Single Tank Tylo: A mission on the edge of possibility?

[Ultimate Steve]

1 hour ago, AeroGav said:

Any suggestions on how my design can be optimised ?  Obviously, relegating Jeb to a chair is one thing.     Forgoing the mk3 engine mounts is another - but drag will increase a lot.  That means more jet engines, which do have a mass that must be accelerated to 1500m/s / 25km.    More to the point,  that horizontal, hypersonic cruising climb to orbit on NERV power might not be efficient with higher atmospheric drag.   Maybe try a zoom climb out of the atmosphere, and conduct the final acceleration from 1500 to orbital velocity above 60km and separate the aerodynamic parts before doing so?   However that means even more jet engines to get the necessary TWR.   If the zoom climb wasn't quite sufficient, the NERVs will suffer gravity losses thrusting upwards trying to keep us from falling back into the atmosphere.

I have not actually flown my design yet, but I stuck the whole Mk3 fuselage in a fairing. Not sure if it's worth the extra weight.

[herbal space program]

I'm getting there.  My Imgur account is Borked but I will fix that soon. I put 5 Nervs + 20 decoupleable Rapiers on the MK3 LF fuselage with a Mk1 lander can and a chute and took off vertically. That config by my calculations can land ~5 km/s of fuel on Tylo, and it made LKO with ~6.5 km/s on my last attempt. I can probably get this up to 7 with enough patience. Is that going to be enough? It's close! As soon as I get to a high enough Ap taking off from Tylo, I can jettison all but one of my 5 Nervs, cutting the mass of my craft in half, so my actual dV is going to be significantly more than what I  make LKO with. I will investigate this more the next time I can play.

Edited April 18, 2018 by herbal space program

[EpicSpaceTroll139]

11 hours ago, herbal space program said:

I'm getting there.  My Imgur account is Borked but I will fix that soon. I put 5 Nervs + 20 decoupleable Rapiers on the MK3 LF fuselage with a Mk1 lander can and a chute <snip>

Remember with 1.4 we have Kerbal parachutes so you can probably ditch the craft chute. Should help with the ∆v, if only a little. 

Edited April 18, 2018 by EpicSpaceTroll139

[Ultimate Steve]

49 minutes ago, EpicSpaceTroll139 said:

Remember with 1.4 we have Kerbal parachutes so you can probably ditch the craft chute. Should help with the ∆v, if only a little. 

We already didn't have to have parachutes due to the fact that the terminal velocity of a Kerbal is not sufficient to kill him/her if he/she falls into water.

[EpicSpaceTroll139]

1 hour ago, Ultimate Steve said:

We already didn't have to have parachutes due to the fact that the terminal velocity of a Kerbal is not sufficient to kill him/her if he/she falls into water.

True, but then you couldn't land on the VAB or something like that

[herbal space program]

5 hours ago, EpicSpaceTroll139 said:

Remember with 1.4 we have Kerbal parachutes so you can probably ditch the craft chute. Should help with the ∆v, if only a little. 

I guess if I were going to go the ECS route, that would be a key consideration, but I'm not going there unless/until  I become truly desperate! The dry weight of the tank alone is over 7T, so unless I'm ditching my lander can the weight of the chute alone won't make much difference, and I'm too lazy to make Jeb climb in over and over again. 

One place  that I might save weight is that I'm currently using small hardpoints and structural fuselage segments to side-mount my Nervs. If I switched to radial decouplers and used my reaction wheels as engine mounts instead of having them in the main stack, I could save like 0.6t. I might try that next...

BTW, I got a new Imgur account, so here's a short album of my current rig getting to LKO:

 

Album a/smYL3 will appear when post is submitted

Edited April 18, 2018 by herbal space program

[herbal space program]

 

