Featured image credit: SpaceX
Lift Off Time
|May 4, 2021 – 19:01 UTC | 15:01 EDT|
|Starlink V1.0 L25 (Starlink RF Mission 2-2): the 26th Starlink mission|
|Falcon 9 Block 5 B1049-9; 61 day turn around|
|Launch Complex 39A (LC-39A), Kennedy Space Center, Florida, USA|
|15,600 kg (~34,000 lbs) (60 x 260 kg, plus dispenser)|
Where did the satellites go?
|Starlink Shell 1; 550 km circular low-Earth Orbit (LEO), initial orbit: 53.06° 287 x 255 km|
Did they attempt to recover the first stage?
Where did the first stage land?
|632 km downrange on Of Course I Still Love You|
Tug: Mr. Jonah; Support: GO Quest
Did they attempt to recover the fairings?
|The passive fairing half was successfully recovered from the water ~680 km downrange by Shelia Bordelon; the active half was lost|
Were the fairings new?
|The active half has flown two previous times and the passive half is new (41 day turnaround time)|
This was the:
|– Fastest turnaround time of a fairing half ever at 41 days (previous record: 49 days)|
– 116th Falcon 9 launch
– 58th Falcon 9 flight with a flight proven booster
– 62nd re-flight of a booster
– 13th re-flight of a booster in 2021
– 83rd booster landing
– 13th launch for SpaceX in 2021
– 2nd 9th flight of a booster
– 34th SpaceX launch from LC-39A
– 39th orbital launch attempt of 2021 (38th successful launch)
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Where to watch
How did it go?
SpaceX’s Starlink V1.0 L25 (Starlink 25) mission successfully launched 60 Starlink satellites atop its Falcon 9 rocket. The Falcon 9 lifted off from Launch Complex 39A (LC-39A), at the Kennedy Space Center, in Florida, United States. Starlink 25 marked the 25th operational Starlink mission, boosting the total number of Starlink satellites launched to 1,565, of which 1,494 are still in orbit around the Earth.
In filings with the FCC, Starlink 25 is also known as Starlink RF Mission 2-2. The RF stands for “radio frequency,” and suggests that the satellites are not equipped with inter-satellite laser communication links. It is not known what the “2-2” signifies.
Starlink is SpaceX’s internet communication satellite constellation. The Low-Earth orbit constellation will deliver fast, low-latency internet service to locations where ground-based internet is unreliable, unavailable, or expensive. The first phase of the constellation consists of 5 orbital shells.
Starlink is currently in the “Better Than Nothing Beta,” allowing anyone in approved regions to order or preorder. However, for now, only higher latitudes are fully covered, so people of lower latitudes are currently only able to pre-order Starlink. After 28 launches SpaceX will achieve global coverage, but the constellation will not be complete until ~42,000 satellites are in orbit. Given SpaceX’s current Starlink production and launch rate, Starlink will have global coverage, excluding the poles, by the middle of 2021.
Once Starlink is complete, the venture is expected to profit $30-50 billion annually. This profit will largely finance SpaceX’s ambitious Starship program, as well as Mars Base Alpha.
Each Starlink V1.0 satellite has a compact design and a mass of 260 kg. SpaceX developed a flat-panel design, allowing them to fit as many satellites as possible into the Falcon 9’s 5.2 meter wide payload fairing. Due to this flat design, SpaceX is able to fit up to 60 Starlink satellites and the payload dispenser into the second stage, while still being able to recover the first stage. This is near the recoverable Falcon 9’s payload capacity to LEO, at around 17 tonnes.
For how small each Starlink satellite is, each one is packed with high-tech communication and cost-saving technology. Each Starlink satellite is equipped with 4 phased array antennas, for high bandwidth and low-latency communication, and two parabolic antennas. The satellites also include a star tracker, which provides the satellite with attitude data, ensuring precision in broadband communication.
The Starlink satellites are also equipped with an autonomous collision avoidance system, which utilizes the DOD’s debris tracking database to autonomously avoid collisions with other spacecraft and space junk.
Currently, the Starlink satellites being launched into polar orbit have a laser communication system on board. This system is currently in version 0.9, however SpaceX is expecting all new Starlink satellites to be equipped with it by next year.
To decrease costs, each satellite only has a single solar panel, which simplifies the manufacturing process. To further cut costs, Starlink’s propulsion system, an ion thruster, uses krypton as fuel, instead of xenon. While the specific impulse (ISP) of krypton is significantly lower than xenon’s, it is far cheaper, which further decreases the satellite’s manufacturing cost.
