At 1:12 a.m. Beijing time on February 26 (12:12 p.m. local time on February 25), SpaceX's Falcon 9 carrier rocket launched another group of Starlink satellites into the air, and 50 Starlink satellites were sent into a 315-kilometer-high orbit.
SpaceX is seeking permission from the Federal Communications Commission (FCC) to send up to 30,000 next-generation Starlink satellites into orbit, sparking some opposition and criticism. In a Feb. 8 letter, NASA outlined its concerns about SpaceX's proposals, such as increasing the probability of starlink satellites colliding with other space objects, could also interfere with other satellites and ground-based science.
In response to these objections and criticisms, SpaceX published the article "SpaceX'S APPROACH TO SPACE SUSTAINABILITY AND SAFETY" on its official website on February 22, the full text of which is translated as follows:
Image source: SpaceX
SpaceX was founded to revolutionize space technology and expand life to more planets. SpaceX is the world's leading delivery service provider and proud to be the first private company to carry astronauts to and from the International Space Station, and the first and currently the only company to complete a manned orbit mission for all. As such, SpaceX is strongly committed to maintaining a safe orbital environment, protecting manned spaceflight, and ensuring that the environment remains sustainable in future Earth orbit and beyond.
SpaceX has demonstrated its commitment to space security through its actions and has invested significant resources to ensure that all of SpaceX's launch vehicles, spacecraft, and satellites meet or exceed space safety regulations and best practices, including:
Design and manufacture of highly reliable mobile satellites with proven reliability of more than 99%
Operate at low altitudes (below 600 km) to ensure that there is no persistent space debris, even in the event of a very low probability of satellite failure in orbit
SpaceX inserts satellites at particularly low altitudes to verify their safety status before instructing them to ascend to a station/orbit
Transparently share orbital information with other satellite owners/operators
Develop advanced collision avoidance systems to take effective action when a risk exceeds a safety threshold
With space sustainability in mind, SpaceX has driven state-of-the-art technologies in key technology areas, such as running satellites in challenging lower altitude orbits, maneuvering and active deorbiting using sustainable electric propulsion, and ongoing contact with satellites using inter-satellite optical communications. SpaceX is working to become the world's most open and transparent satellite operator and encourages other operators to share orbital data with SpaceX, keeping the public and governments informed of the details of operations and practices.
SpaceX continues to innovate and strive to accelerate the development of space technology. Currently, SpaceX is providing much-needed Internet connectivity to people around the world through the Starlink Satellite Constellation, including underserved and remote parts of the world. Here are SpaceX's operating principles, demonstrating SpaceX's commitment to sustainability and safety in space.
Design and build safe, reliable and perishable satellites
As the satellite's altitude continues to decrease, it encounters an increasing atmospheric density. Initially, these atmospheric molecules will hit the satellite, but as the density of the air increases, a high-pressure shock wave will form in front of the satellite. As the satellite slows down further and descends into the atmosphere, its orbital energy will be transferred to the air, heating the air molecules into plasma. The hot plasma sheath envelops the satellite, causing its temperature to rise sharply. Starlink satellites are designed to die when they re-enter Earth's atmosphere, meaning they pose no threat to people or property on the ground. Extinction design requires an investment in significant engineering resources, and this often requires increased cost and even quality of SpaceX satellites, such as SpaceX's decision to use aluminum instead of composite outer-wrapped pressure vessels as fuel tanks for propulsion systems. SpaceX has used this method to safely de-orbit more than 200 satellites. By building reliable, fragmented satellites, planning active de-orbit procedures, and designing for full demiseability, SpaceX ensures itself to maintain the sustainability and safety of its space.
Very low track insertion
In addition to designing and building very reliable satellites, SpaceX further reduces risk by deploying satellites to very low orbits relative to industry standards. SpaceX deploys satellites at low altitudes (below 350 kilometers) and uses SpaceX's most advanced electric propulsion thrusters to propel the satellites to operating altitudes of about 550 kilometers, and then, using its technological advances, SpaceX maintains the satellite's controlled flight at these low altitudes. By deploying the satellite to such a low altitude, any SpaceX satellite that does not pass the initial system inspection (of course, this probability is extremely low) can still use the thruster to quickly and actively de-orbit, or passively de-orbit through atmospheric resistance. This approach is not without complexity or other challenges. This was best evidenced by the Feb. 3 Satellite launch, which was most evidenced by the increased drag of the geomagnetic storm that led to premature de-orbiting of 38 satellites. Despite these challenges, SpaceX strongly believes that low insertion heights are key to ensuring responsible space operations.
