Vertical Lift – Not Just For Terrestrial Flight Larry A. Young Army/NASA Rotorcraft Division Ames Research Center Moffett Field, CA Abstract Autonomous vertical lift vehicles hold considerable potential for supporting planetary science and exploration missions. This paper discusses several technical aspects of vertical lift planetary aerial vehicles in general, and specifically addresses technical challenges and work to date examining notional vertical lift vehicles for Mars, Titan, and Venus exploration. for planetary exploration and science Introduction missions (fig. 1). Initial results have been quite promising. As a result of this The next few years promise a unique early work, the utility of rotorcraft, convergence of NASA aeronautics and VTOL vehicles, and hybrid airships for space programs. NASA planetary Mars exploration and planetary science science missions are becoming missions as a whole can be technically increasingly more sophisticated. justified as follows. Manned and robotic exploration of the solar system planets would be greatly Why vertical lift vehicles for planetary enhanced through the development and exploration? For the same reasons why use of robotic aerial vehicles. Since the these vehicles are such flexible aerial 1970’s a number of Mars (fixed-wing) platforms for terrestrial exploration and Airplane concepts have been proposed transportation: the ability to hover and for Mars exploration. fly at low-speeds and to take-off and land at unprepared remote sites. Further, The Army/NASA Rotorcraft Division -- autonomous vertical lift planetary aerial in collaboration with the Center for Mars vehicles (PAVs) would have the Exploration -- at NASA Ames has been following specific advantages and performing initial conceptual design capabilities for planetary exploration: studies of Martian autonomous rotorcraft • Hover and low-speed flight AHS/AIAA/RaeS/SAE International Powered capability would enable detailed Lift Conference, Arlington, VA, October 30- November 1, 2000. and panoramic survey of remote flight control; autonomous systems work sites; based on vertical lift vehicle applications; high-frequency open- and • Vertical lift configurations would closed-loop smart structures/actuators. enable remote-site sample return to lander platforms, and/or precision placement of scientific probes; • Soft landing capability for vehicle reuse (i.e. lander refueling and multiple flights) and remote-site monitoring; • Hover/soft landing are good fail- safe ‘hold’ modes for autonomous operation of PAVs; • Vertical lift PAVs would provide greater range and speed than a surface rover while performing detailed surveys; Figure 1 – Vertical Lift Planetary Aerial • Vertical lift PAVs would provide Vehicles as ‘Astronaut Agents’ greater resolution of surface details, or observation of atmospheric phenomena, than an Ultimately, the objective of this paper is orbiter; to inspire the vertical flight research community to consider and to embrace • Vertical lift vehicles would the concept of vertical lift planetary provide greater access to aerial vehicles and to participate in their hazardous terrain than a lander or ultimate development and use. Specific rover. opportunities for vertical life PAVs in planetary science and some of the PAV In addition to the potential science and design challenges are presented in this technology benefits resulting from the paper. Ongoing work, including that in development and use of vertical lift academia, is also described. planetary aerial vehicles, there are substantial opportunities for technology transfer from a vertical lift PAV development effort. These technology Opportunities transfer opportunities include: advanced high-efficiency propeller or proprotor As noted earlier, work is being pursued designs; precision guidance, navigation at the Ames Research Center’s and control at low altitudes and near- Army/NASA Rotorcraft Division on a terrain obstacles; adaptive (inner-loop) Martian autonomous rotorcraft for scientific exploration of Mars. Why not, though, a Venusian hybrid-airship? Or, a Titan VTOL? Or, alternatively, Figures 3 and 4 are approximate why not any number of vertical concepts estimates of the speed of sound and that could provide unique mission kinematic viscosity for various different capability for planetary science? planetary bodies in the solar system. These estimates were derived in This paper examines the question of the reference 2. feasibility of vertical lift planetary aerial vehicles. In particular, discussion in the paper will be directed at the three planetary bodies in our solar system Neptune where vertical lift vehicles might prove Uranus feasible. Table 1 is a summary of the Saturn key surface atmospheric properties for Mars, Titan, Venus, and