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What's the most you can do in 7 tons?


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Mission Statement

Everyone knows the number seven, everyone's seen it, everyone's heard it, no one more than the number six. Six constantly cowers below it, for seven viciously tore apart and ate nine. Today at the KSC, it is our chief goal and mission to cower below the number seven just as much as six does every single day. Henceforth, any mission we complete will weigh in at a wet mass (Kerbals not included) of less than seven tons. 

The Challenge

Build and fly a craft that does something, anything, in less than seven tons wet mass (Kerbals not included). Can you flyby the Jool moons and come back in under seven tons? Can you visit Dres in under seven tons? Can you land on both the Mun in under seven tons? That's for you to decide and to prove. If this thread picks up I might make a badge.

The Rules

- The entire craft without its crew must weigh less than seven tons.

- The craft does not have to be an SSTO

- ISRU and surface mining are allowed.

- The craft does not have to return to Kerbin.

- Post a screenshot of your craft in the VAB/SPH showing its mass.

Leaderboard / Proof of Concept

- @JacobJHC Video here. 6.81 Tons. This is my proof of concept submission. It is a tiny SSTO mission for a tiny Gilly.

- @Pds314 Post here6.65 Tons. Duna landing with 1,900 excess delta-v.

 

 

 

Edited by JacobJHC
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Went to Duna. Lander broke on impact. Maybe I should have made the engines hit first since they have 1 m/s more impact tolerance than the tank.... Or just stayed onboard and suicideburned. 2000 Delta V gone lol.

ofCXd7l.png

Edited by Pds314
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Aaaand it doesn't matter how much Delta-V you have if you can't face prograde because your COM and COT are at the same point. Basically if it reaches this much fuel remaining while still in thick atmo that's mission failure by uncontrollable design.

uimaNWH.png

But hey: On Duna with a rocket chair with >1900 atmospheric Delta-V. That's something....

8p9HwO0.png

Edited by Pds314
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Current launch vehicle. Mass without Val is ~6.65 tonnes. I may have room to turn the Duna mission from direct ascent into Apollo style if I use the full 7 tonnes or close and cut back on the overpowered transfer/circularization stage, which would also let me considerably reduce the Lander fuel load. Shown at stage 1 burnout, but stage 1 still attached and burning fuel from stage 2 as linear asparagus booster.

2ISY9JL.jpg

Edited by Pds314
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Payload of 634 kg, with ionic propulsion and a delta-v of 11.3 km/s. The main problem is that it can only do 140 m/s at once before running out of electricity. screenshot771.png

Total launch mass is 6.95 t

screenshot770.png

Now the question is figuring out what I can do with all this delta-v. Maybe a series of landings on low gravity moons (Minmus, Gilly, Pol and Bop). And maybe I should remove some fuel to add some electricity.

 

EDIT : After a bit of redesigning, here is my final version, 6.991 t at launch. Delta-v has been slightly reduced to 10.9 km/s but more electricity means it will be able to do 250 m/s at once (which is enough to land on all low gravity moons). I have decided to settle on a tour of the four low gravity moons (Minmus, Gilly, Pol and Bop) and then if there is enough fuel remaining do something.

screenshot772.png

EDIT 2 : I discovered that the OKTO2 doesn't have any reaction wheel, so I added one and removed some fuel from the second stage. Now total launch mass is 6.841 t.

Edited by esmenard
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Mass of an empty tank is 1/9th that of mass of a full tank, but can be made full by ~1.9 tonnes of kit? (Including necessary launch clamp mass)

Hmmmmmm

Advantage: 5.1 tonnes of empty mass is a lot bigger than 7 tonnes of full mass.

Disadvantage: needs an hour at 100000x timewarp before launch because of zero percent thermal efficiency without a radiator. Literal Earth years of fueling delay on the pad.

 

It appears however that a single 10 kg radiator can fix that and cut it down to anywhere from a few kerbal days a couple Kerbal years.

Edited by Pds314
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"- ISRU and surface mining are allowed."

