Lifters Wanted!

[whitejj01]

Hello there!

for some time now, my kerbals have been pondering how they're going to get the 50-ton ARES Pre-supply missions to duna.

unfortunately, they have no knowledge of building lifters that are capable of this.

They Need Your Help!!

please, if you have a 50-ton duna-capable lifter, post it! The ARES I crew are counting on you!

 

note: the only mod allowed is TweakScale.

bonus points if it looks awesome.

Thank you in advance!

[steuben]

I guess if it can lift 1kt to 1000kmx1000km it could probably do 50 t to Duna. Do you want conventional RL styled designs or allowed by engine?

[whitejj01]

RL?

[steuben]

RL -> _R_eal _L_ife

[septemberWaves]

50 tonnes to Duna with just stock parts + tweakscale? I can do that. Do you want a propulsive capture or aerocapture? Also, do you need the 50 tonnes to get to the surface of Duna or just Duna orbit?

Also if you have a download for the payload it would help. I can design for a specific payload mass but if you want landing systems too then that could influence the design choices.

Edited February 25, 2017 by eloquentJane

[Cunjo Carl]

Oh! Sounds like @eloquentJane and @steuben have you covered, but if you need even larger payloads delivered in the future let me know. Stock heavy lifters are my thing, and v1.2 has made them a total treat.

[steuben]

A rough blueprint of the Bell-KT, reporting name: Kitty. The whole class of lifter got its name because when the payload rings the boosters your doomed. Her drawback is that it is very inelegant. You lift straight up to 80 km, turn right, circularise, and then rendezvous.

12.7 kt, fueled, without payload, on the pad. you just strap your payload into the centre and away you go. 

Delta V on the pad is 9.1 km/s, unloaded

727 parts, again before payload and any additional struts.

Cunjo chuck yours into the mix anyways.

 

 

Edited February 26, 2017 by steuben

[septemberWaves]

I think I can improve on that part count, as well as style. Experience playing in scaled-up versions of the Kerbol system means that I'm used to designing big rockets.

[septemberWaves]

Behold, Mars 5A. I made good use of Tweakscale to create this lifter that can transport 50 tonnes to low Duna orbit in style. I hope it's fine to tweakscale up to 5 meters, otherwise this would be more difficult to get right.

I'm just working out some staging difficulties, and then I'll provide a download.

EDIT: Sorry, you'll have to use someone else's launch vehicle. Tweakscale is apparently full of bugs that cause this rocket to either explode upon staging or to simply not stage at all.

Edited February 26, 2017 by eloquentJane

[Rune]

Give a man a fish, and you will feed him for one day. Teach him how to fish, tough...

How to build a 50 mT rocket to Duna:

1- Figure out what you need:

Some handy dV charts say that to get to Low Duna Orbit (LDO), we need about 1,6km/s from Low Kerbin Orbit. That is what our upper stage needs, to get the payload to Duna, so we'll start there and build the launcher to LKO under it. Seems we won't need that much actually, since the budget to LKO is twice that (3,5km/s). I'd say two-three stages will be ideal for the whole job, going by the rule of thumb of 'one stage per 2km/s'.

 

2- We grab our test payload on the VAB, and either get some handy tool like KER, or we work out our dV the goold old fashion way, with Tsiolkovsky's rocket equation and pen and paper (or the windows calculator). In that case, the good old russian says with an Isp of 350 (Poodle), we need a Mass ratio of about 1.6. We'll play it safe and build some margin, of course, because I don't like to put debris in orbit, and thus like to finish circularization on the departure stage. But let's build the dummy mass simulator first!

3-Around that, we build our in-space stage. TWR matters very little, so we just chuck fuel until we have the ratio we want, and add accessories like solar power, batteries, a probe and reaction wheels. This is our 'smart' stage, the rest will be just dumb rockets. Notice how I also did an interstate with a fairing, because I used a 2.5m engine. It looks very nice to do things like that.

3- And now we need to boost this to LKO, so let's build a rocket under it. The dV budget for LKO is 3.5km/s, so we need more than one stage, because 3,5 is right on the edge of what stock TWR and tankage ratios allow (it can be done, but it's tricky). I like the stage-and-a-half concept (a core with a lot of fuel and low TWR with boosters to get it off the pad), so let's go with that, but you can also build two stages. Still, for this the core is just putting one big engine and enough fuel to bring its TWR close to one:

There, 1.15. Could be even less, because it will get help form the boosters, but the main thing is to get as much dV out of it as we can (almost 3km/s), most of what we need, leaving just the boosting job for the boosters.

4-Add the boosters, fix the staging so all engines are lit on liftoff, and look at what KER says:

What do you know, it's almost bang on 3,5km/s and TWR 1.5 at liftoff! I'm getting good at eyeballing this, those are pretty much the numbers you want. Anyhow, if they aren't, you should fix things. To get more dV, you need more fuel on the core. To get more TWR at liftoff, you need moar boosters. TWR at second stage separation is less of a hassle, because by then the core will be half-empty and thus it will have much more than the 'about one' we allowed in the previous step.

