The planetary lander delivery challenge

[SLAMS]

Also I think I have a fully built stock hard lander/lift vehicle, total weight was around 290 tons(it was 260 but I overkilled it a bit). MechJeb can't fly but it works on manual. Unfortunately the Kraken eats it when I try to simulate an SOI change. Even then it takes forever to accelerate out of orbit...

[liorg1993]

I have the sneaking suspicion Aerospikes are going to get nerfed, they are just too powerful/efficient.

I don't think the devs will be taking out parts during this stage of development, it would break too many ships.

As for the 200-300 m/s fall, the chutes will probably be assisted with a powered descent(I will be using Mechjeb for the first few landings to learn when to throttle).

The Aerospikes are powerful and efficient enough to slow me down without wasting too much fuel.

[Apotheosist]

I have the sneaking suspicion Aerospikes are going to get nerfed, they are just too powerful/efficient.

Also Nova stated that chutes would only slow you to 200-300 meters per second on the desert planet. Which is faster than a dead fall at lower altitudes on Kerbin, so a better test would be a hard landing(no chutes), then add chutes for the actual mission to compensate for the lack of air resistance.

I agree with you that the aerospkies will probably get rebalanced, and I think they should be.

The chutes on the craft in the images can't slow it enough for a soft landing on their own, I always need to use some thrust. On the desert planet it would be the same sequence, just that I would require more use of the engines to slow down. I try to use the minimum of parachutes, and make most use of the engines that we already have. The parachutes are just to help control and regulate the descent, and they also provide a hint as to the actual height of the ground; the parachutes open 500m above actual ground level. This is a great help when trying to come to a safe landing using as little fuel as possible.

The lander part of my interplanetary ship as seen in the images weighs 75.6 tons, The first stage has about 3800 m/s of delta-v (very probably enough for the interplanetary burn and a powered descent on a planet's surface), then the rocket in the middle with the pair of SRB's releases, and it has enough delta-v in its two stages (three if you count the SRB's) to go to the mun and back when flown carefully, (about 7500 m/s delta-v, or less) which should get us home.

Edited August 28, 2012 by Apotheosist

[Markus Reese]

What I have been working on of late for at least atmospheric landings is fiddling with VTOL spaceplane landers instead of parachutes. Right now my biggest hinderance with the kerbin tests are the way landing gears keep settling into the surface of the planet. Going to be testing a new idea tonight by using two ships to travel with. This way I will only need to build an SSTO for getting off the planet, and the second ship will provide de-orbit burn. Guess I am going to have to practice my orbital interceptions.

[Nori]

Just in case you find it interesting, here are pictures of my interplanetary spaceship, which can go to the Mun twice.

http://imgur.com/a/a0MHt

Not a bad design, but you end up carrying around a lot of dead weight when the tanks empty. You could try mounting the engines on the side and stage the lower tanks when they empty. Would probably save you a bit.

Yeah the Aerospikes will probably get nerfed, sadly... I hope to make up for it they lower the weight of staging equipment. They are much to heavy IMHO.

To the topic creator. I like your lander, but I think you could design it a bit more efficiently which would make it easier to launch it. The landing gear for instance. Do you really need eight of them? Couldn't you mount four on the inner tanks? You seem to like having a lot of power, but that many engines ends up being wasteful. You'd probably be better off halving the amount of engines, which would still get you plenty of power. I just can't help but think that the small fuel tanks with the engines under them is wasteful. 200 fuel isn't going to go far for each engine and do you really need 2000 thrust? Remember that as you use fuel your weight goes down and you won't need as much thrust to land as to take off. If you want a weight to thrust ratio of 2 (more than that is wasteful) than you would only need 800 thrust for the weight of this rocket. Remove four engines and change the small tanks to large ones.....

Just some thoughts.

[SLAMS]

I agree with you that the aerospkies will probably get rebalanced, and I think they should be.

Agreed. That's why I'm not using them, to avoid a pending nerf bat.

I just don't see how you are getting so much more efficiency, have you moving to a higher Kerbol orbit in that craft to test a rendezvous?

Also you have no RCS and no control surfaces? Just a single ASAS that I can spot. How can this be controlled in orbit, or are you down to the lander stage at that point? Is your lift and Transition stage combined or do you shed all those 3M tanks and engines before transitioning to another orbit?

[Apotheosist]

Not a bad design, but you end up carrying around a lot of dead weight when the tanks empty. You could try mounting the engines on the side and stage the lower tanks when they empty. Would probably save you a bit.

