Physics Student

Reliable Eve Reentry and Ascent Vehicle

22 posts in this topic

Hi fellows!

I'd like to share a project I've been working on for a while now. I'd also like to hear your thoughts and opinions on it.

The Vehicle is called "EAV4" (Eve Ascent Vehicle for 4 Kerbals).

Mods with parts:

- Kerbal Engineer Redux

- Mech Jeb

- Build with Ven Stock Revamp installed, but only stock parts are used, so it should work without the mod)

 

It's pure stock now.

 

Craft File (just the spacecraft)

 

All in one Craft to launch from Kerbin

 

It's goals -in decreasing order- are:

 

- reliability (aerodynamic stabilizers and heatshield seperate cleanly, it doesn't wake the kraken)

- ease of use (it's always stable both on reenty and ascent, has a reasonable margin of error and lands on parashutes only)

- simplicity (no need of being refueled on the surface, reasonable staging setup, low part count Edit :cool:)

- versatillity (it should be able to ascent from anywhere on EVE)

- mass-efficiency 

- low tech level (the aerospike engines and the inflatable heat shield are the highest-tec parts)  Had to dump that one

- elegance (that's a matter of opinion, I find it rather beatiful)

 

Here  is a demonstration of it's capabillities.

 

It's designed to be propulsively captured by a transfer stage and then aerobrake into a circular EVE- Orbit. That's why it has the poodle stage on top. There's a probe core facing the other direction for doing that.

 

Edited by Physics Student
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Think you have some non-stock tanks there. I couldn't load the craft file in my stock game. 

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13 minutes ago, Foxster said:

Think you have some non-stock tanks there. I couldn't load the craft file in my stock game. 

The only non-stock parts should be the MechJeb and KerbalEngineer modules.

Maybe Ven Stocks revamb messes with the stock parts?

the only fuel-tanks are fl-T 100, 200 and 800

Edited by Physics Student

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1 minute ago, Physics Student said:

The only non-stock parts should be the MechJeb and KerbalEngineer modules.

What are the tank-like bits in the middle with the vertical stripes?

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8 minutes ago, Foxster said:

What are the tank-like bits in the middle with the vertical stripes?

those are fl-T800. Ven Stock Revamb changes the textures.

@Foxster I've just tested it in a near-stock install, it works for me.

 

 

Edited by Physics Student

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Some general stuff whilst you figure out what is not stock in the craft...

Dump the landing stuff before ascent: chutes, landing struts, antennas, solar panels, ladders, etc. 

Reconsider the use of Thuds, their isp is not great compared to, say, aerospikes. 

Streamline to the max. The biggest issue with Eve is drag, even more important than mass in many cases. You have some flat-topped tanks with chutes on them, think about disposable radial chutes instead. Also make sure you don't have any sticky-out bits like batteries, experiments, etc left on when ascending. 

Check if you really need all those fins. If you de-prioritise the upper tanks so they empty last it will help with stability and could mean you need less fins. 

 

Edited by Foxster

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Thanks a lot for your Ideas.

Pannels, ladders and radial chutes all detach before liftoff.

The Thuds have a bad ISP, Yes. I need them for their gimbal capabilities on the very first seconds after liftoff. If the vehicle is standing on a slope, they are the only thing that gets the rocket pointed towards the sky. they'll be detached as soon as we're flying straight. Do you have a better Idea here?

the big chutes are only on the boosters that detach first, so we don't have to carry them for too long. The ascent is very slow at this point too, so drag isn't such a big issue. We have nosecones on the other 4 Booster wich will be building up higher velocities.

Less fins? They're our only source of control after detaching the thuds. There is a reaction wheel on the upper stage, but that is too few control for my taste.

I must add safety to the list.

 

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If you keep the mass low then four smaller elevons at the bottom should give you enough attitude control after liftoff to get it flying vertically. 

But I think you are mostly there and I really like the idea of the four Kerbals scrunched into the shell. I've used two mk1 crew cabins before, be interesting to see how it compares to your rocket. 

One more thought: I tend to find higher TWR is best - you want to punch up out of soup as quickly as you can. 

