陆家嘴美食团购:Satellite Classification

Satellite Classification

First of all, it is worth defining what we mean by a small satellite. The commercial space sector is typified by the Geostationary communications satellite, ranging in on-orbit mass from 1000kg to well over 4000kg. Current trends are for the in-orbit mass of these spacecraft to increase to 8000-12,000kg.

For many other applications, there have been trends towards smaller spacecraft, with particular emphasis on reducing cost and development time scales. For the purpose of these pages, a mass below 500kg is considered a small satellite, however the mission development philosophy is also relevant, to distinguish the new generation of small satellites from the more traditional small satellites that typified the early exploration of space. 

The spirit of the small satellite world has been encompassed by the slogan "Faster, Better, Smaller Cheaper", although various high profile failures of NASA spacecraft have made this phrase less popular . Nevertheless, small satellite projects are characterised by rapid development scales for experimental missions when compared with the conventional space industry, with kick-off to launch schedules ranging from just six to thirty-six months. Leading-edge or terrestrial COTS technology is routinely employed  in order to provide innovative solutions and cheaper alternatives to the established methods and systems. As such they permit lighter satellite systems to be designed inside smaller volumes. Frequently, traditional procedures, with roots in the military and manned space programmes, can no longer be justified, and low cost solutions are favoured to match the reducing space budgets. So in many ways "Faster, Better, Smaller, Cheaper"  is a philosophy and an objective in small satellite programmes.

Many terms are used to describe this rediscovered class of satellites, including SmallSat, Cheapsat, MicroSat, MiniSat, NanoSat and even PicoSat and FemtoSat! The US Defence Advanced Research Projects Agency refers to these as LightSats, the U.S. Naval Space Command as SPINSat's (Single Purpose Inexpensive Satellite Systems), and the U.S. Air Force as TACSat's (Tactical Satellites). Nevertheless, in recent years a general method of classifying satellites in terms of deployed mass has been generally adopted. The boundaries of these classes are an indication of where launcher or cost tradeoffs are typically made, which is also why the mass is defined including fuel ('Wet mass').

Group name Wet Mass Large satellite >1000kg Medium sized satellite 500-1000kg Mini satellite 100-500kg Small Satellites Micro satellite 10-100kg Nano satellite 1-10kg Pico satellite 0.1-1kg Femto satellite <100g

Within this classification, the term "Small Satellite" is used to cover all spacecraft with in-orbit mass of less than 500kg. The small satellites we are concerned with throughout these pages are therefore satellites weighing approximately less than 500kg.

Another definition proposed by the IAA for inexpensive small satellites is

• The programme must have an unusual or unconventional approach.
• The mission must fill a clear gap
• The programme must have a short lead time  

The mass distribution for small satellites as launched is plotted below, and  illustrates that there are no clear mass boundaries. What can be said is that there are periods where spacecraft within certain mass classes are either rare or absent. For instance there is a general lack of spacecraft in the 100-200kg towards the end of the 1990's. These gaps appear as a result of available launch opportunities of small satellites.