Friday, 27 August 2021

First positive observations of the LED beacon of the NAPA-2 6U cubesat


On June 30, 2021, a Falcon 9 launched several cubesats in a rideshare launch called Transporter-2. One of the payloads was a 6U cubesat called NAPA-2

This cubesat was built by the Dutch company ISISpace in Delft (the same company that built Brik-II) for the Royal Thai Air Force. It is an IMINT satellite, carrying two small Earth observation camera's. It is in a 97.5 degree inclined sun-synchronous 520 x 540 km orbit with passes around local midnight and noon.

This is the NAPA-2 cubesat after assembly (image courtesy of ISISpace): the 6U cubesat measures about 10 x 20 x 30 cm.

image (c) ISISpace, used with permission.

NAPA-2 has an interesting novelty: it carries a beacon of 12 bright LED's that can be switched on and off by the satellite operators. 

It is an experiment to see if such a bright artificial lightsource on the satellite can aid in optically tracking it.

The past few days saw the commissioning of this feature. ISISpace had asked me whether I could try to image the LED beacon from Leiden. Attempts to image it were made on three nights. 

The first attempt, on August 24 using a 1.4/85 mm lens, was negative.

The second attempt was on August 25. The operators had reorientated the satellite such that the LED's were pointing at the groundstation. This attempt was marginally positive: it was seen but the satellite was extremely faint and barely visible and the trail was lost in the noise background in a frame stack.

A third attempt was made last night, in the early hours of 27 August. This time I used a more powerfull lens, the Samyang 2.0/135 mm. The camera was a WATEC 902H2 Supreme operating at 25 frames/s.

The result was a positive detection: the LED beacon of the satellite, although faint, was unambiguously imaged. The range to the satellite was 598 km during the observation. It was imaged around culmination at 61 degrees altitude in the east.


click to enlarge


Below is the video: the object, coming into the FOV from the right, is very faint, but visible. It disappears near the center of the image because the LED was switched off: the operators operated it is a "3-seconds-on, 1-second-off" mode last night.

Below is a framestack of 60 frames from the video (2.4 seconds of footage). A faint but unmistakable trail can be seen entering the FOV from the right: the LED beacon of NAPA-2! The bright star near the bottom of the image is 13 Persei.

Below is a negative image version of the same stack: and a positive version where I pushed the image such that the trail comes out better.



It should be noted that the cubesat was imaged in a part of it's trejactory where it was in Earth shadow: so all the light solely comes from the 12 LED's!

This is the LED array on the satellite (image courtesy of ISISPace):

image (c) ISISpace, used with permission.

Amazing that 12 LED's are visible from a distance of almost 600 km! 

The LED beacon does not operate continuously: it is only briefly switched on when passing over a tracking station (in this case, my observing location). It reaches an Rmag of about +10.

Below are the astrometric residuals relative to CSpOC elset 21239.30175625 (angles are in degrees, delta T in seconds), showing the good match:

     STA   YYday HH:MM:SS.sss   AZ     EL     XTRK     deltaT   Perr
( 1) 4353  21239 00:52:38.401   78.0   60.9   -0.02     0.02    0.023
( 2) 4353  21239 00:52:38.441   77.9   60.9   -0.02     0.04    0.033
( 3) 4353  21239 00:52:38.600   77.7   60.9   -0.02     0.03    0.030
( 4) 4353  21239 00:52:38.920   77.2   61.0   -0.02     0.03    0.025
( 5) 4353  21239 00:52:38.960   77.2   61.0   -0.02     0.06    0.044
( 6) 4353  21239 00:52:39.241   76.7   61.0   -0.02     0.03    0.031
( 7) 4353  21239 00:52:39.561   76.2   61.0   -0.02     0.03    0.031
( 8) 4353  21239 00:52:39.600   76.2   61.0   -0.02     0.05    0.044
( 9) 4353  21239 00:52:39.761   75.9   61.0   -0.02     0.03    0.025
(10) 4353  21239 00:52:39.801   75.9   61.0   -0.03     0.04    0.041

rms     0.03367

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