A 97 - 31331 Mars 2001 Aerobot / Balloon System Overview

In late 1995, a study was initiated at the Jet Propulsion Laboratory (JPL) of a 2001 Mars Aerobot/Balloon System (MABS) Mission Participants included NASA Goddard Space Flight Center, Wallops Flight Facility (WFF), Lockheed Martin Aeronautics (LMA), the French Space Agency (CNES) Toulouse Space Center, NASA Ames Research Center (ARC), and Space Dynamics Laboratory (SDL) plus numerous industrial partners. The purposes of the study were to 1) determine technical feasibility of a long duration 2001 aerobot mission in the Martian atmosphere, 2) formulate a baseline concept, 3) identify pre-project technology requirements, and 4) develop a preliminary cost, schedule and plan. The study scope included definition and identification of mission concept technical issues including science instruments, gondola, balloon system design, entry vehicle and cruise spacecraft design, and launch vehicle performance considerations. Key constraints on the mission study were a 2001 Mars launch opportunity (although 2003 and 2005 were also examined), a Delta launch vehicle, maximum use of Mars Surveyor Program (MSP) cruise and entry systems, the use of Mars Global Surveyor and MSP orbiter for relay communications capabilities and a 90 day mission duration. Key assumptions of the study included 1) a gondola mass on the order of 10 kg including science instruments, (plus deployable science packages), 2) "constant" density altitude, superpressure balloon design without landing capability, and 3) cruise altitude of 5-8 km above reference level. The study effort concluded that the MABS mission is feasible based on conservative assumptions on environmental conditions and technical readiness, provided early and significant NASA investment in balloon system technology is initiated. Background In the mid-1980s, the French and the Soviets began studying a Martian Aerostat mission for the 1994 Mars opportunity. The French were to supply the balloon system and the Soviets were to provide the gondola and deliver the system to Mars. The system design concept eventually evolved into a 6-micron thick mylar balloon which would be overpressure during the day, descending to the surface during the night (Ref. 1). At night, the balloon would rest on the surface on a guiderope or "anding snake" suspended from the gondola. The mass of the landing snake on the surface relieved negative buoyancy so that the gondola did not touch the ground. The mission was to last about 10 days before gas leakage reduced lift and kept the balloon from ascending during the day. As early as 1992 the joint program was experiencing the detrimental effects of the collapse of the Soviet Union. The immediate impact was a slip of the launch to at least 1996. This programmatic uncertainty also resulted in funding and related technical difficulties within the French program. By early 1995 it was clear the mission would need to be delayed again, this time to 1998. The French continued a scaled-back development program which had significant successes but also had some nagging balloon deployment failures. The shift of the mission arrival date to 1998 meant that the mission would be arriving in the Northern hemisphere in winter when high surface winds (>30 rn/s) were to be expected. The implications of the high winds meant that a balloon which descended to the surface on a landing snake could be destroyed if the drag on the snake became too high. Eventually, due to a combination of programmatic and related technical problems, the program was canceled. In 1994 another Mars balloon concept called the Mars Aerial Platform (MAP) mission was proposed under the NASA Discovery Program (Ref. 2). The Copyright©1997 by the American Institute of Aeronautics and Astronautics, Inc. The U. S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government purposes. All other rights are reserved by the copyright owner. D ow nl oa de d by K er ry N oc k on J un e 5, 2 01 5 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .1 99 714 47 Copyright© 1997, American Institute of Aeronautics and Astronautics, Inc. MAP design consisted of a 12-micron, biaxial nylon 6, supperpressure balloon envelope and a small, 7 kg gondola. The balloon was designed to float at a "constant" density altitude in nominal Martian environmental conditions. A two-balloon mission was proposed which included small surface meteorology packages on the entry vehicle. The MAP mission included a number of innovative features but was criticized for the lack of technology readiness primarily in the balloon envelope design. Both the Martian Aerostat and the MAP mission concepts have had a significant influence on the MABS design, the primary points of departure being balloon envelope material and design and the assumption of conservative environmental factors. A significant advance in material design concepts was achieved during the MABS effort. These advances were due primarily to 1) the realization of the difficulty in finding both fracture resistance and toughness in a single-component envelope, 2) the focus of the NASA long-duration stratospheric superpressure balloon program on similar balloon envelope material concepts, and 3) composite material design prototyping and testing carried out in the study. The resulting material concept has twice the strength-to-weight ratio of previous Mars balloon envelope material candidates. Contributions of Aerobot/Balloons to Mars Exploration The science experiment potential of a Mars Aerobot/Balloon includes 1) imaging the surface at a scale and resolution relevant to future lander and rover operations, 2) high resolution visible images and IR spectroscopy, 3) collection of data at hundreds of scientifically interesting sites, 4) detection and mapping of subsurface ice and water, 5) in situ measurements of atmospheric properties and winds, and 6) deployment of surface packages at interesting sites for exploration. The need for ultra-high resolution remote sensing which cannot be easily obtained from orbit is driven primarily by the desire for increasing the probability of successful Mars landings, rover operation and sample return. After the Viking landings, engineers considered themselves lucky that both landers survived without damage due to large boulders found near the landing sites. The MSP landers are smaller and thus susceptible to damage or adverse effects of smaller, more numerous rocks. At this time, the landing hazard of these landers has yet to be quantified, however, it is clear that imaging data of the order of 20 cm resolution would be important to the assessment of landing success probability and site selection. In addition, this class of imaging would be important to rover operations planning and rover site selection. At least part of this issue has been resolved by the inclusion of descent imaging capability for future rover missions. Unfortunately, such imaging only provides after the fact information which can be used for post-landing (if successful) traverse operation planning and only then within a kilometer of the landing site. Aerobot data, on the other hand, could provide both medium resolution (2 m/pixel) wide area and ultrahigh resolution sampled coverage which can be used to optimize and select future sites for rover operation. Currently there are about 80 major geologic units identified from Viking data. It is not practical to expect to be able to collect samples from all of these sites and return them to Earth in the near future. An aerobot, with high resolution imaging and spectral instruments, could assist in the process of selecting optimum landing sites to maximize the variety of terrains sampled. In addition, such data enables calibration of global maps and data sets taken from orbital platforms.