National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology
Aerobraking Cost/Risk Decisions David A. Spencer Jet Propulsion Laboratory California Institute of Technology Robert Tolson North Carolina State University National Institute of Aerospace
Deep Space Systems Session Georgia Tech Space System Engineering Conference Atlanta, Georgia November 10, 2005 November 10, 2005
Deep Space Systems Session Space System Exploration Conference
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National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology
• • • • • •
Agenda
Motivation for this Paper A Brief History of Aerobraking Aerobraking Risk Cost Aerobraking Cost/Risk Trades Conclusions
November 10, 2005
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Past Aerobraking Missions
Magellan
MGS
Odyssey
1993 70 days 1,220 m/s
1997-1998 400 days 1,220 m/s
2002 77 days 1,090 m/s
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November 10, 2005
Discover Magazine Award for Techological Innovation, 1994
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Odyssey Orbit Period During Aerobraking Actual
Plan
20 18 16 14 12 10 8 6 4 2 0 24-Oct
31-Oct
7-Nov
November 10, 2005
14-Nov
21-Nov
28-Nov
5-Dec
12-Dec
19-Dec
Deep Space Systems Session Space System Exploration Conference
26-Dec
2-Jan
9-Jan
16-Jan
23-Jan
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Odyssey Aerobraking Periapsis Altitude
160
150
140
130
120
110
100
90 24-Oct
31-Oct
7-Nov
14-Nov
21-Nov
28-Nov
5-Dec
12-Dec
19-Dec
26-Dec
2-Jan
9-Jan
16-Jan
Date
November 10, 2005
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Key Aerobraking Risk Areas
• • • • •
Orbit-to-orbit density variations Structural loads and thermal cycling Communications failure Spacecraft safing Human error
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Orbit-to-Orbit Density Variations
2.25
2
1.75
1.5
1.25
1
0.75
0.5
0.25
0 24-Oct
31-Oct
7-Nov
14-Nov
21-Nov
28-Nov
5-Dec
12-Dec
19-Dec
26-Dec
2-Jan
9-Jan
16-Jan
Date
November 10, 2005
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National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology
Probabilistic Risk Assessment
• Assumptions: Generic aerobraking orbiter – 90-day aerobraking phase – 300 main-phase orbits with Odyssey-like heating corridor – 150 walk-out orbits targeting lower heating
Aerobraking Risk Area
Prob. of Failure
Orbit-to-orbit density variations
0.018
Structural loads & thermal cycling
0.011
Communications failure
10-6
Spacecraft safing
3 x 10-4
Human error
2 x 10-5
• Estimated reliability of aerobraking phase: 0.97 November 10, 2005
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National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology
Generic Orbiter Mission Risk
Mission Phase
•
Success Probability
P(Launch)
0.96
P(Cruise)
0.99
P(Orbit Insertion)
0.95
P(Aerobraking)
0.97
P(Science)
0.99
P(Success|Aerobraking)
0.867
P(Success|No Aerobraking)
0.894
Inclusion of aerobraking for our generic orbiter mission lowers overall probability of mission success from 89.4% to 86.7% (2.7%)
November 10, 2005
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Odyssey Aerobraking Cost Summary
Aerobraking Planning & Development
$1450 K
Navigation, Spacecraft Team, Mission Planning & Sequencing, Test & Training
Aerobraking Operations
$4810 K
Mission Management, Navigation, Spacecraft Team, Mission Planning & Sequencing, Atmospheric Advisory Group, DSN Scheduling, Ground Data System
Science Team
$3050 K
Science Operations & Data Analysis
Total Aerobraking Costs (FY’02$)
$9310 K
Note: Costs are estimated based upon number of people and duration of work period. Costs shown are in FY’02$. DSN costs not included. November 10, 2005
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Generic Orbiter Aerobraking Cost
• To generate a cost estimate for a generic (Odyssey-like) 90-day aerobraking phase… – Odyssey aerobraking ops and science costs are scaled up to a 90-day mission phase; planning costs stay the same – Costs are inflated from FY’02$ to FY’06$ – DSN costs are estimated assuming continuous 34m coverage, based on DSN rate table ($2.6M)
• Resulting estimated cost is $15M.
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Aerobraking Cost/Risk Trade
• If actual costs were the only consideration, the decision on whether to baseline aerobraking would be straightforward. – Compare estimated cost of aerobraking ($15M for our generic mission) with the cost of a larger launch vehicle to enable purely propulsive capture. Choose the lower cost option. – This is the approach commonly taken by proposal teams.
• However, this decision process completely ignores the added risk introduced by the addition of the aerobraking phase. • The key question is: how much is it worth to “buy down” the risk of aerobraking through buying a larger launch vehicle? November 10, 2005
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How Much is it Worth to Buy Down Aerobraking Risk?
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology
•
Assume our generic mission has a total mission cost cap of $450M. – Roughly $425M (including L/V) will be invested in the mission by the point of aerobraking completion. – Remaining $25M represents cost of flight operations and data analysis during the science mission.
•
The Probabilistic Cost of Failure is calculated by multiplying the amount invested ($425M) by the reduction in mission success probability due to aerobraking (0.027). Result: $11.5M – This is how much aerobraking risk is worth.
•
•
The “effective cost” of aerobraking is equal to the planned cost of aerobraking ($15M) plus the probabilistic cost of failure ($11.5M). Result: $26.5M The Project Manager should be willing to spend up to $26.5M to procure a larger launch vehicle, to enable purely propulsive capture. November 10, 2005
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• •
Conclusions
Aerobraking is an enabling technology that allows significant propellant savings (typically 300-600 kg), and lowers launch costs. There are inherent risks with aerobraking. – Strawman PRA indicates that the probability of failure for a 90-day aerobraking phase with Odyssey-like heating rates is about 3%.
• • •
The increase to the mission risk posture should be considered when making the aerobraking cost/risk decision at the inception of the mission. The “effective cost” of aerobraking is the planned aerobraking cost plus the probabilistic cost of failure. The effective cost of aerobraking should be compared with the incremental cost for a larger launch vehicle to enable purely propulsive capture. – If the incremental cost for a larger launch vehicle is less than the effective cost of aerobraking, the larger launch vehicle is a wise investment.
•
Applying this concept to early mission trade studies and proposal evaluations is a necessary step toward making appropriate cost/risk decisions…and it’s good system engineering! November 10, 2005
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