( CNN ) -- NASA 's plans to fly a fifth and final space shuttle mission to service the Hubble Space Telescope have suffered another set-back . Atlantis was prepared to launch in September before an onboard computer failed , delaying the mission . Hubble managers say ground testing of a critical replacement computer that they hope to install on the orbiting telescope is taking longer than previously expected . And that means an additional flight delay . `` Delivery in April to support a May launch , I think is a fair thing to say , '' said Hubble program manager Preston Burch . `` Right now I think we have a very good chance of meeting a readiness date in that time frame . '' The additional delay is just the latest dip in an emotional rollercoaster ride for the Hubble team over the past few months . In late September , astronauts were mere weeks away from launching to Hubble aboard the space shuttle Atlantis , with spacewalks planned to make the telescope more powerful than ever and extend its expected lifespan an additional five years . That flight had to be postponed when the onboard computer that downlinks scientific data to the ground suddenly failed on September 27th . While that problem has been corrected using a back-up system , NASA managers have decided the computer needs to be completely replaced in order to keep a fully redundant back-up capability available . A spare computer was built prior to Hubble 's launch in 1990 , and has been warehoused at the Goddard Space Flight Center in Maryland ever since . Initially , engineers had hoped that spare could be quickly tested , certified `` flight ready , '' and shipped to the Kennedy Space Center in Florida to be packed aboard Atlantis in time for a February launch . But a closer evaluation of the spare shows more than six months of work will be needed to get it ready to fly . Among other issues , it was partially disassembled other the years so that parts could be used for other systems . It has been largely put back together , but now programming anomalies are cropping up . And once engineers get it in good working order , it will have to go a battery of environmental tests to make sure it is ready to hold up in the harsh conditions of space . But the engineers are confident that they will eventually overcome all the obstacles . `` We 've gotten a lot smarter about the condition of this unit over the last four weeks , said Burch . `` We do n't want to take any chances in bringing a box up there that is n't going to be 100 % working to the absolute best that it can . So we want to take some extra time and make sure that we subject this to a very rigorous test program and we do n't want to leave any stones unturned on the way to the launch pad . ''
NASA 's plans to service Hubble Space Telescope suffer another setback . Ground testing of a critical replacement computer taking longer than expected . `` Delivery in April to support a May launch , '' NASA manager predicts . More than six months of work will be needed to get it ready to fly .