SpaceX Falcon 9 Block 5 - IXPE - Launching December 9, 2021
Screenshot from SpaceX Webcast of the launch of IXPE
Mission Rundown: SpaceX Falcon 9 Block 5 - IXPE
Written: August 4, 2022
Staring at Stars with My third Eye
SpaceX successfully launched the Imaging X-Ray Polarimetry Explorer (IXPE) mission on their Falcon 9 rocket B1061-5 for NASA.
The Falcon 9 lifted off from Space Launch Complex 39A (LC-39A), at the Kennedy Space Center in Florida, United States at 06:00 UTC - 01:00 EST, December 9, 2021.
The IXPE spacecraft is the first dedicated to measuring the polarization of X-rays from cosmological sources.
It’s launching Wednesday, December 9, 2021 at 01:00 EST, from Launch Complex 39A (LC-39A). Starlink V1.5 Group 4-7 first stage booster B1061-6 will land on JRTI - ‘Just Read The Instructions’ around eight and a half minutes after liftoff.
After boosting the second stage along with its payload towards orbit, the first stage will perform a 20 second re-entry burn to slow the vehicle down in preparation for atmospheric reentry. The booster will then perform a 20 second landing burn aboard SpaceX’s autonomous spaceport drone ship JRTI.
SpaceX will also recover both fairing halves in the Atlantic Ocean with the recovery vessel Bob, named after Demo-2 Astronaut Bob Behnken.
B1061-5 will have made its fifth flight after launching the following missions:
B1061-6 did perform a static fire test at 12:18 EST December 4 after refurbishment and waiting for an east coast launch out of the Cape. SpaceX has omitted this safety precaution several times so far. It is not required to perform a static fire test on ‘inhouse’ missions like Starlink, which saves money and time before the launch.
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 fairings are a brand new pair type 3.2. Both fairings were salvaged after the landing. Active fairings are equipped with four pushrods to separate the two fairings.
Fairings have evenly spaced venting ports that have been redesigned a number of times by having first ten, then eight and now having their venting ports built as close pairs along the fairing edge. This prevents saltwater from the ocean from flooding and sinking the fairing, and makes refurbishment toward the next flight easier.
The fairings are equipped with acoustic cotton tiles that dampen the shock waves from the sound of the launch. Starlink Satellites are launched without acoustic tiles.
Two and a half minute after liftoff the 2nd stage will perform an inclination change from 28.5° to reach 0.2° at 540 km altitude that should take about 3.7 km/s of delta v. The 2nd stage will do a long sliding dogleg burn over equatorial Africa.
2nd stage just basically made a left turn onto the equator. Screenshot of SpaceX webcast.
IXPE is light enough to make that possible. SpaceX will probably launch directly into a orbit with a ~185km perigee and a ~540km apogee, with the apogee being very near the descending node so that the inclination change can be more efficient.
The second Stage 2 burn, which combined a 28.5° plane change and circularisation, caused an overall reduction in velocity, which is counter intuitive to say the least.
Indicated inertial velocity at the start of the burn is 25,474 km/h or 7076 m/s, and at shutdown it is 25,377 km/h or 7038 m/s, a reduction of 38 m/s.
Also, due to the burn occurring at a yaw angle averaging some 88.5°, the inertial acceleration starts negative, and only goes positive in the last third of the burn, peaking at less than 1g. The true acceleration of the stage would have been far higher, perhaps peaking at around 8g, the limit for IXPE.
However, it is important to remember that SpaceX webcasts telemetry displays inertial velocity (velocity relative to the launch site), not orbital velocity (velocity ignoring the rotation of the Earth).
At an altitude of 600km, and an inclination of 28.5°, the difference between inertial and orbital velocity is about 467 m/s, and once the plane change is complete, at 0° inclination, the difference increases to some 531m/s. So, although the displayed inertial velocity has reduced, the orbital velocity has actually increased slightly, circularizing the orbit.
The Science Payload
The Imaging X-Ray Polarimetry Explorer (IXPE) is a NASA space observatory comprised of three identical telescopes, which will measure the polarization of cosmic X-rays. The observatory will study the magnetic fields of many cosmological targets, including active galactic nuclei, quasars, pulsars, supernova remnants, magnetars, neutron stars, and black holes. These cosmological objects are surrounded by high-energy X-ray radiation environments which can be polarized, and studying this can provide information about the environments in which they were created.
Boom deployment test at Ball Aerospace. Human for scale. Credit: Ball Aerospace or NASA
The mission is expected to last two years, during which it will have two primary scientific objectives. Firstly, to better understand radiation processes and the properties of cosmic X-ray sources. Secondly, to study general relativity and quantum mechanics in extreme environments.
The observatory will feature a set of three identical telescopes, each operating independently for redundancy. Each of the systems has a 4-meter focal length mirror which focuses X-rays onto a popularization-sensitive imaging detector. These systems are all mounted on one optical bench which is co-aligned with the pointing axis of the spacecraft.
The mission was announced in January 2017 and has been developed by NASA’s Small Explorer program (SMEX). IXPE was built by Ball Aerospace & Technologies, and the telescope’s principle investigator is Dr. Martin C. Weisskopf, the chief X-ray astronomy scientist at NASA Marshall Space Flight Center, and project scientist on the Chandra X-ray Observatory.
The mission not only involves NASA but has many international collaborators. The spacecraft’s X-ray polarization detectors have been provided by the Italian Space Agency (ASI), and other collaborators include Stanford University, the University of Colorado Boulder, McGill University, MIT, and OHB Italia.
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