Reinhart Mk.1

If I ever make it back from Eve

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9 minutes ago, herbal space program said:

Eve's atmo [...] drops off much more steeply above 25km

On the contrary. It remains comparatively soupy until very high up, then drops sharply (all non-Kerbin atmospheres do, btw). Head over to the wiki and don't just look at the shape of the plot, but check where the 10² and 10³ markers actually are.

However, while important in terms of heat and drag losses, I don't think this has a practical effect for terminal velocity. You can brush up against that in the lower atmosphere, much longer and harder than you would on Kerbin, but beyond 15, 20km -- pfffrt.

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26 minutes ago, Laie said:

On the contrary. It remains comparatively soupy until very high up, then drops sharply (all non-Kerbin atmospheres do, btw). Head over to the wiki and don't just look at the shape of the plot, but check where the 10² and 10³ markers actually are.

However, while important in terms of heat and drag losses, I don't think this has a practical effect for terminal velocity. You can brush up against that in the lower atmosphere, much longer and harder than you would on Kerbin, but beyond 15, 20km -- pfffrt.

OK, perhaps I didn't say that quite right. I guess what I meant to say that the slope fro Eve is higher overall, which means that TV increases more quickly with altitude there than on Kerbin, and that this is especially felt in that 20-30 km band on Eve, where TV increases quite sharply from something within your likely range of velocities to something beyond it. IOW, to strictly maintain TV through that band, you would have to accelerate faster than the likely TWR of your rocket. So if you're making a practical rocket, the best way to offset that is to exceed TV earlier in  your profile so that you can stay closer to it when it starts to rise really fast. I think that's it anyway. How else do you explain the good dV-to-orbit performance of these TWR >3 rockets?

 

 

Edited by herbal space program

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Yeah, just did a quick check: on my not overly pointy rocket shown a few pages back, MJ reported a terminal velocity starting at 200, creeping to 300@5km, and just when I thought I might be getting there the figure ran away: then 600@10km and rising fast, 3km/s by 30km.

Certainly none of my rockets is at any risk of reaching terminal velocity at any time.

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34 minutes ago, Laie said:

Yeah, just did a quick check: on my not overly pointy rocket shown a few pages back, MJ reported a terminal velocity starting at 200, creeping to 300@5km, and just when I thought I might be getting there the figure ran away: then 600@10km and rising fast, 3km/s by 30km.

Certainly none of my rockets is at any risk of reaching terminal velocity at any time.

Wow, I thought that would have been closer to TV on Kerbin at those altitudes.  I just did a quick check on my rocket, and assuming it's roughly like yours TV-wise, I'm getting close with mine at some points but not actually exceeding it anywhere. Who knew? Moar boosters it is then!

Edited by herbal space program

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you guys have helped out so much, when i built my first lander i had no idea how faulty it was. anyways last night i was too tired to do any kind of aerobrake so lets see how this one goes. i still have yet to actually LAND my lander, still stuck on the rentry but i think its mainly due to impatience

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Distract yourself with your phone, you'll need that, a safe aerobrake atitude is around 70 km (at least for that direct ascent lander).

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18 minutes ago, GRS said:

Distract yourself with your phone, you'll need that, a safe aerobrake atitude is around 70 km (at least for that direct ascent lander).

i actually forgot this from all the designing so thank you hahah

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Remember, you generally also need a 10m heatshield at the back end (relative to entry direction) to keep it from flipping. I ended up using airbrakes, Vernors (ok, I probably didn't actually need those), and an inflatable heat shield to keep my beast hot-side-forward.

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8 minutes ago, StrandedonEarth said:

Remember, you generally also need a 10m heatshield at the back end (relative to entry direction) to keep it from flipping. I ended up using airbrakes, Vernors (ok, I probably didn't actually need those), and an inflatable heat shield to keep my beast hot-side-forward.

What I found was important with those back-end shields was to mount them pointy side-up, because they really like to flip if they are the other way around, even if they are at the back end of your ship.

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45 minutes ago, StrandedonEarth said:

Remember, you generally also need a 10m heatshield at the back end (relative to entry direction) to keep it from flipping. I ended up using airbrakes, Vernors (ok, I probably didn't actually need those), and an inflatable heat shield to keep my beast hot-side-forward.

after several tries and a few "strategically"placed reactin wheels i'm now in orbit of eve with an AP of 6m, everything's going well so far, these nuke engines are helping lower the AP alot quicker. about to start aerobraking with the 4 vectors this huge fuel tank. wish me luck AGAIN :confused:

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No worries, Eve is Pain for the first time, Get Hyperedit for testing purposes.

