Itâ€™s been a busy weekend for the Chinese space industry! On Saturday the China National Space Administration (CNSA) launched three new high resolution Gaofen-1 optical Earth Observation satellites from the Taiyuan Satellite Launch Centre in the north western Shanxi Province of China.
The three new satellites, called Gaofen-1: 02, 03 and 04 respectively, were launched intoÂ sun-synchronous 645 km orbits at 03:22 GMT on the 31st March. They all carry two high resolution cameras, which are capable of acquiring multispectral data at eight metre spatial resolution, and this improves to around two metre resolution for the panchromatic band.
They are believed to be the next generation of the Gaofen-1 satellite which was originally launched on the 26th April 2013. It also carried the two high resolution cameras, but alongside had a wide field imager which is not included on the latest launches.
Saturdayâ€™s satellites will operate as a constellation offering a revisit time of two days, with the orbit repeating itself every fifteen days. However, for the foreseeable future, the constellation will also include the original Gaofen-1 satellite and will provide an impressive one-day revisit time and eleven day global coverage. The data from these satellites will be used for applications such as disaster warning, environmental monitoring, construction, transportation and emergency response.
The contrast to these launches was the re-entry of the Tiangong-1 space lab into Earthâ€™s atmosphere on Monday 2 April at 00:15 GMT. Tiangong-1, which translates as Heavenly Palace 1, was originally launched on 29 September 2011. It had a two year operational lifecycle and has orbited the Earth unmanned for almost five years. During 2017, it was announced that the CNSA no longer had any control over Tiangong-1 and that it would gradually fall back to Earth over the coming eighteen months.
This satelliteâ€™s demise has caused a lot of public interest. Due in part to greater interest in space debris, but also due to the size and difficulty of determining exactly where it might fall to Earth!
End of life satellites falling back to Earth isnâ€™t a rare occurrence, on average around one satellite each week enters our atmosphere and over a year this equates to around 100 tonnes of metal. The vast majority of this burns up in the atmosphere and apart from offering an interesting occasional fireball backdrop to the sky, it has no impact. Occasionally some of the debris does fall to Earth although most of this tends to be over water.
The difference here is size and mass. Tiangong-1 was 12 m long with a diameter of 3.3 m and had a launch mass of 8,506 kg â€“ although obviously this will be less now.
Tracking space debris is becoming more and more important, and there were 14 space agencies/organisations, collectively known as the Inter Agency Space Debris Co-ordination Committee, tracking Tiangong-1 including NASA, ESA, European national space agencies, JAXA, ISRO, KARI, Roscosmos and the Chinese CNSA themselves.
Despite all of this effort focussed on Tiangong-1, it was very difficult for this group to forecast what debris might fall to Earth and where it might hit. Even when they confirmed entry, it was suggested that debris could hit somewhere in the South Pacific which is a very vague, and large, area.
Generally, it is being reported that most of the space lab burnt up in the atmosphere. However, despite all the effort placed tracking the object in space, there is no similar arrangement to track any debris that might reach the Earthâ€™s surface and so no-one is sure how much, if anything, actually made it back. It may be the coming days, weeks or even months before we find anything that hit land and we may never know if it did hit the ocean.
This weekend just goes to show that the space industry is constantly changing.