3 Kerbal years after launch...

I realized the TWR was too low for liftoff, as the rocket had gained about 25 tonnes of fuel.... xD

hyZNu6k.png
 

Edited by Pds314
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Intended as a worldhopper, with the planned destination path being Minmus, then the Mun, then Duna, then Ike, then Dres, then if is still intact go for Jool 5. All as an SSTO, this craft was overweight as well. The 300 kN Skiff engine suffers somewhat at low altitude and I did not pay attention to just how much, so it initially had <1.0 TWR and burned a lot of fuel on the ground. The result is I only had enough fuel to circularize. I will try to get something of this sort that can actually reach Minmus though to refuel. If I can reach Minmus, I can go pretty much anywhere because it should have 4661 Vacuum Delta-V. So even a Jool 5 landing mission would be within its reach since it could just refuel after touchdown on Tylo. Annoyingly, Kerbin is the ONLY object it has any hope of reaching orbit from where it cannot take off at full fuel.

I think the solution might be to give it a serious cut to its fuel tank and maybe possible its engine, and eliminate the 300 kg of heavy landing legs in favor of tiny grip pads, but add strap on boosters that are sacrificial. Another option that would be less destructive overall to its performance might be to use parasite engines instead of boosters. I.E. spamming Twitches to be jettisoned mid-flight would probably give it a reasonable TWR.

Another option would be to use the non-gimballing Kodiak engine, then supplement it with either Cub Verniers or Twitches. Seeing as the Kodiak has superior performance at liftoff but weighs 350 kg less than the skiff, this would drastically improve liftoff performance, at the cost of reduced maximum delta V if most of the Twitches or Cub Verniers aren't staged.

 

it should be kinda close but I think 4 Cub Verniers and Kodiak with no heavy lander legs would let it lift off with a TWR of >1.2 without cutting into fuel tank mass.

KROZ34R.png

Edited by Pds314
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After many more redisigns, and many launch attempts with either TWR or delta-v being way to low, I have finally successfully launched my probe into orbit. It's now in orbit and slowly increasing its apoapsis on its way to Minmus. The rest of the mission will come as an imgur album when it's finished.

This is the final design, 6.991 t at launch wyc2Lrr.png

 

And here is the probe in orbit, during one of its orbit raising burns lTuwt9F.png

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It has nearly clawed its way up from LKO.... I think I will still need to add detachable boosters or drop tanks tho. Or a more drastic option might be staging the central engine off and just learning to live with 128 kN of thrust. It would have difficulty with getting off of Tylo tho if I did that. =O

OloWtCR.png

WOyHq9s.png

Edited by Pds314
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Minmus intercept but no landing yet.

l1kGs8R.png

I should have the fuel for a Duna intercept, but I suspect I would have great difficulty landing with only ~100 Delta-V. Although maybe if deploy my Kerbal's parachute several kilometers up, I could slow the rocket to under 160 m/s and have a shot at landing it.

Edited by Pds314
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Note to self: land during the day.....

But still, it is a landing. No matter how botched. I still had 14 m/s of Delta-V in the tank.
PJgalq2.png
I can't believe it has come to this but... I'm gonna add a reaction wheel. =O I think if I finnaggle the fairing around I should be able to spare the weight. Without the wheel this thing is just too difficult to control. Honestly I'll bet this actually will reduce cosine losses too.

Edited by Pds314
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Aaaaaand... uh... what?
Apparently, on Minmus, it melts Kerbals when the convertotron is active. Meaning it should kill its pilot, refill autonomously over the course of about 3 Kerbal Years, 46 Kerbal days, and be ready for a hop to pretty much anywhere with like 4.3 km/s of Delta V, only requiring a new pilot.
cjHhLR2.png

Edited by Pds314
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4 hours ago, Pds314 said:

Apparently, on Minmus, it melts Kerbals when the convertotron is active. Meaning it should kill its pilot, refill autonomously over the course of about 3 Kerbal Years, 46 Kerbal days, and be ready for a hop to pretty much anywhere with like 4.3 km/s of Delta V, only requiring a new pilot.

Thanos and Avengers Meme Templates (Page 2) - Newfa Stuff

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4 hours ago, tfantonsen said:

Can you EVA him to a safe distance and have him wait about 3 Kerbal Years, 46 Kerbal days, or do he need to start the process with no hope of EVA in time?

I think EVA is possible but I will need to deploy the fairing first. Which complicates Duna and already-marginal Laythe (marginal because I would need to takeoff with about half fuel), But it shouldn't make them impossible.

Edited by Pds314
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