Orbital Dynamics of an Oscillating Sail in the Earth-Moon System

The oscillating sail is a novel solar sail configuration where a triangular sail is released at a deflected angle with respect to the Sun-direction. As a result, the sail will conduct an undamped oscillating motion around the Sun-line due to the offset between the centre-of-pressure and centre-of-mass. In this paper, the resulting oscillatory motion of the acceleration vector is exploited to design new families of periodic orbits in the Earth-Moon circular restricted three-body system. In particular, the effect of adding an oscillating sail to the family of Lyapunov orbits at the L1- and L2-points as well as the family of distant retrograde orbits (DROs) is investigated. Because the solar sail Earth-Moon system is non-autonomous (due to the apparent orbital motion of the Sun), the sail’s oscillating period, the orbital period and the period of the Sun around the Earth-Moon system all need to be commensurable in order for the orbits to be repeatable over time. Using a differential correction technique, orbits that satisfy these constraints can be obtained and the results comprise new families of periodic orbits that are parameterised by the required sail performance. In addition to exploiting the oscillating sail for generating new orbit families, this paper also investigates its potential for orbital transfers. By combining a systematic search method with a local optimiser, oscillating sail parameters and orbital parameters can be obtained that enable transfers between classical Lyapunov orbits at the L1-point, connections between classical Lyapunov orbits at different Lagrange points as well as transfers between orbits within the family of classical DROs

Novel solar sail mission concepts for Space weather forecasting

This paper proposes two novel solar sail concepts for space weather forecasting: heliocentric Earth-following orbits and Sun-Earth line confined solar sail manifolds. The first exploits a solar sail acceleration to rotate the argument of perihelion such that aphelion, where extended observations can take place, is always located along the Sun-Earth line. The second concept exploits a solar sail acceleration to keep the unstable, sunward manifolds of a solar sail Halo orbit around a sub-L1 point close to the Sun-Earth line. By travelling upstream of space weather events, these manifolds then allow early warnings for such events. The orbital dynamics involved with both concepts will be investigated and the observation conditions in terms of the time spent within a predefined surveillance zone are evaluated. All analyses are carried out for current sail technology (i.e. Sunjammer sail performance) to make the proposed concepts feasible in the near-term. The heliocentric Earth-following orbits show a reasonable increase in useful observation time over inertially fixed, Keplerian orbits, while the manifold concept enables a significant increase in the warning time for space weather events compared to existing satellites at the classical L1 point

Cylindrically and spherically constrained families of non-Keplerian orbits

This paper introduces new families of Sun-centered non-Keplerian orbits (NKOs) that are constrained to a three-dimensional surface such as a cylinder or sphere. As such, they are an extension to the well-known families of two dimensional NKOs. For both the cylindrical and spherical types of orbits, the equations of motion are derived in an appropriate reference frame, constraints are introduced to confine the orbit to a cylindrical or spherical surface and further constraints allow the definition of the set of feasible orbits. Additionally, the phase spaces of the orbits are explored and a numerical analysis is developed to find periodic orbits within the set of feasible orbits. The richness of the problem is further enhanced by considering both an inverse square acceleration law (mimicking solar electric propulsion) and a solar sail acceleration law to keep the spacecraft on the cylindrical or spherical surface. These new families of NKOs generate a wealth of new orbits with a range of interesting applications ranging from solar physics to astronomy and planetary observation

