Delfi-C3 reentry forecast updates (periodically updated post)

 

[ Post last updated:  14 Nov 2023  12:45 UTC ]

In my October 25 blogpost I presented imagery of the iconic 3U cubesat Delfi-C³ (2008-021G) taken by my tracking camera. I also provided a reentry forecast in that post, that I updated several times.That reentry is currently (mid November 2023) very near.

I am now consolidating the reentry forecasts in this current, periodically updated blogpost.

While late October the reentry forecast was still shifting to a later date with each orbit update, that shift is now flattening out, but the forecast is still fluctuating. 

A geomagnetic storm that caused aurora at middle latitudes on Nov 5/6 has had a clear effect in speeding up orbital decay (the 'dip' can be seen in the digrams below). Over the weekend 11-12 November, solar activity was more mild than forecast, making the reentry forecast slowly shift to a later time with each orbital update.

My current "aftercast", based on a mid-November 13 orbit modelled in GMAT, is reentry on 13 November 2023, nominally near 20:39h UTC +- 1.5 hours (please note the uncertainty interval!), i.e. between 19 - 22 UTC (and likely  between 20 - 21 UTC)

A SatEvo/SatAna analysis results in a very similar, if slightly earlier, time (nominally 19:34 +- 1.5h UTC). I do not expect it survived to November 14.

The orbit determination on which these 'aftercasts' are based, is from about 3 orbital revolutions before the forecasted reentry moment. This orbit can be of bad quality, as in these final stages, orbit determination is tricky.

Here is how the reentry forecast has been developing so far (note the sudden downward developing trend due to the Nov 5/6 geomagnetic storm):

click diagrams to enlarge

 

This is probably the last reentry forecast update (or rather "aftercast" by now), as I do not expect new orbital elements to be released between this update and the reentry

(Note: forecast data in tabular form are at the bottom of this post)

This is the Delfi-C³ ground-track over the current uncertainty interval (spanning two orbital revolutions) in the forecast:

 

click map to enlarge

These reentry predictions are based on a tumbling satellite with, due to the tumbling, an average drag surface of about 60% of the maximum drag surface. Previous experience with modelling reentries in GMAT has shown this to be a reasonable value for a tumbling object. 

What makes these reentry forecasts challenging, and creates the large uncertainties in the reentry position is a combination of things. One is the, even at short timescales, varying solar activity and it's influence on the upper atmosphere, which cannot be well predicted or captured by the model. Second, during the last orbits just before reentry, all kind of gas flow mechanisms around the spacecraft are taking place, which alter tyhe cdrag it expriences. Moreover, in this final stage where the spacecraft meets a more thicker resistance of the upper atmosphere, it sometimes auto-stabilises itself in a least-drag orientation, prolonging survival slightly. Last but not least: in the last moments of the spacecraft's life, when it is in a very low, fast changing orbit, orbit determination becomes difficult, affecting tehe quality of the last orbital elements available for the forecast.

I do not expect a TIP to be issued for this object. TLE updates might end a few hours before the actual reentry, after which CSpOC issues an 'administrative decay'.

Delfi-C³ 's orbit had decayed to below 187 x 177 km by mid 13 Nov 2023, and the cubesat was coming down increasingly fast, as can be seen in the diagrams below (the orbit was dropping by almost 100 km/day mid 13 Nov 2023):

 

click diagrams to enlarge

click diagram to enlarge

Note that Delfi-C³ is very small and lightweight (2.2 kg and 30 x 10 x 10 cm) and the reentry will have been completely harmless. The friction with the molecules in the atmosphere will heat up the spacecraft during its final moments, untill it burns up completely, at altitudes above 50 km. The current ground-track where it can come down, is almost completely over Ocean.

The operators of Delfi-C³ have put out a call to radio amateurs to try to receive and decode telemetry from the cubesat. Software to decode is provided here. The goal is to try to follow Delfi-C³ and get telemetry as close to reentry as possible.

Note that Delfi-C³ only sends telemetry when it is in sunlight, and not continuously as after 15 years the system is showing issues. The frequency is 145.870 MHz, it is sending 1200 Bd BPSK packages. See also here. 

