REBR-W2 Fails to Send Data During Fiery Ride to Earth
The Reentry Breakup Recorder-Wireless 2 finally returned home today, but failed to send data as the Cygnus cargo craft burned up in the atmosphere.
The year and a half in space may have proved too much for the REBR-W2, which was designed for a relatively short duration mission on orbit.
While it may have collected the data from various wired and wireless sensors installed in the Cygnus, the Iridium satellite, which uploads data sent from the REBRs to a website that can then be accessed by Aerospace scientists, never received the data from the REBR-W2.
“The return of data from REBR-W, and the REBR predecessors, is highly risky,” said Dr. Mike Weaver, director of the Fluid Mechanics Department and project manager for REBR-W. “For the previous REBRs, we received data from three out of four reentries. For REBR-W, it has been on orbit for a year and half, and we don’t know what ionizing radiation events may have occurred to upset our electronics. Even without that unknown, the reentry breakup process is like a hypersonic train wreck – very violent.
“We are confident that REBR-W2 had plenty of battery life remaining, and that was definitely not a problem,” he added.
The Cygnus, an Orbital ATK cargo craft, was released from the International Space Station Tuesday, June 14. Cargo crafts carry supplies to the ISS and carry away trash and other refuse for disposal during controlled, destructive reentries into the South Pacific Ocean.
The REBR-Ws are designed to collect and transfer reentry data from vehicles returning to Earth from space. They measure hull temperatures at four locations, tumble and breakup dynamics, pressure changes, structural frequency response, and speed changes. They essentially function as a black box, and are designed to survive the breakup on the host vehicle during its reentry. It then “phones home” while still falling to Earth and sends all its data to an Iridium satellite orbiting space, which then uploads the data to a website. This data is downloaded and used to validate the results from simulations done with models.
“We use physics-based models to predict the trajectory, the heating environment, the temperature changes, how the vehicles come apart, and how many pieces can survive reentry,” Weaver said. “We need to be able to compare predictions with actual results. We can compare the models with data collected from ground testing, but that doesn’t capture all aspects of reentry. All this data can give better understanding of what is happening.
“We’ve flown four REBRs before and collected dynamics data from three; we were the first to do that. Aerospace is a leader in that area,” he added.
The REBR is the predecessor of the REBR-W, which has the additional capability to record and collect data through both wireless and wired external sensors, a benefit not included with the original REBR.
Aerospace, through its connection to the Air Force’s Space and Missile Systems Center, is responsible for assessing the risk for all Department of Defense missions to and from space, and part of that assessment includes reentries and space debris. Because of Aerospace’s work with REBRs, funded by the Air Force, NASA contracted Aerospace to produce a series of REBR-Ws to validate reentry models in anticipation of the ISS eventually coming back to Earth. The DoD’s Space Test Program provided integration and safety support for the REBRs and REBR-Ws.
The REBR-Ws record the internal events surrounding a reentry breakup. What completes the picture is an external, visual record of those same events.
The SETI Institute, which partners with NASA Ames to support scientific and technical missions, was onsite in a plane, watching for the reentry and documenting what they see. SETI Institute, which adopted its name from the collective term for the scientific search for extraterrestrial intelligence and life, has interests in objects reentering the Earth’s atmosphere.
“SETI Institute is looking at the building blocks for life, astrobiology, and likes to observe reentry and characterize the types of temperatures involved,” Weaver said.
Although the REBR-W2 failed to send any data to the Iridium satellite, the observation campaign was a complete success, Weaver said.
Half the funding for this observation campaign came from Aerospace, and the Federal Aviation Administration provided the other half, as they also have a need to assess reentry risks for commercial spacecraft. The plane carried twelve researchers from around the world, including Janna Feeley from Aerospace. Aerospace’s Dr. Bill Ailor will lead Aerospace assessment of data returned from the plane.
Weaver said he and his team had hoped to collect details from inside Cygnus with REBR-W2 and from outside with the help of SETI Institute. Had the REBR-W2 been successful, it would have been the most comprehensive coverage of reentry breakup ever, he said.
Voyage to Space
The second REBR-W’s journey, which was supposed to be short and sweet, instead turned into a saga spanning over a year and a half, far longer than the anticipated couple of months.
The current REBR-W, dubbed REBR-W2, replaced the original REBR-W1 after the explosion of the Antares launch vehicle in October 2014. Aerospace had a replacement built, tested, packed up, and off to NASA two short and frantic weeks later.
The REBR-W2 finally made it up to the ISS in January 2015, and was scheduled to return on the ATV-5 at the end of February. But, four days before the European ATV-5 was scheduled to depart ISS, one of its three power systems began to fail, and the European Space Agency decided to change from a shallow reentry to a steep reentry to avoid the risk of the surviving debris crash landing in populated areas. The REBR-W2 would have to wait for another host vehicle to reenter the atmosphere.
“ATV-5 was to fly a shallow reentry to mimic that of ISS when it is eventually de-orbited,” Weaver said. “A steep reentry was less useful to NASA to validate models, but also REBR-W2 software is expecting an ATV-5 shallow reentry and planned engine burn characteristics. There are ATV-5 events used to trigger REBR-W responses; the REBR-W software would not behave properly on an ATV-5 steep reentry. We had to rapidly evaluate our options, and decided to keep REBR-W2 at ISS to wait for an appropriate reentry opportunity.”
Aerospace and NASA assessed possibilities for another seven months, when NASA decided to put all ISS reentry experiments indefinitely on hold, and gifted REBR-W2 back to Aerospace to do with it what Aerospace and DoD Space Test Program chose. Promising discussions had already been held with Orbital ATK for use of their Cygnus as the host vehicle. With a relatively small investment of new funding from the Air Force, Aerospace focused REBR-W2 on achieving DoD model validation objectives.
After going over the programmed algorithms in great detail, with valuable insight by Aerospace’s Dr. Brian Hardy, it was determined the Cygnus would be a viable solution with only minor modifications to its original trajectory, which Orbital ATK made with no interference to their normal operations, Weaver said. The only change to the REBR-W2 system itself was sending a replacement temperature sensor up with the Cygnus when it launched to the ISS in March of this year because the original sensor already with the REBR-W2 in space would not fit anywhere useful in the new host vehicle.
But this mission would not be possible without the man on the inside–the astronaut living in the ISS who installed the REBR-W2 in the Cygnus and activated it Monday, June 13.
“The astronaut doing all the work on ISS was Jeff Williams,” Weaver said. “He reviewed our crew procedures and REBR-W overview, then installed and activated the REBR-W2 and its external sensors. Inside Cygnus before launch, astronaut Tom Marshburn participated in a fit check, alongside Aerospace’s Geoff Maul, and even selected a couple sensor locations for us.”
“And then we were ready for this mission,” he added.