urn:nasa:pds:context:target:astrophysical.gravitational_waves 1.0 1.13.0.0 Product_Context 2020-07-30 1.0 Original urn:nasa:pds:radiosci.documentation:document:armstrong.2006 target_to_document A review paper by John Armstrong titled "Low-Frequency Gravitational Wave Searches Using Spacecraft Doppler Tracking"; originally published in 2006, revised in 2016. Barisch, B. C. (2000). The Science and Detection of Gravitational Waves, https://labcit.ligo.caltech.edu/~BCBAct/talks00/Alberta/LakeLouisepaper.PDF Overview of gravitational waves before they were observed. The LIGO Scientific Collaboration; the Virgo Collaboration (2019). "GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs". Physical Review X. 9 (3): 031040. arXiv:1811.12907. https://doi.org/10.1103/PhysRevX.9.031040 Gravitational Waves Astrophysical Gravitational waves are perturbations of space-time caused by the creation or destruction of mass. Although detected using the Laser Interferometer Gravitational-wave Observatory (LIGO), they had not been observed using radiometric techniques as of 2019.