Mastodon Engines on Eve

[Xurkitree]

What is the Isp os the KE-1 Mastodon engine from Making History on EVE ASL and 7000m? Can any one find some numbers on it? Graphs would be nice. I don't have the DLC, so I can't check for myself. 

What about other engines too? 

[Chel]

I also don't have Making History, but I believe this thread should be moved to 'Gameplay Questions and Tutorials'. 

[DeltaDizzy]

Isp for engines is determined by something called a FloatCurve(some info), which can be graphed in game by using a mod. For the stock Rhino engine, it looks like this:

atmosphereCurve
{
	key = 0 340
	key = 1 205
	key = 5 0.001
}

Now you should be able to graph it and get your answers!

[Mrcarrot]

Let me see here...

The Mastodon's Atmosphere Curve:

atmosphereCurve
{
	key = 0 290
	key = 1 280
	key = 9 0.001
}

 

Edited November 5, 2018 by Mrcarrot

[Snark]

Moving to Gameplay Questions.

[Zhetaan]

@Xurkitree:

At 7000 m, Eve's atmosphere is approximately 1.7 atm of pressure.  Sea level is 5 atm of pressure.  The quadratic spline says that the Mastodon's Eve sea-level I_sp is about 180-190 and its 7 km I_sp is about 265-275.  These are very rough guesses, so please take them with the entire shaker of salt.

Edited November 5, 2018 by Zhetaan

[FinalFan]

Thank you for the info @Zhetaan although that's very disappointing if true.  I haven't played with Making History yet but it seems like the Mastodon is pretty underwhelming for any purpose other than Apollo recreations.  I was hoping that its lowest-in-game falloff of only 10 isp to 1 atmosphere from vacuum (because its vacuum isp is garbage) would at least translate to best-in-game isp at Eve sea level (because slower falloff).  It's sad if that's not the case.  

I just bought MH due to the sale and I'll test your result experimentally when I finish a couple of things.  

[edit: Even according to your math, though, I suppose it's at least somwhat competitive with the Mammoth, so it can fill the gap between it and the Aerospike.  I expect worse Isp but perhaps better TWR, but haven't tested yet or done math as good as Zhetaan.]  

Edited November 5, 2018 by FinalFan
edit

[OhioBob]

@FinalFan, Zhetaan's numbers are in the ballpark, but I checked it more accurately.  At Eve sea level the Mastodon's ISP is 152.5 s.  At 7000 m the atmospheric pressure is 1.6 atm, and the Mastodon's ISP is 265.4 s.

Edited November 5, 2018 by OhioBob

[FinalFan]

2 minutes ago, OhioBob said:

@FinalFan, Zhetaan's numbers are in the ballpark, but I check it more accurately.  At Eve sea level the Mastodon's ISP is 152.5 s.  At 7000 m the atmospheric pressure is 1.6 atm, and the Mastodon's ISP is 265.4 s.

Whoa, 152 isn't even close to competitive with the Mammoth/Aerospike based on the pre-MH graph I'm looking at.  Thanks for the info! 

Basically it's an expensive, less powerful Twin Boar.  

[EvermoreAlpaca]

I'm not at my desktop atm, but let me note that I've tried a lot of different engine configurations on Eve, and have yet to match the performance of the Vector for the lower stage.  Part of the reason is the vector is extremely compact, with minimal body drag.

[OhioBob]

1 hour ago, EvermoreAlpaca said:

I'm not at my desktop atm, but let me note that I've tried a lot of different engine configurations on Eve, and have yet to match the performance of the Vector for the lower stage.  Part of the reason is the vector is extremely compact, with minimal body drag.

Yep, the Vector and the Dart are really the only engines that work halfway decent on Eve.  And, of course, the Mammoth is just four vectors, so it too is good if you need something that large.

Below is a comparison of ISP vs. altitude for some engines on Eve.  The Able, Viper and Cobra are from Eve Optimized Engines, but the Vector and Dart (Aerospike) are on there too.

