getting a science lab to minmus without massive rockets

[mrklaw]

I want to try and get a mobile processing lab onto minmus, and then fly a lander there to go suck up some science. But I'm having trouble getting a decent rocket - this is my first time trying to lift anything pretty heavy - about 12 tons all-in.

I'm trying to use rockomax tanks for the matching size, but the biggest engine i have is the skipper. Should i wait until i have a bigger engine?

Edited May 22, 2015 by mrklaw

[mackadelik]

Make sure you are doing the asparagus staging. I don't recall using that engine much because I worked hard to unlock the mainsail, but it will probably get you there. If you haven't done asparagus staging before you should definitely look into it on a vid/reading it up. Its easy and it will change your Kerbal Space life! If this info didn't help, share some pics or describe what issues you are having. Is it an orbit issue? Direct flight issue? Or "can't get out of the atmosphere issue? Good luck and happy building!

[cephalo]

I think you can do it with enough skippers. I got a big lander about that size on the Mun and Minmus with them. I used the same rocket for both missions. It was pricey though, make sure you can grab contracts to pay for it. I had an obscene stack of 7 skippers for the bottom stage along with as many SRBs I could fit. If you're playing on hard mode I wouldn't try it my way, as it took a few tries to get it to orbit without mishaps. I also had a comfortable middle stage with plenty of dV, which I could use to slow my lander down to a landing trajectory after orbiting the target.

[Invader Jim]

I have used five skippers and simple asparagus staging. Fuel tanks from engines 2 and 4 feed 3 and 5. Tanks 3 and 5 feed the center (#1). I use 8 SRB also.

The SRBs run out and are dropped. Engines 2 and 4 run out of fuel next and are dropped. Engines 3 and 5 run out next. When I drop them engine 1 has a full tank and above it is my final stage which is something similar to your picture. I fire all SRBs and all five engines at once and then use the throttle to keep my TWR below 2.5 as fuel is used up.

[Anglave]

That looks like a pretty reasonable payload for the Skipper.

Under it:

Stack Decoupler, Orange Tank, Skipper.

2x Radially around the central orange tank:

Radial Decoupler, Orange Tank, Nose Cone, Skipper, Strut from the outer orange tank to the inner. (one per should be enough, put it someplace that seems like it'll help keep the tank from wiggling about).

Note: It helps if you put all of these orange tanks at the same "height", so that all the engines under them sit flat on the launch pad together.

Put your camera inside one of the radial orange tanks and alt-click the radial decoupler. This makes a copy of the decoupler and everything attached to it. Zoom out and attach this (copied) pair of "booster stacks" so they're offset 60° radially around your central orange tank from the first pair. (and at the same height as the first pair). The radial orange tanks should be nearly edge-to-edge but not intersecting.

Make another copy of the stack by alt-clicking the radial decoupler. Attach the third pair of boosters to your central tank, again offset by 60°. We've made a ring of boosters (three pairs) around our central orange tank. All of the tanks in the ring should be nearly (but not quite) touching one another, and at about the same height on the central stack, and attached to it via radial decouplers and struts.

Run a Fuel Line (still in 2x symmetry) from the first pair of boosters to the second (tank to tank). Then run another fuel line from the second pair to the third. Finally, add a fuel line from the third pair of boosters to the central tank.

Now we need to adjust the staging. First make sure all of the skippers light at the same time (drag all the engines to the bottom of your staging list on the right).

Then the next thing should be ONE pair of radial decouplers, the ones holding on the "first" pair of boosters. (The ones with fuel lines coming FROM them only). If you mouse over the decouplers in the 3D view, it'll highlight them in the staging list. You'll need to create a new (empty) stage, and drag the correct pair of decouplers into it.

Then the next stage is the second pair of decouplers, holding on the second pair of boosters, and the next stage is the final pair of decouplers.

At which point, you're left with the (full of fuel) central orange tank and skipper, pushing your payload. Hopefully high above Kerbin.

I don't have the game open so I can't test the TWR or ÃŽâ€v of this arrangement, but the general concept should be capable of moving that payload off Kerbin. If you have a low TWR on the launch pad, some SRBs might be useful. Generally I don't care for them, but a ring of them around this design might help get it moving off the pad. (The skipper's ASL thrust is a bit low for lifting much payload).