@Nori, You may well have a point that I just can't see. I'm not quite sure I know what you mean about carrying dead weight. Or mounting the engines on the side and staging the lower tanks.

The tanks that the landing legs are attached to, make a wide, stable base for the lander. The tanks are usually close to empty by the time you land on Kerbin (or potentially, any other planet). This means you have a stable base to land on, which does not weigh very much for the job it does. This lander can land on both land and water without capsising, which is quite important for when you're ready to launch the return rocket. It's a floating launch platform if you happen to land in liquid.

[r_rolo1]

@Apotheosist

I think he means that the first stage has to carry a lot of empty fuel tanks for a lot of time and that you could probably optimize that with ease.

And your lander is nice. I would probably replace the 2 big chutes for 4 small ones ( for balance reasons ) and would find a way of not having those SRBs ( I really don't like SRBs ) but I like the design.

[Nori]

@Apotheosist

I think he means that the first stage has to carry a lot of empty fuel tanks for a lot of time and that you could probably optimize that with ease.

And your lander is nice. I would probably replace the 2 big chutes for 4 small ones ( for balance reasons ) and would find a way of not having those SRBs ( I really don't like SRBs ) but I like the design.

Basically what he said. Those tanks are 2 mass per when empty. You have 16 of them, so by the time the last of the fuel is out you are carrying around 32 mass worth of empty tanks. If you setup staging to get rid of 4 of them each time they empty you could get a bit more thrust out of the engines. It is a bit of a design problem though as it can be hard to mount the engines on the side. Just a thought on something to try.

@ liorg1993: I'm going to download your lander and see if I can't figure out a way to launch it. Sadly can't do that till I get home though.

Are you set in stone to use your lander exactly as configured or could I try tweaking it a bit (assuming it is still rather similar)?

[Apotheosist]

I just don't see how you are getting so much more efficiency, have you moving to a higher Kerbol orbit in that craft to test a rendezvous?

Also you have no RCS and no control surfaces? Just a single ASAS that I can spot. How can this be controlled in orbit, or are you down to the lander stage at that point? Is your lift and Transition stage combined or do you shed all those 3M tanks and engines before transitioning to another orbit?

I have not sent my ship into Kerbol orbit to test a rendezvous, but I'm confident it has the required delta-v.

Control is a little bit of an issue. The first version didn't even have an ASAS, and tended to rotate. So I added the ASAS and it helped keep the craft from rotating. It still requires patience to maneuver, since it has no vectored engines in that stage, only 3 aerospikes.

I am down to the lander stage once I am in Kerbin orbit. In fact the lander stage does some of the latter burn to orbit. It then also does the burn into Kerbol orbit and rendevous and landing on the planet.

My lift and transition stage is not combined, once I reach the surface of the planet and I want to come home, I shed those 6 3m tanks and two aerospikes and keep only The center part. The center part uses two SRB's, one Aerospike and one 3m tank in the first stage, then the 1m tank and small vectored engine. I should really show more pictures.

Here, these pictures show the lift and transition stage (return rocket) seperating and lifting off from the lander/launch platform. There is also an image of the SRB seperation. The SRB's provide a lot of power at liftoff, so there is no real need to thrust with the aerospike while SRB's are burning, or you will just waste fuel pushing through the atmosphere. http://imgur.com/a/qNRlq

[liorg1993]

@Nori: Feel free to tweak it it as you see fit.

@Apotheosist: I've been having serious issues launching your rocket into orbit.

It's common that rockets wiggle a bit during takeoff in the game but with your design any slight movement during separation of the outer fuel tanks would mean complete and utter destruction of the middle section.

[Apotheosist]

@r_rolo1, Thanks for the compliments on the lander, I also have always disliked SRB'S, Originally I just had two 1m tanks attached directly to the 3m tanks with fuel lines feeding the 3m tank. However, I needed to add the ASAS for stability, and after I did that it's thrust to weight at liftoff was too low, thus too inefficient for my liking. I considered adding more liquid engines, however I realised I could actually reduce the overall weight of the rocket, even with the ASAS, and have a high enough thrust to weight by using two SRB's. The small SRB's in this version are much better than in previous versions. They actually have a higher specific impulse than any liquid engine I think. They might need rebalancing.