Edited November 5, 2018 by OhioBob

[FinalFan]

Here's my answer to the OP's question:  I concur with OhioBob that the Eve-sea-level Isp of the Mastadon is 152.5, but I recorded an Isp at approximately 7,000m of 238.7 instead of the 265 that he calculated.  I didn't hit 265 Isp with the Mastodon until more like 11,000m. 

Oh, by the way, @OhioBob:  is that graph slightly outdated?  I was unable to experimentally confirm your graph's representation of the Vector and Aerospike Isp curves using the in-game item screen tool.  My experience was that that your graph paints a relatively informative portrait, but the specific numbers are significantly off above sea level, as in the above example. 

As for where I differed from the graph, the Vector didn't catch up to the Aerospike's Isp for me until a little over 8 km (instead of under 4) and didn't fall behind again until right about 18 km (instead of 12.3). 
(Aerospike:  8km—266.1; 18km—303.3; Vector:  8km—265; 18km—303)

As for the main point of my experiment, the Mastodon, after starting out a staggering 41 Isp behind the Vector as you pointed out, caught up to about 15 Isp behind the Vector at 12-15km (close to 15 behind in that whole range) before the Vector pulled away again. 

My experiments also suggest that Eve reaches 1 Kerbin atmosphere at around 14.6 km, which is substantially higher than the "about 10km" I've heard being traditionally quoted by other people.  (I measured the Vector at 295.0 at 14,575m and this was consistent with my measurements from other engines.)

Edited November 6, 2018 by FinalFan
tweaked characterization of graph, moved answer to OP to top of post

[OhioBob]

3 hours ago, FinalFan said:

Oh, by the way, @OhioBob:  is that graph slightly outdated?

Well son of a gun, they changed Eve's atmosphere.  The pressure curve has been completely redone.  I have no idea when that happened.  Here's the new one from the Kittopia dumps:

Spoiler

	pressureCurve
	{
		key = 0 506.625 0 -0.04423852
		key = 15000 95.6891 -0.01304926 -0.01304926
		key = 25000 18.07334 -0.003012223 -0.003012223
		key = 40000 3.5 -0.0005689354 -0.0005689354
		key = 50000 0.1217772 -2.02962E-05 -2.02962E-05
		key = 60000 0.02300074 -3.8335E-06 -3.8335E-06
		key = 70000 0.004344278 -7.24E-07 -7.24E-07
		key = 80000 0.0008205283 -1.368E-07 -1.368E-07
		key = 90000 0 -2.58E-08 0
	}

 

And here's the old one for reference:

Spoiler

	pressureCurve
	{
		key = 0 506.625 -0.08693577 -0.08693577
		key = 9723.525 113.4918 -0.0149408 -0.0149408
		key = 20000 29.0968 -0.003046887 -0.003046887
		key = 45000 0.82 -6.321458E-05 -6.321458E-05
		key = 80000 0.0035 -9.886503E-07 -9.886503E-07
		key = 90000 0 0 0
	}

 

It looks like one of the main things they changed was to make the pressure in the lower part of the atmosphere decrease more slowly with increasing height.  The pressure at 7000 m is now about 2.53 atm, rather than 1.6 atm as previously stated.  I now compute the Mastodon's ISP at that height as 239 s, which agrees with your number.  And you're right, the pressure drops to 1 atm at an altitude of 14,579 meters.  It also looks like they decreased the air pressure in the upper atmosphere (above about 46 km).

The graph I posted is over 2.5 years old and is based on the old atmosphere.

 

Edited November 6, 2018 by OhioBob

[Aeroboi]

On 11/5/2018 at 5:23 AM, Xurkitree said:

What about other engines too? 

Too? You mean instead... To me personally the only engines of best choice are Aerospike, Vector, Mainsail, Twin boar and Mammoth. The mastodon is ridiculously overpriced and then the amount of Thrust and it's horrendous ISP. I know you can make nice working mastodon type EAV's but they're a lot bulkier, heavier and more costly.

