NASA considering commercial Mars data relay satellites

[Blackstar]

Little frustrated with the agency’s progress in this area myself. 

Thinking about this a bit more, it was probably a lack of opportunity. The last NASA Mars orbiting mission was MAVEN, which reached Mars in 2014. So they didn't have any other opportunities to put a laser in orbit around Mars since then. And they were not about to fly a dedicated tech development mission. But still, if you don't fly it, it doesn't exist. Was there really no other way to do a substantive test of the technology? (That's a rhetorical question.)

[VSECOTSPE]

Guessing it is the  power requirement for an orbital emitter and receiver, likely a laser. Don't think it is practical for laser beams to go through the atmospheric column as a means of high data rate communications between deep space and the ground.

The NRL work I was talking about was for Earth satellites, not deep space.  Emitter and receiver stay on the ground.  Retro-reflectors with electro-optical shutters on the s/c.  Because the emitter and receiver are on the ground, they can be arbitrarily large/overpowered to overcome atmospheric turbulence and/or employ adaptive optics, although clouds may be the killer for practical operation.  The tech evolved out of satellite laser rangefinding (SLR) work.  There are papers showing that 10Mbps links can be closed for satellites over 1000km up using existing SLR ground equipment.  And Japan and Italy have demoed if I understand correctly.  But again, clouds or something else I don’t understand may be practical application killer.

There should be no technical showstoppers to optical comms from deep space distances.  We have and can build insanely sensitive infrared telescopes on Earth; the spacecraft does not necessarily have to send a powerful signal.  The right wavelengths minimize atmospheric losses.  Multiple telescopes around the globe get around the cloud issue since at those distances, the spacecraft is illuminating half the Earth.  But as RF keeps advancing, it may be hard for optical to catch up on data rates.  May require RF to hit a wall first.

[Don2]

I looked at Deep Space Optical communications and wasn't that impressed. Firstly there is the cloud issue. The other thing is that the data rates aren't all that fast. Using a 5m receiving telescope on the ground, it looks to be about 5Mbits/s at average Mars distances. That is about the same as the RF communication system on MRO. The flight terminal is about 29 kg and consumes 76W, so it is not super light weight or low power.

https://www.lpi.usra.edu/opag/july2014/posters/9-DSOC_OPAG_Poster.pdf
https://www.nasa.gov/sites/default/files/atoms/files/tglavich_dsoc.pdf

What I think  would make it more attractive is if you could integrate imaging. It uses a 20cm telescope, which is roughly the same diameter as the LORRI instrument on New Horizons.  Being able to do imaging and communications through the same aperture would keep weight down. You might also consider integrating laser altimetry.

A big problem for a Mars comms relay is lack of funds. One possible solution is to use money from the technology development budget. That would require demonstrating a lot of new technology. An advanced optical communications terminal that also does imaging is one possibility. Others are:

1/ Demonstration of the new High Performance Spacecraft Computing multi-core radiation hardened processor.
https://ntrs.nasa.gov/api/citations/20190033894/downloads/20190033894.pdf

2/ Investigation of the performance of commercial cell phone and automotive processors in space. Ingenuity has done very well with its cell phone chips. Perhaps other commercial chips might be useful as auxiliary processors.

3/ Demonstration of the ability of the Deep Space Atomic clock to simplify navigation and cut operations costs.
https://www.researchgate.net/profile/Todd-Ely/publication/269049269_Advancing_Navigation_Timing_and_Science_with_the_Deep_Space_Atomic_Clock/links/53f21fb50cf272810e4c9934/Advancing-Navigation-Timing-and-Science-with-the-Deep-Space-Atomic-Clock.pdf?origin=publication_detail

4/ Missile defense interceptor kill vehicles carry telescopes and presumably have high delta-v. That is an attractive combination for planetary missions. Perhaps they would make a good basis for a small planetary probe. According to Wikipedia, the Exoatmospheric  Kill Vehicle used by the National Missile Defense system has a mass of 64kg. At very least, some of the components might be useful for building small spacecraft that are far more capable than cubesats.
https://en.wikipedia.org/wiki/Exoatmospheric_Kill_Vehicle

5/ Demonstration of a phased array x-band antenna. Fighter aircraft use these as radars, but they can also communicate. Apparently the Japanese have one on their Mercury Magnetospheric Orbiter which is part of the Bepi-columbo mission. This would be used to communicate with rovers on the surface.

6/ Investigation of higher radio frequencies such as the 90GHz (W band). This wouldn't offer any benefits with existing DSN antennas because they are not designed for such high frequencies and they are at low altitude. However, I think it would be interesting to see what performance the James Clerk Maxwell Telescope on Mauna Kea might achieve in these bands.
https://en.wikipedia.org/wiki/James_Clerk_Maxwell_Telescope
https://ipnpr.jpl.nasa.gov/progress_report/42-154/154E.pdf

You probably couldn't afford to demonstrate all these items. You would have to do enough to justify using technology development funds.

[deadman1204]

Would optical communication be lower power than a standard RF one?

[StarryKnight]

Quote from baldusi:
From what I understand, GEO birds are pretty much deep space hardware, save for navigation and comm payload. GEO birds actually use the Earth to keep its pointing, while all telemetry and control are executed with a permanent beam directly pointed to the bird. But they do perform maneuvers with INS and startrackers when going to its orbital position. Also, the GEO environment is from a radiation and thermal pov pretty much deep space. Doing 15 to 20 years is also par for the course, if you are not worried about orbital debris.

Not really.  They don't have star trackers, just sun and earth sensors.  thermal is not quite the same.

