Abstract:
This research on Reusable Launchers was motivated by the need
to reduce substantially the cost of space transportation. The
specific objective was to- explore the perception that
launcher reusability is the key to achieving these major cost
reductions. The exploration was achieved by undertaking a
comparative system study on potentially feasible reusable
launcher concepts, using a consistent set of design tools, a
standard analysis methodology and a standard reference
mission.
To set the background f or the research, the results of an
extensive literature review are 'presented on the vehicle
studies and technology developments that are engaged across
the world on reusable launchers. Comprehensive vehicle
studies appear to be engaged without justification for the
choice of selected concepts in the absence of results from
comparative system studies of reusable launchers. Technology
developments also appear to be engaged without clear links to
needs derived from vehicle system studies.
The challenge of reusability is then addressed. Firstly, to
set the performance and cost targets of reusable launchers,
the capabilities of current expendable launchers are derived.
Secondly, to establish the operational requirements for
reusable launchers, the probable space transportation needs
for the early 21st century are derived. Thirdly, the concepts
and characteristics of reusable launchers are derived,
allowing the selection, on a rationale basis, of a short-list
of 13 potentially feasible reusable launcher concepts for
analysis in the research. The performance equations of reusable launchers are 'then
derived, leading to the preparation of the comparative
analysis tools.
The major work-of the research, which ''comprises the
performance analysis, technical feasibility assessment and
cost"analysis of each candidate vehicle are, then presented
and compared-.
A set of acceptance requirements for performance,, technical
feasibility and operational costs - of reusable launchers is
then -derived. The results of the comparative analysis for
each candidate launcher are then measured , against these
requirements. The results of the comparative analysis show
that only 2 of the' 13 candidate reusable launcher concepts
are able to meet all the acceptance'requirements. These two
acceptable vehicles are both rocket-propelled. They are, ýin
order of preference:
a single-stage-to-orbit, rocket-propelled, vertical
launch and vertical landing vehicle;
a two-stage-to-orbit, rocket-propelled, vertical launch
and horizontal landing vehicle.
The operational ''costs per launch for these two'vehicles,,
based on a utilisation plan of 3 vehicles operating for 20
years at a launch rate of 12 launches per year, was
calculated to be about 20 % of the current costs of the
European Ariane 44L expendable launcher. This warrants their
further evaluation in a thorough feasibility study. The more complex, air-breathing propelled, horizontal launch
and landing vehicles were found to be unable to meet the
performance, technical feasibility and cost requirements:
Several vehicles were found to be unable to deliver a
positive payload mass to orbit;
Several vehicles were found to have technology
requirements that were deemed to be infeasible to
achieve;
Several vehicles were found to have operational costs
ranging from equal to double that
-of
the European Ariane
44L expendable launcher,, which -was- adopted as a
comparative reference vehicle.
The contributions of this research to the advancement of
knowledge on reusable launchers are:
a clear identification of the performance, capability
limits of 13 plausible reusable launcher concepts;
an analysis methodology for determining the performance
capability limits for any reusable launcher concept;
a clear identification of the reasons. for the poor
practical performance of air-breathing propulsion
systems for Earth-to-orbit launchers, which results from
their installed operational characteristics.