Nexus

Height: 61.4m

Diameter: 3m

10.5t to LEO, 2t to GTO with Phoenix, 1t to TLI with Phoenix

Additively manufactured

Carbon Composite

194 ton wet mass, 196 ton with Phoenix

First stage powered by 6 Helios M and a central Helios L engine

Second stage powered by Helios XL Engine

Optional “Phoenix” Kick Stage powered by Phoenix Engine for high energy orbits

Fully reusable

Propulsively Landed first stage, parachute on second stage, inflatable heat shield + drogues on kick stage

RTLS: First Stage lands on landing pad close to checkup facility, second & kick stages land in lake at SLC

Overview

Nexus is a two-stage, fully reusable medium-lift launch vehicle capable of delivering 10.5t to LEO, as well as 2t to GTO and 1t to TLI with its optional Phoenix Kick Stage. It is additively manufactured and assembled by the HAL-9000 Carbon Composite 3D Printer. The vehicle is 50.2m in height, with a 3m diameter. The interstage widens to 4m to accommodate the second stage heatshield. The vehicle has a wet mass of 194t and a dry mass of 32.4t. Nexus is designed to deploy satellite constellations and light GTO satellites. Due to its 3m diameter fairing size - much smaller than the usual 5m diameter - it cannot deploy traditional space station modules, but can deploy lightweight inflatable modules to LEO, which was its original purpose before it turned primarily into a megaconstallation deployer, however, inflatable space station modules still played a large role in Nexus’ development process.

Nexus’ first stage is powered by 6 Helios Engines in a “Hexaweb” with a central Helios L Engine with a longer nozzle for more efficiency at high altitude. The second stage is powered by one Helios XL Engine with an extending nozzle for extremely high vacuum efficiency, with the drawback being that if it were to fire at low altitudes for a propulsive landing, the engine would encounter critical flow separation and likely RUD. Nexus’ propellant is stored at 1 MPa (10 BAR) to increase density, as well as being subcooled, further increasing density, and therefore increasing propellant capacity, while not requiring any extra tankage.

The Methalox has many additives in it to increase thrust and isp by as much as 30%, as well as slightly increasing density. The engine have improved turbopump and injector efficiency, all of this gives the Helios engine 389s Isp at sea level, and 422s in a vacuum, with 718 kN thrust ASL, and 778 kN thrust in a vacuum, while consuming 188 kg/s of Methalox. Being balanced for use in thin atmosphere, the Helios L has 379s Isp ASL and 436s Isp in a vacuum, as well as having 649 kN ASL and 745 kN in a Vacuum, while burning 174 kg/s. The Helios XL is largely optimised for vacuum use, so has just 248s Isp ASL, but a truly nutty 450s Isp in a Vacuum, despite running on Methalox. It has 603 kN ASL, and 1,004 kN in a Vacuum, eating 223 kg/s of Methalox.

Flight Profiles

After the 6 outer Helios Engines throttle up, the launch clamps release and the rocket ascends. After reaching 10km, engine set 2 (3 of the 6 outer engines) shuts down and the central Helios L ignites. This switch leads to better efficiency at high altitude, as well as reducing propellant consumption while keeping a good TWR.

Once the fuel levels reach 10% in the first stage, engine set 1 shuts down, and the central engine throttles as low as it can, as well as firing its RCS to push itself away from the second stage. During this, the interstage mechanically opens into two parts, releasing the second stage. As the interstage opens, six robotic arms on the underside of the second stage retract, splitting the hexagonal heatshield into triangles and bringing them out of the way of the engine exhaust, and pulling them up to the side of the engine. The second stage engine ignites and it continues to orbit.

While the heatshield is retracting and the second stage burns to orbit, the first stage flips around, staying horizontal and aiming for the launch site. The interstage closes and four grid fins extend from the top of the fuselage. The central engine throttles up and the booster performs a RTLS boostback burn before locking its heading retrograde.

Upon reentry, the booster uses the grid fins and its precise nav system during descent to perform a pinpoint suicide burn on the landing pad. After descending to just 50km, the booster performs a reentry burn with engine set 1, lowering its speed to just below Mach 1. Over the landing pad, it ignites the central engine, performing a suicide burn and safely landing on the pad.

After reaching orbit, the second stage opens its fairings and releases the payload / Phoenix kickstage before deorbiting, protected by a heat shield that lowers around the engine, protecting it during reentry. Grid fins deploy, guiding the second stage during reentry. After the heat dies down, the fairings open again to create more drag and the parachute deploys, letting the stage land softly at the launch site.

In the case of the kickstage, which is only used for high-energy orbits (GTO, TLI, etc.). The kickstage lights its Phoenix Engine and deploys its solar arrays, boosting to the desired orbit, releasing the payload, and then deorbiting. The payload adapter of the kickstage is highly heat shielded, resisting the conditions of reentry, allowing the kickstage to parachute back to the launch site.

Important Notes!

Everything is operated by Action Groups, except for the strongback, which you just have to set slider 1 to max to retract.

This craft is made for RSS, it may well be an SSTO in JNO scale lol

Stage 2 & Kickstage let you time warp while burning so things don’t take a bloody eternity to get done

This rocket is very temperamental and hard to master - don’t worry if something goes horribly wrong, it’s not a skill issue, it’s just the rocket is finicky lol :)

Nexus Crew: https://www.simplerockets.com/c/OAYV20/Nexus-C