themis fdmo review introduction − 1 october 5, 2004 mission overview and status vassilis...

THEMIS FDMO Review Introduction − 1 October 5, 2004

MISSION OVERVIEW AND STATUS

Vassilis Angelopoulos

THEMIS was selected on March 20, 2003as the next NASA/MIDEX mission (#5) to study the:

Onset and evolution of magnetospheric substormsOnset and evolution of magnetospheric substorms

•Addresses a 30yr old question (the holy grail) in magnetospheric physics•A 5 spacecraft (probe) mission•Single launch vehicle (Delta 2925)•Launch on October 19 of 2006•In Tail (midnight) February 21, 2007/2008•Two year nominal duration•Details at: http://sprg.ssl.berkeley.edu/themis


Covered in this presentation

• Mission objectives• Redundancy and resilience• Overview of launch and placement• RCS, ACS and Operational modes

Outline


Status

•PDR – peer: Oct 8/9/15/16, 2003, Mission: Nov 13-14, 2003

•Confirmation: April 22, 2004: Launch reset request to October 19, 2004.

•CDR – peer: Apr – Jun 2004, Mission CDR: Jul 13-18, 2004.

•Delta thermal review: Aug 10, 2004

•1st MIWG held at Boeing, Huntington Beach: Aug 30, 2004

•Instrument status

•All ETUs tested

•Flight production started

•EM IDPU I&T to be completed by Oct 18, 2004

•Instrument Suite EM test review: November 5, 2004

•F1 instruments ready by end of December, 2004

•Bus status

•Flight production started

•Bus I&T starts: March 2004


TIME HISTORY OF EVENTS AND MACROSCALE

INTERACTIONS DURING SUBSTORMS (THEMIS)

RESOLVING THE PHYSICS OF ONSET AND EVOLUTION OF SUBSTORMS

Science Team

Principal InvestigatorVassilis Angelopoulos, UCBProgram ManagerPeter Harvey, UCBMission Operations ManagerManfred Bester, UCBGSFC technical partnershipMark Beckman, MESA (former GN&C)Industrial PartnerSWALES Aerospace, Inc., Beltsville MD


Auroral eruptions and substorms

Auroral eruptions…

AuroraAurora

…are a manifestation ofmagnetospheric substorms

MAGNETOSPHERESO

LAR

WIN

D

EQUATORIAL PLANE


Most important science resultand its science impact

Answers how substorms operate

– Explains how magnetospheres process solar wind energy

– Explains how auroras erupt

MERCURY: 10 min EARTH: 3.75 hrs JUPITER: days

ASTROSPHERE

GALACTIC CONFINEMENT

SUBSTORM RECURRENCE:


Mission elements

Probe conjunctions along Sun-Earth line recur once per 4 days over North America.

Ground based observatories completely cover North American sector; determine

auroral breakup within 1-3s …

… while THEMIS’s space-based probes determine onset of Current Disruption and

Reconnection each within <10s.

: Ground Based Observatory


First bonus: What producesstorm-time “killer” MeV electrons?

Affect satellites and humans in space

Source:

– Radially inward diffusion?

– Wave acceleration at radiation belt?

THEMIS:

–Tracks radial motion of electrons

•Measures source and diffusion

•Frequent crossings

–Measures E, B waves locally

ANIK telecommunicationsatellites lost for days to weeks

during space storm


Second bonus: What controls efficiencyof solar wind – magnetosphere coupling?

Important for solar wind energy transfer in Geospace

Need to determine how:– Localized pristine solar wind features…

– …interact with magnetosphere

THEMIS:

– Alignments track evolution of solar wind

– Inner probes determine entry type/size


THEMIS is unique and timely

Solves major long-standing question in magnetospheric physics (NAS)– Self-sufficient, ideally complements current SEC line

– Global context for Cluster (2006/7), MMS (2010), LWS (Rad. Belt Storm Probes: 2012)

A scientific and technological pathfinder for future SEC missions– Pre-requisite to Space Weather prediction

– Identifies causal relationships for MagCon

– Low cost highly integrated probes inanticipation of future Constellations

Inspires K-12 students– Hands-on involvement of high-school

students: ground magnetometer curators

First University-managedmulti-satellite project

– Expands NASA partnership with Academia

– Trains scientific, technological and industrial workforce of future




Outline


Identical instrumentation provides high science margins and fault tolerance

• Instrument redundancy:– SST-ESA energy

overlap– FGM-SCM frequency

overlap– P1/P2 redundant

instrumentation (only directional flux needed in one of two).

