minimum-time problem resolution under constraints for low...
Post on 30-Jan-2020
7 Views
Preview:
TRANSCRIPT
Page 1
ASTRIUM
Minimum-time problem resolution under
constraints for low-thrust stage trajectory
computation
Nathalie DELATTRE
ASTRIUM Space Transportation
Page 2
ASTRIUM
• Purpose :
– Taking into account new technology for upper stage and/or satellite like solar propulsion or electric propulsion, reassessthe satellite launcher task sharing
– The payload is considered at the telecommunications system on board satellite (usually considered as the satellite payload)
• Two tools are available to answer the question
Introduction
Page 3
ASTRIUMLaunch analysis :Insertion by low thrust stage
• MIPELEC : resolution of minimum-time problem
– Quick optimisation tool, initially developed under a thesis
at CNES, then industrialised through EADS-ST and CNES
shared contract by LAAS (CNRS)
– finds the optimal command for minimum time transfer
(continuous thrust)
– applications: slow insertion from Earth orbit to escape
orbit by electrical, solar-thermal or nuclear propulsion
– very user-friendly tool
– very quick optimisation solving (~ 1 min)
– used for any advance-project, but does not consider
constraints like eclipses or visibility constraint by ground
station
Page 4
ASTRIUMLaunch analysis:Insertion by low thrust stage (2)
• TOPE : resolution of minimum-time problem under constraints
– finds a quasi-optimal command for minimum time transfer
including constraints (quasi-continuous thrust)
– takes eclipses into account (burn interruption during
shadow period) and visibility constraint (burn possible
only during given set of ground station visibility)
– applications: slow insertion from Earth orbit to escape
orbit by electrical, solar-thermal or nuclear propulsion
– very user-friendly tool
– quick optimisation solving (a few minutes)
– successfully benchmarked with MIPELEC for the
unconstrained case
Page 5
ASTRIUMELECTRIC PROPULSION FOR SATELLITES (1)
Satellites market analysis
-Payload characteristics
(required power system)
-Short and long terms scenarios (EP, mixed,
chemical satellites repartition)
Satellites model
LEO/MEO & GEO applications
-Architecture model
mass repartition = f(payload)
-Costs model (fabrication)
-Constraints (Van Allen,…)
Propulsion data
-Electric & mixed propulsion models
mass, thrust, Isp = f(power)
-Constraints
-Costs model (EP, mixed, chemical)
Launchers data
-Characteristics
-Launch costs models
Satellites associated costs
-Insurance
-Operator’s investment
-Satellite exploitation
-Maximum transfer duration
(operators constraint)
Reference satellites selection
LEO/MEO & GEO applications
-Propulsion characteristics
-Mass repartition
-Constraints
-Short term
Mission analysis
LEO/MEO & GEO applications
-Injection strategy trade-off
-Impact on launcher filling ratio
-Comparison with competitorsShort term economical aspects
LEO/MEO & GEO applications
-Global cost (operators point of view)
-Gain assessment (comparison with classic
chemical satellite)
Phase 2
Short term scenario synthesis
Europe launchers positioning vs competitors
(sensitivity wrt satellites market scenario)
Short term
Mission and Market considerations
Phase 1
Work logic
Page 6
ASTRIUM
Satellite á propulsion électrique - Transfert en temps minimum de MEO (7 deg) vers GEO avec contrainte d’éclairement
-30000 -10000 10000 30000
-40000
-35000
-30000
-25000
-20000
-15000
-10000
-5000
0
5000
10000
15000
20000
25000
30000
35000
40000
km
Deformation de l’orbite avec zone d’eclipse
km
ELECTRIC PROPULSION FOR SATELLITES (2)
Page 7
ASTRIUM
INJECTION ORBIT (ORBIT 1) ELECTRICAL PROPULSION
BEGINNING (ORBIT 2)
STRATEGY
designation Za / Zp / 7° designation Za / Zp / 7°
100% chemical GTO 200 / 35 786 / 7
MEO Za / Za / 7 = orbit 1100% electrical GTO+ Zp / 35 786 / 7 = orbit 1
GTO 200 / 35 786 / 7 GTO+ Zp / 35 786 / 7
subGTO 200 / Za / 7 MEO Za / Za / 7hybrid
supGTO 200 / Za / 7 supGTOZp / Za / 7
with (Za+Zp)/2 = 35786 km
ELECTRIC PROPULSION FOR SATELLITES (3)Scenarios
Page 8
ASTRIUM
Satellite á propulsion électrique : masse initiale 3410 kg, poussée 1N, ISP 1700s
