There and back again - A Jool 5 Tale

[MiniMatt]

 

There & back again - A Jool 5 Tale

(under the Eye of Kraken's all seeing gaze)

 

Chapter 1 - Mission & Launch

Chapter 2 - Jool arrival & Laythe

Chapter 3 - Vall

Chapter 4 - Tylo and why we hate Tylo

Chapter 5 - Pol. It's so pointy

Chapter 6 - The Bop Bounce

Chapter 7 - Home & Epilogue

 

Chapter 1 - Mission & Launch

 

The mission

To send a fellowship of five hairy-footed Kerbals on a journey to each of Jool's five moons, planting flags and plundering science as they go. No mods save for Kerbal Engineer Redux.

Barring a single satellite mission to Jool some versions back, which was mauled to death by a herd of stampeding krakens shortly after entering Jool's SOI, I have never been to Jool. Despite playing KSP for well over a year, the only places I've ever planted flags are the Mun, Minmus, Duna, Ike, Gilly, and Eeloo. This was going to be an adventure. Things would (and did) break down, not work as planned. Unforseen problems and wobbly landings awaited.

The ship

230 tons & 234 parts in low Kerbin orbit, designed to be highly modular so as to keep mass at reasonably sensible levels.

Comprising:

 

• Single core lander module with no engines or fuel, just science gathering equipment & RCS
• Laythe module which docks with the core to add wings, a RAPIER engine, and fuel
• Main lander module which docks with the core to add two nuclear engines, fuel and landing legs - this configuration will land us on Vall, Bop & Pol and form the ascent stage of Tylo. It also, when docked at the rear of the mothership, forms one third of the mothership's main propulsion.
• Tylo descent module, which docks underneath the main lander module, providing a skipper engine, landing legs & plenty of fuel for safe and easy (hah! read on) Tylo descent
• Hab/Lab module to store all the science, clean out gunked up experiments, provide crew living quarters, and eventually return safely to Kerbin under parachute.
• Ion tug module. To save fuel the mothership won't circularise into a low orbit round each moon, rather it will stay in a high elliptical orbit around each, while the ion tug will effortlessly (hah!) and speedily (taking liberties now) ferry the lander configurations into lower orbit and back to the mothership.

 

The launch

Went for a single launch eliminating the need to dock all the modules together in LKO or refuel. The new rocket parts introduced in 0.23.5 have made me lazy and in contrast to the meticulously engineered mothership, the launcher was thrown together adding MOAH BOOSTERS until everything got up into orbit. Result was a 1500 ton monstrosity that handled hideously but got me into orbit with a handy 400dv remaining in the powerful launch stage.

With no consideration given to launch windows, and no course plotting mods, I happily stumbled across a ~2000 delta-v intercept path with Jool. The burn time for this though - even taking into account the ~400dv provided by the powerful remnants of the launch stage, would be around 17 minutes. Had to split the ejection burn into two: an initial 6 minute burn, lapping around to the periapsis once more before initiating an 11 minute burn. A slight 12dv correction burn put us on a perfect intercept with Jool, and we were on our way.

Edited December 30, 2015 by MiniMatt
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[MiniMatt]

 

Chapter 2 - Jool arrival & Laythe

 

Jool arrival

The plan is to aerobrake into Jool, leaving us with a perfect intercept with Laythe. Few plans survive first contact with Jool. After consulting (extremely useful) Jool aerobrake charts I tweaked the mothership's periapsis down to 118km in Jool's atmosphere. Unfortunately I was travelling far far faster than anticipated and hit Jool's upper atmosphere at over 9,800 metres per second. Not a complete disaster the resultant aerobrake left me with in Jool orbit with an apoapsis perfect for setting up a Vall intercept instead.

Hastily re-writing mission plans, I figured I could probably park the mothership at Vall & ion tug the Laythe lander to Laythe and back. Yet the kraken was smiling, and the mere act of spending 2.4 delta-v to lift the Joolian periapsis out of the atmosphere left me with a Laythe intercept! Back to plan A. A 71dv inclination correction burn followed to put me on course for a Laythe aerobrake.

Laythe

Laythe, it turns out, is very particular about her aerobrake heights. Like a giant blue Goldilocks, not too much and not too little, altitude must be just right. First quickload of the mission was needed to learn this lesson. But after a further 70dv correction burn it turned out a 23km periapsis put the mothership in a nicely elliptical orbit around Laythe.

