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Optimal Eve gravity turn?


Gordon Fecyk
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I finally managed to build a reasonable craft for Eve Space Program that can get to Eve orbit with about 1300-1400 m/s dV left. In career mode, with only Tier 3 and 4 parts. Craft file here, uses OhioBob's Eve Optimized Engines. After several attempts, my best effort is in this video here.

The biggest challenges of the current incarnation of the Eve Space Program mod are the lack of biomes outside of the KSC, and the distance of most survey contracts; the KSC is a quarter of a world away from where the game puts those surveys. This leaves part tests, science grinding around KSC, and a full fundraising campaign strategy (25% of reputation going to funds) to pay for building upgrades. Otherwise I'd be using a lot better parts for this craft. As it stands, the only remaining source of decent science is Gilly, and I can't reach that and get back on 1400 m/s. I didn't do any dV math really; just tried plotting to Gilly's orbit needing 1425 or so m/s, and came up short just by 20+ m/s.

That being said, I remember someone saying that ascending from Eve's surface to orbit needs a launch profile that goes straight up for a large part of the ascent, then starts the gravity turn very high up. With this craft I find I can start my turn just around 20 km, and also before staging away the last of the Adam engines and going to my first non-EoE; the Swivel, close to 35-40 km. Then some careful throttling and I can get to about 1400 m/s orbit speed before staging away the Swivel and going to my Terrier, finally closing my orbit with maybe 2/5th of my fuel.

What would be a better ascent profile for launching into Eve orbit? Where to start turning away from vertical? At what altitude and at what speed should I have a pitch of 45 degrees?

If you try this craft, note that Eve Space Program's launch pad is only at 450 m altitude, and I'm using tank priorities and decoupler fuel crossfeed to use a hybrid of onion staging and asparagus staging, so watch the tank levels on ascent.

[Update 15 APR] There's so much good advice here I can't mark any one answer as correct. I upvoted all of the good answers and gave out likes.

Edited by Gordon Fecyk
Added caveman tag and video link
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OK, after considerable time, and remembering I had enough tech for launch clamps, I finally came up with this:

EveOrbiter2-3-3.png

Here's the craft. Requires OhioBob's Eve Optimized Engines as before. The launch profile goes something like this:

  1. Highlight first engine stage, select SAS Hold, then launch.
  2. Stage first six engines away, followed by next six engines. Keep monitoring those fuel tanks.
  3. At 10 to 13 km up depending on payload mass, select SAS Prograde, or try your best to follow prograde.
  4. Stage away next three engines when empty.
  5. Stage away final four engines; by this time ship should point around 45 degrees at 45 to 50 km up, and have orbital speed just over 1 km/s. If not, abort and restart.
  6. Continue following orbital prograde up to apoapsis of your choice, close your orbit as normal.

This four tourist contraption has a payload mass of 3.38 tonnes. It uses one extra small reaction wheel. And as the engineer's report tells us, it just fits on the Tier 2 launch pad. Returning didn't even require any ablator on the heat shield, but things got hairy at 40 km on the way down. Autostrut saved the craft, and it returned safely. Video is coming.

Edited by Gordon Fecyk
Grammar
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It depends quite a bit on your craft TWR profile and aerodynamics (even more than on Kerbin).  The more streamlined and more overpowered your craft, the earlier you can probably afford to start the turn.  Also, if you have rear fins to stabilize, you can probably start earlier since those will make your nose resist dropping.

On my latest lander, I believe I kept the SAS locked on Radial-Out until around 7-8 KM altitude, and then very gradually started a turn.  I can't remember exactly when I hit 45 degrees, but I think it was a little on the late side (I tried to err on the side of a steep ascent rather than turning too sharply and getting stuck).  

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You ought to look through the Challenges sub-forum to see whether anyone has figured optimal Eve ascents.  If not, I suggest putting this question to them.  You've already got your own attempt and the example craft; if you turn it loose among the people there I guarantee that you will get either the best humanly-possible ascent profile or confirmation that you already have that profile.  A cursory first-pass search shows the Eve Rocks challenge (from version .90, so not at all the same) and a couple of lightest/smallest lander challenges, which all operate from the idea that whatever comes up is not going to reenter.  The idea of an optimal ascent is probably touched on in those challenges, but the mission profile that starts on Eve with the intent of returning there introduces new difficulties that these earlier challenges simply do not address.

