Robotic exploration of the surface and atmosphere of Venus - CiteSeerX

Acta Astronautica 59 (2006) 570 – 579 www.elsevier.com/locate/actaastro

Robotic exploration of the surface and atmosphere of Venus夡 Geoffrey A. Landis∗ NASA John Glenn Research Center, 21000 Brookpark Road, Cleveland, OH 44135, USA Received 6 June 2005; received in revised form 2 February 2006; accepted 12 April 2006 Available online 22 June 2006

Abstract Venus, the “greenhouse planet,” is a scientifically fascinating place. The US National Academies of Sciences listed a Venus surface in situ explorer as one of the highest priority planetary science missions. A mission concept for a robotic mission to study the surface and atmosphere of Venus has been designed. The mission includes both surface robots, designed with an operational lifetime of 50 days on the surface of Venus, and also solar-powered airplanes to probe the middle atmosphere. At 450 ◦ C, and with 90 atmospheres of pressure of carbon-dioxide atmosphere, the surface of Venus is a hostile place for operation of a probe. The mission design trade-off looked at three options for surface operation: developing technology to operate at Venus surface temperatures, using an active refrigeration system to lower the temperature inside a “cool electronics enclosure,” or developing a hybrid system, where the computer system and the most temperature-sensitive electronics are on an aerial platform at lower temperature, and less sophisticated surface electronics operate at the ambient surface temperature. This paper presents the mission objectives, discusses the technology options for materials, power systems, electronics, and instruments, and presents a short summary of the mission. © 2006 Elsevier Ltd. All rights reserved.

1. Introduction 1.1. Background Venus, the “greenhouse planet”, is a scientifically fascinating place. This mission design study focuses on Venus, sometimes called Earth’s sister planet due to the fact that it is closest to the Earth in distance, and similar to Earth in size. Despite its similarity to Earth, however, the climate of Venus is vastly different from Earth’s [1–4]. Understanding the atmosphere, climate, geology, and history of Venus could shed considerable light on our understanding of our own home planet. 夡

Paper IAC-04-Q.2.A.08, presented at the International Astronautical Federation Congress, Vancouver BC, October 4–8, 2004. ∗ Tel.: +1 216 433 2238; fax: +1 216 433 6106. E-mail address: [email protected]. 0094-5765/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2006.04.011

Venus has been explored by a number of missions from Earth, including the Russian Venera missions which landed probes on the surface [1], the American Pioneer missions which flew both orbiters and atmospheric probes to Venus [1], the Russian “Vega” mission, which floated balloons in the atmosphere of Venus [2], and most recently the American Magellan mission which mapped the surface by radar imaging [2,3]. While these missions have answered basic questions about Venus, telling us the surface temperature and pressure, the elevations and topography of the continents, and the composition of the atmosphere and clouds, scientific mysteries still abound. 1.2. Science goals Venus is of considerable interest to terrestrial atmospheric science, since of all the planets in the solar

G.A. Landis / Acta Astronautica 59 (2006) 570 – 579

system, it is the closest analogue to the Earth in terms of atmosphere. Yet Venus’ atmosphere is an example of “runaway greenhouse effect” [3]. Understanding the history and the dynamics of Venus’ atmosphere could tell us considerable insight about the workings of the atmosphere of the Earth. It also has some interest to astrobiology [3,5]. Crisp [6] calls the environment of Venus “among the most enigmatic in the solar system.” He notes that, although the volatile inventory of Venus are not yet well characterized, existing measurements suggest that the relative abundances of the noble gases in its atmosphere are much more solar-like than those on the other two terrestrial planets. Similarly, although today Venus has an inventory of water that is a hundred thousand times less water than Earth, the deuterium to hydrogen ratio in the atmosphere is on the order of 150 larger for Venus than for Earth. Since hydrogen is more easily lost from the atmosphere than deuterium, this suggests that the original amount of water present on Venus may have been comparable or larger than that on Earth. The detailed process and timing of this large loss of water are not known, leaving a large blank area in efforts to understand the history and change of the surface and atmosphere. Likewise, the cycle of sulfur in the Venus atmosphere is not yet understood. The sulfur interacts with the surface minerals, which serve as a repository of sulfur. Are there presently active sources of atmospheric sulfur, in the form of volcanoes or gas vents? The details of the atmospheric dynamics of Venus are also not yet understood. Although the surface of Venus rotates very slowly, with a 242-day period, the atmosphere at the cloud level and higher moves around the planet a period of 4 days, 60 times faster than the surface. The question of exactly what mechanism supports this atmospheric super-rotation is a question that has eluded detailed explanation since its discovery by spacecraft in the early 1970s. The US National Academies of Science Space Studies Board decadal study, New frontiers in the solar system: an integrated exploration strategy [7], ranked a Venus surface in situ explorer as one of the five highest priorities for Medium-class future missions.1 The Space Studies Board listed “Fundamental Science Questions” to be addressed by science missions. They list three questions fundamental to our understanding of the solar 1 The missions recommended by the Space Science Board were

