QB50计划
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Presentations were made on other projects involving constellations of small satellites that were open to international cooperation: the QB50 mission, an international network of 50 double CubeSats for multi-point, in situ, long-duration measurements in the lower thermosphere and for re-entry research; the CANEUS shared small satellites for collective safety, security and prosperity, and an effort to create a low-cost, internationally shared space-based data collection and distribution backbone with exceptionally low barriers to entry for participating nations; and the six-satellite Bright-star Target Explorer (BRITE) constellation (with two satellites each to be provided by Austria, Canada and Poland), which would conduct high-precision photometry of bright stars.
Mission objectives
QB50 has the scientific objective to study in situ the temporal and spatial variations of a number of key constituents and parameters in the lower thermosphere (90-320 km) with a network of 50 double CubeSats, separated by a few hundred kilometres and carrying identical sensors. QB50 will also study the re-entry process by measuring a number of key parameters during re-entry and by comparing predicted and actual CubeSat trajectories and orbital lifetimes.
Space agencies are not pursuing a multi-spacecraft network for in-situ measurements in the lower thermosphere because the cost of a network of 50 satellites built to industrial standards would be extremely high and not justifiable in view of the limited orbital lifetime. No atmospheric network mission for in-situ measurements has been carried out in the past or is planned for the future. A network of satellites for in-situ measurements in the lower thermosphere can only be realised by using very low-cost satellites, and CubeSats are the only realistic option.
Why explore the lower thermosphere
The lower thermosphere (90-320 km) is the least explored layer of the atmosphere. Atmospheric Explorers were flown in the past in highly elliptical orbits (typically: 200 km perigee, 3000 km apogee); they carried experiments for in-situ measurements but the time spent in the region of interest below 320 km was only a few tens of minutes. Nowadays, sounding rocket flights provide the only in-situ measurements. While they do explore the whole lower thermosphere, the time spent in this region is rather short
(a few minutes), there are only a few flights per year and they only provide measurements along a single column. Powerful remote-sensing instruments on board Earth observation satellites in higher orbits (600–800 km) receive the backscattered signals from atmospheric constituents at various altitudes. While this is an excellent tool for exploring the lower layers of the atmosphere up to about 100 km, it is not ideally suited for exploring the lower thermosphere because there the atmosphere is so rarefied that the return signal is weak. The same holds for remote-sensing observations from the ground with lidars and radars.
The multi-point, in-situ measurements of QB50 will be complementary to the remote-sensing observations by the instruments on Earth observation satellites and the remote-sensing observations from the ground with lidars and radars. All atmospheric models, and ultimately thousands of users of these models, will benefit from the measurements obtained by QB50 in the lower thermosphere.
Advantages of a low-Earth orbit
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,
The orbit of the International Space Station (ISS) is usually maintained between 335 km (perigee) and 400 km (apogee). If a network of many CubeSats is launched into an orbit that is above that of the ISS there is a danger of collision with the ISS when the orbits of the CubeSats decay due to atmospheric drag. If the initial orbit of the CubeSats is below 330 km there is no danger of collision.
All 50 CubeSats will be launched from Murmansk in Northern Russia into a circular orbit at about 320 km altitude, inclination 79°. Due to atmospheric drag, the orbits of the CubeSats will decay and progressively lower and lower layers of the thermosphere will be explored without the need for on-board propulsion, 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. 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.
On all other missions, CubeSats are a secondary payload and they have to accept the orbital requirements of the primary payload (usually higher orbital altitudes) which are often not ideal for the CubeSats. On QB50, the CubeSats are the primary pa
yload.
Programmatics
For the QB50 network, double-unit CubeSats (10x10x20 cm) are foreseen, with one unit (the ‘functional’ unit) providing the usual satellite functions and the other unit (the ‘science’ unit) accommodating a set of sensors for lower thermosphere and re-entry research. The sensors will be identical for all 50 CubeSats. 38 CubeSats are envisaged to be provided by universities in 22 European countries, 8 by universities in the US, 2 by universities in Canada and 2 by Japanese universities. Interest to participate in QB50 has also been expressed by over 20 universities in Australia, Brazil, Chile, China (The People‘s Republic of China), Egypt, Israel, Peru, Puerto Rico, Russia, South Africa, South Korea, Taiwan, Turkey and Vietnam.
The QB50 Project will be kicked-off on 27 July 2011 during the Second QB50 Workshop at VKI, provided that the European Commission selects the QB50 Project. A proposal was submitted to the 4th Space Call in the 7th Framework Programme of the EC by VKI and several collaborating institutions on 25 November 2010.
All 50 CubeSats will be launched together on a single launch vehicle, a Russian Shtil-2.1. The initial total network size in orbit is determined by the deployment sequence (one CubeSat every orbit or every 2 or every 3 orbits) and the separation speed, and can be selected anywhere between 10,000 and 20,000 km. The launch is planned for June 2014. 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 CubeSats.
In 2011, the selection of the standardised sensors will be made by the QB50 Sensor Selection Working Group, the selection of the initial orbital altitude and the initial separation between CubeSats in the network by the QB50 Orbital Dynamics Working Group.
The intention is to provide free of charge to the participating CubeSat teams the launch cost, the custom-designed deployment system, the standardised sensors for atmospheric research, launch services and interfaces to the launch vehicle authorities, environmental testing (if requested), transport of the 50 CubeSats to the launch site and CubeSat checkout testing during the launch campaign. This is very attractive to the CubeSat community and there is a lot of interest to participate in QB50.
Participating CubeSat teams are free to use any space left in the ‘functional’ unit of the double CubeSat for a technology package or a sensor of their own choice. The teams are expected to supply the required documentation in a timely manner, participate in the major Project reviews, support the environmental test campaign (but not the launch campaign), operate their CubeSat in orbit and provide their science data and limited housekeeping data within 6-9 months after launch to the QB50 Data Processing and Archivin
g Center.
How can a CubeSat team participate in QB50?
The first step for a CubeSat team to get involved in QB50 is the submission of a Letter of Intent (LoI). Such an LoI is not a commitment, it is only an expression of a serious interest in participating in QB50. The LoI briefly summarises the QB50 Project, specifies the responsibilities of the CubeSat team, for example, the provision of a flight model CubeSat by a certain date and later the operation of the CubeSat in orbit, and specifies what is expected from the managing organisation VKI, for example, the provision free of charge of the launch vehicle and the sensors for atmosperic research. A draft LoI can be obtained from C. Asma (asma@). Up to now (20 January 2011), 60 LoIs have been received.