Ultimate Grand Tour (at least for Demo)

[sevenperforce]

Ever since I started playing the demo, I've always wanted to do one particular thing: plant flags on Minmus and the Mun in a single launch, then return home for a propulsive landing without parachutes. It's that last bit that makes this goal almost impossible. Landing on Minmus and the Mun in a single launch with demo parts is challenging, though doable. But the additional mass of engines and fuel for the propulsive landing (a la Dragon 2) makes the whole launch vehicle need to be exponentially larger. Plus, the small, flimsy landing legs in the Demo don't really provide much clearance for a lander, and the lack of a heat shield makes it rather difficult to design a lander which can carry enough fuel to land on Minmus, the Mun, and Kerbin while still remaining passive aerodynamic stability for re-entry.

Anyway, after a lot of iterative designing, I finally got something that I think will do the trick.

To start with, the lander:

Lots of part clipping, of course; I really had no other way to control COM and bending moment. There is a good deal of RCS propellant clipped in around the base to keep the COM low (both for stable munar landings and for aerodynamic stability on re-entry) and the feed lines are carefully designed to drain the uppermost tanks first. There's just enough of the hatch unblocked to allow EVA, and the built-in ladder is just within reach when the landing legs are deployed.

Orbital maneuvering drop tanks:

The drop tanks allow the lander's engines to be used for maneuvering and insertion burns without robbing the lander of fuel, and they're just high enough to clear the ground if by some miracle they still have fuel reserves when I land on Minmus. They also serve as an additional thrust anchor to avoid putting all the thrust on a single column.

Upper stage and booster drop tanks:

The upper stage basically just does the orbital insertion, with three drop tanks to be shed via stack decouplers when empty to squeeze out a little extra dV. I'm clipping tanks heavily so there's quite a difference when I drop these tanks. The central engine burns out before the six peripheral engines. TWR for this stage is almost exactly 1:1 with vacuum ISP and vacuum thrust, so a slightly-lobbed trajectory will be helpful but not an essential requirement.

Core booster:

This is a mammoth. I knew there was no way I would be able to fit enough engines onto a single stage to get this big of a monster off the pad, so I created an eight-engine clipped cluster to drop at the base of single columns. There are four of these, providing a combined 591 metric tonnes of thrust at sea level, but there are a total of ten fuel tank columns. Heavy strut-stitching keeps this whole stack stable; the six fuel columns without engine clusters feed into the tops of the other columns to help keep the COM forward. The central cluster burns out before the other ones, and it's necessary to downthrottle significantly right before burnout to prevent the pogo effect from ripping the booster apart. This stage has a lot of RCS propellant clipped into it as well, up top, with a veritable blanket of thruster blocks near the base. The fins help more than you would think.

Strap-on boosters:

Even with all thirty-two engines on the core booster, the vehicle's TWR is barely above 1:1, so I added three densely-clipped parallel booster columns with the same engine clusters to get it off the ground more quickly. Strut-stitching is ridiculously important here; I tried launching without struts and the three boosters curled up like the tentacles of a squid. Thankfully, the struts all separate properly at staging, so only one set of decouplers is required.

Altogether, she masses a whopping 712 metric tonnes...certainly not the heaviest thing one can launch, but pretty big for using only LV-T30s. She sits on her engine bells since there is no way the demo's shoddy launch clamps could hold her. It's also not possible to put any additional stack decouplers underneath, as the fairing on the LV-T30s would get stuck in these clusters and RUD.

I flew her once today but accidentally mashed Shift after the Minmus insertion burn and wasted a bunch of fuel, so I ended up stranded in Munar orbit after planting my second flag. Going to try again tomorrow; will post pics.

[Mad Rocket Scientist]

That looks crazy!  I can't wait for the pictures.

[Majorjim!]

5 minutes ago, Mad Rocket Scientist said:

That looks crazy!  I can't wait for the pictures.

What am I looking at here? I'm tempted to dl the demo again to give this a go.

[sevenperforce]

11 hours ago, Majorjim! said:

What am I looking at here? I'm tempted to dl the demo again to give this a go.

It's the biggest stable rocket I've ever been able to build in Demo; I've built larger before but they either crashed the game or ripped themselves apart on the pad. It holds together quite well for its size and 1500+ part count.

