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UoSAT-12's legacy of innovation

Launched 17 years ago, UoSAT-12’s influence on space exploration lives on.
UoSAT-12 was an in-house experimental technology minisatellite for SSTL, designed to test and demonstrate a number of new technologies and techniques to provide enhanced capabilities from the Company’s previous 50kg microsatellite missions.  UoSAT-12 was launched on 21 April 1999 from the Baikonur Cosmodrome and was the first ever commercial mission to be launched on the new DNEPR rocket, created by converting the former Soviet Union’s arsenal of SS-18 Satan missiles into launchers. 

UoSAT-12 in flight configuration


Let’s go back to the genesis of the UoSAT-12 mission.  It arose out of a desire to trial some new technologies and a new, larger platform structure capable of carrying more advanced and demanding payloads – with the hope and expectations that the mission would advance SSTL’s market position with a significant step-change for future customers.  It was a bold step for the Company at the time, and a huge internal investment in R&D but, in retrospect, how did UoSAT-12 perform against such lofty ideals?  Rather well, as it turned out.

Achievements in orbit and enduring legacies for space missions

Showing our pioneering mettle, SSTL crammed a whole lot of new ideas into the design and payloads for UoSAT-12.  We’ve been examining the legacy of the mission and we’d like to think that we aren’t over-stating its achievements with our conclusion that it was a ground-breaking small satellite.  Judge for yourselves – here’s our roundup of UoSAT-12’s impact on SSTL….and, more widely, on space exploration.

The first satellite to have a web address in orbit

Engineers from NASA’s Goddard Space Flight Centre Operating Missions as Nodes on the Internet (OMNI) project worked with SSTL to upload standard Internet software modules to UoSAT-12’s reprogrammable onbard computers after launch.  SSTL’s ground segment engineers installed a standard commercial Internet router in our Guildford ground station and the software was activated on 10th April 2000.  On a subsequent pass our spacecraft operators obtained UoSAT-12’s responses to “pings”, confirming that the spacecraft was operating as a node on the Internet. 

The OMNI team verified automatic spacecraft clock synchronisation using Network Time Protocol, standard File Transfer Protocol, and Simple Mail Transfer Protocol to demonstrate automated file store-and-forward.  On 25th January 2001 UoSAT-12 became the world’s first web server in space when HTTP was used to transfer real-time telemetry and stored image data directly to the user using a standard web browser. 

Satellites had previously been used to provide simple delivery of data bits to support the Internet, but this was the first time that a spacecraft had its own Internet address and was a fully active node on the Internet. 

The OMNI experiment successfully demonstrated that a spacecraft could use standard Internet protocols for end-to-end communications, opening up the way for collaborative future missions involving multiple satellites.

SSTL continued to work with NASA and with CISCO on studies looking at the use of internet protocols in space and, in 2003, SSTL launched our UK-DMC1 satellite which flew a CLEO Cisco router and demonstrated the first use of the Interplanetary Internet v6 in space.  

Merlion Communications Package

The Merlion Communications Package was developed by Nanyang Technological University in Singapore in collaboration with SSTL and was demonstrated in orbit by UoSAT-12.  The Merlion module was, at the time, the most sophisticated communications equipment flown on a Surrey satellite. It demonstrated a new communications technology by employing a frequency-agile digital S-band downlink and a frequency-agile digital L-band uplink, with satellite antennas shaped to provide equal power flux density across the satellite footprint.  The purpose of the experiment was to improve communications coverage from low Earth orbiting satellites in equatorial regions. 

The Merlion Commmunications module under development

Propulsion systems

UoSAT-12 flew two separate propulsion systems; a compressed nitrogen cold gas system and an experimental Electric Propulsion System (EPS) developed by the Surrey Space Centre, which made use of Nitrous Oxide (N2O)  as a propellant in an electrically-heated resistojet thruster for the first time.  

The compressed nitrogen cold gas system was successfully configured to operate in an experimental autonomous mode via new software developed by the Microcosm Corporation. 

The nitrous oxide tanks (red) integrated to the UoSAT-12 structure

The water and nitrous oxide were superheated over a resistive heater element, with 100W of input power resulting in hot gas being expelled through a nozzle to produce 50mN of thrust.  Although we have not used nitrous oxide again as a propellant, it did validate the use of resistojets on small, power-limited spacecraft and led to the development of the low power resistojet that we use today with higher performance xenon and butane systems, currently flying on 23 spacecraft in orbit. 

UoSAT-12's resistojets

Spacecraft structure

SSTL designed a new nonagon spacecraft structure for UoSAT-12 – the first and only 9-sided spacecraft launched as far as we know.  The rationale for the departure from our previously rhomboid platforms was that UoSAT-12 was essentially configured around three of our SSTL-50 microsatellite avionics structures, each carrying different payloads.  The easiest, cheapest, and most efficient way to combine three cubes was to fill in the gaps with solar panels for maximum power, and there you have it – a nine-side spacecraft design! The central void provided an area particularly suitable for the long focal-length camera taking high resolution (for that time) images of Earth. 

UoSAT-12 structure - a nonogon

Microsatellite avionics modules awaiting integration into UoSAT-12

Since then, SSTL has adopted a similar approach in the design of our SSTL-300 series spacecraft, but in this case using a six-sided structure designed to fit efficiently in multiples within a cylindrical launcher fairing, and flying 2.5m resolution imaging optics as the main payload in the central void. 

SSTL-300 (NigeriaSat-2) - a hexagonal structure, encasing the 2.5m optics

New small satellite imaging capabilities

UoSAT-12 flew 3 imaging systems:

A wide angle multi-spectral camera with a 4.8mm focal length capable of capturing a 1000km x 10000km image using  a NIR filter to provide strong contrast between the land and the sea.

