The Genesis mission: unifying science and engineering

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Pergamon

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ActaAstronauttca Vol. 48, No. 5-12, pp. 707-710, 2001 © 2001 International Astronautical Federation. Published by Elsevier Science Ltd Printed m Great Britain S0094-5765(01)00078-9 0094-5765/01 $ - see front

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THE GENESIS MISSION: U N I F Y I N G

S C I E N C E AND E N G I N E E R I N G

Benton C. Clark Lockheed Martin Astronautics Operations Denver 80201, USA

Abstract Design of the Genesis spacecraft mission was derived from top-down flow of a basic and highly challenging science requirement: obtain samples of solar matter of such high quality and low background that the.,,' would sustain investigations of chemical and isotopic composition of the solar system for the coming decades, and well into the 21 ~' Century. Within the framework of several dozen competing mission concepts tbr planetary exploration under NASA's Discovery program, Genesis needed to perform extremely high quality science (solar collection and sample return) for an affordable yet realistic level of effort. Key issues included preservation of collector cleanliness, avoidance of spacecraft-generated con-tamination, control of collector temperatures, simplicity of long-term operation, ability to efficiently reach the L1 operations point, reliability of avionics and other support systems, return to a specific landing locale on Earth, and provision for soft capture of the descent capsule via mid-air parachute snatch. Genesis is now in the final stages of spacecraft testing and system validation, the culmination of a highly inter'oven effort to meet sc,ence objectives with innovative solutions that also satisfy engineering challenges for reliability, affordability, rapid development and a comprehensix.e test program. Genesis is scheduled for launch in February 2001. © 2001 International Astronautical Federation. Published by Elsevier Science Ltd.

the original solar nebula from which our central star, the planets, their satellites, the asteroids and the comets of our solar system were all formed. To avoid contamination fi-om ions associated with the Earth's magnetosphere, and to avoid any biasing effects, this collection must be made far from Earth. A position at the sun-Earth Lagrange point (k I ) has been selected as the location from which this collection can safely be made, yet remain sensibly close to Earth for the expeditious return of collected material.

The GenesisSpacecraft The Genesis spacecraft, shown in Fig. 1 (with Solar Arrays Deployed), is based upon subsystems that have flight heritage from the Stardust Discovery mission and the Mars Surveyor Program spacecraft. Numerous trades and design architecture studies had to be made to incorporate safeguards against contamination, to find affordable soluuons to canister encapsulation and

Introduction The Genesis mission's science objective is to expose high-purity materials and an electrostatic concentrator apparatus to the free space solar wind flux, in order to obtain high-quality samples of the entire spectrum of ions coming from the sun. These ions are representative of the composition of the entire sun, and. by inference are therefore the best available sample of the overall nature of

Fig. I IGenesis with.Solar Arrays Deployed) integrity during ascent and entry, to offer a simplified spacecraft system, to achieve magnetic cleanliness, to host autonomous collector change707

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out m response to differing solar wind regimes, to develop a hey, and relatively large sample return capsule q'SRCI, to minimize operations costs, and to enable rapid progress and launch consLstent with the Discovery program baseline rules. The Genesis spacecraft, Is the result of a major team effc,rt to demgm an entirel3 new concept m scientific spacecraft.

The Genesis Team The concept lot the Genesis missJon was tile inspiration of the Principle Investigator ~P.I.I P.I.. Dr. Don Bumett
hate desires for their roles and ~ n d m g levels. Reasonable compromise is one recipe for achieving a tmssion solution which fits into the Dtscover2,.' constraints on total mission cost, development times, and launch vehicle family. These compromises are founded on trade studies and analyses, which help point the way to decisions that must be made. Our experience has been that hating an extremely open and participatory decision-making process, in the context of a highly competitive Discovery enxironment, has been `'ital for rapidly and efficientl,, coming to closure on mutually agreeable solutions.

