These are the icebreakers that are mounted to the front boxcar of the NASA space shuttle train. Only three are required, but I have supplied a spare. They have the same profile as the SRB covers which follow behind on five flatcars (see Walthers 66' four-truck, heavy-duty cars which are virtually the same as those used by NASA). These frames have been designed to fit on an Atlas Trainman ACF 50' 6" boxcar, which is also used as the spacer cars between the flatcars. My thanks to Morgan Paul for images of his finished models using my designs.
A fellow designer, HODiver, has created the Heavy-Duty 8-axle flatcar deck & truck-mounts, if you are having trouble obtaining the Walthers version. Please see the links below and visit his shop.
https://www.shapeways.com/product/U742EQ92F/66-heavy-duty-flat-car-walthers-design?li=search-results-1&optionId=58755784
https://www.shapeways.com/product/EBX79WBW2/truck-mounts-for-the-hd-flat-car?key=1e99a94c1c131a4980b9dcdc94a30970