The OSIRIS-REx mission will visit the carbonaceous near-Earth asteroid Bennu in 2018 and bring back a sample for analysis in Earth-based laboratories in 2023. In order to understand where the sample comes from as well as to select a sample site, the spacecraft has a number of science instruments with which to characterize the asteroid. One of these instruments is the OSIRIS-REx Laser Altimeter (OLA). OLA is provided by the Canadian Space Agency.
OLA is a LIght Detection And Ranging or LIDAR instrument. A LIDAR is similar to a RADAR but uses light instead of radio waves to measure distance. In OLA’s case, a laser outputs a pulse of light directed toward the asteroid. This pulse reflects back from the surface of the asteroid and a portion returns to the LIDAR. By carefully measuring the time difference between the outgoing pulse and the incoming pulse, the distance can be computed using the speed of light. These time differences are very small. To measure the distance to an object 1 km away, the time difference is about 6.5 millionths of a second! OLA will make this measurement to a very dark asteroid from up to 7 km away with precisions of a few centimeters.
Another unique aspect of the OLA instrument is its ability to point its laser very quickly allowing many measurements to be made without moving the spacecraft. OLA’s measurement speed of up to 10,000 measurements per second combined with a very agile scanning device allows “range pictures”to be taken. You can see how this is done in the figure below.
During OLA’s main observation phase, it will measure the shape of Bennu using 7 cm “pixels”. Since Bennu is approximately a 500-m sphere, we will have more than 160 million measurements of the surface of Bennu! To give you an idea of what this data could look like, here is a simulated “image”.
OLA is made up of two main parts. One contains the lasers, optics and scanning device while the other contains the computer and support electronics. The engineering model is currently being constructed. This model is used to show the design is a good one before the final one that will head to Bennu is built. Some pictures of the work being accomplished by our partners MDA and Optech Inc. are shown below:
The data from OLA will allow the OSIRIS-REx science team to directly measure the surface topography of Bennu as well as to measure the complete shape of the asteroid. This information is important to provide a complete picture of the asteroid as the shape is used along with mass to determine the density of the asteroid, which provides insight into the interior structure of Bennu. OLA will also collect fine-scale topography that will be used to help in selecting the site where the sample will be collected. Finally, OLA helps with the complex job of navigating to and operating around this low-gravity object by providing accurate ranges from the spacecraft to the asteroid.
OLA just passed its critical design review or CDR! Great work has been done by the whole OLA team with fantastic support from the larger OSIRIS-REx project in order to accomplish this milestone. A successful CDR means that, after some testing of the unit above, the next step is building the unit that will launch to Bennu in 2016!