AERODYNAMICS AND FLYING QUALITIES REQUIREMENTS FOR A LONGRANGE
TRANSPORTATION SYSTEM
Rodrigo Haya Ramos (1)
, Jordi Freixa(1)
, Tobias Schwanekamp(2)
, Martin Sippel(2)
, Rafael Molina(3)
(1) DEIMOS Space S.L.U., Ronda de Poniente 19, 28760, Tres Cantos, Spain, Email: [email protected]
(2) DLR, Robert-Hooke-Straße 7, 28359 Bremen, Germany, Email: [email protected]
(2) European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, Netherlands, Email: [email protected]
ABSTRACT
The objective of a long range hypersonic transportation
system is to take advantage of high altitude and high
velocity to perform intercontinental flight in the order of
one hour. The SpaceLiner concept has been proposed by
the Space Launcher Systems Analysis group (SART) of
the German Aerospace Center (DLR). In the frame of
the European Commission project FAST20XX, this
concept has been further investigated in several areas.
This paper presents the results of the aerodynamics and
Flying Qualities activities conducted to support the
design and evolution of the system. Engineering
methods have been combined with rapid CFD analysis
in order to mature the dataset and to increase the
reliability of the Flying Quality analyses. Areas for
further design iteration of the SpaceLiner concept have
been identified.
1. INTRODUCTION
The European Commission (EC) co-funded project
FAST20XX (Future High-Altitude High-Speed
Transport 20XX) aims at exploring the frontier between
aviation and space by investigating suborbital vehicle
concepts (1).
The main focus is the identification and mastering of
critical technologies for such vehicles rather than the
vehicle development itself. The technology
development is based on two advanced suborbital high-
speed transportation concepts one for the medium term
(5-10 years) and another for the longer term (>30 years).
The long term concept is related to suborbital point-to-
point long distance transport in very short time. Within
this type of transportation, the SpaceLiner concept
proposed by the DLR has been investigated [2]. It is a
vertically launched two-stage rocket space vehicle
system concept used to identify technologies required
for suborbital ultra-fast long-range transport of the long-
term future.
One of the areas of investigation for such future
transportation system is Flying Qualities, whose
objective is the characterisation of the performance of
the aerodynamic shape combined with the Mass,
Centring and Inertia (MCI) properties in a given flight
envelope. The Flying Qualities also provide inputs for
the specification of the Guidance, Navigation and
Control (GNC) system and feedback about the
aerodynamic control surfaces sizing.
The Flying Qualities provide an extended
characterisation of the aerodynamic performance of the
shape. Therefore, the reliability of the Flying Qualities
conclusions and recommendations is linked to the
maturity of the aerodynamic database. The aerodynamic
database available in early phases of the design is
normally derived with rapid engineering methods
lacking detailed characterisation of critical effects like
non-linearity and cross-couplings. As a result, initial
conclusions tend to be optimistic about the Flying
Quality performance and hence about the feasibility of a
given aerodynamic shape.
In the frame of FAST20XX it has been mitigated by
combining engineering methods with CFD analyses at
specific flight conditions. The objective is not only the
verification and correction of the dataset but also the
improvement in the estimation of the stability and
control derivatives and the identification of the range of
validity of the engineering methods. Thus, a combined
aerodynamic database covering the expected flight
envelope, (hypersonics to subsonics), angle of attack
and control surfaces deflections as input to the
trajectory, flying qualities and GNC design activities is
created with a higher level of realism. The selected CFD
needs to be rapid enough to explore the complete flight
envelope. Thus an Euler solver with an unstructured
mesh and adaptive Mesh Refinement has been selected.
The objective of the Flying Qualities analyses was to
support the system configuration definition (Centre of
gravity namely), to validate the control surfaces sizing
and to characterise the performance in terms of stability,
controllability and expected static and dynamic
response. For the candidate reference trajectory, the
Flying Qualities have been evaluated in detail both in
nominal condition and with uncertainties for several
SpaceLiner concepts in order to validate the evolution
of the shape and layout.
Main results and recommendations from the early
SpaceLiner concepts to the latest configuration are
presented. The aerodynamic activity was the result of a
joint effort between DEIMOS (CFD for SL4 and SL7),
DLR (engineering AEDB) and ESA (CFD for SL7.1).
