As most are aware, a CubeSat is too small to also carry sensors for significant scientific research. For universities, the main objective of developing, launching and operating a CubeSat is educational. However, when combining a large number of CubeSats with identical sensors into a network, in addition to the educational value, fundamental scientific questions can be addressed which are otherwise inaccessible. Networks of CubeSats have been under discussion in the CubeSat community for several years, but so far, no university, institution, or space agency has taken the initiative to set up and coordinate such a powerful network. For the QB50 network, double CubeSats (10x10x20 cm) are foreseen, with one half providing the usual satellite functions and the other half accommodating a set of identical sensors for lower thermosphere and re-entry research. All 50 CubeSats will be launched together on a single launch vehicle (a Russian Shtil-2.1 or Shtil-2R) into a circular orbit at about 300 km altitude, inclination 79 degrees. The payload mass is about 200 kg (100 kg for the CubeSats, 80 kg for the CubeSat deployment system, 20 kg margin). Due to atmospheric drag, the orbits of the CubeSats will decay and progressively lower and lower layers of the thermosphere will be explored, perhaps down to 90 km. The initial orbital altitude will be selected so that the mission lifetime of the individual CubeSats will be about three months. 34 CubeSats are envisaged to be provided by European universities in 19 countries, 11 by universities in the U.S., 2 by universities in Canada, and 3 by Japanese universities.
A network of CubeSats in the lower thermosphere compared to networks in higher orbits has the following advantages:
- The lifetime of a CubeSat in the envisaged low-Earth orbit will only be three months, i.e. much less than the 25 years stipulated by international requirements related to space debris
- A low-Earth orbit allows high data rates because of the short communication distances involved
- In their low-Earth orbits the CubeSats will be below the Earth´s radiation belts, which is very important because CubeSats use low-cost Commercial-Off-The-Shelf (COTS) components
CubeSat reliability is not a major concern as the network can still fully achieve its mission, objectives even if a few CubeSats fail. For the universities, a short mission lifetime is not a deterrent as for a university the primary purpose of a CubeSat project is educational and the educational objectives can be fully met even if the orbital lifetime is short. The multi-point, in-situ measurements of QB50 will be complementary to the remote-sensing observations of the much larger Earth observation satellites in higher orbits (500-800 km), the in-situ short-duration measurements by experiments on board sounding rockets and the remote-sensing observations from the ground with e.g. lidars. All atmospheric models, and ultimately numerous users of these models, will greatly benefit from the measurements obtained by QB50 in the lower thermosphere.
A QB50 Workshop will be held on November 17 thorugh 18, 2009, at the Von Karman Institute for Fluid Dynamics in Brussels, followed by a Project Kick-Off Meeting on November 19. At the close of 2009/early 2010, the selection of the standardized sensors will be made by the Sensor Selection Working Group, the selection of the initial orbital altitude and the initial separation between CubeSats in the network will be made by the Orbital Dynamics Working Group. Both groups will be composed of atmospheric physicists, experts from ESA´s Directorate of the Earth Observation Programme, and CubeSat PIs. QB50 is planned for launch in mid 2012. By that time, GENSO, the Global Educational Network for Satellite Operations, will be fully operational. It will comprise more than 100 ground stations in different parts of the world, providing nearly continuous uplink and downlink capability for all QB50 CubeSats.
