The Explorer Program started as an attempt to make a reusable interplanetery spacecraft:
Explorer launched on Year 3, Day 267.
Explorer was a testbed for many new technologies – especially the LVN nuclear thrust engines, which are a critical component for all future Explorer spacecraft in addition to the Pathfinder Missions.
The greatest success for the Explorer was landing Kerbals on Gilly, Eve’s small moon! Mitster, Orlas, and Chrisnic made history that day!
When Explorer was designed, it was hopeful that there would be enough deltaV to allow the spacecraft to return to Kerbin orbit. Unfortunately, there was only enough for the return voyage. Thankfully, this is why the LARC (Landing and Return Craft) was designed – both as a vehicle to land on Gilly, and return the crew to the surface of Kerbin if needed! Explorer itself was remotely piloted into a safe orbit away from Kerbin, and is still out there in a wide Kerbol orbit to this day!
The next Explorer spacecraft was Explorer 2 – the first crewed mission to Duna! Launched in conjuction with the Duna Spaceport, this design became the groundwork for every future Explorer mission.
On Year 6, Day 275 Explorer 2 arrived at Duna! After circularizing it’s orbit, the spacecraft began manuevers to dock with Duna Spaceport (which had been remotely launched and piloted to Duna Orbit.)
The Explorer 2 crew went on to perform 3 seperate landings on Duna using the Duna Lander and Duna Spaceport’s fuel reserves. Explorer 2 set the future for the Explorer program!
Explorer 3 was the second Duna mission, and was a slightly modified version of the Explorer 2 spacecraft – this time with more fuel and more life support.
Explorer 3 launched alongside the new Advanced Atmospheric Lander (more commonly known as the Super Duna Lander!)
The Super Duna Lander allowed 3 Kerbals to land simulataneously! Explorer 3 went on to make 3 seperate landings on Duna!
Explorer 4 was the last iteration of the Explorer 2 basic design. Explorer 4’s crew landed on Dres on Year 7, Day 386. The low gravity allowed the Mun-designed lander to perforum 2 seperate landings, “jumping” from one site to another!
Explorer 5 was designed as a testbed for new technologies to reach Jool (as symbolized by the green star on it’s patch!) Notably it was the first interplanetary mission to use cryo-stasis to extend crew range!
Explorer 5 departed Kerbin on Year 9, Day 262.
Having the crew in suspended animation saves deltaV as the crew doesn’t need to bring as much life support, snacks, and other necessities! Explorer 5 arrived at Duna on Year 10, Day 202.
Unlike Explorer 2 and 3, Explorer 5 did only one landing (future missions sent refuelling craft to Duna Spaceport to allow more missions.)
On Year 11, Day 411 Explorer 5 left Duna, and the crew re-entered Cryostasis! On Year 12, Day 285 Explorer 5 made history by being the first interplanetary spacecraft to return to Kerbin orbit after a mission!
Explorer 6 pushed the limits of the Explorer 5 design by sending a crewed mission to Jool’s moon Laythe!
Explorer 6 launched on Year 11, Day 129!
On Year 14 Day 1 Explorer 6 left Laythe and started the return to Kerbin! The crew was already in suspended animation – but the mission proved that life support and the communications network was capable of acceptably safe operations in the Jool system!