Heavy landing on Eve with only parachutes?

[DeepSpaceDutch]

After completing the Jool-5 I am going to attempt something I deemed to difficult for my amateur skills; doing a sea-level return from Eve So I'm going to try this with the thing I'm building shown below. The landing structure is still under construction and I'm wondering if I can land this ~275t monster with chutes alone? Adding breaking engines will really complicate everything, especially as I want to launch everything in one go... I know the atmosphere of Eve is thick, but is it thick enough?

[Mesons]

Sure, you can do it. You'll need to strap on quite a few 'chutes, though, and more importantly: perfectly level ground. The moment your first leg touches down, every single 'chute cuts. This caused my super-heavy lander to swing around and smash apart every time I landed on even a very slight slope (I'm talking just a few degrees). You'll be doing a lot of F9-ing. Just be sure to quicksave before you burn to enter atmosphere so that you can re-select your landing site.

[DeepSpaceDutch]

Sure, you can do it. You'll need to strap on quite a few 'chutes, though, and more importantly: perfectly level ground. The moment your first leg touches down, every single 'chute cuts. This caused my super-heavy lander to swing around and smash apart every time I landed on even a very slight slope (I'm talking just a few degrees). You'll be doing a lot of F9-ing. Just be sure to quicksave before you burn to enter atmosphere so that you can re-select your landing site.

Thanks! Good tips on the level ground, going to send a ScanSat ahead to be sure. I added a "few" engines to the lander structure, making it heavier, but providing around 0.45TWR for around 40s. Maybe this would be just enough to slow down in the last few meters?

[dzikakulka]

If we do not want to guesstimate, maths could be a little complicated.

But we can do the not-so-kerbal assumption that average drag coefficient for your whole ship is 0.2. It's cross-sectional area is 2200m^2 (because mass * 0.008).

Next thing to note is Eves gravity force on that monster - again, assumption at surface level: 4.6MN.

Eve's atmosphere density at 1500m = ~5.3kg/m^3 (please someone do it for me, I'm bad at this).

So let's say 6m/s is safe velocity. We want to have equal drag and gravity forces at 6m/s.

4600kN = 0.5 * 5.3 * 36 * 2200 * Dc

So our wanted drag coefficient is ~21.9.

Every parachute apart from drogue has 500 Dc.

(0.2*275000+(500*0.3)*y)/(275000+0.3y)=21.9 (y = amount of heaviest, mk3 parachutes)

So y = 41605.7. It's quite unexpected but I spent 10 minutes on this and I'd like to know where are the errors, anyone?

Edit oooh wait wait:

Back to drag:

4600kN = 0.5 * 5.3 * 36 * (2200+(0.3y)) * (0.2*275000+(500*0.3)*y)/(275000+0.3y)

y = 13 791 !!!

Edited August 22, 2014 by dzikakulka

[Superfluous J]

Without trying I don't know, but my gut says no.

I strongly suggest you run simulations with Hyperedit in a sandbox save. I ran dozens of tests with my eve lander and redesigned it through 4-5 major design changes each with lots of tweaks before I finally found one that worked for me.

Eve is not to be tackled lightly.

[DeepSpaceDutch]

If we do not want to guesstimate, maths could be a little complicated.

But we can do the not-so-kerbal assumption that average drag coefficient for your whole ship is 0.2. It's cross-sectional area is 2200m^2 (because mass * 0.008).

Next thing to note is Eves gravity force on that monster - again, assumption at surface level: 4.6MN.

Eve's atmosphere density at 1500m = ~5.3kg/m^3 (please someone do it for me, I'm bad at this).

So let's say 6m/s is safe velocity. We want to have equal drag and gravity forces at 6m/s.

4600kN = 0.5 * 5.3 * 36 * 2200 * Dc

So our wanted drag coefficient is ~21.9.

Every parachute apart from drogue has 500 Dc.

(0.2*275000+(500*0.3)*y)/(275000+0.3y)=21.9 (y = amount of heaviest, mk3 parachutes)

So y = 41605.7. It's quite unexpected but I spent 10 minutes on this and I'd like to know where are the errors, anyone?

Edit oooh wait wait:

Back to drag:

4600kN = 0.5 * 5.3 * 36 * (2200+(0.3y)) * (0.2*275000+(500*0.3)*y)/(275000+0.3y)

y = 13 791 !!!

Hahaha, wow, thanks!!

