RV-105 RCS Thruster Block no longer available for use?

[THX1138]

I can't find any information on the fact that I'm unable to launch a rocket I put together earlier because it contains RV-105 RCS Thruster Blocks which are now experimental and not available. Why is such a basic and important component no longer available?

[Nemoricus]

What game mode are you playing in?

[THX1138]

The career one.

[Red Iron Crown]

I'm guessing you're in career mode and haven't unlocked them yet. Maybe you had a part test contract for them that made them temporarily available without unlocking them; when you completed the contract they became unavailable again.

[THX1138]

Aren't contracts a very recent update? I haven't completed a single one and although the contracts list has appeared in bottom left of the VAB, it's empty and contains no contracts. I've had the RCS blocks for a long time. I even have nuclear rocket engines which I'm pretty sure come after the RCS blocks.

[Red Iron Crown]

Contracts are 0.24 and later. Did you move a save over from a previous version? Can you check the tech tree and ensure they're unlocked?

[THX1138]

I don't know what version I have but since it's installed and managed via Steam, I imagine it's always kept up-to-date. Contracts were not present when I installed the game a couple of months ago. I didn't move any saves. The saves were moved automatically or whatever.

I have checked the tech tree and indeed the thruster blocks where unlocked a few tiers ago. In the VAB, they're present but greyed out.

[Red Iron Crown]

Try clicking on the thruster block icon in the tech tree, see if it unlocks. Greyed out is usually a sign of a locked part.

[THX1138]

The sign of a locked part is it not being available in the VAB at all....

Edited August 11, 2014 by THX1138

[AmpsterMan]

seeing as this has become a gameplay question now, I'll kick it over to the correct area so you can get more help.

[Red Iron Crown]

You're right, I was thinking of mod parts not showing in the VAB after adding the mod post career start, which requires manual unlocking in the tech tree, but that obviously doesn't apply here.

Something strange is going on. I usually only see greyed out parts when starting a new ship, some parts cannot be the root part. But that doesn't apply as you're using a previously constructed ship. I take it you're not able to place them on a new ship either?

[Orionkermin]

They changed position on the tech tree so if you had previously unlocked them from their old position they will need to be re-researched in the R&D building.

[Master Tao]

The RCS parts were moved, which locks them in converted saves. You can fix it by editing your save file. That's located in KSP/saves/[your save name]/persistence.sfs

Make a backup copy of your persistence.sfs and open it in a plain text editor (Notepad on Windows). Then find the tech tree entries that look something like this:

Tech
{
    id = advFlightControl
    state = Available
    part = winglet3
    part = Mark2Cockpit
    part = ...
}

Then find these parts listed in the tech nodes and delete them:

    part = winglet3
    part = Mark2Cockpit
    part = advSasModule
    part = probeCoreOcto
    part = RCSFuelTank
    part = radialRCSTank
    part = RCSBlock
    part = linearRcs

Save your persistence.sfs, start your game. You should be able to unlock the parts in R&D.