Thursday, May 23, 2019

Might satellite constellations learn to avoid debris with sensors on satellites?

There were no artificial satellites before Sputnik in 1957.
Today there are about 5,000 with plans for thousands more.
Space debris is problematical.

The European Space Agency (ESA) reported that as of January 2019 there were about 5,000 satellites in space and 1,950 of them are still functioning. Hopefully, those functioning satellites have fuel and thrusters that will enable them to de-orbit and (mostly) burn up in the atmosphere when their useful life is finished. The remaining 3,050 are slowly drifting, along with a lot of debris.

The ESA estimates that there have been over 500 break-ups, explosions, collisions, or anomalous events resulting in fragmentation and they estimate that there are 34,000 debris objects >10 cm, 900,000 from 1 to 10 cm and 128 million from 1 mm to 1 cm. NASA says there are more than 20,000 pieces of debris larger than a softball, 500,000 the size of a marble or larger and many millions so small they can’t be tracked. (watch: NASA's Animation Shows Massive Space Junk Around Earth)

In low-earth orbit (LEO), debris circles the Earth at speeds of about 7 to 8 km/s. However, the average impact speed of orbital debris with another space object is approximately 10 km/s and can be up to about 15 km/s, which is more than 10 times the speed of a bullet. At those speeds, a collision with a small object can do significant damage. This sounds like a disaster waiting to happen and the current and planned proliferation of LEO satellites increases the likelihood of a Kessler Syndrome event -- a cascade of collisions between satellites and the ensuing debris.

As Kessler says "The cascade process can be more accurately thought of as continuous and as already started, where each collision or explosion in orbit slowly results in an increase in the frequency of future collisions." If you aren't worried yet, watch the following short video or read Kessler's 1978 paper.

Kessler's warning was taken seriously and NASA and others have been working on debris mitigation policy and technology for years, but the silver bullet has not been found. The Space Surveillance Network tracks approximately 23,000 relatively large objects and you can query the database here, but what about the millions of objects that are too small to track?

The SpaceX press release for their Starlink Mission hinted at their collision-avoidance strategy, saying that
Each spacecraft is equipped with a Startracker navigation system that allows SpaceX to point the satellites with precision. Importantly, Starlink satellites are capable of tracking on-orbit debris and autonomously avoiding a collision.
That sounds promising, but autonomously resolving and recognizing a marble-sized object that is approaching at up to 15 km/s, computing its trajectory and firing thrusters to avoid a collision can't be done -- even by Elon Musk.

Relatively few debris objects can be tracked terrestrially, but a satellite might be able to recognize a piece of debris and transmit its characteristics to a terrestrial processor, greatly expanding the tracking database. SpaceX may be approaching this as a machine-learning problem in which the entire constellation, not individual satellites, is learning to avoid collisions.

That is pure speculation, but it was triggered by a few thoughts.

For a start, at the end of 2017, SpaceX delivered a space debris sensor (SDS) to the International Space Station. As shown in the following short video, the SDS is capable of monitoring the size, speed, direction, and density of small particles that impact it.

Elon Musk also has a strong interest in machine learning -- he was a co-founder of openAI and his Tesla cars act as sensors uploading driving data that is used for training autonomous vehicles.

Going out to the very end of the limb -- Musk is a fan of science fiction and speculation on the possibility of a swarm of man-made objects learning about existential risks is reminiscent of emergent intelligence in Asimov's fictional planet Gaia or Teilhard de Chardin's noosphere).
Musk opened his Tesla patents and, if SpaceX demonstrates the feasibility of this approach to debris avoidance (and perhaps one-day removal), I expect that he would share this technology with competitors like OneWeb and Telesat and the space agencies of all nations.

Like global warming, space debris is an example of a tragedy of the commons and is a threat to all nations. As the cartoon character Pogo said, "We have met the enemy and he is us." Ironically, global tragedies of commons can unite us.

Friday, May 17, 2019

SpaceX reports significant broadband satellite progress

SpaceX may be approaching debris detection as a machine-learning problem in which the entire constellation, not individual satellites, is learning to avoid collisions.

Starlink size comparison -- novel packaging accomodates
60 satellites in a single launch. (Source)
SpaceX delayed last Wednesdays Starlink launch due to high winds and on Thursday they decided to do a software update and postpone the launch until next week, but they revealed significant progress in their Starlink mission press release and in tweets by and a media call with Elon Musk.

The mission press release said SpaceX has significantly reduced the size and weight of their satellites. Their initial November 2016 FCC filing specified 386 kg satellites that measured 4 x 1.8 x 1.2 meters. In February 2018, they launched two Internet-service test satellites -- TinTin A and B -- that measured only 1.1 x .7 x .7 meters with a total mass of approximately 400 kg. The mass of the Starlink satellites will be only 227 kg, about 43% that of the test satellites. (They are still heavier than OneWeb's 147.4 kg test satellites)

As far as I know, SpaceX has not previously commented on the number of satellites that might be launched at once, but the number was generally estimated as 25-30 after considering constraints on mass, volume, and numbers of satellites per orbital plane. As shown here, they will be launching a surprising 60 flat-packed satellites. Launching 60 satellites also demonstrates continued progress in rocket capability -- this will be the heaviest SpaceX payload ever.

