Wurm PhotonThruster

Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel

EngineeringChallenges

PerformanceParameters

MissionAnalysis

Earth-VenusRendezvous

Earth-MarsRendezvous

Earth-NEARendezvous

Discussion

Summary andConclusions

Mission Analysis andPerformance Comparison for an

Advanced Solar Photon Thruster

Bernd Dachwald1 and Patrick Wurm2

1Faculty of Aerospace Engineering,FH Aachen University of Applied Sciences, Germany

2Institute of Aeronautics and Astronautics,RWTH Aachen University, Germany

2nd International Symposium on Solar Sailing, New York City2022 July 2010

Bernd Dachwald and Patrick Wurm Advanced Solar Photon Thruster 1 / 30

Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


The Flat Solar Sail

The most extensively discussed solar saildesign concept is the flat solar sail (FSS)

Force acting on the ideal FSS:

FFSS = 2P(r)(A cos) cos n

Flat solar sail is used for light-collection and

thrust-direction Coupling betweenattitude and orbit control:

Effective light-collecting sail area A cosdecreases as the sail pitch angle increases

Changes of thrust direction require rotationof the whole solar sail structure (verydemanding for the attitude control systemdue to the sails huge moment of inertia andthe flexibility of its structure)

Ground deployment test of20 m 20 m solar sail atDLR/ESA in 1999 (imagecourtesy DLR)

Ground deployment test of20 m 20 m solar sail at NASAin 2005 (image courtesy NASA)


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


The Simple Solar Photon Thruster

Alternative solar sail design concept is the compound solar sail orSolar Photon Thruster (SPT)

The SPT decouples light-collection and thrust-direction by usingtwo or three mirror elements

The Simple Solar Photon Thruster (SSPT) has two mirror elements(Collector and Director)


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


The Solar Photon Thruster

The Dual Reflector Solar Photon Thruster (DR SPT) has threemirror elements (Collector, Reflector, and Director)

Force acting on the ideal SPT

FSPT = 2P(r)AC cos n


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Advantages of the Solar Photon Thruster

To maximize the change of orbital energy, it is usually desirable tohave a large transversal thrust component (perpendicular to theSun-spacecraft direction)

FSS: FFSS,t = 2P(r)(A cos) cos sin

SPT: FSPT ,t = 2P(r)AC cos sin

Norm

alize

d tra

nsve

rsal

thru

st

0

0.1

0.2

0.3

0.4

0.5

Difference

0

0.1

0.2

0.3

0.4

0.5

Pitch angle [deg]0 20 40 60 80

Normalized transversal thrust FSSNormalized transversal thrust SPTDifference


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Problems of the Solar Photon Thruster

According to previous theoretical studies, the SPT may excel theperformance of a flat solar sail . . . but . . . the previous investigated SPTmodels have several intrinsic oversimplification problems that can notbe disregarded for a thorough performance comparison with the flatsolar sail


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


The ASPT (Advanced Solar Photon Thruster)

We have developed a new Advanced Solar Photon Thruster(ASPT) design concept that avoids the problems of the SSPT andthe DR SPT

We have set the following requirements for the ASPT design:

1 Multiple reflections should be avoided2 The thermo-optical properties of the sail surfaces should be

considered3 Both the Collector and the Reflector are parabolic surfaces4 To avoid undesired torques, the ASPTs center of mass should

coincide with the Directors center of surface5 The finite size of the Director should be considered6 Shadowing effects should be considered


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


The ASPT (Advanced Solar Photon Thruster)

Director is located behind the Collector Collector must have a centerclearance

Payload (S/C bus) is located behind the Director ASPTs center of masscoincides with the Directors center of surface no unwanted torquesTo avoid that the Director can reflect some light rays onto the back side ofthe Collector, there is a minimum pitch angle min


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


ASPT SRP Force Model

The thermo-optical properties are described by the parametersP = {, s, f , b, Bf , Bb}Force acting on the ASPT comprises the force acting on theCollector, the force acting on the Reflector, and the force acting onthe Director

