Kerbin 2 challenge

[Gordon Fecyk]

29 minutes ago, The_Rocketeer said:

could you clarify what the problem with the assertion is?

[...]but the most likely candidate for your current experience is that you are not launching your mission to account for Minmus' orbital inclination.

My problem is with the specific assertion that, "fuel is dV." As in, "if I have twice as much fuel in my craft and nothing else changes, I have twice the dV."

If the thrust and efficiency don't change, dV would increase with more fuel but 2x fuel is not 2x dV. We know this from the Rocket Equation, even without the direct observations I made in last night's mission. It'd be more correct to say, "fuel is a function of dV," or something like that.

As for inclination at Minmus, I didn't bother with a plane change on insertion. It was only 160+ m/s, which is fairly normal for me flying to Minmus. I just made sure to land roughly on its equator so the ejection back to the Mun was more efficient. Also, doing my inclination change to Minmus at Mun PE saved me a lot of dV, in addition to doing the Mun assist.

Not related to the fuel = f(dV) argument, my plotted Mun transfer had a fairly wild but still reasonable inclination, but the burn missed by quite a bit. I ended up plotting a polar Mun insertion to correct it, but again I landed near the equator so my ejection back to Kerbin was more efficient.

Edited February 3, 2017 by Gordon Fecyk
It'd help if I read the whole question, eh?

[Superfluous J]

After much thought, while I still assert that Minmus first is more efficient, I think @regex states it best when he refers to the KSP system as a "toy" system, and the "more efficient" is marginal due to the fact that - really - both moons are really easy to land on dV wise.

A better test would be to be in orbit of Laythe and try to land on both Tylo and Bop. Do you bring the Bop lander with you on the way up and down from Tylo, or the Tylo lander up and down on the way to Bop? I say "Bop first" is better.

The Minmus/Mun difference could easily be a scant few m/s, and drown in minor choices made during transfer between the two.

[Nicias]

Changing the order will change the TWR on both landings. This will change the amount of gravity loss.  That and the plane change are to only places I see asymmetry

[Leafbaron]

1 hour ago, Gordon Fecyk said:

I have a problem with this assertion after flying my attempt last night.

It appeared to take three times more time to do my Minmus insertion at 161 m/s (1m 33s) than it did to do my Mun insertion at 207 m/s (30s). Granted, this is the stock estimated burn time, but this is usually close enough and these are based on full thrust. By Mun insertion, I had just-slightly-less than half of my fuel remaining.

as you burn fuel, your craft becomes lighter, however your engine has the same thrust. So as the ship burns your TWR ratio increases, which allows you to accelerate faster. for instances given those numbers you were accelerating at 1.72 m/s on average for that first burn. and 6.9 m/s on average for the mun burn, even the the ship is lighter and has higher thrust to weight ratio, it's isp is the same which means each unit of LFO it throws has the same change in velocity. 

 

1 hour ago, The_Rocketeer said:

As I pointed out previously, dV depends also on local gravity. It will take less fuel-mass-thrown-out-the-back-of-the-rocket to move the same vessel mass on Minmus than it will on Mun. Your experiment results are interesting, but I would like to see your methodology before accepting it as a groundbreaking development in our understanding. Perhaps there is something about the 'closed loop' flightpath that @5thHorseman and I are overlooking, but I doubt it.

 

@SpaceOdissey still waiting for clarification on the manned/unmanned question.

man, i think you're confusing weight and mass. Mass doesn't change no matter what gravity your in, mass is an objects resistance to acceleration. your ships mass doesn't change just because it is in a lighter gravity or heavier gravity like the Mun and Minmus. Its weight may change but not the mass. 1 kg of XYZ is still 1 kg no matter where in the universe it is. And throwing 1kg of mass out of your rocket is gonna have the same cause and effect on your rocket no matter where you are beeeeeeecaaauuuuuuseeeee the mass of the ship doesn't change, newtons third law. 

We can run through my methodology when ever you'd like if you wish. 

 

 

[regex]

Nowhere in Tsiolkovsky's equation does local gravity matter. The only place where delta-V will differ is where exhaust velocity will differ, like in an atmosphare. You may have other losses but your delta-V does not change with local gravity. Your considerations for this challenge are local TWR at the time of landing and the timing of the Mun/Minmus transfer to make it as efficient as possible.

