The Corporation’s Upper-Stage Workhorse

The Porter’s Successes in Service

Details

• Type: VAB
• Class: lifter
• Part Count: 53
• Pure Stock
• KSP: 1.12.5

General Description

The CS-206 Porter is a medium-sized upper stage designed by DLA Aerospace to haul medium-sized payloads into LKO (Low Kerbin Orbit). It’s still under minor development, but it has flown fairly often on various launch vehicles and has slowly become a reliable workhorse for DLA Aerospace’s orbital rocket launch campaigns.

Powerplant and Propellant

The Porter uses a pair of LV-T91 Cheetah liquid-fueled rocket engines mounted at the bottom, which run on the Gas-Generator or Open Cycle using a hypergolic combination of Unsymmetrical Dimethylhydrazine (UDMH) as fuel and Dinitrogen Tetroxide (NTO) as an oxidizer, and the two engines combined provide up to 250 kN of thrust in a vacuum while operating at ~355 Seconds of specific impulse. Using hypergolic fuels for this upper stage was a major consideration for DLA’s design team, as despite the propellants’ extremely toxic and corrosive nature, it allowed for the stage to remain operational in orbit for a very long time without any of the trouble of cryogenic propellants like Liquid Oxygen (LOX) and Liquid Hydrogen (LH2) that required to be stored at very low temperature and would eventually boil off due to the intense thermal cycling that occurs in LKO. It also drastically simplified the propellant tank management systems and even allowed for lighter and simpler engines as the hypergolic fuels ignite spontaneously on contact, removing a complex and potentially unreliable ignition system. Notably, turbopump exhausts on these engines have small nozzles on them that allow them to provide an extra bit of thrust. A pair of extra tanks of UDMH are also added in the extra space between the bottom and upper stages to cram as much fuel as reasonably possible into the space available.

Control, Staging and Telemetry

The Porter has its probe core/flight computer mounted at the top of the stage, directly below the payload area. It has 4 fuel cells that provide electrical power to the computer as well as a pair of Communotron 16-S antennas are mounted parallel to the raceways on the side of the stage to reduce drag during ascent on it’s first stage, and they provide a link between the Space Center and the stage to maintain data on the health of all of its systems. Other than the 4 degree thrust vectoring provided by the two engines the Porter also features a rather interesting attitude control system. On the sides of the stage there are two small pods containing the Auxiliary Propulsion System, or APS for short. Each APS pod has a set of 3 Cold-Gas Nitrogen thrusters that work together with the APS module on the opposite side to orient the stage into the desired attitude. These thrusters are fueled by a pair of small high-pressure Nitrogen tanks mounted near the engines, with tank pressure coming from passing the nitrogen through the nearby engine’s heat exchanger that is installed before the turbopump’s exhaust. At the bottom of each APS module is also a small solid-fueled Ullage motor that separates the stage from its booster during staging and also settles the propellants at the bottom of their tanks where they can be fed to the engines. They can only be used once, but future versions of this stage may include monopropellant ullage motors to provide the option for multiple engine restarts.

Range and Payload

The Porter is 2.5m in diameter, which means it can accept any booster stage below that is of the same size, or using an adapter. The maximum payload weight is highly dependent on the first stage booster that is used to put this stage into a suborbital trajectory, but this stage has 4,629 m/s of Delta-V completely empty, and with 12.7 tons of weight (which is nearing it’s useful payload limit) it has 2,204 m/s of Delta-V, all in a vacuum. So by itself, this stage has a useful payload limit of about 15 tons to LKO, but again this varies depending on the performance of the first stage.

Conclusion

This is a bit of a more simple and less remarkable upload, but I like to think deeply about simple things like a rocket’s upper stage or other crucial systems that get payloads to very far places. I prefer to start my rocket builds with the upper stages, then building the payload and finally working downwards towards the first stage, launch claps, etc. Since this is a pretty nice and high-detail but low part count stage, I highly suggest trying to build a rocket with it, as especially with mods like Restock, it will leave you admiring the technical beauty of your own work. I highly appreciate all of the upvotes and give a big thanks to all of my followers.

Fly Safe!

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A stock rocket called CS-206 Porter Upper Stage. Built with 53 of the finest parts, its root part is Rockomax32.BW.

Built in the VAB in KSP version 1.12.5.

Some shots of the Porter in Kerbin Orbit. This view really shows off all of the little details I put into this stage, especially in the area near the engines. The APS modules and their thrusters are visible on the sides of the stage, as well as the external UDMH and spherical Nitrogen tanks.

A nice front view showing the probe core, docking port and fuel cells. The docking port is a method I like to use when attaching payloads to stages, as it doubles as a way to potentially reuse or de-orbit the stage.

A Porter releasing its payload, in this case a small communications satellite, but it has the capability to haul much larger payloads as well.