Twofer III - Minmus, Mun, and Return - Do we have enough fuel for this?

[Poppa Wheelie]

Mission Objectives:

• Satisfy several contracts worth some big Funds
  • Establish a base on Minmus
  • Plant a flag on Minmus
  • Establish a station in Mun orbit
  • Haul some tourists around Minmus and Mun
  • Three rescues
• Build, test, and practice orbital assembly of components for reuse on later missions

7 Launches

I started with seven launches to build an orbital assembly station at approximately 125km altitude, and to send the various components of the mission ship to be assembled at that station.

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Launch 1:  John Scalzi, Station Core, and Arm 12. Mission pilot was onboard the John Scalzi. [1 image]

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Launch 2:  Salvage Truss and Arm 6 [1 image]

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After this part of the assembly, I then sent the John Scalzi off to do some rescue and salvage [1 image]

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Launch 3:  Station arms 3 and 9 [2 images]

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I called it Bartlett Station because it looks like a Big X. [1 image]

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Launch 4:  Next I launched the Tourist Module and the Twofer III Kerbin return vehicle (a glider). Remaining crew and tourists were onboard.  [1 image]

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Launch 5:  An assembly of 4 Nerv engines, which ended up with an earlier intercept with Bartlett station than the previous launch.  [2 images]

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The Tourist Assembly and Twofer III return vehicle approached Bartlett Station and docked next.  [4 images]

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Launch 6:  The Mun Station Assembly, containing Hendley Station, Scrounger runabout, and a salvage bay.  [3 images]

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Launch 7:  Minmus Base Assembly, containing Ives Base, Jockey surface rover, and fuel tanks for Bartlett Station.  [4 images]

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Mission Ship Assembly

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With all components at Bartlett Station (except the John Scalzi, which was still out doing rescues), it was time to put all the pieces together.

First up, move the Nerv4 Module under (aft of) the Tourist Module.  [3 images].

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Second step, move the Mun Station Assembly under the Nerv4 Module [2 images]

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Third, move the Minmus Base Assembly under the Mun Station Assembly [3 images]

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Finally, we got the John Scalzi back to Bartlett Station, docked, and then moved the entire assembly under the John Scalzi.  [4 images]

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Do We Have Enough Fuel?

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One of my checklist items at this point was to undock the John Scalzi and check dV.  Intuitively, I “felt” like I should have enough, but I couldn’t figure out a way to calculate what I really had.  The dV Map says I need:

• 1270 to Minmus Intercept and inclination change
• 160 to Low Minmus Orbit
• 160 back to escape Minmus
• 1270 back to LKO
• 860 to Mun Intercept
• 310 to Low Mun Orbit
• 310 to escape Mun
• 860 to get back into LKO
• 100 let’s say I need this much to intercept Bartlett Station once in LKO

TOTAL REQUIRED BY dV MAP:  5300.  And I have 1671 indicated upon undocking from Bartlett Station.  [1 image]

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I knew it shouldn’t take 5300.  I figured that as I dropped off the Minmus Base, and Minmus Station, and dropped all of their assembly parts, I would actually gain dV.  I also figured that I could get a gravity assist from Mun to get to Minmus in less than 930 (what the dV Map calls for for Minmus Intercept without inclination change), and I figured that I could get directly from Minmus Escape to Mun Intercept with a Kerbin assist and without going thru LKO.  I just didn’t know how much any of this would save me.

I decided to go for it, without any real math to back me up.  You’ll see that I did gain and save dV in the ways just described, plus I figured out a couple more ways.  I’ll talk about dV as we go.

Let’s Go To Minmus!

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I then undocked the John Scalzi, and set up a maneuver node to get a Minmus Intercept with a Mun assist, for 871m/s.  See, I’m saving dV already!  [3 images]

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dV Status, after the Minmus Intercept burn:  768
-    1671 starting dV, minus 871 for the intercept burn = 800
-    I must have spent another 32m/s somewhere to end up at 768
-    Either way, neither 800 nor 768 look very promising – Am I in big trouble here?