A wide angle panchromatic camera using a commercial long focal length lens and a 2-dimensional CCD detector array capable of capturing a 10km x 10km image with 10 metres ground resolution using a step-and-stare operation. 

A multi-spectral imager that comprised of two cameras with rotating filters working in tandem and angled to provide a combined coverage of 60km x 30km with a spatial ground resolution of 32 metres (GSD). 

UoSAT-12 acquired its first image on 28 April, 1998 over Texas.  The success of the imagers demonstrated a breakthrough in the order of magnitude reduction in cost for high resolution space imagery – and the technology subsequently led to the first of the constellation of Disaster Monitoring satellites, AlSat-1A  which provided 32m GSD with a wide imaging swath of 600km. 

An image of the Grand Canyon taken from UoSAT-12. Click to enlarge.

In January 2000, our operators used the spacecraft’s advanced and agile Attitude Orbit Control System to point the multi-spectral camera away from the Earth, towards the Moon in order to capture a lunar eclipse

The first SSTL GPS receiver

UoSAT-12 hosted the first flight of SSTL’s own developed SGR-20 space GPS receiver, supporting 5 GPS antennas on the satellite – four on the top and one nadir antenna.  It was a key demonstrator for SSTL’s SGR series of Space GPS Receivers, and sponsored by ESA.  We were able to refine the receiver functioning to suit operation in the orbit environment, and show orbit determination accuracies of around 5 metres.  

The first subsequent customer was the ESA PROBA-1 mission, launched in 2001 carrying an SGR-20, making direct use of the experimentation, development and demonstration on UoSAT-12.  PROBA-1 and its SGR-20 GPS receiver are still operating today, more than 15 years after launch.  The SGR-10 and SGR-20 receivers have been used on most SSTL satellites since then for determining position, velocity and time, as well on other external missions.

The multiple antennas on the UoSAT-12 were used for an important demonstration of GPS attitude determination.  Signals picked up simultaneously by two or more antennas register a phase difference that is related to the orientation, or attitude of the satellite. The experiment showed that an attitude determination accuracy of around 1 degree was possible, completely independent to the other attitude systems on the UoSAT-12.  Real-time processed GPS attitude determination was demonstrated later in orbit on the Topsat-1 mission.  GNSS attitude determination has not been widely adopted by satellites in part due to the rise of star trackers, but there is still an niche where star-trackers are not present.  It is expected that GNSS attitude performance will increase with the availability of multiple GNSS constellations (GPS, GALILEO, GLONASS, Beidou).

Finally UoSAT-12’s downward pointing GPS antenna was employed in an attempt to demonstrate a new remote sensing concept called GPS-Reflectometry. Although the UoSAT-12 experiment did not succeed in this respect, it led onto the GPS Reflectometry experiment on the UK-DMC1 mission that showed the concept was feasible, and in turn this led onto the revolutionary SGR-ReSI instrument on TechDemoSat-1, which will also be flown on the upcoming NASA CYGNSS mission.

Autonomous orbit control

UoSAT-12 was the first (civilian) satellite to demonstrate autonomous orbit control using on-board GPS receivers and the propulsion system to maintain a drag-free orbit over a period of months. 

In September 2000, the autonomous orbit control system, developed with Microcosm USA, operated continuously for 29 days and demonstrated accurate autonomous in-track orbit control under the adverse conditions of long GPS outages and an initial halving of thrust, followed by a return to full thrust midway into the run. Drag-free operation is of use for some scientific applications, and to constellations with rigid phasing restrictions. The experience gained in developing the required autonomous orbit and attitude determination and control has been invaluable to SSTL for subsequent missions.

UoSAT-12 demonstrated a major step in precision minisatellite pointing and attitude control using four reaction/momentum wheels that enabled agile high resolution imaging using the on-board 2-dimensional CCD array camera.

SSTL missions derived from UoSAT-12’s legacy technology

The UoSAT-12 mini-satellite design was a pre-cursor for the SSTL-100 platform developed for the Disaster Monitoring Constellation (DMC), an internationally co-ordinated constellation of Earth observation satellites.  The SSTL-100 platform has been the basis for 10 missions: AlSat-1A, Beijing-1, NigeriaSat-1, BilSat-1, UK-DMC1, Deimos-1, UK-DMC2, exactView-1, NigeriaSat-X, and AlSat-1B.

The imaging capability on board UoSAT-12 influenced the design of the wide-swath DMC constellation satellites, the 4m Beijing-1 and the 1m DMC3/TripleSat spacecraft.

Not just a game-changer for space technology, the UoSAT-12 mission shaped careers

UoSAT-12 provided over four years of operational life, before all fuels on board the spacecraft were expended and the gravity gradient boom was deployed to reduce orbital lifetime   The spacecraft was finally retired and operations ceased in 2003, however the design and technology legacy of UoSAT-12 has most definitely lived on – and the experience of working on such a demanding and pioneering design has had a lasting impact on those spacecraft engineers who were involved in the mission.  Chris Jackson, now a Chief Systems Engineer here at SSTL, worked on UoSAT-12 and says

“I believe that UoSAT-12 was one of the key developments in SSTL’s history and helped shape my career. It got us involved with a number of studies with NASA that led on to work on the use of internet protocols for satellites and, ultimately this led into funding for the Disaster Monitoring Constellation.  The project was complex and pushed us to the edges of possibilities, but we all learned a great deal and I have used my experience in small satellite design on many of the most exciting and innovative of SSTL’s missions since then – including GIOVE-A and the Galileo FOC payloads, and I’m now working on the platform for the Eutelsat ‘Quantum’ geostationary communications mission.” 






07 June 20160 Comments1 Comment

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