Falcon 9, IXPE

Imaging X-Ray Polarimetry Explorer (IXPE) | Falcon 9 Block 5

Lift Off Time
December 9, 2021 – 06:00 UTC | 01:00 EST
Mission Name
Imaging X-Ray Polarimetry Explorer (IXPE)
Launch Provider
(What rocket company launched it?)
(Who paid for this?)
NASA / Italian Space Agency
Falcon 9 Block 5 B1061-5
Launch Location
Launch Complex 39A (LC-39A), Kennedy Space Center, Florida, USA
Payload mass
170 kg (370 lb)
Where did the spacecraft go?
540 km low Earth orbit
Did they attempt to recover the first stage?
Where did the first stage land?
~620 km downrange on Just Read The Instructions

Tug: Doug; Support: Doug
Did they attempt to recover the fairings?
The fairing halves were recovered from the water ~665 km downrange by Bob
Were these fairings new?
This was the:
– 131st Falcon 9 launch
– 72nd Falcon 9 flight with a flight proven booster
– 76th re-flight of a booster
– 27th re-flight of a booster in 2021
– 97th booster landing
– 28th launch for SpaceX in 2021
– 128th orbital launch attempt of 2021
(121st successful)
Where to watch
Official Replay

How Did It Go?

SpaceX successfully launched the Imaging X-Ray Polarimetry Explorer (IXPE) mission atop their Falcon 9 rocket for NASA. The Falcon 9 lifted off from Space Launch Complex 39A (LC-39A), at the Kennedy Space Center in Florida, United States on December 9, 2021. The IXPE spacecraft is the first dedicated to measuring the polarization of X-rays from cosmological sources.

IXPE, mission patch
The IXPE mission patch (Credit: NASA)

What Is The Imaging X-Ray Polarimetry Explorer?

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.

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 an 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.

Centaurus A, black hole jet
A jet coming from the central, supermassive black hole of galaxy Centaurus A. Objects like this will be the target of IXPE. (Credit: NASA/Chandra X-ray Observatory)


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 polarisation 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.

An artistic representation of IXPE in Earth Orbit (Credit: NASA)

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.

First Stage

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.

Falcon 9, launch
Falcon 9 Block 5 launching on the Starlink V1.0 L27 mission (Credit: SpaceX)

Second Stage

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 IXPE is B1061. As IXPE is the booster’s 5th flight, its designation will change to B1061-5. The booster previously supported the launch of Crew-1, Crew-2, SXM-8, and CRS-23.

Falcon 9, booster landing
Falcon 9 landing on Of Course I Still Love You after launching Bob and Doug (Credit: SpaceX)

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, however, at the end of 2020 this program was canceled due to safety risks and a low success rate. On IXPE, SpaceX recovered the fairing halves from the water with their recovery vessel Bob.

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.

IXPE Countdown

00:38:00SpaceX Launch Director verifies go for propellant load
00:35:00RP-1 (rocket grade kerosene) loading underway
00:35:001st stage LOX (liquid oxygen) loading underway
00:16:002nd stage LOX loading underway
00:07:00Falcon 9 begins engine chill prior to launch
00:01:00Command flight computer to begin final prelaunch checks
00:01:00Propellant tank pressurization to flight pressure begins
00:00:45SpaceX Launch Director verifies go for launch
00:00:03Engine controller commands engine ignition sequence to start
00:00:00Falcon 9 liftoff
All times are approximate

IXPE Launch

00:01:12Max Q (moment of peak mechanical stress on the rocket)
00:02:331st stage main engine cutoff (MECO)
00:02:36Stage separation
00:02:442nd stage engine starts
00:03:11Fairing deployment
00:06:401st stage entry burn start
00:07:101st stage entry burn complete
00:08:062nd stage engine cutoff (SECO-1)
00:08:261st stage landing burn start
00:08:521st stage landing burn complete
00:28:372nd stage engine starts
00:29:302nd stage engine cutoff (SECO-2)
All times are approximate

Rocket section adapted from Trevor Sesnic

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