Selection of propulsion characteristics for systematic assessment of future European RLV-options

Reusable launch systems have the potential to significantly impact the space launch service market if both a high reliability and low refurbishment costs can be achieved. This study delves into the Vertical Takeoff and Vertical Landing (VTVL) methodology, as currently employed by SpaceX, and forms a segment of the ENTRAIN study by DLR. This broader study encompasses an examination of both Vertical Takeoff Horizontal Landing (VTHL) and VTVL reusable first stages, exploring their performance across high-level design parameters. This manuscript’s primary objective is to assess the quantitative impact of high-level design factors on launch vehicle performance, particularly in relation to the development of a future European reusable launch system featuring a VTVL first stage. For a two-stage vehicle with a payload performance of 7.5t into GTO, the effect of varying propellant combinations, staging velocities and engine cycles are assessed. The study encompasses an iterative, multidisciplinary analysis and sizing process for ten different configurations. Each design iteration not only entails a structural design analysis but also includes optimization of the ascent and descent trajectories. Finally, the developed vehicle concepts are compared to derive quantitative insights into the trade-offs associated with key design choices.

Comparative analysis of European vertical landing reusable first stage concepts

Wilken,

Stappert

2024

Overview of system study on recovery methods for reusable first stages of future European launchers

Dietlein,

Bussler,

Stappert

et al. 2024

The design of a reusable launch vehicle implies the need to provide for a means to safely retrieve the component to be re-used. Following economic considerations, reusable launch vehicle concepts tend to be designed such that large parts, like entire stages, are to be recovered. These are usually significant in size and weight and have acquired a considerable amount of energy during their primary mission. This poses the challenge of how to recover them in a way that makes it available for further re-uses. In the past and present, different methods were and are used. Depending on the selected recovery method, the system design is very different necessitating different technologies and competencies to be acquired for a successful design. Two major classes of recovery methods can be distinguished: those recovery methods ending with a vertical landing of the reusable stage and those ending with a horizontal landing. Both have their own benefits and drawbacks. In 2016, The German Aerospace Centre DLR has initiated a large in-house study with the aim of investigating, in a comparative manner on system level, both classes of recovery methods on a system level for two-stage-to-orbit launch vehicles with a reusable first stage and an expendable upper stage to be operated within a European context. Fuel choice and engine cycle were major design parameters that were considered during the study. The present paper presents the framework of this study describing the adopted study logic, providing an overview of the major findings obtained at the end of the first study phase and gives an outlook to the work of the second study phase. It ends with providing a view of a possible demonstrator and technology roadmap toward the realization of an operational two-stage-to-orbit launch system with a reusable first stage.

Options for future European reusable booster stages: evaluation and comparison of VTHL and VTVL return methods

Stappert,

Dietlein,

Wilken

et al. 2024

In the past, the majority of system studies on reusable space transportation performed within Europe focused on concepts relying on lift-generating wings for recovery. Recently, vertically landing concepts similar to those deployed successfully by SpaceX have moved to the center of technical attention. Both recovery and landing strategies have their pros and cons and it is not obvious what would be a sound choice for Europe. Therefore, the German Aerospace Center DLR initiated a parametric system study, named ENTRAIN, that evaluates the impact of different return options on the launcher design on a technical level: the vertical take-off, vertical landing method (VTVL) as used by SpaceX compared to the vertical take-off, horizontal landing (VTHL) method as used for the Space Shuttle. Within this study, launchers were designed using different propellant combinations, staging velocities and engine cycles. The designed launchers are evaluated in this paper regarding performance, technical difficulties, operational aspects, size, mass and complexity.