Nope. I know of three commercial GEO satellite builders who have been using star trackers for at least the last 7 years and at least one of them goes back over 10 years. They have sun sensors (usually with coarse resolution) as a backup capability going into safe mode and put the satellite power positive attitude.

[Don2]

Would optical communication be lower power than a standard RF one?

I get 26 kbits/s per watt at maximum Earth-Mars distance for the optical system, and 4.5 kbits/s per watt for the Ka band RF system. So yes, the optical system requires less energy per bit.

Total mass is 96 kg for the X/Ka band telecomms system on MRO which can do 500 kbits/s at max Earth Mars distance. Optical can do an average of 1.5 Mbits/s at the same distance, and weighs 29 kg, so it is lighter and more capable.

However RF infrastructure is already bought and paid for and is much less sensitive to weather. 

[JayWee]

How big would the earth side have to be?

[Don2]

How big would the earth side have to be?

They are using the 5m Mount Palomar telescope to receive and a 1m telescope to uplink. They would like to use 10m class telescopes, but those would probably cost $150 million each. They think they need about eight of those to ensure cloud free reception.

They are using a 5kw laser for uplink. I wonder if they will need restricted airspace around that transmitter.

[edzieba]

Are laser links (with sufficient distance between link endpoints for an assumption of collimation to remain valid) able to operate with a distributed array of transmitters rather than a single large transmitter? They can be local enough for phase locking to not be a huge headache (because maximising synthetic aperture is not even a consideration), but allows a cluster of lower power beams rather than a single high brightness beam with greater optical hazard. Would likely require a single large telescope for reception anyway, though. 

[DanClemmensen]

How big would the earth side have to be?

They are using the 5m Mount Palomar telescope to receive and a 1m telescope to uplink. They would like to use 10m class telescopes, but those would probably cost $150 million each. They think they need about eight of those to ensure cloud free reception.

They are using a 5kw laser for uplink. I wonder if they will need restricted airspace around that transmitter.

They use the 1m telescope to reduce the flux so they don't need to restrict the airspace. 5 kw/(pi*.5m²) = 6.3 KW/m, which is far lower than the flux from a laser pointer.

[baldusi]

How big would the earth side have to be?

They are using the 5m Mount Palomar telescope to receive and a 1m telescope to uplink. They would like to use 10m class telescopes, but those would probably cost $150 million each. They think they need about eight of those to ensure cloud free reception.

They are using a 5kw laser for uplink. I wonder if they will need restricted airspace around that transmitter.

For just comms, your mirrors can be pretty crappy (for astronomy standards). You only worry about aperture and f-number and can take a huge amount of aberrations since you are approaching a single pixel of resolution.

[redliox]

For those 5-10 meter receiving scopes, how far a range can that include?  Mostly we've been presuming Martian distances, but after Europa Clipper and the Uranus probe missions out there (and likely just anywhere in the Solar System) will want to download data faster and in larger quantities which only optical (be it x-ray or infrared) comms can deliver.  One example that comes to mind:

A hypothetical Europa lander...which probably won't have an active JUICE or 'Clipper by time it joins the Jupiter game to play relay for it.  But could a relay in a safe spot like Callisto's Lagrange points do just as well?  And what would the receiver on Earth need to be like to capture a good terabyte or 12 from the Galilean moons?

[DanClemmensen]

For those 5-10 meter receiving scopes, how far a range can that include?  Mostly we've been presuming Martian distances, but after Europa Clipper and the Uranus probe missions out there (and likely just anywhere in the Solar System) will want to download data faster and in larger quantities which only optical (be it x-ray or infrared) comms can deliver.  One example that comes to mind:

A hypothetical Europa lander...which probably won't have an active JUICE or 'Clipper by time it joins the Jupiter game to play relay for it.  But could a relay in a safe spot like Callisto's Lagrange points do just as well?  And what would the receiver on Earth need to be like to capture a good terabyte or 12 from the Galilean moons?

I think the receiving scope for deep-space missions should be in Earth orbit, or perhaps at an Earth-Moon Lagrange point. A multi-mirror scope like JWST, but without the need for extreme cooling and therefore much cheaper. Put the transmitter next to it or use the same telescope for both functions so the far end can track them together.

You mention x-ray and infrared, but unless you are going through an atmosphere you can and should pick something that simplifies the lasers and the optics, like visible light. theoretical bandwidth is not the problem: you can generate as many separate laser channels as you want (thousands, with a femtosecond comb laser) and transmit at high data rates (multiple Gbps) on each channel. The practical constraint is energy per bit, not channel bandwidth.

[ttle2]

How big would the earth side have to be?

They are using the 5m Mount Palomar telescope to receive and a 1m telescope to uplink. They would like to use 10m class telescopes, but those would probably cost $150 million each. They think they need about eight of those to ensure cloud free reception.

They are using a 5kw laser for uplink. I wonder if they will need restricted airspace around that transmitter.

Would it need to be that expensive? For $150 million you get an astronomical-grade 10 m telescope, but is sub-wavelength surface accuracy really needed for receiving? Lower quality light buckets like they use in Cherenkov arrays would be much cheaper.

[Barley]

I am disappointed by the fate of the Ka band demonstrator on MRO.

Ka band was demonstrated, but we'd have learned more if it ran till it broke, or didn't break.  Holding the Ka transmitter in reserve guaranteed it would take longer to get higher capacity RF links.

At some point you need to ignore immediate results and do the engineering to improve future missions, and sometimes that will break things and possibly strand some scientific instruments.

[Don2]

I've replied to ttle and redliox in a new thread here:
https://forum.nasaspaceflight.com/index.php?topic=56579.0