Edited February 3, 2017 by regex

[The_Rocketeer]

6 hours ago, Leafbaron said:

i think you're confusing weight and mass

Nope. The point I'm making is that having a small payload on Mun is considerably more of a problem than having a large payload on Minmus, because we take that payload into a much deeper well on Mun than Minmus. Mass may be mass, but dV cost goes up per mass the deeper into a well you go. It doesn't matter how much dV you bring with you, which obviously doesn't change in vacuum - it matters how much you will need to get out again with the payload mass you brought.

[regex]

5 hours ago, The_Rocketeer said:

Nope. The point I'm making is that having a small payload on Mun is considerably more of a problem than having a large payload on Minmus, because we take that payload into a much deeper well on Mun than Minmus.

That only matters in terms of craft mass and thrust to mass ratio of your engines, delta-V remains unchanged. You may experience losses to gravity with a low TMR but your delta-V doesn't change.

5 hours ago, The_Rocketeer said:

Mass may be mass, but dV cost goes up per mass the deeper into a well you go. It doesn't matter how much dV you bring with you, which obviously doesn't change in vacuum - it matters how much you will need to get out again with the payload mass you brought.

I feel like you need to rethink your wording here. Delta-V is not the issue here, having a decent enough TMR to apply that delta-V is.

If you're as efficient as possible and budget delta-V accordingly it shouldn't matter whether you go to the Mun or Minmus first, so long as your engines can lift the craft at both destinations in the order you land. If your issue is using a less massive craft then, yes, it is probably better to land on Minmus first in order to use smaller engines, but the delta-V budget for a small or large craft will be exactly the same whether landing on the Mun first or Minmus first assuming maximum efficiency and engines that can lift the craft.

[Gordon Fecyk]

Low-Tech Space Plane and 4.5 t Lander to Kerbin 2, "Difficult" Version

I managed to repeat the trip in just over twenty days with a single-stage-to-orbit craft that was just barely under 40 tonnes. With Valentina loaded in the command seat, the craft just hit 40 tonnes.

I won't repeat the entire image set, but you can be assured the flight profile was almost identical. I'll post the most significant changes here along with a craft download link. Note that the craft is designed for Ferram Aerospace under KSP 1.2.2, which is still a developer version only, and as such I was able to reduce the wing and control surface mass at the expense of strength. Aero behaviour may change with the final release.

The Craft, Revised: LTS Kestrel-FCL:

The lander is identical. The lifter changes include reduced wing mass, one less pair of FL-T100 tanks, one less drogue chute, 2 x LV-T30 Reliant instead of LV-T45 Swivel main engines, and reduced fuel and oxidizer. You may inspect the craft file (16 KB zip), but again this is for FAR under KSP 1.2.2 so the mass of the wings and control surfaces will be normal if loaded without FAR installed. Loading Valentina Kerman into the lander's command seat added 80 kg, bringing launch mass up to 39.985 tonnes.

Again, the mission was identical except I took longer to reach 18 km up. The Reliants compensated with +25 kN thrust at the expense of -10 s ISP. Also I could reach Minmus in only 9 days, and the total mission time didn't exceed 21 days. Val had a harder time loading the lander back; I ended up docking with her still inside, but it took a few reloads to eject her from the seat and clear the lander.

I botched the first return attempt and broke the antenna I was using as an aerospike at the nose, so I reloaded from approach and tried again. This was the final result:

Here is the video of the attempt. I cut out a lot of things to fit the music that @Thrimm picked for this craft back in August 2016, but the essentials are there.

Spoiler

 

 

Edited February 4, 2017 by Gordon Fecyk
Added spoiler with video

[Foxster]

We are talking about manned-only here, right?

[The_Rocketeer]

7 hours ago, regex said:

That only matters in terms of craft mass and thrust to mass ratio of your engines, delta-V remains unchanged. You may experience losses to gravity with a low TMR but your delta-V doesn't change.

I feel like you need to rethink your wording here. Delta-V is not the issue here, having a decent enough TMR to apply that delta-V is.

If you're as efficient as possible and budget delta-V accordingly it shouldn't matter whether you go to the Mun or Minmus first, so long as your engines can lift the craft at both destinations in the order you land. If your issue is using a less massive craft then, yes, it is probably better to land on Minmus first in order to use smaller engines, but the delta-V budget for a small or large craft will be exactly the same whether landing on the Mun first or Minmus first assuming maximum efficiency and engines that can lift the craft.

