A new modification kit may be installed into all three of NASA’s Space Shuttle orbiters, enabling them to land back on Earth, unmanned, in the event of an STS-300 scenario.
Such a modification would give the orbiters a fighting chance of avoiding a ditching in the Pacific ocean, which is the current option for a damaged orbiter, while its crew awaits rescue from the “safe haven” of the International Space Station (ISS).
Currently, should an orbiter suffer what is deemed to be serious TPS (Thermal Protection System) damage during ascent, the crew would take up residence at the ISS until another orbiter could be launched to bring the crew home.
Such a scenario would see the damaged orbiter being ordered to de-orbit itself into the ocean – making way for the rescue ship to dock at the ISS.
While this year’s STS-121 is understood to be the only other Shuttle mission to have an STS-300 support contingency, the option will remain throughout the remaining launch manifest – bar the Hubble Space Telescope servicing mission. It is stressed that the chances of such a mission being required is very unlikely.
There has only been one unmanned return to Earth by a Space Shuttle orbiter, successfully accomplished by a competitor from the Soviet Union. The Russian Space Shuttle Buran made the unmanned flight – including launch – in November 1988. The Shuttle was controlled only by flight controllers on the ground, but only just managed to land safely, following major problems during re-entry.
The NASA Shuttle orbiters already have a system that can automatically perform most re-entry functions, with the pilot only taking over during the final section of the return to the landing site. At present, some key tasks – such as lowering the landing gear and deploying a pair of probes that collect airspeed, altitude and temperature data during the last moments of flight – require an astronaut at the controls.
‘All of those things in a theoretical sense can be automated, but they are not currently connected to the computer system,’ said Space Shuttle manager Wayne Hale last year.
However, a ‘modification kit’ is now understood to be available for installation into the fleet, in time for STS-121.
If NASA decides to have the capability to attempt to bring home a damaged orbiter, the ship would carry out the same procedure of re-entry, as she would on a normal return to Earth.
The target landing site would be Edwards Air Force base in California, with the option of waiving off the attempt should any of the automated systems fail during re-entry, or if the damage started to affect the controllability of the orbiter. Should that prove to be the case, the orbiter would be ditched in the Pacific.
Officially, NASA claim the decision has not yet been made to install the modification, although acknowledged work is being undertaken.
‘The capability currently does not exist for the shuttle to return to earth uncrewed,’ said JSC PAO Kyle Herring, ‘but there is some engineering work ongoing that potentially might provide the technical capability at some time in the future.’
Live updates for all three orbiters can be seen here: