The Hubble Origins Probe (HOP) was a proposal for an orbital telescope made in 2005 in response to the first cancellation of the fourth Hubble Space Telescope (HST) servicing mission. It would have used an Atlas V rocket or similar launch vehicle to launch a much lighter, unaberrated mirror and optical telescope assembly, using the instruments that had already been built for SM4, along with a new wide-field imager. It would have cost between $700 million and $1 billion.
Funding for the mission was never allocated; in February 2005, Sean O'Keefe, the NASA administrator who had cancelled SM4, resigned. Michael D. Griffin, NASA administrator after O'Keefe, reinstated the servicing missions, making HOP redundant.
^"Hubble Option" (Press release). Johns Hopkins University Applied Physics Laboratory. 2005. Retrieved 30 June 2013.
^Lawler, A. (2005). "ASTRONOMY: Hearing Highlights Dispute over Hubble's Future". Science. 307 (5711): 831. doi:10.1126/science.307.5711.831. PMID15705817.
^Harwood, William (31 October 2006). "'Go' for Hubble servicing mission". CBS NEWS Space Place. Retrieved 1 July 2013.
Hubble Origins Probe
Replacing Hubble by Francis Reddy on astronomy.com
AIP Bulletin of Science Policy News article, "Witnesses Question Priority of a Hubble Servicing Mission"
NASA Mission Pages: Service Mission 4 (SM4)
Hubble Space Telescope (HST) Service Mission 4 (SM4) Crew Training video (archive.com)