Re: [dtn] LTC timescale (Re: Question regarding RFC 9171 - How to incorporate "Coordinated Lunar Time")

Hi Carsten and Richard

As a comms engineer working on ESA Moonlight, I’m also interested in resolving this. Given timescales, I guess we’ll end up going with UTC even on the moon, but in the longer term there is a need for a standards-based resolution.

- John

> On 12 Apr 2024, at 06:58, Carsten Bormann <cabo@tzi.org> wrote:
> 
> Hi Richard,
> 
> I read your message with interest.
> 
> draft-ietf-cbor-time-tag [1], an approved specification that is currently in the RFC editor queue for publication as an RFC, defines a versatile representation of timestamps in CBOR.
> While DTN BP does not directly use this extended time tag currently, I would imagine that any evolution of its time representations would coordinate to maintain interoperability with the extended time tag.
> 
> [1]: https://datatracker.ietf.org/doc/draft-ietf-cbor-time-tag/
> 
> The extended time tag defines a way to indicate the timescale in use [2].
> This is based on a IANA registry [3] that is currently just listing UTC and TAI [4].
> 
> [2]: https://www.ietf.org/archive/id/draft-ietf-cbor-time-tag-12.html#section-3.4
> [3]: https://www.ietf.org/archive/id/draft-ietf-cbor-time-tag-12.html#section-7.2
> [4]: https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml#timescales
> 
> I would expect that LTC should be added to this registry, and that a short specification could provide information about how this is to be used and how this timescale interoperates with the existing ones.
> 
> Grüße, Carsten
> 
> 
>> On 12. Apr 2024, at 06:46, Rieber, Richard R (US 347R) <richard.r.rieber=40jpl.nasa.gov@dmarc.ietf.org> wrote:
>> 
>> Hello DTN leads,
>> I am a DTN advocate at JPL and working as the Mission Operations Systems Engineer on the CADRE mission. This mission is slated to send 3 shoe-box sized rovers to the moon on Intuitive Machine’s IM-3 lander in Q1 2025. Needless to say, I’m paying attention to all things moon-related and DTN-related.
>> There are two things I want to highlight:
>>    • NASA’s SCaN office has released the LunaNet Interoperability specification, which mandates the use of DTN for communications in Feb. 2023, and
>>    • On 4/2/2024, the White House has tasked NASA with developing a “Coordinated Lunar Time”, amongst other planetary time systems.
>> BP’s DTN Time (see 4.2.6 of RFC-9171) is defined as milliseconds since 2000-001T00:00:00 UTC. How should this change if there is a lunar time system?
>> I would imagine that Lunar spacecraft use LTC for their internal clocks. How do they interpret bundles sent from Earth that are stamped with UTC? Must they internally convert the current LTC to UTC to compare to that bundle’s DTN Time? Similarly, what time system is used in the DTN Time field for bundles created by a lunar spacecraft?
>> Now imagine the Artemis Gateway that may act as a communication relay node. Some bundles would be from Earth and tagged with UTC. Some bundles would be from the moon and may be tagged in LTC. This gets quite confusing.
>> Needless to say, I think the DTN community needs to have a conversation about if and how the protocol must be modified to support different time systems across the solar system. What’s the venue for having that conversation? How would one go about proposing a protocol modification?
>> Thanks in advance,
>> ~Rich
>>   Richard Rieber
>> NASA/JPL
>> Robotics Systems Engineer
>> 347R – Robotics Operations and V&V
>> Richard.R.Rieber@jpl.nasa.gov
>> +1-818-480-2861
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> 
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