A SpaceX Falcon 9 rocket launched a small NASA jobsX-ray astronomy satellite on Dec. 9 to study black holes and neutron stars, serving as an "appetizer" for the launch of the much larger James Webb Space Telescope later this month.
At 1 a.m. Eastern, the Falcon 9 lifted off from Launch Complex 39A at the Kennedy Space Center. The payload, NASA's Imaging X-ray Polarimetry Explorer (IXPE) spacecraft, was released 33 minutes later by the rocket's upper stage.
IXPE, built by Ball Aerospace jobs with telescopes from NASA's Marshall Space Flight Center and detectors from the Italian space agency ASI, will study a number of objects, including black holes and neutron stars, to see how the X-rays emitted by these objects are polarised.
“By doing this mission, we are adding two variables to the astrophysics tool kit to understanding these sources, that’s the degree of polarization and direction associated with the polarization,” said Martin Weisskopf, IXPE principal investigator at NASA Marshall, during a prelaunch news conference Dec. 7.
An example he gave was pulsars. “We have three theories about how the X-rays are produced” by those rapidly spinning neutron stars, he said. “They all predict different polarization dependence.”
The science and operational requirements of IXPE drove it to an unusual orbit, at an altitude of 600 kilometers and an inclination of about zero degrees. “The inclination is very important to us because, in an equatorial orbit, the cosmic ray background is minimum,” Luca Baldini, a co-principal investigator for the mission at Italy’s National Institute for Nuclear Physics, said at another briefing on Dec. 7.
The altitude added Brian Ramsey, deputy principal investigator at NASA Marshall, was driven by a NASA orbital debris mitigation requirement to deorbit in 25 years. “This is the highest orbit we can put it in and still meet that requirement,” he said, with current predictions estimating it will re-enter in 18 years.
IXPE was created in response to this orbit, with the spacecraft designed to fit inside a Pegasus XL rocket. That air-launched vehicle would have flown out of the Pacific Ocean's Kwajalein Atoll to place the spacecraft in that equatorial orbit. However, in surprise, NASA selected SpaceX in 2019 to launch the mission on a Falcon 9 from Florida. SpaceX bid $50.3 million for launching IXPE, significantly less than previous NASA awards for Pegasus XL launches.
IXPE is the smallest dedicated payload launched on a Falcon 9, with an estimated mass of 325 kilograms, according to Julianna Scheiman, SpaceX's director of civil satellite missions, during the prelaunch briefing, but the inclination change consumed much of the vehicle's available performance.
This necessitated the first stage landing on a drone ship in the Atlantic Ocean rather than returning to Cape Canaveral, which was an option for some smaller payload Falcon 9 launches. The booster, which had previously launched the commercial crew missions Crew-1 and Crew-2, as well as the SXM-8 communications satellite and the CRS-23 cargo mission, successfully landed on the drone ship.
Another IXPE requirement led to the use of LC-39A, rather than nearby Space Launch Complex 40, for the launch. “The IXPE spacecraft is very sensitive to acoustic effects” from launch, said Tim Dunn, launch director in NASA’s Launch Services Program, at the prelaunch briefing. LC-39A has a better sound suppression system than SLC-40.
IXPE has a two-year primary mission, but Baldini said there were no consumables on board to exhaust and the X-ray detectors are not expected to degrade. “If everything goes well, I think it’s very possible we can aim for an extension.”
IXPE is the first of two NASA astrophysics missions scheduled to launch in December. In French Guiana, preparations continue for the launch of the James Webb Space Telescope on an Ariane 5 Dec. 22. NASA and ESA announced on Dec. 6 that they had completed fuelling JWST with hydrazine and dinitrogen tetroxide for its thrusters. That fuelling is one of the final steps before JWST is installed on the Ariane 5.
“We have a two-course dinner here,” said Thomas Zurbuchen, NASA associate administrator for science, during coverage of the launch on NASA TV. “This is the appetizer and the main dish is coming in two weeks when we’re going to launch the Webb Space Telescope.”
