LV-T45: can't launch at 120km

[mercuriandruid]

Hello!

Is there any specified altitude for LV-T45 operation? I tried to lauch it once reached ap @ 120km, but it was just *click* sound, nothing happened and when tried once more, next staging step has been executed.

I had 4x FL-T100 attached.

[Foxster]

Think we are gonna need a picture. 

[Snark]

Hello, and welcome to the forums! 

53 minutes ago, mercuriandruid said:

Is there any specified altitude for LV-T45 operation? I tried to lauch it once reached ap @ 120km, but it was just *click* sound, nothing happened and when tried once more, next staging step has been executed.

I had 4x FL-T100 attached.

No, there's no such altitude.  Any engine can be activated at any altitude, including right on the launch pad.

It's true that there are some engines (the so-called "vacuum engines", such as the Terrier and Poodle) which have terrible fuel economy and thrust if you use them at sea level, but even those engines work just great at altitudes over 10 km or so.  And in any case, the LV-T45 isn't one of those-- it works great even right on the launch pad.

About all that I can think of is that there might be something about the design of your ship that's preventing fuel from flowing to the engine.  If you look at the little in-flight "stage display" at bottom left, where it shows the engine, what does the fuel bar say?  Does it show full, or empty?

In any case, it's kinda hard to diagnose without seeing your ship.  Could you post a screenshot of your ship?  It's pretty quick and easy to do:

1. Take an in-game screenshot using F1.  It gets saved to the "Screenshots" folder of your KSP installation.
2. Go to www.imgur.com.  (You don't need to make an account or anything, this works fine anonymously.)
3. Click on the green "new post" button up top.
4. Drag your image into the "drop image here" box that it pops up.
5. As soon as the post is complete, right-click on the image on the imgur page and choose "Copy Image Location".
6. Paste that URL into your forum post here.  It'll get automagically converted into an in-line image.

Good luck!

[Aegolius13]

Are you sure the tanks for the engine still had fuel left?  Sometimes if you accidentally enable crossfeed on a decoupler, your lower engines can eat the upper engines' fuel.

Also, did you check to make sure you were throttled up?  An engine that's "activated" will still not burn if throttle is still at zero -- it will just be responsive to throttle from that point. 

One other possibility is that there are few parts that do not allow crosfeeding, like the heat shields.  So if your fuel was on one side of a heat shield and your engine is on the other side, you won't get any boom.  

 

[qzgy]

I would say to follow what Snark above has done. You can also try directly attaching a fuel line from the tanks to the LVT-45 just to make sure it gets fuel and also right clicking on the engine to see if it is activated. Staging isn't always reliable if you do funny stuff with it.

Really though, better to replace with a LV-909 terrier if you can, if this is the last upper stage

Edited June 26, 2017 by qzgy

[mercuriandruid]

Thanks for replies

here is a screenshot: 

Seems that it's not related to altitude, as in previous attempt I reached orbit at 124km, but then failed to launch again at 82km.

To be precise, I can hear short burst sound and nothing happens. You can see liquid fuel bar, that appeared after engine activation (it's not decreasing). 

Edited June 26, 2017 by mercuriandruid

[Spricigo]

 

another possibilities:

-  Your staging sequence is not correct and you activated a different engine higher in the stack (which have the nozzle blocked and produce no thrust)

-the game consider the engine inside a cargo bay/fairing because a clipping issue or it decoupled from an closed bay/fairing.

 

Just for the sake of completeness, because seems you are in very early career (given the fuel tank you are using and how you are piloting)Edit, after looking at the screenshot the first one is possible.

On 25/06/2017 at 2:28 PM, mercuriandruid said:

 I tried to lauch it once reached ap @ 120km...

I had 4x FL-T100 attached.

Definitely don’t sound like the start of an interplanetary mission for me.

In any case, a picture* of your vessel and a description of the goals may help us to you. We may spot a problem that you didn't even notice, without delving into details that are not relevant for the task at hand.

 

*you need to put the picture in a external host (like the popular imgur) and post the link to the image file.

 

 

Edited June 26, 2017 by Spricigo

[foamyesque]

1 hour ago, mercuriandruid said:

Thanks for replies

here is a screenshot: 

Seems that it's not related to altitude, as in previous attempt I reached orbit at 124km, but then failed to launch again at 82km.

To be precise, I can hear short burst sound and nothing happens. You can see liquid fuel bar, that appeared after engine activation (it's not decreasing). 

 

Your throttle is at zero. Have you tried throttling up?

Edited June 26, 2017 by foamyesque

[mercuriandruid]

50 minutes ago, foamyesque said:

 

Your throttle is at zero. Have you tried throttling up?

That's it!  For some reason, throttle went to zero when activated warp x5. Is that expected behaviour? 

[StrandedonEarth]

51 minutes ago, mercuriandruid said:

That's it!  For some reason, throttle went to zero when activated warp x5. Is that expected behaviour? 

Throttle always goes to zero after exiting warp. It can save some nasty surprises

[Spricigo]

Yes, time warp kills throtle.  Notice that applies to regular time warp but not for physical time warp.

 

If you are interested, I'd like to see the complete rocket, and know where are you going, so I (and others) may give more tailored advicebut on top of my head consider:

-Removing the marked parts and adding a couple of fuel tanks instead. By my math it'll drop the deltaV budget from ~2km/s to 1.95km/s. Minimal difference.

Try to focus a bit more in collecting science in kerbin different biomes

-You are reaching 80km with just 350m/s. To archive orbit you need horizontal velocity, the only reason to going up is to avoid drag*. That means you should use more energy to build up horizontal velocity and less to climb while reducing losses by drag/steering**. Since Kerbin have an atmosphere a gravity turn is advisable, right after launch tip the rocket a few degrees east and let it follow prograde (the exactly time and amplitude of that initial tilt will depend on the particular rocket. Some a rule of thumbs:  reach 10km at 45, maintain time to apoapsis ~1min). The main  advantages are maintaining the thrust aligned to velocity and maintaining your ship mostly parallel to airflow.

-You should consider to focus a bit more on collecting science around KSC to unlock a few parts that will make your attempt to orbit easier (e.g bigger fuel tanks, more optimized vacuum/atmosphere engines(terrier/reliant), stronger SRBs(thumper), radial decouples, nosecones, control surfaces).

*collision with the terrain is just a particular type of drag for that purpose.

**some will add gravity losses. Which in some sense is just to say that one want to go horizontal fast as quickly as possible.