See Space on a Single Engine!

[antbin]

I'm surprised you got so little DeltaV out of it, that thing looks like it should go for miles.

In my experience, half tanks aren't worth using decouplers/fuel lines. Consider an empty half tank weighs 125kg . The decoupler and fuel line weigh 75kg! It's almost worth dragging around a half-empty larger-size fuel tank than boosting the decoupler and fuel line in the first place...

Endlesswaves, rule clarification - do you have to lug 4 tons extra cargo for the the 3-in-1 award, or is Accelerando just playing on hard mode? If so, do you have to lug the 4 tons cargo with you the whole way, or can you leave it in Kerbin orbit?

Edited October 12, 2012 by antbin

[r_rolo1]

I also got to Duna and Laythe with my Afrodite IV ( I have done it wednesday, but was too tired to post ) ...

( sorry for the Laythe first pic but I got a case of invisible water P.S I also have a slight modified version of Afrodite IV in the Duna case ... I just added two extra parachutes. I wanted to see if I could send this back from Duna, so I needed to save a parachute to the eventual Kerbin return ... unfortunately the ship came short in terms of fuel :/ )

As you can see in my Duna landing pic, I had enough fuel to do a return trip if I wanted to if I had not landed ...

On the Duna landing and return ... it is tricky. The best engine for this challenge, the aerospike, can launch about 10 tanks of the 400 l fuel variety from Kerbin surface. That would be sufficient with ease if:

a) We had no Atmosphere in Kerbin and Duna launches ( and still have it for the returns )

We didn't had to correct a lot to get into Duna SoI.

The biggest issue is the Kerbin atmosphere at launch, since it will eat you more than 2200 dV even if you do as much of a perfect ascent as possible. You will lose also around 150 dV to Duna atmosphere when you get out of there, no matter what. And even if we spend extra 150 dV correcting to Duna and Kerbin SoI after launches ( that , besides being both small, also has the issue of the Duna orbit not being perfectly circular and plane aligned with the Kerbin one ), a very conservative estimate, that makes for at best a very tight fit on the dV 10 tanks and a aerospike can give. I've tried two days ago a 9 1/2 tank version and it came short for about 200 dV ( it lacked 80 dV to get a Pe in the Kerbin orbit in the return from Duna )

Edited October 12, 2012 by r_rolo1

[EndlessWaves]

antbin: Fuel lines are currently weightless I believe, despite what the tooltip says.

For Three in One you need a total payload of 4 tons, so either the mk1-2 capsule on it's own, the Mk3 capsule with extra weight or a one person capsule and mods for extra kerbals like the crew tank.

It does need to be capable of landing so if there's any doubt about stability/fuel I'll ask for screenshots but if you decouple 3 tons in low kerbin orbit then take the remaining 3 tons of ship to Duna then you clearly could have landed the whole thing on kerbin.

I've tried two days ago a 9 1/2 tank version and it came short for about 200 dV ( it lacked 80 dV to get a Pe in the Kerbin orbit in the return from Duna )

What about using slingshots around The Mun, Minmus or Ike to save a little? Alternatively Gilly might be easier, and touching down the kerbal without the ship is perfectly acceptable.

[r_rolo1]

In that try I made I actually used 3(!) Ike slingshots when coming down to Duna ( actually that was mostly luck in the first encounter, but the other two were planned ) and that probably saved me 50 dV. IMHO that is far from enough ...

I think it is possible, but the real caveat is the Kerbin drag at takeoff. I think it is possible to snag out some extra dV if I do the ascent just right ( I am currently not that happy with the +/- 4900 dV I'm spending to get to a 70*70 km orbit ... if I could just reduce it to , say, 4700 ... ). I think it is possible to also tune up the Duna ascent a little and with some luck also get a nice Duna encounter without spending 100 dV correcting to get there after leaving Kerbin SoI. But I'm pretty sure it will be a "on fumes" trip even if it works

On Gilly ... problematic as well, because you would need to get to Gilly and circularize it to be able to to a EVA landing, and you can't rely on a atmosphere to slow you down. With some luck, you might get a slingshot from Eve, but I wonder how much dV you would need to circularize after that ...

Edited October 13, 2012 by r_rolo1

[antbin]

Inspired by Mango, I present the Durian B!

Uses Protractor, Kerbal Engineer, and MechJeb add-ons (for flight information). I confess to using SmartASS to hold prograde / radial headings, and the Landing autopilot for aerobraking predictions. Did not engage the ascent/landing autopilot, though.

Managed to fly it to Duna and back with 2/3 of the crew... Shernard cratered while trying to jet-pack down to the Duna surface.

