I’m surprised that NASA envisions an absurdly massive, nuclear-powered “gravitational tug” to avoid “the biggest problem” of a contact-tug’s need to “fir[e] its rocket engine only at specific times” to compensate for an asteroid’s rotation as mentioned in this article. Cassini, in orbit around Saturn, fires its rocket engine “only at specific times” routinely. Voyager-1 and Voyager-2 have been firing theirs “only at specific times” ever since launch in 1977.
Altadena, Calif. The menacing asteroid described in the article seems to have an unusual characteristic. It’s more than 13 times as dense as water, making it heavier than lead and more than 60 percent heavier than solid iron.
John D. Hoshor
Fort Myers, Fla.
Fort Collins, Colo.