Ideally the "boosters" get you up high and moving fast, and the central "core" stage is for circularizing, plane change, and burning to intercept Minmus. However, the core might be a bit low on thrust if you're not yet near apoapsis when you get to it. I suspect one skipper lifting a full orange tank plus your payload is going to have a TWR <1 on Kerbin. If you find that it's not enough thrust, maybe use a gray tank for the central stage instead of an orange tank.

Conversely, if you find you have plenty of thrust at every stage but not enough ÃŽâ€v for the mission, you can experiment with adding more fuel at various stages.

Edited May 22, 2015 by Anglave

[Prepper-Jack]

I would personally go with a Poodle over the Skipper on your lander stage, wrapped with Terriers on the outside tanks, in an Asparagus setup. That should set you safely down on Minmus from LKO. Launching that mass up there would probably need a Skipper, and an asparagus setup of Reliants or Swivels to boot.

[mrklaw]

managed it with an orange tank with a skipper, and 6x radial orange tanks with skippers. TWR was an issue, quite a slow take off, but they burned for long enough to get me into LKO.

Felt amazing to finally land on another world. Then realising that I have no transmitter attached to send back any science.

Is there any way back from that? or do I need to revert and fix?

edit: Reverted to VAB and used Anglave's advice. Ended up with enough fuel to get into minmus orbit without even using my upper stage

Edited May 22, 2015 by mrklaw

[Anglave]

There's no easy way back from that. You either carry the science back yourself, or you transmit it. No simple way to add parts to your craft after it has launched.

It really doesn't take much ÃŽâ€v to return from Minmus. If there's any fuel left in your lander at all, it's worth a shot at returning. From Minmus orbit, a Kerbal can possibly even do it alone with just his jetpack. Without parachutes or a command pod, a lone Kerbal can survive atmospheric reentry and splashdown.

Or, use it as motivation to send a rescue mission. Your Kerbal can EVA and collect the science manually from the experiments, then return to his craft and transmit (or return the results to Kerbin for full value).

-- EDIT -- I forgot you're collecting science from the mobile lab. Yeah, that's not going to work without a transmitter (and a good supply of electricity). You can't "collect" the science manually or transport it, and returning it to Kerbin doesn't work. The mobile lab is a great way to get extra value out of your experiments, but you have to transmit the resulting science.

Edited May 22, 2015 by Anglave

[Prepper-Jack]

Yeah - I wonder. If you attach to the science outpost with a vessel that has a grabbing unit and antenna - will it transmit? Personally, I'd just revert (and have, from the same mistake).

[Anglave]

I would personally go with a Poodle over the Skipper on your lander stage, wrapped with Terriers on the outside tanks, in an Asparagus setup. That should set you safely down on Minmus from LKO. Launching that mass up there would probably need a Skipper, and an asparagus setup of Reliants or Swivels to boot.

I'm not following you here. His lander stage is pictured, and seems to be using a perfectly reasonable set of radial tanks and "spark" (48-7S) engines, which should be plenty to land that on Minmus. If anything I personally might replace the 4 Sparks with 2 Terriers so I'd have a higher TWR (and slightly better ISP) on my landing stage; but even one Terrier masses more than those 4 sparks, so if the sparks provide enough thrust for safe landings, they're fine.

A poodle would be overkill for landing his 12t payload on Minmus, and it masses considerably more (17.5 sparks!) I can't imagine a scenario where the Skipper would ever be a good choice for landing on Minmus, and I don't think anyone here suggested doing so?

- - - Updated - - -

Congrats mrklaw, it sounds like you're well on your way! F1 us some screenshots!

A very similar design can put a similar payload on Duna, or a more substantial payload on Mun or Minmus. (Or a lander or rover to Eve, but it won't be returning).

- - - Updated - - -

By the way, what we did there with the fancy fuel lines and staging is called "Asparagus Staging" and it's a great combination of practical and efficient in KSP. The first pair of tanks feed all of your launch engines (in this case, seven of them). You burn up the mass of the fuel in the first two tanks, and discard the engines that were lifting that mass at the same time you discard the tanks.

This means you keep more full tanks for longer, discard the "empty fraction" of your used tanks more frequently, and discard engines as their thrust is no longer needed. It lengthens your total burn time considerably, and reduces thrust as you reduce your craft's mass (keeping your TWR more constant).

