NASA's long term mission plans involved space-voyages lasting for several years. While Apollo would provide some information on the effect of weightlessness on the human body over short periods of time, the full effects of longer periods was considered an especial concern.
To study the effects of weightlessness over long periods, it was proposed that during the Apollo Applications Program (AAP) a spacecraft carrying two monkeys would be boosted into a 463km (250 nm) orbit using an Apollo Command Service Module (CSM). After a year in orbit the monkeys would be returned to Earth by another CSM.
NOTE: Volume 2 is not available online from the NASA Technical Reports Server (NTRS).
Orbiting experiment for study of extended weightlessness. Volume 1 - Summary
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005148_1968005148.pdf
Orbiting experiment for study of extended weightlessness. Volume 3 - Spacecraft preliminary design
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005421_1968005421.pdf
Orbiting experiment for study of extended weightlessness. Volume 4 - Laboratory test model
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005422_1968005422.pdf
Orbiting experiment for study of extended weightlessness. Volume 5 - Program plans
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005423_1968005423.pdf
Orbiting experiment for study of extended weightlessness. Volume 6 - Orbiting primate spacecraft applications
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005424_1968005424.pdf
Orbiting experiment for study of extended weightlessness Final report
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680004371_1968004371.pdf
Technical feasibility demonstration model of orbiting experiment for study of extended weightlessness
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700019441_1970019441.pdf
To study the effects of weightlessness over long periods, it was proposed that during the Apollo Applications Program (AAP) a spacecraft carrying two monkeys would be boosted into a 463km (250 nm) orbit using an Apollo Command Service Module (CSM). After a year in orbit the monkeys would be returned to Earth by another CSM.
NOTE: Volume 2 is not available online from the NASA Technical Reports Server (NTRS).
Orbiting experiment for study of extended weightlessness. Volume 1 - Summary
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005148_1968005148.pdf
Orbiting experiment for study of extended weightlessness. Volume 3 - Spacecraft preliminary design
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005421_1968005421.pdf
Orbiting experiment for study of extended weightlessness. Volume 4 - Laboratory test model
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005422_1968005422.pdf
Orbiting experiment for study of extended weightlessness. Volume 5 - Program plans
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005423_1968005423.pdf
Orbiting experiment for study of extended weightlessness. Volume 6 - Orbiting primate spacecraft applications
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680005424_1968005424.pdf
Orbiting experiment for study of extended weightlessness Final report
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680004371_1968004371.pdf
Technical feasibility demonstration model of orbiting experiment for study of extended weightlessness
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700019441_1970019441.pdf