2. THE SPACELINER CONCEPT
Since 2005, the Space Launcher Systems Analysis
group (SART) of the German Aerospace Center DLR
has been working on a novel vehicle concept for long
range hypersonic passenger transport. The “SpaceLiner”
is a large, rocket propelled vehicle (length ~60 m) that is
launched vertically with launch and ascent being
assisted by a reusable booster. Both, the hypersonic
passenger stage and the booster utilize liquid
propellants.
In contrast to other hypersonic vehicle concepts the
SpaceLiner does not incorporate radically new or
unproven technologies. Instead, rather conventional
rocket propulsion systems and vertical ascent
trajectories are used. The SpaceLiner concept contains
several technical and logistical challenges, such as
active cooling technologies, passenger accommodation
and safety together with the provision for suitable
launch and landing sites.
The final objective of the SpaceLiner development is to
dramatically reduce intercontinental travel times
compared to today’s subsonic passenger aircraft flights
by travelling at hypersonic velocities. For example, a
trip from Europe to Australia, which is the current
reference mission, will last only 90 minutes carrying 50
passengers. Also other intercontinental routes such as
New York to Australia have been considered.
It is a gain to lose concept, in which the vehicle gains
energy thanks to the rocket stage and hence glides back
towards the destination losing energy by friction. The
profile is suborbital reaching altitudes around 80 km and
speeds around Mach 20.
Several SpaceLiner concepts have been produced. This
paper covers from SpaceLiner 4 concept (SL4) up to
configuration 7.1, named SL7.1.
Figure 1. Artist’s impression of the SpaceLiner7 with
the booster
3. AERODYNAMICS
The aerodynamic dataset (AEDB) is the driver for
Mission and GNC performances. Two main activities
have been carried out. First, an aerodynamic inspection
and verification from a Flight Mechanics perspective to
validate its suitability for design activities. Then, CFD
calculations have been performed to improve the
characterization of the stability derivatives. The
requirements for the CFD matrix have been derived
from the mission, Flying Qualities and GNC needs.
These CFD results have been used to refine the
Aerodynamic Dataset (AEDB) used for engineering
activities. Computations have been performed between
DEIMOS and ESA to support SpaceLiner concepts SL4
to SL7.1.
Figure 1. CAD model of the Spaceline SL4, SL7 and
SL7.1 concepts.
The software used to run the CFD simulations is an in-
house code based on: Euler flow modelling with
tetrahedral spatial discretization; adaptive Mesh
Refinement, feature-based (Mach number has been
implemented for this work) involving anisotropic
remeshing and mesh movement/adaptation; node
Centred, blended anisotropic second- and fourth-order
dissipation; local time stepping. This configuration
ensures good coverage of the flight envelope with
moderate computational resources.
The adaptation feature allows characterising the bow
shock properly. The streamlines and mesh for a 2D
ramp of 20º at Mach 2 are shown in Fig. 2. The
theoretical pressure coefficient is 0.6582, while the CFD
provides 0.6587 at the centreline and 0.6589 at the
wedge. The theoretical shock angle is 53.41º, while the
CFD captures a shock at 53.2º. This benchmark case
validates the use of this adaptive unstructured mesh
solver in supersonic and hypersonic regime.
Figure 2. Streamline and mesh (10584 elements) for a
20º 2D ramp at Mach 2.
An initial aerodynamics of the SpaceLiner 4 concept
was available for the conceptual design of the vehicle.
As long as it is a key input that strongly drives the
Flight Mechanics and GNC performance of the vehicle,
a verification and extension of the dataset through
detailed CFD analyses has been conducted.
A total of 38 CFD cases have been conducted covering
transonic to hypersonic regime with and without
elevator deflection (see Tab. 1). Not all Mach, Angle of
Attack (AoA) and elevator combinations have been
inspected, but those of interest according to the flight
envelope and initial trim assessments. The CFD
representation of the vehicle includes a highly detailed
surface mesh in which all geometrical aspects of the
SpaceLiner CAD geometry have been modelled. Body
flaps and wing elevator have been considered. CFD
results were used to detect artificial steps and gaps and
hence to refine the CAD modelling. The Mach
distribution for Mach 19.8 is shown in Fig. 3.