[EDIT:  as off 11 november, the cubesat seems to have shifted to a backup frequency near 145.934 MHz, as can be seen in this spectogram from my detection in the morning of November 11. The 145.870 MHz frequency is also still intermittently active. So pay attention to both frequencies]

click spectrogram to enlarge

[end of edit]

On the morning  of  Nov 8, during the 7:43 UTC pass, I received thise radio signal of Delfi-C3 from Leiden, the Netherlands (but could not decode the signal), clearly a bit early on the then available TLE:

click image to enlarge

The "stepped" effect is due to attempts to correct the Doppler shift. That Doppler shift (the "s"-shape in frequency due to the Doppler effect in the signal) can be very nicely seen in this spectogram from the same pass as received by my colleagues at Delft University of Technology (image courtesy Bart Root, TU Delft):

click image to enlarge. Image courtesy Bart Root, TU Delft

 

Radio signals from the cubesat were also received by me and the TU Delft station on later dates, most recently in the morning of November 13th during the 7:24 UTC pass:

Nov 13 ~7:24 UTC radio spectrogram from Leiden. Click image to enlarge

Delfi-C³ is a 3U cubesat developed and built at Delft Technical University in the Netherlands, and launched 15 years ago, in 2008.

More on Delfi-C³ on the website of Delft Technical University. There is also a nice background article on it's 15-year anniversary here.

The last (and only!) visual image of Delfi-C3 on-orbit, taken by me on 24 October 2023 from Leiden, the Netherlands, using a WATEC 902H2 Supreme and Samyang 2.0/135 mm lens at 25 fps (image is a frame-stack of 16 frames: the faint trail lower right is Delfi-C3 moving through the field of view. See also blogpost here which also features some video footage):

 

TABLE:  Forecast development in tabular form (most recent one at bottom).
All dates and times are in UTC. Quoted times are nominal times, please take into account the uncertainty intervals that go with them!

orbit date         orbit epoch     reentry forecast + uncertainty      
08 okt 2023 13:52  23281.57810544  05 nov 2023 02:23  ±  8.3  day
09 okt 2023 14:28  23282.60344413  05 nov 2023 08:17  ±  8.0  day
10 okt 2023 19:41  23283.82047902  05 nov 2023 11:00  ±  7.7  day
12 okt 2023 00:53  23285.03692402  05 nov 2023 20:20  ±  7.4  day
13 okt 2023 01:27  23286.06083878  06 nov 2023 18:43  ±  7.4  day
14 okt 2023 00:29  23287.02034889  06 nov 2023 18:53  ±  7.1  day
15 okt 2023 08:42  23288.36296159  07 nov 2023 00:59  ±  6.8  day
16 okt 2023 00:02  23289.00204702  07 nov 2023 04:44  ±  6.7  day
16 okt 2023 15:23  23289.64097529  08 nov 2023 02:01  ±  6.7  day
17 okt 2023 18:58  23290.79063916  08 nov 2023 12:14  ±  6.5  day
18 okt 2023 19:29  23291.81212343  08 nov 2023 21:43  ±  6.3  day
20 okt 2023 00:35  23293.02450124  09 nov 2023 16:03  ±  6.2  day
21 okt 2023 01:04  23294.04489630  09 nov 2023 19:49  ±  5.9  day
21 okt 2023 19:26  23294.80984121  09 nov 2023 22:19  ±  5.7  day
22 okt 2023 19:54  23295.82928392  09 nov 2023 23:43  ±  5.4  day
24 okt 2023 07:03  23297.29389307  10 nov 2023 23:54  ±  5.3  day
26 okt 2023 00:17  23299.01200402  11 nov 2023 11:29  ±  4.9  day
27 okt 2023 00:42  23300.02946319  11 nov 2023 12:23  ±  4.6  day
28 okt 2023 01:06  23301.04628230  11 nov 2023 16:02  ±  4.4  day
28 okt 2023 19:24  23301.80847586  11 nov 2023 18:46  ±  4.2  day
30 okt 2023 00:20  23303.01441157  12 nov 2023 09:54  ±  4.0  day
31 okt 2023 00:41  23304.02910990  12 nov 2023 13:04  ±  3.8  day
01 nov 2023 01:02  23305.04306068  12 nov 2023 17:28  ±  3.5  day
02 nov 2023 11:58  23306.49918974  12 nov 2023 17:44  ±  3.1  day
03 nov 2023 07:42  23307.32139835  12 nov 2023 23:36  ±  2.9  day
04 nov 2023 07:58  23308.33247480  12 nov 2023 19:20  ±  2.5  day
05 nov 2023 00:38  23309.02698061  12 nov 2023 21:03  ±  2.4  day
06 nov 2023 00:51  23310.03600547  12 nov 2023 05:15  ±  1.9  day
07 nov 2023 01:02  23311.04321962  12 nov 2023 09:23  ±  1.6  day
07 nov 2023 13:06  23311.54617034  12 nov 2023 14:38  ±  1.5  day
07 nov 2023 14:36  23311.60900895  12 nov 2023 14:25  ±  1.5  day
08 nov 2023 01:10  23312.04868443  12 nov 2023 15:48  ±  1.4  day
08 nov 2023 13:13  23312.55073768  12 nov 2023 19:28  ±  1.3  day
08 nov 2023 19:14  23312.80157938  12 nov 2023 20:14  ±  1.2  day
08 nov 2023 20:44  23312.86427030  12 nov 2023 20:32  ±  1.2  day
09 nov 2023 01:15  23313.05229412  12 nov 2023 21:16  ±  1.2  day
09 nov 2023 13:16  23313.55332040  12 nov 2023 20:49  ±  1.0  day
09 nov 2023 14:46  23313.61590941  12 nov 2023 20:54  ±  1.0  day
09 nov 2023 19:17  23313.80362555  12 nov 2023 21:54  ±  22.4  hr
10 nov 2023 01:17  23314.05377944  12 nov 2023 23:07  ±  20.9  hr
10 nov 2023 14:47  23314.61604116  13 nov 2023 01:14  ±  17.5  hr
10 nov 2023 20:46  23314.86565574  13 nov 2023 01:32  ±  15.8  hr
11 nov 2023 01:15  23315.05274319  13 nov 2023 02:37  ±  14.8  hr
11 nov 2023 13:13  23315.55109903  13 nov 2023 06:40  ±  12.4  hr
11 nov 2023 19:11  23315.79995400  13 nov 2023 08:42  ±  11.3  hr
12 nov 2023 01:09  23316.04856854  13 nov 2023 10:21  ±  10.0  hr
12 nov 2023 14:34  23316.60695182  13 nov 2023 14:53  ±   7.3  hr
13 nov 2023 00:57  23317.03998349  13 nov 2023 17:11  ±   4.9  hr
13 nov 2023 11:18  23317.47133062  13 nov 2023 19:55  ±   2.6  hr
13 nov 2023 12:47  23317.53274184  13 nov 2023 20:06  ±   2.2  hr

