Featured image credit: SpaceX
Lift Off Time
|September 5, 2022 – 02:09 UTC|
September 4, 2022 – 22:09 EDT
|Starlink Group 4-20 & Varuna; the 25th launch to Starlink Shell 4, and a ridesharing spacecraft|
|Falcon 9 Block 5, B1052-7; 31.13 day turnaround time|
|Space Launch Complex 40 (SLC-40), Cape Canaveral Space Force Station, Florida, USA|
|Starlink: ~15,650 kg (~34,750 lb) (51 x ~307 kg, plus dispenser)|
Varuna: 180 kg
Where are the satellites going?
Starlink Shell 4; 540 km circular low-Earth orbit (LEO); initial orbit: 304 x 316 km x 53.22°
Varuna, 1,056 km circular LEO; initial orbit: same as Starlink
Will they be attempting to recover the first stage?
Where will the first stage land?
|~640 km downrange on Just Read the Instructions|
Tug: Kurt Crosby; Support: Doug
Will they be attempting to recover the fairings?
|The fairing halves will be recovered from the water by SpaceX’s recovery vessel Doug ~644 km downrange.|
Are these fairings new?
How’s the weather looking?
|The weather is currently 80% GO for launch (as of September 3, 2022 12:30 UTC)|
This will be the:
|– 174th Falcon 9 launch|
– 112th Falcon 9 flight with a flight-proven booster
– 116th re-flight of a booster
– 38th re-flight of a booster in 2022
– 140th booster landing
– 66th consecutive landing (a record)
– 40th launch for SpaceX in 2022 (a record)
– 96th SpaceX launch from SLC-40
– 112th orbital launch attempt of 2022
– 1st Starlink mission with rideshares of 2022
Where to watch
What’s This All Mean?
SpaceX’s Starlink Group 4-20 mission will launch 51 Starlink satellites and Varuna — a ridesharing communications test satellite for Boeing — atop a Falcon 9 rocket. The Falcon 9 will lift off from Space Launch Complex 40 (SLC-40), at the Cape Canaveral Space Force Base, in Florida, United States. Starlink Group 4-20 will mark the 58th operational Starlink mission, boosting the total number of Starlink satellites launched to 3,259, of which ~2,992 will still be in orbit around the Earth once launched. Starlink Group 4-20 will mark the 25th launch to the fourth Starlink shell; roughly 35 launches will be required to fill Shell 4.
What is Varuna?
Built for Boeing in order to carry out a technology demonstration, this test spacecraft will evaluate the performance of the V-band communications system envisaged by the company — with the future intention of creating a constellation of 147 satellites. Such an examination will verify the chosen band spectrum’s behavior for transmissions. Manufacturers of ground terminals that will receive signals from this system will get an opportunity of testing and adjust their hardware before it enters operation. What is more, potential customers will also be given a chance to assess the qualities of the service.
To accomplish these goals, the spacecraft built in the context of this commercial program will raise its orbit from where the Falcon 9 launch vehicle will have left it — at about 310 km of altitude — to a larger one at 1,056 km and 54° inclination. Varuna is capable of doing this by itself, as it is assembled with Spaceflight Inc.’s orbital transfer vehicle (OTV), the Sherpa-LTC, as its founding block. Once the final destination is reached, the aforementioned tests will take place during a time span of up to two years. Afterward, Varuna will lower its perigee to 300 km, its orbit becoming elliptic, and in doing so it will favor orbital decay. As expected, this will finally lead to reentry and to the spacecraft’s destruction.
After a mishap that prevented this vehicle to fly in SpaceX’s Transporter-4 mission, it will attempt its maiden flight for a second time, hence the numeral. As previously mentioned, Varuna’s general structure is based on this OTV. As a consequence, it is provided with its own chemical propulsion system — named Polaris — and with four main solar panel assemblies generating up to 46 W of energy each — stored in two battery packs. The general measurements of this test satellite are 0.82 m x 1.42 m x 1.23 m, featuring a mass of 180 kg at launch.
In terms of spacecraft functions, Astro Digital designed and manufactured both the payload for communications testing and the command and control system known as Makalu. These two are separate modules installed on the Sherpa’s ring, where four other slots will remain vacant. In the following picture the space tug — another name sometimes used to speak of OTVs — is presented with all of its slots in use.
Star trackers and gyros offer Varuna the required capabilities for attitude and rate determination, whereas control is obtained by means of reaction wheels and magnetorquer rods. In combination with this assortment of hardware, in-space maneuvering abilities are materialized by the propulsion system. Manufactured by Benchmark Space Systems, it makes use of four Ocelot thrusters burning high-test peroxide (HTP) and isopropyl alcohol (IPA). 32.9 kg of the former and 6.1 kg of the latter are loaded into the spacecraft’s gaseous-nitrogen-pressurized tanks before launch. Polaris can produce 88 N of thrust, achieving a specific impulse of ~300 s.