What kind of lift profile have you tried?

Oh, just thought - how does your crew get in and out of the craft? When I've just been trying it through the walls of a deployed shell things tend to go badly. 

 

Edited by Foxster

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14 minutes ago, Foxster said:

What kind of lift profile have you tried?

TWR is quite low, between 1.2 and 2 in a stage, so I go up slowly, no more than 120 m/s on the first 4 boosters. I don't think drag is such a big issue here, but gravity losses are. The upper 4 boosters build up a bit more velocity (up to 400 m/s) and expierience max Q. They separate in pairs. When only the core is left, at 30 km altitude, I start the gravity turn. This stage sends us suborbital, the last stage has about 2200 m/s to circularize.

Staging:

-All spikes and the Thuds ignite

-Thuds separate just a few seconds after liftoff

-4 boosters detach (the 4 with the parachutes)

-2 boosters detach (the control surfaces help to get a clean separation, also they are arranged in a way to maintain full authority even on the last 2 boosters alone)

-2 boosters detach (and with them all active control surfaces)

-fairing sep

-separation of the Spark upper stage.

Edited by Physics Student

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Pre KSP 1.2 I used to go up to 25km or so before starting the turn, otherwise heatplosion was a serious risk. 

The atmosphere of Eve became a little more forgiving in 1.2 and starting as low as 10km can work now. The thing being to limit the AoA to as close to zero as possible, so keep the turn gentle and watch the AoA

You can learn a bit about efficient lifts by watching the GravityTurn mod fly the craft to orbit and see what it comes up with. I was surprised how the lift was not much like I was using and it found 100s of dV by orbit. Once I got some tips I then flew the missions manually. 

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6 minutes ago, Marschig said:

 

Try to add another inflatable heat shield on the top instead of wings. 

 

I tried that, it's less stable. The grid of wings has proven to be reliable, it keeps the craft pointed retrograde, even at 10g of deceleration.

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For giggles I just had a go at getting four Kerbals in chairs inside a shield to Eve orbit and came up with something weighing 26t that does it from sea level with ~400dV to spare...

onzd51x.png?1

2tGieti.png?1

olmgS2b.png?1

Forgive the oddly offset tanks to make it stable on the ground, was just quicker than messing about with landing struts. 

Edited by Foxster
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25 minutes ago, Physics Student said:

I tried that, it's less stable. The grid of wings has proven to be reliable, it keeps the craft pointed retrograde, even at 10g of deceleration.

Maybe, it depends from lander's design. On my lander second heat shield works well, even without SAS.

E6u8ZJM.png

 

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I'm more of an airbrake-spam type of guy. They are small(ish), lightweight and deployable. 

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59 minutes ago, Foxster said:

Forgive the oddly offset tanks to make it stable on the ground, was just quicker than messing about with landing struts

Your vehicle violates all criteria (except of being lightweight), but I'm properly amazed by what's possible in launch mass. Think I'll start again from scratch.

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Don't throw the baby out with the bathwater! You have a pretty good design going there. 

If you are going to work on minimisation then some important stuff I found is:

Reduce the drag and then mass (& dV needed) can be cut drastically.

Use the thinnest stacks and the smallest number of them that you can.

Use hardpoints rather than decouplers for less drag. 

Use the fewest engines you can. After 100s of Eve craft designs, I'd say that the optimal last stage is a Terrier and FL-T400. 

Shave every gram off the payload. Keep the shield small/light if you use one. 

Use throttle control to maintain prograde and 0° AoA. Don't just go full throttle all the way up. 

Pro tip: Off-setting parts (like above) does not increase their drag. Drag is set by initial placement (as long as you don't rotate the part). 

 

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I'm working on a new iterartion, this time in a new stock imstall.

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The craft has been updated. 

It's now 20% more reliable has 10% more delta-v and is 100% stock. It's now absolutely stable on reentry (no but- or be careful here and there, simply drop it through the atmosphere!) due to its new octagonal star stabilizer. Mass increased marginally and highest tech parts (vector) had to be used to improve safety on liftoff (You want to have gimbal on liftoff).

Edited by Physics Student

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