Monday, January 16, 2023

Hole in Space -- the mother of all video chats


New technology enables new art forms and artists Kit Galloway and Sherrie Rabinowitz (K&S) began working with geostationary satellite links in 1977. Their first work was an experiment in remote dance and music. Video of dancers at The Goddard Space Flight Center in Maryland and an educational television center in California was transmitted to a central control studio where a composite was formed and sent back to monitors the dancers could see. 

First day: "They're in New York? I'm in LA, right?"
Their next project involved remote conversation rather than movement and they called it "Hole in Space" (HiS). The conversation took place in November 1980 between people at two locations, a display window at the Broadway department store at the Century City mall in Los Angeles and a window in the foyer of the Avery Fisher Concert Hall at the Lincoln Center in New York.

They made three two-hour connections. The first day was unannounced -- participants were curious passers-by who just stopped to see what was happening. They took the second day off and some word of mouth had gotten out by the third day. There was also local news television coverage before the final day, so some people made plans to meet distant friends and relatives.

The sessions began at 5:30 Los Angeles time, so illumination was needed. They did not want to attract large crowds by lighting the participants. Instead, they relied on visible light from inside the venues augmented by infrared emitters near the bottoms of the windows.

The terminals consisted of cameras developed by Cohu Industries that were sensitive to both infrared and visible light. (You can see the effect of the heat-sensitive infrared radiation in the glowing cigarettes of some participants). The displays were RCA projection TVs with custom-made 12 by 12-foot vinyl screens. Connections to the satellite ground stations were over microwave links to a mountaintop near Los Angeles and the roof of a tall building in New York.

Third day: conveying emotion as well as content
Communication was provided by Western Union's Westar satellites, which were typically used for things like the distribution of television programs and sporting events like the Los Angeles Lakers basketball games. Western Union provided three uninterruptible two-hour sessions. 

Galloway says the geostationary satellite latency was not a problem (as it had been for dance), but feedback between the speakers and microphones was, so they had operators at each location manually toggling echo cancellation on and off. There was also someone interviewing people in the crowds during the sessions. At one point a speaker failed in Los Angeles, and Rabinowitz had to run upstairs to borrow one from the store's audio-visual sales department.

K&S became aware of terrestrial networking after HiS and in 1984 began their Electronic Cafe project which supported conversations, remote collaborative drawing, and global New Year's Eve "Telebrations".

HiS was done at a time when nearly all data was text (only upper-case if your terminal was a Teletype or keypunch machine). It was done the year Usenet began and was three years before TCP/IP replaced NCP on the ARPAnet, five years before the NSFNET was established, and eight years before we saw the first text-only version of the Web. (See links to these and other milestones here).  K&S's art pieces anticipated modern services like Zoom for meeting online and JackTrip for remote musical practice and performance. 

Here are links to a short, narrated video, 4m 48s, and a longer video produced by K&S, 29m 45s.

I wish there were holes in space between Russia and Ukraine.

Wednesday, January 04, 2023

SpaceX launches "second generation" Starlink satellites

Why did SpaceX designate these satellites as Gen2 rather than Gen1? 

Starlink Gen1 v1.5 vs Gen2 v F9-1 satellites (source)

In interviews last Spring, Elon Musk said the data throughput of the next version of Starlink satellite (Gen2) would be almost an order of magnitude greater than that of the first generation and that the new Starship rocket would be needed to launch them. Regulatory and engineering delays slowed Starship's progress, so the Gen2 satellites Musk referred to at the time have not yet been launched.

Last Fall, SpaceX broadened the definition of Gen2 to include three configurations, designated F9-1, F9-2, and Starship. Musk was referring to the Gen2 Starship version when he described high-capacity satellites last Spring. The SpaceX Falcon rocket will launch F9-1 and F9-2 satellites, but the Starship version will require the Starship rocket. 

Last month, the FCC authorized SpaceX to launch 7,500 Gen2 satellites operating at altitudes of 525, 530, and 535 km and inclinations of 53, 43, and 33 degrees, respectively, using frequencies in the Ku- and Ka-bands. (They had applied for authorization for 29,988 satellites but only 7,500 were approved at this time -- perhaps due to concern over space debris).

Last week, SpaceX launched 54 Gen2 F9-1 satellites and they are close, if not identical, to the earlier Gen1, version 1.5 Satellites SpaceX has been launching recently. Eric Ralph referred to them as "suspiciously similar" and NASA confirmed that they were the same size and mass as the previously launched Gen1 version 1.5 satellites.

Why did SpaceX designate these satellites as Gen2 rather than Gen1? fo

Tim Farrar attributes it to SpaceX gaining a competitive advantage over potential rival Kuiper, saying "It's very clear that SpaceX wants to launch the first Ka-band Gen2 satellites before Kuiper's test satellites to gain a band-splitting advantage." 

In 2018, the FCC granted SpaceX permission to use the 27.5-29.1 GHz and 29.5-30.0 GHz bands for Gen1 Earth-space transmission. Subsequently, SpaceX was authorized to use those bands for its Gen2 satellites and Kuiper was authorized to use 27.5-3,0 GHz for its satellites. The FCC rules say that SpaceX and Kuiper can agree to a spectrum-sharing rule that protects the first-round rights of SpaceX, but if they cannot agree, the first to launch a satellite capable of operating in the frequency band under consideration gets to choose which portion of the spectrum it will use when interference is detected.

Source
A second motivation may have been the Gen2 right to orbit at a 43-degree inclination. Starlink has had insufficient capacity to serve customers in some regions and may have calculated that the 43-degree inclination would ease that congestion in relatively high-price, high-demand regions like the U. S., where Ookla has shown declining speeds for three quarters.

Regardless, the designations Gen1 and Gen2 seem arbitrary, and we won't see a meaningful difference between them until Gen2 F9-2 satellites are launched and we won't see a major difference until Starship is flying and launching Gen2 Starship satellites. 

Update 2/27/2023


Stack of 21 V2 Mini satellites

SpaceX has posted some information about the Gen 2 F9-2 satellites. They are referring to them as "V2 Mini" satellites and say they will have four times the capacity of the Gen 1 satellites. The image shown here shows 21 satellites, presumably the number that can be launched by the current Falcon 9 rocket. As mentioned above, Elon Musk predicts the Starship satellites will be around ten times the capacity of the current satellites. 

The update also lists several steps and links to documents SpaceX is taking to avoid collisions and to reduce reflected light that interferes with astronomy.

There was speculation that the first V2 Mini would be launched on February 23rd, but that launch was postponed until today and Starship is expected to attempt an orbital launch next month. I wonder whether SpaceX will launch more Gen 2 F9-1 satellites -- the answer probably depends upon the ability to ramp up manufacturing of the Minis.