As for addressing your Gilly difficulties, I'd suggest putting all of your focus on unlocking the Tier 5 Clamp-O-Tron Jr and the Tier 2 R&D (for fuel transfer).  If you can make orbit with anything left in the tank, then you can make orbit with a tanker--even if that tanker looks suspiciously like a ship.  The problem then is connecting to that tanker and extracting the fuel.  Thankfully, you can get the part without a Gilly return mission.  It will require some precision piloting, but you can fly by Gilly (total contact time will be minutes, given Gilly's sphere of influence, so I suggest having your science experiments on an action group--I often use landing gear or the abort group for the Tier 2 VAB).  You may want to consider a big stack that launches a probe straight out of Eve's sphere of influence--no gravity turn at all is required on that one; it merely requires that you not overheat the rocket on ascent--and that will get you some solar science at the cost of having a probe on a weird orbit.  Once that's done, the R&D upgrade, if you don't have it yet, only requires Funds.

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4 hours ago, Gordon Fecyk said:

Would be nice, but Tier 5 is out of reach without a massive Funds boost and a research centre upgrade. Contract grinding might get me the centre upgrade, but the science will be really tough to get. The current Eve Space Program mod has only two biomes on Eve and they're both called "Eve's Poles." One's surface and the other's splashed down, and then there's flying low, flying high, and space low. There is more KSC science grinding to be had if I can upgrade the research centre, though. Space high is now reachable with 1400 m/s from LEO, so that will help too.

That's a tough one!  In that case, I definitely urge you to put this question to the Challenges sub-forum.  Maybe you can attract some attention from the KSP Caveman Challenge, too:  for obvious reasons, most Eve ascents use high technology to achieve an economy of mass and part count, but I don't know of any attempt to do a Caveman-style Eve ascent, and they'd be the ones to take this idea and run with it.  They're the people who know how to make orbit on a stack FL-T100 tanks that is stabilised entirely by wishing:  they'd love this.

ETA:  I did a bit of checking, and if you can somehow find, buy, or steal a vessel with 1700 dV, then it is possible to use an Eve-Eve-Kerbin flyby transfer (assuming that Kerbin and Eve have the same orbital characteristics as stock in Eve Space Program), so that is the number you need to be able to do anything other than bounce about on Gilly.

Edited by Zhetaan
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On 4/12/2017 at 10:42 PM, Aegolius13 said:

Also, if you have rear fins to stabilize, you can probably start earlier since those will make your nose resist dropping.

What?! No, just no. All stabilizers do is keep you aerodynamicly stable (pointing prograde).

What causes your nose to drop in a gravity turn isn't any torque from gravity, but vector integration. Three forces accelerate your craft in a ballistic ascent: thrust, drag, and gravity. Since gravity is acting off-prograde, it has the effect of changeing the direction of your velocity as it is integrated WRT time. As your velocity changes direction, drag on the stabilizers creates torque to reorient the craft to prograde. The goal of a gravity turn is to make orbital velocity as you approach 0° AoA so that acceleration due to gravity keeps you traveling in a Kepler orbit.

To reduce nose dropping, simply go faster so gravity acceleration is lower in magnitude and thus effects less velocity direction change.

Edited by ajburges
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5 minutes ago, ajburges said:

What?! No, just no. All stabilizers do is keep you aerodynamicly stable (pointing prograde).

What causes your nose to drop in a gravity turn isn't any torque from gravity, but vector integration. Three forces accelerate your craft in a ballistic ascent: thrust, drag, and gravity. Since gravity is acting off-prograde, it has the effect of changeing the direction of your velocity as it is integrated WRT time. As your velocity changes direction, drag on the stabilizers creates torque to reorient the craft to prograde. The goal of a gravity turn is to make orbital velocity as you approach 0° AoA so that acceleration due to gravity keeps you traveling in a Kepler orbit.

