Lightest Eve Lander Challenge v1.1.x & v1.2.x

[Redshift OTF]

13 minutes ago, Foxster said:

Nice job!

A couple of thoughts if I may...

Those big radial decouplers are very draggy. Small hardpoints much less so. 

You don't need the fuel ducts with KSP 1.2's fuel priority functionality and if you use the latest MJ (released today) it will calculate the dV OK without them. Remember to enable crossfeed on the radial decouplers though. 

If you use a little more fuel in the last stage with 3 Sparks then you will need less engine/fuel in the lower stages. 

You did remember to take the RCS fuel out of the capsule?

Not sure if it would be an issue for that craft because the TWR of the later stages is fairly low but you might want to think about limiting Q to, say, 220000 and/or limiting the angle of attack to 5°. 

Thanks for the tips!

I might swap out the radial decouplers for the small hardpoints. Hadn't used them for ages and forgot they existed until I saw you use them. I have tried the latest release of MechJeb and #663 dev version but it is still not calculating crossflow fuel correctly for me. I'll have to do more research but I can't see what I'm doing wrong.

Possibly more fuel in the upper stage might work but with a flat bottom the top stage creates a fair bit of drag and a smaller upper stage means it fires higher up in the atmosphere were the drag is not much of a concern. It also allows the low drag aerospike second stage to go for longer and it is quite a performer. However, I had to use an un-optimal setup for MechJeb to stop the nose cone and pod from exploding due to over heating so maybe your idea would work better as the overheating stops when the spark final stage is fired due to the lower thrust and a bigger final stage could help and allow me to run a better ascent setup.

Mono-prop was almost left in the pod but I remembered just in time.

[Foxster]

I think I have the hang of how to optimise the lift now. 20.738t...

Video: 

 

[Redshift OTF]

20.738 tons? I never thought I would see an Eve lander go that low. I'm surprised the craft doesn't need something aerodynamic like a nose cone on top. And is the fairing collar necessary? Amazing job. Can the 20 ton barrier be beaten?

[Foxster]

Ah, there is a fairing there, it's quite small but does streamline the nose. A little gamesmanship with the design . (No cheating though I promise). You can see the fairing being ejected 36s into the video. 

Edited December 14, 2016 by Foxster

[Foxster]

1 hour ago, Redshift OTF said:

Can the 20 ton barrier be beaten?

I'm pretty sure it can. I got my last craft to orbit with a useable margin of dV at least once and so some fuel could be shaved off this craft. 

I have also got another little idea but it would be tricky to build it so that it will fly straight. I'll look into that when someone beats my last attempt. 

I am getting a bit concerned though about how repeatable this all is now. The flights are getting wacky and tailored for the craft. I much prefer a craft to have at least some dV margin and for it to be possible for it to be flown by someone without a 50 page manual. 

[EvermoreAlpaca]

I took my 6 ton electric prop assisted Eve lander with the command chair, and made a version with the lander can.  Reached orbit from sea level with a launch mass of 10.220 tons.  If I find time this week i'll see how much improvement I can make on it.

Edited December 14, 2016 by EvermoreAlpaca

[Redshift OTF]

On 14/12/2016 at 9:01 PM, Foxster said:

Ah, there is a fairing there, it's quite small but does streamline the nose. A little gamesmanship with the design . (No cheating though I promise). You can see the fairing being ejected 36s into the video. 

Hey no worries. I like optimisation like that. I did wonder what was getting staged at the end.

23 hours ago, Foxster said:

I'm pretty sure it can. I got my last craft to orbit with a useable margin of dV at least once and so some fuel could be shaved off this craft. 

I have also got another little idea but it would be tricky to build it so that it will fly straight. I'll look into that when someone beats my last attempt. 

I am getting a bit concerned though about how repeatable this all is now. The flights are getting wacky and tailored for the craft. I much prefer a craft to have at least some dV margin and for it to be possible for it to be flown by someone without a 50 page manual. 

Well a challenge is a challenge but I do agree with you. I like to see a light lander that is also user friendly for MechJeb and also beginners. But the building of ultra light landers has made it possible to make 30 ton landers for less able pilots and that is a good thing!

22 hours ago, EvermoreAlpaca said:

I took my 6 ton electric prop assisted Eve lander with the command chair, and made a version with the lander can.  Reached orbit from sea level with a launch mass of 10.220 tons.  If I find time this week i'll see how much improvement I can make on it.

Ah yes, I saw your prop assisted lander and was well impressed! If you can make a version that meets the challenge criteria that would be great to see although I think it already meets criteria 0 anyway.