Each Starlink satellite is equipped with the first Hall-effect krypton powered ion thruster. This thruster is used both for ensuring the correct orbital position, but is also used for orbit raising and orbit lowering. At the end of the satellite’s life, this thruster is used to deorbit the satellite.
A satellite constellation is a group of satellites that work in conjunction for a common purpose. Currently, SpaceX plans to form a network of 11,716 satellites; however, in 2019 SpaceX filed an application with the Federal Communication Commission (FCC) for permission to launch and operate an additional 30,000 satellites as part of phase 2 of Starlink. To put this number of satellites into perspective, this is roughly 20 times more satellites than were launched before 2019.
Of the initial ~12,000 satellites, ~4,400 would operate on the Ku and Ka bands, with the other ~7,600 operating on the V-Band.
Due to the vast number of Starlink satellites, many astronomers are concerned about their effect on the night sky. However, SpaceX is working with the astronomy community and implementing changes to the satellites to make them harder to see from the ground and less obtrusive to the night sky. SpaceX has changed how the satellites raise their orbits and, starting on Starlink V1.0 L9, added a sunshade to reduce light reflectivity. These changes have already significantly decreased the effect of Starlink on the night sky.
Phase 1 Orbital Shells:
|Inclination (°)||Orbital Altitude (km)||Number of Satellites|
The first orbital shell of Starlink satellites will consist of 1,584 satellites in a 53° 550 km low-Earth orbit. Shell 1 consists of 72 orbital planes, with 22 satellites in each plane. This is the shell that SpaceX is currently filling, and it is expected that this shell will be complete by June 2021. Once complete, the first shell will provide coverage between roughly 52° and -52° latitude (~80% of the Earth’s surface), and will not feature laser links until replacement satellites will launch after 2021.
The second shell will consist of 1,584 satellites in a 540 km 53.2° LEO. This updated orbital configuration will slightly increase coverage area and will drastically increase the bandwidth of the constellation. This shell will also consist of 72 orbital planes with 22 satellites in each plane. After the first shell’s completion it is expected that SpaceX will fill this shell alongside with the 4th shell next.
Starlink’s third shell will host 720 satellites in a 70° 570 km orbit. These satellites will significantly increase the coverage area, which will make the Starlink constellation cover around 94% of the globe. SpaceX will put 20 satellites in each of the 36 planes in the third shell.
Shell 4 will consist of 348 satellites in a 97.6° 560 km orbit. SpaceX deployed 10 laser link test satellites into this orbit on their Transporter-1 mission to test satellites in a polar orbit. On April 6, 2021 Gwynne Shotwell said that SpaceX will conduct regular polar Starlink launches in the summer. All satellites that will be deployed into this orbit will have intersatellite laser link communication. Shell 4 will have 6 orbital planes with 58 satellites in each plane.
The final shell of phase 1 of Starlink will host 172 satellites in another 97.6° 560 km low-Earth polar orbit. Shell 5 will also consist purely of satellites with laser communication links, however unlike shell 4 it will consist of 4 orbital planes with 43 satellites in each shell.
Phase 2 Orbital Shells:
The sixth orbital shell of Starlink satellites is permitted to consist of 2,493 satellites in a 42° 335.9 km LEO. This large number of satellites will decrease latency and increase bandwidth for lower latitudes.
The seventh Starlink shell permits SpaceX to deploy 2,478 satellites into a 48° 340.8 km low-Earth orbit. These satellites will further decrease latency and increase bandwidth for lower latitudes.
The final shell of Starlink phase 2 allows SpaceX to deploy 2,547 satellites in a 53° 345.6 km orbit.
SpaceX has until March of 2024 to be half complete with phase 1, and phase 1 must be complete by March of 2027. Phase 2 must be half complete by November of 2024, and be finished by November of 2027. Failure to do so could result in SpaceX losing their dedicated frequency band.
What is Falcon 9 Block 5?
The Falcon 9 Block 5 is SpaceX’s partially reusable two-stage medium-lift launch vehicle. The vehicle consists of a reusable first stage, an expendable second stage, and, when in payload configuration, a pair of reusable fairing halves.
The Falcon 9 first stage contains 9 Merlin 1D+ sea level engines. Each engine uses an open gas generator cycle and runs on RP-1 and liquid oxygen (LOx). Each engine produces 845 kN of thrust at sea level, with a specific impulse (ISP) of 285 seconds, and 934 kN in a vacuum with an ISP of 313 seconds. Due to the powerful nature of the engine, and the large amount of them, the Falcon 9 first stage is able to lose an engine right off the pad, or up to two later in flight, and be able to successfully place the payload into orbit.
