Wolfgang Seboldt

Solar sail technology development and demonstration

Abstract Solar sail technology holds the promise of significantly enhancing the interplanetary infrastructure for low-cost space exploration missions in the new millennium by exploiting the freely available space resource of solar radiation pressure for primary propulsion. Although the basic idea behind solar sailing appears simple, challenging engineering problems have to be solved. Based on promising results obtained during system studies by DLR (in cooperation with NASA/JPL) and ESA, a joint effort for the development and demonstration of the critical technologies on a co-funding basis was initiated in mid-1998. As a first major milestone in terms of demonstration a 20 m ×20 m breadboard model was developed, manufactured and tested in December 1999. It demonstrates the feasibility of a fully deployable lightweight solar sail structure in simulated 0g environment under ambient environmental conditions. The paper summarizes the main results of the ground tests and recommends next steps in solar sail technology development.

ODISSEE — A proposal for demonstration of a solar sail in earth orbit

Abstract A recent pre-phase-A study conducted cooperatively between DLR and NASA/JPL concluded that a lowcost solar sail technology demonstration mission in Earth orbit is feasible. Such a mission, nicknamed ODISSEE ( O rbital D emonstration of an I nnovative, S olar S ail driven E xpandable structure E xperiment), is the recommended approach for the development of this advanced concept using solar radiation pressure for primary propulsion and attitude control. The mission, proposed for launch in 2001, would demonstrate and validate the basic principles of sail fabrication, packaging, storage, deployment, and control. The demonstration mission scenario comprises a low-cost ‘piggy back’ launch of a sailcraft with a total mass of about 80kg on ARIANE 5 into a geostationary transfer orbit, where a 40m × 40m square sail would be deployed. The aluminized sail film is folded and packaged in small storage containers, upon release the sail would be supported by deployable light-weight carbon fiber booms. A coilable 10m central mast is attached to the center of the sail assembly with a 2DoF gimbal, and connected to the spacecraft. Attitude control is performed passively by gimbaling the central mast to offset the center-of-mass to the center-of-pressure generating an external torque due to solar radiation pressure, or actively using a cold-gas micro-thruster system. By proper orientation of the sail towards the Sun during each orbit, the orbital energy can be increased, such that the solar sail spacecraft raises its orbit. After roughly 550 days a lunar polar flyby would be performed, or the sail might be used for orbit capture about the Moon. On-board cameras are foreseen to observe the sail deployment, and an additional science payload could provide remote sensing data of the Earth and also of previously not very well explored lunar areas.

European Sail Tower SPS concept

Abstract Based on a DLR-study in 1998/99 on behalf of ESA/ESTEC called “System Concepts, Architectures and Technologies for Space Exploration and Utilization (SE&U)” a new design for an Earth-orbiting Solar Power Satellite (SPS) has been developed. The design is called “European Sail Tower SPS” and consists mainly of deployable sail-like structures derived from the ongoing DLR/ESA solar sail technology development activity. Such a SPS satellite features an extremely light-weight and large tower-like orbital system and could supply Europe with significant amounts of electrical power generated by photovoltaic cells and subsequently transmitted to Earth via microwaves. In order to build up the sail tower, 60 units - each consisting of a pair of square-shaped sails - are moved from LEO to GEO with electric propulsion and successively assembled in GEO robotically on a central strut. Each single sail has dimensions of 150m × 150 m and is automatically deployed, using four diagonal light-weight carbon fiber (CFRP) booms which are initially rolled up on a central hub. The electric thrusters for the transport to GEO could also be used for orbit and attitude control of the assembled tower which has a total length of about 15 km and would be mainly gravity gradient stabilized. Employing thin film solar cell technology, each sail is used as a solar array and produces an electric power in orbit of about 3.7 MWe. A microwave antenna with a diameter of 1 km transmits the power to a 10 km rectenna on the ground. The total mass of this 450 MW SPS is about 2100 tons. First estimates indicate that the costs for one kWh delivered in this way could compete with present day energy costs, if launch costs would decrease by two orders of magnitude. Furthermore, mass production and large numbers of installed SPS systems must be assumed in order to lower significantly the production costs and to reduce the influence of the expensive technology development. The paper presents the technical concept and an economic assessment as well as results of a recent solar sail deployment ground demonstration at DLRs facilities in Cologne.

HUMEX, a study on the survivability and adaptation of humans to long-duration exploratory missions, part I: lunar missions.