5- Make the whole thing flyable. In order to make things fly good, they have to be sturdy, and they have to be stable. Sturdiness is mostly a function of struts, but since 1.2, we have the handy option of strutting things without them, and I love it for the clean lines. Here I strut the source of forces in the booster to the heaviest part on the stack, which should keep everything very sturdy. I do the same thing with the fairing holding the payload inside:

Stability is mostly keeping the CoM before the center of aerodinamic forces, AKA keep it nose-heavy. The simplest thing is to make sure the tanks on the rear empty first, so you keep a heavy, dart-like nose as your rocket spends propellant. And now we can tweak that with tweakables!

So the lower tanks drain first, which should keep our CoM moving upwards as we fly.

And finally... Test it, see what breaks, fix it, repeat. It will mostly be staging, or stuff during the staging. Maybe you feel that a stage could have less fuel, and another more. Here I would say that booster separation could be a bit less close (add separatrons and stage them correctly), and that that booster is definitely more than enough powerful, so we could increase the upper stage weight, or move some fuel to it, or build another core with a weaker engine. Tinkering is encouraged at this point!

Note how I actually cut the thrust on the circularization burn with a ~20km peri, and stage to end the burn on the upper stage. I had plenty of gas, but if I do that, I ensure that LKO remains uncluttered, so hey, let's be green and stuff. It also means the much smaller in-space stage can maneuver much easier.

And there you go, a 50mT-to-Duna booster, explained.

 

Rune. Some assembly required.

Edited February 26, 2017 by Rune

[whitejj01]

It needs to be RL, propulsive capture, soft-landing craft.

[steuben]

So RL styled launcher, that leaves off the Bell series then.

So you need to get 50 tons to the surface of Duna? Easy. Getting it back off again, well that's going to be your problem. No tech constraints? Time constraints?

Edited February 27, 2017 by steuben

[Rune]

14 hours ago, whitejj01 said:

It needs to be RL, propulsive capture, soft-landing craft.

Well, that's pretty much what I built, minus the landing, assuming RL doesn't mean RSS (which would mean instead of Duna we are talking about Mars). That could also be phrased as: I failed at understanding what you wanted, i.e: did step 1 all wrong. But the step themselves are still fine! The same dV chart I quoted says landing on Duna all propulsively would be 1,3km/s. Considering the thin air will help you a lot, but you want a nice margin to be less than perfect, 1,3km/s will be overkill. That should be as easy as adding a 1.5Mr landing stage, meaning the payload to LKO is about 1.5 times the one on my rocket (since the in-space stage also needs to have 1,5 times the fuel to give the same dV to a x1,5 payload). So add a rocketcrane stage on top of your payload, and build a rocket 1.5 times bigger than one I built. I reckon just adding fuel to the in-space stage, the core, and two extra boosters would do it, but let KER be the final judge.

In a quarter of an hour, tinkering the previous design made this, but I must warn you that I was also tricky here and used a drop tank to not use dedicated in-space engines and instead use the ones on the rocketcrane form LKO all the way to the landing at Duna:

Saves some weight, and it means just uprating the core to its maximum fuel (TWR at booster cutoff is perilously close to one) and adding a couple boosters, which makes for a rather efficient booster that squeezes the most out of each engine. I like that in boosters! But remember, the easy route is just to put 2~2.5km/s stages one under another, for a similar dV budget (~6.5km/s, instead of the ~5 of going to LDO I gave you earlier).

 

 

Rune. Good thing I told you how to do it instead of just giving you the file.

Edited February 27, 2017 by Rune

[whitejj01]

2 hours ago, Rune said:

Rune. Good thing I told you how to do it instead of just giving you the file.

yeah, thanks; I'll probably use that later today:)

It never needs to come back. The MAV (the spacecraft this lifter will be transporting) can regenerate the spent fuel its tanks held, and, 24 months later, carry a crew of 6 kerbals to low duna orbit. from there, the crew get back to keratin via the Kermes, which the MAV's pod docks with.

It's the same thing for the two rovers (heavy stand-up guys) and the three HAB modules.

No tech constraints; the landing of these modules is supposed to be as close to automatic as possible without mechjeb.

Edited February 27, 2017 by whitejj01

[Rune]

5 minutes ago, whitejj01 said:

yeah, thanks; I'll probably use that later today:)

Sure! Tell me if you run into any troubles, but really, knowing your dB budget and with an accurate reading of what your stages can actually do, rocketry is not that hard.

 

Rune. Oh and remember comms! I always forget communications lately. ^^'

[whitejj01]

Just now, Rune said:

Oh and remember comms! I always forget communications lately. ^^'

Same