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RT-5 "Flea" Solid Fuel Booster

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RT-5 "Flea" Solid Fuel Booster
Part image
Solid rocket booster by
Found lying by the side of the road
Cost (total) 200.00 Fund
(dry) 116.00 Fund
Mass (total) 1.50 t
(dry) 0.45 t
Drag 0.2-0.3
Max. Temp. 2000 K
Impact Tolerance 7 m/s
Research Start.png Start
Unlock cost Fund
Since version 1.0
Part configuration solidBoosterRT-5
Testing environments
On the surface ✓ Yes
In the ocean ✓ Yes
On the launchpad ✓ Yes
In the atmosphere ✓ Yes
Sub orbital × No
In an orbit × No
On an escape × No
Docked × No
Test by staging ✓ Yes
Manually testable × No
Solid rocket booster
Maximum thrust (1 atm) 162.91 kN
(vacuum) 192.00 kN
Isp (1 atm) 140 s
(vacuum) 165 s
Fuel con­sumption 15.80 units of fuel/s

Thrust vectoring × No
Fuel 140.0 units of fuel
Burn time (1 atm) 7.5 s
(vacuum) 8.9 s

The RT-5 "Flea" Solid Fuel Booster is a part introduced in version 1.0.

The RT-5 "Flea" Solid Fuel Booster (also known as an SRB) is a solid rocket booster used to provide a short burst of additional thrust to a rocket. It comes as a single unit. The engine and fuel tank are one single part which means that it isn't possible increase the burn time for it by adding more fuel tanks.


With the release of KSP 1.0 and the nerfing of the atmosphere, it was found that the old mainstay RT-10 was vastly overpowered[1] in this new environment (and itself nerfed, being pushed back in the technology tree to Basic Rocketry, reduced in Isp by 32.5% and specific thrust by 39.5%). It is very likely that most players will only use this motor in their first few Career flights, but eventually, there will be someone who will complete a significant mission using only RT-5s for propulsion, as has been done with the RT-10 and Sepratron I in the past.

Product description

While considered by some to be little more than "a trash bin full o' boom", The RT-5 can be seen in use at many space programs, perhaps possibly because it is the only option for many space programs, but nevertheless, this small booster provides a nice kick to lift small payloads to considerable heights. Use with caution, though. Once lit, solid fuel motors cannot be put out until the fuel runs out.


On the bottom of this booster, "CAUTION:CONTAINS BOOM" is written.


  • Initial release


  1. HarvesteR, Experimental Improvements, Devnote Tuesday 2015 April 21