Another question asks why Spirit and Opportunity weren't launched together. My gut response was that multiple-payload launches were less common then than they are today, but I don't actually know if that's true.

What was the first single launch to put two or more independent payloads into Earth orbit?

What was the first time, if ever, that a single launcher put two independent spacecraft on trajectories leaving Earth's sphere of influence?

Not included: multiple-warhead military applications, or balloons deployed from Mercury spacecraft or Gemini's "rendezvous evaluation pod"; the payloads have to go into different orbits, or at least phased substantially in the same orbit.

• Related, but not the same (doesn't deal with the historical part). 1978 - Pioneer is pretty old though :). Does it have to separate in Earth orbit? Or be a set of duplicate probes which are redundant to each other? – Magic Octopus Urn May 20 at 21:41
• Oh wow, I didn't know about that one! I'll at least throw an upvote at it if you make it an answer. I didn't specify where or how they separated, and they were on different trajectories for weeks between separation and Venus arrival. – Russell Borogove May 20 at 23:36

I can't be sure this is the first attempt, but it might be the strangest-looking: GRAB + ELINT. However it was unsuccessful, and in a very big way.

The item on top is called GRAB 1 for Galactic Radiation and Background. However that's a cover:

Galactic Radiation and Background (GRAB) was the covername for Project Dyno ELINT intelligence satellites operated by the U.S. Naval Research Laboratory (NRL) shortly after the Cold War U-2 incident of 1960. The satellites carried two sets of instruments: an unclassified experiment (called Solrad) and a then-classified payload to collect electronic intelligence (ELINT) (called Tattletale). Of five attempted launches, two missions were successful. The program is also known by the later codeword Canes.

• @MagicOctopusUrn search "spiral" and my user name. You could consider adding the antenna tag to your search by including [antenna] in your search string, unless of course someone has thoughtfully deleted the tag from my question(!) as well ;-) – uhoh May 21 at 23:44