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7 hours ago, Laie said:

Yeah, just did a quick check: on my not overly pointy rocket shown a few pages back, MJ reported a terminal velocity starting at 200, creeping to 300@5km, and just when I thought I might be getting there the figure ran away: then 600@10km and rising fast, 3km/s by 30km.

Certainly none of my rockets is at any risk of reaching terminal velocity at any time.

So I decided to do a little Hyperedit  drop test from 10 km  with my own, only slightly pointier but much bigger lifter, and I discovered to my gratification that my TV looks to have been around 330 m/s at SL:

2UmRvHv.png

 

0QeE2EM.png

 

Note that the speed barely changes between 1.7 km and impact, indicating this free-falling craft is at/near TV. And I didn't even bother to stage off the side stacks. That tells me two things: 1) That bigger ships do indeed have less drag/mass than smaller ones in this game, i.e. the big tanks really are better, you just have to get creative about spamming engines onto their undersides, and 2) If I want to get off Eve for the least dV, I need to take this Moar Boosters thing to a whole new level!

Edited by herbal space program

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@herbal space program Good experiment. I love seeing those in KSP.

I strongly recommend folks also try the stock AeroGUI under Alt-F12->Physics->Aero. It’s highly informative when testing.

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On 2/18/2019 at 11:35 PM, 5thHorseman said:

I can't consistently land horizontally ANYWHERE without cheesing reloads.

My friend I have watched that asteroid landing video (several years ago now, wow how time flies) and I know that's false!

 

15 hours ago, GRS said:

(Yes, your eyes are all good, this rocket used only Chemical engines)

Ever since the nerf I don't find the nukes to be worthwhile; for that small an increase in ISP I'd rather just send off a flotilla including refuelers and do the burn in a third of the RL time.

 

On 2/19/2019 at 8:30 AM, herbal space program said:

Well the landing part is pretty awesome, but the taking off part, not so much. In addition to not having the OP airbreathing Rapiers at your disposal, you have to contend with the combination of a 1000 m/s higher orbital velocity and an atmosphere so thick that any kind of efficient winged ascent profile will cause massive heating. I guess the ideal solution would be to land your craft as a glider on an up-slope, stage off the wings, and then take off up the hill, turning vertical and staging off your wheels as you take off.

That's basically my move with my lander. Glide to a nice landing where I want, top off, and go. My initial eve sea level TWR is a touch under 1, so the wings stay on until TWR reaches ~1.3 then they get staged off and the craft just follows a rocket profile. The whole thing is sort of sigmoid shaped.

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5 hours ago, herbal space program said:

That tells me two things: 1) That bigger ships do indeed have less drag/mass than smaller ones in this game, i.e. the big tanks really are better, you just have to get creative about spamming engines onto their undersides, and 2) If I want to get off Eve for the least dV, I need to take this Moar Boosters thing to a whole new level!

In practical testing on hundreds of Eve craft I have found the opposite to be true. 

As you strip more and more of your craft away and reduce drag the dV requirements to reach orbit drop. 

I have a craft that started at 40t and needed 6.6kdV to orbit. Reducing the drag a lot and stripping it to 25t gets the job done for <6kdV. 

Edited by Foxster

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On 2/20/2019 at 8:39 PM, herbal space program said:

bigger ships do indeed have less drag/mass than smaller ones in this game

In RL this is the case as well.

This is a consequence of the square-cube law.  As an object increases in size its mass increases much faster than its surface area.

Bigger ships do suffer lower drag/mass than smaller ones.

In KSP, this seems to be modelled fairly well.

When building spaceplanes it is very important to optimize for drag on a small craft.  This becomes much less significant as the size of the craft increases.


Happy landings!

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15 minutes ago, Starhawk said:

In RL this is the case as well.

This is a consequence of the square-cube law.  As an object increases in size its mass increases much faster than its surface area.

Bigger ships do suffer lower drag/mass than larger ones.

In KSP, this seems to be modelled fairly well.

When building spaceplanes it is very important to optimize for drag on a small craft.  This becomes much less significant as the size of the craft increases.


Happy landings!

This is a factor of how *tall* the stack is. If you just have 1 tank, the wider tank is also taller, so it has less drag per unit mass. It has more mass per frontal area. But you can stack parts, and a tall thin stack is better than a shorter fatter one. Thus you should use the tallest stack that your engine can lift.