Pluto/Kuiper Express, Lunar Aiken basin Sample Return, Jupiter Polar Orbiter, Venus in situ Explorer, and Comet Sample Return. Five additional medium-class missions were judged worthwhile, but not recommended for flight.

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system which are directly addressed by a Venus mission: What global processes affect the evolution of volatiles on planetary bodies? Why do terrestrial planets differ so dramatically in their evolution? How do the processes that shape the contemporary character of planetary bodies operate and interact? In addition, a large number of other important scientific questions remain to be answered. A sample of scientific questions includes: 1. Before the runaway greenhouse effect, was early Venus temperate? 2. Did Venus once have an ocean? 3. What causes the geological resurfacing of the planet? 4. Is Venus still geologically active? 5. What is the “snow” on Venus mountaintops? 6. Can we learn about Earth’s climate from Venus? 7. Could life have existed on Venus in an earlier, pregreenhouse-effect phase? 8. Is the atmosphere of Venus suitable for life? To address these and other scientific questions, a robotic mission to study the surface and atmosphere of Venus has been designed. 1.3. Mission goals At 450 ◦ C, with 90 atmospheres of pressure of carbon-dioxide atmosphere, and shrouded in sulfuricacid clouds, the surface of Venus is a difficult place for operation of a probe. The longest-lived of the Russian Venera landers lasted less than two hours on the surface of Venus. One American Pioneer probe made it to the surface and survived about an hour. It is clear that the surface of Venus is an extremely hostile environment! The objective was to develop a concept and technology for science-driven, technology-enabled exploration of Venus surface and atmosphere. The mission includes both surface robots [8], designed with an operational lifetime of 50 days on the surface of Venus, and also solar-powered airplanes to probe the middle atmosphere [9–11]. We assume precursor probes (such as the ESA Venus Express mission) will give us enough information to chose exploration sites. The mission requirements are: • baseline mission duration: 50 days, • mission elements will operate at multiple latitudes across the planet, • mission elements will operate at multiple altitudes, including the surface,

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• seismometers emplaced at a minimum of four surface locations, • No night operations required. 2. Mission concept 2.1. Mission overview The mission design study evaluated airplanes and aerostats for the atmospheric element, and looked at both rovers and stationary elements for the atmosphere. The final choice of elements was to use a solar-powered airplane for atmospheric exploration, and a nuclear isotope powered rover for the surface mission. For a wide range of coverage of the planet, four rovers and four airplanes were baselined. Each rover can deploy up to three separate seismometer packages. For probing the atmosphere to levels below the level at which the airplanes can fly, small probe dropped by the airplane are used. The mission design trade-off looked at three options for surface operation: developing technology to operate at Venus surface temperatures, using an active refrigeration system to lower the temperature inside a “cool electronics enclosure,” or developing a hybrid system, where the computer system and the most temperaturesensitive electronics are on an aerial platform at a lower temperature, and less sophisticated surface electronics operate at the ambient surface temperature. The third approach was selected for the detailed mission design. Fig. 1 shows the mission concept in schematic, with a dedicated airplane associated with each surface rover. (The airplane shown in Fig. 1 is the original conceptual design; during the study, the design evolved to the versions shown in Figs. 3 and 4.) The airplane carries the rover’s computer, and the electronics package on the rover itself is a simple package with discrete components, made using only hightemperature semiconductors. The global mission comprises the four surface rovers, each with a dedicated aerial platform carrying the computer and control electronics, four additional airplanes dedicated to the atmospheric survey, a communications relay satellite, twelve seismometer stations emplaced by the rovers, and a number of atmospheric drop probes. Nuclear electric propulsion was chosen as the baseline transportation option [12]. 2.2. Venus airplane The trade-study considered operation of balloons, dirigibles, and airplanes. The summary of the trade-off is shown in Table 1.

