Why Does the RFP Specify CASSSCs?

CASSSC is an acronym for Cargo Accommodations in Standard Space Shipping Container.  It is pronounced “cask”, the word for standard cargo containers on sailing ships of the 1700s and 1800s.  The purpose of CASSSCs is to enable launch vehicles and spacecraft to be unloaded and loaded quickly, and to be able to transfer cargo to other vehicles without requiring that interfaces be reconfigured.  Interfaces are the attachments between each payload and the vehicle, typically mechanical (clamps or latches), avionics (commanding and data), and power.  

Historically, payloads on launch vehicles are individual satellites, experiments, modules (e.g., of International Space Station, ISS), and other hardware that customers pay to have flown to space.  The complement of all payloads on a specific launch or mission is called the “cargo” for that launch or mission.  Each payload is designed and optimized for its own mission:  it may be a communications or navigation satellite, a scientific mission that will go to Mars orbit, or meals for astronauts on ISS.  Most satellite payloads are designed to weigh as little as possible, in order to get as much lifetime as possible from the amount of fuel onboard for station-keeping in orbit or propulsion to a distant destination.  Payloads consider it unfortunate that they must be designed to tolerate launch loads, an environment that they must endure for less than half an hour.  As a consequence, each payload wants to optimize for a different configuration of interfaces–which requires launch vehicles to be configured differently in order to keep each customer happy.

On Expendable Launch Vehicles (ELV), like Delta and Atlas, this has meant designing the top of the rocket, and sometimes the fairings that cover the cargo, differently for each customer.  This is inefficient, so most launch providers now offer a few standard configurations from which customers can choose the one that works best for each payload.  Asking for a unique, non-standard configuration incurs more cost.

On a reusable launch vehicle like the Space Shuttle, providing a unique interface configuration for each customer required literally removing all of the interface hardware from the prior mission, and installing different interface hardware for the next mission–a process that typically required about 12 months of design and analysis, and 6 weeks of hardware removal and installation.  Latches on the vehicle and compatible trunnions on payloads were standard, but had to be installed in different locations for each cargo configuration.  Power and avionics were provided through four Standard Mixed Cargo Harness (SMCH) units, which were moved to different locations and provided unique connectors for each customer.

In the past, transportation industries on Earth had a similar problem:  each item was loaded in ships, train boxcars, or truck trailers by hand or forklift, and the closest things to interface standardization were cargo nets and pallets.  In 1956, an entrepreneur named Malcom McLean loaded a ship en route from Newark, New Jersey, to Houston, Texas, with 58 identical large metal boxes (later called containers), and demonstrated that a ship could be unloaded and loaded in days instead of weeks, enabling ships to spend more time at sea where they made money, instead of waiting in port for cargo handling.  The entire cargo industry changed, and now standard cargo containers are loaded by a supplier; travel on ships, trains, and trucks; and are opened only when they get to the customer.  

The first known suggestion that cargo could be containerized and interfaces could be standardized on space vehicles was in 1987 on a Rockwell International proposal for the National AeroSpace Plane (NASP).  Although that vehicle was never built, Rockwell engineers kept refining the idea of space cargo containerization on proposals for subsequent vehicles, and in 1996 had a design for their X-33 Reusable Launch Vehicle (RLV) proposal that received high praise from the payload community.  RLV had one configuration of standard interfaces for cargo containers, and payloads could install inside their container any way they wished.  Payloads too big to fit inside the standard container had an option to configure themselves to accept the vehicle’s standard interfaces for container exteriors.  Unfortunately, NASA chose the rival VentureStar design for the X-33 contract, and that vehicle also became just another unflown memory.  A later adaptation of the cargo container concept designed for the Space Shuttle, to eliminate the requirement to move latches and SMCHs for each flight, was never funded. 

The Space Settlement Design Competition predicts that cargo containerization and interface standardization for space launch vehicles remains, however, a valid concept, will someday in the future be adopted, and will revolutionize the space cargo industry in the same manner that cargo containers revolutionized freight on Earth.  Besides, SSDC Co-Founder Anita Gale led the Rockwell (and later Boeing) teams that refined the space cargo containerization concept.  Exterior dimensions specified for CASSSCs described in SSDCs are the same as for that Rockwell RLV:  15-foot “rounded-corner-square” cross-section, 30 feet long, capable of carrying 35,000 pounds.  Presume that CASSSCs can be customized to be made of different materials, pressurized or not, enclosed or open framework, sometimes providing unique services to their contents.  What’s important is that the vehicles on which CASSSCs are carried always see the same interfaces and provide the same services to each CASSSC, no matter what is inside or what the CASSSC looks like on the outside.