18 hours ago, FinalFan said:

I haven't played with Making History yet but it seems like the Mastodon is pretty underwhelming for any purpose other than Apollo recreations.

Totally agree! That's kind of the shorter answer I gave Xurkitree above.

5 hours ago, FinalFan said:

My experiments also suggest that Eve reaches 1 Kerbin atmosphere at around 14.6 km, which is substantially higher than the "about 10km" I've heard being traditionally quoted by other people. I measured the Vector at 295.0 at 14,575m and this was consistent with my measurements from other engines.)

Does the density layer change across many versions and has been done in the past? I have tested this and I always thought it was 12.5 km? I can't recall which version, I believe 1.3.1

[Zhetaan]

Thanks for the check, @OhioBob.  I keep getting errors because my approach is inaccurate.  May I ask after the method you're using to model the curve?

2 hours ago, Aeroboi said:

Does the density layer change across many versions and has been done in the past? I have tested this and I always thought it was 12.5 km? I can't recall which version, I believe 1.3.1

The changelog on the wiki says that Eve's pressure curve was redone in v1.2, but that page also has the outdated graphs, charts, and tables--don't trust the information there.  Good catch, @FinalFan.

[FinalFan]

You know, after all this is said and done, I love your mod @OhioBob but I just got [forum censored me lol] off and said "I'm going to make the Mastodon decent at something" and brute-forced the .cfg file to zero out at 19 atmospheres instead of 9.  Now it still has 280 at sea level and 290 in vacuum but on Eve it starts at about 224.5. 

Oh and apparently the 2.5m-3.5m structural adapter no longer quite fits the 2.5m end.  Don't ask me why. 

Edited November 6, 2018 by FinalFan
"liquided", no thanks ...

[OhioBob]

4 hours ago, Zhetaan said:

The changelog on the wiki says that Eve's pressure curve was redone in v1.2, but that page also has the outdated graphs, charts, and tables--don't trust the information there.

I've revised the Wiki, both the main body and the table giving pressure versus altitude.  Unfortunately it won't let me upload a revised graph.
 

Quote

I keep getting errors because my approach is inaccurate.  May I ask after the method you're using to model the curve?

I use this... http://www.braeunig.us/KSP/AtmoTutorial/FloatCurve.xlsx

Particularly nice is the second sheet.  We can enter in the curve data and it convert it to polynomial equations.  Using the equations we can calculate the values at any point along the curve.

[OhioBob]

8 hours ago, FinalFan said:

You know, after all this is said and done, I love your mod @OhioBob but I just got [forum censored me lol] off and said "I'm going to make the Mastodon decent at something" and brute-forced the .cfg file to zero out at 19 atmospheres instead of 9.  Now it still has 280 at sea level and 290 in vacuum but on Eve it starts at about 224.5.

The main issue I have with the Mastodon is its cost.  It's slightly smaller than the Mainsail but costs 22000 vs. 13000 for the Mainsail.  There is nothing special about the Mastodon that sets it apart from other engines to justify its high cost.  If it cost the same as, or maybe a little less than, the Mainsail, it would be a fine engine as far as I'm concerned.  Its vacuum ISP stinks, but it's not that much worse than many other engines.  And it has the best sea level thrust-to-weight ratio in the game.

Where I find the Mastodon most useful is when I need to cluster together many large engines,  because of its optional 1.25 m connection node.  I would probably prefer to use the Mainsail because of its lower cost, but the Mainsail has only a 2.5 m connection node.  Clustering a group of Mainsails together on a large engine plate looks horrible.  (Squad really needs to add some variants to the old engines in a future update.)