FASPT = FC + FR + FD (1)

Each force component was calculated with the method developed byL. Rios-Reyes and D. L. Scheeres (L. Rios-Reyes and D. L. Scheeres:Generalized Model for Solar Sails. Journal of Spacecraft and Rockets,42(1):182-185, 2005)


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Force on the Collector

Force on the Collector:

FC = 2P(r)piR2C

[2a1,C

1

ln

(4 +

4 +

)+

+ 2a2,C1

(4 +

4 +

)+

a3,C2

(1 )]

r

P(r) : solar radiation pressure at distance r from the sunRC : radius of the Collector

RR : radius of the Reflector , radius of the Collectors center clearing : inverse of the light concentration ratio, =

(fRfC

)2=(RRRC

)2=

ARAC

fC : focal distance of the CollectorfR : focal distance of the Reflector

AC : effective Collector area, AC = piR2C

AR : effective Reflector area, AR = piR2R

: measure for design compactness, =(RCfC

)2=(RRfR

)2ai,C : derived thermo-optical properties of the Collector (i {1, 2, 3})

PC = {C , sC , f ,C , b,C , Bf ,C , Bb,C} {a1,C , a2,C , a3,C}r : Sun-spacecraft unit vector


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Force on the Reflector

Force on the Reflector:

FR = 2P(r)piR2C[a1,Ca1,R

1

ln

(4 +

4 +

)+

+ a1,Ca2,R1

(4 +

4 +

)+

a1,Ca3,R4

(1 )]

r

P(r) : solar radiation pressure at distance r from the sunRC : radius of the Collector : inverse of the light concentration ratio : measure for design compactnessai,j : derived thermo-optical properties (i {1, 2, 3}, j {Collector, Reflector})r : Sun-spacecraft unit vector


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Force on the Director

Force on the Director:

FD = 2P(r)AD,i

[a1,Ca1,R

8

((a1,D cos + a2,D)n + a3,D r

)]

P(r) : solar radiation pressure at distance r from the sunAD,i : effective light collecting area of the Director : inverse of the light concentration ratioai,j : derived thermo-optical properties (i {1, 2, 3}, j {Collector, Reflector, Director}) : Director pitch anglen : Sail normal (unit) vectorr : Sun-spacecraft unit vector

For the computation of AD,i , three different cases have to be considered(see paper).


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


ASPT Engineering Challenges

Although the light isnot concentrated inone single point onthe Reflector surface(as for the SSPT),the Reflector and theDirector are exposedto an enormousradiation flux

0.5

0.5

1

1

1

1.5

1.5

1.5

1.5

2

2

2

2.5

2.5

2.5

33

3.53.5

4

RC/R

R = f

C/f

R = 1/1/2

r [AU]

5 10 15 20 25 300.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.5

1

1.5

2

2.5

3

3.5

4 [TeU]

= 4

Radiator temperature as a function of lightconcentration and solar distance

1 TeU , 933 K: Melting temperature of aluminum


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


ASPT Engineering Challenges

To avoid the destruction of the Reflector sail film, its temperaturemust remain much below 1 TeU

At 1 AU solar distance, a light concentration ratio as small as 11.2results in T > 0.5 TeU for = 4

For the Reflector of an ASPT with a reasonable light concentrationratio, these results show that the commonly projected sail filmmaterials can not be used without having an active cooling system ormuch better reflective properties

In any case, demanding thermal and/or structural requirements forthe Reflector and Director mirror elements (that we have consideredby a (moderate) mass penalty)


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


ASPT Parameters and Mass Calculation

We have used a complex model to calculate the ASPT mass for agiven characteristic acceleration (see paper)

The ASPT launch mass for a given characteristic acceleration isobtained from the solution of a constrained non-linear optimizationproblem

We have used the following input parameters (see paper):