3.5-stage rocket with parallel boosters on the first stage and drop tanks on the second and third stages, with the third stage doubling as an EVA-capable lander with functioning legs. I'm going to tweak a few more things, like adding partial crossfeed and an engine drop to the first stage, and then I'll upload the craft file before flying.

I make no guarantees that this will have comparable performance in the full game so playing it in demo is probably a good idea.

Edited December 23, 2016 by sevenperforce

[sevenperforce]

All right, here's the craft file!

Sitting on the launch pad at sunrise...here goes nothing.

It's so big, by the way, that even timewarping to sunrise on the pad caused enough physics lag to pogo a little.

[The Space Dino]

Oh my gawd, that's a monster of a demo rocket....

[sevenperforce]

I flew the mission yesterday! Well, most of it. I saved on an aerobraking trajectory and I'll finish it early next week and post pictures. 

Once you get used to the lag, she is actually a real pleasure to fly. The RCA block blankets give plenty of control authority and so you basically just have to control how closely you chase the falling prograde on the way up. Plus, the sleek form factor (ten columns from S1 through S3) cuts down on drag pretty significantly. Can't wait to get pics up.

There's a fuel flow anomaly on the core booster that leads to one radial cluster burning out before the others, so I had to do some clever trim work to compensate and get nearly simultaneous burnout. But she is ridiculously powerful. Once the first stage separates she sprints into orbit.

Had two fuel problems on the way; I aimed for the top of a mountain on Minmus but I ended up in a landing zone so high that my HUD still thought I was in orbit, so my retrograde and speed indicators were all wack. Had to land without SAS or a display, which wasted some fuel. Then, I accidentally warped in the wrong direction when I was taking off from the Mun and had to burn hard to prevent catastrophe. 

So I was pretty short on fuel...but then I realized I had a TON of remaining RCS propellant. It ended up being enough for my Kumar escape burn, which allowed me to reserve enough bipropellant for landing!

So here goes....

[sevenperforce]

And, success!

Starting at the beginning and going all the way through....

Spoiler

I had to remove the drop engines on the central column because they got caught between the other three core clusters, but that didn't make too much of a difference. After attempting to fly it once, I realized that partial crossfeed hurts post-separation TWR so significantly that it's not worth it. This means the parallel boosters burn for longer and my TWR at separation is high enough to maintain a depressed trajectory. If you download the craft file, be sure to remove the crossfeed lines (unless, of course, you want to give it a go that way, in which case, be my guest).

On the pad:

3, 2, 1...

Liftoff!

Starting the nose-over pretty early to take advantage of my higher TWR without crossfeed. If you're patient, she's a real beast. As I said, lag is pretty significant early in the launch. Simulating fifty-six engines and almost 1600 parts simultaneously is no easy task. This probably goes without saying, but if you fly this, don't even think about warping early during the launch.

40 seconds into the flight, 80% of launch mass, Mach 0.64, about twenty seconds from parallel booster MECO. Acceleration down to 1.6 gees due to increasing drag. Unfortunately I don't think the boosters will last through Mach 1, but transonic aero in the demo isn't as punishing as in the full game so it's not too big of a deal. I'm glad I removed crossfeed; the TWR is balanced really well through this phase so she does an efficient gravity turn almost without input.

Closing on parallel booster MECO!

If the demo's radial decouplers were more powerful (I suppose I could have edited the .cfg just for this effect) I could have gotten a lovely Korolev clover. Instead, the parallel boosters just slide down barely clear of the core booster. There's significant exhaust plume impingement, though, which makes for a nice blue glow on the receding boosters:

After parallel booster separation, acceleration drops to barely above one gee due to drag. It's a really good thing I didn't use crossfeed or I'd be in a lot of trouble here.

I'm really pleased with the overall form factor. Past rockets I've tried to build really got fat at the bottom but clipping the tanks vertically and using the clusters at the bottom keeps a much sleeker, real-world look.

Jeb does a pretty good job holding her on a heading. I took pains to use sextuple symmetry.

10 km high, Mach 0.9, 61% of GLOW, with a nice ascent trajectory and a safe TWR. Just over a minute after launch.

Just under 13 km and we are supersonic!