 

Edited November 6, 2018 by OhioBob

[FinalFan]

3 hours ago, OhioBob said:

The main issue I have with the Mastodon is its cost.  It's slightly smaller than the Mainsail but costs 22000 vs. 13000 for the Mainsail.  There is nothing special about the Mastodon that sets it apart from other engines to justify its high cost.  If it cost the same as, or maybe a little less than, the Mainsail, it would be a fine engine as far as I'm concerned.  Its vacuum ISP sticks, but it's not that much worse than many other engines.  And it has the best sea level thrust-to-weight ratio in the game.

Where I find the Mastodon most useful is when I need to cluster together many large engines,  because of its optional 1.25 m connection node.  I would probably prefer to use the Mainsail because of its lower cost, but the Mainsail has only a 2.5 m connection node.  Clustering a group of Mainsails together on a large engine plate looks horrible.  (Squad really needs to add some variants to the old engines in a future update.)

That's true; I haven't been appreciating that its TWR has a slight edge over even the mighty Mammoth.  That may possibly outweigh the extra weight in fuel burned on a short lived initial stage.   (On the launchpad, three Mastodons have the same weight as a Mammoth and 4.4% more thrust, while the Mammoth has 5.4% better Isp.)  And while the Isp gets much worse, it never entirely loses its edge in TWR.  

And the Mastodon's gimbal is a healthy 5°, while the Rhino (4°) is the only other engine in its weight class to beat 2°.  In fact, the Vector (10.5°) is the only bottom-mounted engine that beats it on that score, and only the much smaller Bobcat matches it.  So I have to take back what I said about the Mastodon not having any stand-out features.  

That leaves the glaringly obvious cost issue.  At 22k a pop, the cost when clustering quickly becomes ridiculous.  The Vector (18k) has a similar problem but obviously it, unlike the Mastodon, has the Mammoth.  

But I think pricing it the same as the Mainsail would go too far in the other direction.  Given the engine's qualities and the inherent versatility that the Mammoth by its nature completely lacks, I think pricing them at exact parity (comparing one Mammoth to 3 Mastodons) would be selling the Mastodon at a significant discount.  (Now that you've opened my eyes to seeing its virtues instead of fixating solely on its glaring performance flaw.)

Just off the top of my head, 15,000 seems appropriate.  It means you pay a premium versus the one trick pony Mammoth but the price isn't completely out of whack with everything else ... even the Vector.  

Edited November 6, 2018 by FinalFan
Note explaining why suddenly argue against lowballing the price after calling it garbage

[OhioBob]

1 hour ago, FinalFan said:

Just off the top of my head, 15,000 seems appropriate.

That seems reasonable.  I could live with anything in the 13000-15000 range.  But 22k is just ridiculously overprice.  There's nothing about it that demands that kind of price tag.

[bewing]

13 hours ago, OhioBob said:

It's slightly smaller than the Mainsail but costs 22000 vs. 13000 for the Mainsail.  There is nothing special about the Mastodon that sets it apart from other engines to justify its high cost.  If it cost the same as, or maybe a little less than, the Mainsail, it would be a fine engine as far as I'm concerned.

The Mainsail is totally OP and underpriced for what it does. It's not a valid comparison point for any engine.

 

[OhioBob]

1 hour ago, bewing said:

The Mainsail is totally OP and underpriced for what it does. It's not a valid comparison point for any engine.

I think it's priced just about right.  Just looking at the stock engines, the Twin-Boar is underpriced, the Rhino and Vector are overpriced, and the others are about right.  If we plot price versus thrust, we can draw a line from the Poodle to the Skipper to the Mainsail to the Mammoth.  The Mainsail might be slightly underpriced, but not by much.  A price of 14000 would fit the line nearly perfectly.

[FinalFan]

12 hours ago, bewing said:

The Mainsail is totally OP and underpriced for what it does. It's not a valid comparison point for any engine.

If I'm not mistaken, it has 37% the Mammoth's launchpad thrust and 40% of its weight with worse Isp and equal engine gimbal at 33% of the cost.  The comparison to the Twin Boar hardly bears mentioning.  What is totally OP about it?  Or, alternatively, what is the big difference in what it does?