How did robotic Mars missions prepare the ground for crewed plans?

Robots were meant to prepare the ground for a decision about human exploration, not to make a piloted Mars expedition inevitable.

• The 1989 schedule was a proposal. NASA officials outlined robotic exploration of the Moon in 1995–2000, robotic precursors at Mars in 2001–2010, and a Mars expedition after 2010. That sequence expressed a planned progression, not a record of missions completed on those dates^[1].
• The 1990s plan became more targeted. In 1997, NASA’s human-spaceflight and space-science programs agreed that a planned 2001 Mars Surveyor lander should carry experiments relevant to future crews, including a compact system to test making propellant from Martian resources. The source describes this as a planned experiment, not a demonstrated result^[2].
• Pathfinder and Sojourner did complete surface work. Pathfinder landed at Ares Vallis on 4 July 1997 using airbags; Sojourner then drove around the landing area and analysed the composition of rocks and dirt. These missions demonstrated landing and local robotic investigation, not the planned propellant test or a human mission^[3].

The link was therefore practical and conditional: robotic missions could supply information and test techniques useful to human-mission planners, while a national decision and firm timetable for sending people remained absent. The source does not state that sample return was a prerequisite^[4].

Would you also like to know how NASA’s approach to piloted Mars planning changed after the Space Exploration Initiative collapsed?AskAnswer complete. One follow-up option available.