WASHINGTON — A Falcon 9 launched a pair of NASA science missions March 11 that will explore the infrared universe and study the solar wind.
The SpaceX Falcon 9 lifted off from Vandenberg Space Force Base in California at 11:10 p.m. Eastern. It placed into sun-synchronous orbits the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) spacecraft and the four satellites of the Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission. All five spacecraft were in contact with controllers and functioning as expected after launch, the agency stated.
NASA elected to launch SPHEREx and PUNCH together, using the excess capacity in the Falcon 9 originally procured for SPHEREx since both missions were going to similar orbits. It is part of an approach by NASA to take advantage of rideshare launch opportunities.
“This is a real change in how we do business,” Mark Clampin, acting deputy associate administrator for science at NASA, said at a March 7 prelaunch briefing. “We can maximize the efficiency of launches by two payloads at once.”
“We at SpaceX are big fans of rideshare,” said Julianna Scheiman, director of NASA science missions at SpaceX. While the company has flown many commercial rideshare missions, this was the first for NASA’s Launch Services Program. Two more NASA rideshare launches are planned for later this year by SpaceX, of the IMAP and TRACERS heliophysics missions, she noted.
The launch of SPHEREx and PUNCH was delayed by nearly two weeks, primarily because of launch processing issues. “We had a series of integration issues that came up,” Scheiman said. That included problems with equipment called an impedance mismatch assembly to mitigate launch environments that required new fasteners. That contributed to a “larger portion” of the delay, she said.
When the spacecraft were encapsulated in the payload fairing, technicians found a leak in the pneumatic system that separates the fairing in flight. That required removing the payload fairing to repair the leak before reinstalling it. Weather also delayed transport of the encapsulated payload from the payload processing facility to the launch pad.
Another issue, she said, was a “high-priority range operation” that required SpaceX to pause launch preparations. That is an apparent reference to the X-37B spaceplane that landed at Vandenberg early March 7.
There were additional delays after that pre-launch briefing. NASA and SpaceX called off a March 8 launch attempt because of an unspecified issue with the Falcon 9, while a March 10 attempt was scrubbed less than an hour before liftoff due to poor weather and a “ground data-flow issue” with SPHEREx.
Looking at the universe in a new way
SPHEREx is a NASA medium Explorer-class mission with an overall cost of $488 million that will perform an all-sky infrared spectroscopic survey. It will image the sky in 102 wavelength bands from 0.75 to 5 microns, using a wide-field telescope with a diameter of 20 centimeters. The spacecraft will be able to complete a single scan of the entire sky in six months.
“Even though SPHEREx uses a small telescope, it looks at the universe in a new way,” said Jaime Bock, principal investigator for the mission at Caltech, during a briefing in January about the mission. “This new capability allows us to address some of the most compelling questions in astronomy.”
Those questions fall into three key themes: studying the early universe, including the era of cosmic inflation immediately after the Big Bang; the formation and evolution of galaxies through the history of the universe; and measurements of water and organic materials in the Milky Way galaxy.
“The discoveries that SPHEREx are going to make, it’s going to answer a fundamental question: how did we get here?” said Shawn Domagal-Goldman, acting director of NASA’s astrophysics division, at the January briefing.
The 502-kilogram spacecraft was built by BAE Systems, which also developed the telescope at the heart of the mission. The telescope is an all-aluminum “free-form optic” design, said Brian Pramann, SPHEREx program manager at BAE Systems, in an interview. That design was driven by mission requirements to have a wide field of view and operate at cryogenic temperatures while fitting into a constrained budget.
“We pulled from a number of different heritage programs at BAE that we’ve flown with similar instrument designs, none exactly like the SPHEREx telescope, and so we were able to pull and piece together some of the design components it’s using,” he said.
“This is an Explorer mission, so you have to find novel ways to extract as much of the science” within its budget, said Alberto Conti, vice president and general manager for civil space at BAE Systems. “So, a very lightweight, new design telescope was warranted.”
SPHEREx has a distinct appearance thanks to three concentric cones, known as photon shields, that are designed to shield the telescope and instrument from the sun. “It’s a passive cryo telescope. There’s no cryocooler sitting at the heart of this thing,” said Pramann. While the design looks simple, he said the mission had to work to minimize mass while being able to withstand the rigors of launch, while also minimizing any contamination of the cones that could degrade their thermal performance.
Three-dimensional mapping of the corona
The secondary payload on the launch was PUNCH, a $150 million small Explorer mission flying four 64-kilogram satellites. Three of the satellites carry wide-field imagers to observe the sun while the fourth has a narrow-field imager.
“PUNCH fills in that science puzzle between the sun’s outer atmosphere, the corona, and the Earth,” said Joe Westlake, director of NASA’s heliophysics division, at a Feb. 25 briefing.
The four spacecraft will work in conjunction, taking images of the sun using different polarizing filters as well as unpolarized images. Scientists will use the images to construct three-dimensional maps of the corona to study how it transitions into the solar wind and the effects of events like coronal mass ejections, or CMEs, from the sun that can create space weather events at Earth.
“The PUNCH scientists hope to better understand the entire inner solar system from the sun, through the corona, out into the inner solar system, and how that material impacts Earth,” said Nicholeen Viall, PUNCH mission scientist at NASA’s Goddard Space Flight Center, at that briefing.
She noted that PUNCH will be able to observe not just large CMEs that other missions can rack but also smaller ones. “The sun is never quiet,” she said. “It’s constantly having little explosions. So, even when there’s not a big space weather event, even when there’s not a big CME, there’s still little events that constantly bombard our Earth. PUNCH is the first instrument to have the sensitivity and the resolution to be able to see that daily space weather.”
PUNCH is part of fleet of NASA heliophysics spacecraft that will soon grow even larger. Westlake noted that while most of the people involved in the SPHEREx/PUNCH launch would return home after launch, his staff would stay at Vandenberg. Another heliophysics mission, a trio of smallsats called Electrojet Zeeman Imaging Explorer (EZIE) to study the aurora, will launch on the SpaceX Transporter-13 rideshare mission scheduled for as soon as March 15.
