We describe the requirements and associated technology development plan for the communications data link from low mass interstellar probes. This work is motivated by several proposed deep space and interstellar missions with an emphasis on the Breakthrough Starshot project. The Starshot project is an effort to send the first low mass interstellar probes to nearby star systems and transmit back scientific data acquired during system transit within the time scale of a human lifetime. The about 104-fold increase in distance to nearby stars compared to the outer planets of our solar system requires a new form of propulsion to reach speeds of approximately 20% of the speed of light. The proposed use of a low mass sailcraft places strong constraints on the mass and power for the Starshot communications system. We compare the communications systems in current and upcoming solar system probes, New Horizons and Psyche, against the requirements for Starshot and define Figures of Merit for the communications capability in terms of data downlink rate multiplied by distance squared per unit mass. We describe current and future technology developments required for the on-board transmitter (signal generation, signal distribution, and beamforming) and for the near-Earth communications receiver (low-cost large aperture telescopes, high resolution spectrometers, and single photon counting detectors). We also describe a roadmap for technology development to meet the goals for future interstellar communications.
KEYWORDS: Telescopes, Sun, Satellites, Large Synoptic Survey Telescope, Signal to noise ratio, Device simulation, Space telescopes, Large telescopes, Solar system, Photons
Large or even medium sized asteroids impacting the Earth can cause damage on a global scale. Existing and planned concepts for finding near-Earth objects (NEOs) with diameter of 140 m or larger would take ~15-20 years of observation to find ~90% of them. This includes both ground and space based projects. For smaller NEOs (~50-70 m in diameter), the time scale is many decades. The reason it takes so long to detect these objects is because most of the NEOs have highly elliptical orbits that bring them into the inner solar system once per orbit. If these objects cross the Earth's orbit when the Earth is on the other side of the Sun, they will not be detected by facilities on or around the Erath. A constellation of MicroSats in orbit around the Sun can dramatically reduce the time needed to find 90% of NEOs ~100-140 m in diameter.
The Laser Astrometric Test of Relativity (LATOR) is a Michelson-Morley-type experiment designed to test the Einstein’s general theory of relativity in the most intense gravitational environment available in the solar system – the close proximity to the Sun. By using independent time-series of highly accurate measurements of the Shapiro time-delay (laser ranging accurate to 1 cm) and interferometric astrometry (accurate to 0.1 picoradian), LATOR will measure gravitational deflection of light by the solar gravity with accuracy of 1 part in a billion, a factor ~30,000 better than currently available. LATOR will perform series of highly-accurate tests of gravitation and cosmology in its search for cosmological remnants of scalar field in the solar system. We present science, technology and mission design for the LATOR mission.
Spacecraft carrying optical communication lasers can be treated as artificial stars, whose relative astrometry to Gaia reference stars provides spacecraft positions in the plane-of-sky for optical navigation. To be comparable to current Deep Space Network delta-Differential One-way Ranging measurements, thus sufficient for navigation, nanoradian optical astrometry is required. Here we describe our error budget, techniques for achieving nanoradian level ground-base astrometry, and preliminary results from a 1 m telescope. We discuss also how these spacecraft may serve as artificial reference stars for adaptive optics, high precision astrometry to detect exoplanets, and tying reference frames defined by radio and optical measurements.
KEYWORDS: Semiconducting wafers, Space operations, Sun, Directed energy weapons, Solar energy, Sensors, Stars, CMOS sensors, Computer aided design, Space reconnaissance
The long standing approach to space travel has been to incorporate massive on-board electronics, probes and propellants to achieve space exploration. This approach has led to many great achievements in science, but will never help to explore the interstellar medium. Fortunately, a paradigm shift is upon us in how a spacecraft is constructed and propelled. This paper describes a mission concept to get to our Sun’s Gravity Lens at 550AU in less than 10 years. It will be done by using DE-STAR, a scalable solar-powered phased-array laser in Earth Orbit, as a directed energy photon drive of low-mass wafersats.