The Mun flyby went well.  The tourists thoroughly enjoyed it.  [1 image]

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After the flyby, I had another dV moment.  You’ll notice the fuel tank at the very back of the train.  I had not set this up properly for deorbiting at Kerbin, so I figured I would transfer the fuel out of the tank and deorbit the tank and the rest of the assembly into Minmus.  As soon as I transferred the fuel out of this tank, dV went from 768 to 1281.  For whatever reason, the fuel in this tank was not being used by the dV calculator.

dV Status, after transferring fuel:  1281

Next, as I started to work on a maneuver for Minmus orbital insertion, I realized that Ives Base has plenty of fuel, and engines.  These were meant for its Minmus landing, but I had plenty enough dV for it to obtain orbit and do the landing.  So I separated the Minmus Base Assembly, and set up separate maneuvers for each of them.  [4 images]

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dV Status, after separating the Minmus Base Assembly:  1693 (just over what we launched with)

After these separate orbital insertion burns were calculated, I wondered if I would have enough time to burn them both.  If they were supposed to burn too closely in time, I would have to do one of them early, and one of them late.  After checking the actual Universal Time for each burn, I figured I had several minutes after the completion of burn 1 before the start of burn 2.

At Minmus

At Minmus we have to deploy the surface base, plant a flag, and do one rescue.

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I inserted both the John Scalzi and Ives Base into orbit, then lowered the Pe of Ives Base to land on the Greater Flats.  [2 images].

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Land Ives Base

Ives Base passed only 119m over the tallest terrain before reaching the Greater Flats.  [2 images]

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The landing went well.  [2 images]

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I drove Jockey, the base surface rover, to the western end of the Greater Flats.  [1 image]

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Dock John Scalzi with Hilts Station

Next, it was time to dock the John Scalzi with Hilts Station (placed in Minmus orbit on a previous mission).  [3 images]

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dV Status, after orbital insertion, inclination, and Hilts Station rendezvous:  1517

Land the James Lovell

Real-life astronaut James Lovell went to the moon twice, and never got to land.  So I named this lander after him, and it gets to do a whole bunch of landings on Minmus.  I had placed this lander at Hilts Station in an earlier mission.

Since I had a contract to plant a flag on Minmus, I might as well take advantage of it.  Our three crewmembers boarded the James Lovell lander, and landed.  [4 images]

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I drove the James Lovell west until we reached Ives Base, then drove Ives Base to the western end of the Greater Flats.  Then drove the James Lovell the rest of the way.  Docked the James Lovell with Ives Base, so the crew could spend the night in the lab.  [6 images]

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Flag Ceremony

In the morning, the crew took some photos, planted the flag, got back in the lab for experience upgrades, then got back in the James Lovell for departure.  [4 images]

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Return James Lovell to Hilts Station

Pop a wheelie!  [1 image]

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Light the engines, lift off, match orbits with Hilts Station, [7 images]

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Rescue Lizming

We refueled the James Lovell, removed one crew, and departed again.  James Lovell stopped at the Salvage Assembly of the John Scalzi, attached a docking port junior to the James Lovell nose, and another to the top.  [3 images].

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We then plotted an intercept node followed by a velocity matching node, approached Lizming’s Craft, attached a docking port to it, and docked.  [3 images]

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Next, we transferred Lizming, lowered Pe to deorbit the debris, detached the debris, raised Pe, and returned to Hilts Station.  [2 images]

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Everyone, including Lizming, transferred to the John Scalzi, and we were ready to depart. [1 image]

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dV Status upon departing Hilts Station:  1518.  That’s 1 more than when we arrived!  I’ll take it.

One of these days, to the Mun!

At the Mun we need to deploy an orbital Station, and do one rescue.

