We Have Identified SkyCube
I didn't expect to write this update.
For most of the past 3 weeks, there had been no definitive contact with SkyCube from any ground station. Although some 915 MHz signals were heard when a candidate object passed overhead, none of them were conclusive. We've been unsure which of the 5 objects released from ISS on Feb 28th is really SkyCube, and all information provided to us by other teams indicated that the official designation of 39569 = SkyCube is wrong.
On March 14th, a Russian amateur radio operator (Dmitry Pashkov, UB4UAD) reported a 915 Mhz signal which looked suspiciously like a SkyCube telemetry tweet. But the signal was not decoded, and the date/time it was received, plus the direction which his antenna was pointing, indicated that the signal came from the wrong satellite (specifically, 39569, identified as LithuanicaSAT-1).
On Friday, March 14th, we used the 60-foot radio dish at Stanford University to attempt contact. No response was received. We had been preparing to declare the satellite lost.
Back from the Dead
This all changed last night. While reviewing our server logs, we discovered that the Central California ground station had recorded a response from SkyCube on 27 March 2014 at 07:52:47 UTC. At that time, the station was pointed at object 39567, at an elevation angle of about 33 degrees and a range of 700 km.
The ground station received a 915 MHz signal, which was was digitized, decoded, and passed to our server along a secure SSL connection. It was an encrypted 16-byte sequence. Our server decrypted the sequence to the following meaning:
Battery voltage = 8250 mV
Solar panel current = 0, 0, 0, 1, 0 mA
Date/Time = 2014/01/27 14:55:15
System uptime = 2301542.12 seconds
Processor temperature = 16.7 degrees C
Here's what this means: the battery was near fully charged. The solar panel current readings, all near zero milliamps, make sense because the satellite was passing over the ground station at night. The low processor temperature is consistent with this - we see temperatures of 25 - 40 C when testing our satellite in sunlight.
SkyCube is programmed to think it's midnight, January 1st, 2014 when it first powers on. If this happened when SkyCube deployed on 28 Feb 2014 at 07:30 GMT, then it would think the current date is Jan 27th when the transmission was received on March 27th. (We never sent it a SET_TIME command to tell it the correct date.) The system uptime of 230154 seconds means that the processor has been running continuously for 26.7 days.
This data packet came over an SSL-secured connection from the IP address of the Central California ground station. To get passed to our server, its first 8 bytes had to be correct. The packet decrypted and passed CRC validation. The decoded data was sensible. There's just no way this could be anything but a response from the real SkyCube in orbit.
Why now? What's next?
SkyCube is still alive, in space, and has been operating for at least 27 days. And we know know, definitively, that it's NORAD object 39567. But why are we only hearing from it now?
Partly, it's because we've spent a lot of time listening to the wrong objects. Until now we could not prove which one was ours. And we now also suspect that only one or two of SkyCube's solar panels deployed on day 1. That would explain why so many initial contact attempts failed. Only one or two radio antennas were exposed, and the satellite had to be facing just the right way to pick up a signal from the ground.
Right now, we're sending commands to release the solar panels. Those may or may not work. If the solar panels & radio antennas remain stuck, then occasional, sporadic broadcasts may be all we ever get. But this is still a huge improvement from where things stood 24 hours ago. We now know definitively which satellite is ours, and where it's located at all times. We know that it's been operating for many weeks and survived hundreds of orbits. We know that the ground stations and server infrastructure designed to talk with SkyCube's C2 radio on orbit can actually do so; this had not been proven before.
And we also now know that an amateur team can build, manifest, and orbit a satellite that functions in space, on a shoestring budget funded by volunteers around the world, a few dollars at a time. No matter what happens next, that's groundbreaking history that you helped create, and you should all feel proud to be a part of it.
Thanks for making it happen.
-Tim, Rouslan, Scott, Kevin, Mark, and the rest of Team SkyCube