STS-135 (ISS assembly flight ULF7) is the final mission of the American Space Shuttle. It uses hardware originally processed for the STS-135 contingency mission, as the Launch On Need (LON) rescue mission designated to support STS-134 was not ultimately needed. The mission launched on 8 July and is scheduled to land on 20 July 2011. The four person STS-135 crew was the smallest of any shuttle mission since April 1983’s STS-6. The mission’s primary cargo was the Multi-Purpose Logistics Module (MPLM) Raffaello and a Lightweight Multi-Purpose Carrier (LMC). The flight of MPLM Raffaello on Space Shuttle Atlantis also marked the first and only time that Atlantis hauled an MPLM to space.
Although the mission was authorized, it initially had no appropriation in the NASA budget, raising questions about whether the mission would fly at all. On 20 January 2011, program managers changed STS-335 to STS-135 on the flight manifest. This allowed for training and other mission specific preparations. On 13 February 2011, program managers told their workforce that STS-135 would fly “regardless” of the funding situation via a continuing resolution. Until this point, there had been no official references to the STS-135 mission in NASA official documentation for the general public.
During an address at the Marshall Space Flight Center on 16 November 2010, NASA administrator Charles Bolden said that the agency needed to fly STS-135 to the station in 2011, due to likely delays in the development of commercial rockets and spacecraft designed to transport cargo to the ISS. “We are hoping to fly a third shuttle mission (in addition to STS-133 and STS-134) in June 2011, what everybody calls the launch-on-need mission… and that’s really needed to [buy down] the risk for the development time for commercial cargo,” Bolden said.
The mission was included in NASA’s 2011 authorization, signed into law on 11 October 2010, but funding remained dependent on a subsequent appropriation bill. United Space Alliance signed a contract extension for this mission, along with STS-134; the contract contained six one-month options with NASA in order to support continuing operations.
The US government budget approved in mid-April 2011 called for $5.5 billion for NASA’s space operations division, including the space shuttle and space station programs. According to NASA, the budget running through 30 September 2011 ended all concerns about funding the STS-135 mission.
Atlantis will ferry extra supplies to the International Space Station. Since the ISS program is likely to be extended to 2020, the station will likely require more spare supplies after the shuttle retires. A shuttle extension would allow the crew to maintain the completed space station, but an ISS extension was never intended to be a guaranteed shuttle program extension, and the shuttle program is officially to end after STS-135. Therefore, the more delivery of excess supplies for the station, the better.
Multi-Purpose Logistics Module (MPLM) Raffaello will make up the majority of the payload. The MPLM will be filled with 16 resupply racks, which is the maximum that it can handle.
The Lightweight Multi-Purpose Carrier (LMC) will also be carried on this mission. The External Thermal Cooling System (ETCS) Pump Module (PM) on ESP-2, which failed and was replaced on orbit in August 2010, is planned to have a ride home on the LMC so that a failure analysis can be performed on the ground. The Robotic Refueling Mission will ride up to the station on the underside of the LMC to be placed onto the ELC-4.
Atlantis will carry the Robotic Refueling Mission (RRM) developed by the Satellite Servicing Capabilities project at the Goddard Space Flight Center (GSFC). It plans to demonstrate the technology and tools to refuel satellites in orbit by robotic means. After the proof of concept, the long-term goal of NASA is to transfer the technology to the commercial sector.
RRM will include four tools, each with electronics and two cameras and lights. Additionally, it will have pumps and controllers and electrical systems such as electrical valves and sensors.
The RRM payload was transported to the Kennedy Space Center in early March 2011, where the GSFC team will perform the final preparations for space flight. Once up in the International Space Station, RRM will be installed into the ELC-4. The Dextre robot will be used during the refueling demonstration.
This mission is the third flight of the TriDAR sensor package designated DTO-701A (Detailed Test Objective), a 3D dual-sensing laser camera, intended for potential use as an autonomous rendezvous and docking sensor. It was developed by Neptec Design Group and funded by NASA and the Canadian Space Agency. Previously TriDAR was flown twice on STS-128 and STS-131, aboard Space Shuttle Discovery. TriDAR provides guidance information that can be used for rendezvous and docking operations in orbit, planetary landings and vehicle inspection/navigation of unmanned rovers. TriDAR does not rely on any reference markers, such as reflectors, positioned on the target spacecraft. To achieve this, it relies on a laser based 3D sensor and a thermal imager. Geometric information contained in successive 3D images is matched against the known shape of the target object to calculate its position and orientation in real-time.
The sensor is installed on the exterior airlock truss next to a Trajectory Control System (TCS) sensor. The TriDAR hardware was installed in Atlantis’ Payload Bay on 6 April 2011. On STS-135 TriDAR will also be used to demonstrate technology for autonomous rendezvous and docking in orbit. The crew will have a laptop set up to display the information that is acquired by the system, however it will not be used to provide information to the Shuttle’s TCS.
The failed ammonia pump module that was replaced in August 2010 is expected to be returned inside Atlantis’ payload bay. Also, a problematic Common Cabin Air Assembly (CCAA) Heat Exchanger (HX) is expected to be returned inside the MPLM.