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Constellations for Space Physics Missions: Advantages and Feasibility

Vassilis AngelopoulosSpace Sciences Laboratory, UC Berkeley

and

Jet Propulsion Laboratory

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Introduction• Since the 90’s the global forcing of Earth’s space

environment became understood in an average sense, thanks to individual satellite missions and their fortuitous correlations. This resulted in good statistical models (space-climate) but left the details of space environment prediction (space-weather) for future endeavors.

• The epitomy of those missions was the ISTP program, an armada of $0.5-1B satellites placed in the solar wind (WIND), magnetotail (Geotail), and poles (POLAR), more recently enhanced by ACE, SOHO and Explorers FAST, TRACE and IMAGE.

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ISTP MOST IMPORTANT FINDINGS (http://istp.gsfc.nasa.gov)

1. The deep magnetotail does not hold the key to magnetosphere dynamics. The "action" appears to be much closer to Earth ...

2. Collisionless reconnection is "the" most important energy transfer process between the solar wind and magnetosphere ...

3. The terrestrial plasma source mass quickly loads the outer magnetosphere after solar events and thereby may be a catalyst or driver, rather than a consequence, of magnetospheric dynamics.

4. Shock fronts in the solar wind can be so steeply angled that they reach Earth before they are observed at L1. This is currently causing many uncertainties in the reliable modeling of the geospace response.

5. Different phases of a single solar cycle produce widely varying solar wind input conditions to the magnetosphere and, in turn, a widely varying cycle of dynamic response within the magnetosphere.

The future resides with answering new science questions that have come from these discoveries.

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NASA’s Mid-90’s realization that Constellations are necessary next step• Fall 1997 AGU session on Constellations• Proceedings of papers on necessity and feasibility

of Constellations (on line at:)

http://sprg.ssl.berkeley.edu/ConstellationClassMissions )• Pathfinder for Solar Terrestrial Probes missions

(STEREO, MMS, GED, MC)• Roots of smaller constellation efforts (ST5,

THEMIS, SWARM)

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From Sun To Earth• Important for Earth’s magnetosphere are:

– Coronal Mass Ejection (CME) generation– Solar Energetic Particle (SEP) production

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CMEs: Evolving 3D objects• Generation mechanism unclear (relation to flares

and their shocks?).• CME production cannot be predicted by imaging

solar processes alone, currently.• CME evolution is complex, out of ecliptic• CME geometry affect geoeffectiveness:

– B-field (|B|, Bz) at Earth.

– Particle acceleration, connection to Sun

• Main inhibitor to progress is imaging of tenuous CME at birth and its evolution against ambient solar wind thereafter.

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STEREO: Imaging CMEs out to 1AU• Understand CME triggers• Characterize CME propagation• Discover mechanisms and sites

of energetic particle acceleration• Develop a 3-D, time-dependent

model of the ambient solar wind.

INVESTIGATIONS:SECCHI (Imaging: EUV, WhiteLight)

SWAVES (Remote Sensing Waves)

IMPACT (In Situ)

PLASTIC (In Situ)

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SEP production: Where, how, when?• Flares or CMEs?• Ambient wind, or site

precursors?• CME topology: local

modulation of SEP fluxes – before they reach 1 AU

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LWS-IHS: INNER HELIOSPHERIC SENTINELS• Four Spacecraft in 0.25x0.75 AU orbits at various mean

anomalies; using Venus fly-by insertion.

• Study:– Timing and dispersion to identify source location

– Acceleration mechanism pinned with help from imaging

– SEP seed populations in ambient solar wind

– SEP transport and decay rates in the inner heliosphere

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• Solar wind and magnetosphere have sharp plasma boundaries that are structured: Clusters study microphysics, gradients, curls and HF waves.

• Solar wind and magnetosphere have internal structures and self-organization. Constellations study correlations and wave-numbers over large baselines.