• Each probe has:

1FGM1ESA (i/e)2SSTh (2heads, i/e)1SCM4EFIs (4spin plane)2EFIa (2axials)

Selected instruments built en masse before

Instruments required to achieve Primary Mission Objective

Measurement goals P1 P2 P3 P4 P5

Tim

e History of E

vents

P3,4&5 monitor CDP1,2 bracket Rxtres<30s, Y<±2RE

FGM

1SSTh

2EFIs

FGM

ESA

2SSTh

2EFIs

FGM

ESA

1SSTh

FGM

ESA

1SSTh

FGM

ESA

1SSTh

Macroscale Interactions

Track rarefaction wave, inward flows, Poynting with B<1nT, V/V~10%

FGM

ESA

FGM

ESA

FGM

ESA

FGM

ESA

Radial/cross-sheet pressure, velocity and current gradients require P/P~ V/V ~ B/B ~10%, non-MHD

FGM

ESA

FGM

ESA

2EFIs

FGM

ESA

2EFIs

FGM

ESA

2EFIs

Cross-tail pairs measure FLRs, KH, ballooning on B, V, P @ 10s and fast modes on Bxyz and Exy @ 60 Hz

FGMESA SCM

FGMESA

SCM 4EFIs2EFIa

FGM

ESA

2EFIs

FGM

ESA

SCM 4EFIs2EFIa

TO

TA

L

Minumum mission (Red)

Baseline add-ons (green)

FGM

1SSTh

2EFIs

FGM

ESA

2SSTh

SCM2EFIs

FGM

ESA

1SSTh

SCM 4EFIs2EFIa

FGM

ESA

1SSTh

2EFIs

FGM

ESA

1SSTh

SCM 4EFIs2EFIa


Probe conjunctions well understoodBASELINE: >10 substorms/yr i.e., 188hrs/yr (achieved w/ 5 probes in 2 yrs).

MINIMUM: >5 substorms in 1 year, i.e., 94hrs in 1 year (w/ 4 probes, x2 margin).

– computations include lunar, solar, drag, J2 terms

– YP1/2/3/4/5<±2RE; ZP3,4,5/NS<±2RE; ZP1,2/NS<±5RE

• Ascent design is optimal for science

– maximizes conjunctions, minimizes shadows

• … immune to launch insertion errors

– small, piece-wise Vs increase placement fidelity

• … and immune to probe insertion errors.– Can withstand insertion error of V=40cm/s on any probe (V control is 100 times better; knowledge requirement is 3 times better, capability is >10times better)

Actual conjunction times in 1st year

Target orbit P1 P2 P3 P4 P5Period (days) 4 2

Apogee (RE) 30 19 12 12 12

Perigee (RE) 1.5 1.2

Inc @ midtail

Drift @ apg., @6:30UT

Knowledge @ apg.

Y<1RE/month

100 km

1

1.16

<7o <9o


Descope list and science-relatedrisk mitigation factors

• Re-positioning allows recovery from failure of critical instruments on some probes• Graceful degradation results from partial or even full instrument failures

– Instrument frequency and energy range overlaps

– Complete backup option for EFI radials (need 2 in most probes but have 4)

– Relaxed measurement requirements (1nT absolute is not permitted to drive team, but rather a nicety)

– Substorms come in wide variety; can still see large ones with degraded instruments

• Minimum mission can be accomplished with a reduced set of spacecraft requirements– EMC and ESC requirements important for baseline but less severe for minimum mission