Compare this to the simple 6x radial onion design. In the simplest form, we have exactly the same parts (except the fuel lines). If we light all 7 engines at once, we have the same initial mass, thrust, and obviously TWR. But all of the engines will burn for the whole duration of the flight, and all burn out at the same time. The total burn time will be much shorter, and half way through the flight we'll be lifting seven half-empty fuel tanks, as well as still lifting the mass of all seven engines. By the end of the flight, our TWR will be ridiculously high, because we're still using all 7 engines to lift a small fraction of the original mass, so we're paying (in fuel) to lift useless engine mass.

Anyway, this is why discarding empty fuel tanks as soon as you can is a good idea, and discarding engines as soon as they're no longer necessary. An imaginary "ideal" rocket would lift only full tanks and only enough engine power to maintain a perfect TWR at 100% throttle (somewhere near 1.3 for main ascent) from second to second.

Asparagus is a relatively simple way to approximate this behavior.

Edited May 22, 2015 by Anglave

[mrklaw]

thanks, it was a huge amount of fun just watching my shadow getting closer and closer. Now onto a little science gathering minmus hopper which should be easier to get up there.

I have parachutes on that lander - if I have enough thrust to get a return, would the mobile lab survive reentry? Otherwise I was thinking to just leave it there, and send over something with three seats to bring them back at some point in the future. I might even do that quickly so my scientists get an XP boost from the trip, and then put them back in to be more productive lab guys

[Anglave]

Minmus hopper

Generally speaking, returning the mobile science lab is kind of a waste. They produce more science the farther they are from Kerbin. I think your plan of "shuttling" scientists to and from the lab is the better one.

Edit -- incidentally, I updated my previous post. Also, I've been working on gathering my own sort of "KSP Knowledge base". Feel free to check it out if you're interested.

[DancesWithSquirrels]

Actually, you can add stuff to your ships, if you have the Klaw unlocked, but that's probably far above your current tech tree level. In a 0.90 game I realized that my Dres explorer had been been launched without the satellite and probe landers I had spent so much time on - so I sent up a ship with two side-mounted probes, each with RCS and a Klaw on a separator to clip them to my main ship.

If you have a docking port on your ship, you could just dock a RCS equipped probe with an antenna too, adding it to your lab equipment, but I'm guessing that's not an option at this point.

[mrklaw]

just to throw a spanner in the works, I noticed this 6+1 orange tanks/skipper arrangement is costing me about 85k which all goes down the pan after launch (or can KSC recover any of that?). So I was wondering if I could whack a probe on it and recover it. But that means getting the entire thing into orbit without ditching tanks - so no asparagus. Also probably means leaving some fuel after circularising so I can slow down and probably a little extra for slowing desent (parachutes probably won't be enough).

Anyone done this, or should I just ignore the cost of launch?

[Murph]

just to throw a spanner in the works, I noticed this 6+1 orange tanks/skipper arrangement is costing me about 85k which all goes down the pan after launch (or can KSC recover any of that?). So I was wondering if I could whack a probe on it and recover it. But that means getting the entire thing into orbit without ditching tanks - so no asparagus. Also probably means leaving some fuel after circularising so I can slow down and probably a little extra for slowing desent (parachutes probably won't be enough).

Anyone done this, or should I just ignore the cost of launch?

In the long run, 85k is not a particularly expensive launch. Whether it is for you right now or not, only you can say. With reasonable rep, one good contract pays for that.

For me, I'd just ignore the cost.

[Chaos_Klaus]

Well, to be honest ... I think you are all completely overbuilding your rocktets. 11,8t is not extremely heavy for a payload.

Here is a fairly simple design that will put it into orbit and still have fuel to spare:

http://i.imgur.com/Nb4BjI5.jpg

I made a dummy payload. The tank is for adjusting the weight.

It uses a Poodle engine for the high altitude and orbital stage and a quarter size 2.5m tank. One single skipper engine and an orange tank form the atmospheric stage. Three Thumper SRBs help with TWR on the pad, igniting together with the Skipper.

The Thumpers help reach 270m/s pretty fast. After decoupling them, the rocket has a TWR of little above 1. That way the rocket reaches a velocity just below the transsonic regime fast and then stays at that velocity until it passes 10km. TWR of the main staige is rising as ISP rises and the rocket gets lighter. at around 30km the poodle takes over, slowly pushing the rocket further into orbit. At this altitude can use all the efficient engines designed for vacuum.

