Gareth W. Hughes

Solar polar orbiter: a solar sail technology reference study

An assessment is presented of a Solar Polar Orbiter mission as a Technology Reference Study. The goal is to focus the development of strategically important technologies of potential relevance to future science missions. The technology is solar sailing, and so the use of solar sail propulsion is, thus, defined a priori. The primary mission architecture utilizes maximum Soyuz Fregat 2-1b launch energy, deploying the sail shortly after Fregat separation. The 153 × 153 m square sail then spirals into a circular 0.48-astronomical-unit orbit, where the orbit inclination is raised to 90 deg with respect to the solar equator in just over 5 years. Both the solar sail and spacecraft technology requirements have been addressed. The sail requires advanced boom and new thin-film technology. The spacecraft requirements were found to be minimal because the spacecraft environment is relatively benign in comparison with other currently envisaged missions, such as the Solar Orbiter mission and BepiColombo.

GeoSail: An Elegant Solar Sail Demonstration Mission

In this paper a solar sail magnetotail mission concept was examined. The 43-m square solar sail is used to providethe required propulsion for continuous sun-synchronous apse-line precession. The main driver in this mission was found to be the reduction of launch mass and mission cost while enabling a nominal duration of 2 years within the framework of a demonstration mission. It was found that the mission concept provided an excellent solar sail technology demonstration option. The baseline science objectives and engineering goals were addressed, and mission analysis for solar sail, electric, and chemical propulsion performed. Detailed subsystems were defined for each propulsion system and it was found that the optimum propulsion system is solar sailing. A detailed tradeoff as to the effect of spacecraft and sail technology levels, and requirements, on sail size is presented for the first time. The effect of, for example, data acquisition rate and RF output power on sail size is presented, in which it is found that neither have a significant effect. The key sail technology requirements have been identified through a parametric analysis.

Solar Sail Hybrid Trajectory Optimization for Non-Keplerian Orbit Transfers

SOLAR sails have long been seen as an attractive concept for low-thrust propulsion.They transcend reliance on reaction mass and have the ability to provide a small, but continuous, acceleration. Because propellant mass is not an issue, high-performance sails can enable new exotic non-Keplerianor bits (NKOs)1 that are not feasible for conventional chemical or electric propulsion.A constant out-of plane sail force is utilized to raise the spacecrafts orbit high above the ecliptic plane in two- or three-body systems. Potential beneŽfits to the science community are large. Circular, displaced orbits can be used to provide continuous observation of the solar poles or to provide a unique vantage point for infrared astronomy. (There is much less resolution-limiting dust out of the ecliptic plane enabling smaller telescope mirror dimensions for equivalent performance.) Very high performance sails can even levitate, in equilibrium, at any point in space.

Technology Requirements of Exploration Beyond Neptune by Solar Sail Propulsion

This paper provides a set of requirements for the technology development of a solar sail propelled Interstellar Heliopause Probe mission. The mission is placed in the context of other outer solar systems missions, ranging from a Kuiper Belt mission through to an Oort cloud mission. Mission requirements are defined and a detailed parametric trajectory analysis and launch date scan performed. Through analysis of the complete mission trade space a set of critical technology development requirements are identified which include an advanced lightweight composite High-Gain Antenna, a high-efficiency Ka-band travelling-wave tube amplifier and a radioisotope thermoelectric generator with power density of approximately 12 W/kg. It is also shown that the Interstellar Heliopause Probe mission necessitates the use of a spinning sail, limiting the direct application of current hardware development activities. A Kuiper Belt mission is then considered as a pre-curser to the Interstellar Heliopause Probe, while it is also shown through study of an Oort cloud mission that the Interstellar Heliopause Probe mission is the likely end-goal of any future solar sail technology development program. As such, the technology requirements identified to enable the Interstellar Heliopause Probe must be enabled through all prior missions, with each mission acting as an enabling facilitator towards the next.