[1] [2] [3] [4] [5] With recent technologies a complete mission can be placed on a wafer including, power from an embedded radio nuclear thermal generator (RTG), PV, laser communications, imaging, photon thrusters for attitude control and other sensors. As one example, a futuristic 200 MW laser array consisting of 1 - 10 kw meter scale sub elements with a 100m baseline can propel a 10 gram wafer scale spacecraft with a 3m laser sail to 60AU/Year. Directed energy propulsion of low-mass spacecraft gives us an opportunity to capture images of Alpha Centauri and its planets, detailed imaging of the cosmic microwave background, set up interstellar communications by using gravity lenses around nearby stars to boost signals from interstellar probes, and much more. This system offers a very large range of missions allowing hundreds of wafer scale payload launches per day to reach this cosmological data reservoir. Directed Energy Propulsion is the only current technology that can provide a near-term path to utilize our Sun’s Gravity Lens.
High-resolution active laser ranging systems for Moon, Mars and beyond are analyzed. Both stand-alone laser-ranging
transponders, and laser-communications systems configured to provide millimeter-level ranging data are analyzed. It is
shown that a combined dual-function laser-communications and laser-ranging system is feasible.
This paper addresses the issue of modeling the white light fringe. We developed analytic technique for extracting the phase, visibility and amplitude information as needed for interferometric astrometry with the Space Interferometry Mission (SIM). The model accounts for a number of instrumental and physical effects and is able to compensate for a number of operational regimes. In particular, we were able to obtain general solution for polychromatic phasors and address properties of unbiased fringe estimators in the presence of noise. For demonstration purposes we studied the case of rectangular bandpass filter with two different methods of optical path difference (OPD) modulation -- stepping and ramping OPD modulations.
A number of areas of further studies relevant to instrument design and simulations are outlined and discussed.
The Space Interferometry Mission (SIM) is a space-based long-baseline optical interferometer for precision astrometry. One of the primary objectives of the SIM instrument is to accurately determine the directions to a grid of stars, together with their proper motions and parallax, improving a priori knowledge by nearly three orders of magnitude. The basic astrometric observable of the instrument is the pathlength delay, a measurement made by a combination of internal metrology measurements that determine the distance the starlight travels through the two arms of the interferometer and a measurement of the white light stellar fringe to find the point of equal pathlength. Because this operation requires a non-negligible integration time to accurately measure the stellar fringe position, the interferometer baseline vector is not stationary over this time period, as its absolute length and orientation are time-varying. This conflicts with the consistency condition necessary for extracting the astrometric parameters which requires a stationary baseline vector. This paper addresses how the time-varying baseline is `regularized' so that it may act as a single baseline vector for multiple stars.
The last decade of the 20th century has seen the development of extremely sensitive instruments based on new emerging technologies. These instruments, which are widely distributed on Earth and currently being deployed in space, have provided the means necessary to prove more deeply into the nature and evolutionary history of the universe. Together with a noticeable progress in providing a less expensive launch services, this made a significant impact on a number of areas of fundamental research. One of such areas is the research in relativistic and gravitational physics. Motivated by the opportunities offered by the future Space Interferometry Mission, we discuss high-precision astrometric measurements and their significance for the relativistic gravitational theory.
The Space Interferometry Mission (SIM) will be NASA's first space-based optical interferometer. SIM will produce a wealth of new astronomical data and serve as a technology pathfinder for future astrophysics missions. The SIM architecture uses a 10-m Michelson interferometer in Earth- trailing solar orbit to provide 4 microarcsecond precision absolute position measurements of stars down to 20 magnitude. The corresponding parallax accuracy allows distance measurements to 10 percent accuracy on the far side of the Galaxy. With high-precision proper motions derived during its 5-year lifetime, SIM will address a variety of science questions relating to the formation and dynamics of our Galaxy. Using aperture synthesis, SIM will image in the visible waveband to a resolution of 10 milliarcsec, and will demonstrate interferometric nulling with suppression of the on-axis starlight to a level of 10-4. In this paper we present selected topics from the SIM science program focusing on some specific astronomical questions to be addressed.
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