Non-keplerian orbits using hybrid solar sail propulsion for earth applications

Strathclyde theses - ask staff. Thesis no. : T13430Half a century of space technology development has provided a wealth of new space applications. However, many still remain to be explored. Examples include increased geostationary coverage and new opportunities to enhance polar observation. This thesis investigates both of these opportunities using families of non-Keplerian orbits, while demonstrating the potential of hybridised solar sail and solar electric propulsion (SEP) to enable these orbits. Due to an increased number of geostationary spacecraft and limits imposed by east-west spacing requirements, GEO is starting to get congested. As a solution, this thesis creates new geostationary slots by displacing the geostationary orbit out of the equatorial plane by means of low-thrust propulsion. A full mission analysis and systems design is presented as well as an investigation of a range of transfers that can improve the performance of the displaced GEO and establish its accessibility. The analyses demonstrate that only hybrid propulsion can enable payloads to be maintained in a true geostationary orbit beyond the geostationary station-keeping box for lifetimes comparable to current GEO spacecraft. The second opportunity, enhancing polar observations, is investigated by designing optimal transfers from low Earth orbit (LEO) to an Earth pole-sitter orbit that allows the spacecraft to hover above the polar regions. Both high-thrust (upper-stage) and low-thrust (spiral) transfers are considered and show that hybrid propulsion increases the mass delivered to the pole-sitter orbit compared to a pure SEP case, enabling an extension of the mission. In addition, transfers between north and south pole-sitter orbits are investigated to overcome limitations in observations during the polar winters. Again, hybrid propulsion reduces the propellant consumption compared to pure SEP, while increasing the polar observation time. Overall, hybrid propulsion is proven an enabling propulsion method that can enable missions that are not feasible using only a solar sail and can extend the mission lifetime and/or payload capacity with respect to an SEP only mission.Half a century of space technology development has provided a wealth of new space applications. However, many still remain to be explored. Examples include increased geostationary coverage and new opportunities to enhance polar observation. This thesis investigates both of these opportunities using families of non-Keplerian orbits, while demonstrating the potential of hybridised solar sail and solar electric propulsion (SEP) to enable these orbits. Due to an increased number of geostationary spacecraft and limits imposed by east-west spacing requirements, GEO is starting to get congested. As a solution, this thesis creates new geostationary slots by displacing the geostationary orbit out of the equatorial plane by means of low-thrust propulsion. A full mission analysis and systems design is presented as well as an investigation of a range of transfers that can improve the performance of the displaced GEO and establish its accessibility. The analyses demonstrate that only hybrid propulsion can enable payloads to be maintained in a true geostationary orbit beyond the geostationary station-keeping box for lifetimes comparable to current GEO spacecraft. The second opportunity, enhancing polar observations, is investigated by designing optimal transfers from low Earth orbit (LEO) to an Earth pole-sitter orbit that allows the spacecraft to hover above the polar regions. Both high-thrust (upper-stage) and low-thrust (spiral) transfers are considered and show that hybrid propulsion increases the mass delivered to the pole-sitter orbit compared to a pure SEP case, enabling an extension of the mission. In addition, transfers between north and south pole-sitter orbits are investigated to overcome limitations in observations during the polar winters. Again, hybrid propulsion reduces the propellant consumption compared to pure SEP, while increasing the polar observation time. Overall, hybrid propulsion is proven an enabling propulsion method that can enable missions that are not feasible using only a solar sail and can extend the mission lifetime and/or payload capacity with respect to an SEP only mission

Agile solar sailing in three-body problem : Motion between artificial equilibrium points

This paper proposes a range of time-optimal, solar sail trajectories between artificial equilibria in the Sun-Earth three body system to create an agile solar sailing mission. This allows different mission objectives to be fulfilled at different AEPs during different stages of the mission. The analyses start from a solar sail at the sub-L1 point (sunward of the classical L1 point) which is targeted by NASA’s Sunjammer mission (launch in 2014) for advanced space weather warning. From this sub-L1 point, trajectories are investigated that: 1) take the solar sail to an AEP in the ecliptic plane, but slightly trailing the Earth to be ahead of the Earth in the Parker spiral to potentially increase space weather warning times even further; 2) take the solar sail to and between AEPs displaced above or below the ecliptic plane for high-latitude observations; 3) take the solar sail from the vicinity of the L1 point to the vicinity of the L¬2 point for additional Earth observations, geomagnetic tail investigations and astronomical observations. To find time-optimal trajectories, the optimal control problem associated with each of the transfers is defined and solved using a direct pseudospectral method. The resulting time of flights are reasonable, ranging from 85 days to 232 days, and the transfers are very smooth, requiring only a minimum solar sail steering effort in most cases. Since all results are generated for a sail performance equal to that of the Sunjammer sail, the proposed trajectories provide interesting end-of-mission opportunities for the Sunjammer sail after it retires at the sub-L1 point