I got this into orbit with 600m/s of delta v left in FAR.

Remember that you do not need extremely high Thrust to weight ratios. 1.4-1.6 is enough! I've gone with more here, becaus I timed the booster burnout with reaching a desired speed at a lower TWR for the rest of the rocket.

Edited May 24, 2015 by Chaos_Klaus

[Foxster]

Would this do you?

The main stage is enough to get to an 80km orbit. You can then decouple and deorbit the lifter for a landing near the KSC...

The lander has easily enough dV to get to the surface of Minmus...

Craft file: https://www.dropbox.com/s/ydxze38nndrh187/Minmus%20minimum%201.craft?dl=0

You might need to tweak a couple of things depending what you have unlocked but generally it's serviceable.

Edit: Whoops, forgot a ladder to the ground for surface samples. They can jump that bit or you can add one.

Edited May 24, 2015 by Foxster

[mrklaw]

I'm going to try both solutions - I just brought my scientists back for an XP bump (all 2*now), but I only have 153,000 credits left. Can't afford to keep sending expensive disposable stages into space.

[Chaos_Klaus]

Again ... look at my design above.

Engines are the expensive part. You use four skippers, I use one and a poodle. That's way cheaper. SRBs are cheap, too.

Don't bring too much engine!

[Foxster]

Again ... look at my design above.

Engines are the expensive part. You use four skippers, I use one and a poodle. That's way cheaper. SRBs are cheap, too.

Don't bring too much engine!

Are all the lifter parts of yours recoverable?

[mrklaw]

Again ... look at my design above.

Engines are the expensive part. You use four skippers, I use one and a poodle. That's way cheaper. SRBs are cheap, too.

Don't bring too much engine!

I tried your design but when the boosters ran out, the single skipper wasn't enough - I guess my upper stages were a little to heavy compared to yours. I'll see if I can get the weight down - yours should be good to lift 12 tons to orbit?

[Chaos_Klaus]

Yes. If your payload is a little larger, I'd suggest adding more boosters (maybe use 4 or 6) and reduce the thrust limit on them a little to make them burn longer. The next stage should have a TWR of just above 1.

When the boosters are decoupled, it is ok for the craft to not accellerate. At least it should not slow down. I chose this configuration because it is wasting fuel to try to overcome the soundbarriere below maybe 10km, because of the high transsonic drag.

[Windspren]

Just use your normal Minmus rocket. It will work if you dump the lander and the CSM and just have the lab on the rocket.

[mrklaw]

Chaos_Klaus - thanks to your image and advice, I tried tweaking things and for a lighter payload (shuttle to pick up science from minmus). I managed to get the launch stages down from 7 jumbo 64+skippers and then a rockmax 32+skipper, down to 3 jumbo 64+skipper and then a rockomax 16 + poodle. That was enough to get me all the way to minmus and even had a little fuel spare when I jettisoned the poodle stage before landing.

Next question - more a curiosity. Can I get this back from minmus?

it has 8 RCS thrusters and 250 monoprop (which in hindsight wasnt needed to land on minmus), and I have 227 liquid fuel left for the 4xspark engines. Plus 4xradial parachutes. Enough to get me on a return path? And will that thing survive re-entry/landing - i.e will the kerbonauts survive?

My science guys will be there for a while, and I can always send something up to bring them home - but if it can get home in one piece it'll save me time and money.

[Zephram Kerman]

I'm a bit late to the party here, sorry. In those cases where you need more power for a rockomax tank, before unlocking Heavy Rocketry, you can instead "cluster" multiple engines under the fuel tank.

Use the tiny nose cone, surface attach with radial symmetry to the bottom of the tank. This leaves the nosecone attach node available for a bunch of Reliants with one Swivel in the center. You can do this with 3, 4, 5, 7, or 9 engines! For the the one with 9 engines, atttach them to the sides instead; it looks a bit like SpaceX's Falcon 9. I think it was Temstar that discovered clustering way back in the day.

If you add a probe core, a tiny battery, and four radial parachutes, the Swivel alone is enough to (sometimes) soft land the thing for refunds. This was inspired by Brotoro, who has several fun to read mission reports that involve 'reusable' launchers.