Www.strath.ac.uk/[email protected] Solar Sail Mission Applications and Future Advancement 20 - 22 July 2010 Malcolm Macdonald The

www.strath.ac.uk/[email protected]

Solar Sail Mission Applications and Future Advancement

20 - 22 July 2010

Malcolm Macdonald

The Second International Symposium On Solar SailingThe New York City College of Technology of the City University of New York, Brooklyn, New York, U.S.A.

& Colin McInnes

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Introduction

Photons perturb spacecraft by conservation of momentum

Solar sailing uses the perturbation to reduce propellant mass

Momentum carried by individual photons is extremely small• Requires large reflector to provide a useful momentum transfer

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Absence of reaction mass makes solar sailing romantic Romanticism ≠ Realism

Proponents have traditionallyseen solar sailing as atechnical nirvana

• i.e. the complete solution

Difficulty in advancing low TRL concepts often underestimated

Romanticism

20 - 22 July 2010 Malcolm Macdonald 3Worm Hole Space Art

Solar Sail Mission Catalogue

Diverse range of mission applications have been proposed

Must identify the concepts which are truly enabled• Or, significantly enhanced

Enables development of anapplication-pull technologydevelopment roadmap

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Solar Sail Mission Catalogue

Mission catalogue considers wide range of mission concepts• Allows definition of key characteristics of enabled/enhanced missions

Critical missions act as facilitators to later missions

Application-pull technology development roadmap is thus established


Planet-Centred...and other Short Orbit Period Applications

Highly Non-Keplerian Orbits Inner Solar System Rendezvous Outer Solar System Rendezvous Outer Solar System Flyby Solar Missions Beyond Neptune


Mission Categories


Trajectory design largely restricted to escape manoeuvres• Or, relatively simplistic orbit manoeuvring such as lunar fly-by’s

Significant technology demands on the solar sail• Optimal energy gain requires sail be rotated 180 degrees once

per orbit and then rapidly reset

Other simplisticorbit manoeuvresrequire similarlyagile sailtechnology



Requirement for an agile sail is a significant disadvantage

Two applications identified which don’t require an agile sail• GeoSail and Mercury Sun-Synchronous Orbiter • Use a fixed attitude to independently vary a single orbit

parameter creating a non-inertial orbit


Highly Non-Keplerian Orbits

Requires small, continuous acceleration in a fixed direction

Displace the spacecraft to artificial equilibrium point• A location some distance from a natural libration point


Highly Non-Keplerian Orbits

Continuous thrusting lends well to solar sailing romanticism Two primary applications have been proposed

• Polesitter and Geostorm• Use fixed attitude sail to provide continuous thrust



Approximate UK-DMC FOV

The view from a Polesitter...


Approximate Landsat-7 Enhanced Thematic Mapper Plus FOV

The view from a Polesitter...


The view from a Polesitter...Approximate Deep Space Climate Observatory Scripps-EPIC FOV

Inner Solar System Rendezvous

Sample return to the inner planets discussed extensively• Perceived as high-energy and therefore good for solar sailing

Low-Thrust rendezvous requires v∞ ≈ 0 at target body

Transfer is thus significantly increased• True for bodies which are “easy” to get to, i.e. Mars, Venus• Once captured into a bound orbit typically require an agile sail


Inner Solar System Rendezvous

Mars Sample Return “grab & go” optimal for solar sailing

• 5 – 6 year mission v’s ~2 years for equivalent chemical mission

Venus Sample Return Similar to MRS but with increased

launch mass sensitivity• 1000 m2 sail for sample return leg offers

potential launch cost saving

Mercury and Small Body Sample Return Truly high-energy transfer trajectories

• Only low-thrust propulsion systems offer viable mission concepts

• Solar sailing offering potential benefits

Small Body missions do not typically require an agile sail


Outer Solar System Rendezvous

Low-Thrust rendezvous requires low v∞ at target body

Now even more difficult to “slow-down” with a solar sail Can use gravity assists at large moons to capture

Following capture, all orbit manoeuvres are slow

Consider Europa, Deep inside Jupiter gravity-well

• Long duration

Deep inside Jupiter’s intense radiation belts• Significant shielding required


Outer Solar System Flyby


Removes requirement for low v∞ at target body

Consider a Jupiter trajectory

Outer Solar System Flyby

Jupiter atmospheric probe mission was considered Chemical propulsion was concluded to still be superior

• Due to mass and number of probes required sail was very large

As target moves further from Sun, solar sail propulsion becomes increasingly beneficial• Leading to a peak in benefits for missions beyond Neptune


Solar Missions

Ulysses used Jupiter gravity assist to pass over solar poles• Orbit is highly elliptical; pole revisit time of approximately 6 years

ESA’s Cosmic Visions mission concept Solar Orbiter • Maximum inclination of order 35 deg using SEP

Mid-term sail could deliver spacecraft to solar polar orbit in ~5yrs• SPO is an example of type of high-energy, inner-solar system mission which is enabled by solar

sail propulsion


Beyond Neptune

Significant benefit to missions beyond Neptune

• For either a Kuiper Belt or Interstellar Heliopause mission

Destinations beyond the Heliopause are challenging for solar sailing alone


Event Time

Launch T0

Aphelion passage T0 + 1.5 yrs

Perihelion passage T0 + 2.8 yrs

Sail Jettison (@5 AU) T0 + 3.2 yrs

Kuiper Belt Transit (40 – 55 AU) T0 + 5.7 – 8.3 yrs

100 AU T0 + 12.9 yrs

200 AU T0 + 23.2 yrs

Key Characteristics

Reducing launch mass does not directly reduce mission cost Launch cost is only reduced if the reduced launch mass allows a

smaller launch vehicle to be used Saving 10 – 20 M€ launch costs is 2 – 4 % total cost reduction

• Is that a good cost/risk ratio for the project?

