[amsat-bb] Community Survey Request -- crosslinks, multi-hop packet, and satellite DX

Zach Leffke zleffke at vt.edu
Sun Apr 2 21:29:51 UTC 2017

still working out details, so I can't give concrete answers.  But here 
is the spirit of the idea to try to answer your question (specifically 
about packet crosslink comms, not the S-E range measurements):

One decision that has been made is the Astrodev Lithium radio on UHF 
frequencies (radios have been bought).  Single UHF frequency per bird 
for uplinking and downlinking on (half duplex).  A second common/shared 
UHF freq for the crosslink.  FSK9600/AX.25 UI for all up and down links 
(I'm 99% sure the Lithium can't do AFSK1200, but still investigating, 
and if anyone on the list has experience with the Lithium I'm all 
ears).  Crosslink radio is the RFM69HCW, which is similar to MO-76's 
RFM22 radio, also on UHF freqs.

So a definitely frequency incompatibility with existing APRS fleet.

Other than the frequency incompatibility though, when switched into 
'weekend ops' mode, it would likely be standard FSK9600 up and down, 
AX.25 UI Frame, and APRS 'encoded' packets from/to the ground.  The 
crosslink is a more custom link that would be 'transparent' to the 
operator.  It is still FSK9600, but not AX.25 (based on RFM69HCW chips 
capabilities).  The students are currently playing with prototypes to 
work out the specifics for the crosslink data format.  Its easier to use 
the built in 'packet mode' on the chips, but more flexible (and harder) 
to use the 'transparent mode.'  We're currently examining both options.

So FSK9600/AX.25 UI/APRS encoded up, data decoded and updated per APRS 
digipeat standards, APRS message encapsulated for transport across the 
RFM69 crosslink, then APRS message updated again at the next satellite, 
then downlinked in FSK9600/AX.25 UI/APRS format. The original receiving 
bird will possibly also digipeat on the Lithium radio as well as sending 
to the crosslink radio to 'confirm' reception of the uplink, since the 
crosslink will be different freq, different protocol, still TBD though.  
so 3 freqs (one up, one across, one down), probably two protocols (one 
for up/down, one for across).

As far as software/hardware goes on the ground, standard TNCs capable of 
9600 baud comms should work, much like the current operating mode for 
ARISS packet.  So D700s/710s for sure should be able to play, as well as 
any radio with a 9600 baud data jack (and standard AX.25 TNC) should 
also work.  Any APRS software driving the TNC should work as well.  My 
hope is that any 'special software' that might ride on top of that would 
be available on github for the interested user (likely derived from the 
open source Fox Dashboard currently out there, but again, undergrad 
student project here).

For those interested in the S-to-E measurements, with enough G/T, some 
recommended HW would need to be obtained (according to a 'User Guide,' 
still to be written, but basically some cheap parts from 
Adafruit/Sparkfun) and the same Dashboard mentioned above would have the 
relevant code to use that HW and obtain the data and forward on to our 

Hope that helps clarify the CONOP.

-Zach, KJ4QLP

Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 4/2/2017 4:42 PM, John Brier wrote:
> Would it/could it/should it use the standard APRS mode on 145.825 MHz
> with ARISS path to take advantage of the ISS and PSAT digipeaters?
> That could allow for longer/more robust sat DX opportunities. If it
> were like the existing digipeaters that use APRS it would be easy for
> me to use with my Kenwood TH-D72 but if it required specially
> configured computer software that would be harder for me to use as I
> only have a portable sat setup now.
> 73, John Brier KG4AKV
> On Sun, Apr 2, 2017 at 4:31 PM, Zach Leffke <zleffke at vt.edu> wrote:
>> one clarification point.. all opinions are good, and I'm interested in them.
>> I meant all opinions, whether positive ('Hey that's cool, I'd play') or
>> negative ('stupid idea, will never work') related to the concept of
>> operations, are welcome.
>> -Zach, KJ4QLP
>> Research Associate
>> Aerospace Systems Lab
>> Ted & Karyn Hume Center for National Security & Technology
>> Virginia Polytechnic Institute & State University
>> Work Phone: 540-231-4174
>> Cell Phone: 540-808-6305
>> On 4/2/2017 4:26 PM, Zach Leffke wrote:
>>> Hello fellow satellite nuts!
>>> This email is to humbly request the opinions of those in the Amateur
>>> Satellite Community about the idea of setting new satellite DX records.
>>> Nothing formal, you can email on list or off list as you think appropriate.
>>> So here is the idea:  What if there were a constellation of three
>>> satellites (3 1Us), built by students (undergrads) at three different
>>> universities, but launched together and deployed from the same deployer that
>>> had crosslink packet communications built into the design.  Then, what if
>>> those birds were licensed via the Amateur Radio route (instead of
>>> Experimental as is the norm for most University birds, with some notable
>>> exceptions of course) allowing the entire global amateur satellite community
>>> to use the crosslink capability in an attempt to set new satellite DX
>>> records?
>>> Now, there is a primary science mission (pseudo-range determination as the
>>> constellation separates, different mass and drag profiles for each bird) so
>>> during the work week, science happens, but on the weekends, the
>>> constellation is made available to the community for crosslink packet comms.
>>> Additionally, if your setup has enough G/T to monitor the lower power
>>> crosslink comms, and with a little bit of technical tweaking to your ground
>>> station (you would need GPS based PPS to measure propagation time, maybe
>>> ~$100 invested), you could participate in Space to Earth pseudo-range
>>> measurements that would contribute to a secondary orbit determination goal.
>>> To be clear, the up and down linking for the satellite DX attempts would be
>>> standard FSK9600, AX.25, so as long as your station can do that, you can use
>>> the crosslink path for multi-hop comms.  Its only the S-to-E pseudo range
>>> measurement that would require a bit of additional HW.
>>> Does this sound interesting?  Would you as an operator be interested in
>>> multi-hop satellite packet comms?  Do you think this type of operating
>>> schedule is acceptable (weekends) to justify Amateur Radio licensing instead
>>> of Experimental?  Would you be interested in contributing to the science
>>> mission (S-to-E pseudo-range measurement)?  Would you track the telemetry
>>> downlinks and forward that data on to the mission data warehouse?
>>> Any and all opinions, good or bad, are welcome.  Again, on or off list as
>>> you see appropriate is fine with me.  My goal with this is to get a sense of
>>> what the community's opinion on this topic is and if the constellation were
>>> available for use, how much interest there would be in this type of
>>> operation.
>>> Thanks in Advance!
>>> Sincerely,
>>> Zach, KJ4QLP
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