Requirements Generation Requirements flo`'~-do~,~s are rigidly used, as with traditional programs. However, unhke many pre,.ious projects, this does not occur until the mission concept is fully developed and nearly all trade-off options have been dispensed with. The initial process of conceptualization for Discovery was highly iterative. Through it, the engineering partners became intimately famihar with the needs vs. the desires of the P.I. and his science colleagues, and ~.ice-versa. As the team became more fully molded, each interested partner became tested in the entire systems engineering process. Barriers of m~strust, which can otherwise dexelop, were not present. The hard-pomts of each party became recognized and comprised the initial ensemble of accepted requirements. For example, the Genems collection canister could hate been sigmificantly decreased in xolume and mass if the P.I. had been willing to back down on his mmmlum acceptable area and dixerslty for collector arra.~s, Fig. 2. Furthermore, potential differences in solar x,,md composition as a function of the types of actr,'ity occurring on the sun led to a need to be able to collect on different collectors for three different conditions of solar wind emission from the sun, v,h~ch invoked complexity in tnechanism~ Nonetheless. these P I. reqmrements were e~entually embraced and ,nplemented. A counter-example is how contamination control was mlplemented. It was at first thought to be obx ious that a suite of cold-gas thrusters and an operations constraint that delayed camster opening would be essentml to rnaintain cleanliness of the

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more than is required for the specific mission at hand. Everyone is obligated to make clear their positions to everyone. On the other hand, a P.I. can mandate that a particular science implementation be followed, based on an appreciation, often difficult to quantitate, of the science value for the dollar expended or the risk taken on. Likewise, an engineer may discern an approach, whtch can improve science, reliability, or operability of the mission. The DiscoveD' collaborat.x e environment fosters such considerations and implementations which otherwise may not be brought forward in other management approaches.

Intermediate Issues Fig. 2 Genesis Collector Array (I of 4) ultraclean collectors. Although cold-gas is eminently doable, it complicated the propulmon subsystems, added failure modes, and added mass because of the two-years of operation that would be required. While Genesis was still in the proposal phase, a very detailed systems-level trade analysis was conducted by combining a state-ofthe-art contamination analysis model with plume profile data and spacecraft configuratton reformation to assess other options, at was found that through the combination of ( 1) using ultrapure hydrazine monopropellant for all thrusters, (2) locating the thrusters below the plane of the collection surfaces, and (3) canting nozzles to minimize sunward plume components, the contamination of collectors would be well belov, the minimum threshold of concern. Th~s joint eftbrt between all tour parties (Science Team, JSC, LMAO and JPLI resulted in a spacecraft simplification, which not only increased reliabilib of the system but also reduced ox erall costs.

Implementation Approaches Because the P.I. of a Discoxer~. mission is assigned ultimate responsibility for the design and success of the mission, it is incumbent on the scientists and engineers to work out all differences together. No longer can a scientist insist on something, which is a strong cost driver but has questionable equivalence in science return. No longer can a subsystem engineering lead mstst on a special characteristic for some component that is

Some trade-offs of spacecraft demgn or implementation have no compelling bias for either science or engineering considerations. For example, a spinning spacecraft has been considered to be in many ways simpler, safer system than a spacecraft dependent on full 3-ax~s stabilization. Engineering realities mandate that a spinner approach be one of the options for implementation. This was one reason Genests was baselined tbr this approach. Another, hosteler, was that the solar wind monitors could scan the environment via the spacecraft motion and thereby be simpler in design. Also, the amount of propellants expended to maintain pointing could be less, hence mintmizing the contamination concern. On the other hand, cormnumcat~ons geometries and viewing directions often preclude such approaches. For example, planetar) orbiters typicall3 must haxe articulated appendages or plattbrms, or else reorient themselves frequentl). Neither is panicularl~ cotnpatible x~th a basle spinner mode. Consider three examples o f " G ' " spinners: the Giotto, Galileo and Genems spacecraft. The Giotto mission to Comet Halley could be accomphshed wroth a spinner because the Earthcomet geontetr 3 lbr htgh-gain telecommumcauons was prec]sel 3 known at the time of the tl)b.~ encounter and the instruments onboard could be compatible w~th or even s~ergist~c x~th the rotational motions. The Galileo nuss~on to .Ittp~ter and its moons ~s a dual approach, wtth both spin and despun porltons of the spacecraft. Genests can be a pure spinner and still maintain

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communications with Earth and full solar illumination of its fixed solar panels because of the linear arrangement of the three point locations: sun-L I-Earth. On the other hand, the fact that Genesis must be spin-stable in different configurations - at launch (spinning upper stage) and in its deployed conditions (sample return capsule open; sample canister openl has provided further design challenges. Conclusion

Combining the ambitious deswes of the science community for advancements in spacecraft capability with the Discover.v class limitations on

affordability and implementation guidelines can be accomplished through comprehensive cooperation between all elements involved. By placing ultimate cost and decision responsibility on the source of the mission objectives, the P.I. and his/her science team, yet requiring sound engineering and management, this class of missions can result in very high science value in a quick, aflbrdable implementation. Acknowled2ements

The Genesis Project spacecraft development is funded by NASA and JPL through contract JPL 961202.