The results show that the initial aerodynamics was
appropriate in the hypersonic regime, but refinement
was needed in the supersonic and transonic part, where
larger differences were noticed (Fig. 4). The CFD
results have been used to populate the aerodynamic
dataset. Fig. 5 and Fig. 6 show a comparison of the
longitudinal aerodynamics (lift, drag, pitch moment and
L/D) between the conceptual aerodynamic dataset,
which is based on rapid engineering methods, and the
CFD results at Mach 3 and Mach 10. CFD results
confirm trends of dataset with offsets as expected due to
the simplified pressure coefficient (Cp) characterisation
used in the Newtonian flow model implemented within
the engineering methods.
The CFD results were integrated within the
Aerodynamic Database (AEDB) to create a new release
and solve the issues detected in the initial release:
unrealistic supersonic data and non-linearities and
inconsistent elevator efficiency in some conditions. This
improvement had a significant impact on mission and
Flight Mechanics predictions, which stresses how
relevant is to improve the aerodynamic characterization
since first step to reduce design iterations. The updated
AEDB incorporates preliminary viscous effects.
Figure 3. Mach distribution at Mach 19.8
Table 1. CFD matrix of cases for SL4
Mach AoA Elevator
1.1 to 19.8 0 to 10º -5º to 5º
Figure 4 Raw comparison between the initial database
based on engineering methods and the CFD results
0 5 10-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
CL
AoA [deg]
0 5 100
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
CD
AoA [deg]
0 5 10-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
CM
AoA [deg]
0 5 10 15-3
-2
-1
0
1
2
3
4
5
6
7
AoA [deg]
LoD
Figure 5. Comparison between the conceptual
aerodynamics and CFD at Mach 3 (CD, Cm and L/D)
0 5 10-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
CL
AoA [deg]
0 5 100
0.01
0.02
0.03
0.04
0.05
0.06
AoA [deg]
0 5 10-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
CM
AoA [deg]
0 5 10 15-3
-2
-1
0
1
2
3
4
5
6
AoA [deg]
LoD
Figure 6. Comparison between the conceptual
aerodynamics and CFD at Mach 10 (CD, Cm and L/D)
Figure 7. integration of the CFD results within the
AEDB for engineering activities (lift coefficient)
Fig. 7 shows for instance the lift coefficient from the
updated AEDB and the matching with the available
CFD data as a function of Mach number for several
angles of attack and elevator conditions.
The vehicle evolved during the project towards SL7,
which implemented a new design for the wing. A CFD
campaign was performed to assess the impact into the
major aerodynamic performances, namely in terms of
drag and lift-to-drag ratio. A comparison with the SL4
CFD campaign was conducted (Tab. 2). The hypersonic
efficiency (both cases without viscous correction)
improves in hypersonics and it is similar in supersonics.
Now, at null AoA it is possible to generate lift. There is
a reduction of drag that will be beneficial during the
ascent but it will increase heat fluxes during the entry
phase. The SL7 shape rapidly evolved in terms of wing,
fuselage and empennage towards the SL7.1 concept.
For the SL7.1, a characterisation of the vehicle
aerodynamics was directly conducted through CFD. A
matrix of 36 cases was designed (Tab. 3) to cover the
complete unpowered flight in clean configuration (no
control surfaces deflection). The SL7.1 shape introduces
a higher level of complexity in terms of CFD modelling
compared to SL4. Thus, the following steps were
followed: from the CAD of the vehicle provided at
system level, an initial surface mesh was created and
subsequent surface mesh decimation and smoothing was
performed with YAMS. Volume meshing was
performed for two domains: 6-chord and 20-chord
domain for supersonic-hypersonic and transonic-
subsonic computations respectively. Systematic mesh
adaptation by enrichment and node movement was used.
Table 2. Comparison between CFD for SL4 and SL7.
