Atmosphere-falloff and thruster-types?

Ion-thrusters are less powerfull on planets
Atmospheric-thrusters are useless in space
Hydro-thrusters good allover but consume much fuel

Question: Is there a synergy between ion- and atmospheric thrusters to get in to space? or is there a gap of hight were atmosphericthrusters became useless and ion thrusters are still not powerfull?

the wiki didn´t know atmospheric thrustres.

does someone know the power-falloff of the thrustertypes in highth over ground?

 

my ship has just ions and lifts off fine. you just need MOAR IONS
(+1 if you get the reference)

 

I definately like using a mix of Ion and Hydrogen. I keep an on-off toggle for both, and upon descent to a planet will start with dropping in at max speed (because there is no point in wasting fuel resisting a fall before it is worth resisting) and using forward ion thrust to come in relatively laterally and to guide myself to a good landing spot. When I want to start to slow down I turn on inertial dampeners and feather the on-off for the hydros. Eventually I turn on both and disable inertial dampeners and do the work manually and finally top it off just before landing with both turned on and dampeners with a manual descent by translating down with dampeners on.
For leaving atmosphere, it is full force on both ions and hydros at a 45 degree angle so that both bottom and rear thrust is working against the gravity. On my first attempt taking a freighter sized vessel off of earth, I ran out of hydro but I was high enough to have 0.40 gravity effect and my ions where capable of finishing the job. At that point I found doing an actual gravity turn was working. The only real issue is that the speed limit of 104ish means you cannot use velocity to resist gravity. I think if I speed modded my world to about double I could take better advantage of this. If we had a gravity terminal velocity of the current max but could do faster in space and in atmosphere (with some resistance?) we could probably get a little more out of using our lateral velocity against gravity.

Edit: Amazingly I have not crashed yet..

EDIT: YET.

 

"Ion" thrusters:

Code:

	  <MinPlanetaryInfluence>0</MinPlanetaryInfluence>
	  <MaxPlanetaryInfluence>1</MaxPlanetaryInfluence>
	  <EffectivenessAtMinInfluence>1</EffectivenessAtMinInfluence>
	  <EffectivenessAtMaxInfluence>0.3</EffectivenessAtMaxInfluence>

Atmospheric thrusters:

Code:

	  <MinPlanetaryInfluence>0.3</MinPlanetaryInfluence>
	  <MaxPlanetaryInfluence>1</MaxPlanetaryInfluence>
	  <EffectivenessAtMinInfluence>0</EffectivenessAtMinInfluence>
	  <EffectivenessAtMaxInfluence>1</EffectivenessAtMaxInfluence>
	  <NeedsAtmosphereForInfluence>true</NeedsAtmosphereForInfluence>

PlanetaryInfluence is tied to atmosphere density in the code (Mars-like has a non-breathable atmosphere, for example). The atmosphere doesn't extend as far as the planet's natural gravity field.

In the absence of an atmosphere (space or the moon), ion thrusters have 100% effectiveness. At a atmosphere density of 1 (earthlike or marslike surface) the effectiveness is 30% (less thrust for the same power!).

Atmospheric thrusters have 100% effectiveness at the surface of earthlike or marslike planets, and this linearly decreases to 0% effectiveness as you approach an atmosphere density of 0.3 (i.e. 70% of the atmosphere thickness).

When you are about 1/3 of the way out of the atmosphere, both thrusters have about 53% effectiveness. When you are about 1/2 of the way out of the atmosphere, ions are 65% effective and atmospheric 29% effective. The thrusters have different thrust/power properties however, so the best changeover altitude is 45% of the way from the surface to the thickness of the atmosphere.

EDIT: and I don't know how thick the atmosphere is for the planets or moons, or how that is calculated.

 

Thank you Arcturus. That was a useful answer. So this looks like a real synergy of both thrustertypes (no gap, were both are useless). And it looks like there is no need for hydrogen as the combined power of both types is always near 100%

You have to put more thrusters on the ship for that "Synergy-Drive", but you spare all the hydrogen-periphery. (Tanks and conveyorconnection and ugly hydro-thrusters)

 

I was curious about this myself, so I set about to measure it. I set a station high up (my test world has voxel support off) and created some probes that I dropped from there. The probes had just downward facing thrusters and I measured the deceleration vs. gravity as they fell. A PB recorded position over time and also periodically switch thrust off if the probe reached a hovering state. I tested over the starting base in the Earth-like planet start.

