Post Tue Jul 19, 2011 9:47 am

The SBSS system becomes reality

The SBSS system became reality after the first satellite has been sent to space on 26th of September 2010.
Six years ago, in March 2004, US Air Force has organized a competition for the building of a new system which should detect and track the objects in space, equally if they are active satellites or orbital debris. This data should complete the US Surveillance Network data which currently surveys approximately 19.000 objects from space and will assure the skeleton for what is generic called Space Situational Awareness.
The collected information will mainly be used for military operations but not only, it could equally help the development of the space debris avoiding strategies onboard the ISS or the preparation of the orbital maneuvers for the commercial satellites which should avoid Iridium 33 type events.

The first SBSS-1 satellite (together with the entire ground facilities) part of the Block 10 contract, has been built with an estimated cost of 823 millions dollars-40% going to the satellite itself and another 35 millions paid for the launch.
Northrop Grumman Mission Systems took the first phase of the contract (mission area prime integration) and the Boeing Space Systems & Ball Aerospace the second phase (development of the satellite and the operational aspect).

The new satellite has been built based on a BCP2000 platform (Ball Configurable Platform), weights 1031 kg at launch time and will operate for approximately 7 years. BCP2000 is a versatile platform, developed by Ball Aerospace in order to integrate any kind of Earth observation instrument, and has a very good three axes stable, fast pointing and responsive attitude and orbit control system.

The active control is done using a hydrazine thruster system and the sensor components include GPS receivers, 2 star cameras etc.
The power is generated using 2 solar panels each having 3 independent sections, being free for rotation on two of the axes and being guaranteed to generate at least 840W at EOL (end of life).
The communication is ensured by a powerful X band antenna with a telemetry downlink rate of up to 320Mbp and by an S band antenna for commanding uplink.
We have to mention that the first satellite built on a BCP2000 platform was the Cloudsat launched in 2006, a meteorological satellite operating a special radar for the measurement of the altitude and properties of the clouds.

Coming back to SBSS-1, it should be said that, like in most of the cases of this type when new programs are started, the real agenda was completely different of the initial plan, the launch initially programmed for 2007, slipping finally to September 2010 this mainly due to the delays in the satellite development program and later to the problems accounted with the launcher.

Launched from the Complex 8 of the Vandenberg Air Force in California at 04:41 UTC, the Minotaur 4 rocket placed the SBSS-1 satellite 15 minutes later into a transfer orbit with the height of 540 km and the inclination of 97.99 degrees. From this orbit, the satellite will be moved to the final operational orbit- circular, sun synchronous with the altitude of 630 km.
After this operation is accomplished, it will take US Air Force another 90 days, spent for testing and calibrations, before receiving a full operational satellite.

It was the first orbital flight for a Minotaur 4 rocket after the earlier April suborbital flight of a Minotaur 4 Lite rocket having onboard the Hypersonic Technology Vehicle HTV-2a.
Derived from the old 70s Peacekeeper missiles which were dismissed from operation later in 2005 as part of the Start 2 treat, Minotaur 4, built by Orbital Sciences Corporation, is a 23.8 m long rocket, with a diameter of 2.34 m, a weight of 83 tones and being powered by 4 solid fuel engines.

First stage, built by Thiokol/ATK is powered by a SR118 engine with traction of 2200kN, the second stage built by Aerojet is powered by a SR119 engine having a traction force of 1365 kN, and the third stage built by Hercules Incorporated is powered by a SR120 engine and 329 kN.
The fourth stage is configurable and makes the difference between the standard Minotaur 4 and the Minotaur 4 + powerful version. For the first version, an Orion 38 engine with 32.2 kN of thrust is used-built by the same Hercules Incorporated and used in the past for the Pegasus and Taurus rockets, while for the second version it is used a Star-48V engine built by Thiokol/ATK with 68.6 kN.
The rocket is able to lift into a LEO orbit a satellite weighting up to 1735 kg. The next flight of the launcher is expected for 2011 and will carry onboard a new HTV experiment, the version 2b.

So how does it work the SBSS system? Compared with the terrestrial similar systems (either we speak of radars or telescopes) tracking the object from a space point has the advantage of not being affected by the meteorological conditions, the atmospheric interferences or the moment of the day. The orbital position ensures a longer visibility for a target and not only when it crosses an observation point i.e. as for a ground station.
The idea is not new but it continues the MSX project (Midcourse Space Experiment) launched in 1996. One year later in 1997, left without the cryogenic fuel that was meant to keep the low temperature of the focal plane inside the principal scientific instrument Spirit 3 (Space Infrared Imaging Telescope), the MSX satellite lost the infrared sensor but continued to function with the SBV (Space Based Visible) a sensor capturing normal, visible images.
This functioned until June 2008 when it brooked and finished the MSX mission.

In comparison with the MSX project, the new SBSS-1 brings in attention a 30 cm telescope placed on a platform which can rotate on two of its axes -which means it can assure an individual rotation of the instrument without the need of reorienting the entire spacecraft.
Having a large visual field and 3 component lenses, with a focal plane of 2.4 Mpixels and with a reduced interference of the electronics, the new telescope brings 2 times more sensitivity, 2 times more speed in the detection of possible orbital conflicts and 10 times more processing capacity.
Last but not least, it can monitor not only the geostationary satellites but also the ones from medium MEO orbits or high HEO orbits around the Earth.