SpaceX: NASA Imaging X-ray Polarimetry Explorer Launch

At 06:00 UTC on 2021-12-09 a SpaceX Falcon 9, with the first stage making its fifth flight, launched NASA’s Imaging X-ray Polarimetry Explorer (IXPE) satellite. The small spacecraft contains three identical X-ray telescopes able to measure polarisation of the energetic photons it detects. The spacecraft was placed in an unusual 540 km circular equatorial orbit, chosen to avoid Earth’s radiation belts which interfere with detecting X-rays from distant objects. This is not an easy orbit to reach starting from Cape Canaveral’s 28° latitude. The second stage and payload are placed in an initial orbit whose apogee intersects the equator at the desired altitude, then a second burn at apogee performs the plane change maneuver and circularisation. The Falcon 9 is able to perform this costly maneuver only because the mass of the spacecraft is just 170 kg.

Here is an IXPE mission preview from Everyday Astronaut. I have cued the video to start one minute before launch.


Here is a Scott Manley video on the IXPE satellite, its unusual orbit, and the launch profile SpaceX used to get it there.

IXPE was originally intended to fly on the Pegasus air-launched smallsat launcher, but SpaceX’s bid came in lower than Northrop-Grumman’s for a Pegasus launch, which is why you see such a tiny satellite being launched inside a huge Falcon 9 payload fairing.