Fig. 1. Venus exploration concept.

Earlier studies showed that a solar-powered Venus airplane could fly faster than the local wind velocity [9–11], allowing it to remain stationary at the subsolar point, or else “hover” over a ground location. The current Venus airplane design has evolved from the earlier designs. A significant requirement for the design is that the wing and tail must be design to fold to fit into the aeroshell for transport to Venus and entry into the atmosphere. The unfolding of a candidate design is shown in Fig. 2, which shows the placement of solar cells on top and bottom surfaces of the wings. Foldingwing deployment has been demonstrated on a similarsized test airplane in the ARES project, a demonstrator for a proposed Scout mission to Mars [13,14]. Nominal flight altitude is slightly above the cloud level, 75 km above the surface. The final design configuration chosen is a conventional aircraft planform, with each wing folded about halfway out the span, and a folding propeller.


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Table 1 Atmospheric probe trade-off Balloon • Simple technology • No power required to maintain altitude; power only for instruments and payload • Demonstrated on Venus by the Russian “VEGA” mission • Altitude change possible, but difficult • Location change not possible • Cannot stationkeep or stay in sun Summary: Not enough flexibility for atmospheric science study; not practical as a relay station. Airship • • • • •

Difficult to stow and deploy Altitude change possible, but difficult Speed is slow: Cannot stationkeep Cannot stay in sun

Summary: Too high complexity and too low flexibility. Airplane • Airplane design uses terrestrial experience • Stow and deploy concepts demonstrated by ARES Mars airplane [13,14] • Altitude change easy • Speed allows stationkeeping and continuous sun Summary: Aircraft concept chosen for study.

The vertical tail is doubled, and mounted on the bottom surface rather than the top to fit in the aeroshell. Fig. 3 shows the airplane unfolded for flight. For landing, the design was baselined to fit into a 3.7 m diameter aeroshell (the size of the Viking lander entry system). Fig. 4 shows how it folds to fit in a candidate aeroshell. The corrosive atmosphere of Venus, with clouds composed of sulfuric acid droplets, means that all exposed surface of the airplane must be protected. However, this technology is well understood, since sulfuric acid has been a well-known reagent since ancient times. The Russian VEGA balloon mission, for example, flew at the cloud deck level of Venus for a duration of roughly 50 h without attack by the atmosphere. Airplane design details are given elsewhere [15]. Airplane mass is 103 kg, including instruments. Table 2 shows a breakdown of the system mass of the airplane and 3.7-m entry vehicle.

Fig. 2. Unfolding sequence of the Venus airplane tail and wing, showing solar cells on the top and bottom surface of the wings and tail.

Fig. 3. Visualization of the Venus airplane.

2.3. Venus surface rover The rover is shown in Figs. 5 and 6. The total deployed rover mass is 330 kg, plus a 7% mass margin.