Operates below 600 km
SpaceX operates its satellites at altitudes below 600 km because of the shorter natural orbital decay times at low altitudes than those above 600 km. Starlink satellites operate in "self-cleaning" orbits, meaning that non-motorized satellites and debris will not be able to remain at their original altitudes and de-orbit due to atmospheric resistance for 5 to 6 years (usually faster), see Figure 1. This significantly reduces the risk of persistent orbital debris and greatly exceeds the current 25-year de-orbit standard from the Federal Communications Commission and internationally (which SpaceX considers obsolete and should be further reduced). Natural de-orbiting of satellites or debris from altitudes above 600 km poses a higher risk of debris from a long-term orbit than in lower orbits. Several other commercial satellite constellations are designed to operate at a height of more than 1,000 kilometers, and if these satellites fail before deorbiting or do not deorbite by active debris removal, it will take hundreds of years to deorbit naturally, as shown in Figure 1. SpaceX has invested a lot of effort and money in developing satellites that fly at lower altitudes, including investments in complex attitude and propulsion systems. SpaceX hopes to develop an active debris removal technology in the short term, but it doesn't exist yet.
Satellites with a mass-to-area ratio of 40 kg/m2 have orbital life at different starting altitudes and average solar cycles.
The graph above shows how the amount of debris changes with the orbital altitude. Debris from satellite collisions flying at altitudes above 600 kilometers will remain in orbit for decades, and there is a risk of generating orbital debris at every passing altitude when they deorbit.
The amount of debris in the longitudinal orbital layer per 1 km thick varies with orbital height.
Information transparency and data sharing
SpaceX transparently and continuously shares the details of the Starlink network with governments and other satellite owners/operators. SpaceX strives to ensure accurate, relevant and up-to-date information on space security and shares its own space posture awareness with all operators. SpaceX shares high-fidelity future position and speed prediction data (ephemeris) for all SpaceX satellites.
SpaceX shares propagatible ephemeris and covariance (statistical uncertainty of predictions) data on Space-Track.org and encourages all other operators to do the same, as it makes it more meaningful and accurate to calculate collision risk. SpaceX is also committed to making SpaceX's ephemeris more accessible to everyone by accessing Space-Track.org viewing relevant data without the need to log in.
In addition to providing satellite ephemeris, SpaceX voluntarily provides routine system health reports to the Federal Communications Commission. The reports show the status of spaceX satellite constellations, including a summary of the operational status of the satellite fleet, and the number of maneuvers performed to reduce the probability of collisions with other objects. Figure 3 shows an example of the number of maneuvers performed by The Starlink satellites over a six-month period from June 2021 to November 2021.
SpaceX maneuvers from July to December 2021 (3,300 in total).
Collision avoidance system
To complete safe space operations in a scalable manner, SpaceX developed and equipped each SpaceX satellite with an airborne autonomous collision avoidance system to ensure that the satellites can maneuver autonomously to avoid possible collisions with other objects. If the probability of a conjunctive collision is greater than one in 100,000 (i.e. one-tenth of the industry standard "one in 10,000"), the satellite will plan for avoidance actions. When operating for any conjugate program, the satellite also takes care to avoid inadvertently increasing the risk of other conjugation that exceeds the same threshold.
By default, Starlink satellites assume responsibility for all conjugal events; SpaceX coordinates with other operators after receiving high probability conjugation information with another maneuvered satellite. SpaceX operators are on call 24/7 to coordinate and respond to inquiries from other carriers, which can obtain contact information for urgent requests via Space-Track.org. If other operators prefer to take responsibility for the maneuver themselves, SpaceX will order the Starlink satellites not to maneuver for an event.
In addition to collision avoidance maneuvering, Starlink satellites can also autonomously "dodge" the coincidence, adjusting their attitude to the state where the cross-section in the potential convergence direction is as small as possible (like the edge of a piece of paper), thereby reducing the probability of collision by another 4 to 10 times.
Compared to the worst-case direction (left), SpaceX's "avoidance" maneuver (right) minimizes the cross-sectional area on the potential collision direction (perpendicular to the image plane outward).
SpaceX's collision avoidance system has undergone a comprehensive review of NASA's Conjunction Assessment and Risk Analysis (CARA) program, which is part of SpaceX's Space Act Agreement (SAA) with NASA, under which NASA is based. to avoid a collision between NASA's science spacecraft and the SpaceX satellite.
SpaceX is proud of its evolving approach to design, testing, and operations to improve the sustainability and safety of space, which is critical to accelerating space exploration while bringing internet connectivity to the world. SpaceX urges all satellite owners/operators to make similar investments in sustainability and safety and to make the operation of satellites transparent. SpaceX encourages all owners/operators to generate high-quality ephemeris and covariance for inspection by the U.S. 18th Space Control Squadron and to publicly share this information with others to maximize coordination and ensure a sustainable and safe space environment in the future. Ultimately, space sustainability is a technical challenge that can be effectively managed through proper risk assessment, information exchange, and appropriate implementation of technical and operational controls. SpaceX can work with all parties to ensure that space is available for humanity to use and explore for generations to come.
reference:
[1] SpaceX official website https://www.spacex.com/updates/
[2] Official Announcement of China Manned SpaceFlight Office http://www.cmse.gov.cn/gfgg/