<iframe class="imgur-album" width="100%" height="800" frameborder="0" src="http://imgur.com/a/ha2ic/embed"></iframe>

Edited October 13, 2012 by antbin

[joshblake]

Hi,

This is my first post here.

I was actually working on minimal rockets a few days ago, so I'm going to enter my "Min Orbit Ic" rocket. Achieve a minimum 70km x 70km orbit. I'm going for these distinctions:

• Minimalist record (8.7 tons per flight engineer, 8.6 per Mechjeb)
  
• High Efficiency award
  
• Safety Last award
  

Bill Kerman was next in line to pilot and he's, well, not very good, so MechJeb pretty much ran the whole flight. Only add-ons used were MechJeb and Kerbal Engineer Redux.

<iframe class="imgur-album" width="100%" height="550" frameborder="0" src="http://imgur.com/a/VqHym/embed"></iframe>

On one of the early test flights, I had a dock collar and parachute as well and the landing back at KSC runs out of fuel at an altitude of 2m, so it literally was empty when it landed. (No parts destroyed by the drop.) After removing those I have a little extra fuel remaining but not much.

[r_rolo1]

Nice, but I'll try to beat it Anyway, good thing to have nerves of steel for a powered landing in Kerbin: I've done it to exaustion as training and it is not easy even with Mechjeb if your fuel budget is short.

[EndlessWaves]

Welcome to the forums Josh, and congratulations on the minimalist record. I think you might have to go for an unpowered landing to get smaller than that.

At least bill didn't get chucked out of the airlock like Shernard, had he slowed down to terminal velocity or was he still decelerating when he hit? I do like the ship design though.

r_rolo: Yeah, 4900 does sound a little high. It might be worth tinkering with mechjeb's flight path a little.

[antbin]

Wow, tidy design Josh. Reminds me of Kosmo-Not's mini-mun ships from back in 0.15. I don't see how that minimalism can be beaten, the only weight savings could be taking one half-tank off... can 2.5 tanks even make orbit?

Shernard jumped out the airlock, he was trying to cover his gambling back home on mission Exceptional Achievements. It seems possible to jetpack to the Duna surface, but I was far too impatient and didn't keep him aloft long enough to kill his horizontal velocity. Also, I swear he landed on impacted an uphill slope, Duna is hilly!

The Durian is 151 tons, almost as heavy as possible to lift with 1500 thrust. It uses zero struts, just the 3m-to-1m adapter that's wide enough to hang 6 big tanks and angled for stability. I'm amazed Accelerando got 159 tons off the pad without drifting into the launch tower!

Edited October 14, 2012 by antbin

[joshblake]

@antbin Thanks! It turns out that with 2.5 tanks (half tank in center, same design otherwise) you can get to orbit, but you can't get back to KSC or do a powered landing. This requires adding a parachute, which will actually hold the whole last stage; however, the additional parachute weight mean you can't get to orbit!

@EndlessWaves: Thanks! Due to the parachute weight and how the stock tank sizes work out I think powered may be the smallest that can fulfill the requirements.

@r_rolo1: Good luck!

[EndlessWaves]

What about a pair of winglets? At 0.02tons each the pair are only 40% of the weight of a parachute so they may allow you to get into orbit and slow you down enough for a survivable landing. Mechjeb's default settings also aren't perfectly efficient so you may be able to optimise the ascent profile a bit.

Wings will also allow you to get off the ground with less than 10 kilonewtons per ton so 200 tons on 1500 thrust can definitely get to 10-15km. Whether you can get the efficiency high enough to have enough fuel to make orbit I'm not sure. I've tried a couple of times myself but I was probably a bit ambitious and didn't bring enough thrust to make orbit above the atmosphere.

Edited October 14, 2012 by EndlessWaves

[r_rolo1]

I *think* it might be possible to do with with 2,5 tanks, but it might require manual landing (MechJeb does not burn optimally in landings ) and a carefully crafted ascent. Atleast that is what I'll try ( oh and with a diferent kind of of rocket than joshblake )

[r_rolo1]

As I do not like to lie, here is Suicide I

<iframe class="imgur-album" width="100%" height="550" frameborder="0" src="http://imgur.com/a/r4Mze/embed"></iframe>

Actually the fuel came short in the landing ( last second possible activation of the Mechjeb land button, just because it is faster to throttle up than my fingers mashing the keyboard ), but I was already pretty close of the floor and the ship did not gained enough speed to smash the engine ( I was already " back into the drawing board in how to save alittle more fuel" when the fuel failed, but as it worked ... ) ... I guess that you can create the "Lucky as hell" category for this one *lol*

I used Mechjeb ( duh ) and the protractor mod ( that one was mainly out of force of habit, but also to track the dV I was spending in flight ). I do think you can get slightly more effective in the ascent, circularize a little lower and spend less fuel in the return by aiming at a higher Pe and spend a lot of time aerobraking until coming down, but I'm quite skeptic that you can use less fuel tanks ...

