Stock system grand tour, in 14.4 tons

[camacju]

Hello everyone!

The capstone of stock KSP missions is the “grand tour” - landing on every planet and moon in the Kerbol system. (You can technically land on Jool but that’s not traditionally counted). A single launch grand tour is a feat of precision engineering, careful mission planning, and the dedication to actually fly fifteen landings and return safely.

The first mission I'm really proud of was a grand tour mission (which was also my first ever Eve return), and I posted an album of it on this forum. The mothership looked something like this:

And this was the entire craft:

Like most grand tours, this is a very large rocket, and I completed this mission mostly through pure brute force. I did use some gravity assists, but this rocket absolutely conforms to the "More Boosters" philosophy more than anything. This was done in October of 2020, shortly after I started playing the game, and you can see that in the distinct lack of optimized craft design. But that was two years ago, and since then I've gotten much better at craft optimization, gravity assists, piloting, and the game in general.

Probably the best example of this was the Eve lander of this early mission, which looked like this:

It’s a pretty large lander and way overbuilt for Eve, but it got the job done.

And then a while ago I did a 7.5 ton Eve mission, which I later cut down to just under 7 tons. This is still the record for lowest mass kerballed Eve return without abusing “magic wing” type glitches, even without ISRU. It gave me an idea - since this Eve lander was so much smaller than my first one, could I make a grand tour mission, but this time putting a special focus on minimizing mass?

I first started thinking about a minimalist grand tour in February of 2022, but exams prevented me from doing much more. I revisited the concept in June, and managed to cobble together something vaguely resembling a craft - but I was occupied with graduating college, and it never flew. Here’s a picture of it anyway - it is similar in concept to my final design:

This was only part of the final craft, and was already projected to be much smaller than my previous grand tour - at the time I estimated a final mass of around 20 tons. As far as I’m aware, this would still be the lowest mass grand tour ever, as the lightest I know of is Brad Whistance’s 25 ton craft which made heavy use of ISRU. But this was unsatisfying - I was still leaving a lot of mass on the table. My original grand tour mission used Mammoth engines on the first stage. I wanted to have the mass of my entire craft be less than the fifteen tons of a single one of those engines.

About a month ago, I finalized the design of the craft:

14.45 tons - well within my mass goal of 15 tons. As you’ll see, I could have pushed this even lower, but I chose not to because I had already met my goal.

A breakdown of the craft design is below.

Spoiler

4648 kg launch stage. The wings at the front aren't strictly required to lift off but they're useful for balancing the fuel. Also has a fairing for the less aerodynamic parts of the craft, a landing gear also for balancing, and some clipped fuel tanks. This is actually enough fuel to get all the way into orbit and then some, making this craft a SSTO. This is the first place where the mission isn't optimal - it would be better to remove fuel until I need to circularize with xenon instead of liquid fuel and oxidizer, and to launch with slightly less liquid fuel. 

1258 kg Tylo lander. This is a simple two stage Spark powered lander, where the kerbal is expected to finish orbital insertion with an EVA jetpack. This lander could have fuel margins tweaked, or the reaction wheel removed entirely and control achieved purely through gimbal, but that wasn't necessary.

483 kg Duna/Vall lander. This has an Ant engine and a reaction wheel, which could have been replaced with a Spider engine for extra weight savings. The Kerbal's personal parachute is used for Duna landing and takeoff because it saves fuel and is lighter than a normal parachute.

2105 kg Eve lander. For my low mass Eve mission, this went through 13 iterations before arriving at the state it's in right now. I cannot think of any way to reduce the mass of this without resorting to magic wings.

The first stage is a propeller, used for both landing and ascent. It takes the Eve lander up to 36 kilometers at a very low speed - the basic fins are slower, but are much lighter and have a higher altitude limit than the DLC prop blades. I've gotten up to 47 kilometers on a basic fin propeller, but at some point the mass of propeller for the given payload becomes too large. 36 kilometers seemed like a good compromise.

The second stage is a rocket powered by three Twitch engines. When it burns out, I'm at 56 kilometers altitude with apoapsis above Eve's atmosphere and about 950 m/s of horizontal speed.

The third stage is a rocket chair with two Ant engines and one Spider engine, which provides all the attitude control. I wait until I reach 90 kilometers to deploy it as it isn't very aerodynamic. The burn time of this stage is spent skimming the top of Eve's atmosphere and managing vertical velocity carefully to be near zero, and it takes me to 2650 m/s surface speed. Note that this stage's engines are also burning during the second stage burn, which decreases specific impulse but increases thrust-to-weight ratio - and on Eve, high thrust is important.

The final stage is the Kerbal's EVA pack, about half of which is needed to finish circularizing into a 100x100 km orbit.