Perhaps I am beating a dead horse here, judging from the lack of any comments from others, but I do think this might actually just be doable. The notion of Kerbals pushing ships with EVA packs did not seem like it would work at first, since they can't use them while on ladders or strapped into an ECS, but I was ultimately able to contrive a crew capsule with decent heat protection, consisting of a fairing base with an ECS, some batteries, a couple of panels,  a small RW unit, and a nosecone mounted on a stack of cubic octagonal struts for 0.37t, which also allowed the pilot to leave the seat and still remain contained inside the fairing so that they could lodge themselves against the front of the strut enclosure and push. Based on the weight of a single Kerbal vs. that capsule, I estimate it will have ~150m/s when it decouples from the mother ship, since an individual Kerbal, based on my past experience, has about 600m/s. It has since occurred to me that I can probably get as much as 250m/s if I use two Kerbals, with the added benefit that I can have one controlling the vessel while the other pushes, without which I think that faithfully executing maneuver nodes would be more or less impossible. As by my own calculations I am only coming a few 100m/s short of the goal with the best lifter I can make, this does not actually seem quite hopeless. So far, the best I have been able to do is 6.8km/s on LKO with a new, winged lifter, but I can probably sill improve on that. Anyway, here are some pix of what I have currently:

Album a/84Bc0Mw will appear when post is submitted

More later!

Edited April 25, 2018 by herbal space program

[AeroGav]

@herbal space program

As well as not getting a Rapier engine snagged after jettison,  I have another way to improve the design.

I've  been torn by the need to save weight and lower drag.  The problem is there are no mk3 decouplers , so if you  use some kind of mk3 to 2.5m adapter on both ends of the mk3 tank, you can only jettison the bits forward and aft of these adapters.  Thus , a majority of the streamlining part mass is carried all the way to and from Tylo.

But,  if you offset the 2.5m nose cone so it's partially inside the mk3 to 2.5m adapter, after firing the decoupler, the 2.5m cone and mk3 adapter will be occupying the same space and this should trigger an explosion that destroys both.     Ship is likely to flip out severely,  but out of the atmosphere there should be plenty of time to bring that under control.

Also, my design had 6 nukes.   Dropping to the optimal 5 will give better delta V as well  (after punching off 3 engines i gained 2k delta v in orbit)

 

[Gordon Fecyk]

On ‎3‎/‎26‎/‎2018 at 11:22 AM, AeroGav said:

The mk3 tank has a mk3 mount at both ends for streamlining purposes.  Unfortunately the stock game does not have a mk3 decoupler, so these must come all the way to Tylo and back.

What does the stock aero do to a 2.5m stack separator or 3.75m decoupler when used with mk3 tanks?

I once clipped in a 1.25m stack separator into mk2 tanks to build this thing (Skip to 5:25 for the separation):

The rear 1.25m to mk2 adapter and engine detached from the rear of the craft via an embedded 1.25m stack separator.

Granted this was Ferram Aerospace so it probably ignored the decoupler, but this plane seems to fly in stock aero without much trouble.

[herbal space program]

5 hours ago, AeroGav said:

I've  been torn by the need to save weight and lower drag. 

That is indeed a key tradeoff, but if you are going to fly that thing to orbit with Rapiers, I would say that drag is the larger concern. If you have the right amount and configuration of engines and wings, you can get your rig to almost 1600m/s , 25km altitude, and ~500m/s ROC on just air at ISP=3200. With that, you can boost to orbit on a purely prograde trajectory, expending only ~550m/s after the jets stop working. When making long-range space planes, I've always used the lowest TWR of nukes that would efficiently get me to orbit from there, but of course this is a little different because of the high TWR you need to land on Tylo. Even so, the blunt front end of that tank is basically just a no-go in terms of flying to orbit.  It will cap your speed well below that goal and heat up like the devil as well. If you want to see why, just use the F12 aerodynamic overlay. So you need to put some adapters/nosecones up there. On the back, you don't really need adapters. I used the 3.75m engine plate from the MH expansion (much lighter than the Mk3 engine mount), filled all slots in the 4+1 configuration, and clipped small nosecones backwards into the back ends of all the Rapier engines. With that, the drag of the main fuselage is not so bad. Of course even with all that, I still don't have quite enough dV to get the job done on LKO, so I'm thinking about other strategies.

5 hours ago, AeroGav said:

But,  if you offset the 2.5m nose cone so it's partially inside the mk3 to 2.5m adapter, after firing the decoupler, the 2.5m cone and mk3 adapter will be occupying the same space and this should trigger an explosion that destroys both.     Ship is likely to flip out severely,  but out of the atmosphere there should be plenty of time to bring that under control.