Parameter Dimension FSS ASPTmin [deg] 0 35max [deg] 90 55SA [g/m

2] 22.7 22.7 - 0.05R [g/m

2] - 80D [g/m

2] - 80CB [g/m] - 150mPL [kg] 75 75min - 1/400RR,max [m] - 2.285Optical model real variableac [mm/s2] variable variable


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Comparison of the Solar Sail Launch Masses

Laun

ch m

ass [

kg]

100

120

140

160

180

200

220

240

260

Characteristic acceleration [mm/s2]0.1 0.12 0.14 0.16 0.18 0.2

real FSSOCIRID ASPTOCORID ASPTOCOROD ASPT

Optical models: OCIRID stands for a (real) optical Collector, an idealReflector, and an ideal Director (. . . and so on)


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-Venus Rendezvous:Mission Description

The solar sails are launched from Earth onto an interplanetarytrajectory with zero hyperbolic excess energy (C3 = 0)

The solar sails have to spiral towards the Sun

Orbit-to-orbit rendezvous (to obtain the constellation-independentabsolute flight time minimum)

Final constraints for successful rendezvous:

Distance to Venus 6.0 105 km (< mean SOI)Relative velocity to Venus 0.5 km/s


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-Venus Rendezvous:Results

Flight time overcharacteristicacceleration Flig

ht ti

me

[day

s]

400

600

800

1000

1200

1400


real FSSAkimaInt real FSSOCIRIDAkimaInt OCIRIDOCORIDAkimaInt OCORIDOCORODAkimaInt OCOROD

OCIRID: 74.7 - 78.3 %OCORID: 83.3 - 87.4 %OCOROD: 96.8 - 98.8 %

ASPT flight times w.r.t.FSS flight times

Flight time overlaunch mass

Fligh

t tim

e [d

ays]

400

600

800

1000

1200

1400

Launch mass [kg]100 120 140 160 180 200 220 240 260





Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-Mars Rendezvous:Mission Description


The solar sails have to spiral away from the Sun

Orbit-to-orbit rendezvous


Distance to Mars 5.5 105 km (< mean SOI)Relative velocity to Mars 0.1 km/s


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-Mars Rendezvous:Results


ht ti

me

[day

s]

1000

1500

2000

2500

3000

3500



OCIRID: 73.2 - 81.5 %OCORID: 83.6 - 88.6 %OCOROD: 96.3 - 99.6%



Fligh

t tim

e [d

ays]

1000

1500

2000

2500

3000

3500

Launch mass [kg]100 120 140 160 180 200 220 240 260


OCIRID: 91.3 - 102.6%OCORID: 112.2 - 121.3 %OCOROD: 137.2 - 153.5 %



Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-1996FG3 Rendezvous:Mission Description

1996FG3 is of great scientific interest and can be accessed relativelyeasily


The solar sails have to perform a considerable change of orbitaleccentricity (eEarth = 0.0167 e1996FG3 = 0.3499)Orbit-to-orbit rendezvous


Distance to 1996FG3 3.0 105 kmRelative velocity to 1996FG3 0.1 km/s


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-1996FG3 Rendezvous:Results


ht ti

me

[day

s]

800

1000

1200

1400

1600

1800

2000

2200

2400






Fligh

t tim

e [d

ays]

800

1000

1200

1400

1600

1800

2000

2200

2400

Launch mass [kg]100 120 140 160 180 200 220 240 260


OCIRID: 101.1 - 114.0%OCORID: 122.4 - 136.6 %OCOROD: 149.4 - 165.8 %



Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Earth-1996FG3 Rendezvous:Trajectory and Steering Angles

21

01

2 21

01

2

0.04

0.02

0

0.02

0.04

y [AU]x [AU]

z [AU]

TrajectoryEarth orbit1996FG3 orbit

FSS withac = 0.10 mm/s

2

Pitch

ang

le [d

eg]

0

20

40

60

80

Clock angle [deg]

0

50

100

150

200

250

300

350

Flight time [days]0 500 1000 1500 2000

Steering angles(black: pitch angle, blue: clock angle)


