w AIAA Balloon Technology Conference 1999 Venus Aerobot Multisonde Mission By: James A. Cutts ('), Viktor Kerzhanovich o_ j. (Bob) Balaram o), Bruce Campbell (2), Robert Gershman o), Ronald Greeley o), Jeffery L. Hall ('), Jonathan Cameron o), Kenneth Klaasen v) and David M. Hansen o) ABSTRACT requires an orbital relay system that significantly Robotic exploration of Venus presents many increases the overall mission cost. The Venus challenges because of the thick atmosphere and Aerobot Multisonde (VAMuS) Mission concept the high surface temperatures. The Venus (Fig 1 (b) provides many of the scientific Aerobot Multisonde mission concept addresses capabilities of the VGA, with existing these challenges by using a robotic balloon or technology and without requiring an orbital aerobot to deploy a number of short lifetime relay. It uses autonomous floating stations probes or sondes to acquire images of the (aerobots) to deploy multiple dropsondes capable surface. A Venus aerobot is not only a good of operating for less than an hour in the hot lower platform for precision deployment of sondes but atmosphere of Venus. The dropsondes, hereafter is very effective at recovering high rate data. This described simply as sondes, acquire high paper describes the Venus Aerobot Multisonde resolution observations of the Venus surface concept and discusses a proposal to NASA's including imaging from a sufficiently close range Discovery program using the concept for a that atmospheric obscuration is not a major Venus Exploration of Volcanoes and concern and communicate these data to the Atmosphere (VEVA). The status of the balloon floating stations from where they are relayed to deployment and inflation, balloon envelope, Earth. In this paper, we describe the VAMuS communications, thermal control and sonde mission concept and discuss a proposal to deployment technologies are also reviewed. NASA's Discovery program to apply this concept for the Venus Exploration of Volcanoes INTRODUCTION and Atmospheres (VEVA) mission. A primary Despite a number of successful missions to goal of the paper is to describe the progress in observe the surface and interior of Venus, a validating the key technologies needed for the number of fundamental questions about the mission. planet have yet to be resolved. The Venus Geoscience Aerobot (VGA), identified in VENUS AEROBOT MULTISONDE NASA's Roadmap for Solar System Exploration MISSION CONCEPT (Fig I (a) and Ref 1), would make multiple The environment of Venus present major excursions from high altitude in the Venus challenges for scientific exploration. A thick atmosphere to conduct observations at or near the atmosphere of carbon dioxide, with a surface surface in order to address these questions. The pressure of 90 bars and clouds and haze in the VGA mission requires a number of new upper reaches totally obscures the planet's technologies (Ref 2) including high temperature surface from remote observation from orbit balloon materials, gondola thermal control except using radar imagery. The surface systems and reversible fluid altitude control that temperature is about 460°C and therefore long will require a significant investment and at least duration surface vehicles for in situ investigation five years of development. The VGA also require radioisotope powered refrigerators or high temperature electronics or both and become Aff'diations: complex and extremely costly. Short duration (1) Jet Propulsion Laboratory, California observations in the lower atmosphere using small Institute of Technology, Pasadena California expendable sondes that survive for a few hours (2) NASA Headquarters, Washington, D.C. are a more practical solution. However, to be effective as an exploration tool, these sonde (3) Department of Geology, Arizona State 1 American Institute of Aeronautics and Astronautics Concepts for Venus Surface Exploration Earth . v.,._ .,_. i....l_ .,. _ ¸ • s _,... -,..._ .=du_.=,m,,,w ,,,_,.. --A_lli_ t..lul, lbr I,,m_e Fig 1 Comparison of Venus Geoscience Aerobot and Venus Aerobot Multisonde must be able to communicate large amounts of data during their limited lifetime. In particular, Sonde Deployment: Aerobot deployment makes the acquisition of high-resolution aerial imaging it possible to sequence deployments and target from near the surface of the planet for a number sondes based on what has already been learned of targets of high scientific interest is of high from earlier missions. A radar map of Venus was priory. obtained by the U.S. Magellan mission in the 1980s and allows important scientific target to be The innovative feature of the VAMuS mission identified. From a float altitude of about 60-kin, concept is to use aerobots (balloons) as both a the sondes can be dropped with an accuracy of a delivery system and a high data rate few kin, which is much better than could be communications relay for multiple low cost achieved from a direct entry. sondes. By using an aerobot for sonde delivery and data relay it is possible