The vector is the king of lifting tall stacks... that's a lot of power for a 1.25m diameter. It can lift a lot of 1.25m tanks above it.

On 2/20/2019 at 3:53 AM, Reinhart Mk.1 said:

yeeeeeep it needed to be refueled but i got it into orbit

I've gotten better at building them and i'm trying to make a "fleet" that makes sense and isn't too flashy or expensive

I think we need another thread for this SSTO... There are many design changes that could be made, and you could change your ascent profile to get a lot more out of it.

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This is why I only do one way trips to Eve to avoid all the engineering nightmare of getting off Eve.

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3 hours ago, kni0002 said:

This is why I only do one way trips to Eve to avoid all the engineering nightmare of getting off Eve.

It's not that bad !

Eve isn't really that bad, i finished a round trip with my 'Eve Centurion" rocket, this time, below 1 km ASL.

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6 hours ago, Foxster said:

In practical testing on hundreds of Eve craft I have found the opposite to be true. 

As you strip more and more of your craft away and reduce drag the dV requirements to reach orbit drop. 

I have a craft that started at 40t and needed 6.6kdV to orbit. Reducing the drag a lot and stripping it to 25t gets the job done for <6kdV. 

You can talk about testing hundreds of craft, but upthread we just did the experiment now! If you drop a 2.5m stack upside down from 10km, it only reaches a TV around 200 m.s, and if you drop a 5m stack, it reaches over 320 m/s. QED! The bigger your rocket is for the same shape, attitude, and TWR, the less it will be affected by drag, period. And like I said before, I'm relieved to discover that because if it weren't so then our aerodynamic model would be complete rubbish. I think your problem in trying to design a larger efficient lifter was probably just that you didn't have enough TWR, because the standard engines and mounts don't allow you to build stacks with enough TWR to take advantage of their better aerodynamics. For my 5m stack, I need to be going over 300m/s as soon as I get off the ground as possible, then I need to drop all those extra boosters and proceed at a TWR that follows the TV curve as much as possible through a perfect gravity turn. With the stack I dropped upthread, I reached orbit for right around 6.5km/s flying it by hand, and I haven't even gotten close to the needed TWR values to make it optimal. When I've done that, if you like we can do a head-to-head test with whichever of your hundreds of smaller craft you want to pull out. I'll even install McJeb for the occasion!

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1 hour ago, herbal space program said:

You can talk about testing hundreds of craft, but upthread we just did the experiment now! If you drop a 2.5m stack upside down from 10km, it only reaches a TV around 200 m.s, and if you drop a 5m stack, it reaches over 320 m/s. QED! The bigger your rocket is for the same shape, attitude, and TWR, the less it will be affected by drag, period. And like I said before, I'm relieved to discover that because if it weren't so then our aerodynamic model would be complete rubbish. I think your problem in trying to design a larger efficient lifter was probably just that you didn't have enough TWR, because the standard engines and mounts don't allow you to build stacks with enough TWR to take advantage of their better aerodynamics. For my 5m stack, I need to be going over 300m/s as soon as I get off the ground as possible, then I need to drop all those extra boosters and proceed at a TWR that follows the TV curve as much as possible through a perfect gravity turn. With the stack I dropped upthread, I reached orbit for right around 6.5km/s flying it by hand, and I haven't even gotten close to the needed TWR values to make it optimal. When I've done that, if you like we can do a head-to-head test with whichever of your hundreds of smaller craft you want to pull out. I'll even install McJeb for the occasion!

It's all very well testing stuff like that but it don't bring home the bacon ;)

Very happy to do this whenever you like.

I suggest a payload of a mk1 command pod to 105km +/-2 circular Eve orbit from HE coords Lat -0.423, Lon -59.859. Stock parts and physics. Craft file and video to be posted. Autopilot fine with me. Lowest launch dV wins. 

(I think that what you are not really taking into account is that larger craft need more, bigger and draggier engines, couplings, nosecones, etc. They will all add up and eliminate any theoretical advantage of bigger tanks).  

Edited by Foxster

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1 hour ago, herbal space program said:

The bigger your rocket is for the same shape, attitude, and TWR, the less it will be affected by drag.

This is because if it is the same shape, it is also taller. That means that you are stacking more stuff above the same frontal area. Try testing a 4xstack of 1.25m tanks, compared to a single 1.25m tank... Of corse with fins and nose caps, and the same mass.

You want the tallest stacks possible, and you get that with 1.25 tanks, and the vector, like foxster said.

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