After filtering out the non-thrust parts and outliers, I got the following for the atmospheric thrusters:

Given the likely error, I'd say it's safe to say that atmospheric thrusters vary linearly from 100%-0% power over a distance from center of 60km to 70km. (This is on what I assume is a 120km planet, where the distance to the lowest surface point would be 60km.)

For ions:

Here, I would say 30%-100% over 60km to 75km.

(For completeness, I also tested hydrogen thrusters and, as expected, the measured points were right on the 100% line.)

Whether hydrogen can be skipped will be highly ship dependent. For example, the red ship has acceleration:
a=(2*3600000)/2634123=2.73 m/s^2

Even with ions at 100%, the distance where it can just barely hover is:
r=(67250^7 * 9.81 / 2.73)^(1/7)=80.72km
Well above where atmospheric thrusters cut off (70km). It's far enough out that you would likely need a massive number of ions to be able to skip hydrogen.

The blue ship has a higher thrust-to-mass ratio:
a=(2*3600000+6*288)/1353614=6.60 m/s^2

Running the number, we find out that the hover point is affected by falloff (r above came out below 75k) so now we have to account for falloff too:
0=(0.7/15000)*r^8 + (0.3-0.7*60/15)*r^7 - 9.81/6.60*67250^7
Solving for r gives:
r=72.47km

Which is still above where atmospheric thrusters become useless.

At significant efficiency penalty.

 

Based on your data, my viewing of the code via C# reflection, and this excerpt from the planet generator sbc file for earthlike:

Code:

	  <MaximumOxygen>1.0</MaximumOxygen>
	  <SurfaceGravity>1.0</SurfaceGravity>
	  <DefaultSurfaceMaterial Material="Rocks_grass" MaxDepth="1"/>
	  <DefaultSubSurfaceMaterial Material="Stone"/>
 
	  <HasAtmosphere>true</HasAtmosphere>
	  <Atmosphere>
		<Breathable>true</Breathable>
		<OxygenDensity>0.9</OxygenDensity>
		<Density>1.0</Density>
		<LimitAltitude>2.0</LimitAltitude>
	  </Atmosphere>
 
	  ...
 
	  <MaterialsMaxDepth Min="4000" Max="4000"/>
	  <MaterialsMinDepth Min="20" Max="20"/>
 
	  <HillParams Min = "-0.01" Max ="0.12"/>

The code multiplies the planet radius (i.e. 60 km) by the hill max number (0.12) and by the limit altitude (2.0) to get an atmosphere thickness of 14.4 km. So on the earthlike worlds the air density (planetary influence) is 1 at the surface, and 0 at 14.4 km altitude, linear in-between.

You also need more electrical power to run all the combined ion and atmospheric thrusters since the power demand does not drop with less effective thrust. Perhaps double the number of batteries or reactors?

 

This is so interesting.
@JoeTheDestroyer : good job there! so it looks like there is a gap where we just have to fire hydro-thrusters to leave atmosphere.
--> so if we are compelled to use hydros on a ferry we can spare the effort of a Synergy-Drive and put just hydros and Ions. FUCK!

To put batteries everywere in the unused spaces of a ship is far more easy as to integrate a hydro-periphery. and to charge your batteries you need at least just one simple solar panel minimum. and go fishing in the meantime.

 

Interesting, that's quite close to what I got for ion thrusters.

I wonder why what I got for atmospheric thrusters is so far off. I thought it was odd as I assume it's the same code for all thrusters... I would have liked to check the code, but I'll wait until Keen updates github before I do any code diving.

Edit: Nevermind, I missed the 0.3 planetary influence on atmospheric thrusters. Accounting for that, gives a 10.08km operating range, pretty close to what I measured.

 

Not necessarily, though I expect significant sacrifices will need to be made.

Let's try some scenarios. First, we know above ~10km atmospheric thrusters are useless, so ion thrusters must, at a minimum, provide enough thrust to counter gravity at this height. At this height, ion thrusters only have 79% of their max thrust and gravity is 7.3130 m/s^2.

Thus, at a minimum, the ship must have free space acceleration (using ions) of 9.257 m/s^2 (7.313/0.79). In other words, your ship will need to accelerate from zero to the speed cap in ~11 seconds.