Jeb undocked the lander in it's Laythe configuration, dipped his craft's orbit into the atmosphere and let gravity, air, wings, and a little assistance from the rapier engine bring him to land on one of Laythe's islands. The Laythe lander performed *flawlessly* (this would prove to be the first and last time such a statement could be made). Perfectly controllable at slow speeds a gentle landing was easily possible and some of the prettiest screenshots in my library were added. Laythe is soooo pretty.

Take-off was again flawless, and whilst atmosphere drop-off is sharper than Kerbin, orbit was achieved. Not quite enough orbit to reach the mothership, only attaining a 60km/200km elliptical, but that's an excuse to give the ion tug it's first outing. Wings and engines were blown off the core lander module into an eternal orbit around Laythe. There are no prettier graveyards in the solar system.

The Ion Tug arrived quickly enough, but getting the ~2 ton lander core back to the mothership was.... slow. In total 750 units of xenon gas were burnt by the single ion engine - ~26 minutes spent burning. Still, not too bad, the little tug did everything asked of it, and whilst not rapid, it was at least efficient. I would later learn the difference between tugging a two ton lander core and a forty seven ton Tylo lander.

Everything redocked and re-arranged at the mothership, the core lander is now docked onto the main lander module and the complete configuration docked at the fore of the ship. First design flaw of the day spotted as my core lander module's retractable solar panel can, in this configuration, not extend without hitting fuel tanks. We'll be fine, there are a couple of static panels on there too.

Departure

Ready for departure to Vall, the mothership now (sans laythe module) reckons it has ~7000dv available (later realised this was also reporting the ion tug DV as I'd left it's engine activated, so this figure is slightly optimistic), it now masses 174 tons with 208 parts.

540dv escape burn plotted from Laythe to Vall, 35dv mid journey correction burn.

Edited December 30, 2015 by MiniMatt
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[MiniMatt]

 

Chapter 3 - Vall

 

Vall

A 240dv capture burn put me in orbit around Vall, and a 12dv correction tweak setup the orbit such that "in space near" and "in space high over" science could be gathered. At this stage I notice I've thus far only used 7 units of RCS fuel, having brought 908 in total. I may have brought too much, and carting around that 3.4 ton, 750 capacity RCS tank was perhaps a poor design choice, costing me delta-v.

Bill takes the hotseat for landing, flushed with the success found at Laythe, and flushed with perhaps a little too much vodka (was a Friday evening) I set off confident. After all I've landed on moons hundreds of times. What could possibly go wrong? "Don't underestimate Vall", I was warned. I underestimated Vall.

Safe in the knowledge that my lander, in this configuration had around 3,000m/s delta-v, more than sufficient for Vall, I belted down to the surface on a steep impact trajectory from high orbit. And promptly fell over on contact. Nothing was destroyed however, so I attempted a horizontal takeoff. This proved to be.... spectacular. So another quickload needed to provide a second landing attempt. This time I got it right, but nevertheless my recklessly confident approach was highly inefficient, wasting 1,700dv just to land on Vall.

Thankfully, the remaining 1,300dv proved more than sufficient to get back into orbit, but once again, not quite sufficient to return to the mothership, and as such, once more the ion tug had to come down to rescue my lander craft. Only 300 or so units of xenon burnt in rescue, indicating around ten minutes spent firing the ion engine.

Departure

Refuelling the lander resulted in the mothership reporting around 5,700dv available - still looking very good - especially as next stop we'll be ditching a rather heavy Tylo descent module. 140m/s of that delta-v was spent initiating a burn from Vall to put us on an intercept course with Tylo. Bob's in the pilot seat for Tylo. He looks nervous.

Edited December 30, 2015 by MiniMatt
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[MiniMatt]

 

Chapter 4 - Tylo and why we hate Tylo

 

Tylo

A 100dv burn was required to capture into a Tylo orbit. It all went downhill from there.

Knowing that dv would be tight, the ion tug was launched to ferry the lander down into a lower circular orbit. After over half an hour of burning, the lander's orbit was still highly elliptical. In the form of 47 tons of Tylo lander the little ion tug had finally met it's match. So that plan was scratched, instead of reducing the apoapsis down into a low circular orbit, we'd shave the periapsis down to around 20km, come in very fast and very low, and perform a full thrust horizontal suicide burn to land. On the night side. Without landing lights. With razor thin fuel margins. What could possibly go wrong?