[tseitsei89]

https://www.youtube.com/watch?v=1ZeWPFozVps&feature=youtu.be

Here is the first sub 20 tons for you

http://imgur.com/a/IF69O 19.675t

@Foxster Are you using some kind of exploit (some kind of clipping thing?) that makes the game think that the lander can is inside the fairing even if it isn't?

 

Also if we want to keep improving we will soon need some new ideas besides just taking less fuel and optimizing the ascent profile

 

 

Edited December 18, 2016 by tseitsei89

[Foxster]

Oh good, I've been waiting for someone to post a submission so that I could submit a lighter craft. 

Yes regarding the clipping, though "exploit" is probably a bit strong. It's a pretty marginal or even zero advantage when you add in the drag of the fairing and the mass it adds.

I have built one that had zero drag for all the main parts. But it threw itself apart . 

Luckily there is nothing in this challenge's rules about being "creative". 

And, yes, we need a radical change now. There's only so many engines though. 

[tseitsei89]

3 minutes ago, Foxster said:

Oh good, I've been waiting for someone to post a submission so that I could submit a lighter craft. 

Yes regarding the clipping, though "exploit" is probably a bit strong. It's a pretty marginal or even zero advantage when you add in the drag of the fairing and the mass it adds.

I have built one that had zero drag for all the main parts. But it threw itself apart . 

Luckily there is nothing in this challenge's rules about being "creative". 

And, yes, we need a radical change now. There's only so many engines though. 

Yep I know it can't give huge (if any) advantage since I can keep getting these results also. looking forward to seeing your next entry

[Foxster]

18.793t...

(MJ isn't reading the dV correctly, it's actually about 5400).

 

[foamyesque]

10 hours ago, Foxster said:

18.793t...

(MJ isn't reading the dV correctly, it's actually about 5400).

 

 

I call shenanigans. 18.5s of Vector burn time is 1200 units of LFO. A replication based on those burn times and delta V numbers clears 21t, without adding things like the fairing, nose cones, etc. Something's afoot.

Edited December 20, 2016 by foamyesque

[Foxster]

I can only say that your calculation is wrong. I don't know how you calculated what you did but both tseitsei89's last craft and mine come in at less than 21t and both have video evidence of making a stable orbit from sea level. 

As I said, MJ is incorrectly reporting the dV and burn times for my last craft. It is known that MJ has not yet got the calculation right for fuel being passed across bi-directional couplers using the new fuel priority mechanics. 

The only "shenanigans" I used was some creative rearrangement of the small tanks in the drop tanks using the offset tool to allow a reduction in part count and drag. There is nothing in the challenge's rules against that.  

Edited December 20, 2016 by Foxster

[foamyesque]

56 minutes ago, Foxster said:

I can only say that your calculation is wrong. I don't know how you calculated what you did but both tseitsei89's last craft and mine come in at less than 21t and both have video evidence of making a stable orbit from sea level. 

 

I'm not doubting that the orbits happened, but something's weird. A Vector has a vacuum Isp of 315s and a vacuum thrust of 1000kN, for a mass flow of ~0.325tonnes per second. 18.5s of burn works out to ~6t of fuel.Tthat's 1200 units, which is 6.75 tonnes worth of tankage (e.g. a -800 and a -400). Two sets of that is 13.5 tonnes, plus four tonnes for the Vector to 17.5, then another 0.6 tonnes for the lander can, then another 2.25 tonnes for the -400, then another 0.5 tonnes for the Terrier. That's 20.85 tonnes, plus decouplers and nosecones. I don't see any errors in my math, and it KER agrees with me, so there's a doublecheck on that.

So either MJ is reading wonky or your parts have different stats than mine...

Edited December 20, 2016 by foamyesque

[Foxster]

I am definitely someone who builds and flies these craft by the seat of my pants so I cannot correct your maths on fuel useage.

The part list is: 

Lander can: 0.6

Fairing: 0.108t

Small nose cone (clipped inside fairing and lander can): 0.01t

FL-T400 tank: 2.25t 

Terrier engine: 0.5t 

TR-18A decoupler: 0.05t

FL-T800 tank: 4.5t 

Vector engine: 4.0t 

TR-2V coupler: 0.015t

30 x Oscar-B tanks: 6.75t (this is one stack (along with small nose cones and TR-18A), split using the offset tool to balance either side of the craft)

Small nose cone: 0.01t

Total: 18.793t 

The vector is fed first by the Oscar-Bs and then they are de-coupled when empty. It then runs on the FL-T800. Finally that and the Vector are dropped for the last stage of the Terrier and FL-T400. 