1518 kg  "mothership." This module contains all the refills of fuel that I'll need for the mission - a lot of xenon, a tank of rocket fuel reserved for the Duna segment, and a cargo container with extra jetpacks. I didn't actually plan to use a third jetpack anywhere in the mission, as I use less than a full jetpack for Eve and then a full jetpack plus a bit of the EVA cylinder for Tylo. The third jetpack was a contingency in case I somehow found myself running out of xenon and needed a landing on one of the lower gravity moons like Minmus or Pol.

4376 kg Laythe lander. Laythe ascent vehicles can get a lot lighter than this, but that wasn't the goal here. Every single part on this craft is used for some purpose other than Laythe. The Rapier, air intake, wings, and landing gear are all useful for Kerbin ascent, and the wings hold liquid fuel used for Rapier open cycle flight on Kerbin. The upper stage contained in the fairing is an ion tug, which is used for the remainder of the mission. This means that there is zero launch mass penalty with this Laythe lander except for a bit of xenon, which is very light. Contrast this to a dedicated Laythe lander, which may only weigh a bit over one ton, but is only used for Laythe - I would be well over fifteen tons of launch mass.

The idea for this is taken from Brad Whistance's 6 ton Jool-5 mission.

591 kg ion tug. This single ion engine gets a lot of work done. I added just enough battery capacity that it can land on Eeloo without any trouble. 

I could have used this to land on Vall also, but I decided to simply bring more liquid fuel rather than worrying about staged batteries - I needed the lander for Duna anyway so it wasn't a big mass penalty.

I made a video showcasing this mission, also.

I've put my comments on it (time stamped) in a spoiler box below.

Spoiler

0:07 This is a pretty standard SSTO flight path. I stay at sea level until around 450 m/s and then begin climbing to avoid heat. I actually began the climb pretty late and almost melted the front wings, but survived.

0:18 The flight path continues with leveling off at somewhere between 19 and 23 km depending on wing load, before switching on the rockets and climbing the rest of the way to orbit.

0:25 I intended for the single ion engine to do the interplanetary transfer here, but I had spare rocket fuel - why not use it? After it runs out however, I need a lot of kick burns, some of which I didn't show in the video.

0:31 I love gravity assists! But in this case, they're actually necessary for the mission. My extremely low TWR means I will not be able to complete an Eve transfer directly. So I use multiple gravity assists off the Mun and Kerbin to wind up enough energy to get to Eve. This has the additional benefit of requiring 200-250 m/s less delta-v than a standard Eve transfer.

0:45 Now that the Kerbin ascent is done, the Rapier engine is dead weight, and I've got two more dedicated landers for the Jool system. Naturally, that's my first destination. I place the craft into a highly elliptical orbit of Laythe because it takes very little delta-v to escape Laythe's orbit, and with gravity assists, it takes very little delta-v to obtain an encounter with another planet or moon (single digits is common)

0:54 This Laythe landing took a lot of attempts. I basically quickloaded and tried to bounce onto the wheels every time until I ended up succeeding. The spring characteristics on these landing gear were optimized for a much larger craft, leading to a lot of bouncing.

1:06 I didn't intend for parts to burn off here (including my only liquid fuel tanks), but it didn't really matter as I had more than enough electricity to circularize on the ion engine.

1:33 Tylo has high gravity and no atmosphere so efficient landings need to be very precise. I tried to start my burn as closely as possible to 0 degrees North, 85 degrees 30 minutes West, and altitude of 9750 meters.

2:10 I landed on a steep slope here so I fired the ion engine immediately to avoid sliding off a cliff - I did come to a stop on the surface with the help of ion thrust however.

2:38 Around this time my game's visuals started breaking. The Ant engine's plume is barely visible and the night side of planets becomes incredibly dark. You can see that the Ant engine is on by looking for the plume's outline or the Kerbal Engineer delta-v reading decreasing.

3:49 I actually hadn't planned on bringing a Kerbal parachute - this happened by accident when I neglected to check my crew before launching. (I didn't even plan to bring Jeb!) Fortunately, I was able to use this to my advantage.

4:30 I transfer directly from Duna to Dres, which tends to create a larger capture burn, and I cannot capture on a single charge. So I burn at periapsis to both execute a plane change and to set up another Dres encounter later.

4:36 I use a technique here called "V_inf leveraging." By executing a maneuver in deep space such that my orbit becomes more tangent to that of Dres, my capture burn is reduced. Sometimes, this reduction exceeds the magnitude of my deep space maneuver, so I'm saving delta-v. This also facilitates capture burns on a limited battery charge. (cough cough benjineer)

4:53 This is misinformation - Dres doesn't actually exist. I'm simply landing on an unusually large and detailed asteroid.

5:10 Now, the entire craft leaves Laythe orbit because it's easier to bring everything with me than keep returning to Laythe. Time for more gravity assists!

5:29 The capture is done with ions because basic fins are fragile and burn up easily. They can survive aerobraking but require a lot of babysitting as shown in the subsequent clip.

5:45 Spin2Win decoupling probably isn't needed here ... but it's so Kerbal! I couldn't resist.