So it's friday night, I've had a few beers. But do I read this correct; y being 13791, that means I need that number of 500Dc parachutes?

- - - Updated - - -

Without trying I don't know, but my gut says no.

I strongly suggest you run simulations with Hyperedit in a sandbox save. I ran dozens of tests with my eve lander and redesigned it through 4-5 major design changes each with lots of tweaks before I finally found one that worked for me.

Eve is not to be tackled lightly.

I was actually thinking of that, never used HyperEdit though. Really want to try this first without doing that

[MarvinKitFox]

(0.2*275000+(500*0.3)*y)/(275000+0.3y)=21.9 (y = amount of heaviest, mk3 parachutes)

so:

dragC * (ship mass in kg), + paraDragC * (parachutemass in tons) times.... waitaminnit.

Shipmass in Kg, but parachute mass in tons? Or are you calculating needed kilograms of parachute?

in which case your answer is about 46 chutes

AHA

http://ksp.freeiz.com/ agrees with us. It states chutes needed as 45. (at 1500 m)

at sealevel, need is only 36

and if you willing to accept 10m/s, chutes is 13.

I suggest adding about 15 chutes, and a small few tons of seperatron retrobrakes, for the last 1 second.

Edited August 22, 2014 by MarvinKitFox

[SRV Ron]

Placing non returnable probes on Eve is easy. A parachute alone is enough. Planning on returning them not so easy. The ships are so large that they are prone to being damaged upon contact with the surface.

[dzikakulka]

So it's friday night, I've had a few beers. But do I read this correct; y being 13791, that means I need that number of 500Dc parachutes?

It probably means that someone better at math should come and do this all over again.

But if you don't mind modding you could insall RealChutes mod and use it's chute config manager. It has everything you need (you can write down numbers and then come up with a number for stock stuff).

@Marvin

Right, I'm dumb. But it still gives stupid stuff

[Pecan]

Since you've added the engines I highly recommend your chutes are drogues. They should slow you down so much that your engines are left with very little work to do.

[indroth]

I usually strap on some extra small fuel tanks and use my launch engines to soften the landing. You don't need a TWR of more than 1, so you can turn on just a few for landing if necessary, although it may be optimal to turn on as many as possible so you have a short soft landing burn. Obviously, solids need to stay off until you launch. As an added bonus you can attach all the landing paraphernalia (parachutes, landing legs, girders etc). to these tanks so everything is dropped on launch.

[Nori]

Did you try using RealChutes? AFAIK it will help you calculate what you need to do this...

http://forum.kerbalspaceprogram.com/threads/57988

[juanml82]

Remember that quickloading in the atmosphere will cut your parachutes, so don't rely on that. And getting the right landing spot will take several tries - Eve will try its best to destroy your engines the moment you touch down.

I might be wrong, but I think you should use drogues as well. My only Eve landing and return so far had plenty of those. You can also configure them to open earlier, at 5000 meters. All those struts should hold the lander together when the chutes open.

You might want to use winglets instead of reaction wheels to control your lander in Eve's atmosphere. They are lighter and good enough. My lander had an outer ring of RCS which I should have complemented with reaction wheels. I used it to maneuver in space and detached it before beginning the descend.

And remember to attach decouplers to the landing gear and the parachutes, so you get rid of them when taking off.

Finally, have you tried to put that lander into Kerbin's orbit? You have to do it without staging and the aerospikes won't let you attach anything below them. Any additional booster you may need to reach LKO will have to be attached radially.

[dzikakulka]

Okay, again, y = amount of mk16 chutes, all units SI:

Whole vessel mass: 275000 + 300y

Whole vessel cross-sectional area: 0.008 * (275000 + 300y)

Whole vessel drag coefficient assuming 0.2 for eveything araort from chutes: (275000*0.2 + 300*500*y)/(275000+300y)

Eve surface gravity force: 275000*16.7 = 4592500 =~~4600000

Eve density at 1500m: 5.3

Drag formula: Fd = [0.5] * [velocity^2] * [density] * [drag coefficient] * [cross sectional area]

Fd = 4600000 ->

0.5 * 6^2 * 5.3 * (275000*0.2 + 300*500*y)/(275000+300y) * 0.008 * (275000 + 300y) = 4600000

y = 39815

Please point out errors

Sources: http://wiki.kerbalspaceprogram.com/wiki/Atmosphere#Drag, http://wiki.kerbalspaceprogram.com/wiki/Parachute, http://wiki.kerbalspaceprogram.com/wiki/File:Atmosphere_kerbin_eve.png

[Kasuha]

In my experience, you need about the same amount of chutes on Eve as on Kerbin. Eve has greater gravity but also thicker atmosphere.