The rover lands directly on a parachute: after the aeroshell is jettisoned, there is no separate “lander” vehicle. High-temperature parachute material such

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• rover science: tilt and mobility power measurements characterize surface properties. 3.2. Surface: seismic stations A minimum of four seismic stations is required for seismometry. Additional stations are desirable. Since each rover carries three seismic stations, both the magnitude and direction of arrival of seismic waves can be independently measured at each station. • Each station measures acceleration in three axes. 3.3. Atmospheric platform instrumentation The airplane instruments comprise: Fig. 4. Venus airplane folded into aeroshell for entry into the Venus atmosphere.

as glass–fiber cloth is required. Due to thick atmosphere, parachute descent velocity is low (roughly 12 times lower than parachute descent velocity on Earth. The vehicle will detect the transverse velocity relative to surface during descent, and will rotate on the parachute system so that the velocity is in direction of wheel rotation, to avoid tipping over on landing (note that Venus surface winds are low, and the transverse speed at landing will be only a few meters per second. The parallelogram deployment system for the wheels provides a shock-absorbent strut. A similar “Land on Wheels” technique is now baselined for 2009 MSL Mars rover, with similar vertical velocities, so this descent approach should be possible for the Venus rover. Fig. 7 shows the rover packaged into the entry aeroshell, with the wheels retracted on parallelogram struts. Table 3 shows the mass breakdown. 3. Mission elements 3.1. Surface: rover instrumentation The rovers are assumed to be similar in size and capability to the Mars exploration rover vehicles. The onboard instruments are: • • • •

camera (stereo imaging); X-ray diffraction; mass spectrometry; atmospheric science: temperature, pressure, wind;

• • • • • • • •

camera; mass spectrometer; aerosol particle size; temperature, pressure, wind speed (three axes), altitude; optical depth, total and direct solar flux, upward (albedo) flux; microscope; electric fields; possible addition: radar.

3.4. Deep atmosphere probes The probe instrumentation comprises: • • • • •

mass spectrometer; aerosol particle size; temperature, pressure, wind speed, altitude; electric fields; possible addition: radar reflector.

3.5. Orbiter No instrumentation is currently baselined for the orbital transfer vehicle or the orbital com relay. Possible orbiter instruments include radio science, particle and fields instrumentation, lightning detection, radar, trace gas composition measurement by spectrometry, and global wind measurements. A radar instrument could operate in bistatic mode, with the spacecraft illuminating the planet and the aircraft receiving the radar, or vice-versa. 4. Technology selection A significant element of the project was selection of technology for the operation.


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Table 2 System mass breakdown summary for Venus aircraft and aeroshell/entry system System description

Mass fraction (%)

Mass (kg)

Source

Airplane Heatshield structure Heatshield TPS Backshell structure (gussets, separation ftgs, paint, vent, etc.) Backshell TPS Parachute system Airplane deployment mechanism (separation from backshell) Misc. (COMM, power, ballast, etc.) Total entry mass Contingency mass

20 7 13 12 8 10 15 15 100 30

103 36.05 66.95 61.80 41.20 51.50 77.25 77.25 515 155

NA Pioneer Pioneer Pioneer Pioneer Pioneer Mars airplane Mars airplane

Total with contingency Note: Mass fractions based off Mars airplane data Venus pioneer.

670

RCS system description

Quantity

Mass (kg)

Source

Hardware Marquardt 100lbf thrustera Rockwell 25lbf thrusterb Fuel tank Oxidizer tank Pressurant tank Associated hardware (valves, fittings, line) Propellant/Pressurant Fuel Oxidizer Pressurant Total RCS wet mass

NA 2 6 1.0 1.0 1.0 NA NA 45.4 l 45.0 l NA

51.9 8.0 25.0 5.42 5.409 3.655 4.345 103.9 39.0 64.4 0.5 155.8

NA Historical data Historical data Historical data Historical data Historical data Historical data NA V = 350 m/s V = 350 m/s V = 350 m/s

Mass summary

Mass (kg)

Aeroshell payload package RCS dry mass RCS propellant/pressurant Total dry mass Total wet mass

670 51.9 103.9 721 825

a Marquardt R-4D-1/10 (lsp 300s, Vac Thrust = 444N, Fuel Biprop-N204/Hydrazine). b Rockwell (Rocketdyne) R-1E-3 Shuttle vernier, lsp = 225s, Vac Thrust 111N, Fuel Mono-Hydrazine.

4.1. Surface power system

Fig. 5. Final design of the Venus Rover CAD model with wheels deployed, perspective view (visualization by Shawn Krizan).

