Multipurpose Laser Instrument for Interplanetary Ranging, Time Transfer, and Wideband Communications^†

Round 1

Reviewer 1 Report

The bandwidth limitation is a long standing problem for satellites for planetary exploration. This applies in particular for high resolution imaging payload. From this point of view this paper offers an interesting study that outlines the advantage of an optical link between the Earth (orbit) and any of the exploratory targets in the solar system. The approach taken here is not only addressing the data transfer from the earth to any of the planets, but also identifies additional benefits that come with the inclusion of precise optical ranging and time transfer. Several typical space application scenarios are quantitatively examined in a very general numerical way, starting from the inner planets and reaching as far as the minor planet Pluto. Orbit considerations are discussed as well as the link budget and the pointing and point ahead requirements, including the effect of the long travel time of the light signals. This is enough to demonstrate the feasibility of the suggested approach and invites a deeper study of a potential system layout that utilizes this approach.

The paper is well written and provides the necessary quantitative support in order to show the soundness of the proposed method. With respect to the scope of this paper I am not missing anything in this discussion. Therefore I suggest to accept the paper for publication.  

Author Response

Dear Reviewer #1,

Thank you for your supportive review of my recent paper submitted to Photonics. I have attached a revised paper which includes some minor edits ,notably Eq. (5),  and a revised Section 7 which provides greater detail regarding the design of the communications detector and surrounding integrating detectors used during opposite terminal acquisition and centering of the communication beam. I hope you will find these revisions helpful.

Sincerely,

John Degnan

Author Response File: Author Response.docx

Reviewer 2 Report

1. Use of Single Photon detectors based receivers are discussed in detail.

2. Complete end to end communication using LASERs is explored in this work.

3. Specific uplink and downlink parameters are considered for the work.

4. The work looks good and throws up a new avenue for fully optical links in deep space explorations.

5. The equations, figures and other calculations are justified from technical and mathematical aspects.

6. Mathematical aspects on the scenarios that could disturb the fully optical link can be explored to adjudicate its performance.

7. Generally, any communication link is characterized by SNR, BER and total losses in the link. More importance can be given on these parameters.

Author Response

Dear Reviewer #2,

Thank you for your supportive review. In response to your request, I have included additional references to Bit Error Rates (BERs) in the text and greatly modified section 7 of the paper in an attempt to hopefully better explain the proposed target acquisition and terminal axis coalignment procedures through the use of a defocused laser beam and an external integrating detector array surrounding the central communications detector.  I should also mention that there was a typo in Eq. (5) that has been corrected.

The revised manuscript is attached with the recommended changes in red type.

Sincerely,

John Degnan 

Author Response File: Author Response.docx