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Hugh Lewis Profile picture
@ProfHughLewis
Jul 29, 2020 • 3 tweets • 2 min read • Read on X
In this extract from the @SpaceX response to the @FCC there is a calculation that might be relevant if satellites were molecules in an ideal gas (or perhaps if addressing risks from small #spacedebris) but is not appropriate when considering large objects or constellations. Image
This highlights a lack of #spacedebris expertise & experience, and reliance on a model (DAS) that is not understood.
As the analysis of SOCRATES data has indicated, the reality is very, very different from what @SpaceX is expecting. Satellites are not randomly distributed around the Earth and are not travelling in random directions.

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More from @ProfHughLewis

Hugh Lewis Profile picture
May 15, 2023
Welcome to this month's look at #Starlink conjunction risk mitigation manoeuvres. Through 30 April 2023, I estimate that Starlink satellites have made a total of > 45,000 manoeuvres to mitigate the risk of colliding with other space objects [1/n] Graph showing the cumulativ...
A better relationship to consider is the one between the (cumulative) number of manoeuvres and the (cumulative) number of Starlink satellites launched. The growth is a non-linear function of the number of Starlink satellites [2/n] Graph showing the cumulativ...
Here, I looked at the manoeuvre estimates/reports in 6-monthly intervals, corresponding to the reporting periods used by SpaceX. Additionally, I added a prediction to the end of 2024 based on an exponential fit through 30 April 2023. [3/n] Graph showing the number of...
Read 6 tweets
Hugh Lewis Profile picture
Sep 15, 2022
I've been thinking about the new proposed @FCC "five-year rule" for #SpaceDebris mitigation & wanted to share some analysis & thoughts. Whilst I think the intentions are good I believe the implications of the change are poorly understood. Let me explain... [1/n]
As @brianweeden's excellent thread explains, "The new proposed ruling would require all FCC licensed satellites that end their life in LEO to re-enter the atmosphere within 5 years, and ideally ASAP." [2/n]
The justification provided by the @FCC is that "a shorter benchmark would promote a safer orbital debris environment." [3/n] Image
Read 31 tweets
Hugh Lewis Profile picture
Sep 14, 2022
Latest analysis for #Starlink & #OneWeb shows these two constellations accounted for 42% of all close approaches within 5 km predicted by #SOCRATES at the end of August, with Starlink alone accounting for 29%. [1/n]
On average, #SOCRATES predicts that each #Starlink satellite will now experience 1 close approach within 5 km with a non-Starlink object every day, and each #OneWeb satellite will experience 3.4 close approaches with a non-OneWeb object every day. These rates are increasing [2/n]
Here's the same data from [2/n] plotted with respect to the number of satellites in each constellation in orbit, clearly showing #SOCRATES predicts that #OneWeb satellites experience more close approaches (within 5 km) per satellite than the #Starlink satellites [3/n]
Read 13 tweets
Hugh Lewis Profile picture
Jul 5, 2022
A follow-on from yesterday's thread with a note about averages. In a #SOCRATES report from 30 June 2022 the average collision probability for each #Starlink conjunction was 3.7E-6 but the range of values can be broad (chart shows data since 2019) [1/n]
Chart showing frequency of conjunctions at different collisi
#SOCRATES predicted some events with a collision probability > 1E-2 (1-in-100) & some with a probability < 1E-7 (1-in-10,000,000). The average value might seem to be almost negligible & you might think all conjunctions would be similar, but that's not the case [2/n]
In addition, some #Starlink & #OneWeb satellites experience more conjunctions than others. Most satellites experience relatively few encounters but a few satellites are involved in a relatively large number (charts shows data for 7 days from 30 June 2022) [3/n] Chart showing the frequency that Starlink and OneWeb satelli
Read 8 tweets
Hugh Lewis Profile picture
Jul 4, 2022
Welcome to my (delayed) monthly analysis of @CelesTrak #SOCRATES conjunctions. Since 1 March 2019, SOCRATES has predicted about 9 million unique conjunctions within 5 km involving active or derelict payloads. This is a thread focused on those involving #OneWeb & #Starlink [1/n] Chart showing the average daily number of conjunctions withi
#OneWeb payloads have accounted for ~500,000 unique conjunction predictions since 1 March 2019 (5.5% of all predictions made), while #Starlink payloads have accounted for ~1.1 million (12.5%) [2/n]
On 1 March 2019 #SOCRATES predicted ~3860 unique conjunctions within 5 km. On 30 June 2022 the corresponding number was ~10,160, an increase of ~160%. #Starlink accounted for ~2570 (25%) & #OneWeb accounted for ~1250 (12%) [3/n]
Read 14 tweets
Hugh Lewis Profile picture
Apr 27, 2022
In advance of my monthly analysis of #Starlink conjunction data I wanted to share some additional analysis undertaken over the last few days. It's a work in progress but here's a thread looking a little deeper at the #SpaceX approach to #Starlink orbital space safety [1/n]
#SpaceX provided some relatively detailed information about its approach in a briefing to the #FCC (here: ecfsapi.fcc.gov/file/108107102…) and in an update on the website (here: spacex.com/updates/index.…) [2/n]
My focus has mostly been on understanding the implications relating to the choice of the probability threshold for collision avoidance manoeuvres. With the #SOCRATES #Starlink data now running across nearly 3 years we can gain some insights that may be useful [3/n]
Read 35 tweets

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