Technical Resource Allocations
Michael Pryzby
NASA’s Goddard Space Flight Center
15b - 1
Technical Resource Allocations
Flight Dynamics
Delta V
Propellant
NASA’s Goddard Space Flight Center
15b - 2
dV/Fuel Mass Allocation
•
Assumes 1480 kg wet launch mass
–
•
Given dV budget, determine fuel mass assuming maximum wet mass at liftoff
–
•
MRD-24: The launch vehicle must be capable of delivering a 1480 kg payload to a trajectory with a C3 > 1.85
Derives allocation for spacecraft dry mass
dV budget determined by analysis & lunar mission experience
–
MCC1 allocation is 3-sigma, could be improved by performing maneuver earlier than 24 hours but holding
worst case
•
•
–
–
LOI allocation is deterministic, detailed analysis exists to support, all physics not a function of perturbations
Stationkeeping is deterministic, detailed analysis exists to support, actual dV cost is only 150 m/sec, may
move extra 30 m/s to margin
•
–
MRD-12: The primary mission shall be conducted in a circular mapping orbit with a nominal mean altitude of 50 +/- 20
km (altitude is measured to mean lunar surface).
Extended mission is place holder only, allows many options for unknown extended mission, could be used for
contingency in mission orbit if needed
•
–
MRD-25: TLI accuracy at orbiter sparation from the LV third stage shall be within +/- 3 m/sec (TBR) (3-sigma) of target
inertial velocity.
FDS 2.3.1: LRO shall perform an MCC1 maneuver at L+24 (TBD) hours to correct for LV dispersions.
MRD-22: LRO shall carry sufficient consumables to allow for a four year extended mission in a low maintenance orbit.
Margin is 20 m/s
•
•
LOI and extended mission dV should not be used to calculate dV percent margin
8% dV margin on MCC1 and SK dV budgets (22% if 30 m/s moved from SK to margin)
NASA’s Goddard Space Flight Center
15b - 3
dV/Fuel Mass Allocation
Mission Phase
LRO Baseline dV
(m/sec)
Fuel Mass
(kg)
Comments
MCC
75
52
3s, MCC @ L+24 hours
Lunar Insertion – 1st burn
391
210
1st insertion burn, finite dV, any launch date,
20% off-pulsing
Lunar Insertion – All other
burns
535
288
All other insertion burns, finite dV
Station-keeping
180
77
+/- 20 km altitude, 3s including errors
Extended Mission
125
48
Placeholder only
Margin
20
8
Momentum Unloading
16
Other
14
Total
1326
De-spin, Residuals, Pressurant
713
* Assumes 1480 kg launch wet mass
NASA’s Goddard Space Flight Center
15b - 4
Technical Resource Allocations
Mass
Consumables
Spacecraft Wet Mass
Spacecraft Dry Mass
NASA’s Goddard Space Flight Center
15b - 5
Mass
• Technical Resource Allocations Document, 431-SPEC-000112
– Mass allocations budges include:
• Spacecraft Allocation – Wet
• Spacecraft Allocation - Dry
• Wet Mass Allocation (Consumables)
• Allocation Derivations:
– Spacecraft Wet Mass Allocation
• MRD-1: The max allowable spacecraft mass – 1480 kg
• MRD-24: The launch vehicle must be capable of delivering a 1480 kg payload to
a trajectory with a C3 > -1.85
– Wet Mass Allocation
• Derived from dV / Fuel Mass Allocation
– Spacecraft Dry Mass Allocations
• Derived from Current Best Estimates
• Contingency based upon Design Maturity Factor
NASA’s Goddard Space Flight Center
15b - 6
Wet Mass Allocation - Consumables
Allocation
Subsystem
Components
Comments
SubSystem
Mass (kg)
Consumables
715.30
Propellant
713.0
Pressurant
2.3
Derived from Delta V budget - includes 3s
Table 3-2 - Spacecraft Wet Mass Allocation - Consumables
NASA’s Goddard Space Flight Center
15b - 7
Spacecraft Mass Allocation - Wet
Allocation
Subsystem
Components
Comments
SubSystem
Mass (kg)
L/V Wet Mass Capability
1480.00
MRD Req’t: 1.2.10
Derived Wet Mass Allocation
715.30
Propellant Budget derived from
Delta V budget
