Screenshot from SpaceX Webcast of the Starlink Grp. 2-7 launch. Time to clean the camera lens
Mission Rundown: SpaceX Falcon 9 - Starlink Grp. 2-7
Written: March 4, 2023
On second thought
SpaceX’s Starlink Group 2-7 mission will launch 51 Starlink v1.5 satellites atop a Falcon 9 rocket. The Falcon 9 will lift off from Space Launch Complex 4 East (SLC-4E), at the Vandenberg Space Force Base, in California, United States.
Starlink Group 2-7 will mark the 74th operational Starlink mission, boosting the total number of Starlink satellites launched to 4,053, of which ~3,756 will still be in orbit around the Earth once launched.
Starlink Group 2-7 will mark the fifth launch to the second Starlink shell which took place Friday on March 3, 2023 at 10:38:50 PST (18:38:50 UTC).
The booster supporting the Starlink v1.5 Group 2-7 mission is B1061-12; the name implies that the booster has supported eleven previous flights.
B1061-12 will have made its twelfth flight after launching its next mission:
Upon successful landing, the Falcon 9 boosters designation will change to B1061-13.
NOTAM with flight path and recovery area 661 km downrange. Blue dot marks OCISLY position
Following stage separation, the Falcon 9 will conduct a reentry burn lasting 20 seconds and a 21 second landing burn. These two burns aim to land the booster softly on SpaceX’s autonomous spaceport drone ship Of Course I Still Love You.
B1061-12 didn’t perform a static fire test after refurbishment while waiting for a West coast launch out of Vanderberg. SpaceX has omitted this safety precaution many times. It isn’t required to perform a static fire test on inhouse missions like Starlink or if the external private customers wish to save time.
The used fairings, which have flown one and four times before, will be retrieved by NRC Quest in the Pacific Ocean close to OCISLY. The fairings are now programmed to return towards the drone ship using the RCS gas thrusters and parachutes.
Ballistic falling fairings days are out. Boost ‘blow’ back with Nitrogen gas reigns.
The Starlink satellites
Starlink is SpaceX’s internet communication satellite constellation. The low-Earth orbit constellation delivers 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 version 1 of the constellation will not be complete until all five shells are filled.
Once Starlink generations 1 and 2 are 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 by now 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 internal wide payload fairing.
Due to this flat design, SpaceX was able to fit up to 60 Starlink satellites and the payload dispenser onto the second stage, while still being able to recover the first stage. This is near the recoverable 16 ton payload capacity of the Falcon 9 to LEO.
As small as the first generation Starlink satellites are, each 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.
Starlink v1.5 satellites are also equipped with a satellite laser communication system. This allows any 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, utilizing the US Department of Defense (DOD) debris tracking database to autonomously avoid collisions with other spacecraft and space junk.
Each satellite has a single solar panel, which simplifies the manufacturing process. To 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, its purchase price 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.
Stack of 21 Starlink v2.0 ready to be encapsulated in its fairing prior to be launched with a stack of 51 Starlink v1.5 satellites standing by ready to go in the corner. It's getting busy around here
SpaceX’s ‘Starship Class’ Starlink V2.0 satellites are even larger, more powerful satellites meant to be launched with the Starship launch vehicle.
While little is known about these satellites thus far, it is known that they mass roughly 1,200 kg and feature a twin-solar array design, to increase power delivered to the satellite.
And according to SpaceX CEO and CTO Elon Musk, the satellites will have an order of magnitude more bandwidth, higher speeds, and with 10x better performance.
In the future, Starlink V2.0 satellites will act as cell towers, providing worldwide cell phone coverage to T-Mobile customers. Musk has stated that each of these satellites will have roughly 2-4 Mb/s of bandwidth per cell phone zone, which will allow for tens of thousands of SMS text messages per second or many users placing phone calls.
While this technology is primarily meant for contacting emergency services worldwide (similar to Apple’s connect to satellite feature on the iPhone 14 series), it will also be able to be used for sending non-emergency-related messages.
The Falcon 9 launch
A typical Starlink mission begins with the countdown that has a traditional 35-minute long propellant load sequence which begins with RP-1 (a refined form of kerosene) loading on both stages and liquid oxygen (LOX) loading on the first stage only.
Loading of RP-1 on the second stage wraps up first at the T-20 minute mark followed by the usual “T-20 minute vent” as the oxygen purging begins on the pipelines of the Falcon 9 Transporter/Erector (T/E) that supplies fluids and power to the vehicle. LOX load on the second stage begins about four minutes after that at T-16 minutes.
Engine chill commences at the T-7 minute mark with a small flow of LOX going into the turbopumps on all nine Merlin engines on the first stage. RP-1 loading on the booster then wraps up about a minute later at the T-6 minute mark.
LOX load on the first and second stages ends at around the T-3 minute and T-2 minute mark respectively, and the rocket takes control of the countdown at the T-1 minute mark.
Engine ignition is commanded at T-3 seconds allowing them to achieve maximum thrust and pass final checks before committing to launch and if engine checks look correct, the ground clamps release the rocket for liftoff at the expected T0 time.
After liftoff, Falcon 9 climbs away from the launch site, pitching downrange as it maneuvers along its pre-programmed trajectory. Approximately 72 seconds into the flight, the vehicle passes through Max-Q — the point of maximum dynamic pressure, where mechanical stresses on the rocket are the greatest.
