Why won't this get off the ground?

[Atraxa]

For whatever reason, it's not acknowledging my image link, so unfortunately it needs to be done the old-fashioned way:   https://imgur.com/a/n74CJMX

Here's my confusion: My understanding of TWR is that anything greater than 1.0 will go up. Obviously, the closer you get to 1.0 the slower it is and can be maddeningly slow when very close to it, but most of my rockets launch around 1.43-1.70 TWR when all is said and done. I have been using chemical rockets thus far with more or less a decent amount of success. I recently got some snazzy new nuclear engines and found that this engine in particular, the NV-GX "Emancipator" Atomic Rocket Motor, had a moderate amount of thrust at sea level, (I've previously been using nuclear engines in vacuum only) so I thought I'd give it a try on the first stage. My TWR is reading as 4.58(5.39) on Kerbal Engineer Redux for that stage, as you can see in the screenshot. And yet, when I try to launch it just floats back down to the ground. That should be enough TWR to launch me out like an ICBM. So...what gives? I can obviously swap that out for a Mainsail or whatever and swap the tanks back to Liquid Fuel+Ox with their own engines, but I just want to understand why this is behaving this way. Is this just me misunderstanding the info KER is giving me?

Just so that it's clear, I do not normally have trouble launching rockets into orbit. I am far, far from an expert at this game, but I've put boots on Duna in career mode and brought them back home, so I'm like...lower-intermediate? I guess?

[Bej Kerman]

1. What mod are you using for the tanks?

2. Did you set KER to simulate sea level, and what do the stock readouts say?

3. Copy link address and paste into the message box as so:

[Atraxa]

2 minutes ago, Bej Kerman said:

1. What mod are you using for the tanks?

2. Did you set KER to simulate sea level, and what do the stock readouts say?

3. Copy link address and paste into the message box as so:

Firstly, thank you for trying to help! 

1. It's hard for me to say what is and isn't stock at this point as I've been playing with mods since the end of my first week in KSP. I believe** they are stock. They're the Rockomax X200 series. I had them set to Liquid Hydrogen to accommodate the needs of the nuclear engine.
2. I have never touched the settings of KER. I just looked around at some of the buttons at the top of the window and found that the Body is set to Kerbin and the altitude is set to 0km, so I can only assume that means it's set to sea level.

3. Forgive my ignorance, but isn't that what I did? I am clearly misunderstanding you, though, because you wouldn't have said that if it's what I had done. I first tried the "insert image from URL" button in the bottom right and did just that and each time I hit "accept/OK" it just blinked and nothing happened, so I gave up after a minute of trying it, then just pasted the link into the body of the text. What have I done wrong?

Seriously, thanks for taking the time to help.

[Bej Kerman]

10 minutes ago, Atraxa said:

16 minutes ago, Bej Kerman said:

1. What mod are you using for the tanks?

2. Did you set KER to simulate sea level, and what do the stock readouts say?

3. Copy link address and paste into the message box as so:

Firstly, thank you for trying to help! 

1. It's hard for me to say what is and isn't stock at this point as I've been playing with mods since the end of my first week in KSP. I believe** they are stock. They're the Rockomax X200 series. I had them set to Liquid Hydrogen to accommodate the needs of the nuclear engine.
2. I have never touched the settings of KER. I just looked around at some of the buttons at the top of the window and found that the Body is set to Kerbin and the altitude is set to 0km, so I can only assume that means it's set to sea level.

3. Forgive my ignorance, but isn't that what I did? I am clearly misunderstanding you, though, because you wouldn't have said that if it's what I had done. I first tried the "insert image from URL" button in the bottom right and did just that and each time I hit "accept/OK" it just blinked and nothing happened, so I gave up after a minute of trying it, then just pasted the link into the body of the text. What have I done wrong?

Seriously, thanks for taking the time to help.

1. Ok

2. DId you actually check to see if altitude sets the pressure or if it just changes the local gravity? Try clicking the Atmospheric tab.

