90 Day Study Lander Credit - © Mark Wade

Following the Ride Report, the Bush administration indicated a willingness to support a new manned space initiative after completion of the space station. To provide alternates for presidential consideration, NASA management completed a 90-day study in October 1989. This estimated the cost of going to Mars as $ 258 billion (including $141 billion contingency). The plan used the then-current collection of planned NASA infrastructure hardware - Space Station Freedom, Orbital Transfer Vehicles, aerobraking to accomplish the mission.

One result of the Ride Report was the Space Exploration Initiative. As part of this an Outreach Program solicited competing ideas from industry, government labs, NASA centers, and academia. This produced a large number of conflicting ideas. NASA's vision of the future was embodied in its 90-day study. But other players were making the their voices heard at the White House, including Lawrence Livermore Laboratory with a plan for a quick, cheap landing using inflatable technology, and Los Alamos National Laboratory with a call for a return to the nuclear thermal technology of the 1960's.

• Summary: Large integrated NASA/Contractor effort, results well documented, includes design, schedule and cost
• Propulsion: Nuclear thermal
• Braking at Mars: aerodynamic
• Mission Type: conjunction
• Split or All-Up: split
• ISRU: ISRU
• Launch Year: 2017
• Crew: 4
• Mars Surface payload-metric tons: 23
• Outbound time-days: 200
• Mars Stay Time-days: 600
• Return Time-days: 200
• Total Mission Time-days: 1000
• Total Payload Required in Low Earth Orbit-metric tons: 1300
• Total Propellant Required-metric tons: 840
• Propellant Fraction: 0.64
• Mass per crew-metric tons: 325
• Launch Vehicle Payload to LEO-metric tons: 140
• Number of Launches Required to Assemble Payload in Low Earth Orbit: 3
• Launch Vehicle: Shuttle Z

• Portree, David S. F., Humans to Mars: Fifty Years of Mission Planning, 1950 - 2000, NASA Monographs in Aerospace History Series, Number 21, February 2001. Excellent overview of American plans for sending men to Mars.

• Griffin, Brand; Thomas, Brent; Vaughan, Diane, A Comparison of Transportation Systems for Human Missions to Mars, AIAA 2004-3834, 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit ,11-14 July 2004.