Our Nexø II rocket is ready and will be launched in the spring of 2018.

The Nexø II rocket will be  the most advanced rocket build and launched by CS so far. The Nexø rocket class is a technology demonstrator in advance of building the significantly bigger Spica rocket that will take our astronaut to space. Thus, Nexø is an important part of the Spica roadmap and the technology developed and used in the Nexø class will be used in the Spica rocket.

Design and development

Just as Nexø I the Nexø II rocket is powered by our own BPM5 engine providing a nominal thrust of 5000 N running on ethanol and liquid oxygen. It has a body diameter of 300 mm, a total length of 6.7 m and a dry weight of about 178 kg. With a target filling ratio of 85% propellants it will carry 114 kg propellants for a Gross Lift-Off Weight (GLOW) of 292 kg.

Nexø II is actively guided by our own custom build Guidance and Navigation Computer (GNC). A set of four graphite jet vanes are used as the Thrust Vector Control system (TVC) commanded by the GNC. The system is identical to the one successfully used on the Nexø I mission. The animation below illustrates the perfect performance of the TVC system on the Nexø I rocket.

Nexø I flight animation

So what’s new ?

Nexø II is in many aspects identical to Nexø I, we have however implemented a few changes and newcomings:

  • Dynamic Pressure Regulation (DPR) including a 6000 standard liter (20 liter @ 300 bar) helium tank
  • Problematic LOX tank vent valve changed for cryo compatible model
  • LOX tank filling monitored by capacitive gauge

Dynamic pressure regulation

The simplest way to operate a liquid propellant rocket is by Pressure Blowdown (PBD). A mode of operation where the propellant tanks are typically filled to 2/3 capacity with liquid and the last third is filled with pressurized gas. The pressurized gas is then used to drive the engine. Nexø I flew in this way.
Second up on complexity ladder comes Dynamic Pressure Regulation (DPR). In this mode there is no significant ullage in the propellant tanks, they are filled close to 100%. Instead a pressure tank with gas under very high pressure and a set of control valves are integrated into the system. This system can then supply the propellant tanks with feed pressure as the tanks are emptied. Nexø II will fly using such a system.

We’ve earlier tested a DPR system on our teststand with our BPM-5 rocket engine with good results. Here you can see a short video from one of our test burns:

BPM-5 DPR Burn

 

The DPR system on Nexø II is very similar to the system we know from the test stand, the main difference is the pressure tank. On the test stand it consist of two common diving bottles totaling 24 liters. Such diving bottles are obviously too heavy, so for Nexø II we purchased a 20 liter composite tank, which is approved for 300 bar. The tank itself weighs 12 kg.

Read more about Dynamic Pressure Regulation in this blog: Nexø II DPR

Capacitive level sensor for liquid oxygen.

To ensure correct filling of the LOX tank during launch preparations we have recently developed a capacitive level sensor calibrated for liquid oxygen. This will allow us to fill the LOX tank with a significantly higher accuracy than what was possible on Nexø I. More information on our inhouse developed capacitive level sensor is available in the video below.

Building a Capacitive Liquid Oxygen Level Sensor

Expected flight performance

The primary consequence of the implementation of the DPR system is that Nexø II can have a higher filling ratio and better propellant efficiency than Nexø I. This means that Nexø II will have significantly more total impulse available. It is however also heavier.

With a GLOW if 292 kg and an effective thrust of 4500 N (10% lost to drag on jet vanes) Nexø II will accelerate at an initially modest 5.6 m/s^2 when leaving the launch tower. After 43 seconds of flight it will have depleted its propellants and reached a speed of 1280 km/h or Mach 1.14 at an altitude of 7 km. From here it will coast to apogee at 12.6 km. Upon descent it will deploy a ballute and parachute based landing system to land in the ocean.

Thus Nexø II is neither intended to set altitude or speed records. It is entirely a demonstrator vehicle that will hopefully show we are on track for implementing the same technology in the Spica rocket.