OBSERVATIONS FROM SCOTLAND                            28 May 2008                                GM1SXX

Batteries in Satellites?  Who needs em!

The ancient and interesting Oscar7 satellite has been happily operating without batteries for a number of years, since it 'came back from the dead'.  Granted, it's performance is severely hampered by the serious degradation of its solar panels, the glass cover-slides of which will have been darkened by exposure to severe cosmic radiation dose over several decades in a fairly high near circular, near polar orbit.

This subject of today's article is a brand new battery-less satellite that's nearing launch, the triple CUBESAT Delfi-C3.

 Normally I wouldn't waste my time chasing any of the 'me too' CUBSATS but this one is different. The designers have chosen a triple CUBESAT configuration which promises a decent power budget and rather than fly batteries, which on CUBESATS are usually of measly capacity, they have elected to use the space available for a number of experiments including I believe a linear transponder.  HURRAH!  At last a, 'Educational'  bird with some justifiable AMATEUR RADIO content to appeal to other than its designers.  Guys, I'd take my hat off to you , if I had one! Delfi-C3's primary science mission will take three months after which the amateur radio transponder will be turned on.  I'm very much looking forward to this mission.  The transponder will have a downlink power of around 400mw and if the bird ends up in its predicted 630km, circular, 97.91 degrees near polar,  sun-synchronous orbit, it should be a very useful bird indeed.

Possibly the most unusual thing about this mission will be the lack of any onboard batteries. The primary mission doesn't require batteries, so this will be a great opportunity to determine how useful a battery-less amateur radio satellite could be. 

Batteries have been the demise on many satellite missions, both amateur and commercial. The electronics on board satellites can be made to cope well with the conditions of operating in space. Chips can be rad-hardened to cope with the increased cosmic radiation dose and failures in the electronics are thankfully quite rare.  Batteries are rather different. Charger controllers (BCR's) can manage the changing of batteries to prolong their working lives and prevent outgassing that would eventually lead to loss of electrolyte but batteries rely on 'wet chemistry' and in a LEO bird in particular, they are subjected to many charge-discharge cycles per day. Add to that, the abuse of satellites by 'alligators' running excessive uplink power and you can understand why batteries have a hard life.  For sure, batteries have come a long way, and particularly in terms of power density. Modern batteries are much lighter and hold more charge than their earlier counterparts. The bad news is that they still use wet chemistry and need careful management in order to prolong their operating lives. Of course for DELFI-C3, there may well have been another reason for not using batteries and that could be increased space for experiments. One look at the photos shows that the designers have packed a lot of electronics into this little bird. 

The really good news about Delfi-C3 is that it carries a linear transponder.

DELFI-3 does not consist of 'standard' CUBESAT modules 'bolted together', instead it consists of a stack of PCB's connected by metal rods and spacers running through the board edges. This electronics assembly slides into a sheet metal sleeve that carries the deployable solar arrays. The arrays will be deployed after separation by cutting a Dyneema line using a resistor pack.

The body 'sleeve' also carries thermal control coatings. It's a VERY ingenious little craft.

Click on the thumbnails for High-res photos.

The reader is encouraged to check out the following pages.

DELFI-C3 Press Site    Main Site    Amateur Radio    Delfi-C3 News.

73 AL.
GM1SXX

The information below originates from the DELFI-C3 website.

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Wouter Jan Ubbels, PE4WJ, Delfi-C3's project manager of electronic systems and communications at the Delft University of Technology in the Netherlands reports that their satellite is being integrated and tested in preparation for launch in September or October, 2007. (This may slip to later in the year.. GM1SXX)

The Delfi team has posted photos of the satellite integration work at: http://www.delfic3.nl/photoblog/.

Delfi-C3 is a 3-unit CubeSat carrying redundant radio transceivers, connected to the antenna system by a hybrid combiner. Both transceivers consist of a UHF front end, a command receiver, linear IF, telemetry generator and the final stages capable of 400mW RF power.

Delfi-C3 contains no batteries because it's primary mission is to perform a solar cell and sun sensor experiment so the spacecraft will only be active when in sunlight.

The first three months of the mission will perform the science mission, in which the spacecraft will be transmitting 1200 bit/s  AX.25 telemetry on the primary or backup VHF downlink.  (See http://www.delfic3.nl for frequency information.)  Telemetry will be transmitted once per second.

A Java application will be available for download from the website to display telemetry in real time, and upload it to Delfi's central server in Delft. A soundcard application in Java is planned to be available to decode the BPSK signal. The MixW software package will also be compatible with the telemetry signal.

After three months, the linear transponder will be activated, with a  40kHz bandwidth. In transponder mode, a CW beacon will be active instead of BPSK telemetry.  It will transmit a message saying "hi hi de delfi-c3 delfi-c3". Since Delfi-C3 will transmit with only 400mW of downlink power, earth stations will need to prepare a good receive
system.

TLE's will be anounced on the website (http://www.delfic3.nl)  once they are available.  Preliminary parameters of the orbit are:
 + altitude: 630km circular
 + inclination: 97.91 degrees
 + sun-synchronous

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