Hmmmmm...I'm starting to notice that one of my outside clusters seems to be drinking fuel faster than the other two. The central cluster is supposed to MECO first. Not sure if I got a bad fuel line somewhere or something else, but I'll cut three of the engines on that cluster and roll 120 degrees to keep symmetry. My RCS blankets give me control authority for days so I should be able to stay stable. Even if the anomalous thruster cuts out early, this roll will ensure I nose up rather than nosing down.

Second star to the right and straight on 'til morning....

The engines are starting to glow quite a bit; tying each cluster to a single tank means they don't sink heat quite as well as they normally would. They won't overheat before MECO, though. I probably should have put an action group on the central cluster to reduce its thrust alone, but it's not going to make much of a difference. Downthrottled to just under 40% in anticipation of central MECO. I've also reactivated those three engines from before, as the consumption anomaly seems to be balanced out. Acceleration is a lot lower than I'd like right now but oh well.

Central MECO! Throttling back up as fast as I can. Since I'm still low enough for a bit of drag, I need to loft my trajectory a bit to make sure my second stage has enough acceleration.

Asymmetric MECO due to that thrust anomaly, but I only have the barest residual fuel so I'll cut the main engines and stage before I put myself in a spin.

Successful first stage separation (okay, more like first stage disintegration, but this is KSP after all)! Jeb seems pleased enough. Very close to apoapse, closer than I'd like, but we are high enough now that the second stage should be able to keep us aloft without too much drag.

Second stage ignition is successful. Those fairings are pesky as hell. Pulling 0.93 gees; hopefully I can get up to one gee before apoapse. Thankfully gravity has already started to drop off (yay Kerbin!) so my actual TWR is high enough to nose up and pray.

Success! Over a gee and still behind apoapse, so full throttle and on into orbit! Going to keep a close eye on my drop tanks so I can get rid of them as soon as possible.

With the tanks clipped so heavily, it can be tricky to see exactly which one still has fuel in it, so here you go. Lag is starting to disappear now so things happen fast.

Drop tank separation! Lots of boom but no damage to the spacecraft. The central engine will die out first here. Outer ring of tanks are "full" and I'm almost in orbit! Since I have plenty of thrust now, I can handle the drag from being low in the atmosphere; Oberth effect is my friend here.

Downthrottling as I slowly work toward a stable orbit as efficiently as I can.

Went in and limited engine thrust so I can be more precise. Wishing I would have lofted my trajectory a touch more, but I feel like this is still more efficient despite some of the drag losses.

Finally out of the atmosphere, and just 31 m/s from a stable orbit! I can breathe easy now...ironically.

Orbit achieved!

Time to plot some nodes; going to go all the way to Minmus first. I'll start with a plane change and then hit the gas for the Hohmann transfer.

Starting the second burn...

S2 separation and third stage/lander engine ignition!

Second burn complete!

Slightly worried about fuel; I still have a bit in my drop tanks but not as much as I would like. Anyway, we'll see how things go.

Getting ready for my Minmusian orbit injection burn.

Ain't that beautiful?

Injection burn begun! Going to watch these drop tanks closely.

Gotta land on the lit side.

Ah, space.

Drop tanks expended; last staging event!

Gear deployed. I really don't have another reason to retract it from here on out.

The ground is moving fast.

I can save fuel by landing on this plateau, right?

Not pulling a ton of deceleration because I have a LOT of fuel left. That's why I came to Minmus first.

Uh oh. Why does my HUD still say orbit?

Turns out the landing plateau I selected was high enough to still be considered orbit, so I turned off my HUD and SAS and I'll fly in blind.

Touchdown! Still technically in orbit!

Jeb feels proud.

Onward and upward!

Only a few seconds of burn gives me a high enough apoapsis to plan circularization.

Not too much for reaching orbit...

Here we are! Now to wait until I'm lined up for a plane change and Hohmann transfer to the Mun.

Round and round she goes, and where she stops, nobody knows!

Okay, I'm proud of this. Plane change and Hohmann transfer together.

I'll post the next leg next!

Pausing for now...

Edited December 27, 2016 by sevenperforce

[sevenperforce]

Where we we? Oh, yes, we had plotted a trajectory out of Minmusian orbit and on toward the Mun! Picking up where we left off....

Spoiler

I hadn't really expected to end up perfectly in a plane around the Mun's equator, so I'm pleased with this. The would-be gravitational slingshot is cool to see too.

Burning gingerly into a lunar orbit.