The nine first-stage engines continue to power Falcon 9 for the first two minutes and 27 seconds of the mission, until the time of main engine cutoff (MECO), at which point all nine engines shut down near-simultaneously.
Stage separation normally occurs four seconds later, with the ignition of the second stage’s Merlin Vacuum engine coming about seven seconds after staging.
While the second stage continues onward to orbit with its payload, the first stage coasts upward to apogee — the highest point of its trajectory — before beginning its trip back to Earth. The booster refines its course toward the landing zone before attempting to softly touch down on the deck of one of SpaceX’s three drone ships.
Two or three burns are required to secure the safe return and landing of a Falcon 9 booster depending on the chosen landing site. A boost back burn nullifies the horizontal speed from about 7000 km/h plus to a 1000 km/h negative if a return to launch site is chosen.
Normally a free fall trajectory is chosen which requires a re-entry burn designed to break the speed into the denser atmosphere. The Merlin 1D# engines start in a 1-3-1 sequence with the center engine 9 starting 4 seconds before lighting up engine 1 and 5 in a burn lasting 14-16 seconds ending with a 2 second center engine solo burn.
The re-entry burn last 20-22 seconds and the booster is now falling and steering through the denser atmosphere with the 6x8 feet grid fins. A last landing burn performed by the Merlin 1D# center engine is timed to the last millisecond securing the aiming and breaking of the boosters speed. The booster landing has now been performed 175 times.
Using a drone ship for booster recovery allows SpaceX to launch more mass in a payload on Falcon 9 than it would be able to launch on a return-to-launch-site mission.
In the meantime, the second stage carries on with the primary mission. After stage separation and Merlin Vacuum engine ignition, the payload fairing halves are jettisoned, thereby exposing the satellites to space.
Much akin to the Falcon 9 first stage, the fairing halves can be recovered and reused, using a system of thrusters and parachutes to make a controlled descent into the ocean where they will be picked up by a recovery vessel.
Second-stage engine cutoff (SECO-1) takes place just over eight and a half minutes into the flight. Other engine burns to modify or increase the deployment orbit will follow if the mission requires it, such as on Group 2-7 which used a second burn before deploying the Starlink v1.5 group 2-7 satellites.
The Starlink satellites are deployed into a low orbit so any faulty or non-functional spacecraft will quickly re-enter the atmosphere and be destroyed. Working satellites will raise themselves into a more stable orbit, where they will undergo checkouts before heading to their final operational orbits.
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. The second shell is currently holding 255 Starlink v1.5 satellites.
After spacecraft separation, the second stage will perform a deorbit burn for proper disposal, ensuring that reentry takes place in the south Pacific Ocean.
The Falcon 9 rocket
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 Falcon 9 can put some or many payloads in different orbits on 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 mission extension package it has a gray strip, which helps keep the RP-1 warm in sunlight, an increased number of composite-overwrapped pressure vessels (COPVs) for pressurization control, and additional TEA-TEB.
SpaceX is the first entity ever that recovers and reflies its fairings. After being jettisoned, the two fairing halves will use cold gas thrusters to orientate themselves as they descend through the atmosphere. Once at a lower altitude, they will deploy drogue chutes and parafoils to help them glide down to a soft landing for recovery.
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.
Comparison of Type 1 and 2 with measurements based on pixels - Type 2 are 5-6 inches thicker
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.
SpaceX used boats with giant suspended nets 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 2-7, SpaceX will attempt to recover the fairing halves from the water with their recovery vessel NRC Quest.
There are three known types of 34 x 17 foot fairings used by SpaceX to protect payload during ascent through the atmosphere. The first type had 10 evenly spaced ventilation ports in a circle on the bottom part of the fairings. This type was not aerodynamic enough to carry a parachute and ACS - Attitude Control System.
The aerodynamic balance during descent must have made them prone to stalling, or they burned up too easily. ACS gas tanks, flight orientation computers and ACS thrusters must have helped with these problems during development of type 2 fairings.
The second type is a slightly thicker fairing with only 8 evenly spaced ventilation ports in a circle on the bottom part of the fairings. The ventilation ports release the pressurized Nitrox gas during ascent, but let seawater in which makes it harder to refurbish the fairings after recovery from the ocean.
In 2021, SpaceX started flying a new “upgraded” version of the Falcon 9 fairing. The third type has 8 ventilation ports in pair’s near the edge of the fairings.
Some old type 2 fairings have been rebuilt and reused in Starlink launches. That have been a test program to develop the type 3 fairings to prevent saltwater from the ocean from flooding and sinking the fairing, and makes refurbishment toward the next flight easier.
Lately it’s apparent that the fairings are actively being aiming for the droneship in order to speed up the recovery process and cut corners of the time table. The fairing is actively breaking its speed and turning back before deploying its parachute at the last moment.
Another solution is a ‘vertical’ boost lifting the fairings apogee so the ballistic trajectory is changed aiming for a landing nearer the droneship. It’s equivalent to raising the angle on a water hose giving the water stream an higher arc but giving it a shorter reach.
It’s not clear whether or not the cold gas nitrogen thrusters alone are capable of doing a ‘boost back’ or a ‘push up’ so the fairings can alter their forward momentum mid-flight.
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