1. Air density at a height of 120 km, from visual observations of 1967–95a
2. Table of Earth Satellites;Pilkington;1969–1973. Royal Aircraft Establishment, Farnborough (R.A.E.) Tech. Rept. 74105,1974
3. Observing Earth Satellites;King-Hele,1966
4. Satellite Observing Notes;Brierley,1974