Very High Delta-V Missions To The Edge Of The Solar System And Beyond Enabled By The Dual-Stage 4-Grid Ion Thruster Concept
- Paper number
IAC-06-D2.8.-C3.5.-D3.5.-C4.7.03
- Author
Dr. Cristina Bramanti, European Space Agency (ESA), The Netherlands
- Coauthor
Dr. Roger Walker, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Dr. David G. Fearn, EP Solutions, United Kingdom
- Coauthor
Dr. Dario Izzo, European Space Agency (ESA)/ESTEC, The Netherlands
- Year
2006
- Abstract
As optical and IR imaging telescopes have become ever more sensitive and image processing ever more powerful, the existence of the Edgeworth-Kuiper Belt (EKB) has been truly confirmed with the discovery of over 500 Kuiper Belt Objects (KBOs) between 30 and 50 AU distance in the last decade alone. The discovery in 2004 of a new object called Sedna at 90 AU distance and with an orbit well beyond the EKB has, for the first time, given a possible glimpse at the inner part of the hypothesised Oort cloud, a predicted shell of billions of icy proto-comets extending halfway to the nearest star. As such, these extremely interesting minor planets represent prime targets for in-situ characterisation by interplanetary spacecraft. At the end of 2004 after 28 years, the Voyager 1 spacecraft reached a distance of 94 AU from the Sun and sent back data indicating that it had reached a crossing of the “termination shock” of the solar wind at the edge of the Sun’s magnetosphere. Beyond the shock is the heliopause, the pressure balance interface between the plasma of the solar wind and that of the Very Local Interstellar Medium (VLISM). Despite this data, models of the heliopause distance are still open to large uncertainty and precise properties of the interstellar medium remain very unclear. The only way to determine these properties and truly understand the nature of interstellar space is again by in-situ measurements, particularly of the magnetic field and low-energy cosmic rays, beyond the heliopause, which implies reaching a distance of 200 AU within a 30-year mission duration. However, the delta-V requirements for both outer planet and KBO orbiter and local interstellar probe spacecraft are very high for reasonable mission durations. The conventional mission design approach assumes the reliance upon the biggest heavy launch vehicle available, stacked with multiple boost stages to provide maximum Earth escape velocity, and coupled with a Jupiter swingby in order to lower the spacecraft delta-V budget to within levels achievable by present or near-term propulsion system capabilities. The result is a 1000 kg 1 kW-class RTG powered spacecraft with a minimum of two ion engines. A new concept for an innovative Dual-Stage 4-Grid (DS4G) ion thruster has been studied and experimentally proven in the laboratory. The concept offers substantial improvements in specific impulse over the current state-of-the-art, at the expense of a higher power-to-thrust ratio and hence thrust. Operating at a beam potential of 30kV with Xenon propellant, the predicted performance of this advanced thruster is a specific impulse of 19,300 s, with specific power of 100 W/mN. The very high specific impulse makes the thruster optimal for use on very high delta-V missions such as those discussed above. In the paper, we present the basic concept, design and measured performance of the advanced dual-stage gridded ion thruster and assess its potential benefits and exploitation of this technology for Kuiper Belt Object rendezvous, inner Oort cloud object rendezvous and Interstellar Explorer missions. Such benefits could include a reduction in the spacecraft wet mass and/or launcher excess velocity leading to use of lower cost launchers compared to present systems, or improvement in mass margins and less stringent mass reduction of payload/subsystems, but only if the total mission duration is not excessive. The top-level mission requirements and constraints, mission analysis trade-offs, propulsion system optimisation and preliminary mission and system designs will be described in detail for kW-class RTG-powered spacecraft. The mission analysis trade-offs are based on low-thrust trajectory optimisation with or without multiple gravity assists. Finally, we discuss the engineering challenges to be solved and critical technology developments needed to realise these missions in the future.
- Abstract document
- Manuscript document
IAC-06-D2.8.-C3.5.-D3.5.-C4.7.03.pdf (🔒 authorized access only).
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