Learn Russian: Телепортация — это миф, поэтому учёным некого отправлять в космос. - Teleportation is a myth, therefore scientists have no one to send into space.

How would we rewrite the second half of this sentence to use this lesson's topic and say 'therefore scientists are unlikely to send anyone into space'?

You would change the structure completely. Instead of the 'no one to send' structure (учёным некого отправлять), you would use the nominative case for scientists and the particle вряд ли. It would become: поэтому учёные вряд ли кого-то отправят в космос. Notice that некого changes to кого-то (anyone); because вряд ли acts on a grammatically affirmative verb, it takes indefinite pronouns rather than negative ones.

Why is учёным in the dative case here?

It is because of the некого + infinitive construction. In Russian, when expressing that 'someone has no one to [verb]' or 'someone has nothing to [verb]', the person experiencing this lack takes the dative case. It translates literally to something closer to 'for scientists, there is no one to send.'

I learned that 'nobody' in the accusative case is никого. Why use некого here?

некого (spelled with е and stressed on the first syllable) is a special pronoun used specifically to mean 'there is no one to [do something]'. It is always paired with an infinitive. If you used никого, you would need a standard nominative subject and a negated verb, like учёные никого не отправляют (scientists are not sending anyone), which loses the nuance of 'there is nobody available to send'.

Why use the imperfective verb отправлять instead of the perfective ?