3. That's not the image URL, that's an Imgur URL. Right click the image and click "Copy Image URL".

[vossiewulf]

Click on the Compact button in KER, that will limit its display to TWR (thrust/weight ratio) and delta V per stage and make sure the Atmo button is on. Your first stage needs to have a TWR of > 1. However for best results, launch TWR needs to be 1.3-1.4. Don't go higher than that as the rocket will accelerate too fast and then you have heating and possible burning up issues. And don't go lower than that as it wastes massive amounts of fuel for very little vehicle acceleration. 

[VoidSquid]

1 hour ago, Atraxa said:

1. It's hard for me to say what is and isn't stock at this point as I've been playing with mods since the end of my first week in KSP

Yeah, that sounds very familiar, but fortunately there's solution for this: 

From your screenshot, I strongly agree with what @Bej Kerman already said, KER's default is to display vacuum values (which are what one is usually interested, e.g. the magic "3400 m/s to orbit" is referring to vac. dv), not ASL. You could cross check with the stock display (lower right corner, the delta v symbol), I'd bet your ASL TWR is below one. Or just click the Atmospheric button in KER, that should give you the ASL values as well.

Edited July 13, 2020 by VoidSquid

[ElWanderer]

KSP's delta-v calculation (which defaults to sea-level) says about 700m/s instead of the 4.5km/s that KER is displaying, which also ties in with the Isp and thrust being awful in an atmosphere.
The other thing to check is whether the engine needs a lot of time to spool up to full thrust. I usually stage the engine first, then the docking clamps. Admittedly, very few stock engines spool, but it is good practice to avoid dropping launchers onto the pad!

 

[Spricigo]

7 hours ago, Atraxa said:

My TWR is reading as 4.58(5.39) on Kerbal Engineer Redux for that stage, as you can see in the screenshot.

yep, but in vacuum and for stage S3.  That is after 

6.releasing a pair of launch clamps

5.releasing another pair of launch clamps

4.dropping the side tanks.

3.using set orbit to put that thing in space.

so...

7 hours ago, Atraxa said:

Is this just me misunderstanding the info KER is giving me?

yes. [atmospheric] button need to be pressed and staging need to b corrected to give the correct seal  level statistics.

7 hours ago, Atraxa said:

this engine in particular had a moderate amount of thrust at sea level, 

 Need to be at least 736kN to get that craft of the pad. 

Edit:when asked nicely, Google told me the emancipator is from kerbal-atomics and have 621kN at sea level. IOW moar booster are required.

Aso, had you tested it in space? It's possible that is a issue with that particular engine/mod not working properly.

 

 

 

Edited July 13, 2020 by Spricigo

[Streetwind]

I recommend using the stock dV readout, now that we have it. It is reliable, customizable, and easy to use.

1.) Click on the total dV readout in the lower right corner. The one right above the "reset" button. This pops out the advanced stage info. You can also pop this out or collapse it for each individual stage by clicking that stage's header.
2.) Click on the stock dV app button in the toolbar at the bottom. It's the fourth button from the right in your screenshot. Here you can customize what the advanced stage info actually shows you. And you can toggle the relevant parent body as well as whether you want sea level, a custom altitude, or vacuum.

Oh, and @Spricigo is right - check yo stagin'! Something is screwy in the sequence as it is in the screenshot. Getting a correct readout from any dV simulation - no matter whether it's KER or stock or MechJeb - is dependant on having the correct staging sequence for your rocket configured.

Edited July 14, 2020 by Streetwind

[jimmymcgoochie]

1- Staging is wrong, you’re dropping the clamps and then the side tanks before even engaging the main engine. That won’t end well.

2- Emancipator is a vacuum engine and will be considerably less effective at sea level. It also burns uranium and is very heavy and expensive, so stick with a more traditional launch rocket or try the ‘scylla’ nuclear aerospike which is built for launches and is also in Kerbal Atomics (I’m fairly sure) and which burns hydrogen/oxidiser at low altitudes and pure hydrogen for better ISP but lower thrust later on.

3- Not strictly related to the engine, but that adapter under the fairing is the wrong size and will likely produce some odd drag. Switch to a larger one which fits the top and bottom and will also have more fuel in it too.