Communications Services Project: commercial successor to TDRSS

[edzieba]

Several Starlinks have launched 'secretly' (not announced beforehand, identified only by that USA-number objects were deployed and camera views of presence of an unexpected Starlink deployment plate) on previous missions now. Since the NRO operate a limited number of satellites in a limited number of orbits, it would take relatively few planes of Starlinks dedicated to NRO use to provide the required coverage.

However, these would need to be modified rather than 'stock' Starlinks, as many NRO satellites operate well above the Starlink plane: antennae would need to be added facing up as well as down. There's also the question of what satellites exactly they would be talking to: any existing NRO satellites would not be capable of doing so, so this new constellation would only be usable with newly launched NRO satellites rather than 'legacy' satellites (e.g. the KH-11s). Finally there's the imminent DoD constellation: whilst the NRO no longer strive to stay under a self-imposed $1bn budget cap (the source of the headache with SDS' 'shared' operation and non-NRO ownership) getting someone else to foot the budget for a system they will be using both keeps their own budget slimmer, and aids obfuscation of their operations. Utilising the Transport Layer is a very obvious alternative to operating their own parallel network, and aids in interoperability and the ability to multiple-source (even if the NRO do decide they need their own dedicated sub-constellation, using Tracking Layer satellites and laser link standards to do so aids in supply chain management and ability to multi-source).

[Jim]

Several Starlinks have launched 'secretly' (not announced beforehand, identified only by that USA-number objects were deployed and camera views of presence of an unexpected Starlink deployment plate) on previous missions now. Since the NRO operate a limited number of satellites in a limited number of orbits, it would take relatively few planes of Starlinks dedicated to NRO use to provide the required coverage.

Not really.  It would take many since FOV is small and the need to relay to the ground station in the USA

[Jim]

However, these would need to be modified rather than 'stock' Starlinks, as many NRO satellites operate well above the Starlink plane:

No, basically just above by less than 200km or below the orbit.

[edzieba]

Several Starlinks have launched 'secretly' (not announced beforehand, identified only by that USA-number objects were deployed and camera views of presence of an unexpected Starlink deployment plate) on previous missions now. Since the NRO operate a limited number of satellites in a limited number of orbits, it would take relatively few planes of Starlinks dedicated to NRO use to provide the required coverage.

Not really.  It would take many since FOV is small and the need to relay to the ground station in the USA

The relay is handled by inter-satellite links, only the first local hop needs to be RF. As long as there is a complete ring for a given orbit then data can be relayed to CONUS from any point in that ring without any ground stations. FoV may be a concern, but by looking 'up' instead of down at the surface the potential coverage area per satellite is much closer to a 180° dome than you can achieve from ground level (no ground clutter, vastly smaller keep-out areas) though with the solar array shadow now added as a new problem. Both link ends need active pointing/beamsteering, but that's already the case for SDS/TDRS user-side links, and already the case for all Starlink-side links.

However, these would need to be modified rather than 'stock' Starlinks, as many NRO satellites operate well above the Starlink plane:

No, basically just above by less than 200km or below the orbit.

The problem is the Starlinks are very low (500km), and many NRO satellites are high LEO, MEO, or GEO (e.g. the Jumpseats, Orions, etc) and thousands of km above them. Even the KH-11s spend most of their time at higher altitudes. SDS and TDRS only needed to face down or sideways (and only sideways to 'fixed' relative locations) which is not the case for an LEO constellation.
Putting the Starlinks (or similar smallsat telecomms satellite, I'll just keep using Starlink for brevity) into an MEO or GEO orbit means you now need higher RF power, to tackle a harder laser pointing problem (or need to use more satellites in to fill out a given orbit with reduced spacing), and lose the passive disposal capability for the cheap-and-replaceable design paradigm.

If the constellation is only intended to be used with new NRO satellites orbiting exclusively at LEO at/below 550km that would be different, though, but would limit the missions those satellites could perform (e.g. the continuous staring of GEO SIGINT and COMINT birds).

[Jim]

Only LEO spacecraft uses relay.  Higher orbits don’t  need it since they always see the ground station.
And KH-11 is real time relay during low passes

[DanClemmensen]

Only LEO spacecraft uses relay.  Higher orbits don’t  need it since they always see the ground station.
And KH-11 is real time relay during low passes

This is true for all prior and existing satellites because they use RF frequencies that can penetrate the atmosphere fairly well. Future satellites may use lasers or RF frequencies that do not penetrate the atmosphere very well, because the transceivers are lower mass, size and power for the same data rates. In this case they will need relays to convert to the proper RF frequencies.

[Zed_Noir]

Never mind the needs of the NRO and the USSF. What are the NASA needs for a replacement TDRS network?

[Jim]

Only LEO spacecraft uses relay.  Higher orbits don’t  need it since they always see the ground station.
And KH-11 is real time relay during low passes

This is true for all prior and existing satellites because they use RF frequencies that can penetrate the atmosphere fairly well. Future satellites may use lasers or RF frequencies that do not penetrate the atmosphere very well, because the transceivers are lower mass, size and power for the same data rates. In this case they will need relays to convert to the proper RF frequencies.

Not applicable here

[soltasto]

Never mind the needs of the NRO and the USSF. What are the NASA needs for a replacement TDRS network?

At the end of the day they need satellites with Software defined radios/relays that can potentially cover MEO, LEO and obviously below. They need to work in the S-band for sure, with Ku and Ka bands being also very important. I guess they also would not dislike having C and X bands available.