Now in a tight orbit, will I be able to get down to the surface and back up? Current remaining dV is 1.993 km/s (just from looking at my readouts) and deorbiting is going to cost me around 570 m/s, plus whatever I need for landing. Then I need 700 m/s to get back to Kerbin, leaving me with 723 m/s of dV for both landings. Doable? Well, we'll see, won't we?

Low thrust, hold retrograde all the way down. Not too worried about gravity losses.

It is ridiculously hard to find a flat landing place on the Demo Mun. I lucked out on this one!

Landed!

There and back again. Now to go home.

About as clean a trajectory as I can plot from this point.

Here's where my Apollo 13 happened. I got my apoapsis about as high as I wanted it and then tried to warp, only to realize that I was moving in the wrong direction. So I blew through a bunch of fuel getting a stable orbit. At this point, I barely had enough fuel for Munar escape, let alone a propulsive landing. What was to become of me?

But wait! I have a ton of monoprop. If I dump it, it will lower my dry mass quite a bit and I might even manage to get well on the way to Munar escape.

Here goes!

Munar escape achieved, and I've STILL got a ton of monoprop! Though this burn took a LONG time to be sure....

Made it into an aerobraking trajectory on monoprop alone! Boy, I'm glad I packed that extra.

I picked a high periapse so I could spread out the re-entry heating. Wouldn't do to burn up after all this time. Plus, I want a chance of actually selecting a landing point on land.

Up until this point I hadn't quicksaved even once, but now I will.

Burning a bit more monoprop off at periapse just for fun.

Glamour shot!

Several successive passes to lower apoapsis.

Using some more monoprop for a plane change.

Periapsis dropped a bit so I burned some to bring it up.

First bit of noticeable re-entry heat, though still making successive passes.

Last orbit! I'm low enough that I won't make it out of the atmosphere before my apoapsis drops below 70 km. This has been the challenge, here; the argument of my apoapse was such that I was consistently on the night side of Kerbin during aerobraking, which wasn't ideal. By iteratively raising and lowering my periapse with small monoprop burns, I needed to bring my apoapse down gradually enough that I would aerobrake through the terminator and come down over land. I think I've got it.

Perfect! I'll come down somewhere over that desert, I think. I'm not always good at planning specific re-entries landing zones when aerobraking is involved. Quicksaving again.

Superb!

Still not really feeling any re-entry heat.

Here it comes. Retracting landing legs just to be on the safe side. Final quicksave!

Limiting thrust on these engines to give myself a little more room for fine adjustment on the landing. It will make the suicide burn less efficient, but I think I have enough fuel.

Burning away all but the barest margin of monoprop.

Peak heating fades, so I'm deploying landing legs to make myself as draggy as possible. Jeb seems awfully cool for pulling 3.5 gees.

Fitting to have the Mun in the background. My accelerometer is right at one gee so I know I'm right around terminal velocity. These plains are at an altitude of around 1000 meters so a well-timed suicide burn should start around 2200 meters. I'm really glad I got the lander's aerodynamic stability settled; my SAS is on but it's not having to do any work at all. Clipping FTW!

Suicide burn, engage! Thank the Kraken that I'm on the daylit side of the planet in a fairly flat area on land, so I can see my shadow clearly.

A half-kilometer above ground and under 100 m/s, so I'm downthrottling to 1.6 gees. 

Final approach, seconds from engine burnout and pulling 1.5 gees.

Touchdown!

Definitely not enough fuel to go anywhere else!

Jeb is already missing the Mun.

Well, that's all, folks! Might not seem like much, but it was a personal goal, and it's harder than you think, given the significant constraints of Demo. I'd love to see if anyone else can tackle this, either using my ship in demo, using another design in demo, or even using the standard game but limiting yourself to demo parts.

Until next time!

[SpaceDirt]

Oh dear... that's BIG for the Demo.

[53miner53]

That is awesome!

[sevenperforce]

One potential way to cut down on part count and help with the lag would be to edit the .cfg files on the LV-T30 to make them eight times more powerful, and edit the .cfg on the Science Junior to make it mass 8.75 tonnes. Then the "big engine" could be an LV-T30 under a science junior (since the SJ allows fuel flow), and the other engines could all be thrust-limited to 12.5%. Identical performance and mass ratio but a lot better game performance.