I think it is the 18.5s you are getting hung up on. The numbers are not reliable in either MJ or KER since 1.2 because of the issue I mentioned above that both don't calculate correctly when you have the potential for engines to continue to run after the fuel in their stage is exhausted because additional fuel can be drawn from the next stage through a bi-directional feeding de-coupler. 

I think what both tools are showing as 18.5s of burn time is the potential for the Vector to use the Oscar-Bs, the FL-T800 and the FL-T400, which in practice does not happen as I stage off the Vector and FL-T800 once it is empty, preventing that stage using the fuel in the FL-T400 too. 

 

Edited December 20, 2016 by Foxster

[foamyesque]

Hm. MechJeb is reporting your burn times wrong, then. As listed you do get 5500m/s vac dV (more or less), but the burn time on the second stage should only be the 12.4s (as it was in your immediately prior submission).

 

Okay, so it's all MJ's fault. WORKS FOR ME.

(EDIT: offset abuse to trick the physics engine like that makes me sad though )

Edited December 20, 2016 by foamyesque

[Foxster]

3 minutes ago, foamyesque said:

Okay, so it's all MJ's fault. WORKS FOR ME.

You withdraw your call of shenanigans?

[foamyesque]

Just now, Foxster said:

You withdraw your call of shenanigans?

 

Nah, it's just aimed at MJ now

[Foxster]

To be fair to Sarbian, it is complicated now. How to decide when a stage is empty? It could be either when the fuel in its tanks is gone or when the engines in it are starved of fuel.

MJ continues to use the latter and that can be wrong as the tanks in a stage can be empty but it can draw fuel from the next stage through a de-coupler  

The suggestion in the MJ development thread has been of providing a option for us to choose which scenario to base the staging calculation on. 

If I disable the crossfeed of the decouplers and add a fuel duct like this then does MJ's number's make more sense?...

Edited December 20, 2016 by Foxster

[foamyesque]

Yeah, that's what I do with KER to check my numbers on crossfed stages now too. And yes, that matches up with what should be the case.

[Foxster]

OK, that's all good then.

I think I'll leave the fuel duct in and the de-couplers with crossfeed off. It's only a little more mass and it makes it easier to see what is happening and for the dV to be shown accurately. 

Not sure where to go next with this challenge. It is getting pretty marginal now and I had to do some offsetting that works and is not against the challenge's rules but is definately dodgy in terms of realism.  I mean, I have tanks floating in the air that somehow feed each other . 

Edited December 20, 2016 by Foxster

[Redshift OTF]

Haha, with these Eve landers you are really spoiling us! I am a bit of a fan off the No Limits Offset feature so I can't complain that you used it although the craft might breach the "offend the majority of users on this forum" scale with floaty fuel tanks. It still passes the mission criteria though so it's a new record!

Is this the limit though? For one Vector, probably yes but can a combo of other engines do the same job? Aerospikes can be jettisoned giving extra DeltaV on later stages although this challenge seems to be more about getting 1000 m/s as quickly as possible before the last stage fires.

And like I said, if you get bored you can always go for the Category 0 option, a Kerbal in a seat in a service bay as long as it is below 100m.

[Foxster]

31 minutes ago, Redshift OTF said:

And like I said, if you get bored you can always go for the Category 0 option, a Kerbal in a seat in a service bay as long as it is below 100m.

Ah, but when it gets very light it becomes more about aerodynamics than mass. You have to reduce the first to gain dV and so you can reduce the second. That means that saving a little mass on a capsule but the craft becoming more draggy as a result might mean the craft is no lighter. 

[tseitsei89]

On 12/19/2016 at 8:57 PM, Foxster said:

18.793t...

(MJ isn't reading the dV correctly, it's actually about 5400).

 

Okay I give up. You win. 

You broke the drag model quite well...

Now I'm not saying that you cheated (rules of the challenge obviously allow what you did), but I'm not really interested in that kind of trickery where you actually have to fool the physics engine with all kinds of gamey tricks. 

But once again congrats I can't go any lighter than that

[Foxster]

I like to think that this kind of stuff is sometimes what the challenges are about. Pushing the envelope, seeing just what is possible in KSP with a bit of creativity and experimentation. It is still all stock, whereas most people would have needed to resort to modded parts or physics to achieve anything close to what we did with a handful of stock parts that were cleverly arranged. 

Anyway, in the next release of KSP, I bet Eve will change again in some subtle ways and we can do this all again, maybe with a few new parts to mix things up and make it all interesting anew.