Polymeric materials for Solar Sail: The combined effects of polymer thickness, radiation, and temperature
- PDF / 77,279 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 202 Views
NN1.6.1
Polymeric materials for Solar Sail: The combined effects of polymer thickness, radiation, and temperature David L. Edwards1) and Mircea Chipara2) 1
NASA MSFC Marshall Space Flight Center, Huntsville, Alabama Indiana University, Bloomington, IN
2)
ABSTRACT The feasibility and the performance of solar sail depend critically on the availability of light materials and extremely thin polymeric films. The main requirements imposed on solar sail materials are analyzed in depth. The potential effects of the space environment are discussed in detail, with emphasis on the radiation-temperature-polymeric film thickness relationships. It is shown that the radiation component of the space environment triggers two competing degradation processes (erosion and depolymerization) and that both processes act towards the decrease in the glass transition temperature. INTRODUCTION The solar sail endeavor is an innovative low-thrust project that exploits the momentum transferred by solar photons to a large, highly reflective, low mass structure. This passive propulsion attempt depends critically on the availability of lightweight materials with outstanding mechanical, thermal, electrical, and optical capabilities. For such a drastic reduction of spacecraft weight, it is mandatory to use composites and nanocomposites based on polymeric matrices. Far and very far term missions are expected to last for several years, imposing the use of materials with very long lifetime and eventually with self-healing capabilities. These requirements are augmented by the harsh conditions of the space environment such as ionizing particles, extreme temperatures, IR, and UV radiations capable to trigger or to enhance degradation processes occurring in polymers and composites. The project was tested in 1993 (Znamya) when a small solar sail with an area of 10 m2 and an average areal density (AAD) of about 20g/m2 was tested by Russia. The AAD is defined as the ratio between the total weight of the solar sail and the area of the reflective polymeric membrane. A flight demo is scheduled in 2005-2006 [1]. It is expected that solar sails will dominate far and very far-term missions (interstellar missions). To achieve this goal AAD less or equal to 1 g/cm2 are required. The actual technology (commercial) is capable of building a solar sail with an AAD of about 10-20 g/m2. PHYSICAL PROPERTIES OF SOLAR SAIL MATERIALS a). Large area membranes The large area membrane is the most important component of the solar sail. Its physical properties are extremely important for the success of the mission. The most important requirements for the solar sail membrane are:
NN1.6.2
1. Excellent reflectivity and reduced absorption. The material should present a reflectivity higher than 90% and a reduced absorption to prevent the heating of the polymeric membrane above its melting temperature. In most cases the required reflectivity is obtained by depositing a very thin metallic (Al) film on the polymer. 2. The solar sail has to be deployed in space as an inflatable struct
Data Loading...