That seems pretty desperate. Couldn't you just use a smaller decoupler and offset the parts together? For my designs so far, this idea has been a nonstarter, since my control pod was attached to the front of those adaptors. I am however currently thinking about putting an ECS on the blunt front end of the tank, decoupling everything from that once on orbit, and flying my Kerbal to that seat on EVA. The original control pod would then stay in Kerbin orbit, with the idea being that the pilot of the Tylo mission could leave the main ship and rendezvous with it to de-orbit. The Mk1 pod has enough onboard MP that it could de-orbit without any fuel from the mother ship if you put RCS thrusters on it, and the free Kerbal has about 600m/s dV. Anyway, we'll see about that...

[Ultimate Steve]

As far as the nose cone debate, I'm not sure if this is more mass efficient than the nose solutions, but you could stick the whole thing in a fairing.

[herbal space program]

12 minutes ago, Ultimate Steve said:

As far as the nose cone debate, I'm not sure if this is more mass efficient than the nose solutions, but you could stick the whole thing in a fairing.

Those fairings are actually quite a bit heavier that the corresponding stock adapters/nosecones for the same areal coverage, and they provide next to no heat protection to boot. 

Edited April 27, 2018 by herbal space program

[tseitsei89]

On 4/25/2018 at 6:28 AM, herbal space program said:

 

Perhaps I am beating a dead horse here, judging from the lack of any comments from others, but I do think this might actually just be doable. The notion of Kerbals pushing ships with EVA packs did not seem like it would work at first, since they can't use them while on ladders or strapped into an ECS, but I was ultimately able to contrive a crew capsule with decent heat protection, consisting of a fairing base with an ECS, some batteries, a couple of panels,  a small RW unit, and a nosecone mounted on a stack of cubic octagonal struts for 0.37t, which also allowed the pilot to leave the seat and still remain contained inside the fairing so that they could lodge themselves against the front of the strut enclosure and push. Based on the weight of a single Kerbal vs. that capsule, I estimate it will have ~150m/s when it decouples from the mother ship, since an individual Kerbal, based on my past experience, has about 600m/s. It has since occurred to me that I can probably get as much as 250m/s if I use two Kerbals, with the added benefit that I can have one controlling the vessel while the other pushes, without which I think that faithfully executing maneuver nodes would be more or less impossible. As by my own calculations I am only coming a few 100m/s short of the goal with the best lifter I can make, this does not actually seem quite hopeless. So far, the best I have been able to do is 6.8km/s on LKO with a new, winged lifter, but I can probably sill improve on that. Anyway, here are some pix of what I have currently:

Album a/84Bc0Mw will appear when post is submitted

More later!

If you allow pushing with kerbals, couldn't you get infinite dv since you can just get back in to the pod when low on EVA fuel and it magically fills up again? Or has that been changed lately? Haven't tried in a while...

[herbal space program]

16 hours ago, tseitsei89 said:

If you allow pushing with kerbals, couldn't you get infinite dv since you can just get back in to the pod when low on EVA fuel and it magically fills up again? Or has that been changed lately? Haven't tried in a while...

I guess that would be true if the design involved an actual pod, but I was using an ECS when I was considering it, and those definitely don't give you a magic refill. I'm moving on from that idea anyway, because even with my stripped-down ECS/fairing/nosecone pod, the process of pushing was agonizingly slow and awkward.

 

....Also, I have a petition for the OP,  @Lirtosiast: Since this is looking just the other side of possible the way it is now, any chance we could loosen the rules just a bit by allowing the use of whatever RCS monopropellant is provided by the various available control pods? That might just tip the balance, and it would enable the implementation of some creative strategies.

Edited April 28, 2018 by herbal space program

[herbal space program]

...So after flailing away for several more days, I still can't seem to get that tank on LKO with the required 5 Nervs and any more than 6.85 km/s of dV left. Any landable pseudo-pod that I've been able to create so far that the pilot can push on EVA seems to gain me at most 200m/s, and they are all a really serious pain to fly.  I hate to give up on a challenge like this, but at this point I basically have to conclude that it's close but not doable, no matter how much heroic piloting you can bring to it, nor even if you automate everything with McJeb and Precise Node. I don't think it actually requires quite the 8+ km/s dV that OP tallied, but I don't see how to shave more than 500m/s off that estimate, and I'm still well short of that. Great edge case though, and if somebody can prove me wrong they will win my everlasting admiration, and as many likes as I can heap on them. I suspect most have already concluded the same thing, but it was fun trying!