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion



21

01

2 21

01

2

0.04

0.02

0

0.02

0.04

y [AU]x [AU]

z [AU]


OCIRID withac = 0.10 mm/s

2

Pitch

ang

le [d

eg]

35

40

45

50

55

Clock angle [deg]

0

50

100

150

200

Flight time [days]0 500 1000 1500



Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion



21

01

2 21

01

2

0.04

0.02

0

0.02

0.04

y [AU]x [AU]

z [AU]


OCORID withac = 0.10 mm/s

2

Pitch

ang

le [d

eg]

35

40

45

50

55

Clock angle [deg]

0

50

100

150

200

250

300

350

Flight time [days]0 500 1000 1500 2000



Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion



21

01

2 21

01

2

0.04

0.02

0

0.02

0.04

y [AU]x [AU]

z [AU]


OCOROD withac = 0.10 mm/s

2

Pitch

ang

le [d

eg]

35

40

45

50

55

Clock angle [deg]

0

50

100

150

200

250

300

350

Flight time [days]0 500 1000 1500 2000



Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Discussion of the Results

Mean ASPT flight time with respect to FSS flight time for the samecharacteristic acceleration:

Earth-Venus Earth-Mars Earth-1996FG3

OCIRID 76.6 % 78.3 % 88.4 %OCORID 85.7 % 85.9 % 97.3 %OCOROD 97.8 % 98.4 % 109.2 %

For the same characteristic acceleration, the ASPT performsgenerally better than the FSS

Worse ASPT performance for the Earth-1996FG3 rendezvous than forthe Earth-Venus and the Earth-Mars rendezvous

For the Earth-1996FG3 rendezvous, optimal solar sail steering requiressmall and large pitch angles due to the large eccentricity change

Because of the constrained ASPT pitch angle(35 deg 55 deg), the eccentricity can not be changedeffectively


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Discussion of the Results

Mean ASPT flight time with respect to FSS flight time for the samelaunch mass:

Earth-Venus Earth-Mars Earth-1996FG3

OCIRID 94.4 % 97.1 % 108.8 %OCORID 115.1 % 117.7 % 131.6 %OCOROD 141.6 % 145.1 % 160.3 %

For the same launch mass, the ASPT performs generally worse thanthe FSS


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Summary and Conclusions

According to previous theoretical studies, the compound solar sailmay excel the performance of a flat solar sail

We have introduced a realistic design concept and simulation modelfor a compound solar sail, termed Advanced Solar Photon Thruster,or ASPT, that does not suffer from oversimplifications

To compare its performance with respect to the conventional flatsolar sail, we have calculated time-optimal transfer trajectories toVenus, Mars, and a near-Earth asteroid

The ASPT typically achieves shorter flight times than a flat solar sailwith the same characteristic acceleration

However, it is not superior to the flat solar sail, if one compares thelaunch masses when realistic optical properties and structural massesare assumed

Our results show that the smart idea of a compound solar sail doesnot withstand closer scrutiny. Based on technical complexity,scalability, and performance, the flat solar sail seems to provide thebetter design choice


Introduction

FSS

SPT

ASPT

ASPT Model

SRP ForceModel



MissionAnalysis



Earth-NEARendezvous

Discussion


Mission Analysis andPerformance Comparison for an

Advanced Solar Photon Thruster

Bernd Dachwald1 and Patrick Wurm2

1Faculty of Aerospace Engineering,FH Aachen University of Applied Sciences, Germany

2Institute of Aeronautics and Astronautics,RWTH Aachen University, Germany

2nd International Symposium on Solar Sailing, New York City2022 July 2010


IntroductionThe Flat Solar Sail (FSS)The Solar Photon Thruster (SPT)The Advanced Solar Photon Thruster (ASPT)

ASPT ModelSRP Force ModelEngineering ChallengesPerformance Parameters

Mission AnalysisEarth-Venus RendezvousEarth-Mars RendezvousEarth-NEA RendezvousDiscussion of the Results

Summary and Conclusions

Documents

Wurm PhotonThruster