Reduction must be a significant percentage of mission total

Can sub-divide all solar sail missions into two classes Class One

• Solar sail is used to reach a high-energy target, after which the sailis jettisoned by the spacecraft

Class Two• Uses continuous thrust to maintain an otherwise unsustainable

observation outpost


Venus escape at end of sample return mission

Mercury and high-energy small body Sample Return missions Outer solar system planet fly-by

Oort Cloud

Key Characteristics


Non-Inertial Orbitssuch as GeoSail or a Mercury Sun-Synchronous Orbiter Highly Non-Keplerian Orbitssuch as Geostorm and Polesitter Kuiper-Belt fly-through

Solar Polar Orbiter Interstellar Heliopause Probe

Planetary escape at start of mission

Mars missions

Outer solar system rendezvous and centred trajectoriesLoiter at the Gravitational Lens

Enabled orSignificantly Enhance

Marginal benefit No benefit

Class Two

Class One

Key Characteristics

Positive Characteristic

Very High Energy transfer trajectoryInner Solar SystemHighly Non-Keplerian and Non-Inertial orbitsFinal stage in a multi-stage systemFly-by beyond the orbit of Neptune


Negative Characteristic

Mars and Venus rendezvousOuter Solar System rendezvousShort orbit period with rapid slew manoeuvresHigh radiation environmentHigh pointing stability requiredRequired to rendezvous with a passive bodyFly-by beyond solar gravitational lens

Key Missions

GeoSail Earth-centred, non-inertial orbit ~40 m square sail, at an assembly loading of ~35 g m-2

• To provide heritage to later missions, the design is required to be more demanding than considered in isolation

Solar Polar Orbiter Close solar mission, rapid polar revist ~150 m square sail, at an assembly loading of ~8 g m-2

• Sail slew rate of 10 deg per day required

Interstellar Heliopause Probe 200 AU in ~15 – 25 years ~150+ m disc sail, at an assembly loading of ~2 g m-2


Application Pull...

The culmination of any technology roadmapmust be enabled by previous milestones

IHP requires a sail architecture withlow assembly loading



...Technology Development Route

Current applications are clustered about the mid to far term

IKAROS Design point@ 200 m2 & 75 gm-2

Future Advancement Roadmap

Current applications are clustered about the mid to far term To much risk in attempting to directly jump to, say, SPO

Initial flight tests must provide confidence in the technology and a clear path towards some enabling capability

• JAXA sounding rocket deployments an excellent example of this• Risk was spread across several tests and led to IKAROS



Requirement exists to backfill the roadmap Either develop new mission concepts, or Re-engineer the mission concepts and the vision of the

future of solar sailing• Removing the gap between near and mid-term applications


Advancement Degree of Difficulty

Consider the concept of Advancement Degree of Difficulty• AD2 categorises risk, from 0 – 100 %

Consider system level engineering risk of solar sailing• The programmatic risk of an advanced technology demonstrator

is found to be, at best, acceptable• And, dual development approaches should be pursued to

increase confidence

The AD2 of solar sailing must be reduced



Romanticism ≠ Realism Spacecraft engineering realism seeks to evolve technology

Consider solar sail propulsion as a spectrum of advancement


Secondary propulsionPerturbation

Primary propulsion

Requires reaction mass to counteract

Attitude control systems

Traditional solar sail vision

Now

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Solar sailing for attitude control is well established• Used on many GEO spacecraft – often called a “trim tab”• Used by Mariner 10 and MESSENGER spacecraft• Used by Hayabusa

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Solar sailing is a mature technology Programmatic risk in advanced solar sailing can be

reduced by hybridising the propulsion

Mariner 10 & MESSENGER both used a small kite No reason why other inner solar system missions would

not similarly benefit Missions could be primarily SEP, with a secondary sail Can incrementally balance and then switch this

• AD2 is thus significantly reduced



Hybridisation of solar sail mission with SEP can significantly enhance the mission



Hybridisation of solar sail mission with SEP can significantly enhance the mission Consider a hybrid sail/SEP Geostorm variant

• A 45-m square sail, at an assembly loading of ~45 g m-2

• Storm warning time is doubled!


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Sail Area (m2)

MeSR

IHP

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Kuiper Belt

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VenusSR

MeS-S

Geostorm

GeoSail

?

?

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May not needsails >50 – 100 m


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1000 10000 100000

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MeSR

IHP

JAtPSbSR

SPO

Kuiper Belt

Polesitter

VenusSR

MeS-S

Geostorm

GeoSail

?

?

?

?

IKAROS Design point@ 200 m2 & 75 gm-2

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Www.strath.ac.uk/[email protected] Solar Sail Mission Applications and Future Advancement 20 - 22 July 2010 Malcolm Macdonald The