Three major differences that make “Space Systems” unique and set them apart from a non-space system are:
- The Space Environment
- Unattended Operation
- And The Implications of The Ultimate High Ground
The Space environment is extremely harsh. It places additional constraints on the design and operation of satellites, components, and parts of the space segment. The Space environment is characterized by:
- Near Total Vacuum
- Ambient thermal inputs varying from direct sun illumination in one direction to the near absolute zero of deep space in other,
- Passage through belts of charge particles and and magnetic fields
- Persistent bombardment of protons and electromagnet radiation from the sun,
- Man-Made or natural micro-particles and space debris.
These constraints must be factored into the design of the space assets to assure their long-term survival and operation. Special test facilities such as thermal vacuum chambers are required to verify that the hardware can operate in the space environment. In addition, high vibration, acoustic, shock and other environments during launch and deployment into the operation orbit require careful characterization, design, and testing to prevent irreversible failures during launch and early on-orbit operations.
The space segment of all military space systems developed so far operates unattended. If a component fails on-orbit, only remote maintenance actions can be carried out. Such actions must usually be preplanned and take advantage of provisions designed into the SV such as redundant hardware or re- loadable software. Satellites are usually designed to eliminate or at least minimize single point failures. Increasingly, redundancy has been designed into the launch segment as well. Additionally, space parts go through a stringent qualification process for reliability to avoid premature failure and loss or degradation of intended capability. Care is taken to verify that the hardware has a positive margin with respect to the launch and space environments. When a software defect affects the operation, the satellite must be capable of being placed in a safe-mode until the defect can be identified and corrected. Therefore, software that could cause the irretrievable loss of a mission is validated through such steps as extensive simulations, sometimes with flight hardware in the loop.
The Ultimate High Ground
Military forces have strived for the high ground for millennia because of the advantages it provides including the increased ability to observe or survey the opposition and the operational environment, maintain line-of-sight communications with friendly forces, and orient oneself with respect to the enemy and the surrounding terrain. Space provides the ultimate high ground so it is not surprising that current military space systems provide for surveillance of both potential enemies and the meteorological conditions in the operation theatre as well as communications and navigation. The cost to build and launch satellites means that each must be exploited to the extent practical by all land, sea, and air forces. As a result, many of the space programs are joint programs to provide capability to be used in joint operations by elements of all the military forces and sometimes, in conjunction with allied forces. The user equipment for such systems can become deployed on a wide range of platforms and therefore rival or even exceed the cost of the satellites and launch vehicles so that the Systems Engineering task of balancing effectiveness and cost can be still more demanding and important.