FINAL 'aftercast':
13 nov 2023 15:53  23317.65534723  13 nov 2023 20:39  ±   1.5  hr

A Goodbye to Delfi-C3

Delfi-C3 tracklet on a stack of 16 video frames, 24 Oct 2023

 (note: new reentry forecasts are now published in a separate dedicated blogpost)

Earlier this year, my TU Delft colleague Stefano Speretta asked me if I could try to I imaged a pass of the TU Delft-built 3U cubesat Delfi-C³ (2008-021G). 

It next took a long time due to initially unfavourable observing geometries and - when the observing geometries got better - the Dutch weather, but I finally managed to successfuly image it in late evening twilight of 24 October 2023. 

Above is a stack of 16 video frames showing the tracklet created by the cubesat; below is the actual video footage, shot with a WATEC 902H2 Supreme camera and Samyang 2.0/135 mm lens at 25 fps (the object is very faint in the footage, due to it being very small in size):

 

Delfi-C³ (2008-021G) is a 3U cubesat and was the first cubesat built in the Netherlands. It was launched on 28 April 2008 from Satish Dawan in India on a PSLV rocket, as part of a rideshare mission.

It was built by students of Delft Technical University (my current employer) as the first in what was to become a line of Dutch-designed-and-built cube- and pocketsats. It carried at that time experimental technology (autonomous star sensors and thin-film solar panels) and an amateur radio responder. More information on the cubesat, its mission and the technology onboard can be found at the TU Delft website.

Although no longer operational, there is occasionally still radio telemetry received from the cubesat by our TU Delft Rooftab Radio lab.

 

Delfi-C³ in stowed condition (image: TU Delft)

Delfi-C³in deployed condition (image: TU Delft)

Fifteen years after launch, it is time to say Goodbye this very successful cubesat. It has less than half a month to live.

 

[post NO LONGER UPDATED below. Instead refer to this new dedicated post here for new reentry forecast updates]

Initially launched into a 615 x 635 km, 98.0 inclined orbit, the orbit has now decayed to 321 x 324 km (status as of 3 Nov 2023), and the cubesat is coming down increasingly fast, as can be seen in the diagrams below (currently, the orbit is dropping by 4 km/day (status 3 Nov 2023)):

click diagrams to enlarge

click diagram to enlarge

 

Delfi-C³ will probably reenter into the atmosphere and burn up somewhere mid-November 2023 (depending on how solar activity develops over November).

Here is the evolution of my GMAT reentry forecast so far (ignore the error bars and quoted  reentry date uncertainty for now, as this far before reentry they still have little meaning, due to the uncertainty in future solar activity):

click diagram to enlarge

The initial shift of the forecast over time towards a progressively later date is slowing down. My best guess at this moment (3 Nov2023) is reentry mid-November, around 12-14 November 2023, plus-minus a few days.

I will update this figure over the coming days and weeks, as the reentry forecast develops. 

