LightSail Readiness Check
We are pleased to provide this report from our LightSail Program Manager, Dr. Bruce Betts, in advance of an upcoming blog post by our own LightSail embedded reporter, Jason Davis to be published next week. Watch for that story in the coming days!
LightSail 2 Pre-Ship Review
By Bruce Betts
Director of Science and Technology and LightSail Program Manager
We held the LightSail 2 Pre-Ship Review (PSR) yesterday and it went very well. The PSR brought together the LightSail team as well as some external reviewers at Planetary Society headquarters in Pasadena to evaluate the status of the spacecraft and how close it is to being ready to ship. Pre-Ship Reviews are fairly standard in the spacecraft industry. It is a chance to thoroughly review what has been done to the spacecraft both in terms of software and hardware updates, as well as to review testing that has been done.
Many changes have been made to LightSail 2 based on what we learned from the LightSail 1 mission and on what we’ve learned in testing of LightSail 2. During the PSR we reviewed these changes as well as testing that was done to ensure that those changes did not introduce new problems.
Our software has been significantly upgraded compared to LightSail 1. Of course, when you make a software change, you need to thoroughly test the software to make sure that there are no bugs and that the new software hasn’t affected some other part of the system. One example of our many software changes is the addition of timers as backups in case something goes wrong unexpectedly. Software timers monitor important processes such as transmitting data to the ground. In that case, if it does not detect any transmission, then after one minute, it kills the radio transmission process (the spacecraft is designed to transmit a beacon every 7 seconds). The software will repeat this one more time before eventually resorting to rebooting the computer. In space, as with your home computer, sometimes problems can be fixed, or at least worked, through a reboot. You can learn more about the many hardware and software improvements we’ve made to LightSail 2 in Jason Davis’ blogs at sail.planetary.org/missioncontrol.
We also did a general review of the status of issues that had been identified over the last couple years. Engineers keep careful lists and associated documentation and discussion of issues that arise. They’re basically extremely well-documented "things to do" lists. Issues range from major spacecraft problems to be addressed, to minor things that arise in testing, to reminders to create appropriate documentation to help during actual spacecraft operations. Only a small handful of the 244 formerly open issues still remain open, and they mostly deal with creating documentation for operations.
The bottom line result from the review is that we are in excellent shape; we could ship now if we needed to and feel good about it. But, because we have the time, there are some minor issues identified that we want to look into, and additional tests that we want to run. We are still considering a couple minor changes to the flight software. After all changes are made, then we will do extensive testing of the final software.
Preparing LightSail 2 is just one part of a complex process leading to launch. Because of launch slips and other parts of the process, we have always chosen to do more tests, more fixes, and then more testing again. We continue with that mentality in order to best ensure mission success. It is of course far better to find issues and fix them on the ground than to try to deal with an issue that you may or may not be able to fix in orbit.
So, what are the puzzle pieces leading towards launch? LightSail 2 will first be integrated into a P-POD (Poly Picosatellite Orbital Deployer), the device that will actually deploy the spacecraft once in orbit using a spring mechanism. Members of the LightSail 2 team will actually do this integration. LightSail 2 will fly to space inside another spacecraft, Prox-1, a Georgia Tech spacecraft. Prox-1 have not had their formal PSR yet. When Prox-1 is ready to ship, and depending on the launch schedule, both spacecraft will be shipped to the Air Force Research Laboratory (AFRL) in Albuquerque, New Mexico where the 2 spacecraft will be integrated together, and then go through combined testing at AFRL: environmental testing such as vacuum tests, thermal tests and vibration tests, all of which we’ve already performed on LightSail 2 as a separate spacecraft. Prox-1 is part of the Air Force University Nanosat Program (UNP). We are all part of a set of payloads called STP-2 (Space Test Program-2). Eventually all STP-2 spacecraft will be integrated into a SpaceX Falcon Heavy Rocket.
When Will LightSail Fly?
We will fly on the 2nd flight of the Falcon Heavy, whose schedule has continued to slip. We could launch as early as this Fall, but until the first flight of the Falcon Heavy launches, we will likely not have a very firm launch schedule. Whatever happens, following our PSR, we now know that we can confidently deliver our spacecraft whenever the process is ready for it. In the meantime, we will continue to use the extra time to improve our spacecraft, and test, test, and test.