Coefficient M = 2
AoA = 10 deg M = 2.31
AoA = 0 deg M = 19.6
AoA = 6 deg
CFD SL7 CFD SL4 CFD SL7
CFD SL4 (M=2)
CFD SL7 CFD SL4
CD 0.1071 0.1205 0.0204 0.0209 0.0105 0.0133
LoD 4.6592 4.8880 1.1814 ~0 6.0286 4.2556
Table 3. CFD matrix of cases for SL7.1
The same CFD code has been used to cover from
hypersonics to subsonics with different grids. Fig. 3
shows the comparison of the Mach field at Mach 0.9 for
two angles of attack. Transonic behaviour is observed in
the leeward side with the formation of an aft shock
wave that becomes stronger and moves forward as the
angle of attack increases from 6º to 10º.
Fig. 8 to 10 show the Mach contour and the surface and
fluid grid in subsonics and hypersonics. The efficiency
of the mesh adaption procedure is verified in
hypersonics, where more elements are needed.
Figure 8. Mach 0.9 alpha 6 & 10, Mach contours
Figure 9. Mach 0.4 alpha 0, Mach contours (left) and
Figure 10. Mach 0.7 alpha 7, Mach contours (left) and
Figure 11. Mach 10 alpha 6, Mach contours (left) and
grid (right). NNODES~0.5e5 NELEM~2.7e5
grid (right). NNODES~0.5e5 NELEM~2.7e5
grid (right). NNODES~5.5e5 NELEM~3.5e6
An aerodynamic dataset (AEDB) has been built around
this CFD campaign covering from subsonics to
hypersonics. Elevator efficiency as been added using
engineering methods and hence it will require future
refinement using dedicated CFD analyses.
The drag, lift and pitching moment coefficient with
respect to the Moment Reference Centre (MRC) is
shown in Fig. 12 as a function of Angle of Attack
(AoA), Mach and elevator deflection. Trimmability for
an AoA of 10º is achieved in nominal conditions down
to subsonic. Trends are deemed adequate for the Flying
Qualities analyses.
Starting from the raw AEDB tables, an application rule
has been created to calculate longitudinal aerodynamic
coefficients C as well as the stability and control
derivatives needed for Flying Qualities and GNC:
C=(C0(,M)+CDE(,M,e)+CDBF(,M,bf))(1+UC(M)) (1)
Where C0 is the coefficient in clean configuration (no
control surfaces deflection) and CDE and CDBF are the
contribution of the wing elevator and body flap.
Uncertainty is modelled as a scale factor dependent on
Mach as a first approach.
0 5 10 150
0.2
0.4
AoA [deg]
CD
dE = -10 deg
0 5 10 15
0
0.5
1
1.5
AoA [deg]
CL
dE = -10 deg
-30 -20 -10 0 10 20 30-0.2
0
0.2
dE [deg]
CM
AoA = 10 deg
Figure 12. SL7.1 aerodynamic database
4. FLYING QUALITIES
Flying Qualities (FQ) constitute the exhaustive
performance metrics for the aerodynamics combined
with the Mass, Centering and Inertia properties of the
vehicle. The classical definition of Flying Qualities for
airplanes is applicable for re-entry vehicles: Flying
Qualities are defined as the stability and control
characteristics that have an important bearing on the
safety of flight and on the […] ease of flying an airplane
in steady flight and in manoeuvres. However, aircraft
Flying Qualities are not directly applicable and a
specific approach and methodology is required.
According to the Space Vehicles classification for
Flying Qualities (FQ) proposed in [3], the SpaceLiner
vehicle is of Class III, space plane, which comprises
winged vehicles that generate aerodynamic lift through
its body and wings and whose manoeuvrability exceeds
that of lifting bodies (Class II) and capsules (Class I).
The SpaceLiner flight covers hypersonic entry flight,
descent and approach and landing into runway.
Therefore, categories A, B and C apply.
In a hypersonic vehicle the angle of attack profile is
strongly linked with the mission feasibility and hence its
selection and assessment cannot be uncoupled from the
trajectory design. The objective is the evaluation of the
Centre of Gravity (CoG) box provided by system team
and the identification of the associated entry corridor.
This process provides the range for the design of the
nominal angle of attack profile during the entry and
identifies the available corridor for trajectory design.
The Flying Qualities analyses are performed with the
Flying Qualities Analysis (FQA) Tool. This FQA Tool
will enable a Flight Mechanics engineer to follow the
steps that build the FQA Framework to successfully
perform the required flight qualities analyses within a
given program. The FQA Tool software package has the
flexibility to connect to different vehicles models (e.g.
capsule, space plane and lifting body) and data. The
FQA Tool performs computations based on the user’s
inputs (mainly: vehicle models, flying quality
objectives) in order to derive the criteria allowing the
characterization of the flying quality of the vehicle and
the definition of guidelines for the design of the GNC
for the atmospheric re-entry.
