Environmental Engineering Reference
In-Depth Information
The Laser Interferometer Space Antenna (LISA) mission concept specifies
spacecraft that measure passing gravitational waves. LISA will be a constella-
tion of three spacecraft that uses laser interferometry for precise measurement
of distance changes between widely separated freely falling test masses housed
in each spacecraft (Fig. 3.3 ). The spacecraft are at the corners of an approxi-
mately equilateral triangle about 5 million kilometers on a side in heliocentric
orbit. The science instrument is created via laser links connecting the three
spacecraft. It is formed by measuring to high levels of precision the distances
separating the three spacecraft (i.e., the test masses) via the exchange of the
laser light. From the standpoint of Bus FSW providing spacecraft attitude
and position control, the number of sensors and actuators that must be inter-
rogated and commanded is at least twice the number associated with a more
traditional mission. Similarly, the number of control modes is double that of
a typical astrophysics mission, as are the number of parameters solved-for by
the state estimator.
The Big Bang Observer and the Black Hole Imager are part of the Beyond
Einstein program that will further test Einstein's general theory of relativity.
The Big Bang Observer will explore the beginning of time and will build on
the LISA mission to directly measure gravitons from the early Universe still
present today. The Black Hole Imager mission will calculate the aspects of
matter that fall into a black hole by conducting a census of hidden black
holes, revealing where, when, and how they form.
The Stellar Imager mission will help increase understanding of solar/
stellar magnetic activity and its impact on the origin and continued existence
of life in the Universe, structure and evolution of stars, and habitability of
planets. It will also study magnetic processes and their roles in the origin and
evolution of structure and the transport of matter throughout the Universe.
The current baseline architecture for the full Stellar Imager mission is a space-
based, UV-Optical Fizeau Interferometer with 20-30 1-m primary mirrors,
mounted on formation-flying “mirrorsats” distributed over a parabolic virtual
surface whose diameter can be varied from 100 m upto as much as 1,000 m,
depending on the angular size of the target to be observed (Fig. 11.1 ) . The
hub and all of the mirrorsats are free-flyers in a tightly-controlled formation
in a Lissajous orbit around the Sun-Earth Lagrange L2 point. The mission
will also use autonomous analysis of wavefronts and will require real-time
correction and control of tight formation flying.
The Solar Imaging Radio Array (SIRA) mission will be a Medium ex-
plorer (MIDEX) mission and will perform interferometric observations of low
frequency solar and magnetospheric radio bursts. The primary science tar-
gets are coronal mass ejections (CMEs), which drive radio-emission-producing
shock waves. A space-based interferometer is required because the frequencies
of observation ( < 15 MHz) do not penetrate the ionosphere. SIRA will re-
quire 12-16 microsatellites to establish a sucient number of baselines with
separations on the order of kilometers. The microsat constellation consists
of microsats located quasi-randomly on a spherical shell, initially of radius
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