 

• First attempt wasn't too bad. Fire both the ascent nukes and descent skipper at full thrust at 1 minute prior to 20km periapsis. This timing turned out to be bang on *perfect*, bringing me down to about 100m/s at 1000m from the surface. Slight gravity misjudgement led to my final descent accelerating far quicker than thought. Bob died.
• Second attempt: Going ok! 7m/s descent just 300m to go - and then the skipper ran out of fuel; nukes were insufficient to hold aloft the full mass & I wasn't quick enough to undock the descent stage before we hit the ground at 40m/s. Bob survived. The ship didn't.
• Third attempt: Disabled docking port crossfeed midway through the burn to ensure skipper had enough fuel. In final seconds of landing I couldn't quite find balance point of thrust in time. Most of the craft survived. The important bits, however, did not.
• Fourth attempt: Textbook. Apart from the landing. Misjudged last moment before contact (landing lights would have been really helpful) & didn't kill thrust in time. Toppled over.
• Fifth attempt: As per the fourth. Being on the night side was really hurting. Toyed with idea of orbiting till periapsis is in daylight. Got increasingly worried about lander design - SAS is insufficiently strong to keep the lander upright if some rather shallow angles or lateral forces are present on contact.
• Sixth & seventh attempt: As per the fourth and fifth. Decided to orbit a few months till daylight and make next attempts where seeing the ground is possible. Discovered that orbiting my way into daylight was not an option. Seems my elliptical orbit is aligned with the sun, such that the periapsis is always in the dark...
• Eighth attempt: Experimented with timing of suicide burn. Was not a successful experiment.

 

At this stage I took a second quicksave in the final moments of an otherwise successful burn, allowing for repeated attempts at the troublesome final landing.

...

 

• Fifteenth attempt: LANDED! 380 units of fuel left, allowing for a full ascent stage and 20 units of fuel left in the descent to give a teensy initial boost.

 

This is why we hate Tylo.

Science and flag planting was undertaken with haste, the quicker to be off the cursed moon.

Take off wasn't exactly a walk in the park either. Undocked the spent descent stage a couple of seconds into flight as it ran out, then pointed at 45 degrees and hoped it would be plain sailing from there on. Gravity had other plans as she dragged my now puny 1.2TWR into a hillside.

This is another reason why we hate Tylo.

Eventually however, a 70km circular orbit was achieved. The ion tug headed back to the mothership to refuel before travelling back down to rendezvous with our spent lander, now shorn of it's Tylo descent stage fat I hoped the journey back up to the mothership wouldn't be too onerous. I was wrong.

I was quite biblically wrong. Spent a good 90 minutes initiating 30 or so separate burns to bring the lander up to the mothership. That little ion tug did just about OK at Laythe and Vall, but here it's woeful.

This is also why we hate Tylo.

Eventually however I reached the mothership. And as Tylo's final "screw you" I realised I'd made a mothership design error - the mothership, now sans Tylo descent stage presented no docking ports which wouldn't foul my lander's engines. So had to split the lander once more into it's component modules, docking the core cabin at the front, and the lander engines/legs at the rear.

Departure

The sooner the better. Glancing at xenon fuel reserves I realised I'd now burnt through 4346 units of xenon gas. At the 0.48/s burn rate of my single ion engine that's 9000 seconds spent operating that engine - TWO AND A HALF HOURS.

99dv burn to escape Tylo without bothering to line up a firm encounter - close enough would be fine, just get me off this rock! Once escaped a further 78dv, followed by another 5dv burn set up an encounter with Pol. We're headed to Pol next because Bop requires a large inclination change - if we visit that last we'll only need to make that inclination burn once rather than twice.

Edited December 30, 2015 by MiniMatt
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[MiniMatt]

Chapter 5 - Pol. It's so pointy

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Pol

Such a relief after Tylo. Rookie Richnie took the helm for this one and performed flawlessly. Ish.

A 400dv capture burn put us in a 114km/18km elliptical around Pol.