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 five orbital shells.
Starlink is currently available in certain regions, allowing anyone in approved regions to order or preorder. After 28 launches SpaceX achieved near-global coverage, but the constellation will not be complete until ~42,000 satellites are in orbit. 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 V1.5 satellite has a compact design and a mass of 307 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 payload capacity of the Falcon 9 to LEO, around 16 tonnes.
As small as each Starlink satellite is, each one is packed with high-tech communication and cost-saving technology. Each Starlink satellite is equipped with four 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.
Each Starlink V1.5 satellite is also equipped with an inter-satellite laser communication system. This allows each satellite to communicate directly with other satellites, not having to go through ground stations. This reduces the number of ground stations needed, allowing coverage of the entire Earth’s surface, including the poles.
The Starlink satellites are also equipped with an autonomous collision avoidance system, which utilizes the US Department of Defense (DOD) debris tracking database to autonomously avoid collisions with other spacecraft and space junk.
To decrease costs, each satellite 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 for both ensuring the correct orbital position, as well as 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.
|Inclination (°)||Orbital Altitude (km)||Number of Satellites|
The first orbital shell of Starlink satellites consists of 1,584 satellites in a 53.0° 550 km low-Earth orbit. Shell 1 consists of 72 orbital planes, with 22 satellites in each plane. This shell is currently near complete, with occasional satellites being replaced. The first shell provides coverage between roughly 52° and -52° latitude (~80% of the Earth’s surface), and will not feature laser links until replacement satellites launch.
Starlink’s second 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. This shell is currently being filled, along with Shell 4.
Shell 3 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. SpaceX launched an additional three satellites to this shell on the Transporter-2 mission. On April 6, 2021, Gwynne Shotwell said that SpaceX will conduct regular polar Starlink launches in the summer, but this shell is now the lowest priority and is expected to be the last filled. All satellites that will be deployed into this orbit will have inter-satellite laser link communication. Shell 3 will have six orbital planes with 58 satellites in each plane.
The fourth shell will consist of 1,584 satellites in a 53.2° 540 km LEO. This updated orbital configuration will slightly increase the 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. This shell is currently being filled alongside Shell 2.
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 3, it will consist of four orbital planes with 43 satellites in each plane.
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 complete half of Phase 1 and must fully complete Phase 1 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 its 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 triethylaluminum and triethylborane (TEA-TEB), which instantaneously burst into flames when mixed in the presence of oxygen. 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 composite-overwrapped pressure vessels (COPVs) for pressurization control, and additional TEA-TEB.
Falcon 9 Booster
The booster supporting the Starlink Group 4-20 mission is B1052, which has supported six previous flights. Hence, its designation for this mission is B1052-7; this will change to B1052-8 upon successful landing.
|B1052’s missions||Launch Date (UTC)||Turnaround Time (Days)|
|Arabsat-6A||April 11, 2019 22:35||N/A|
|STP-2||June 25, 2019 06:30||74.33|
|CSG-2||January 31, 2022 23:11||951.70|
|Starlink Group 4-10||March 9, 2022 13:45||36.61|
|Starlink Group 4-18||May 18, 2022 10:59||69.88|
|KPLO||August 4, 2022 23:08||78.51|
|Starlink Group 4-20||September 5, 2022 02:09||31.13|
Following stage separation, the Falcon 9 will conduct two burns. These burns aim to softly touch down the booster on SpaceX’s autonomous spaceport drone ship Just Read the Instructions.
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 touch down the fairing half in the ocean softly. SpaceX used to attempt to catch the fairing halves, however, at the end of 2020, this program was canceled due to safety risks and a low success rate. On Starlink Group 4-20, SpaceX will attempt to recover the fairing halves from the water with their recovery vessel Doug.
In 2021, SpaceX started flying a new version 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.
All times are approximate
|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|
Launch, Landing, and Deployment
All times are approximate
|00:01:12||Max Q (moment of peak mechanical stress on the rocket)|
|00:02:29||1st stage main engine cutoff (MECO)|
|00:02:33||1st and 2nd stages separate|
|00:02:39||2nd stage engine starts|
|00:08:05||1st stage entry burn start|
|00:06:36||1st stage entry burn complete|
|00:08:05||1st stage landing burn start|
|00:08:27||1st stage landing|
|00:08:45||2nd stage engine cutoff (SECO-1)|
|00:45:25||2nd stage engine starts (SES-2)|
|00:45:27||2nd stage engine cutoff (SECO-2)|
|00:49:28||Spaceflight’s Sherpa-LTC deploys|
|01:12:23||Starlink satellites deploy|