Precise Formation-Flying Telescope in Target-Centric Orbit: the Solar Case

We present the general concept of a telescope with optics and detectors mounted on two separate spacecrafts, in orbit around the telescope’s target (scopocentric or target-centric orbit), and using propulsion to maintain the Target-Optics-Detector alignment and Optics-Detector distance. Specifically, we study the case of such a telescope with the Sun as the target, orbiting at $\sim $ ∼ 1 AU. We present a simple differential acceleration budget for maintaining Target-Optics-Detector alignment and Optics-Detector distance, backed by simulations of the orbital dynamics, including solar radiation pressure and influence of the planets. Of prime interest are heliocentric orbits (such as Earth-trailing/leading orbits or Distant Retrograde Orbits), where thrust requirement to maintain formation is primarily in a single direction (either sunward or anti-sunward), can be quite minuscule (a few m/s/year), and preferably met by constant-thrust engines such as solar electric propulsion or even by solar sailing via simple extendable and/or orientable flaps or rudders.

Location and stability of distant retrograde orbits around the Moon

ABSTRACT Recently has grown the interest of placing natural or artificial objects in the neighbourhood of the Moon. We numerically investigate a region of retrograde orbits around the Moon associated with the C Family of periodic orbits and the quasi-periodic orbits that oscillate around them (Broucke 1968; Winter 2000). We have given continuity to Winter (2000) investigations by introducing a more realistic dynamical scenario, one based on the four-body Sun–Earth–Moon–particle problem. Our results showed that the region of stability diminished to approximately 4 ${{\ \rm per\ cent}}$, the original size encountered for the circular-restricted three-body problem (CRTBP), mainly due to the Sun’s gravitational perturbations. None the less, the size of the region continues to be significant and we were able to found distant retrograde orbits (DROs) around the Moon with eccentricity following e = 2.259 63 × 10−6a + 0.238 45 (standard error of 1 ${{\ \rm per\ cent}}$) and semimajor axis values of the initial osculating orbits, varying between 110 000 and 185 000 km, remaining stable for a time span of 104 lunar periods. This set of distant orbits from the Moon are characterized by a narrow range of acceptable initial positions (0.8–0.83) and velocities of ∼0.5, in the rotating Earth–Moon frame. The out of plane amplitude oscillations of $\pm 15\, 000$ km presented by these DROs are a natural outcome of the significant Moon’s inclination of 5.15°. Some results presented on this work can be useful for lunar missions, such as the ones that would require prolonged stays around the satellite and use stable distant orbits as ‘parking’ orbits, such as the advanced concepts of NASA’s Asteroid Redirect Mission, proposed a few years ago.

Coverage Analysis of Lunar Communication/Navigation Constellations Based on Halo Orbits and Distant Retrograde Orbits

With more and more missions around the Moon, a communication/navigation constellation around the Moon is necessary. Halo orbits, due to their unique geometry, are extensively studied by researchers for this purpose. A dedicated survey is carried out in this work to analyse the coverage ability of halo orbits. It is found that a two-satellite constellation is enough for continuous one-fold coverage of the north or the south polar regions but never both. A three-satellite constellation is enough for continuous one-fold coverage of both north and south polar regions. A four-satellite constellation can cover nearly 100% of the whole lunar surface. In addition, the coverage ability of another special orbit – distant retrograde orbit (DRO) – is analysed for the first time in this study. It is found that three satellites on DROs can cover 99·8% of the lunar surface, with coverage gaps at polar caps. A four-satellite constellation moving on spatial DROs can cover nearly the whole lunar surface. By combining halo orbits and DROs, we design a five-satellite constellation composed of three halo orbit satellites and two DRO satellites. This constellation can provide 100% continuous one-fold coverage of the whole lunar surface.