Now, how much thrust do we need from atmospheric thrusters?

Minimum ion, hover at surface
The smallest atmospheric thrust we could need is to hover at the surface. So we need to take gravity at surface (9.81 m/s^2), subtract the ion thrust at surface (2.7771 m/s^2), giving us the needed thrust maximum from atmospheric thrusters of 7.0329 m/s^2.

However, looking at the plot below and comparing the thrust available at different heights (blue dashed line) to gravity (black line) we see that the ship has too little thrust to overcome gravity early on.

Minimum ion, hover at midpoint
We need more thrust to overcome gravity. Looking at the plot, we can see the critical point is where the constant gravity region ends, which is at the midpoint of the atmospheric region, 7.2km.

At that point, the ion thrusters will provide 6.0170 m/s^2 of acceleration (65%).

This leaves 3.7930 m/s^2 that must be provided by atmospheric thrusters. At this height, they only provide 28.57% of max thrust. So at surface, in other words maximum, thrust must be 13.2754 m/s^2 (3.793/.2857).

On the plot, we can see (red dashed line) that we now always have enough thrust to oppose gravity. But we need about 20% more atmospheric thrusters than ion thrusters to do it.

Ion hover at midpoint
Another possibility is to have enough ion thrust to hover at the critical point, and add just enough atmospheric thrust to make up for losses at lower heights.

In this case, we need free space ion thrust of 15.0923 m/s^2 (9.81/0.65). (That is enough to get from zero to the speed cap ~7 seconds.)

Then, the remaining thrust we need (at the surface) is 5.2823 m/s^2 (9.81-0.3*15.0923), which must be supplied by atmospheric thrusters.



(I should note that there is an optimal balance point where the rate of loss of atmospheric thrust is equal to the rate of gain of ion thrust. It's a little more complicated to calculate so I didn't bother, but it should be somewhere in between the two extremes I've presented here.)

So it is possible to skip hydrogen, but you will be devoting a large amount of your ship to thrusters. I suspect it will only be practical for small, non-cargo carrying type vessels (fighters, passenger ferrys, etc).

 

how much ship mass max Kg a single downfaced thuster (atmospheric, ion, hydrogen) can hold up to mantain it in mid air with inertia dampeners on?

 

woot 14km high atmosphere is too much for a 60km planet should be max 10% (6km) or even less of planet diameter, so atmosphere altitude scale with planet dimension and his density effect thruster eficiency per thruster typess, very good to know!

 

As we've been discussing, this depends on how high the object is you're wanting to levitate, both because (on two types) the thrust varies with height and so does gravity.

So the best I can do is give you a chart so you can look up the value for your given situation:

If you want the value for other sized thrusters it will scale linearly. So, for example, if you want the value for a large ship small atmospheric thruster, then take the value from the chart, divide by 3 600 000, and multiply by 350 000.

The earth-like planet is 120km diameter.

This has not been my experience. One of my early tests had me building a probe with a single downfacing atmospheric thruster. As I flew it, I watched the power usage drop steadily as I got higher, coinciding with the drop in effective thrust.

Although I agree, it should use the same power regardless.

 

i downloaded a mod to give the hydro thrusters 10 times energy

no other way to get my ship to earth......atleast in one piece.

 

we need a mod or an indicator integrated in cockpit like the altimeter and horizon marker to know the atmospheric density, an indicator that shows the efficiency related to thruster type, like 3 icons for ion, hydrogen, atmospheric and a % indicator or a colored indicator (green, yellow, red) so we can combine thrusters on the fly

 

I tried to look into the programmable block API to figure out if this is already possible.
But there is only a "Documentation.chw" file instead of the .chm.
Seems like Keen messed up the API docs again...

 

The first thing I built on planets (in creative) was a small cockpit with enough atmo thrusters and power to fly around. Depending on how light you make it, 6-8 downward ions+2 atmo downward thrusters will get you into space. If you fly straight up, your velocity from the atmo thrusters will get you far enough for the ion thrusters to take over. My speed goes down to 50-60m/s before the ions can accelerate the ship.

Personal Transport Pod


I worked on iterations of this ship to get it spaceworthy, add a battery and connector etc. In the end I have 2 atmo thrusters and 8 ions pointing down. The 8 ions are useful enough on planets, and I have a single ion pointing in all the other directions for space flight. Autopilot works like a charm when going to space. When coming back down automatically, My first GPS waypoint needs to be 2000m above the ground to give autopilot enough time to slow down. The next is 1000m high, and the last is near ground level.