Max Dry Mass Allocation
764.70
Remaining mass
Table 3-1 - Spacecraft Mass Allocation - Wet
Table 3-2 - Spacecraft Wet Mass Allocation
NASA’s Goddard Space Flight Center
15b - 8
Spacecraft Mass Allocation - Dry
Allocation
Subsystem
Components
SubSystem
Comments
Mass (kg)
Total Dry Mass
710.3
Concept J
Spin balance Weight
25.0
Place holder
S/C Bus Subtotal
Mechanical
595.5
155.1
Mechanisms
52.8
Thermal
32.4
Power
76.2
ACS
63.4
PDE
16.8
Propulsion (Dry Mass)
105.8
C&DH
19.5
S Comm
12.6
Ka Comm
18.5
Electrical
CRaTER
40.0
89.9
6.4
Diviner
11.9
LAMP
5.3
LEND
23.2
LOLA
15.3
LROC
19.0
Mini RF
12.6
Instruments Subtotal
Table 3-3- Spacecraft Mass Allocation - Dry
NASA’s Goddard Space Flight Center
15b - 9
Mass Allocation Summary
EQUIPMENT LIST
Subsystem
Components
CURRENT
Allocation
BEST
SubSystem
ESTIMATE (kg) Mass (kg)
L/V Wet Mass Capability
1480.0
Derived Wet Mass Allocation
Max Dry Mass Allocation
Total Wet Mass Estimate / Allocation
Consumables
Total Dry Mass
Dry Margin Remaining - CBE / Allocation
% Margin based on Dry Mass - CBE / Allocation
1480.0
715.3
764.7
1348.1
715.3
632.8
131.9
20.8%
1425.6
715.3
710.3
54.4
7.7%
Comments
LV Capability
Propellant Budget derived
from Delta V budget
Remaining mass
Concept J
Margin
Margin
– Margins meet GOLD requirement (20%) – 20.8% on CBE
– Allocation – 710.3 kg
– Current Best Estimate – 632.8 kg
– Max Dry mass – 764.7 kg
– System Margin – 54.4 kg (7.7%)
• Or 79.4 kg (11.2%) including spin balance mass
– Assume 1480 max LV capability
NASA’s Goddard Space Flight Center
15b - 10
Technical Resource Allocations
Power
Un-Switched Power
Instrument Heater Power
Switched Power
NASA’s Goddard Space Flight Center
15b - 11
Power Allocations
• Technical Resource Allocations Document, 431-SPEC-000112
– Power allocations include:
• Un-Switched Power
• Instrument Heater Power – Operational & Survival
• Switched Power
• Spacecraft Power Allocations
– Switched and Un-Switched
• Derived from Current Best Estimates
• Contingency based upon Design Maturity Factor for each switch
– Heater
• Operational heater power allocations for each instrument/component are based
on Beta=90° cold case orbit average predictions plus margin.
• Survival heater power allocations for each instrument/component are based on
Safe-hold orbit average predictions plus margin
NASA’s Goddard Space Flight Center
15b - 12
Power Allocation Driving Requirements
• Worst Case is based on “S+Ka Orbit” mission phase from LRO Mission Concept
of Operations Document, 431-OPS-000042 as documented in the Master
Equipment List
• Driving Requirements
– Power System
• MRD-103: System sized for 823W On-Orbit Average
– Solar Array Properties
• 1849W @ 35V
• EOL properties for 14 month design life
– Battery Spec
• Max Depth of Discharge (DOD) is 30%
• EOL properties for 18 month design life
• Nominal 28V output
– Energy Balance for Beta 0 case
• 48 minute eclipse
• full battery recharge in single orbit
NASA’s Goddard Space Flight Center
15b - 13
Power Allocation - Un-Switched
Subsystem
Comm
C&DH
C&DH
ACS
ACS
ACS
ACS
Thermal
Thermal
Power
Components
TT&C XPDR Stack (Rec)
COMM Card
C&DH Backplane
Reaction Wheels
Reaction Wheels
Reaction Wheels
Reaction Wheels
Essential S/C Survival HTRs Prime
Essential S/C Survival HTRs Redundant
PSE
Allocation
Avg (W)
11.0
17.6
43.5
7.7
7.7
7.7
7.7
37.5
37.5
44.0
Table 4-1- Un-Switched Power Allocations
NASA’s Goddard Space Flight Center
15b - 14
Power Allocation – Instrument Heaters
Instruments
CRaTER
Diviner
LAMP
LEND
LOLA
LROC
Mini RF
Components
Operational Heater
Survival Heater
Operational Heater
Survival Heater
Operational Heater
Survival Heater
Operational Heater
Survival Heater
Operational Heater