The Merlin engines are ignited by TEA-TEB. During static fire and launch the TEA-TEB is provided by the ground service equipment. However, as the Falcon 9 first stage is able to propulsively land three of the Merlin engines (E1, E5, and E9) contain TEA-TEB canisters to relight for the boost back, reentry, and landing burns.
The Falcon 9 second stage is the only expendable part of the Falcon 9. It contains a singular MVacD engine that produces 992 kN of thrust and an ISP of 348 seconds. The second stage is capable of doing several burns, allowing the Falcon 9 to put payloads in several different orbits.
For missions with many burns and/or long coasts between burns, the second stage is able to be equipped with a mission extension package. When the second stage has this package it has a grey strip, which helps keep the RP-1 warm, an increased number of COPVs for pressurization control, and additional TEA-TEB.
Falcon 9 Booster B1049
The booster that supported Starlink 25 is B1049, which had flown eight previous times. As Starlink 25 marked the booster’s 9th flight, it changed its designation to B1049-9.
|B1049’s missions||Launch Date (UTC)||Turn Around Time (Days)|
|Telstar 18V||September 10, 2018||N/A|
|Iridium NEXT-8||January 11, 2019||123|
|Starlink V0.9 L1||May 24, 2019||133|
|Starlink V1.0 L2||January 7, 2020||228|
|Starlink V1.0 L7||June 4, 2020||149|
|Starlink V1.0 L10||August 18, 2020||75|
|Starlink V1.0 L15||November 25, 2020||99|
|Starlink V1.0 L17||March 4, 2021||99|
|Starlink V1.0 L25||May 4, 2021||61|
Following stage separation, the Falcon 9 conducted 2 burns. These burns softly touched down the booster on SpaceX’s autonomous spaceport drone ship Of Course I Still Love You.
Falcon 9 Fairings
The Falcon 9’s fairing consists of two dissimilar reusable halves. The first half (the half that faces away from the transport erector) is called the active half, and houses the pneumatics for the separation system. The other fairing half is called the passive half. As the name implies, this half plays a purely passive role in the fairing separation process, as it relies on the pneumatics from the active half.
Both fairing halves are equipped with cold gas thrusters and a parafoil which are used to softly touch down the fairing half in the ocean. SpaceX used to attempt to catch the fairing halves in nets on GO Ms. Tree and GO Ms. Chief. However, at the end of 2020 this program was cancelled due to safety risks and a low success rate. On Starlink 25, SpaceX attempted to recover both the active and passive half from the water with their recovery vessel Shelia Bordelon.
SpaceX is currently flying two slightly different versions of the Falcon 9 fairing. The new “upgraded” version has vents only at the top of each fairing half, by the gap between the halves, whereas the old version had vents placed spread equidistantly around the base of the fairing. Moving the vents decreases the chance of water getting into the fairing, making the chance of a successful scoop significantly higher.
Fairings on this mission
On this mission, the passive passive fairing half was new. The active half had supported two previous missions: Starlink V1.0 L9 and Starlink V1.0 L22. This marked the fastest turn around time of a fairing half ever, at 41 days.
– 00:38:00 SpaceX Launch Director verifies go for propellant load.
– 00:35:00 RP-1 (rocket grade kerosene) loading underway.
– 00:35:00 1st stage LOx (liquid oxygen) loading underway
– 00:16:00 2nd stage LOx loading underway
– 00:07:00 Falcon 9 begins engine chill prior to launch
– 00:01:00 Command flight computer to begin final prelaunch checks
– 00:01:00 Propellant tank pressurization to flight pressure begins
– 00:00:45 SpaceX Launch Director verifies go for launch
– 00:00:03 Engine controller commands engine ignition sequence to start
– 00:00:00 Falcon 9 Liftoff
Starlink 25 Launch, Landing, and Satellite Deployment*
00:01:12 Max Q (moment of peak mechanical stress on the rocket)
00:02:32 1st stage main engine cutoff (MECO)
00:02:36 1st and 2nd stages separate
00:02:44 2nd stage engine starts (SES-1)
00:03:03 Fairing deployment
00:06:58 1st stage entry burn complete
00:08:37 1st stage landing
00:08:47 2nd stage engine cutoff (SECO-1)
00:45:45 2nd stage engine starts (SES-2)
00:45:45 2nd stage engine cutoff (SECO-2)
01:04:42 Starlink 25 payload deploy
* All times are approximate