– Observation strategy can be tuned to power loss (turn-on/off) and thermal constraints (tip-over/back)

– Fuel and mass margins for 1st year (minimum) are 30% larger than for a two year (baseline) mission




Outline


Probe Carrier Assembly (PCA = 5 Probes + Probe Carrier) on L/V

Probe Carrier Assembly (PCA = 5 Probes + Probe Carrier) on L/V

Probe Carrier Assembly (PCA) on Delta 3rd StageProbe Carrier Assembly (PCA) on Delta 3rd Stage

Delta II Launch From KSC

• Dedicated Delta 7925-10• 10’ Composite Fairing

required to accommodate five Probes on the Probe Carrier in the “Wedding Cake” configuration

• PC stays attached to Delta 3rd stage after probe dispense minimizing orbital debris

• Each probe dispense from the PCA is coordinated with but independent of the other probes

• No single probe anomaly precludes dispense of remaining probes

• Boeing provided ordnance fired from 3rd stage blows all clampbands to initiate separation

Standard Delta 10 ft. Fairing Static Envelope

3712 PAF

THEMIS Launch Configuration

THEMIS Launch Configuration

Star 48 3rd Stage


Mission profile is robust

Pre-Launch

(6hrs)

Launch

(25min)

Check-out & ascend

(60days)

Science ops

(2yrs)

Re-entry

•Checkout

•Countdown

•2nd stage burn

•Spin-up

•3rd stage burn

•Spin-down

• Probe dispense • Bus check-out, reor

• Dply mags/check instr.

• Place to Orbit. - 6 side thrustings

- 6 reor/fire/reor sequences

• Deploy EFI

•Minor ctrl ops (all):– 22 side-thrustings– 2 inclination changes

•M

inor ctrl ops (Side-thrusts, finish by E

OM

+9m

o) - 8

side

-thru

sting

s

• P

assive re-entry thereafter (1-10yrs)

• Fuel consumption, maneuvers and contacts during ascend: validated with GMAN.


BOL Daylight Loads & Power vs Solar Aspect Angle(15W Htrs+10.5W BAU for 35 min Eclipse, 24 hr orbit)

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140 160 180

Solar Aspect Angle (deg)

Po

wer

(W

atts

)

Heater Power

Daylight Loads

Daylight Power

Probe power positive underany release season/orientation

Except for a subset of February/Marchlaunch, which (with current elements)can result in longer shadows


Mission overview: Fault-tolerant design hasconstellation and instrument redundancy

D2

925

-10

@ C

CA

S

Instrument I&TUCB

Mission I&TSwales

Encapsulation

& launch

BGS

OperationsUCB

Probe instruments:ESA: Thermal plasma (UCB)SST: Super-thermal plasma (UCB)FGM: Low frequency magnetic field (TUBS/IWF)

SCM: High frequency magnetic field (CETP)EFI: Electric field (UCB, LASP)

Ground

SST

ESA

EFIa

EFIs

FGM

SCM

Tspin=3s




Outline


• Probe bus is a single string design with selected redundancy

• Power positive in all attitudes with instruments off (launch, safe hold modes)

• Passive thermal design using MLI and thermostatically controlled heaters tolerant of longest shadows (3 hours)

– Spin stabilized probes point within 13° of ecliptic south and have inherently stable thermal environment

• S-Band communication system always in view of earth every orbit at nominal attitude.In view for greatest part of orbit in any attitude

• Passive spin stability achieved in all nominal and off-nominal conditions

• Monoprop blow down RCS (propulsion) system is self balancing on orbit

Antenna

4x Side Solar Panels

Top Deck

4x Radial EFIs

Axial EFIBooms

SCM Boom

FGM Boom

2x Top Solar Panels

2x SSTs2x

Tang. Thruster

RCS Fill / Drain Valves

ESA

Shunt

2X Propulsion Tanks

Transponder

Battery

Sun Senor

ESA/IDPU

BAU

IRU

Single Point

GroundHarness Bridge

(harness not shown)

