Last week, OSIRIS-REx continued Outbound Cruise operations. The spacecraft is currently 47.6 million km from Earth and is executing a program designed to study and reduce the presence of water on the spacecraft.
During routine in-flight testing of the spacecraft’s thermal properties earlier this year, the mission’s navigation team noticed an unexpected minor acceleration of the spacecraft when the Sample Return Capsule (SRC) was exposed to sunlight. The mission team determined that this small thrust was caused by the outgassing of water that had been adsorbed by the SRC’s heat shield and backshell before launch. Retention of water in blanketing and other materials – and the subsequent outgassing of this water – occurs with all spacecraft. For OSIRIS-REx, it was determined that when the SRC is exposed to the Sun at a distance of <1.0 AU, this trapped water escapes and imparts a small thrust. While this small thrust would not be a problem for other missions, the gravity at the target asteroid Bennu is low enough that even this small amount of thrust could make orbital operations more difficult for OSIRIS-REx.
To better understand the outgassing effects on the spacecraft’s trajectory – and to bake out much of the remaining water before the spacecraft arrives at Bennu – the OSIRIS-REx mission team designed an outgassing program for execution starting earlier this fall. The choice of timing took into account both the spacecraft’s proximity to the Sun (<1.0 AU) and the fact that there were no science activities planned during this period. The outgassing program is being run concurrently with Outbound Cruise operations and does not affect the timing of the spacecraft’s arrival at Bennu.
Starting in mid-October, the spacecraft has been placed into various attitudes to expose different parts of the SRC to direct sunlight and initiate outgassing. Priority is given to the portions of the SRC that will face the Sun during asteroid proximity operations. The mission team has been able to detect and measure the rate of outgassing at each attitude and has determined that water is being removed as expected. The goal is to reduce the outgassing to the point where the spacecraft can fly the planned baseline trajectories around Bennu without modifications, and preliminary indications show that the program is progressing toward this goal. The program is scheduled to run through early January 2018.
The spacecraft continues to operate nominally. This last week the team updated some of the spacecraft’s onboard navigation files and, on Nov. 20, OSIRIS-REx’s downlink rate increased to 2 kbps from 200 bps.
OSIRIS-REx has travelled 1.17 billion km since launch and still has 824 million km to go until it arrives at Bennu.
Last week OSIRIS-REx continued Outbound Cruise operations. The spacecraft is currently 39 million km from Earth and 55 million km from Bennu.
Last week the spacecraft maintained normal operations for its Outbound Cruise Phase. On Nov. 13, the spacecraft’s communications downlink rate decreased to 200 bps from 10 kbps. The spacecraft continues to communicate back to Earth through its low gain antenna (LGA).
On the ground this last week, the OSIRIS-REx Science Team gathered in Tucson, Ariz. for its bi-annual meeting. This meeting focused on further refining the science planning processes that will be implemented when the spacecraft arrives at Bennu.
OSIRIS-REx continued normal Outbound Cruise operations last week. As of today, the spacecraft is 57 million km from Bennu, traveling at 8 km/sec relative to Earth. The one-way light time for transmissions from the spacecraft back to the ground is 100 seconds, which is an increase of 15 seconds in the last week. The spacecraft’s communications downlink rate remains at 10 kbps.
Last week the spacecraft maintained normal operations for its Outbound Cruise Phase. OSIRIS-REx is currently 25.6 million km from Earth and is traveling at approximately 28,000 km/h relative to Earth. One-way light time for transmissions from the spacecraft back to the ground is 85 seconds.
This past week, the mission took advantage of the spacecraft’s long outbound cruise to study the spacecraft’s thermal profile. As part of the exercise, the spacecraft was placed into certain orientations that it will employ during asteroid proximity operations in order to more precisely determine the thermal properties of each part of the spacecraft. As different spacecraft components were exposed to the Sun, the team measured how quickly they warmed and cooled. This in-flight characterization of OSIRIS-REx’s thermal properties will help the team more accurately predict the spacecraft’s thermal state while the spacecraft is operating close to Bennu.
