CTS-7 Stallion SSTO
by ssTALONps
uploaded 2015-12-11
stock spaceplane
#SSTO #cargo #airdrop #interplanetary


Up-scaled version of CTS-5, the Stallion is known for it’s efficient performance and distinctive bottom-opening cargo bay. Capable of putting ~40t to 100x100km LKO. Intended to operate on both Kerbin and Laythe; current variant designation is C.

Ascent profile (full load)

  1. Rotate at ~90m/s.
  2. Pitch up and maintain 10~15deg pitch angle.
  3. Around altitude of 10km, you should’ve hit Mach 2~3.
  4. Around altitude of 15km, pitch down to 10 deg.
  5. Around altitudes of 25km, switch to rocket mode.
  6. Around altitude of 35km, pitch down to prograde.
  7. Keep burning until desired apoapsis is met.
  8. Circularize at AP.


  • Stock?: Yes
  • Version: 1.0 ~ 1.0.5
  • Type: Heavy cargo shuttle
  • Crew: 4 (remote operation capable)
  • Operational weight: 122.29t
  • Empty weight: 44.29t
  • MTOW: ~165t
  • Payload capacity: ~40t
  • Propulsion: 8x RAPIER
  • Size: 24.2m x 18.5m x 5.7m
  • Part count: 132

Development history

[This development history shares many elements with CTS-5 Skymule]

As soon as update 1.0 came online, it immediately became obvious that designing sleek cargo SSTO was now possible without slapping on as many engines you can (such as 20x RAPIERs on CTS-3 Starlifter). To replace now-obsolete CTS-3, a pre-1.0 box wing behemoth that could take single orange tank to orbit, a new SSTO development plan was initiated.

The development plan dictated that the new SSTO must not have more than 8 RAPIER engines, must be capable of lifting ~20t to LKO, and optionally have rear-docking capability for possible interplanetary delivery. In addition to that, perfect mass balance was to be achieved via distributed engine layout, a feature previously seen on CTS-3.

While development ensued and the first prototype performed well beyond expectations, I realized that orbit-to-ground payload delivery was difficult with original design. At that time, no cargo ramp was available for vanilla installation. This meant that payload detachment after landing was downright impossible, let alone parachute assisted dropping without inverted flight.

The potential solution was simple; bottom-side opening cargo bay. This could enable unobstructed payload delivery to ground and potential re-attachment using AGU. But then again, a new problem arose; main gear placement. How could one attach the main gear solidly without getting in cargo bay’s way or situating too far from center of gravity?

And the ultimate solution; retaining bottom-side opening cargo bay, the main gears moved to mid-mounted wing. For this, I had to use largest landing gear possible, the LY-99. With struts properly installed, the main gear assembly became rigid with potential shock absorbing achieved with wing.

Thus became one of the most widely fielded SSTO in my fleet, CTS-5 Skymule. Small enough to be used on Laythe without problem, and big enough to satisfy orbital fuel depots around Kerbin and Jool’s satellites. Balanced engine layout and docile flight characteristics was loved by almost all Kerbal pilots.

[End of sharing]

After successful development of the Skymule, it became clear that I grossly underestimated potential performance that can be achieved with 8x RAPIER. So even with CRG-50 cargo bay, problem of limited volume capacity consistently occurred. And with development of longer but more powerful NRX-L nuclear range extender and TRS-1200 traversal resource scavenger, the need for larger payload bay became apparent. It was decided to add single CRG-25 segment to payload bay.

Having almost the same dimension as its predecessor, the CTS-7 Stallion has significantly improved cargo capacity of ~40t (although fulfilling that potential comes down to problem of how can one pack so much stuff in cramped space). It gradually replaced its older brother and now performs as dominant cargo shuttle on both Kerbin and Laythe. Even the advent of next generation SSTOs equipped with 1.0.5 cargo ramp could not and won’t dare challenge this long-living leviathan in terms of efficiency and ease of operation.

Current C variant has gone through massive reform:

  • RCS fuel supply now situates outside of cargo bay with slightly increased capacity.
  • A single tail strike-proof wheel was added.
  • Additional liquid fuel supply of 1600 unit was added to stretched rear engine assembly.
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