Radial EFIs

Bus Overview


• Blowdown N2H4 system design

• Two Interconnected tanks • Lightweight, High Performance System• Robust, self-balancing fuel management

(as on ISEE, ACE)

• Components flown on dozens of missions, integrated by Aerojet

• Readily Available Components• Arde Inconel propellant tanks on order• Carleton P/N 7149 pressurant tank from ST5• All other components are off the shelf

• Robust• Thruster arrangement provides for partial

redundant function with degraded performance• Meets all Range Safety Requirements• Heritage design based on ISEE-3

and ACE

Reaction Control System (RCS):A Hydrazine Orbit/Attitude Control System

Tank 1F/D Valve

T1 A1 T2 A2

Tank1 Tank 2

Thrusters

P

PropellantP/V Valve

20 m20 m 20 m 20 m

40 m

40 mSystemFilter15 m

LatchValve

Orifice

Low Side PressureTransducer

GN2

P

PressurantP/V Valve

Pressurant Tank

Solenoid Valve

NC Pyro-Valve

High Side PressureTransducer

Tank 2F/D Valve


Propulsion System RecentUpgrade for Additional Fuel

Re-Press Pressure Profile

0

50

100

150

200

250

300

350

400

450

0 5 10 15 20 25 30 35 40 45 50

Prope llant Expended (kg)

Sy

ste

m P

res

su

re (

ps

ia)

Propellant Load: 48 kgAverage Steady State Isp: 222 s

•Tanks are launched 93% full•Initial blowdown occurs quickly

•One time actuation of pressurant tank•Repress back to full pressure•Larger volume depressurizes slowly

Profile-averaged Isp=223s for continuous thrusting210s for pulsed at +/-30deg pulse


Thruster Placement

Two axial, parallel thrustersfor reors, and major orbitchanges

Two radial, parallel thrustersfor spin control and minor

orbit changes


ACS sensors

• Sun Sensor provides spin pulse and elevation angle

• FGM science sensor doubles up as TAM ACS sensor

• Two Solid State Gyros (Inertial Reference Units) for tactical use; provide x, y


• Slew/precession control– Sun synchronous thrusting

– Major circle reor performed bypiece-wise continuous Rhumb line reor

• Spin up/down– Continuous and/or sun synchronous

• Axial thrust– Continuous

• Side thrust– Sun synchronous thrusting

• None of the above (i.e., no thrusting) = “safe mode”– Fault protection to return to “none of the above” if anomaly is detected

• Thrusters commanded off under following conditions:– Sun aspect angle out of bounds– Spin rate out of bounds– Thruster control electronics Watch Dog Timer time out– Processor reboot

RCS operational modes


• Replaced check valve with solenoid valve–Prevents hydrazine fuel from condensing into (colder) pressurant tank at a needed 10^-6 scc/se

• Open trade to negate mass growth since CDR:–Utilize the same RCS components but in a repress-then-regulate mode–Solenoid valve to perform regulation at 300psi, increasing Isp to 224.4s–By increasing fill to 97.5% the system also improves deltaV by 36m/s

Design modifications since CDR


Backup Slides


Baseline L1 Req’s pertaining to orbit design

• S-2 Current Disruption Onset Time– Determine current disruption onset time with t_res<30s, using two near-equatorial (within 2Re of magnetic

equator) probes, near the anticipated current disruption site (~8-10 Re). Current disruption onset is determined by remote sensing the expansion of the heated plasma via superthermal ion flux measurements at probes within +/-2Re of the measured substorm meridian and the anticipated altitude of the current disruption.

• S-3 Reconnection Onset Time– Determine reconnection onset time with t_res<30s, using two near-equatorial (within 5Re of magnetic

equator) probes, bracketing the anticipated reconnection site (20-25Re). Reconnection onset is determined by measuring the time of arrival of superthermal ions and electrons from the reconnection site, within dY=+/-2Re of the substorm meridian and within <10Re from the anticipated altitude of the reconnection site. …..

