Ellipses and dashes

The agency’s administrator, Sean O’Keefe, canceled what was to be the final Hubble servicing mission...--it was too risky.

The agency’s administrator... canceled what was to be the final Hubble servicing mission--it was too risky.

...Sean O’Keefe canceled what was to be the final Hubble servicing mission on the grounds that--it was too risky.

You say, "But wait--that's not fair!"

You say, "But wait... that's not fair..."

You say, "But wait... that's not fair!"

You say, "But wait that's not fair--"

You say, "Hmmmm... The answer might be D."

You say, "The answer is--D!"

You say, "Hmmm--the answer is D..."

The Hubble Telescope had been almost canceled at least twice and then delayed following the explosion of the shuttle Challenger in 1986.

The Hubble Telescope had been almost canceled at least twice--and then delayed--following the explosion of the shuttle Challenger in 1986.

The Hubble Telescope--had been almost canceled at least twice and then delayed following the explosion of the shuttle Challenger in 1986.

...it’s 25 years in space and counting for the Hubble Space Telescope which has had a perilous existence--political storms, physical calamities, and time.

--it’s 25 years in space and counting for the Hubble Space Telescope which has had a perilous existence... political storms, physical calamities, and time.

Ellipses indicated you've omitted words or information

Ellipses indicate a pause in speech

Ellipses consist of 3 sequential periods

Ellipses are for hiding information

Interrupt sentence structure

A pair of dashes acts like parenthesis

A dash can be used like a colon

A dash omits information