The Mk5 Block II has been finalized! This bigger variant of the Mk5 adds power with 4 strap-on boosters and an extended liquid fuel tank. The strap-on boosters are an upgraded version of the Mk1-B booster, which can now output 21.795kN of thrust at sea level with greater efficiency as opposed to 18.75kn. Upon liftoff all 5 lower boosters will ignite for a total thrust-to-weight ratio of 5, which is 1G greater than the Mk5 Block I to help compensate for both the increased mass & length, which could cause the rocket to stand up a bit more as lift at the nose will have a greater torque effect with the nearly 1m extension. The strap-on boosters will burn for just over 6 seconds before being decoupled to leave the core booster firing with enough thrust to continue pushing at 3+Gs for another 15 seconds before it too is discarded. The third stage booster has been set to a TWR of 2 at 9km ASL and once ignited will burn for 15.5 seconds. The stage four liquid booster will be able to burn well over a minute or two depending on how its throttle is set during ascent.

The added power of the Block II should allow us to extend our reach into space beyond the boundaries of Low-Kerbin Orbit (LKO) which extends from 70km – 250km above Kerbin’s atmosphere. Although the rocket is almost 500kg heaver than the Block I it still manages to deliver almost 1km/s more deltaV, which when modeled with the highest Mk5 trajectory pushed our apokee out beyond 300km – and that was assuming a coast period up into the vacuum of space after the LF/O engine burnt out so with a continuous burn from the Block II’s double-capacity liquid fuel tanks we may even be able to get higher.

All this speculation will be put to the test when we launch our first Block II, which is currently scheduled to occur no earlier than November 15th. The launch date & time will be finalized later this month after we see how the Block I performs, as any defects found with it will also most likely affect the Block II. Despite the 4 added boosters Lead Engineer Simon reports that the VAB will only need two additional days to install them, giving us roughly a 2.5 week minimum turnaround between Block II launches as opposed to the 2 weeks needed for the Block I. Additional details can be viewed in the blueprint below.