5:48 Warp rates from 10-100x will massively decrease heating on all parts. I don't know why but it's the only way this thing can survive Eve reentry, and it still almost explodes as you can see from the thermal gauges.

5:51 This ascent took close to an hour. I wasn't tabbed into KSP for most of that time, which is why the RPM and mouse look a bit weird (I sped this up 128x)

6:07 I've been using a trick called "Magic hand" where if you pick up an item using EVA construction or a similar mechanic like inventory transfers, the mass of the item disappears. This isn't ever necessary to complete the mission - I'm just padding my margins by a few tens of m/s, which I could easily fill with more jetpack usage.

6:34 The first Gilly landing was not recorded but I didn't quicksave recently - so I just flew the Gilly landing again. It's such a low mass body that this really didn't waste any fuel and it was easier than finding the proper save game.

6:47 Again, V_inf leveraging is necessary here because Moho is so close to the sun that relative velocities are very high. I didn’t need the extra delta-v but this makes capturing much easier.

7:44 To get to Eeloo more easily, I encounter Jool first, and then use Laythe to reduce relative velocity. I then use a second Jool gravity assist to do my plane change. This results in a much smaller capture burn than transferring directly from Kerbin. These orbits take a long time to meet up - but Kerbals are biologically immortal, so I have all the time in the universe.

9:05 I left over 1000 xenon in low Kerbin orbit. I brought far too much with me on this mission (along with the backup jetpack), but it's better to have it and not need it. Again, there are a lot of inefficiencies here, but my goal was to go under fifteen tons and I met that specific goal.

9:10 I tried to land on the Administration building's helipad but I stalled just short of it ):

 

Edited November 10, 2022 by camacju

[Leganeski]

Great concept, creative craft design, and superb video editing! As someone currently hauling around a 355-ton mothership for my own grand tour, this mission is seriously impressive.

I noticed (from the Distant Object Enhancement planet labels) that you had Quack Pack installed; are you planning to do a mission there in the future?

26 minutes ago, camacju said:

5:45 Spin2Win decoupling probably isn't needed here ... but it's so Kerbal! I couldn't resist.

How could anyone? It's so much more convenient than having to deorbit and then reorbit after dropping the lander.

[camacju]

10 hours ago, Leganeski said:

I noticed (from the Distant Object Enhancement planet labels) that you had Quack Pack installed; are you planning to do a mission there in the future?

I was actually planning to do at least one quack pack landing in this mission but I felt burnout coming and decided to end the mission early.

I do absolutely  plan to make a Quack Pack showcase in the future though. 

[Ultimate Steve]

Wow, I just noticed this, its amazing! I didn't know it was possible to do Eve that light.

I've been a bit obsessed with low mass missions lately.

A few weeks ago I did a low-ish mass conventionally fueled mission to Moho and back to prove to a reddit commenter it could be done with a reasonably sized rocket without resorting to minimalism... But that just made me want to go minimalist. I spent a bunch of time continuing to pare that down and I got it pretty small into the single digit tons, my stumbling block was the Kerbin ascent, low margin atmospheric ascents are the bane of my existence. It ended up though that I had accidentally optimized the vacuum segment to pretty much the world record. Unfortunately there isn't usually that much room for innovation in low mass records these days, but as you have so proven, the low mass grand tour is the exception!

I messed around with a lot of designs earlier today for a low mass grand tour, and I was coming in significantly under my goal of 100 tons (vehicle is not finalized yet), so I decided to see what the record was, and I saw this, and it has given me some ideas.

Seeing as until now I've stubbornly refused to learn gravity assists, I don't think I will beat 14.4 tons, but I've decided to give it a go and see how low I can go.

Any secret to those basic fins not exploding on the way down on Eve other than lots of gentle aerobraking and physics warp?

Also I never have seen anyone use Magic Hand before, that's a good name for it. I don't think I'll be relying on it, but I wonder how else this could be exploited.

[camacju]

11 hours ago, Ultimate Steve said:

Unfortunately there isn't usually that much room for innovation in low mass records these days

There’s actually a surprising amount of room for improvement still. The only records I consider untouchable are Brad Whistance’s Jool-5 in six tons, and maybe his 2 ton Moho mission, but even these might have mass shaved by more gravity assists. Everything else is very beatable. (I actually have some craft “in storage” that break a low mass record, I just haven’t bothered to fly them yet).
 

11 hours ago, Ultimate Steve said:

Any secret to those basic fins not exploding on the way down on Eve

Lots of physics warp and also running the propellers at a slow speed, which lets the blades briefly shield each other from heat. Takes a lot of attempts though.  
 

11 hours ago, Ultimate Steve said:

I wonder how else this could be exploited

You can use this trick to land on every body besides Laythe, Tylo, and Eve with just the EVA pack. You’d put an inflatable airlock into the “magic hand” storage, and then climb in to refresh the EVA propellant. It’s quite a bit too exploity for my taste however. 

Edited December 13, 2022 by camacju