The present invention relates to a packaging arrangement for a spacecraft computer designed to conduct experiments in a hostile environment of outer space. The computer has high density packaging of very large scale integration (VLSI) circuits. Heat is removed by direct contact with each heat producing item in the computer, which direct contact is provided for most integrated circuit chips by a heat conductive plane located between the chips and a printed circuit board. From the heat conductive plane, heat is further removed through direct contact with a housing adapted for physical connection to a cold plate for heat conduction thereto. All heat producing elements are in physical contact with heat transferring devices to transfer essentially all heat to the cold plate. The housing and heat transferring devices eliminate unwanted electromagnetic interference and help reduce galactical radiation especially of the x-ray frequency type. However, the subject invention still provides a lightweight, economical computer that has additional features of (1) ease of access for diagnostic checks of the computer, and (2) reprogrammability of the erasable programmable read only memory (EPROM).