I was saying something a little different, but admittedly not in a very precise way.  In my experience launching from Eve (testing identical rockets with and without fins), the one without fins dropped much more sharply once I started my pitchover maneuver.  I think this is aerodynamic in nature; not the phenomenon you're talking about.  The same thing happens on Kerbin when you pitch over too sharply with a rocket that has no fins and/or poor control authority; Eve's thick atmosphere just seems to amplify the effect.  

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A craft without fins will resist the *start* of the pitchover maneuver. When you pitchover you are turning from prograde which the fins resist. So it takes longer to actually do the pitchover. So for the same control inputs a fin-less rocket might pitch more. Of course, the depends on the details of the two craft. If the fins have control authority, they can help with the pitchover too. 

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7 hours ago, Aegolius13 said:

It depends quite a bit on your craft TWR profile and aerodynamics (even more than on Kerbin).  The more streamlined and more overpowered your craft, the earlier you can probably afford to start the turn.  Also, if you have rear fins to stabilize, you can probably start earlier since those will make your nose resist dropping.

The craft has a set of Tier 3 AV-R8 winglets, though I could probably scale back on the number of winglets I'm using. At first I had twelve of the things on the bottom stage, but reduced that to six. Likewise there used to be six AV-R8s on the third stage but I reduced that to three.

I probably should have posted images. At first the first four stages were a flat mess with stupid transonic drag, and then I lowered stages three and four, followed by lowering stages one and two. The FAR installation I had then stopped complaining about high transonic drag. The first four stages are nineteen FL-T800 tanks with LV-T35 Adam engines; the low expansion variant of the LV-T30 Reliant from Eve Optimized Engines, followed by one LV-T45 Swivel + FL-T800 on Stage 5 and one LV-909 Terrier + FL-T800 on Stage 6. A Mk1 Pod + heat shield tops the mess off. Autostruts, fuel crossfeed and tank priorities abused to Hell to keep the part count down.

I have three AV-R8 fins to use on Stage 4 to go with four LV-T35s, and while this is still in pretty thick atmosphere I have just enough pitch authority to start my turn.

Guess a video clip would be in order. I'll have to post that later though.

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5 minutes ago, Zhetaan said:

I'd suggest putting all of your focus on unlocking the Tier 5 Clamp-O-Tron Jr and the Tier 2 R&D (for fuel transfer). 

Would be nice, but Tier 5 is out of reach without a massive Funds boost and a research centre upgrade. Contract grinding might get me the centre upgrade, but the science will be really tough to get. The current Eve Space Program mod has only two biomes on Eve and they're both called "Eve's Poles." One's surface and the other's splashed down, and then there's flying low, flying high, and space low. There is more KSC science grinding to be had if I can upgrade the research centre, though. Space high is now reachable with 1400 m/s from LEO, so that will help too.

I'll take a shot at escaping Eve SOI, may be tough with only Tier 2 VAB and launch pad. But if I can escape Eve SOI I should be able to at least fly by Gilly.

Oddly the Mk1 pod doesn't have a heating status when I turn on F11 to show part temperatures. Maybe that's a concession to the difficulty of returning from LEO, but I can get up there with only 60 Ablator on my heat shield and still return with 15+ or so Ablator left.

Managed to get to Tier 2 Astronaut Complex and Tracking Station at least. And Mission Control was my first upgrade. Hopefully, rescue contracts from LEO come up, and then my funds problem would be solved.

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Since you are so close and docking seems to be out of reach,  I will suggest something very kerbal:

Design a pusher tug,  using a mesh of landing legs to hold the other ship in place. Use it to provide the extra m/s you need and get the tech you need for Jr docking port. 

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OK I'm uploading a video showing the craft I'm trying to launch. I wanted to finish that before looking here for answers, so you can all see what I'm struggling with.

The version in the video has fins that have some control authority, and if Valentina here were a one-star pilot she could follow prograde and solve much of this herself; this mission was mostly to get her that experience. I may have too many fins in this case, and I can scale them back. There's some balance between aerodynamics and gravity here, and everyone's pointing me 'prograde' to a solution. :rolleyes: /me ducks

Between Val's mission here, and me sending Bob up on some part test contracts and gathering orbital and high air EVA science, I managed to scrape enough points to unlock the Jr docking port. Funds are running low though, so I'll grind some part tests out. We're Gilly-bound.

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