Power systems considered for the rover power included microwave beamed power, solar power, and radioisotope power systems. The radioisotope system was selected based on the technology availability. Both thermoelectric and dynamic (Stirling conversion) options were analyzed; the Stirling converter was selected based on the higher efficiency lead to a lower number of Pu isotope heat source units. A power requirement baseline of 400 W was picked. In addition to the power system, a Stirling refrigeration system was designed. The power level of this system was selected to allow the electronics enclosure to be cooled to 300 ◦ C, the maximum operating temperature of a high-temperature microcontroller to operate.

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The details of the analysis of the Venus-surface dynamic isotope power system [16,17] and refrigerator [17–19] is given elsewhere. The analysis case assumed a hot-side temperature (Th)=1350 K, and radiator temperature (Tr) = 870 K. The calculated thermodynamic efficiency was 27.5% resulting in a total efficiency of 23.4%). For a total GPH heat input Qh = 1740 W, the heat rejected, Qr = 1267 W, and the total power produced = 478 W. As discussed in Section 4.4 below, a high-temperature motor is used as a generator to convert the mechanical power into electrical power. 4.2. Rover electronics

Fig. 6. Final design of the Venus Rover CAD model, with wheels in deployed state: side and front views (visualization by Shawn Krizan).

Fig. 7. Rover packaged into the 2-m diameter descent aeroshell (visualization by Shawn Krizan).

The 400 W power system was sized to provide sufficient power to allow the refrigeration system to be run, if this is required, although the baseline rover design analyzed used ambient-temperature electronics, and did not include a refrigeration system.

The rover surface elements were designed to use electronics that can be implemented with high-temperature discrete electronics. Silicon carbide was selected as the technology of choice, since high-efficiency transistors have been demonstrated on the material, at NASA Glenn and elsewhere [20–22]. To demonstrate the ability of the technology, a design for a 450 ◦ C radio receiver to be implemented in SiC electronics was breadboarded and tested, using off the shelf room temperature components which have performance characteristics similar to those of SiC bipolar devices operating at 450 ◦ C. A superheterodyne receiver was designed. The central idea of the circuit design is that a receiver could be designed such that nearly all of the components could be fabricated on SiC dice. The result is a small, highoperating temperature device, which could find applications in industry as well as space exploration. In a practical receiver the operating frequency would likely be higher (50–100 MHz) and SAW resonators would be used. Resonator technologies for high temperature include GaPO4 , langasite [23], and SiC MEMS devices. A transmitter could be built using similar circuit concepts. The design was tested using available Si JFET components simulating characteristics of SiC devices. The “proof of concept” device demonstrated that today’s components can be integrated into a design capable of Venus surface operation. 4.3. Moving parts Lubrication for operation of components at high temperatures can be difficult. A number of approaches were examined. High-temperature silicon nitride (Si3 N4 ) bearings were chosen. This technology has been developed by the Air Force Research Laboratories as a hightemperature ceramic bearing, and, using cesium silicide lubricant, has been tested to 1250 ◦ F (675 ◦ C) for 50 h.


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Table 3 System mass breakdown summary for Venus surface rover and aeroshell/entry system System description

Mass fraction (%)

Mass (kg)

Source %

Rover Heatshield structure Heatshield TPS Backshell structure (gussets, separation ftgs, paint, vent, etc.) Backshell TPS Parachute system Lander with airbags Misc. (COMM, power, ballast, etc.) Total entry mass Contingency mass

50.0 7.0 13.0 12.0 8.0 10.0 0.0 0.0 100.0 7.0

330 46.20 85.80 79.20 52.80 66.00 0.00 0.00 660 46

NA Pioneer Pioneer Pioneer Pioneer Pioneer Pioneer Pioneer

Total with contingency Mass fractions based off Venus pioneer large probe.