Survival Heater
Operational Heater
Survival Heater
Operational Heater
Survival Heater
Allocation
Avg (W)
2.0*
2.2
45.6
31
9.1
12.6
2.0*
2.0*
35.2
45
12.8
43.7
TBD
TBD
* - Current analysis shows no heater power is necessary
Table 4-2 – Instrument Heater Power Allocations
NASA’s Goddard Space Flight Center
15b - 15
Power Allocation - Switched
Subsystem
Components
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument
Instrument/thermal
Instrument/thermal
C&DH
S Comm
Ka Comm
ACS
ACS
ACS
Prop PDE
Prop PDE
Prop PDE
Prop PDE
Prop
Prop
Mechanisms PDE
Mechanisms PDE
Thermal
Thermal
Thermal
Thermal
CRaTER
Diviner
Diviner Operational Heater (HOLD)
Diviner Survival Heater (HOLD)
LAMP PRIME
LAMP REDUNDANT
LEND
LOLA
LROC
LROC Optics Decontamination
Mini RF
System Instrument Operational Heaters
Instrument Survival Heater
SSR
TT&C XPDR Stack (xmit)
Ka Transmitter complement
Inertial Measurement Unit
Star Trackers
Star Trackers
PDE
Pressure Transducers
Prop Valve Actuator
Prop Valve CAT BED
Prop Heaters Prime
Prop Heaters Redundant
S/A & HGA Control Electronics
S/A & HGA Release & Deploy
Gimbal Heaters Prime
Gimbal Heaters Redundant
Spacecraft Operational Heaters
Deployable heaters
Allocation
Avg (W)
5.9
19.6
0.0
0.0
4.86
4.86
13.0
39.4
27.6
98.0
7.5
37.5
37.5
44.1
15.3
61.6
33.0
10.3
10.3
37.5
3.2
24.5
16.5
84.3
84.3
46.0
40.0
25.0
25.0
62.5
20.0
Table 4-3 - Switched Power Allocations
NASA’s Goddard Space Flight Center
15b - 16
Power Allocation Summary
• Margins meet GOLD requirement at SRR (15%) – 21% on CBE
– On-Orbit Average designed for 823W power system (MRD-103)
– Power Allocations set at 745W max for S+Ka Orbit, Beta 0 case
• 10%+ margin on power system
– Current Best Estimate for worst case power average is 680.4W
• S+Ka Orbit from Mission Concept of Operations Plan
• Margin = 21%
NASA’s Goddard Space Flight Center
15b - 17
Technical Resource Allocations
Flight Software
Processor Memory
1553 Bus
NASA’s Goddard Space Flight Center
15b - 18
Data Allocations – Key Assumptions
•
•
•
•
750 Processor or equivalent
GNC Software resident on Main Processor
Using cFE for core FSW
Interfaces include only:
– 1553 bus interface
– 1355 (Spacewire)
• Baseline no science data processing/compression onboard
NASA’s Goddard Space Flight Center
15b - 19
Flight Software Allocation Summary
Met hod
Average CPU
CPU Deadlines
PROM
FSW SRR*
LRO SRR
Margin
50%
50%
Margin
>50%
50%
>50%
EEPROM
50%
44%
RAM
50%
>80%
PCI Bus
75%
N/A
1553 Bus
30%
47%
Spacewire (1355)
TBD
UART/Serial I/F
50%
Comment s
64 K PROM for Boot Loader Only
(SDO heritage)
2 banks of 2M each
cFe and other heritage s/w makes
estimate quite mature
20 MRAM
No cPCI Backplane
Only 1 UART (LAMP)
* From GSFC-STD-1000 (GOLD Rules - FSW)
NASA’s Goddard Space Flight Center
15b - 20
LRO Processor Memory Utilization
Task
cFE
Memory Scrub
Checksum
Bus controller
Software Bus
Health & Safety
Time Code
Event Services
Memory Dwell
Software Manager
OS (VxWorks)
OS Libraries
File Manager
Telemetry Output
Command Ingest
Stored Commands
Data Storage
Tlm & Statistics
CFDP
Inst. Support
Attitude Control
Ephemeris
GNC
Total
NASA’s Goddard Space Flight Center
EEPROM
(KB)
77
15
30
87
DRAM
(KB)
170
17
44
142
11
22
Comments
cFE Actuals
GPM
GPM
GPM
Part of cFE
Part of cFE
Part of cFE
8
40
210
16
20
37
21
47
74
27
100
50
96
26
122
9
47
242
62
65
76
42
307
192
47
400
168
128
28
156
1114
2364
Estimate of 750(TBR)
Estimate of 750(TBR)
GPM
GPM
GPM
GPM
15b - 21
1553 Allocation
Subsystem
C&DH
Power
Comm
GN&C
CRaTER
Diviner
LEND
LOLA
Total
NASA’s Goddard Space Flight Center
Bits/sec
658
3058
2662
21536
89867
28160
3083
9552
158576
Percentage
0.22%
1.02%
0.89%
7.18%
29.96%
9.39%
1.03%
3.18%
52.86%
15b - 22