• S-4 Simultaneous Observations– Obtain simultaneous observations of: substorm onset and meridian (ground), current disruption onset and

reconnection onset for >10 substorms in the prime observation season (September-April). Given an average 3.75hr substorm recurrence in the target tail season, a 2Re width of the substorm meridian, a 1Re requirement on probe proximity to the substorm meridian (of width 2Re) and a 20Re width of the tail in which substorms can occur, this translates to a yield of 1 useful substorm event per 18.75hrs of probe alignments, i.e, a requirement of >188hrs of four-probe alignments within dY=+/-2Re.


• S-6 Earthward Flows– Track between probes the earthward ion flows (400km/s) from the reconnection site and the tailward moving

rarefaction wave in the magnetic field, and ion plasma pressure (motion at 1600km/s) with sufficient precision (dV/V=10% or V within 50km/s whichever is larger, dB/B=10%, or B within 1nT whichever is larger, dP/P=10%, or P within 0.1nPa whichever is larger) to ascertain macroscale coupling between current disruption and reconnection site during >10 substorm onsets (>188hrs of four-probes aligned within dY of +-2Re).

• S-7 Pressure Gradients– Determine the radial and cross-current-sheet pressure gradients (anticipated dP/dR, dP/dZ ~0.1nPa/Re) and

ion flow vorticity/deceleration with probe measurement accuracy of 50km/s/Re, over typical inter-probe conjunctions in dR and dZ of 1Re, each during >10 onsets. The convective component of the ion flow is determined at 8-10Re by measurements of the 2D electric field (spin-plane to within +-30degrees of ecliptic, with dE/E=10% or 1mV/m accuracy whichever is larger) assuming the plasma approximation at t_res<30s.

• S-8 Cross-Current Sheet changes– Determine the cross-current-sheet current change near the current disruption region (+/-2Re of meridian, +-

2Re of measured current disruption region) at substorm onset from a pair of Z-separated probes using the planar current sheet approximation with relative (interprobe) resolution and interorbit (~12hrs) stability of 0.2nT.

• S-10 Cross-Tail Pairs– Determine the presence, amplitude, and wavelength of field-line resonances, Kelvin-Helmholz waves and

ballooning waves on cross-tail pairs (dY=0.5-10Re) with t_res<10s measurements of B, P and V for >10 substorm onsets.

… continued: Baseline L1 Requirements


Minimum L1 Req’s pertaining to orbit design

• 4.1.2.2 Current Disruption Onset Time– Determine current disruption onset time with t_res<30s, using two near-equatorial (within 2Re of magnetic

equator) probes, near the anticipated current disruption site (~8-10 Re). Current disruption onset is determined by remote sensing the expansion of the heated plasma via superthermal ion flux measurements at probes within +/-2Re of the measured substorm meridian and the anticipated altitude of the current disruption.

• 4.1.2.3 Reconnection Onset Time– Determine reconnection onset time with t_res<30s, using two near-equatorial (within 5Re of magnetic

equator) probes, bracketing the anticipated reconnection site (20-25Re). Reconnection onset is determined by measuring the time of arrival of superthermal ions and electrons from the reconnection site, within dY=+/-2Re of the substorm meridian and within <10Re from the anticipated altitude of the reconnection site. …..

• 4.1.2.4 Simultaneous Observations– Obtain simultaneous observations of: substorm onset and meridian (ground), current disruption onset and

reconnection onset for >5 substorms in the prime observation season (September-April). Substorm statistics discussed in S-4 point to a requirement of >94hrs of four probe alignments.

• Lifetime– THEMIS instrument and spacecraft shall be designed for at least a 2-yr lifetime

• Launch– THEMIS will be launched into an orbit with Ra=12Re, Rp=1.1Re and INC=9.5deg, prior to 03/2007.

– Launch window = 40 min

– Prefered (not required) launch season = August 2006 +/- 2 months (now October 19, 2006).

themis fdmo review introduction − 1 october 5, 2004 mission overview and status vassilis...

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