At Earth’s vicinity

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Cluster: Resolving spatio-temporal ambiguities• Cluster can tell a passing from an evolving structure• Can measure curl(B)=J, verify gradB=0, curlV on occasion• Cluster primary emphasis (orbit strategy) in the cusp• Other regions also visited: tail, ring current, magnetopause.• Revolutionized space research, casting new light on old

observations• 4 spacecraft

• dr=0.1-2RE

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MMS: Understanding reconnection• Reconnection a universal process, still elusive• Only in the magnetosphere can it be studied in detail• Microphysics of ion diffusion region crucial and electron

diffusion region likely important (requires 1PDF/5msec)• Scale sizes of 10 debye lengths (5km) likely important• Sufficient resolution and measurement capability to

determine relative contributions to generalized Ohm’s law:

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MMS: implementation• Four spacecraft in very tight formation• High time resolution measurements• High data volume and accurate orbit control• 300kg/sc wet, ~300M mission, Launch=Jan. 2009

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MMS implementation

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Large scale correlations: Substorms(the breathing mode of the magnetosphere)

• Substorms are fundamental modes of magnetospheric energy processing (not continuous but store-and-release)

• Result in auroral eruptions that start very localized• Trigger unclear: Reconnection? Current Disruption?

MERCURY: 10 min EARTH: 3.75 hrs JUPITER: days

ASTROSPHERE

SUBSTORM RECURRENCE:

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Auroral eruptions are localized…

AuroraAurora

…and are a manifestation oflocalized magnetospheric substorms

MAGNETOSPHERESO

LAR

WIN

D

EQUATORIAL PLANE

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THEMIS: The When, where and howof magnetospheric substorms

• 5 identical probes, aligned capture 10 substorms/year• In situ particles and fields

at nightside (primary)• Bonus: dayside and

radiation belt science• 130kg/sc wet, $180M

launch=2006

• Scales: 1-30RE

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THEMIS Constellation concept

SST

ESA

EFIa

EFIs

FGM

SCM

Tspin=3s

D2

925

-10

@ C

CA

S

Instrument I&TUCB

Mission I&TSwales

Encapsulation

& launch

BGS

OperationsUCB

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Earth’s magnetic field:Variable and evolving

• Accurate separation of external influences needed tounderstand interior’s strength and evolution

• Must be at distance from crustal fields, and have space-time differentiation to tell what’s internal and what’s from space.

• Open questions related to:– What is the mantle electical conductivity

– How does the geodynamo interact with the mantle field?

– Whats is the lithospheric magnetization?

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ESA’s SWARM: Best ever survey of Earth’s field

• Separate space-time ambiguity

• Resolve internal (geodynamo) from external (space current) field sources

• Three spacecraft mission

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Magnetospheric Self-Organization:Complexity leading to Order

• There exist multiple, simultaneous acceleration sites• Cross-coupling between them affects global evolution• Like weather monitors linked with telegraph that brought

about a revolution in our understanding of the baroclinic instability in weather in late 1800s, dense network of space-buoys needed to resolve evolving pressure systems, flow channels and current-generating flow vortices.

• Need simple instrumentation; the power is in the numbers

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MC/DRACO mission

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Feasibility

Two approaches (NASA taking both):• Investing in development of low-mass spacecraft

to design for large science-craft numbers (NMP’s ST-5 is a prelude to MC/DRACO).

• Focus the science and live with existing instruments to beat costs (THEMIS is an example of how efficient management of resources, both science and technical, pays off).

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ST5-Constellation pathfinder• 3 microsats with magnetometer sensors,

in polar orbits with cold-gas capability for orbit adjustments.

• Testbed for miniature X-band transponder, Thermal controls, CMOS Ultra-low power logic.

• Testbed for multiple launch and frisbee deploy ( http://nmp.jpl.nasa.gov/st5 ).

• Launch=Feb 2006 on PegasusXL.

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THEMIS recipe for build to cost• Design a simple spacecraft and stick to it, by having flexibility in science

• Pick instruments that have demonstrated:– Manufacturability, ease in I&T by design

– Have been delivered in numbers before

– Heritage in team members as much as hardware

• Have a tightly coupled systems-science-technical team

• Manage reserves at PM level, do not divulge else they are lost

• Bottom-up development, top down enforcement

• Always develop parallel paths for critical items

• Once design is proven, RESIST CHANGE, else it is multiplied by 6 (incl. Spare).

• Always seek technical solution to technical problems (can we get help, can anyone else do it) before applying more schedule or cost

• Face the facts early, and mitigate risk, hope cannot get one to the end

• Clean line of management: NASA itself will often blow that.

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Constellations: Future• Scientific needs for multi-point measurements are

abundant; they are the next mode of doing science• Requirements on instrumentation remain similar as on

single missions (separations are large enough and knowledge crude enough)

• Main challenges are manufacturability in large numbers and total mission cost.

• Cost is dealt with modest initial investment in process or mass, or by traditional management practices sensitised to multiple builds.