The last couple of decades has seen growth in the commercial sector of companies providing services and hardware to the space industry – no longer the sole preserve of government departments. One such enterprise is the Swedish Space Corporation, which heads up a group of companies around the world specialising in satellite missions and space operations.
SSC Group cater for a wide variety of clients and their space programmes, and frequently launch sounding rockets and balloons from the Esrange facility just outside Kiruna in Northern Sweden. This is ideally situated in the middle of a large and unpopulated landmass, enabling easy recovery with little to no possibility of a rocket landing in the sea.
The technological challenges are many, as you would expect, and launching a balloon or sounding rocket (itself worth vast sums of money, let alone its payload) out of the Earth’s atmosphere requires absolutely meticulous preparation. Naturally a part of this lies in the craft’s GNSS guidance capabilities, which require the installation of a ‘space qualified’ receiver.
The sale and export of GNSS receivers falls under the limitations imposed by the Wassenaar Arrangement, controlled by forty-one countries who determine and maintain a list of technologies that require licensing and export controls. Founded in the 1940s as the Cold War was beginning, it was originally named CoCom (Coordinating Committee for Multilateral Export Controls) and was designed to control the export of weaponry from each member state.
The definitions of what should fall under CoCom became broader as new technologies came into existence – such that it was no longer a restriction solely on munitions and defence, but also on “dual-use goods and technologies.” In other words: devices, software, or the training and assistance to use them, that were being employed in everyday life but which could also find a place within an ordnance system.
CoCom was disbanded in the early nineties and replaced with the Wassenaar Arrangement in 1994. GNSS receivers were already included by this time, to ensure that they could not be used to guide ballistic missiles. Their functionality was restricted to a maximum speed of 1000 knots (approx. 1850kmh) and an operating altitude no higher than 18,000m. Anyone who needed this capability would have to apply for the relevant government licensing; once acquired they are then able to put them to use beyond the proscribed limits.
The balloons that SSC send up - primarily for atmospheric research, astronomy, and weather monitoring – don’t ascend particularly quickly or have a very fast course-over-ground speed; but they can reach 45km altitude so the receiver must be space qualified even if it doesn’t need high-dynamic capabilities. The rockets are a different matter, managing to travel at up to 12,600kmh and 800km altitude, so the receivers used in these craft are some of the very best available.
However, given that in space exploration and mission planning, nothing at all can be left to chance, SSC have a requirement to test how the receiver will cope with the launch and trajectory profiles of their rockets and balloons, and that the Wassenaar restrictions are not present. They now use a LabSat simulator to conduct these tests.
One issue they have encountered in the past is that after receiver firmware changes – for constellation updates, for instance, or to deal with the leap second – faults or bugs can be introduced. Gunnar Andersson, Senior Technical Advisor from SSC explains:
“We sometimes will make a request to a receiver manufacturer for changes to be made in their firmware, and sometimes they will issue new code simply because they are updating older chipsets. However we must always test to ensure that the latest firmware is space-enabled – because if a rocket gets up to 18,000m and suddenly loses its position, we have a fundamental problem and probably a mission failure. We also make small changes to our systems and these too need to be verified prior to launch. LabSat is ideal for this.”
Until relatively recently, Gunnar and his colleagues had been making use of a simulator located in Munich.
“This was OK,” he says “but access to it was difficult and it was a long way away so it was inconvenient. We really needed something at base. Using the LabSat on a trial was ideal and allowed us to ensure that it was the right equipment.”
Some issues needed to be overcome, however, before SSC were able to make full use of the LabSat’s capabilities. Whilst it was possible to create scenarios using the SatGen simulation software for a launch and orbit, further development was required so that the flight path could include a descent – something that had not been required in the past. Julian Thomas, Racelogic MD:
“We already have customers who use LabSat and SatGen for space applications – scenarios including launch and planetary orbit. However SSC found that the software wasn’t capable of creating a scenario that included their launch and descent pattern, along with their projected G-force and jerk rates, and the general high dynamics of their rockets.
“Once we understood the requirement we were able to make the necessary changes and within a week they were successfully testing.”
“Our rockets achieve altitudes of between 100km and 800km, with a launch acceleration of up to 20g and occasional jerk rates of up to 50g – very dynamic. The SatGen software couldn’t create this initially but we found the Racelogic support to be very good and they solved the problems quickly.
“Next we want to use our LabSat on a rig to test our antenna system. Most of our rockets spin during ascent for stability reasons, but this can cause a problem with the GPS signal as it introduces an extra phase shift. Our intention is to fit the antenna and LabSat to a turntable and record the signal which we can replay, in order to optimise our antenna and receiver settings.”