Having to do the docking shuffle to re-arrange the lander (thanks to my design oversight discovered at Tylo) is a pain, but Richnie, flushed with so much POWAH at his disposal, belted down to Pol's surface. Remembered to tweak thrust levels down to Pol-gravity-appropriate levels mid way down, landed and promptly fell over on the low gravity bounce.

But! He managed, by disabling the rear RCS thrusters, to right himself via judicious expenditure of monopropellant. Science was plundered and flags were planted.

Taking off was again such a refreshing change after Tylo - managed to take off right into an intercept and dock (after the accursed shuffle) with the mothership. Having vastly more delta-v on hand than Pol demands ensured no outing of the ion tug was necessary.

Mothership now reports 4,878m/s delta-v remaining to take us to Bop and then home!

Departure

By this stage, knowing I had fuel to waste, I'd got rather lazy with intercept planning - more efficient departures and encounters are likely possible. Took 114m/s to escape from Pol followed by a hefty 304m/s inclination change to line up on the same plane as Bop. A further 102m/s mid journey tweak was then needed to set up a close encounter of the Bop kind.

Edited July 28, 2014 by MiniMatt

[MiniMatt]

Chapter 6 - The Bop Bounce

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Bop

A mere 30m/s was all required to capture around Bop. Mothership reports 4320dv available. Unless further disaster befalls us the vast majority of the fuel currently locked up in the lander can, once Bop is complete, be added to this. Thompnie is strapped in for the final Joolian landing.

Assembled the lander for the final time in orbit. Failed to properly align up the ladders but reasoned that Bop's gravity is so low that where we're going, we don't need ladders. Thompnie could easily jump to the cabin door.

Tweaked engine thrust down to 20% to account for Bop's low gravity and came in for a soft low-grav landing.

Bop is very hilly. Level landing spots are rare. Did the "Bop Bounce" upon landing, flipped end over end over end, eventually flopping onto my side, just as with Pol - indeed just as with every first landing attempt other than Laythe. My lander design is really too tall, too narrow, and (possibly) under torqued. This time RCS wasn't quite enough to right the lander against Bop's fractionally stronger gravity compared to Pol. Figured that, unlike on Vall, a horizontal takeoff might be possible so went ahead with science and flag related activity.

Luckily, this time a horizontal sliding takeoff was possible without explosively losing parts. The final docking shuffle was completed, science loaded into lab, and spent 2.2dv taking the mothership down into a lower orbit to collect "in space near" science I forgot to do on first arrival.

Departure

All Kerbonauts are now back in the hab or lab modules. Having transferred remaining lander fuel back into the mothership, we now have 4835 dv to take us home. We could, at this stage, ditch the lander engine module, the core lander module, and the ion tug, saving at least 8 tons and granting us more delta-v. But as fuel reserves look ample we'll avoid littering up the system, and bring the whole lot home. Vessel masses 92.9 tons, with 168 parts.

A tiny 16.3dv burn is necessary to bring us out of Bop orbit and back under Jool's sphere of influence. The journey home will be detailed in the next, final, post.

Edited July 29, 2014 by MiniMatt

[MiniMatt]

Chapter 7 - Home & Epilogue

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Departure

On occasions I've thought this mission was blessed. Then I remember Tylo and wince. But in intercept/encounter planning it has proceeded unbelievably smoothly. Without any consideration to launch windows, without any node-planning or auto navigation mods, every intercept has been found easily and for modest delta-v.

Within the Joolian system this is arguably down to the system characteristics - with unusually large moons in close orbits, it's frankly harder to not hit anything. Manoeuvring around the Joolian system is easy, and surprisingly cheap. It's also a staggeringly pretty system with two or three moons visible at any given time and giant Jool-rises over the horizon.

What's been more lucky has been arrival and departure from Jool - a very reasonable 2000dv route from Kerbin to Jool was found at the beginning of this journey, so I was somewhat staggered to find a 1274dv route back home that got me within 368 thousand km of Kerbin. A further 85.3dv inclination tweak was necessary, followed by 3.3dv fine tuning to setup a close Kerbin flyby.

Total DV required to get home: a mere 1362.6 delta-v.

Arrival

A ~30km periapsis into Kerbin was chosen - coming in rather fast so hoped a deep aerobrake would be sufficient.

By this stage I'd decided I'd be ditching all non-essential parts (ie. everything but the hab/lab module), allowing them to burn up. Earlier in the mission I'd planned to keep the fuel/drive section, the ion tug & the lander modules up in Kerbin orbit for future use. But the mission has shown up so many little flaws, tweaks I'd like to make, that realistically I'll not use them again, so it's best to declutter.