The speed and density of satellites in
low-earth orbit increase the likelihood
of a cascading debris collision. Source
The current and planned proliferation of low-earth orbit satellites increases the likelihood of a Kessler Syndrome event -- a cascade of collisions between satellites and the ensuing debris. The satellites will be equipped with krypton powered thrusters that will enable them to autonomously avoid collisions with on-orbit debris that is large enough to track. The thrusters will also be used to de-orbit obsolete satellites causing 95 percent of all components to quickly burn in the atmosphere.

But, what about small, untracked objects? Low-earth orbit satellites move very fast and even if a satellite had the resolution and pattern-recognition capability to "see" debris in its path, it would not be able to maneuver quickly enough to avoid a collision. That point was raised in this online discussion and a possible solution suggested -- the entire constellation could dynamically pool and share data from each satellite as well as use NORAD tracking data, which Musk mentioned during the media call.

SpaceX may be approaching this as a machine-learning problem in which the entire constellation, not individual satellites, is learning to avoid collisions using its shared data as well as data from other sources like NORAD. One can imagine sharing such data with competitors like OneWeb and Telesat or even with Russia, China or India. (Elon Musk is known to read science fiction -- this speculation is reminiscent of Azimov's Gaia or Teilhard de Chardin's noosphere).

The prospect of launching 60 satellites at once and a shared-data approach to collision avoidance have grabbed my attention, but Musk's tweets and media call were also highly informative -- a few examples:
All that and they have yet to launch the satellites -- stay tuned.

Wednesday, May 08, 2019

Satellite Internet Service Progress by SpaceX and Telesat

This has been a busy week in the race to deploy constellations of low-earth orbit (LEO) Internet-service satellites.

Telesat LEO-1, artist's conception.
Credit SSTL.
In their quarterly report, Telesat mentioned progress in two, disparate markets. As I noted earlier, they have signed their first LEO customer -- Omniaccess a provider of connectivity to the superyacht market. Telesat is a Canadian firm and the quarterly report also said Canada's 2019 Federal budget included a commitment to using LEO satellite services to help bridge the digital divide. They will be serving Russian oligarchs and rural Canadians.

Telesat also announced that the two teams they contracted with to develop overall satellite and ground system proposals, Airbus and a consortium of Thales Alenia Space and Maxar Technologies, had significantly advanced their detailed designs for the complete system, having completed the system definition and risk management phase of the program. Telesat will continue their collaboration with both teams and will select a prime contractor later this year.

Telesat's coolest development was the announcement that they had demonstrated 5G mobile backhaul. They collaborated with Vodaphone and the University of Surrey in a test of their experimental satellites and recorded round trip latency of 18-40 milliseconds. The demonstration supported video chatting, Web browsing and simultaneous streaming of up to 8K video. The team also transferred 4K video to the edge of the 5G network. SES is already providing mobile backhaul using their middle-earth orbit satellites and it seems that the new LEO constellations will be competing with them. This will be an important application for rural areas and developing nations.

Telesat has signed launch contracts with Jeff Bezos’ Blue Origin and they plan to be operational by 2022. (Bezos will also be a Telesat competitor, but his LEO project has just been announced).

SpaceX also made the news. SpaceX president and chief operating officer, Gwynne Shotwell, confirmed that the launch scheduled for May 15 will include "dozens" of Starlink Internet-service satellites.

She characterized these as "demonstration" satellites and said they would not include satellite-to-satellite laser communication links. Bulent Altan, CEO of satellite laser company Mynaric, estimates that their laser terminals will cost around 250,000 euros in quantities of 1,000. SpaceX will have 4 in each satellite and they plan to start offering broadband service once they have 800 satellites in orbit -- in the 2020-2021 time frame.

OneWeb will forego inter-satellite optical links in their initial constellation, but they seem to be making steady progress in antennas for satellite-to-ground communication. Both are key technologies for LEO satellite Internet service.

Shotwell said that depending on how the demonstrations proceed, from two to six Starlink launches could follow by the end of this year. In the past, they referred to these as "operational" satellites. Maybe the switch to "demonstration" means they will use them as a marketing tool and the number of launches later in the year will be determined by sales.

Update 5/11/2019

TMF Associates suggests that the FCC may be favoring SpaceX Starlink and that the upcoming launch may carry as many as 40-50 satellites. The post also suggests that they may be launching so many satellites in order to generate publicity to spur further investment which has been difficult during the past year.