Back on Earth, the ground team continues to be busy planning spacecraft operations and science observations for Bennu proximity operations, which will begin in August 2018 and continue through sample collection, scheduled for July 2020.
As of Oct. 23, the OSIRIS-REx spacecraft is traveling at approximately 25,000 kph relative to Earth. The spacecraft is approximately 17 million km from Earth and 57.7 million km from Bennu. But because Bennu is orbiting around the Sun and isn’t stationary, the spacecraft must still travel 948 million km before it can catch up to the asteroid.
On Oct. 16, the spacecraft’s communications downlink rate decreased to 10 kbps. Because of the low data rates and other mission planning activities, no science observations are planned through Jan. 7, 2018.
Last week, the OSIRIS-REx spacecraft continued on its new post-EGA trajectory toward Bennu. A REXIS Solar X-Ray Monitor testing and calibration activity began Oct. 9 and ran through Oct. 12. On Oct. 7, the spacecraft’s communications downlink rate decreased to 40 kbps from 200 kbps. The spacecraft continues to communicate back to Earth through its low gain antenna (LGA).
As of Oct. 16, the OSIRIS-REx spacecraft is approximately 12.9 million km from Earth and has traveled around 1.03 billion km since launch. It has another 970 million km to travel before it reaches Bennu.
The mission’s instrument teams and science working groups continue to actively process EGA science observations for the OCAMS, OVIRS, OTES and TAGCAMS instruments. Early indications show outstanding performance of the instruments, giving confidence that they will operate as designed at Bennu. Although the EGA maneuver and subsequent observations went smoothly overall, the science operations team is looking at lessons learned from EGA on both planning and ground tools to assess whether there are further improvements that could be made for Bennu operations.
As of Oct. 9, the OSIRIS-REx spacecraft is approximately 8.8 million km from Earth and its one-way light time is around 30 seconds.
Following a successful Earth Gravity Assist on Sept. 22, the spacecraft engaged its OCAMS and TAGCAMS cameras and OTES and OVIRS spectrometers on Sept. 22, Sept. 25 and Sept. 28 to observe the Earth and Moon. The instruments operated nominally and the mission team was able to use the opportunity to exercise its science operations procedures and calibrate the spacecraft’s instruments. Images and spectra of Earth and images of the Earth and Moon were also released. A final day of observations is scheduled for Oct. 2.
The mission’s navigation team determined that the spacecraft’s post-EGA trajectory was on course as planned. As a result, the trajectory correction maneuver (TCM-6) scheduled for Oct. 4 was cancelled.
On Friday, the OSIRIS-REx spacecraft completed its planned Earth Gravity Assist.
Last week, the OSIRIS-REx spacecraft maintained nominal operations as it continued on a trajectory toward Earth for its scheduled Sept. 22 Earth Gravity Assist (EGA). On Sept. 14, the spacecraft’s communications downlink rate increased to 300 kbps from 200 kbps as the spacecraft’s distance to Earth continues to shrink. The spacecraft is currently communicating through its low gain antenna (LGA).
As of Sept. 18, the spacecraft is 2.6 million km from Earth and its one-way light time is around 9 seconds.
This week, OSIRIS-REx’s navigation team determined that the spacecraft’s 23 Aug. trajectory correction maneuver (TCM-3) accurately set the spacecraft on the correct trajectory for its Sept. 22 Earth Gravity Assist (EGA). This means that there will be no need to execute TCM-4 or TCM-5, which were originally scheduled to further target the spacecraft at the optimal EGA aim-point.
Preparations for EGA continue for the team on the ground. In particular, the instrument teams are getting ready for science observations of Earth and the Moon as the spacecraft swings by Earth and continues on a new orbital plane out toward Bennu.
As of Sept. 11, the spacecraft is 6.5 million km from Earth, having traveled 933.9 million km since launch on Sept. 8, 2016.