@Nori, I know what you mean now. However this is just the way I design my rockets. As the fuel tanks empty, the thrust to weight increases gradually, which corresponds to decreasing air density as you move through the atmosphere. I'm not sure what help it would be to have more stages to drop more empty mass. By my design philosophy, in this current version of KSP the optimum number of stages to get to orbit is two or three.

@liorg, Yeah, I forgot to mention that it's best to shut down the core engine before seperating the six outer boosters, then gently thrusting away from them, to avoid them hitting your centre booster.

[Nori]

@Nori, I know what you mean now. However this is just the way I design my rockets. As the fuel tanks empty, the thrust to weight increases gradually, which corresponds to decreasing air density as you move through the atmosphere. I'm not sure what help it would be to have more stages to drop more empty mass. By my design philosophy, in this current version of KSP the optimum number of stages to get to orbit is two or three.

It is true that less stages are easier and sometimes more optimal (especially considering the game doesn't like big rockets). I think that might change in future versions though. Probably by making decouplers weigh less and empty tanks more.

Not trying to sound overcritical of your design or anything (hopefully you didn't take my comments the wrong way). I'm just curious how it would work with more decouplers and a higher center of thrust. Everyone has different design philosophies; I personally dislike carrying around empty tanks any longer than I have to. But like you said, the game in its current state does favor lesser stages.

But in any case I'm gonna download your craft file and see if a few more stages ends up making it more efficient or not, just for fun. I do really like your lander design and I don't know if I ever would have thought of SRBs that late in the game. Definitely different thinking which is cool!

Man, so many things to try out when I get home now.

[Apotheosist]

Not trying to sound overcritical of your design or anything (hopefully you didn't take my comments the wrong way). I'm just curious how it would work with more decouplers and a higher center of thrust. Everyone has different design philosophies; I personally dislike carrying around empty tanks any longer than I have to. But like you said, the game in its current state does favor lesser stages.

Fear not, I did not think you were being overcritical. I am actually very welcoming towards criticism, it helps me get new angles and ideas on things that I could not have thought of on my own. I also try to give constructive criticism to other people on their ideas. Sometimes people do take it the wrong way, but I never mean to be derogative, so when someone gives feedback and constructive criticism to my designs, I am sure they dont mean to be derogative either. It is a good way to learn from one another.

I am also curious as to what differences would be caused by adding more stages and such, and I like to theorise about these problems mathematically. I'm currently on half of a little investigation into staging, and what effect it has on delta-v compared to the weight of the overall rocket. As you said it depends on the relative weight of the decouplers and the empty tanks. Too many stages and the rocket gets heavy with decouplers. Too few stages and you end up carrying too much weight in empty tanks. It would be nice to have an equation which tells us how many stages we should have to maximise delta-v from a given mass. So that's what I'd like, but I think the maths might be above my level

[Nori]

Well I'm hoping they will decrease the weight of decouplers to give incentive for more stages... 0.5 for the large decoupler is crazy heavy...

@liorg1993: So I played around with your lander quite a bit and got a design I like. It is still very similar to your initial one however. I also managed to launch it into a 75k orbit while barely touching the lander's fuel. It isn't quite perfect yet though. I ran out of time to finish tweaking it, for instance I am thinking about replacing the first SRBs with the larger 400 thrust ones as that first stage has a low thrust to weight ratio...

So this design mostly meets your criteria. On my computer the first two stages do kill the FPS a bit, but those are discarded before you get to 5k anyway, so shouldn't be a issue. The rocket is very symmetrical and stable, so you can just hit "T" and full throttle ahead.

I tested it and I can get to the Mun and land (well I didn't have time to land, but I sort of crash landed and had enough fuel) before the outer lander tanks run empty. Then you dump those on take off, orbit the Mun, transfer to Minmus, land there (notice the second set of lander legs?) and you should have plenty of fuel to take off and land on Kerbin.

Lemme know what you think and if you have any ideas for tweaking the stages to be a bit more efficient.

Edited August 29, 2012 by Nori

[Apotheosist]

@liorg1993, I have also tried modifying your Lander, and I'm quite pleased with the result. I called it "Heavy Lander Lite". I could have started from scratch, but I wanted to keep it as similar to your original lander as possible, while drastically reducing it's weight. The last stage is unchanged, but I have changed the stages before the last. Where you had two stages, I have replaced them with a single stage. This single stage consists of 6 FLT-400 fuel tanks, 6 parachutes, four landing legs and two aerospike engines. Your original lander had a mass of 41.43 tons, the redesigned version has a mass of 23.38 tons. Using only the aerospikes in this stage is more efficient because they have a higher ISP. Even using only the aerospikes this gives a thrust-to weight ratio on Kerbin of 2.18, which is easily powerful enough. I read somewhere else on the forum that the optimum thrust to weight for atmospheric flight is 2.

