket SSTO mass efficiency of tanks are playing key role.

I never thought of that, thank you. It would make it come closer to my original design idea as well as a little more efficient. I checked the stats between S3 and Mk3 and S3 have 79.0 fuel/ton and Mk3 have 80.4 fuel/ton. Not a big difference but still.

[Umami]

Try to use in construction only Mk3 rocket tanks and Mk3 adapters. There are best tanks in game for current time, on the contrary, S3 tanks have less efficiency then standard tanks. For rocket SSTO mass efficiency of tanks are playing key role.

Rune. May I suggest you are losing a lot of fuel real soon due to low atmospheric isp?

Thank you guys for the feedback. I am happy to report that Mk.2 is now completed. Not just better but in my opinion also prettier.