Frè, Pietro (2013), "7", Gravity, a geometrical course (dalam bahasa English), 1:Development of the theory and basic physical applications (ed. 1), New York: Springer, m/s. 276, Bibcode:2013ggc1.book.....F, doi:10.1007/978-94-007-5361-7, ISBN978-94-007-5360-0, diarkibkan daripada yang asal pada November 20, 2020, dicapai pada October 14, 2020CS1 maint: unrecognized language (link)
doi.org
"Radio-Radar Telescope Will Probe Solar System". Electrical Engineering. 80 (7): 561. July 1961. doi:10.1109/EE.1961.6433355.
Frè, Pietro (2013), "7", Gravity, a geometrical course (dalam bahasa English), 1:Development of the theory and basic physical applications (ed. 1), New York: Springer, m/s. 276, Bibcode:2013ggc1.book.....F, doi:10.1007/978-94-007-5361-7, ISBN978-94-007-5360-0, diarkibkan daripada yang asal pada November 20, 2020, dicapai pada October 14, 2020CS1 maint: unrecognized language (link)
Frè, Pietro (2013), "7", Gravity, a geometrical course (dalam bahasa English), 1:Development of the theory and basic physical applications (ed. 1), New York: Springer, m/s. 276, Bibcode:2013ggc1.book.....F, doi:10.1007/978-94-007-5361-7, ISBN978-94-007-5360-0, diarkibkan daripada yang asal pada November 20, 2020, dicapai pada October 14, 2020CS1 maint: unrecognized language (link)
Frè, Pietro (2013), "7", Gravity, a geometrical course (dalam bahasa English), 1:Development of the theory and basic physical applications (ed. 1), New York: Springer, m/s. 276, Bibcode:2013ggc1.book.....F, doi:10.1007/978-94-007-5361-7, ISBN978-94-007-5360-0, diarkibkan daripada yang asal pada November 20, 2020, dicapai pada October 14, 2020CS1 maint: unrecognized language (link)