The mass ratios of the Heavy Lander and the Lite version are almost exactly the same, I think less than 0.5% difference. This suggests that (ignoring any fuel bugs) they should have the same delta-v. However if you're only using aerospikes as I mentioned, it actually gives more delta-v.

The Lite lander uses four large parachutes and two small parachutes for landing. This was to fine tune the descent speed as close to your original lander as possible. I measured the descent speed on the heavy lander to be 8.2m/s at touchdown, the lite version only 0.1m/s less at 8.1m/s.

It should be considerably easier to build a delivery rocket for the lighter lander. However I would like to try out Nori's design.

@Nori, I could check this myself, but do you know the mass of your redesigned lander?

Ship: http://www./?bz4yia520osvxc9

Pics: http://imgur.com/a/7WHOA

[Nori]

Sorry don't know off the top of my head. It is probably very similar to his original weight, maybe a wee bit more. Like I said in my prior post I ran out of time designing last night, so I didn't get a chance to get screenshots or put in more info.

If I get time tonight I'll probably tweak it a bit more and I still want to look at your two designs.

Just looked at the pics; that is a nice looking lander!

[Oggula]

Pretty sure that baby is far too wide to launch without being top heavy and unbalanced, not to mention the staging is quite inefficient. My lander is also 40 tonnes, but is much taller and narrower. https://www.yousendit.com/download/TEhVblRwQk5RWUtKUmNUQw

[Nori]

Pretty sure that baby is far too wide to launch without being top heavy and unbalanced, not to mention the staging is quite inefficient. My lander is also 40 tonnes, but is much taller and narrower. https://www.yousendit.com/download/TEhVblRwQk5RWUtKUmNUQw

Are you referring to the topic creator's lander?

[EndlessWaves]

Here's my attempt at creating a launcher for you. [ATTACH]32179[/ATTACH]

I did modify the lander slightly, fixed ladder replaced by folding, un-needed brace and nosecones removed and landing legs placed on the inner tanks instead of the outer ones. The landing legs still extend further than the outside tanks so I really can't see it causing any stability issues short of a 50°+ slope.

I don't know if you've flown a jet engined rocket before but the engines do take time to spool up so you need to start the engines, wait six seconds or so and then hit space to release the clamps. Unfortunately this design turned out to be almost precisely the right amount of jet fuel and second stage power so you need to be fairly precise on launch or you won't get clear of the first section of atmosphere and the second stage aerospikes won't be able to keep lifting. If you get it right they'll only drop down to around 30m/s before they start accelerating again. There's probably 3-4 seconds either way of the perfect release point so it's not sensitive enough to be a pain, just something to be aware of.

The jets do get up to fairly high speeds by the end of their run so if you've got mechjeb flying it then you may be able to get it up more efficiently than my ham-fisted manual piloting.

Stick ASAS on at the launchpad and it'll fly itself for the first and second stages. I did get some pogo-ing once it was in space (despite telling your kerbals not to taunt the Kraken) but on my three test runs it never fell apart. It's somewhat unwieldy in space and I didn't want to put RCS on your lander as you'd left it off so placement wasn't optimal but I did have enough fuel to wrestle it into an orbit and get approximately 1,100m/s of DeltaV after that before the final stage of the launcher was discarded and your lander was free to fly.

It does have an aerospike for the final engine but it could probably be switched to the most efficient one to get a bit more D/V. The strutting was done on an as needed basis but I think I ended up with a reasonable number. Changing the turbojet fuel tanks might also save you a bit of weight but I did it 'properly' (jetfuel for jet engines) in case 0.17 makes them specific.

[liorg1993]

@EndlessWaves

I'm sorry but I'm not gonna be home for the next two days and won't be able to test out your rocket.

I'll be home Friday evening and I'll try to test it then if I find the time.

[Nori]

@EndlessWaves. Dang that is a lot of jet engines..

[EndlessWaves]

@EndlessWaves. Dang that is a lot of jet engines..

3 sets of 3 at 6x symmetry, so 54 of them. Now you've pointed it out it does seem rather a lot, that's 8100 thrust for 300-350 tons of rocket so it may well work with only 2/3 of the jets.