"Servicing Mission 4 will be the heaviest servicing mission to date," explains Preston Burch, Associate Director of the Astrophysics Projects Division and Program Manager for Hubble Space Telescope. "It will be carrying approximately 22,500 pounds of hardware onboard. We'll be using four carriers inside the Shuttle cargo bay to carry all the new science instruments, replacement hardware, tools for the astronauts, and to attach Hubble to the Shuttle while the astronauts are working on it."
Each time astronauts upgrade the Hubble Space Telescope (HST), the new equipment rides to orbit on specialized pallets called carriers. These carriers are reusable and some go through modifications prior to a servicing mission based on needs. In previous missions, only three carriers were needed. The new fourth carrier, SLIC, utilizes an advanced design and composite materials to save weight so Atlantis can carry more into orbit.
The Flight Support System (FSS) is the structure which holds HST and provides power and computer interfaces while it is berthed to an Orbiter during Servicing. Mike Kienlen, HST Deputy Project Manager at Goddard explains, "Although the FSS has flown on every Hubble mission, FSS is a new carrier for SM4. A lot of effort went into getting the FSS ready for this flight. We have new or rebuilt motors, a completely recertified electrical system, and all the mechanisms have been taken apart and rebuilt."
The Orbital Replacement Unit Carrier (ORUC) will hold COS and an IMAX camera, which will document the mission for a future film on Hubble. Because of the late addition of the IMAX camera, some significant structural changes had to be made to the carrier.
The Multi-Use Logistics Equipment (MULE) carrier will carry the replacement SIC&DH, the Relative Navigation System (RNS), Hubble's New Outer Blanket Layers, or NOBLs, a variety of contingency tools and crew aids, a spare Rate Sensor Unit, and a contingency Electronic Control Unit.
The Super Lightweight Interchangeable Carrier (SLIC) will contain the WFC3 and Hubble's new batteries. SLIC is the first all-composite carrier ever to fly in the Manned Space Flight Program.
+ Read More about the new equipment carrier SLIC
The below image shows the four SM4 carriers and their planned position within the Atlantis shuttle cargo bay.