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From Minmus to the Mun

Plotted and burned a Minmus escape that resulted in a Mun encounter.  [2 images]

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dV Status after Minmus escape burn:  1434
-    This Minmus escape burn cost 84m/s, almost half what the dV map shows
-    And I’m going to get the Minmus SOI to Mun SOI at no additional cost
-    I’ll still need an inclination change at Mun

Flew several days from Minmus to Mun, circularized, adjusted inclination, and lowered orbit.  [8 images]

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This one is almost like a Google Doodle.  [1 image]

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dV Status after achieving desired Mun orbit:  1246
-    190 to achieve orbit, adjust inclination, and lower both Pe and Ap

At the Mun

Put Hendley Station In Place

I released Hendley Station from its assembly, and oriented it Normal.  Then I had to clear the struts from around Hendley Station by “pulling up” using the John Scalzi reaction wheel.  [3 images]

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I moved a small tug from the Salvage Assembly to Hendley Station.  [1 image]

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dV Status after dropping off Hendley Station and the small tug:  1281
-    A gain of 35

Rescue Thombo

Our pilot and engineer then launched the Scrounger, intercepted, rendezvoused, and captured Thombo’s Hulk with the claw.  [7 images]

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We transferred Thombo to the Scrounger, deorbited his Hulk, and returned to the John Scalzi to drop Thombo and Jatop off.  [5 images]

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Return Scrounger to Hendley Station

Immediately after transferring crew, Jatop departed again for Hendley Station.  [4 images]

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Return Jatop to the John Scalzi

I think this is the longest jetpack EVA I’ve ever done.  I didn’t record the total distance, but it was over 5km.  It was 5.8km at the end of the jetpack flight.  [7 images]

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Deorbit All Remaining Assemblies

Oriented retrograde, lowered Pe, oriented prograde, undocked everything aft of the Nerv4 Assembly, and raised Pe.  [3 images]

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dV Status after deorbiting maneuver:  1444
-    A gain of 163

Rescue Siglorf

Siglorf’s Wreckage was in very high Kerbin orbit, with a very high relative inclination.  This is the last part of the mission before we can go home.

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We plotted a Mun escape that intersected Siglorf’s orbit at very close to our Descending Node, adjusted inclination at the DN, intercepted, matched velocity, approached, and grabbed him with the John Scalzi’s claw.
This was actually the easiest docking I’ve ever done.  I think because the orbit was so high, the orbital curves were much flatter.  It was easier to aim right at him, and stay aimed right at him.  I flew the claw right into him with no “docking” work with the RCS.  [13 images]

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dV Status after Siglorf Rescue:  923

Next Stop, Bartlett Station

Can we get home from here?

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First step was to change inclination again.  This cost 186.5m/s.  [1 image]

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dV Status after inclination change:  736

This is when I realized I didn’t have enough dV.  The Siglorf Rescue was pretty expensive.  I saw that I had enough to intercept, but not enough to match velocity for rendezvous.  My next thought was to spend all remaining fuel to lower both Pe and Ap, and then have someone bring me more fuel (I do have more fuel in LKO).  But that led me to think about … aerobraking!

This is the first time I’ve ever done aerobraking.  There should be a World First award for this.  I had no idea what Pe altitude to shoot for.  I tried 39k and 49k.  Both resulted in spectacular explosions.  59k worked very well, though.  

dV Status after lowering Pe to 59k for aerobraking:  354
-    That was 382 to lower Pe

I took several photos on each pass, made a spreadsheet with all kinds of data, graphed the resulting Ap after each pass, and really nerded out.  But the bottom line is that I did 20 passes, starting with a predicted Pe of 59,938.5m.  For all 20 passes I let the Pe ride, and never raised it back up between passes.  These 20 passes dropped the Ap from 8 million meters, to ???, at a cost of 0 m/s dV.

Aerobraking [3 images]

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Before pass 1.

Parts were still getting hot on pass 15.

At the end of pass 20.

dV Status after 20 aerobrake passes:  still 354

At the Ap after the 20th aerobrake pass, raised Pe out of the atmosphere, then intercepted, rendezvoused, and docked with Bartlett Station.  [6 images]

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dV Status upon docking with Bartlett Station:  176

Let’s Head For The Barn!