Transfert en temps minimum de GTO+ (14000km / 35786km / 0deg) vers GEO
Durée du transfert : 38.52j / Masse consommée : 199.56kg / Nombre de révolutions : 46.05
0 5 10 15 20 25 30 35
15000
20000
25000
30000
35000
40000
alt
itu
de (
km
)
Altitudes apogée et périgée (km)
date (j)0 5 10 15 20 25 30 35
3220
3240
3260
3280
3300
3320
3340
3360
3380
3400
masse (
kg
)
Masse totale (kg)
date (j)
ELECTRIC PROPULSION FOR SATELLITES (4)
Page 9
ASTRIUMSTOTS (1)
� Propulsion system principles: 3 sub-systems
�Concentrator Array and Tracking System (CATS)
which collects and focuses the sun light
�Receiver Absorber Converter (RAC)
which converts the concentrated sunlight into usable heat used to vaporise LH2
�Propellant Feed and Storage System (PFSS)
which stores the propellant and feeds the engine
Solar-Thermal Orbital Transfer Stage
Page 10
ASTRIUM
� Intermittent thrust mode
� Same architecture as described before, except that the RAC is now a Receiver
Accumulator Converter
� Introduction of a thermal storage mass heated by solar energy
� The heat is later extracted by the propellant for propulsion purpose
� The transfer is made of succession of thrusting and recharging phases, driven by the
RAC temperature
Highest admissible
temperature
Lowest admissible
temperature
Thrusting Thrusting Thrusting
Recharging RAC
(eclipse case)
Recharging RAC
(no eclipse)
Perigee
first
Apogee
next
� Goal of the study
� Design the optimal components of the solar-thermal engine together with the payload
optimisation process for the transfer from LEO to GEO
STOTS (2)
Page 11
ASTRIUM
� One orbit model
inputs: � current orbit characteristics (apogee, perigee, inclination)
� sun relative location, solar flux
� state of the propulsive system thanks to a model (RAC temperature, PFSS state, …)
� control: mass flow, boost location (apogee or perigee) and duration, inclination correction
Solving process: � estimation of eclipse duration on the current orbit
� estimation of power at the entrance of RAC (CATS model)
� RAC heating during balistic sun lighted phase
� PFSS functionning
� RAC characteristics (temperature, phase change, Isp(t), F(t), ∆V delivered, Isp, F)� gravity losses estimation (see later)
� apogee, perigee and inclination modification after the boost
� To avoid large gravity losses, the boost durations have to be optimised depending
on the amount of heat accumulated by the RAC
� The sun lighted duration increases while raising the apogee, so the boost duration
may be increased
Use of a linear model Tboost(iorb) = Tboost (1) + T’boost . iorb
Where iorb = orbit number, Tboost (1) and T’boost are the optimised parameters (2 for apogee, 2 for perigee)
STOTS (3)
Page 12
ASTRIUM
� The one orbit model is used several
times until the final conditions are
reached
Global performance of the system
� Design of the propulsion system:
The 3 most influent parameters have been selected:
� Energy storage mass (≈RAC mass)allows to increase Isp, but then mass balance penalised
� CATS area
� Mass flow
STOTS (4)
Page 13
ASTRIUM
PFSS model
Input : pressure, external flux
Output : TVS, heater , self-
pressurization , going out
propellant characteristics (H prop),
mass (M PFSS), geometry
RAC model ( ballistic and boost )
Input : material , insulation , storage
mass, initial temperature
Output : final temperatures (GH2,
RAC), phase change, Isp(t), F(t),
MRAC
CATS model
Input : solar area , solar flux,
optical efficiency ,
concentration ratio
Output : power at the
entrance of RAC (P CATS),
mass (M CATS)
Orbit characteristics :
Input : Apogee ,
Perigee , Sun location
Boost
Input : propellant
flow rate (q prop)
Output : duration (t boost)
Ballistic phase :
Output:
eclipse durations , lit
ballistic phase (t sun)
PCATS
tsunqprop, tboost
qprop, tboosttsun
Hprop
Global performance :
Output : ∆V, duration , mass
budget, payload mass
MCATSMPFSS
MRAC
Orbit performance :
Output : ∆Vboost,
<Isp>, <F>
∆Vboost
ORBIT LOOP
� Whole optimisation process
Criterion: maximise payload
Parameters (7):
� MRAC
� Qprop
� CATS area
� Tboost(1) and T’boost for apogee
� Tboost (1) and T’boost for perigee
STOTS (5)
top related