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RCS system description

Quantity

Mass (kg)

Source

Hardware Marquardt 100lbf thrustera Rockwell 25lbf thrusterb Fuel tank Oxidizer tank Pressurant tank Associated hardware (valves, fittings, line) Propellant/Pressurant Fuel Oxidizer Pressurant Total RCS wet mass

NA 2 6 1.0 1.0 1.0 NA NA 45.4 l 45.0 l NA

51.9 8.0 25.0 5.42 5.409 3.655 4.345 103.9 39.0 64.4 0.5 155.8

NA Historical data Historical data Historical data Historical data Historical data Historical data NA V = 350 m/s V = 350 m/s V = 350 m/s

Mass summary

Mass (kg)

Aeroshell payload package RCS dry mass RCS propellant/pressurant Total dry mass Total wet mass

706 51.9 103.9 758 862

a Marquardt R-4D-1/10 (lsp 300s, Vac Thrust = 444N, Fuel Biprop-N204/Hydrazine). b Rockwell (Rocketdyne) R-1E-3 Shuttle vernier, lsp = 225s, Vac Thrust 111N, Fuel Mono-Hydrazine.

4.4. High-temperature motors and actuators For mobility on the surface, it is necessary to provide both motors for primary motion, and also actuators for moving mechanical arms, instrument covers, and deployment of devices. A number of technologies have been tested for high-temperature operation, as shown in Table 4 [24–28]. A high-temperature electric motor, developed at NASA Glenn for jet engine applications is appropriate for primary power. This is an eight-pole radial magnetic bearing has been modified into a switchedreluctance electric motor capable of operating at a speed as high as 8000 rpm at a temperature as high as 1000 ◦ F (540 ◦ C). The motor is an experimental

prototype of starter-motor/generator units proposed to be incorporated into advanced gas turbine engines and that operate without need for lubrication or active cooling. Issues addressed in the development of the coils included thermal expansion, oxidation, pliability to small bend radii, microfretting, dielectric breakdown, tensile strength, potting compound, thermal conduction, and packing factor. The motor had undergone 14 thermal cycles between room temperature and 540 ◦ C and had accumulated operating time > 27.5 h at 540 ◦ C [24]. For actuations, a linear actuator developed at the University of Sheffield [25,26] is appropriate. This actuator has a force of 500 N with a 1 mm throw, and has been demonstrated at 800 ◦ C.

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Table 4 Operating temperature and technology status for possible motors and actuators for use on Venus Motor or actuator

Max. temp. (◦ C)

Status

Baker Hughes GeoThermal Swagelock pneumatic Rockwell Scientific SiC NASA Glenn R&T high-temperature actuator NASA Glenn switched-reluctance motor [24] U. Sheffield Linear actuator [25,26] NASA Glenn/MSU RAC smart materials project NASA Glenn/MSU RAC smart materials [27] NASA Glenn/MSU RAC smart materials [27] NASA Glenn langasite [23] and lanthanum titanate [28] piezoelectric

160 200 200 400–600 540 800 150 500 1000 750

Commercial Commercial Development 400 ◦ C prototype, 600 ◦ C research Demonstrated Technology demonstrator Shape memory (SMA): commercial SMA: material demonstrated SMA: high-temperature goal Piezoelectric material demonstrated

Table 5 Pressurant choices Gas

Liquid density at 25 ◦ C (kg/m3 )

Vapor pressure at 25 ◦ C (MPa)

Thermal conductivity (W/MK)

He N2 Ar CO2 Xenon propane HFC-23 HFC-236fa

125 808 1400 468 2953 500 670 1360

– – – 5.9 6 0.9 4.732 0.27

0.152 0.0258 0.0177 0.0167 0.00565 0.0179 0.0131 0.0042

Other technologies being developed for actuators include high-temperature shape-memory alloy [27] and piezoelectric [23,28] actuators. The ceramic materials langasite (La3 Ga5 SiO14 ) [23] and lanthanum titanate [28] have both demonstrated piezoelectric action at temperatures of over 750 ◦ C. These may be appropriate for low-power actuation of small mechanical devices such as latches and covers, and for fine motion control. The materials required for actuators from these materials have been demonstrated at the temperatures of interest, but mechanical actuators have yet to be made. 4.5. Pressurant If the electronics are at Venus pressure, the interior needs to be sealed from atmosphere. The mass required for a pressure vessile to withstand 92 bar surface pressure of Venus is impractical, and hence it is desirable that interior of the electronics enclosure should be pressurized to prevent it from being crushed. Several approaches to pressurization were investigated. If the pressurant is a gas at standard temperature, a cylinder of compressed gas could be brought to Venus and the enclosure pressurized on descent. A more practical approach is to use a material that can be transported as a liquid, and then vaporizes at the equilibrium