Low-thrust trajectories design for the European Student Moon Orbiter mission

The following paper presents the mission analysis studies performed for the phase A of the solar electric propulsion option of the European Student Moon Orbiter (ESMO) mission. ESMO is scheduled to be launched in 2011, as an auxiliary payload on board of Ariane 5. Hence the launch date will be imposed by the primary payload. A method to efficiently assess wide launch windows for the Earth-Moon transfer is presented here. Sets of spirals starting from the GTO were propagated forward with a continuous tangential thrust until reaching an apogee of 280,000 km. Concurrently, sets of potential Moon spirals were propagated backwards from the lunar orbit injection. The method consists of ranking all the admissible lunar spiral-down orbits that arrive to the target orbit with a simple tangential thrust profile after a capture through the L1 Lagrange point. The 'best' lunar spiral is selected for each Earth spiral. Finally,comparing the value of the ranking function for each launch date, the favourable and unfavourable launch windows are identified

Novel pole-sitter mission concepts for continuous polar remote sensing

The pole-sitter concept is a solution to the poor temporal resolution of polar observations from highly inclined, low Earth orbits and the poor high latitude coverage from geostationary orbit. It considers a spacecraft that is continuously above either the North or South Pole and, as such, can provide real-time, continuous and hemispheric coverage of the polar regions. Despite the significant distance from the Earth, the utility of this platform for Earth observation and telecommunications is clear, and applications include polar weather forecasting and atmospheric science, glaciology and ice pack monitoring, ultraviolet imaging for aurora studies, continuous telecommunication links with polar regions, arctic ship routing and support for future high latitude oil and gas exploration. The paper presents a full mission design, including launch (Ariane 5 and Soyuz vehicles), for two propulsion options (a near-term solar electric propulsion (SEP) system and a more advanced combination of a solar sail with an SEP system). An optional transfer from the North Pole to South Pole and vice-versa allows viewing of both poles in summer. The paper furthermore focuses on payloads that could be used in such a mission concept. In particular, by using instruments designed for past deep space missions (DSCOVR), it is estimated that resolutions up to about 20 km/pixel in the visible wavelengths can be obtained. The mass of these instruments is well within the capabilities of the pole-sitter design, allowing an SEP-only mission lifetime of about 4 years, while the SEP/sail propulsion technology enables missions of up to 7 years

Hybrid low-thrust transfers to eight-shaped orbits for polar observation

In this paper, transfers from low Earth orbit (LEO) to so-called eight-shaped orbits at the collinear libration points in the circular restricted three-body problem are investigated. The potential of these orbits (both natural and sail displaced) for high-latitude observation and telecommunication has recently been established. The transfer is modelled by distinguishing between a near-Earth phase and an interplanetary phase. The near-Earth phase is first assumed to be executed with the Soyuz Fregat upper-stage, which brings the spacecraft from LEO to a highly elliptic orbit. From there, the interplanetary phase is initiated which uses low-thrust propulsion to inject the spacecraft into one of the eight-shaped orbit’s manifolds. Both solar electric propulsion (SEP), solar sailing and hybridised SEP and solar sailing are considered for this phase. The objective is to maximise the mass delivered to the eight-shaped orbit starting from a realistic Soyuz launch vehicle performance into LEO. Optimal trajectories are obtained by solving the optimal control problem in the interplanetary phase with a direct pseudospectral method. The results show that (over the full range of propulsion techniques) 1564 to 1603 kg can be injected into a natural eight-shaped orbit. Within this relatively small range, hybrid propulsion performs best in terms of mass delivered to the eight-shaped orbit, while SEP enables the fastest transfer times. With the interplanetary phase optimised, the upper-stage near-Earth phase is replaced by a multi-revolution low-thrust spiral. Locally optimal control laws for the SEP thruster and solar sail are derived to minimise the time of flight in the spiral. Both pure SEP and hybrid spiral show a significant reduction in the mass required in LEO to deliver the spacecraft to the eight-shaped orbits. While hybrid propulsion did not stand out for the use of an upper-stage near-Earth phase, it does for the use of a low-thrust spiral as it significantly reduces the spiral time with respect to the pure SEP case

Design and trade-offs of a pole-sitter mission

This paper provides a mission analysis and systems design of a pole-sitter mission, i.e. a spacecraft that is continuously above an Earth Pole, and can provide real-time, continuous and hemispherical coverage of the polar regions. Two different propulsion strategies are proposed: solar electric propulsion (SEP) and SEP hybridized with a solar sail. For both, minimum-propellant pole-sitter orbits and transfers are designed, assuming Soyuz and Ariane 5 launch options. A mass budget analysis allows for a tradeoff between mission lifetime and payload mass capacity (up to 7 years for 100 kg), and candidate payloads for a range of applications are investigated