THEMIS FDMO Review Introduction − 1 October 5, 2004 MISSION OVERVIEW AND STATUS Vassilis Angelopoulos THEMIS was selected on March 20, 2003 as the next NASA/MIDEX mission (#5) to study the: Onset and evolution of magnetospheric substorms Onset 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
31
Embed
THEMIS FDMO Review Introduction − 1 October 5, 2004 MISSION OVERVIEW AND STATUS Vassilis Angelopoulos THEMIS was selected on March 20, 2003 as the next.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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
THEMIS FDMO Review Introduction − 2 October 5, 2004
Covered in this presentation
• Mission objectives• Redundancy and resilience• Overview of launch and placement• RCS, ACS and Operational modes
Outline
THEMIS FDMO Review Introduction − 3 October 5, 2004
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.
– 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
THEMIS FDMO Review Introduction − 14 October 5, 2004
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
THEMIS FDMO Review Introduction − 15 October 5, 2004
Covered in this presentation
• Mission objectives• Redundancy and resilience• Overview of launch and placement• RCS, ACS and Operational modes
Outline
THEMIS FDMO Review Introduction − 16 October 5, 2004
• Fuel consumption, maneuvers and contacts during ascend: validated with GMAN.
THEMIS FDMO Review Introduction − 18 October 5, 2004
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
THEMIS FDMO Review Introduction − 19 October 5, 2004
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
THEMIS FDMO Review Introduction − 20 October 5, 2004
Covered in this presentation
• Mission objectives• Redundancy and resilience• Overview of launch and placement• RCS, ACS and Operational modes
Outline
THEMIS FDMO Review Introduction − 21 October 5, 2004
• 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
THEMIS FDMO Review Introduction − 22 October 5, 2004
• 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
THEMIS FDMO Review Introduction − 23 October 5, 2004
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
THEMIS FDMO Review Introduction − 24 October 5, 2004
Thruster Placement
Two axial, parallel thrustersfor reors, and major orbitchanges
Two radial, parallel thrustersfor spin control and minor
orbit changes
THEMIS FDMO Review Introduction − 25 October 5, 2004
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
THEMIS FDMO Review Introduction − 26 October 5, 2004
• 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
THEMIS FDMO Review Introduction − 27 October 5, 2004
• 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
THEMIS FDMO Review Introduction − 28 October 5, 2004
Backup Slides
THEMIS FDMO Review Introduction − 29 October 5, 2004
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.
THEMIS FDMO Review Introduction − 30 October 5, 2004
• 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
THEMIS FDMO Review Introduction − 31 October 5, 2004
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).