The system context makes reference to operational
context in which the system or the simulator will
operate, giving indication of its interaction with the
environment in terms of inputs and outputs. Fig. 13
presents the context use of the FQA Tool. The user of
the FQA Tool will be an experienced flight mechanics
analyst. It will use the FQA Tool to derive the criteria
allowing the characterization of the flying quality of the
vehicle and the definition of guidelines for the design of
the GNC for atmospheric re-entry. The FQA Tool can
also interface with an external Worst Case Analysis
Tool for the identification of worst-case combinations
of dispersions for the flying quality analysis.
Flying Qualities
Analysis
Framework
Tool
Flying Quality of Vehicle
Flight Mechanics
Analyst
Vehicle AEDB
Flight data
Trajectory GNC Guidelines
Worst-Case
Analysis Tool
Environment
Vehicle FCS
Figure 13. FQA Tool Context
Uncertainties must be incorporated in the Flying
Qualities analyses since the first step as they might
change the feasibility and hence conclusions at system
level. For instance, Fig. 14 and Fig. 15 show the angle
of Attack corridor for a given CoG position for the SL4
concept with and without uncertainties. This corridor is
limited by trim authority, minimum L/D performance
and static stability. The supersonic and hypersonic
regime shows a feasible corridor with wide margins for
AoA design. However, if uncertainties are considered,
the corridor shrinks and it is practically closed in the
Mach 7 to Mach 10 region, which is critical due to the
transition from hypersonic AoA to supersonic AoA.
For what concerns the SL7.1, the Angle of Attack
corridor has identified several areas for improvement
either on the aerodynamic side or in the system layout.
It is shown in Fig. 16. A minimum angle of attack in
hypersonics is needed to guarantee longitudinal stability
in the region with high heat fluxes. There is a stability
barrier that prevents the vehicle from being stable for
Mach lower than 11. The vehicle is trimmable is the
whole domain except in low supersonics, where
saturation occurs. It indicates the need of using the body
flap to improve the trim authority and/or to revisit the
control surface sizing.
For the angle of Attack profile coming from an
optimised trajectory (black wide line in Fig. 16), a
Monte Carlo campaign has been performed to assess the
trim, stability and controllability characteristics of the
SL7.1 concept against uncertainties and perturbations.
Perturbations on the Mass, Centre of Gravity and Inertia
properties, aerodynamics, trajectory and angle of attack
have been considered (Tab. 4)
-0.05
-0.05
-0.05
-0.05
-0.0
5
-0.0
5
-0.0
5
-0.0
25
-0.0
25
-0.025
-0.0
25
-0.025
-0.0
25
-0.0
25
-0.02
5
-0.0
25
-0.0
1
-0.0
1-0
.01
-0.0
1
-0.0
1
-0.0
1
-0.01
-0.0
1
-0.01
1 11 1
2
2
2 2
3
3
3
3
3
3
3
34
4
Mach
Ao
A (
de
g)
AoA entry corridor, AEDB1.1 with k222 extrapolation, 99%ile with 90% CI, COG [-34.566; 0; -1.056] m
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 220
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20d
E = -35 deg
SM = 0.0
SM = 0.0
LoD
Figure 14. SL7.1 AoA corridor
Table 4. Uncertainties considered in the FQ analyses.
