[amsat-bb] Re: CubeSat launch 27Mar07 6:46:35UT

[W.J. Ubbels]

Hi all,

with the discussion about the upcoming CubeSat launch in mind, and since 
we have not been able to update our website regularly just a couple of 
words from the Delfi-C3 office:) We are currently very busy integrating 
the spacecraft. Although it's a 3-unit CubeSat, it's still very, very 
small... so that gives some headaches sometimes:)

Delfi-C3 carries two redundant (primary and backup), and almost similar 
radio transceivers, connected to the antenna system by a hybrid combiner 
which also takes care of generating the correct phase relationship 
between the antennas. Both transceivers consist of a UHF frontend, a 
command receiver, linear IF, telemetry generator and the final stages 
capable of 400mW RF power. Each transceiver is housed on a single 96 x 
90mm board. Our tight power budget allows only one transmitter to be 
active at all times.
Delfi-C3 contains no batteries, one of the reasons being the fact that 
it's primary mission is to perform a solar cell and sun sensor 
experiment which depend on the presence of sunlight. Therefore, the 
spacecraft is only active when in sunlight. Of course, since there's no 
such thing as a free lunch, this has made the design complicated on an 
other level, especially software-wise. (proper boot-up sequences etc.)

The first three months of the mission are what we call the "science" 
mission, in which the spacecraft will be transmitting 1200 bit/s AX.25 
telemetry on either the primary or backup VHF downlink frequency, 
frequency information can be found on our website http://www.delfic3.nl
Telemetry is contained in UI frames, with roughly one frame every 
second. All detailed information regarding telemetry will be announced 
on the website as well.
Modulation is Raised Cosine (in time) BPSK, more or less similar to that 
of the Microsats. Therefore, owners of a PSK TNC such as the NB-96/PSK-1 
combo can use them with the software (written in JAVA) that we will 
supply (will be made available via our website). This software package 
connects to the TNC in KISS mode, and allows you to display telemetry in 
real time, and upload it to our central server in Delft. Since PSK TNC's 
are not that common anymore in today's shacks, and PC's are, we are 
developing a soundcard application in JAVA that can be used with the 
telemetry decoding software. An other option is to use the popular mixw 
program, which can demodulate BPSK and emulate a KISS TNC.

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.  This CW beacon is actually transmitted as double 
sideband, with two carriers spaced 1200Hz apart. It will transmit a 
message saying "hi hi de delfi-c3 delfi-c3". Beacon power is set at 10dB 
below transponder PEP, users are requested to limit uplink power to the 
necessary minimum to maintain a proper downlink, while not driving the 
AGC excessively high. Since Delfi-C3 can indeed be considered a 
"hardsat", with only 400mW of downlink power, it is wise to pay 
attention to a good receive system. The transponder IF is very basic, 
consisting of ceramic filter to set the bandwidth, an amplifier chain on 
10.7MHz and a fast-attack / slow-decay AGC. You can listen to an audio 
clip of the first transponder test QSO (in Dutch...) between PA3WEG (who 
designed the local oscillators) and PE4WJ at 
http://www.delfic3.nl/wavs/Delfi-C3_transponder_link_with_QRM.mp3
(Mind you, there is some QRM in the file that might sound a bit like 
Leila, but this is pure coincidence)

With regard to the orbit, TLE's will be anounced on the website 
(www.delfic3.nl) once they are available, for now I can give the 
following preliminary parameters:
-altitude: 630km circular
-inclination: 97.91 degrees
-sun-synchronous
-LTAN: 10:30

Ok, back to satellite building now:)

Best 73,

Wouter Jan Ubbels PE4WJ

-- 
W.J. Ubbels MSc.
Delfi-C3 project manager electronic systems and communications
Faculty of Aerospace Engineering
Delft University of Technology
www.delfic3.nl
PE4WJ