Thanks for this, you point out both why I'm not being understood and why I'm right. And yes I have been somewhat misuing the term dV. I have been thinking of it as a statistic on KER without regard to the effect of TMR.

The question is whether a craft of Radius 0 parts can land on both moons and return to Kerbin without exceeding a starting mass of 5t. Assuming the same craft will land on both moons, it is obvious that TMR will be considerably better on the second moon than it is on the first. It is also obvious that since Mun has a larger and stronger gravity field, the effect of a lower TMR is exaggerated here compared with on Minmus - low TMR in deep gravity wells requires longer burns, so lower mass in stronger gravity is always better than higher mass in weak gravity for the same engine with the same thrust.

And speaking of engines, it is obvious to me that the Spark is the only suitable Radius 0 engine for the Ultimate difficulty.

[Foxster]

Thought I'd give it a go with jets>rockets>ions at ~12t on the pad...

Album (view from bottom to top): http://imgur.com/a/ZZ95E

Lots of room for improvement but gave up trying for <5t and 0.625 parts. Might come back to that. 

PS - Wouldn't have been possible to do the Mun first, TWR was too low. 

 

 

Edited February 4, 2017 by Foxster

[Teilnehmer]

The Ultimate Level.

• 0.625 m parts only.
• Under 5 t of mass (4.989 t).
• No refueling.
• No docking.
• No Hyperedit, no autopilot mods (MechJeb used for info and node editing only).
• No debug menu, no cheating etc.

 

Edited February 5, 2017 by Teilnehmer

[Teilnehmer]

On 1/29/2017 at 7:05 AM, SpaceOdissey said:

Dificulty ranges:

Easy: Hyperedit allowed

Hm… Well… OK…

 

[Gordon Fecyk]

10 hours ago, Teilnehmer said:

The Ultimate Level

I wonder if that KORC tool takes ion engines into account. Nine tonnes, indeed.

Not to mention, Teilnehmer's craft is super easy to reproduce from the screen shot alone. The only thing I couldn't figure out was whether he skimped on LFO or Xenon to get the mass under five tonnes. And whether he considered Valentina's mass in the total launch mass. Apparently kerbals are massless until they exit various command parts, and then they're 80 kg with full EVA kit.

This deserves the @Turbo pumped and @Cupcake... seals of approval for micro-engineering.

10 hours ago, Teilnehmer said:

Easy: Hyperedit allowed

hah hah hah hah hah hah hah

Here, let me get out my 2.5m lander can and do a whole tour of the system, including the surface of the sun.  I wondered if SpaceOdissey was serious about that.

[Foxster]

12 hours ago, Teilnehmer said:

The Ultimate Level.

• 0.625 m parts only.
• Under 5 t of mass (4.989 t).
• No refueling.
• No docking.
• No Hyperedit, no autopilot mods (MechJeb used for info and node editing only).
• No debug menu, no cheating etc.

 

• No craft safely returned. 

I think we can forgive you though as the crewman made it OK 

Nice job. 

[daniel911t]

I managed to complete the Legend level!  Took a bunch of tries, but it was a lot of fun.  Thanks a lot for the suggestion by the OP.  

My big breakthrough was when I realized that I could get a Mk1 lander can with a single ion engine to have a greater than 1:1 TWR on the moon.  That was a super light experimental craft that lacked heatshields or parachutes, but it proved the concept.  With all the survival gear I was able to get a good TWR with 4 ion engines.
 

 

I got to orbit with plenty of leftover delta V.   The Jets are way more efficient than SRB's from ground to about 25K.  

 

Decided to go to the Mun first.  Took much more delta V than I had calculated, but I had a big reserve too.

After departing the Mun I put myself in an elliptical orbit outside the Mun.  The transfer window to Minmus ended up being the long way around - glad life support isn't a part of the equation.

Should really have taken this screen cap on the mun too... forgive me.

Then I had so much delta V leftover that I decided to settle back into a nice low energy orbit around Kerbin before re-entry.  Even then I melted my solar panels - but I was done with them anyway.
 

Overall I loved this challenge!  It really pushed me to think light and to design differently.  Thanks so much for coming up with it!

 

 

Edited February 5, 2017 by daniel911t
First post, I didn't know how to add pictures.

[Teilnehmer]

3 hours ago, Gordon Fecyk said:

The only thing I couldn't figure out was whether he skimped on LFO or Xenon to get the mass under five tonnes.

In the video, you can see the resource panel. I’ve taken away some LfO. I also could skimp on Xenon though — some spare Δv has left.