Table 6 Properties of HFC-236fa as a pressurant HFC 236fa • Stores as liquid for flight • Vaporizes at Venus temperature • Inert • Thermal conductivity 20 times lower than air • Used as a fire suppressant: does not decompose to outgassing of HF at high temperature

temperature of the electronics enclosure. Several such gases were investigated (Table 5). The pressurant selected was the hydro-fluorocarbon HFC 236fa. This has the advantage of extremely lowthermal conductivity (Table 6). 5. Conclusions A design study for a mission to investigate the surface and atmosphere of Venus was completed. The mission included both atmospheric platforms as well as a surface rover. Both airplane and surface rovers were designed for a 50-day operating life. In order to operate the rover at the high operating temperature at the surface of Venus, only high-temperature electronics were used on the surface, and the computer and control system is


mounted in an atmospheric platform overhead, flying at an altitude where the ambient temperature is Earthlike. Acknowledgments This study was funded by the NASA Revolutionary Aerospace Systems Concepts [29] Theme 1: “Looking for Life and Resources in the Solar system”. A project like this is the sum of the work of a large number of people. I would like to acknowledge: • The Venus Robotic Exploration Design team at NASA Glenn: Geoffrey Landis (Project Lead), Stan Borowski, Randy Bowman, Bob Cataldo, Anthony Colozza, José Davis, Joe Flatico, Dale Force, Melissa McGuire, Kenneth Mellott, Phil Neudeck, Larry Oberle, Thomas Packard, Phillip Paulsen, Bryan Smith, Craig Williams. • The RASC Venus mission team at NASA Langley: Patrick A. Troutman (RASC technical manager), Marianne Rudisill (RASC 2004 Theme 1 manager), Darryl J. Caldwell, Rob Kline, Shawn Krizan, Dan Mazanek, Jennifer Parker, Teresa Ross, Josh Sams, Bob Stevens, Fred Stillwagen, Chris Strickland, Russell Witt. References [1] D.M. Hunten, L. Colin, T.M. Donahue, V.I. Moroz, Venus, University of Arizona Press, Tucson, AZ, 1983. [2] S. Vougher, D. Hunten, R. Phillips (Eds.), Venus II, University of Arizona Press, Tucson, AZ, 1997. [3] D.H. Grinspoon, Venus Revealed, Perseus Publishing, Cambridge, MA, 1997. [4] J.B. Pollack, Atmospheres of the terrestrial planets, in: J.K. Beatty, A. Chaikin (Eds.), The New Solar System, third ed., Cambridge University Press, Cambridge, 1990, pp. 91–103. [5] G. Landis, Venus: the case for astrobiology, Journal of the British Interplanetary Society 56 (2003) 250–254. [6] D. Crisp, et al., Divergent evolution among Earth-like planets: the case for Venus exploration, planetary decadal study community white paper, Solar System Exploration Survey (2001) 2003–2013. [7] National Academies of Science Space Studies Board, New Frontiers in the Solar System: An Integrated Exploration Strategy, National Academies Press, Washington, DC, 2002. [8] G.A. Landis, Robots and humans: synergy in planetary exploration, Acta Astronautica 55 (2004) 985–990. [9] G.A. Landis, Exploring Venus by solar airplane, in: AIP Conference Proceedings, vol. 552, American Institute of Physics Press, College Park, MD, 2001, pp. 16–18. [10] G.A. Landis, C. LaMarre, A. Colozza, Atmospheric flight on Venus: a conceptual design, Journal of Spacecraft and Rockets 40 (2003) 672–677. [11] G.A. Landis, C. LaMarre, A. Colozza, Venus atmospheric exploration by solar aircraft, Paper IAC-02-Q.4.2.03, Acta Astronautica 56 (2005) 750–755.

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