In KSP, I have a contract to test the Kickback SRB in orbit. That seems impossible to me, how do I get a huge SRB like that into orbit? Remember, I can't light it up until it's in orbit or the contract isn't fulfilled. Also, I only have up to the third tier (or fourth if you count the "start") of technology researched plus Heavy Rocketry in the fourth tier.

  • Perhaps if you post a picture of your unlocked tech tree and how much money you have left, someone could "apollo13" this.
    – spenibus
    Commented Jul 19, 2015 at 9:53
  • I could be wrong, but I don't think you need to wait until the prereqs to activate the engine -- you can use it, and then right-click on it mid-flight and select "Run Test" when the requirements are met. It's been a while, but I remember doing this at some point.
    – Tim S.
    Commented Jul 20, 2015 at 16:46
  • I've been using full kickbacks in orbit as ejection stages for probes. The launcher has a lot more kickbacks on it.
    – Joshua
    Commented Feb 11, 2017 at 0:25

1 Answer 1


The trick to make this easier is to lower the amount of solid fuel in the booster when you build your ship.

The S1 SRB-KD25k "Kickback" Solid Fuel Booster has a dry mass of 4.5 tonnes and is capable of carrying 2500 units of solid fuel.

Solid fuel has a density of 0.0075 tonnes per unit, therefore a fully loaded booster carries an additional 18.75 tonnes (2500 * 0.0075) for a total mass of 23.25 tonnes.

In the VAB, right-clicking the booster opens a menu that allows you to select the amount of fuel it contains. This value can be lowered from 2500 to 250.

Doing so brings the total mass of the booster to 6.375 tonnes (4.5 + 250 * 0.0075). That's a little under 30% of its original mass.

  • <slaps forehead> Why didn't I think of that?! Thanks! Commented Jul 19, 2015 at 17:49

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