Do someone wants the craft file? I think that the staging is self evident from the first pic ( 2 opposite half tanks drop each stage until you get to the central stage, that is only a half-tank, the capsule, a aerospike and Mechjeb + protractor. Fuel lines are similar to my Afrodite series ones, that is, asparagus-like ( not asparagus because I only have a central engine though ) ) , but if someone wants it, I'll post it.

Edited October 15, 2012 by r_rolo1

[joshblake]

rolo: Nice. I see you used the good luck I wished you! One of my versions (Min Orbit Ib) uses the same tank layout. IIRC I was able to do a safe powered descent with that configuration; however, the total mass and drag is slightly higher due to the extra radial decouplers and dropping the half tank dry mass earlier doesn't make up for it. For this challenge, minimum mass rules so I went with the simpler configuration.

[zarakon]

Is there some trick to getting these aerospike engines to actually attach to the rocket? Sometimes it works just fine, and sometimes they refuse to go on..

[r_rolo1]

They are tricky to attach but I have two tricks that work relatively well:

1) Put landing legs at the side of the tank you want to attach the aerospike. Does not work always.

2) The more complicated one: mount tanks radially from something, check if any of them will attach the aerospike , reduce the symmetry to 1, attach the aerospike to one of the tanks that greened out before, remove that tank+ aerospike and them put it where you want it.

@joshblake

I think that real deal here is to know how to do maximize your power landing fuel and I even I jumped the boat on this one and started burning a little early ( otherwise the fuel would had been enough ). I already had done a lot of tests on that for other challenges and I know that the terminal speed in Kerbin for most ships is around 130 m/s. Knowing that, the altitude you were going to land ( I landed a little too high for my taste, but I was only testing out ), the TWR at the time and the aerospike thrust and ISP, it is relatively easy to know exactly when to push the burn button ... in my case it was somewhere around 500 m from the surface. My problem was that I mashed the button at the moment I saw a 5 appearing in the mechjeb altimeter first digit and not when I saw 500 , so the fuel ended up when I was 10-20 m from the surface :/

BTW i do not think that the issue is dropping the dry mass but with dropping the dry mass sooner .That is what makes it worthwhile to use half tanks instead of full ones in this kind of drop tanks configurations: you carry dry mass with you less time thus you save some fuel because of that. OFC there is a limit but IMHO in this small ships the dry mass is such a big contributor to your fuel spendings that the extra initial mass of the decouplers is not enough to shade it up.

[EndlessWaves]

Is there some trick to getting these aerospike engines to actually attach to the rocket? Sometimes it works just fine, and sometimes they refuse to go on..

Yeah, they can be a bit of a pig. Attaching them to something else first can help, as can trying them on the other end of the fuel tank and then rotating the whole arrangement.

r_rolo: You definitely qualify for the safety last award for that flight, as well as minimalist of course. It's amazing how little fuel you need to land on Kerbin, that might be an interesting challenge in it's own right.

Has anyone experimented with the little engine yet? It looks like it should lift off upwards at around 660-670L of fuel but it's half a ton lighter so you're lifting 1.3 tons of engine and capsule instead of 1.8 tons.

[r_rolo1]

You mean the LV-909 ? For the orbit and back it might just work ... The issue is to get a TWR of atleast 1 It also has the issue of underperforming in high atmospheric pressures, unlike the aerospike ...

P.S On the fuel needed for a kerbin landing ... well, as I stated in a not so clear fashion above, you need around 130 dV to do it ( or in other words, you need enough dV to cancel your terminal velocity ... supposing that you're falling in oblique enough angle to make the aerobraking matter ) + whatever fuel you need to put you in a low enough Pe to get enough atmosphere for braking ( as you can see , I used about 40 dV for that ). That means a surprisingly small ammount of fuel if your ship is light enough and if your engine does not choke in High atm pressures. You can actually do it on RCS only fairly easy if your comp does not choke near kerbin ( like mine does ), but you'll need more than one nozzle for that ( hence making it unfit for this challenge ) and you will have to that manually ( mechJeb RCS management is simply terrible )

Edited October 15, 2012 by r_rolo1

[joshblake]

Rolo: Good points. I'd like to explore this further but don't want to thread-jack this thread. If you started a new challenge thread around minimizing fuel usage to get the specific craft (your half-tank craft) to 70x70 orbit then land back to KSC, I'd participate.

I did experiment with different ascent profiles within MechJeb and manually, but didn't find any that were more efficient than the default ascent autopilot settings. Not saying that there aren't, but I was focusing on repeatable MechJeb flights, for science.