What you really need on Eve, though, is a good landing gear. If it can land on Kerbin, make it twice.

[KerikBalm]

*X*Question: Why are you using ASAS units instead of inline reaction wheels? those are heavier and provide the same torque.*X*

Nevermind, I see now that ASAS units are now .02 lighter, and produce almost double the torque.... I guess that changed in .24

The previous ASAS was inferior in every way to the Inline wheel, and was said to be kept in just so old designs weren't broken (back when you needed the ASAS module to get SAS to function)

Also, I question the use of SRBs beyond the first stage lifting from Kerbin.

I can't really tell from the picture... Are you landing a truss structure with those flat tanks with aerospikes on them to soften the landing, and then the ascent vehicle leaves behind the girders and such?

From what I think is your ascent vehicle, I wonder if the TWR is enough. Also, couldn't you save weight on your lander by getting rid of the "soft landing" aerospikes, and instead run fuel lines to the engines of your ascent vehicle?

Edited August 22, 2014 by KerikBalm

[MarvinKitFox]

Please point out errors

In your first calculation, you are correctly calculating the KILOGRAMS of parachute you need.

(not count, kilograms.)

[Galane]

My Eve lander and return vehicle is in here http://partsbyemc.com/pub/Eve-pack.zip Consider this pack interesting but mostly made obsolete by recent changes in KSP. The small lander on top of the drilling rover has been put out of balance by part mass changes in .24.x so it's now unusable. (Doesn't have any mono tanks anyway so docking it would have been a pain.)

The manned lander is based on a design I found on the old Spaceport. That one was much more spread out, included a couple of rovers and other things, and could only just barely bring one Kerbal in a chair back to orbit.

My much revised and compacted design uses six gas bags to lift to "launch" altitude (around 24K) so it can be landed at any ground level.

No reason to not share my design since it's based on someone else's design. I think I included operating instructions in the Zip for the lander. Should have a list of the mods needed. If not then...

Quantum Struts, Kethane+ unofficial 0.88.1 update, the old Stretchy Tanks/SRB (works fine with .24.2), KAS+ unofficial .24.2 compatibility update, ReStock Reloaded, Hooligan Labs airship parts, quite possibly KSPX and... not sure what else it might require for the whole set.

[Cerberus738]

This was my first attempt at landing a return vehicle on eve.... all that planning on kerbin and it bounced once on eve and fell apart. sadly i quicksaved right above the ground... not sure why i did that

I'm trying again with landing gears instead of the girder segments on the bottom. I expect they will absorb some of the shock during landing instead of just bouncing.

Edited August 23, 2014 by Cerberus738

[Mesons]

In my experience, you need about the same amount of chutes on Eve as on Kerbin. Eve has greater gravity but also thicker atmosphere.

What you really need on Eve, though, is a good landing gear. If it can land on Kerbin, make it twice.

Exactly my experience, and what I was going to suggest. This takes out all the unnecessary calculation, too. You want to try with a completely full lander too, so you could use the debug menu for fuel for your test.

[cantab]

Indeed, as I learnt from my low-tech Mun landings, the girders make bouncy legs. Much easier to touch down with real landing legs.

[einsteiner]

0.5 * 6^2 * 5.3 * (275000*0.2 + 300*500*y)/(275000+300y) * 0.008 * (275000 + 300y) = 4600000

Please point out errors

0.5 * 6^2 * 5.3 * (275000*0.2 + 300*500*y)/(275000+300y) * 0.008 * (275000 + 300y) = 4600000

0.5 * 6^2 * 5.3 * (275000*0.2 + 300*500*y) * 0.008 = 4600000

275000*0.2 + 300*500*y = 6027254

300*500*y=5972253.7

y = 39.82

The right side of the original equation really should include the weight of the parachutes themselves, but it only changes the answer a little (41.57 vs 39.82)

[Galane]

I tried several iterations using girders but they'd always break off. At the time, MechJeb was having a few difficulties with Eve landings such as not starting the suicide burn *quite* soon enough and a few builds wouldn't lower the gear until just before impact.