Turns out a 30km periapsis was almost but not quite enough to capture the mothership in Kerbin orbit - a hasty retro burn while climbing through the atmosphere was also required to place the ship in a degrading orbit. The next lap would be it's last.

Landing would be at night, not ideal, but at least it would make for a spectacular sight from the ground. Undocked the three sections (lander core, hab/lab module, and fuel/drive - this last also having ion tug & lander legs/engine modules attached) at 30,000m and they span off to become splintering fireballs in the night sky. Six radial parachutes proved amply sufficient to land the hab/lab module containing all that lovely science (oh and five kerbals, yes they're important too).

Results

What a lot of SCIENCE we got! I'd transmitted some earlier crew/eva reports during the mission so total recovered might not be maximum, but 17,291 science points recovered - of those, 525 points were incidentally gathered high over the sun on the outbound journey, so 16,766 science recovered from the Joolian system.

As this mission also started in KSP version 0.24 (and finished in version 0.24.2) we also had contracts! I'd not paid a great deal of attention to these, but had managed to pick up exploration contracts for Bop, Pol, and Jool, bringing in a total of 1,267,330.18 funds and 3,049.565 reputation.

The cost of the complete vessel on the launchpad, including LKO lifter is 840,243.1 funds (in 0.24.1+ prices - 0.24.0 prices were fractionally different) - so I can even say this mission paid for itself!

Mothership delta-v breakdown

Kerbin - Jool: 2012dv

Jool - Laythe: 143dv

Laythe - Vall: 827dv

Vall - Tylo: 240dv

Tylo - Pol: 582dv

Pol - Bop: 550dv

Bop - Jool: 16dv

Jool - Kerbin: 1363dv

Total Mothership dv expended: 5,733dv

Now obviously, for future missions, I'll add at least 10% wiggle room to that total, plus at least another 700 to account for my seemingly lucky Kerbin return. And need to account for fuel taken by lander refuelling that's not seperately staged. Also need to account for mass that might be ditched along the way, such as at Laythe & Tylo. But future missions should be a lot better optimised.

Epilogue

So, sage advice, gather round younglings:

• You don't need to bring tons of RCS fuel. I burnt a total of 214 units. At least 100 of those were spent trying to supplement the ion tug's woeful thrust at Tylo, and in addition, thanks to the modular design (and a slight design oversight) I had to perform an above average number of docking manoeuvres. Carting a 3.4 ton 750 capacity RCS tank half way round the solar system and back is madness.
  
• Ion tugs work only if you're extremely patient, have autopilot mods, or have extremely light weight landers (don't ask a single ion engine to tug more than say 4 tons around Tylo) - I possessed none of these things.
  
• EVAing to gather science from equipment and dump in lab is a pain if equipment is all over the place. Endeavour to have all probes, cannisters, and bay doors, accessible from the cabin door, or from ladders connected to the cabin door.
  
• Highly modular landers add lots of efficiency but make sure modularity isn't compromising your design. Key ease of use principles like a wide, squat design is vital on both low and high grav worlds.
  
• Don't underestimate the low grav moons of Pol & Bop - an 8m/s landing on the Mun will be fine, but on low grav moons you'll bounce and tumble and roll.
  
• Remember the "fine controls" key (capslock on Windows)
  
• Think through how every configuration is going to dock in every scenario. The order you arrange modules on the launch pad may not be the order they're in midway through the mission.
  
• Remember to pack landing lights - at some point circumstance may force a night time landing and without them your job becomes ten times harder.
  
• Remember to thank Ziv for issuing and maintaining such an inspiring, achievable yet challenging objective. It will bring joy back in to your Kerballing no matter how jaded & cynical you've become.
  
• Don't worry about winging it - in many ways, it's a surprisingly forgiving challenge, odd things can go wrong and you can work around them. You don't need to plan everything out to minute detail - if it feels right, then launch
  

Edited July 30, 2014 by MiniMatt

[Meithan]

I just finished going over through the whole voyage. Fantastic stuff, sir, I loved it!

And as someone who's actually designing his own Jool 5 mission, I thank you for all the tips and insights. They'll be certainly put into practice soon.