European Space Agency

Objectives

The L-XTA fulfils the delivery of Xenon gas for current and future hybrid & full electric propulsion (EP) systems, in particular for geostationary satellites such as Electra and Neosat.

The price competitive tank design and manufacturing approach enable maximum flexibility for the satellite prime with respect to volume, manufacturing time, and system performance. Our manufacturing methods minimise both lead-times as well as fabrication costs whilst remaining fully compliant to ECSS guidelines.

 

Challenges

The key challenge of the L-XTA project was to achieve the lowest possible tank mass while complying with stringent ECSS requirements. This was successfully demonstrated using state-of-the-art fracture mechanics analysis, NDI methods, and via established heritage including Leak Before Burst (LBB) testing from the recent HeHPV programme.
Qualification of both “tank families” is achieved with respective qualification test models (900 l for Family 1 & 440 l for Family 2) and the applied loads envelope the entire family volume range.
Satellite primes as well as ESA were involved throughout the project from early definition through to testing. Although this posed a logistical challenge, it offered the tremendous benefit of allowing detailed interactions, thereby helping to ensure customer satisfaction and achievement of their objectives.

Benefits

The L-XTA offers a low-weight, high-performance solution for the storage of large volumes (300-900 l) of Xenon for Electric Propulsion missions. Its large size offers significant advantages compared to a multi-tank approach. This single-tank solution offers: 
  • reduction of integration requirements for customer
  • minimisation of feedlines, heaters, thermal hardware, etc., thereby also increasing system reliability
  • minimisation of contamination sources compared to multi-tank approach
  • optimisation of available space envelope
Its advanced COPV design enables high-pressure (187 MEOP), long-term storage of Xenon with ease of installation to the satellite platform via equatorial attachments. The applied design & qualification loads carefully envelope all relevant launch vehicles. This offers customers high flexibility in their launcher selection.
Titanium was selected as the liner material to provide both the lowest possible tank mass as well as ECSS compliance.
The selected supply chain includes efficient, lean, and regional suppliers and also considers REACH and obsolescence topics. All components and materials are ITAR-free.
The dome manufacturing approach avoids use of forgings such that standard sheet material is utilised and the production time reduced to a minimum.
Despite its large volume, the achieved tolerance are exceptionally tight and fully compliant with customer requirements.  Applied automation practices lead to a high reproducibility. 
 

Features

L-XTA design, materials, and manufacturing methods were selected in order to maximise the relevant heritage and lessons learned of past programmes.  These programmes include the 1620-1910 l Alphabus Propellant Tank (ARTES 8), 40-90 HeHPV (ARTES 34) and Small Geo Xe-Tank (ARTES 11).
The tank design consists of a thin-walled (~0,8 mm) titanium liner. This liner is filament-wound by a carbon fibre epoxy composite. The resulting composite overwrapped pressure vessel (COPV) is integrated with a composite skirt that enables straightforward integration to the satellite Central Tube via metallic bolts.
In order to cover a comprehensive volume range of 300-900 liters, two dedicated “tank families” were established, each with a common diameter. 
  • Family 1 (600-900 l)
  • Family 2 (300-500 l)
Within each family, the tank volume is adapted via the length of its cylindrical section.
New and advanced manufacturing and inspection facilities enable cost-effective and reproducible quality control, particularly for critical processes.  This includes an automated eddy current inspection of domes and liners as well as industrialised TIG welding of the closure welds.

System Architecture

The L-XTA consist of a thin-walled welded titanium liner and a composite overwrap (COPV). The liner is composed of two domes and a connecting cylinder. The cylinder can vary in length to enable any volume within the overall range of 300-500 l (Family 2) or 600-900 l (Family 1). The domes are machined in-house from a preform to a wall thickness of ~0,8 mm. Pole-caps may include an outlet tube or blind caps as per customer preference and are EB-welded to the upper and lower domes as a fluid interface.
The liner is over-wrapped with a filament-wound, carbon fibre epoxy composite, and in a subsequent step an integral composite skirt is applied.
After machining of the attachment lugs in the composite skirt, integration to the satellite Central Tube is performed via metallic bolts.

Plan

The L-XTA project began in early 2016 with a Specification Requirements Review (SRR) that involved the satellite primes, future satellite operators and ESA. The Preliminary Design (PDR) and Critical Design Reviews (CDR) were successfully held in Fall 2016 and 2017, respectively. Qualification via an Engineering Model (EM) and two dedicated Qualification Models (QM) conclude the final phase with a Qualification Review (QR) in Q2 2019.

Current status

The 900 l Family 1 Engineering Model (EM) is undergoing testing from Q3 to Q4 2018. Of note, the EM testing regime is identical to the rigorous qualification test regime of the QMs. Qualification model manufacturing as well as the first flight model started in early 2018 with delivery in early 2019.

Status date

Wednesday, May 13, 2020 - 14:35