Peer review of: Daylight space debris laser ranging (2020)

REVIEWERS' COMMENTS: 

Reviewer #1 (Remarks to the Author): 

 

As you know, single-shot precision of space debris laser ranging can achieve up to the level of 
decimeter for space debris, higher 1 to 2 orders of magnitude than microwave radar and optical 
tracking technologies. It is very helpful for precise orbit determination, orbit check and cataloging of 
space object and will also be important for enhancing the capabilities of collision avoidance warning 
and building a dynamic database for tracked space debris. In addition, compared with the optical 
tracking technologies, laser ranging technology can be used to observe space debris in earth shadow 
or daytime due to monochromatic, which will be helpful for extending the observation arc. 

 

More than 95% of space debris were in low earth orbit (LEO), their orbital periods are about one and 
half an hour, it passed the observation station quickly and the passed time is about a few minutes. 
Space debris are only visible within a few hours around sunset or sunrise. In this manuscript, stars 
with magnitude of 8 and more than 40 different space debris objects were visualized during daylight 
by using 780nm long pass filter and the ﬁeld of view per pixel equaling to the angular size of the 
object. Inaccurate predictions of about 1km was improved by a real time detection software and 
532nm firing 80mJ laser pulses with 3ns pulse length at 200Hz with 16W was used and the laser 
beam is expanded to 7cm diameter. A 50 cm diameter receive telescope is used to detect the 
reflected photons and focuses the incoming light to a C-SPAD. To decrease noise during daylight 
laser ranging the field of view of the receive telescope is limited to approx. 100µrad and filters are 
used to limit the spectral bandwidth. Therebefore, several rocket bodies of space debris were 
measured during daylight. 

It’s very useful to space debris for removal missions, conjunction warnings and avoidance 
maneuvers. 

The job of this article is an innovative and great work for space debris laser ranging because it is the 
first space debris laser ranging results during daylight. 

I suggest this manuscript published. 

 


Reviewer #2 (Remarks to the Author): 

This is a thorough piece of work that takes forward the well-established geodetic technique of 
satellite laser ranging (SLR) into the very active field of space debris tracking. In particular the work 
builds upon the existing knowledge that laser ranging, using sufficiently powered lasers, can be 
applied to 'non-cooperative' targets that do not carry retro reflectors and demonstrates clearly that 
the technique can be used during the daytime. This is technically challenging work, where the 
authors have solved poor signal-to-noise issues in order to detect optically the target satellites as 
well as in realtime correcting the omnipresent errors in existing orbital predictions; both these steps 
are required in order to obtain sufficient laser returns that unambiguous range measurements may 
be secured and extracted from the noise background that is inevitable in daytime conditions. The 
authors point out that this advance to tracking debris in daytime means that a given laser station will 
vastly increase its yield of observations of this important class of orbiting object. The detail of the 
techniques employed are clearly set out, such that other interested tracking stations might rapidly 
get up to speed; the authors offer their data and algorithms to the interested members of the space 
debris community, which is to be applauded. Just a few typos and suggestions for better wording 
have been marked on the annotated manuscript. Graham Appleby 

 


Reviewer #3 (Remarks to the Author): 

This is an excellent paper, which should be published. It is good solid scientific work and represents 
well what can be done with laser ranging starting from an Earth based station. My only regret is that 
the authors did not at least mention the option of a space based laser station which will have none 
of the disadvantages of atmospheric distortion, limited observation time, atmospheric nonlinear 
refraction, larger background signal, etc. I appreciated the authors mentioning the goal of matching 
projected pixel area to the size of the target. I especially enjoyed their discussion of all the detectors 
and lasers now available for this work. Their data is excellent.