Your technique of mashing the throttle at the last minute sounds like the Soyuz "soft landing" breaking engines which fire at a height of 1m. Of course, Soyuz is under parachute at that time.

[r_rolo1]

For that launch in particular I used 10km to 45km in the Mechjeb ascent autopilot, with the aim of 72 km ( it helps having some leeway ). I do not recall if I made any corrections on the gravity turn in it self, though ...

[antbin]

If you started a new challenge thread around minimizing fuel usage to get the specific craft (your half-tank craft) to 70x70 orbit then land back to KSC, I'd participate.

Me too. The old "Max altitude with the supplied spacecraft" thread generated a lot of insight into how to be a better rocket scientist.

Since minimalist spacecraft tend to be pretty optimal/unoriginal (there's only so many ways to arrange 3-5 tanks and one engine) might as well make the challenge about flying skill rather than design.

[Kanharn]

My Ion ship the Dragonfly can make it to almost any planet and return home safely. I also use it to ferry Kerbs to my World space station and Mun research center.

I know I actually mixed up a few of the rules on this challenge but I thought it warranted a post.

Edited October 16, 2012 by Kanharn

[MInecraft]

How to win this|press ctrl alt shift D

[joshblake]

I think that real deal here is to know how to do maximize your power landing fuel and I even I jumped the boat on this one and started burning a little early ( otherwise the fuel would had been enough ).

Alright! I pulled up my half tank ship and modified it to have a half central tank rather than a full. (So basically identical to yours.) I also spent time refining each stage of the mission - launch, deorbit and aerobraking, and landing rocket, flying manually except when MechJeb really does a better job.

Results - with a 7.5 ton ship (2.5 tanks - 1000 liters of fuel, starting delta-v of 3987 m/s), I achieved 71x71 orbit, then immediately did a minimal deorbit burn and used almost a complete orbit of aerobraking, and landed safely back at KSC with 7.27 liters of fuel remaining, or 72 m/s of delta-v remaining.

This should either tie me and r_rolo1 for minimalist, or put me ahead slightly if you account for the unused fuel.

or it didnt happen...

<iframe class="imgur-album" width="100%" height="550" frameborder="0" src="http://imgur.com/a/vdWh1/embed"></iframe>

This included two very small (2 m/s, then 1 m/s, total of 0.35 liters together) course corrections. The pics account for all uses of fuel.

The landing was near perfect. I took screenshots just before and just after firing the landing rockets. I fired them by hitting the MechJeb Land button. (MechJeb was off during re-entry except for the course corrections.) Below a critical altitude, MechJeb Land will immediately fire full throttle until achieving the desired touchdown speed, then target coasting in at touchdown speed for the last few meters. That takes too much fuel, so I figured out I could mash the land button at an altitude of about 50 m and the full throttle with the distance remaining slowed me down enough. Once touching down, MechJeb cuts the throttle so I have remaining fuel.

Doing the maths - the before photo shows my vertical speed as -108 m/s with 194 m/s of delta-v (with engine off prior to landing rocket.) The after photo shows me landed with 72 m/s delta-v remaining (with engine off after landing rocket shutdown.) The ideal landing would fire full throttle at the last moment with just enough time to reach a safe* velocity right at the ground. In my case, I used 194 m/s - 72 m/s = 122 m/s in between those two screenshots, arresting approximately 108 m/s of velocity. I suspect that I hit it slightly earlier than I could have and MechJeb coasted for a moment, resulting in the 14 m/s of excess fuel wastage.

* Safe velocity meaning velocity which the rocket can withstand hitting the ground without destroying anything.

I did try hitting the LAND button later, attempting 40 m altitude, but either that is too low, I hit it late, or the game glitched, and I destroyed everything except the capsule and MechJeb!

Took a bit earlier than the landing (1km altitude) but Jebediah is a cool cucumber.

Oops, burned the rockets too late and destroyed most of the rocket. Jebediah is a bit upset, but any landing you can walk away from...

This landing mechanism would make for a good add-on or enhancement to MechJeb.

Edited October 16, 2012 by joshblake
fixing image gallery

[r_rolo1]

Congrats, joshblake I do find your ship design familiar for some reason though I told you that was possible to land with some fuel in stock with that design. And also congrats on landing in KSC 1.

About that landing method ... well I basically developed it in a challenge in 0.16 to land something in Kerbin that wasn't supposed to be able to land ( that is, no engines, no parachutes, no landing legs and no flat bottom ) for the tests. That is how I know, among other things, what is the terminal velocity of most things in Kerbin It is a very unforgiving method, though, as you learned, and it delivers some quite high g forces.

Now, back on going to Duna and back. It's proving to be quite harder than i thought