The European Space Agency has recently initiated a study of the human responses, limits and needs with regard to the stress environments of interplanetary and planetary missions. Emphasis has been laid on human health and performance care as well as advanced life support developments including bioregenerative life support systems and environmental monitoring. The overall study goals were as follows: (i) to define reference scenarios for a European participation in human exploration and to estimate their influence on the life sciences and life support requirements; (ii) for selected mission scenarios, to critically assess the limiting factors for human health, wellbeing, and performance and to recommend relevant countermeasures; (iii) for selected mission scenarios, to critically assess the potential of advanced life support developments and to propose a European strategy including terrestrial applications; (iv) to critically assess the feasibility of existing facilities and technologies on ground and in space as testbeds in preparation for human exploratory missions and to develop a test plan for ground and space campaigns; (v) to develop a roadmap for a future European strategy towards human exploratory missions, including preparatory activities and terrestrial applications and benefits. This paper covers the part of the HUMEX study dealing with lunar missions. A lunar base at the south pole where long-time sunlight and potential water ice deposits could be assumed was selected as the Moon reference scenario. The impact on human health, performance and well being has been investigated from the view point of the effects of microgravity (during space travel), reduced gravity (on the Moon) and abrupt gravity changes (during launch and landing), of the effects of cosmic radiation including solar particle events, of psychological issues as well as general health care. Countermeasures as well as necessary research using ground-based test beds and/or the International Space Station have been defined. Likewise advanced life support systems with a high degree of autonomy and regenerative capacity and synergy effects were considered where bioregenerative life support systems and biodiagnostic systems become essential. Finally, a European strategy leading to a potential European participation in future human exploratory missions has been recommended.

Gossamer Roadmap Technology Reference Study for a Multiple NEO Rendezvous Mission

A technology reference study for a multiple near-Earth object (NEO) rendezvous mission with solar sailcraft is currently carried out by the authors of this paper. The investigated mission builds on previous concepts, but adopts a strong micro-spacecraft philosophy based on the DLR/ESA Gossamer technology. The main scientific objective of the mission is to explore the diversity of NEOs. After direct interplanetary insertion, the solar sailcraft should—within less than 10 years—rendezvous three NEOs that are not only scientifically interesting, but also from the point of human spaceight and planetary defense. In this paper, the objectives of the study are outlined and a preliminary potential mission profile is presented.

Potential Solar Sail Degradation Effects on Trajectory and Attitude Control

Paper on the potential for solar sail degradation effects on trajectory and altitude controls.

Gossamer roadmap technology reference study for a solar polar mission

A technology reference study for a solar polar mission is presented. The study uses novel analytical methods to quantify the mission design space including the required sail performance to achieve a given solar polar observation angle within a given timeframe and thus to derive mass allocations for the remaining spacecraft sub-systems, that is excluding the solar sail sub-system. A parametric, bottom-up, system mass budget analysis is then used to establish the required sail technology to deliver a range of science payloads, and to establish where such payloads can be delivered to within a given timeframe. It is found that a solar polar mission requires a solar sail of side-length 100–125 m to deliver a ‘sufficient value’ minimum science payload, and that a 2.5 μm sail film substrate is typically required, however the design is much less sensitive to the boom specific mass.

Flexible Piloted Mars Missions Using Continuous Electric Propulsion

The potential of continuous propulsion systems for future space is outlined and compared to impulsive propulsion (chemical and nuclear-thermal). Although the results are related to piloted Mars missions, some of the stated issues hold true for a broad range of space missions with high-velocity increments, for example, sample return missions. It is demonstrated that for piloted Mars missions the use of impulsive propulsion can lead to very inflexible missions with a long total mission duration, whereas continuous electric propulsion does not only guarantee short total mission durations with moderate masses but also a high degree of flexibility. This can be achieved with a continuous electric propulsion system that has a thrust level of 100 N and a specific impulse of 3000 s, which is not too futuristic for piloted Mars missions in 2030 and beyond.

Gossamer Roadmap Technology Reference Study for a Sub-L1 Space Weather Mission

A technology reference study for a displaced Lagrange point space weather mission is presented. The mission builds on previous concepts, but adopts a strong micro-spacecraft philosophy to deliver a low mass platform and payload which can be accommodated on the DLR/ESA Gossamer-3 technology demonstration mission. A direct escape from Geostationary Transfer Orbit is assumed with the sail deployed after the escape burn. The use of a miniaturized, low mass platform and payload then allows the Gossamer-3 solar sail to potentially double the warning time of space weather events. The mission profile and mass budgets will be presented to achieve these ambitious goals.

Flight Opportunities from Mars to Earth for Piloted Missions Using Continuous Thrust Propulsion

For a piloted Mars mission, the inbound flight (Mars to Earth) is actually the most restricting space-part of the mission – especially if short flight times and short stay times at Mars are required. In this paper, different electric propulsion systems (different thrust levels, specific impulses, and thrust to weight ratios) and different flight strategies for a crewed return from Mars are analyzed and compared to high thrust propulsion systems (chemical and nuclear thermal). This is done with respect to feasibility, flight times, propellant consumption, and influence on the roundtrip problem for launch opportunities within 2016-2031. It is demonstrated that with moderate continuous thrust levels and specific impulses (100N, 3000 s) – even for short stays at Mars – Earth return trips are feasible with moderate propellant needs and within reasonable inbound flight times of 200 to 350 days.