to deliver more After deployment from the aerobot, each sonde sondes with higher accuracy and acquiring more will descend rapidly towards the surface. At an data than when sondes are delivered to Venus by altitude of about 3-km, the descent is arrested by direct entry. Capture at Venus takes place by a parachute or gliding device that permits an low-tech aeroentry eliminating the need for a extended data acquisition near the Venus surface. costly propulsion or aerocapture stage. There is Carried by the fast counter- rotating high altitude no requirement for the use of a relay spacecraft winds the aerobot will be carried rapidly to the or orbiter at Venus. west of the probe. The descent speed of the sonde, the thermal survival time and the period Each aerobot upon emplacement consists of" for which the floating station remains within gondola and sondes suspended from a range of the sonde are roughly commensurate, superpressure balloon. The balloon maintains permitting about 15-30 minutes of high rate the vehicle on a surface of"constant atmospheric imaging data near the surface. density in the Venus atmosphere except for perturbations caused by downdrafts and probe Communications Since the distance from the deployments. Superpressure balloon deployment sondes to the aerobot is measured in tens of kms, and inflation was successfully demonstrated in high data rate communications (from 100kbps to 1985 in the Venera Vega balloon mission. Each 2 Mb/sec) is possible with compact low power of two Venera Vega balloons was tracked for two UHF (400MHz) transmitters and omnidirectional days in the Venus atmosphere. antennas on the probes and an omnidirectional 2 American Institute of Aeronautics and Astronautics receivingantennaontheaerobot.Thesedataare Volcanoes and Atmospheres (VEVA) mission stored on the aerobot for later transmission to was proposed to the Discovery program in June Earth. Since the Venus-Earth distance is 1998 by a team led by Professor gonald Greeley measured in tens of millions of kilometers, the of Arizona State University (4). The VEVA free space communications loss is a factor of 10 _2 team included participants from JPL, Lockheed higher. However, the characteristics of the Martin Corporation, Goddard Space Flight aerobot platform makes it possible to bridge this Center and several universities. The VEVA gap and return the data recovered by the probes proposal incorporated many of the featm:eS of the in their short life time. Higher power transmitters VAMuS mission concept. can be deployed on the aerobot than on the probe and the relative stability of the platform and the VEVA Science Theme: The goal of VEVA is to benign thermal environment permits the use of a characterize the surface and lower atmosphere of directional antenna for communication with Venus to determine if the planet has suffered a Earth. The large directional antennas of the Deep periodic global catastrophic resurfacing. The Space Network are used to pick up the signal. A specific objectives of VEVA involve acquiring data rate of I0 to 20 kb/sec appears feasible the first-ever-aerial photography of the surface of permitting return to Earth of all the data from the Venus and definitive in s/tu determination of the probes in • few tens of hours well within the composition of Venus in its lower scale height. - Take Other Data I -- ___'._._%1 , Eauinox --- i t [3irection of balloon dr, ' _ t_ t (and planet rotation) is t _ __.../_/, ] I clockwise • _i _ _"._Y / , / P-inalTransmd . \', ___%2(_")/_. ' to Earth Balloon Drift __ . ,.'_"_ _.i • -,, _ - __D .'_ Earth • ..... _" _ Incoming Sun _awae=_ Hyperbola Fig 2: The geometry of Venus at the time of the VEVA mission. Atmospheric winds carry the balloon Gondolas •round the planet in 7 days serving as • science platform and radio relay for the drop sondes design lifetime of a Venus superpressure balloon. The VEVA system consists of: • Two balloon platforms floating at 60 km VENUS EXPLORATION OF VOLCANOES altitude AND ATMOSPHERE (VEVA) MISSION • Two atmospheric chemistry sondes deployed NASA's Solar System Exploration Program immediately after entry at Venus includes a program of "core missions" • Eight small imaging sondes released to formulated by scientific advisory groups targeted sites during balloon traverses reporting to NASA and the competitive Discovery Program, in which missions are Mission Overview: The VEVA mission involves conceived and led by individual scientific the delivery of two identical payloads to Venus investigators. The Venus Exploration of with a launch in 2004 and arrival and entry at 3 American Institute of Aeronautics and Astronautics .i ;II ', I I Z flu t,' i_ , .,..° It Fig 3: (a)The sonde support ringsuspended from the VEVA gondola keeps the weight of sondes centered on the gondola aftereach sonde release(b) the gondola provide structuresupport for the sclenceInstruments and the communlcations antennae to enable collectionand return of sciencedata. Venus about six months later (Fig 2).