New reentry forecasts are now published in a separate dedicated blogpost.

I do not expect a TIP to be issued for this object. Recent experience shows that TLE updates will probably cease some 2-3 days before the actual reentry, after which CSpOC issues an 'administrative decay'.

Delfi-C³ is very small and the reentry will be completely harmless, with the cubesat burning up completely.

Launching cubesats from the X-37B OTV 5: lifetime modelling with GMAT

image: USAF

Last week, CSpOC issued catalogue entries for three cubesats released as part of the X-37B mission OTV 5.

It concerns USA 295 (2017-052C), USA 296 (2017-052D) and USA 297 (2017-052E). No orbital data are given, but the catalogue entry did explicitly indicate that all three are no longer on orbit.

That cubesats were released as part of this X-37B mission had been clear from a US Air Force statement made after completion of the OTV 5 mission in October last year. The wording of that statement is however ambiguous: while most analysts take it to mean the cubesats were released by OTV 5, it is also possible that they were released as ride shares by the upper stage of the Falcon 9 rocket that launched OTV 5 in 2017.

In this blog post, I will do an academic exercise aimed at guessing when, at the latest, these cubesats could have been released by OTV 5, assuming release from the latter.

OTV 5, the 5th X-37B mission, was launched from Cape Canaveral on 7 September 2017. It landed at the Kennedy Space Center Shuttle Landing Facility on 27 October 2019, after 780 days in space. Unlike previous missions that were all launched in 38-43 degree inclined orbits, this one was launched into a 54.5 degree inclined orbit. Combined with the fall launch date, this meant it took our tracking network a while to locate it on-orbit: the first positive observations were made in April 2018, half a year after launch.

From April 2018, when we started to track it, to October 2019, when it landed, OTV 5 orbitted at various orbital altitudes between 300 and 390 km altitude (see diagram below):

click diagram to enlarge

The CSpOC catalogue entry lists all three cubesats that were released as part of this mission as "no longer on orbit". Assuming they ended their orbital life by natural decay (rather than, for example, being retrieved by OTV 5 again at a later stage, which is in theory certainly possible!), the fact that they were no longer on orbit by 11 February 2020 might yield some constraints on when they could have been released.

To get some idea of the orbital lifetime of a cubesat released from OTV 5, and spurred on to do so by Jonathan McDowell, I ran several GMAT models in which I modelled a 5 kg 3U cubesat released at three altitudes: 400 km, 360 km and 325 km.

We do not know the actual orbital altitude of OTV 5 at that  moment. Nor do we know when the cubesats were released. Hence the three altitude variants. The start point of the modelling was an assumed release into the OTV 5 orbit on October 7, 2017, one month after launch of OTV 5.

For each cubesat, the models were run in two variants: one with the cubesat in minimal drag orientation (0.01 m² cross section), and one with the cubesat in maximal drag orientation (0.03 m² cross section). I used the MSISE90 atmosphere in the model, with historic Space Weather data for October 2017 to February 2020 and estimated solar and geomagnetic activity parameters from the 'early cycle' variant of the GMAT Schattenfile for dates past early 2020.

For the three assumed orbital altitudes and an assumed release one month after OTV 5 launch, the GMAT data produce the orbital decay plots below. In these plots, the red data are for minimal drag orientation, the blue data for maximal drag orientation. If the cubesats in question were similar to NRO's Colony II cubesats, then the red minimum drag orientation curves probably represent the orbital evolution best. If they were more like Colony I cubesats, then the blue maximal drag curves are more representative.

Taking the minimal drag variants, and under the assumption that the cubesats were 3U cubesats and not retrieved on-orbit by OTV 5 at a later stage, the suggestion is a release below 350 km. Released at higher altitudes, they would still be on-orbit.

Assuming reentry before 11 February 2020 after natural orbital decay, a minimal drag orientation and release no lower and no higher than 325 km, the latest possible moment of release would be late August 2018, give or take a month to account for the uncertainties.

It appears we can rule this out however, because we know that OTV 5 was orbiting at 380 km altitude, not 325 km altitude, at that time. So the best guess (although one under many assumptions) is a release some time before August 2018, i.e. within 1 year after the launch of OTV 5.

It is still possible that the cubesats were released at a later date, but next retrieved while still on-orbit by OTV 5. If the cubesats were smaller than a 3U cubesat, a later release than August 2018 is possible as well.

Finally, given the ambiguity in US Air Force Statements on the matter, it is also possible that the cubesats were released from the Falcon 9 upper stage on the day of launch.

For more about the X-37B, and especially the active myth-making that seems to be at play around this secretive space-plane, see my earlier post here.

OTV 5 rising in April 2018. Click image to enlarge