 Why is Crownwall the representative from Earth sent to Vega?
The sight of an Earthman on Vega III, where it was impossible for an outlander to be, brought angry crowds to surround John Crownwall as he strode toward the palace of Viceroy Tronn Ffallk, ruler of Sector XII of the Universal Holy Empire of Sunda. If they carried out the threats of their present attitude, Earth would have to send Marshall to replace him. It had been manned by a dozen adventurous people, captained by Crownwall, and had headed out on its ion drive until it was safely clear of the warping influence of planetary masses. Even if you could get down to the bottom of the ocean and tamper with the bomb, you would only succeed in setting it off, and that's what the Sunda had been in favor of in the first place.
 He was a reasonable option given his prior leadership experience on missions
 He was the only one who was willing to undergo the time travel procedure  He was the only one without connections on Earth, making it easier for him to take time away  He was the default choice once the humans determined that Marshall was not fit for the job  He was a reasonable option given his prior leadership experience on missions