2020 SSTO Fleet + Ground Support Vehicles!

Jamie Logan · March 29, 2020

Hey Everyone!

I haven't posted here in quite a few years, but now that I've gotten back into KSP, I wanted to share what I've been working on for the past few weeks.

We all love Single-Stage-To-Orbit (SSTO) spacecraft for their potential for re-usability, so I wanted to create a system that allowed me to legitimately process and relaunch them without recovering the spacecraft and relaunching from the SPH between missions. To that end, I developed a fleet of three SSTOs with a compliment of ground support and processing vehicles that can be used to fully refuel and prepare an SSTO for return to LKO with newly fitted payloads. The fleet consists of three SSTOs, two mobile gantries, three trucks, two trailers, and a crew transport buggy.

SSTOs

All three ships can reach LKO with between ~500 and ~1,500 m/s of on-orbit delta-V remaining depending on payload mass. All have forward-mounted docking ports and RCS thrusters for rendezvous, docking, payload deployment, etc. All are designed with a center of mass (COM) that remains stationary regardless of fuel levels or payload mass (to the extent that the payload's COM is in the geometric center of the cargo bay). The payload-carrying variants (Mk2 & Mk3) have been tested with maximum-mass payloads (I.E. a fuel tank that takes up the entire cargo bay). All can be de-orbited and landed fully "Dead stick". All have action groups to allow for engine/mode toggle, steering toggle, payload bay toggle, etc. Retract the forward landing gear on Mk1 and both the forward and aft landing gear on Mk2 when towing to allow for steering.

Table 1: SSTO Spec. Summary
SSTO	Mk1	Mk2	Mk3
Max. crew	3	2*	0*
Wet mass (t) (minus payload)	16.2	32.0	162.4
Dry mass (t)	12.2	24.0	73.3
Height (m)	3.8	4.4	6.0
Width (m)	6.4	10.1	13.4
Length (m)	13.2	23.0	37.4
Max. payload mass (t)	-	~7	~50
Max. payload length (m)	-	4.9	10.0
Max. payload diameter (m)	-	1.25	2.5

* Can be exceeded by housing crew in payload.

SSTO Mk1

The smallest of the three, the Mk1 is the primary LKO crew shuttle. It has room for three, and can comfortably get from the KSC to LKO with sufficient fuel to rendezvous with an LKO target and de-orbit, but its payload is limited to crews only. The design is Liquid fuel only, so the RAPIERS are set to run on open cycle exclusively. The single Nerva is used to make the final push to orbit, circularize, and perform on-orbit maneuvers. The choice to go "no oxidizer" is partly for simplicity, and partly because the minimal-drag + high TWR RAPIER configuration makes the final delta-V needed to reach orbit low enough that it can be done with the Nerva. It also means that when fully re-fueled in LKO, the single Nerva will yield enough delta-V to go pretty much anywhere, without any pesky oxidizer/tanks to slow you down.

When launching, set prograde hold with a ~20 deg elevation due east once you pass 300 m/s. The RAPIERS will take you up to around 1000 m/s at 10,000 km, at which point you activate the Nerva. Even though you're still deep in the atmosphere, the Nerva reaches about 700 ISP and nearly vac thrust at this altitude, plus we need to start our apogee kick early since the Nerva alone will yield a fairly low TWR once the RAPIERS flame out completely around 20 km. The time to apogee may start to drop back down once you're on Nerva alone, so nose up to keep it around ~60 sec until your orbital velocity reaches ~2,300 m/s, at which point you'll be safe to reach orbit after a coast to apogee and circularization. It has 4 linear RCS ports housed in the forward and aft mini cargo bays, which are set to toggle open/closed along with the RCS hotkey.

SSTO Mk2

The midsize variant, the Mk2 can take a small payload to LKO along with a crew of two. Its fuel tank, engine, and launch trajectory configuration is virtually identical to that of SSTO Mk1, except with twice the RAPIERS and Nervas. Its RCS ports are contained within the payload bay, so it must be open for any RCS-based maneuvering. The furthest forward and aft tanks are empty; they are for structural/aerodynamic purposes.

SSTO Mk3

The largest of the fleet, the Mk3 is a heavy-payload LKO shuttle. The design is RAPIER-only, and the vessel is unmanned. It can deliver an orange tank to LKO without much fuss. Launching is fairly straightforward; set prograde hold with a ~20 deg elevation due east once you pass 300 m/s. You should bottom-out on open cycle mode around 20 km and ~1750 m/s orbital velocity, at which point you switch to closed cycle to push your apogee up out of the atmosphere and reach orbit. Like the Mk2, Its RCS ports are contained within the payload bay, so it must be open for any RCS-based maneuvering.

Mobile Gantries

The piston array on Gantry Mk3 can be operated using the robotics controller on the side of the claw to ensure that all 10 pistons are operating in unison. Be careful when docking the claw to a payload on a trailer connected to a Truck. Back off the piston right after docking to ensure that the weight of the gantry doesn't force the truck + trailer into the ground and break their wheels.

Mobile Gantry Mk2

This ground support vehicle can be used to transfer payloads to and from SSTO Mk2's cargo bay. It has a single XL piston and a claw to use for payload manipulation.

Mobile Gantry Mk3

This ground support vehicle can be used to transfer payloads to and from SSTO Mk3's cargo bay. It has a compound array with 10 XL pistons and a claw to use for payload manipulation. It also serves as the primary refueling vehicle for SSTO Mk3.

Trucks

Trucks A and C have servos which allow for trailer pivoting. Simply unlock the servo and set the torque to zero after coupling. Use the piston before coupling to align the claw.

Truck A

This ground support vehicle can be used to tow trailers and SSTO Mk1. It has a piston-mounted claw for easy coupling, and the piston is mounted on a servo to allow for trailer pivoting when steering. The spring strength in the tire suspensions sometimes need to be lowered during payload loading/unloading using a gantry, as having Truck A connected to a trailer, a payload, and a gantry can cause the wheels to get a little... jumpy, especially if the gantry piston hasn't been relaxed after connecting. It can be used to tow SSTO Mk2, but this is best done when MK2 is empty after having returned from orbit. A fully fueled Mk2 + payload is best towed using Truck C.

Truck B

This ground support vehicle can be used to refuel SSTOs Mk1 & Mk2 (Mk3 is refueled using Mobile Gantry Mk3).

Truck C

This ground support vehicle can be used to tow trailers and SSTOs Mk1 & Mk2. It has a piston-mounted claw for easy coupling, and the piston is mounted on a servo to allow for trailer pivoting when steering. It can be used to tow SSTO Mk3, but this is best done when MK3 is empty after having returned from orbit. Best practice with SSTO Mk3 is to tow it to the runway while empty using Truck C, and refuel and add payload right before launch. A fully fueled Mk3 + payload can only easily be moved using its own RAPIERS and landing gear steering.

Trailers

Trailer Mk2

This ground support vehicle can be used to carry Mk2 payloads, when towed by Truck A or C. The distance between the two docking ports is slightly larger than that of SSTO Mk2's cargo bay.

Trailer Mk3

This ground support vehicle can be used to carry Mk3 payloads, when towed by Truck A or C. The distance between the two docking ports is slightly larger than that of SSTO Mk3's cargo bay.