Not bad for a personal transporter, but you'll need to go a lot bigger to put loaded cargo containers into "orbit".

 

interesting idea for a space launch ship.
But with only 1 battery how long can you run in survival mode? Is that enough to get into orbit AND return? ... without having to recharge?

 

JoeTheDestroyer, that is excellent data!

I just looked into this myself for the starter Earthlike planet, and found that atmospheric thrusters vary linearly from 100% effectiveness at "sea-level" (which I had to drill down into my planet to reach -I'll get to that in a minute) down to 0% effectiveness at about 10km above "sea-level". I also observed that thruster power demand also decreased in step with the effectiveness -though I suspect that's unintended behavior. Additionally, the Thrust Override slider bar operates more like a "percent of max available thrust" bar for atmospheric thrusters, with the reported thrust not matching the actual output of the engine. Rather annoying that there's no indication for this, but there it is.

I'm defining "sea-level" here as the distance from planet center at which the output of an atmospheric thruster is 100% of what it's rated for. I'm not savvy enough to dive into the source code for the game to figure out exactly how that altitude is established, but it seems to be slightly below the average ground level of the planet. For context, the ambient Oxygen concentration transitions from "High" to "Low" at around 5,875m above sea-level, which corresponds to 35% effectiveness for atmospheric thrusters.
Unfortunately I'm unable to upload my graph at the moment, but I imagine it's very similar to JoeTheDestroyer's.

 

how can we quick check the trhuster efficiency? cuz these value are variable in variable planets, different gravity and different atmosphere make the effective altiitude different... this is why we need some sort of indicator over the altimeter and the oxygen indicator (that make no sense in mars or alien atmosphere sice the have no or low oxygen, there should be alteast an atmospheric indicator that shows the density, for the gravity there is no problem since we have the numeric value of the natural gravity and we know thrusters scale their efficiency and thrust power linearly with G

 

It takes about 5 minutes to get into space, and 5 minutes back. the battery life in creative said 24 mins at full thrust (seemed accurate in survival, tho I accidentally ejected on my way up). There's more than enough juice to get you to space and back. If you coast a lot in space and on the way down you should be fine. There may be enough storage in the connector to build a solar panel on the ship while you're up there, extending your time. There's no oxygen storage, so the vent will only feed you o2 while on "earth".



*edit* The pod works fine on the moon, just a bit slower without enough air to use the atmo thrusters. Havent tried on mars or alien yet.

 

Unfortunately, since there's no way to know your exact distance from the center of any particular planet at any given time, a formulaic solution is out of the question. The only thing I can think of would be to look at actual power consumption of an atmospheric thruster compared to its rated max consumption. At the moment, the power consumption appears to vary in step with the effectiveness of the thruster; so if your thruster is only 30% effective at a given altitude, it will only consume ~30% of its max rated power. However, I believe this behavior to be a bug, so this probably won't be helpful for very long. Even if it is intended behavior and a permanent feature of atmospheric engines, you'd need a script to determine how much power an engine is drawing because they don't report that information directly. You'd have to measure the ship's power consumption at rest with all engines off, then back out thruster power usage from that. It's doable, but not cleanly. I think you have the right of it: we need an atmosphere indicator or some other built-in tool to show us how well the thrusters are performing.

EDIT: Alternatively, you could calculate thruster effectiveness by hand for a given altitude. You can use the ship's reported mass and the local strength of gravity to determine how much force (in Newtons) you would need to make the ship hover exactly. Then, set the override on your ship's atmospheric thrusters to near that force, and slowly increase the override until your ship begins to climb. Divide the power it should take by the power it actually took to get an approximate thruster effectiveness.

This will also tell you how far above effective "sea-level" you are. If you do this for at least two different altitudes, you can figure out how much effectiveness changes with altitude pretty easily, and that will always be true for that particular planet.

 

It's not that hard, actually. Here's one way:
https://forum.keenswh.com/threads/find-planet-center.7373357/

Then you can either look up or measure the other factors that affect efficiency.

 

Oohhh, sweet! A script-savvy individual could use that to generate some kind of efficiency indicator on a textpanel or some such thing. Beyond my abilities, but perhaps I'll take a crack at it at some point.