Screenshot from SpaceX Webcast of the SDA Tranche 0-1 launch. The fog kept lingering overhead
Mission Rundown: SpaceX Falcon 9 - SDA Tranche 0-1
Written: April 2, 2023
Is this AWACS in Space?
SpaceX is transporting a group of satellites for the Space Development Agency in the mission Transport & Tracking Layers 0-1. SDA is lofting eight Transport Layer satellites from York Space Systems and two Tracking Layer satellites from SpaceX.
The rocket carrying Tranche 0-1 is lifting off from Space Launch Complex 4 East (SLC-4E), at Vandenberg Space Force Base, in California, United States.
This is the first of two flights aimed at placing spacecraft into Tranche 0. That is, Flight 1 is tasked with populating one of the two different orbital planes in this tranche for each, both at the same altitude of 950 km (~590 mi) and 89.5 degrees inclination.
Lift Off took place on Sunday, April 2, 2023 at 07:29 PDT - 14:29 UTC from Space Launch Complex 4 East at Vandenberg Space Force Base.
The Falcon 9 with booster B1075-2, its second stage and fairings containing 10 satellites had one previous attempt Friday, before it was halted at T-1 seconds.
B1075-2 will have made its second flight after launching its next mission:
After separating from the second stage, the booster B1075-2 will return to Landing Zone 4 at the launch site. After refurbishment it will be designated as B1075-3. The second stage will be deorbited south of Cape Town a couple of hours after the launch.
The fairings are both reused, flying for the fourth and sixth time with no known previous missions flown together. NRC Quest will recover them 490 km downrange.
The Tranche 0-1 payload
A more correct name for the Tranche 0-1 abbreviated version, Transport & Tracking Layers 0-1, is Transport and Tracking Layers, Tranche 0, Flight 1. The gist of this is a part of test group 0 who will be launched on two flights with Falcon 9 rockets.
It speaks of two components in a defense, low-Earth orbit (LEO) constellation, designated the Proliferated Warfighter Space Architecture (PWSA).
Each of said components is considered a layer, of which the PWSA will consist of seven layers: Transport - Tracking - Battle Management - Custody - Emerging Capabilities - Navigation - Support.
Graphic with the PWSA architecture of the space network of small, medium and large satellites
Tranche 0 represents a technology demonstration through a minimum viable product with enough performance to allow for testing, and exploration of the possibilities it offers. As such, it will feature two orbital planes with 14 satellites in each of them, at 950 km (~590 mi) altitude and 80.0 degrees inclination.
The ‘Data’ Transport Layer will be the backbone of the PWSA architecture, as the Transport Layer designates the group of spacecraft already charged with data-relaying activities. In other words, inside this constellation they will provide communications services.
Populating Tranche 0 of this layer, there will be 20 spacecraft — 10 manufactured by Lockheed Martin and another 10, by York Space Systems. These contractors were awarded by the SDA with USD 187.5M, and USD 94M respectively back in 2020.
In each of these groups of 10, it is believed that seven will be provided with four optical (laser) cross-links, while the remaining three, with two cross-links and two downlinks.
This is how satellites are able to communicate among peers in the same layer (even if they are built by different companies), with satellites in other layers, as well as with defense systems on the surface: land, sea, or even air.
The Tracking Layer will on the other hand operate quite differently. In this case, the satellites in it will remain vigilant for possible detection of ballistic missiles, and, especially, of hypersonic glide missiles, heading toward the US.
These follow much lower trajectories, and can maneuver, which prevents the DoD’s satellites sitting in geostationary orbit (GEO) from responding in time.
In order to do their job, these spacecraft will have a wide field-of-view (WFOV) overhead persistent infrared (OPIR) sensor. Once a missile is targeted by it, the satellite will relay the information of its location and its trajectory through a secure path.
The spacecraft will use its optical cross-links, to talk to the Transport Layer. In turn, this one will talk to whichever asset is needed, e.g. an interceptor.
Back in 2020, the SDA bought the first eight satellites for this layer: four contracted to L3Harris, for USD 193.50M; another four, to a SpaceX-Leidos team, for USD 149M — the first time the U.S. military has announced an order of satellites from SpaceX.
The SpaceX-Leidos team developed a new bus in-house, while SpaceX based its satellites on the Starlink bus. In orbit, these will have to carry out early detection and tracking of the already mentioned threats headed toward the US.
The rocket 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 two minutes 20/30 seconds of the mission, until the time of main engine cutoff (MECO), at which point all nine engines shut down nearly simultaneously.
Stage separation normally occurs 3-4 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 performs a boost back burn for a return trajectory to LZ-4 near the launch site. The booster refines its course toward the landing zone before attempting to softly touch down.
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 over 180 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 this mission which used a second burn before deploying the Tranche 0-1 satellites.
The Tranche 0-1 satellites are deployed into a lower 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 orbit.
After spacecraft separation, the second stage will perform a deorbit burn for proper disposal, ensuring that reentry takes place in the south Atlantic/Indian Ocean.
The rocket vehicle
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 this Tranche 0-1 mission, SpaceX will attempt to recover the fairing halves from the water with the 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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