Time to head for the KSC and conclude the mission.

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All crew transferred to the Twofer III Kerbin Lander, which then undocked from Bartlett Station.  We oriented retrograde, and lowered Pe to 30k directly over the KSC.  [3 images]

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We started reentry with 35 degree pitch.  I realized after a while that the predicted landing location had moved too far west, and was still moving west.  I lowered pitch to 5 degrees, and the landing location started moving slowly east.  [7 images]

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Just at the mountains, I gave the landing to MechJeb Aircraft Approach & Autoland.  I had never used this tool before, and wanted to see how it worked.  I think should have started this automated approach at a lower altitude, or maybe I should have adjusted the default value for Glide Slope to something larger than 2.5.  But, whatever the reason, we came in way too high.  I finally popped chutes over the runway, and had to manually maneuver a little bit to keep from going in the water.  Ended up on the far end of the runway, facing west.  I’m counting this as a runway landing.  [8 images]

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Lessons Learned

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Calculating dV

I don’t know how to calculate fuel requirements for a ship that will be assembled.  For this mission, I don’t see how the VAB dV tool, or the MJ dV tool, could have helped.

I think in situations like this I’ll need to build an Excel spreadsheet, and work backwards with the Rocket Equation.

Any other suggestions?

Orbital Assembly

For the most part, I’m very pleased with how the orbital assembly process worked.  I read somewhere, a while back, about orienting the source and target docking ports to face each other in the normal and anti-normal orientations.  I find this very helpful, and use it whenever possible.

Because I like to do docking in the normal and anti-normal orientation, and because the John Scalzi has a lateral docking port, I tried something with Bartlett Station which didn’t work out.  The big cube at the end of Arm 12 can rotate 90 degrees.  My intent was to dock the John Scalzi with this lateral docking port, using normal and anti-normal orientation, then rotate the cube 90 degrees, so that the big docking port on the aft end of the John Scalzi would be facing anti-normal for the rest of the orbital assembly.  However, that big cube at the end of Arm 12 must have been damaged during launch because it now sits crooked on the arm.

Salvage

I have a lot of junk in space.  My game is hurting for frames per second, and I’m pretty sure the amount of space junk I have is contributing.  My plan when I built Bartlett Station was to pick up the various leftover parts I had in orbit, bring them back to the station, and deorbit them all at once.  I think I actually made my game performance worse by introducing so many docking ports to the station.  And I determined it’s just easier to deorbit debris on the spot (grab or dock with debris, orient retrograde, lower Pe, drop the debris, orient prograde, raise Pe) versus tug it into a different orbit.

I had also planned to bring along on this mission the structure to dock and haul the debris from the three rescues involved.  Once I determined that I wasn’t going to attempt that, the assembly was already at Bartlett Station.  No problem, I thought, I’ll just leave it behind, and deorbit it later.  However, this Salvage Assembly was part of the larger Mun Base Assembly, and I realized that I had attached the docking port between the Scrounger and the Salvage Assembly incorrectly.  If I undocked, the truss structure above the Scrounger would disappear, and I wouldn’t have a way of docking the rest of the Mun Base Assembly to the larger ship.  I was able to use some of this stuff during the mission (two docking port juniors, and the small tug), but the rest was just dead weight that I carried around until released at Mun.

Game Performance, Frames per Second

I think the amount of debris in my game, plus the number of docking ports on Bartlett Station, are affecting my game performance.  I intend to just delete all debris in the tracking station, and deorbit the big Salvage Truss on Bartlett Station.  I’ll do some before and after fps measurements, and will report back on those results later.

That's it for now.  Enjoy!

Edited March 2, 2022 by Poppa Wheelie
To complete the report.

[Vanamonde]

My goodness, that's a lot of parts. 

[Poppa Wheelie]

Yeah, especially at the beginning.