3 hours ago, Gordon Fecyk said:

And whether he considered Valentina's mass in the total launch mass. Apparently kerbals are massless until they exit various command parts, and then they're 80 kg with full EVA kit.

94 kg as MechJeb says. Yes, the Kerbal’s mass is included. The craft is 4.895 t in VAB.

3 hours ago, Gordon Fecyk said:

with full EVA kit.

Wow! I didn’t think about it. I could jettison the EVA kit fuel as I don’t use it.

Hm… What is the mass per unit of the EVA propellant? MechJeb reports no difference in mass between full and empty backpack.

 

Here’s my craft: https://kerbalx.com/Teilnehmer/Pshik

Edited February 6, 2017 by Teilnehmer

[Gordon Fecyk]

20 minutes ago, Teilnehmer said:

94 kg as MechJeb says

Maybe my Valentina lost some weight from all the hard work. Which is odd considering how much beer she drinks in my head-canon.  Using a service bay, seat and Val in EVA suit I get a difference of 0.09 t. But that's just the vessel info tab telling me that; it only has precision to 0.01 t.

I can confirm the game doesn't tell the difference between a full and empty EVA pack in mass. My 'kerbal scale' tells me 0.26 t before and after draining the EVA tank when it should be 0.24 t. That assumes the EVA propellant is a form of monopropellant and five units would have 20 kg mass. Oh well; must be one of those hammerspace things.

Now I'm curious: Can we figure out what the ISP of an EVA pack is supposed to be, based on how long it takes to drain and it having 600 m/s dV? I clocked it to be 3 m 20 s. In an ideal zero gravity frictionless space with massless propellant that seems like 3 m/s² acceleration, and the EVA article tells us this is actually 3.2 m/s² and a thrust of 0.27 kN. With the ISP we could figure out what the dry mass is supposed to be.

[Teilnehmer]

2 hours ago, Gordon Fecyk said:

I clocked it to be 3 m 20 s. In an ideal zero gravity frictionless space with massless propellant that seems like 3 m/s² acceleration, and the EVA article tells us this is actually 3.2 m/s²

Maybe, 3.2 m/s² is the maximum acceleration with almost empty tanks while 3 m/s² being the average?

If so, we know the dry mass:

m_dry = F / a_dry = 270 N / 3.2 m/s² = 84 kg.

I_sp = F Δt / (m_wet − m_dry) = 270 N ∙ 200 s / (94 kg − 84 kg) = 5400 m/s.
I_{sp g₀} = I_sp / g₀ = 5400 m/s / 9.81 m/s² = 550 s.

Too high!
Something must be wrong here.

Edited February 6, 2017 by Teilnehmer

[Gordon Fecyk]

This is getting fascinating!

23 minutes ago, Teilnehmer said:

I_{sp g₀} = I_sp / g₀ = 5400 m/s / 9.81 m/s² = 550 s.

Too high!

I think I'll take this to the Science and Spaceflight forum. This is getting way off topic for this Kerbin 2 flight challenge. Fascinating stuff otherwise.

[Natokerbal]

Can I use an SSTO?

[Zeiss Ikon]

7 hours ago, Natokerbal said:

Can I use an SSTO?

I don't know.  Can you?  I don't see anything in the rules that says you aren't allowed, and one entry used an SSTO to shuttle the lander to and from LKO.  Are you asking "Am I allowed to use a no-staging vessel for the challenge?" -- and if so, again, I don't see anything in the rules against it, though I don't see a category for 100% recovery, either.

[Natokerbal]

I think I will because it's an extra challenge and I like SSTO/Spaceplanes

[TopHeavy11]

One Question: Can I use MechJeb for all the modes?

[SpaceOdissey]

On 5 de febrero de 2017 at 6:15 AM, Teilnehmer said:

The Ultimate Level.

• 0.625 m parts only.
• Under 5 t of mass (4.989 t).
• No refueling.
• No docking.
• No Hyperedit, no autopilot mods (MechJeb used for info and node editing only).
• No debug menu, no cheating etc.

 

Oh wow... So you completed the Ultimate level! I'm impressed...

55 minutes ago, TopHeavy11 said:

One Question: Can I use MechJeb for all the modes?

You can use it but not in the Legend mod or the Ultimate mode.

On 6 de febrero de 2017 at 3:47 AM, Natokerbal said:

Can I use an SSTO?

Of course!