ILEWG
Aerobraking – A mission enabling and fuel saving technique for orbit changes - Venus Express and ExoMars TGO
Håkan Svedhem ESA/ESTEC ILEWG Earth – Venus Trajectory
2 ILEWG Reducing Apocentre altitude ILEWG
June 2016 IPPW-13 Venus Express 4 Specific points to be considered for the test case of Venuis Express
1. Venus Express has a body/solar array layout that results in a dynamically stable attitude. 2. A software mode to operate the spacecraft is during aerobraking is a part of the on board software. Aerobraking was initially foreseen as a backup in case the Venus orbit insertion would fail, however it was never intended to be used as a part of the nominal mission. Only limited testing of this has been performed. 3. Additional high temperature tests have been done on the solar panels, but unidentified hotspots may exist. 4. The most limiting factor on Venus Express is likely to be the aerothermal heat input on the Multi Layer Insulation on the –Z platform. 5. The uncertainty and variable character of the Atmosphere needs to be considered. The aerodrag equation
m a = ½ ρ Cd A v² Parameters to consider
NM BM TTM Pericentre velocity vs Orbital Period
Examples (VEX): Delta-V needed for Reduction of orbital period:
24h-18h 90m/s 18h-16h 42m/s 18h-12h 116m/s
Aim for experimental demonstration of concept: 24h-23h 12 m/s Aerothermal flux limitations
Peak aerothermal XS/C XS/C flux (W/m²) 24° 24°
ZS/C ZS/C ZS/C 7000
6000
5000
4000
3000
2000
1000 Time 0
Beginning of the plateau Middle of the plateau End of the plateau (sun on (sun on the back side of SA) (1) (sun at 12° of SA plane) the cell side of SA) (1)
Thermal constraint due to the solar array Thermal constraint due to the MLI
Note (1) : Depending on the plateau the sun will be illuminating the back side of the SA either at the beginning or at the end of the plateau Optimum conditions for aerobraking at Venus Pericentre Altitude [km] 280
260
240
220
200
180
160 Pericentre Altitude [km] Altitude Pericentre 140
120
100 0 10 20 30 40 50 60 70 80 90 Days after last Pericentre Rise manouevre (30 April) Pericentre Altitude [km] 280
260
240
220
200
180 Walk-In phase 160 17/5-10/6
Aerobraking phase Pericentre Altitude [km] Altitude Pericentre 140 11/6 – 11/7
120
100 0 10 20 30 40 50 60 70 80 90 Days after last Pericentre Rise manouevre (30 April) Preparation for aerobraking: Torque technique for measuring atmospheric density at low altitudes
1. Run movie ILEWG High day to Day variablity from Drag/Torque measurements at 165km
14 ILEWG
Models and measurements of density and temperature
• VIRA (Venus International Reference Model), Hedin model, VTS3 model • Measurements on Venus Express
– Spicav, up to 130 km (only CO2)
– SOIR, up to 150 km (only CO2) – VeRa, up to 95 km – Drag, by radio tracking, 165-180 km – Torque, 165-200 km
15 ILEWG
Polar density, raw torque data
250
200 Altitude [km] Altitude 150
100 1,00E-15 1,00E-14 1,00E-13 1,00E-12 1,00E-11 1,00E-10 1,00E-09 1,00E-08 1,00E-07 1,00E-06 1,00E-05 Atmospheric Density [kg/m3]
June 2016 IPPW-13 16 ILEWG
17 ILEWG Pericentre Altitude evolution
18 ILEWG Delta-v vs date
PC lowering
June 2016 IPPW-13 19 ILEWG
June 2016 IPPW-13 20 ILEWG Atmospheric Density
June 2016 IPPW-13 21 ILEWG Measurements vs. Model results
Polar density, raw torque data
250
200 Altitude [km] Altitude Altitude [km] Altitude 150
100 1,00E-15 1,00E-14 1,00E-13 1,00E-12 1,00E-11 1,00E-10 1,00E-09 1,00E-08 1,00E-07 1,00E-06 1,00E-05 Atmospheric Density [kg/m3]
22 ILEWG Evolution of Orbital Period
23 ILEWG Conclusion on VEX Test
• Efficiency of aerobraking demonstrated: 1 hour 20 min reduction in orbital period in 4 weeks. • Spacecraft capability and robustness confirmed, even at a maximum dynamic pressure of 0.7N/m2 and a heat input of near 7 kW/m2. No damage or reduced performance was observed. • Operational procedures confirmed. • Unique scientific results, providing atmospheric densities in an unchartered region. Actual densities turned out less than half of what was predicted by previous models.
24 ExoMars and the Trace Gas Orbiter
The TGO is the first part of the ExoMars mission, to be followed by the ExoMars Rover and Surface platform to be launched in July 2020 ExoMars is an ESA - Roscosmos joint programme ExoMars is funded within the European Exploration Envelop Programme (E3P) and is a part of the ESA HRE directorate with support from SCI The TGO is a very large spacecraft, with a total mass of 3700kg. The launch mass was 4300kg (including the Schiaparelli, the Entry Descent and Landing Demonstration Model). The height of TGO is about 3.2 m and the Solar array tip-to-tip length is 17.5m
ESA UNCLASSIFIED - For Official Use Application of aerobraking to ExoMars Trace Gas Orbiter
Aerobraking animation
ESA UNCLASSIFIED - For Official Use Aerobraking altitude evolution 160
150
140
130 Altitude [km] Altitude 120
110
100 0 25 50 75 100 125 150 175 200 Aerobraking pass number ESA UNCLASSIFIED - For Official Use Delta-v per pass
3 180,00
2,5 150,00
2 120,00
v [m/s] v -
1,5 90,00
v v per pass [m/s] -
1 60,00
Delta Accumulated delta Accumulated 0,5 30,00
0 0,00 0 50 100 150 200 Aerobraking pass number
ESA UNCLASSIFIED - For Official Use Two typical TGO a/b passes
TGO a/b pass 2017-10-30 TGO a/b pass 2017-11-13 0,012 0,014
0,012 0,010
0,010 0,008
0,008 0,006 0,006
0,004 Acceleration [m/s2] Acceleration Acceleration [m/s2] Acceleration 0,004
0,002 0,002
0,000 0,000 09:17:17 09:20:10 09:23:02 09:25:55 12:17:17 12:20:10 12:23:02 12:25:55 Time Time
ESA UNCLASSIFIED - For Official Use TGO Aerobraking , determined max density Derived160,00 atmospheric density at max point
150,00
140,00
130,00 Altitude Altitude [km] 120,00
110,00
100,00 1,00E-10 1,00E-09 1,00E-08 1,00E-07 Max density [kg/m3] ESA UNCLASSIFIED - For Official Use Evolution of orbital period for planned vs actual aerobraking
ESA UNCLASSIFIED - For Official Use TGO Spacecraft and instrument commissioning will start in April 2018
Science and data relay will start in June 2018 ESA UNCLASSIFIED - For Official Use