Variable SL4 SL7.1 Type Unit
Aerodynamics +/- 1 Uniform -
AOA trim AOA +/- 2 Uniform deg
CoG location – X xG +/ 1 Uniform m
CoG location – Y yG +/- 0 yG +/- 0.1 Uniform m
CoG location – Z zG +/- 0.1 Uniform m
Mass +/- 5% Uniform kg
Roll, Pitch, Yaw inertia [A, B, C] +/- 10% Uniform kg.m2
Figure 15. SL4 AoA corridor without uncertainties
Figure 16. SL4 AoA corridor with uncertainties
5 10 15 20-35
-30
-25
-20
-15
-10
-5
0
5
10
15
Mach
d E [
deg]
5 10 15 20-0.05
0
0.05
0.1
0.15
0.2
Sta
tic M
argi
n [L
ref]
5 10 15 200
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Mach
LoD
[-]
5 10 15 200
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Mach
Pul
satio
n of
Sho
rt P
erio
d [r
ad/s
]
5 10 15 20-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Mach
Dam
ping
of
Sho
rt P
erio
d [-
]
5 10 15 2010
-1
100
101
102
103
104
105
Mach
Tim
e to
Dou
ble
[s]
Figure 17. Longitudinal flying Qualities of SL7.1 for a
trajectory and CoG: 99% range with 90% Confidence
Results are presented in Fig. 17: elevator deflection,
Static Margin (SM), lift-to-drag ratio (LoD), pulsation,
damping and time to double/time to half for the short
period response. The red and blue curves represent the
bounds of the 99% range of variability with 90%
confidence level derived from a 2000 shots Monte Carlo
campaign. The green line corresponds to the mean
value. As anticipated in the entry corridor analysis, only
using the wing flaps it is not possible to trim the vehicle
in supersonics. Stability issues are present below Mach
10. However, the time to double (time required by the
response to a step input to become double) is greater
than 10 s above Mach 4 and hence it does not represent
an issue from a control standpoint. For Mach lower than
4 the instability becomes severe.
This instability has an impact into the GNC physical
architecture (ex: redundancies) and hence in order to
mitigate the impact several actions to be tackled in
future design loops have been identified. For instance,
to improve the system layout by moving the CoG or
revisiting the vehicle wing position and controls
surfaces layout accordingly.
5. CONCLUSIONS
The aerodynamics of a long range transportation
concept like the SpaceLiner has been extensively
characterized though CFD in order to support the
vehicle evolutions.
The resulting aerodynamic database available for the
design is much more mature than the usual databases
available at this stage. This higher level of reliability
also anticipates to early design stages the identification
of issues. As a result, modifications can be rapidly
injected into the design without waiting to later phases
where changes are more difficult to accommodate.
Areas for further maturation and characterisation of the
shape performance have been identified, in particular in
terms of lateral-directional aerodynamics, efficiency and
sizing of the control surfaces and uncertainty policy.
Flying Qualities issues have been identified as a result
of entering into details. It is a valuable input for driving
the future evolutions and consolidation of the shape.
A strong interaction between System and Flying
Qualities/GNC team is required to speed up that shape
maturation.
Uncertainties must be considered since the beginning as
they might completely change the conclusions and
recommendations. It comprises not only aerodynamics
but also the vehicle, for instance in terms of mass
properties design envelope.
CFD Euler based computations combined with
engineering methods has been proven as a effective
approach in terms of availability in early design stages
of a mature aerodynamic dataset for system and
subsystem activities. Flying Qualities are used to
provide a complete and exhaustive picture of the
aerodynamic performances for a given configuration.
6. ACKNOWLEDGMENTS
This work was performed within the ‘Future High-
Altitude High-Speed Transport 20XX’ project
investigating high-speed transport. FAST20XX,
coordinated by ESA-ESTEC, is supported by the EU
within the 7th Framework Programme Theme7
Transport, Contract no.: ACP8-GA-2009-233816.
Further information on FAST20XX can be found on
http://www.esa.int/Our_Activities/Space_Engineering_
Technology/FAST20XX_Future_High-Altitude_High-
Speed_Transport_20XX.
7. REFERENCES
1. Mack, A. et al (2011). FAST20XX: Achievements on
European Suborbital Space Flight. Proceedings of
the 7th European Symposium on
Aerothermodynamic,. Noordwijk, Netherlands:
European Space Agency, 2011, id.35
2. Sippel, M., van Foreest, A., Bauer C., Cremaschi F.
(2011). System Investigations of the SpaceLiner
Concept in FAST20XX. Proc. of 17th AIAA
International Space Planes and Hypersonic
Systems and Technologies Conference, San
Francisco, CA, USA.
3. Haya Ramos, R. at al (2011). Flying Qualities
Analysis for Re-entry Vehicles: Methodology and
Application. Proc. of AIAA Guidance, Navigation,
and Control Conference, Portland, USA