No deltaV or burn time for nuclear engines

[maddog59]

I have a ship with five stock nuclear engines and plenty of liquid fuel. The VAB shows no dV available regardless of whether I set the dV Tool for vacuum or any planet or moon. I could live with that because I could cheat it into orbit to see what was available in the staging sequence. Then something changed, I don't know what, and now, even though there's plenty of LF, I get no dV value in the staging sequence, on the pad or in orbit, and no burn time indicated for any maneuver nodes regardless of how small. 

There's a pair of Sr. Docking Ports between the engine unit and the fuel tanks, but they're set with the cross feed enabled. I've confirmed that the engines are all set to use LF, and in fact if I light them up while in orbit they burn quite nicely. I've restarted the game a couple of times without any luck. 

1) Is it a bug that is preventing me from seeing the dV for the stage in the VAB? Regular engines show the dV values, just not nuclear engines.

2) What can I do to get back my dV values and burn times? 

Edited June 12, 2021 by maddog59

[maddog59]

Update: I was able to solve the second problem: when the IXS Command Module is selected as the Root part, the dV and burn times are missing. When I set any other part to be the Root, then set the control point to be the IXS Command Module (either before or after launch), all is well. 

This has no effect on the problem in the VAB where no dV is shown for the nuclear stage in the dV Tool or the staging preview.

[Serenity]

3 hours ago, maddog59 said:

Update: I was able to solve the second problem: when the IXS Command Module is selected as the Root part, the dV and burn times are missing. When I set any other part to be the Root, then set the control point to be the IXS Command Module (either before or after launch), all is well. 

This has no effect on the problem in the VAB where no dV is shown for the nuclear stage in the dV Tool or the staging preview.

I feel you, fighting through root parts, decouplers and multiple staging its almost an impossible task to calculate Dvs, most of the times even KER and Mechjeb will give up.

My advice is cheat orbit the vessel and create a ridiculous high maneuver and see how much Dv you covered, i know its not the best but that's how i overcome this problem.

Edited June 12, 2021 by Serenity

[maddog59]

I think I'm good as far as getting the ship into orbit and using it... but I'd really like to figure out what is going on with the dV tool in the VAB .  It doesn't seem to matter what I set the root to while in the VAB, the dV tool just won't show anything for any vehicle's nuclear stage, even the simplest.   

[jimmymcgoochie]

You could try using MechJeb or KER to get delta-V read outs, they seem to work when the stock one sometimes doesn’t, but if all else fails just calculate it yourself: delta-V = ISP * standard gravity * natural log (ln) of wet mass / dry mass.

ISP and standard gravity are fixed and known (800s and 9.807m/s/s respectively) so that half of the equation is always 7845.6m/s; you can get the dry and wet masses in the VAB or in flight by enabling the ‘start mass’ and ‘end mass’ options in the stock delta-V widget, which shows them in each stage.

[HvP]

@maddog59 I've had a problem similar to this before.

If I remember correctly, the workaround I found was to click the little plus sign (+) in the staging stack to add a new blank stage to the staging column for every docking port between your engines and the root part. Then drag those empty stages to the top of the staging column.

This worked for me when it happens, but I can't always reproduce the problem that makes it necessary. I also cannot remember if it works in the VAB, but it did work in the flight scene.

[maddog59]

On 6/15/2021 at 4:51 AM, jimmymcgoochie said:

... if all else fails just calculate it yourself: delta-V = ISP * standard gravity * natural log (ln) of wet mass / dry mass.

You clearly have an over-developed estimation of my ability (or willingness) to do math! LOL 

Seriously though, I may give that a try if KER and MJ2 don't provide the info. Thanks!!

On 6/15/2021 at 12:58 PM, HvP said:

...click the little plus sign (+) in the staging stack to add a new blank stage to the staging column for every docking port between your engines and the root part. Then drag those empty stages to the top of the staging column.

This worked for me when it happens, but I can't always reproduce the problem that makes it necessary. I also cannot remember if it works in the VAB, but it did work in the flight scene.

Thanks; I found that solution inadvertently during one of the 'simulation' flights, but couldn't seem to get it to work in the VAB/SPH. It's weird that it only happens with nuclear engines.