Just when everyone thought the story of IMAGE was going to have a Hollywood ending she has displayed a knack for dramatic flare.
On 2018-02-25 at 02:19:19.459 UTC IMAGE ended an approximately 48 hour series of off/on sequences of its TT&C beacon and returned to silence. It’s been over two days now and the beacon has not returned to the air.
The signal sequence in the image above shows the last few minutes of IMAGE’s transmissions.
IMAGE Reminds us “Space is Hard”
Following my report to Dr. Richard Burley at NASA on Friday, February 23rd that IMAGE had suddenly began a series of off/on sequences the spacecraft began exhibiting more of these events more often. The average off period for me in the hours prior to her switching off was about 130 seconds.
At first we thought that the behaviour may be related to the antenna orientation with respect to the observer (me). However, Cees Bassa reported the same sequence of events at the same time as my observations that I shared with NASA. The first image below shows the capture of IMAGE from my station and the image under it shows the same portion of the signal as observed by Cees in the Netherlands. Clearly this is not an antenna shadowing issue.
On Monday, February 26th, Joseph Cavaluzzi, SSMO Systems Engineer, Goddard Space Flight Center (GSFC), reached out advising he had been assigned by Dr. Burley to look into the anomaly. Joseph took my GPS coordinates and is running the math to exclude antenna shadowing as a possibility.
From our experience shadowing of the antenna does not display a sharp step cutoff in signal especially from a slowly rotating spacecraft like IMAGE. The other fact was two widely spaced stations heard the spacecraft’s transmitted characteristics at the same time. Something else is going on here.
Joseph then confirmed that the Applied Physics Lab (APL) was unable to detect IMAGE today.
Backyard Analysis of what IMAGE may be saying…
Over the years we have observed countless spacecraft entering into solar eclipse and one interesting commonality happens to their TT&C beacon signal, the frequency rises.
The image above shows the effect of a solar eclipse on WGS 6 and WGS 8 last Spring. The sharp rise in frequency in the center of the image shows eclipse entrance and the start of the slower decay downwards shows the exit from eclipse. These spacecraft are in their operational states and have serviceable batteries so they do not switch off.
Meanwhile in GEO disposal orbit, DSP-F15 continues to transmit years after being decommissioned. This provides an interesting experimental control to exclude the lack of Sunlight and stress on the spacecraft battery as being the cause of the positive frequency shift anomaly. Below shows a plot of DSP-F15 passing through eclipse. Without a battery it dies immediately upon entry but notice what happens upon egress! The frequency is like what we have observed on the WGS missions and many others. This may imply that the process is thermal and not strongly related to power system loading.
So what we may see when a spacecraft enters eclipse is a cooling effect on the spacecraft bus. Even with heaters and other devices the dramatic change in exterior temperature must certainly challenge the spacecraft systems, if still operational, to maintain temperature stability.
However, the behaviour noted on IMAGE’s carrier is the exact opposite. The frequency change is downwards as noted in the last pass with beacon activity as noted below. Possibly indicative of a rising temperature inside the spacecraft or some portion of it that can effect the frequency of the transmitted signal.
Joseph at GSFC seems to think that the thermal theory is worth consideration.
Is IMAGE really DEAD now?
If this was a movie, it would be the second act where the bad guys have wreaked their revenge on the good guys for succeeding in the first act. IMAGE has a history of feigning death only to appear alive again. I suspect that IMAGE is displaying a behaviour that it likely has been exhibiting over and over since it was noted to switch back on a couple of years ago. This is educated conjecture. But my experience with things technical that go bump in the dark indicates that the odds of me seeing this type of behaviour for the first time is too coincidental.
One thing is for sure, IMAGE knows how to create drama! The third act awaits…