Earth. This Jupiter Titan y y information will be used to examine the y y general aerodynamic attributes of Mars vertical lift PAVs. Earth Venus 0 200 400 600 800 1000 1200 Table 1 – Summary of Planetary Speed of Sound (m/sec) Descriptions (Ref. 1) Mean Gravity! Mean Mean Mean Atmos. Fig. 2 – Estimates for the Speed of Radius (m/s2) Surface Surface Surface Gases Sound (km) Atmos. Atmos. Atmos. Temp. Pressure Density (o K) (Pa) (kg/m3) 6 Venus 6052 8.87 735.3 9.21x10 64.79 CO2 Neptune 96% Uranus N2 3.5% Earth 6371 9.82 288.2 101,300 1.23 N2 78% Saturn O2 21% -2 Mars 3390 3.71 214 636 1.55x10 CO2 Jupiter 95% N2 2.7% Titan Ar 1.6% O2 0.1% Mars Titan 2575 1.354 94 149,526 5.55 N2 65- (Saturn 98% Earth moon) Ar<25% Venus CH4 2- 10% 1E-07 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 Kinematic Viscosity (m^2/sec) Fig. 3 – Estimates of Kinematic ! Viscosity Mean values noted for planet radii and gravity to account for the oblateness of the planet. Mars surface temperature, pressure, and density varies significantly spatially and temporally; surface temperature range of 140-300oK; surface pressure 636±240 Pa. Seasonal Additional data related to planetary CO2 sublimation and condensation at the polar caps atmospheric properties can be found, for (particularly at the southern polar cap) is the chief reason for the atmospheric pressure and density variations. example, in Ref. 3-6. evolutionary processes that led our ‘sister’ planet to be radically different from Earth Despite the considerable amount of data • Determine if planetary-scale ‘green-house’ related to planetary atmospheres, much effects can be halted and/or reversed more data can, and must, be discovered during the course of the development and general application of PAVs. Finally, in addition to the scientific benefits resulting from the employment In establishing the feasibility of vertical of vertical lift vehicles, considerable lift (and other) PAVs, it is not sufficient enthusiasm and support from the to merely question whether or not flight American public could be generated for in extraterrestrial atmospheres is both the demonstration of extraterrestrial theoretically possible. Clearly defined atmospheric flight. planetary science goals and opportunities are also required so that vertical lift PAV designs can be optimized. Table 2 summarizes a partial list of planetary science goals/opportunities in which Mars, Titan, and Venus vertical lift, or rotary-wing, platforms could contribute. Mars, Titan, and Venus are as different from each as they are with respect to Earth. Each planetary body -- each Table 2 – Planetary Science major science/exploration mission, in Opportunities (A Partial List Only) fact -- will entail radically different Science/Exploration Opportunities aerial vehicle design challenges. This will be highlighted in the discussion to Mars • Search for water or past signs of water follow which outlines some thoughts (characterize global distribution) • Search for life or evidence of past life regarding notional vehicle • Understand the atmospheric and geological configurations and design considerations evolution of Mars; perform comparative analyses of the Mars planetary for each of the three planetary bodies in evolutionary process with the other our solar system where a vertical lift terrestrial-type planets in our solar system • Survey for resources that would expand capability might theoretically make exploration capability and support for an sense for exploration/scientific extended human presence on Mars investigation. Titan • Search for the precursor biochemical components of life • Perform atmospheric science studies to understand the unique nature of the Titan Mars atmosphere (i.e. its high density/pressure) • Survey for chemical resources/volatiles that could enable in-situ propellant and fuel Most of the work to date investigating production; resulting propellant could be used for sample return missions to Earth the feasibility of vertical lift planetary and expanded surveys of the other aerial vehicles has focused of rotary- Saturnian moons wing configurations for Mars Venus • Correlate space-based cartographic and exploration. Mars, of all the planetary inferred geological data with detailed bodies in the solar system, holds the surveys in targeted areas using vertical lift PAVs. greatest interest for NASA researchers. • Acquire adequate data to understand the Both the Offices of Space Science and fundamental atmospheric and geological Space Flight actively promote/direct research and engineering effort for the 3500 3.5 (Disk Loading = 4 N/m^2) robotic and, ultimately, human 3000 3 exploration of Mars (fig. 4). Reference 2500 2.5 ) m 7 details NASA' strategic plan for the ( Human Exploration and Development of 2000 2 1500 1.5 Space