Small Body Encounters Using Solar Sail Propulsion

Cometary Rendezvous and Flybys have large V requirements, which impose almost unattainable, and sometimes prohibitive, demands on the propellant budget of conventional, chemical propulsion. Ion Propulsion is a viable alternative, but as the number and difficulty of target objectives increases then the potential of this technology becomes rapidly less attractive. Solar sails exhibit an extremely high effective specific impulse over long mission durations. No propellant is required so that large changes in V could be realised without necessitating the introduction of complex gravity assists, which prolong mission duration and restrict launch opportunities. The endurance of the structures and materials are thus the only limiting factors dictating the number and range of bodies with which the solar-sail propelled vehicle can encounter throughout its lifetime. In this paper we have analysed a number of high-energy, small-body mission scenarios using a parameterised approach to sail control representation. The sail cone and clock angle histories were characterised by linear interpolation across a set of discrete nodes. The optimal control problem was thus transcribed to a Non-Linear Programming problem to select the optimal controls at the nodes that minimised the transfer time while enforcing the cartesian end-point boundary constraints (6 states for rendezvous, 3 for flypast). The Fortran77 optimisation package NPSOL 5.0 was used for this purpose with the variational equations of motion formulated in modified equinoctial orbital elements and integrated using a variable-order, adaptive step-size Adams-Moulton-Bashforth method. We present optimal rendezvous trajectories to Short-Period Comets such as 46P/Wirtanen in 484 days with a sail characteristic acceleration of 1.9 mms-2, and with 2P/Encke in 574 days with a characteristic acceleration of 1.0 mms-2. An analysis using high-performance sails has been conducted to permit fast flyby intercepts of newly discovered Long Period Comets (LPCs). Previous examples adopted were C/1995 O1/Hale- Bopp, C/1995 Y1/Hyakutake, C/1999 T1/McNaught-Hartley, C/1999 F1/Catalina, C/1999 N2/Lynn and C/1999 H1/Lee, to demonstrate the feasibility of a late launch to quickly intercept a new LPC using a solar sail. Since the time between discovery of a new LPC such as Hale-Bopp and perihelion passage was less then 2 years, this then leaves a very short time-span for orbit determination, preparation, planning and operational phases. Preliminary mission analysis shows that a Hale-Bopp perihelion flypast could have been achieved, with a sail characteristic acceleration of 5.0 mms-2, by launching just 209 days before comet perihelion passage. With a characteristic acceleration of 2.0 mms-2 Hale-Bopp could also have been intercepted at its descending node by launching 270 days before nodal descent. The sail could then have returned to rendezvous with the Earth 261 days later, giving a minimum total mission turn-around time of 531 days. An alternative, dual flyby scenario has been investigated, to continue on to C/1997 D1/Mueller, after which solar system escape was reached and arrival at Heliopause would occur in 12 years. Solar Electric Propulsion has been adopted as the primary propulsion system for the DAWN dual asteroid rendezvous mission scheduled for launch in 2006. The objective of this mission is to rendezvous with inner main-belt asteroids, Vesta and Ceres. We have also investigated solar sail adaptation to this mission, for the same launch date and 11 month orbiter stay-times. We have extended the mission objectives to two further asteroids, Lucina and Lutetia, with the aim of demonstrating a Mainbelt Asteroid Survey scenario.

Low cost Mercury orbiter and Mercury sample return missions using solar sail propulsion

The use of solar sail propulsion is investigated for both Mercury orbiter (MO) and Mercury sample return missions (MeSR). It will be demonstrated that solar sail propulsion can significantly reduce launch mass and enhance payload mass fractions for MO missions, while MeSR missions are enabled, again with a relatively low launch mass. Previous investigations of MeSR type missions using solar electric propulsion have identified a requirement for an Ariane V launcher to deliver a lander and sample return vehicle. The analysis presented in this paper demonstrates that, in principle, a MeSR mission can be enabled using a single Soyuz-Fregat launch vehicle, leading to significant reductions in launch mass and mission costs. Similarly, it will be demonstrated that the full payload of the ESA Bepi Colombo orbiter mission can be delivered to Mercury using a Soyuz-Fregat launch vehicle, rather than Ariane V, again leading to a reduction in mission costs.

Sample return from mercury and other terrestrial planets using solar sail propulsion

A conventional Mercury sample return mission requires significant launch mass due to the large AV required for the outbound and return trips and the large mass of a planetary lander and ascent vehicle. It is shown that solar sail spacecraft can be used to reduce lander mass allocation by delivering the lander to a low, thermally safe orbit close to the planetary terminator. In addition, the ascending node of the solar sail spacecraft parking orbit plane can be artificially forced to avoid out-of-plane maneuvers during ascent from the planetary surface. Propellant mass is not an issue for spacecraft with solar sails, and so a sample can be returned relatively easily without resorting to lengthy, multiple gravity assists. A 275-m2 solar sail with a sail assembly loading of 5.9 g/m2 is used to deliver a lander, cruise stage, and science payload to a forced sun-synchronous orbit at Mercury in 2.85 years. The lander acquires samples and conducts limited surface exploration. An ascent vehicle delivers a small cold-gas rendezvous vehicle containing the samples for transfer to the solar sail spacecraft. The solar sail spacecraft then spirals back to Earth in 1 year. The total mission launch mass is 2353 kg, launched using a Japanese H2 class launch vehicle, C3 = 0. Extensive launch date scans have revealed an optimal launch date in April 2014 with sample return to Earth 4.4 years later. Solar sailing reduces launch mass by 60% and trip time by 40%, relative to conventional mission concepts. In comparison, mission analysis has demonstrated that solar-sail-powered Mars and Venus sample returns appear to have only modest benefits in terms of reduced launch mass, at the expense of longer mission durations, than do conventional propulsion systems.

Payload Mass Fraction Optimization for Solar Sail Cargo Missions

SOLAR sailing offers the potential to reduce the required initial mass in low Earth orbit for future piloted Mars missions.1i3 Athough solar sailing does not appear to be suitable for crew transport, it can be an extremely efŽ cient mode of propulsion for the transport of logistics in support of a human crew. This may include premission caching of logistics and/or resupply missions to support long-duration surface stays. Because solar sails do not require reaction mmass, a single solar sail may, in principle, be used for multiple Earth-Mars-Earth round trips. The limit to the number of round trips that can be made by a single solar sail will be dictated largely by the lifetime of the sail Ž lm in the space environment. Previous studies of the solar sail cargo mission problem have considered either point designs1 or have considered speciŽ c launch opportunities.2 However, a key question that arises when considering the use of solar sails for round-trip logistic supply missions is the optimum payload mass fraction of the solar sail. As the payload mass fraction of the solar sail is increased, a greater payload mass is delivered, but the trip time will also increase. Similarly, as the payload mass fraction of the solar sail is decreased, a smaller payload is delivered, but with a shorter trip time. The payload mass fractionthat is selectedshould, therefore,be chosento balancethese two effects and maximize the mean rate of payload mass transfer to Mars.