Kerbal X

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Kerbal X on the launch pad

The Kerbal X is a stock rocket available to all players. It is a reliable, all-around ship capable of reaching orbit fairly easily and thus is a good way for new players who have issues building their own ships to make it into orbit. It has a total mass of 131.62 t and has 74 parts with the launch clamps. It has no RCS Fuel Tank nor RCS thrusters. With the new SAS in 0.21 it has build in SAS functionality.


Kerbal X after dropping all boosters and shortly before advancing to stage 2

The first stage is comprised of three Rockomax X200-32 Fuel Tanks and a Rockomax "Mainsail" Liquid Engine. Also, six liquid fuel booster are staged in an Asparagus design. It has aerodynamical surfaces and a strong structure. The first stage is easily capable of launching the second stage into a parabolic trajectory, with a good horizontal speed at around 90km, thus making it easy for the second stage to make orbit. The full stage with all of its boosters has 2700 kN of thrust, for a thrust-to-weight ratio (TWR) of 2.096. The sole Mainsail and relative fuel tank has a TWR of 2.184 (the total mass of the Kerbal X at that time is 70.02 t).[revisit (table below specifies other values)]

The second stage is a large diameter Rockomax X200-16 Fuel Tank plus a Rockomax "Poodle" Liquid Engine, and the third, final stage consists of only a Mk1-2 Command Pod with a Mk16-XL Parachute. As the second stage also has landing legs and a ladder, and it is hinted by the menu screen where a wreckage similar to the Kerbal X can sometimes be seen, one can deduce that it was intended to land on the Mun. It is capable of doing so, but unfortunately it doesn't have enough fuel to get the crew back home.


The Kerbal X in a 150 km orbit around Kerbin

The first stage's central engine and relative fuel tank has 3177 m/s of ΔV, not mentioning the radial ring of boosters which has approximatively 1003 m/s. This sums up to about 4180 m/s, just about enough to make orbit (4500 m/s), making the Kerbal X a suitable option for orbiting small-to-medium payloads. Some form of propulsion capable to add approximately 350 m/s of velocity is needed on these payloads to complete orbital injection. The maximum payload to Kerbin low orbit of the unmodified Kerbal X is slightly less than 15 tons.

The second stage has 2494 m/s Δv, and the total Δv is 6674 m/s. It is interesting to note that this total impulse is sufficient for landing on the Mun with the piloting skill of the average player, but not for returning to Kerbin afterwards. This is probably intentional: the purpose of the Kerbal X is to present the player with a flyable and somewhat capable rocket design, that nevertheless needs some improvement in order to be fully successful.

6× Booster Stage 1 Stage 2
Engine LV-T45 Liquid Fuel Engine Rockomax "Mainsail" Liquid Engine Rockomax "Poodle" Liquid Engine
Diameter Small Large Large
Mass (t) 9.05 60.52 16.52
Burn time (s) 12.9, 27.9 (+15), 45.7 (+15, +17.8) [Note 1][Note 2] 87.9 - 103.6 [Note 2][Note 3] 139.1
  1. After dropping one booster pair the next one fed all engines except the previous (dropped) two engines causing a longer burn time.
  2. 2.0 2.1 All engines of the booster and first stage ignite at the same time.
  3. Cite error: Invalid <ref> tag; no text was provided for refs named bt

Potential uses

Action Δv (m/s) Feasible
Orbit 4500 Yes
Munar Injection 910 Yes
Mun Landing 1000 Yes
Mun surface orbit 700 No
Mun orbit return  ? No
Minmus Injection 1010 Yes
Minmus Landing  ?  ? Unkown
Solar orbit injection 1400 Yes
Interplanetary travel  ? No

The ability of the Kerbal X to reach orbit with a relatively small rocket for a medium payload (16 t), is significant in its reliability as bigger rockets tends to be more prone to exploding randomly or being unsuited for space travel. The two-stage to orbit leaves no debris and could be economically healthy when in-game budget is implemented.

The Kerbal X would also be suited to place payloads in a synchronous orbit around Kerbin as it has the required Δv to do so and deorbit thereafter.

With the help of gravitational assists it is possible to reach other planets or moons without changing the configuration.


Interesting use of the Kerbal X, with added RCS and a docking port, is a space station docker, allowing crew transfers or module delivery and docking as the ship has a good marge of additional weight it can carries. If placed properly, the RCS thrusters assures an easy docking and the low chance of failure justifies the uses of the Kerbal X as a crew transfer ship has the chance of seeing the crew being killed near zero.

Another uses of the Kerbal X would be to land on the Mun, with added basic functionalities such as RCS and docking port, it would be fairly easy to refuel the ship in Kerbin orbit, possibly with another Kerbal X, and fly it to the Mun, land and eventually come back, or at least, go back to Munar orbit.

If one would be willing to be upgrade the Kerbal X, adding a small intermediate stage that can almost finish orbit would be a big increase in performance as 12% of the fuel is used to finish orbit in optimal situation (accounting it used exactly 4500m/s to make orbit). Of course, one willing to use the Kerbal X often must absolutely add RCS.


The Kerbal X is one of the most successful rockets that can be ordered from a catalog. Despite the original design having been meant for a plastic model, it's proved itself quite dependable as a full-sized craft. The X is capable of achieving orbit around Kerbin, and even features a very optimistic set of landing legs on its upper stage.''