Science Planning and Scheduling in the Multi-Mission Era: Meet the Science Mission Scheduling BranchD. Adler (adler[at]stsci.edu)
You’ve seen Hubble's scientific results and the beautiful OPO images. But how does the whole process get started?
Once Hubble's (and soon, Webb's) annual Time Allocation Committee selects the science programs for a given observing cycle, the Observatory Planning Branch iterates with the Principal Investigators to fine-tune their programs utilizing the Astronomer's Proposal Tool (APT) to get them into a form where they can be scheduled. It's then up to the Science Mission Scheduling Branch (SMSB), with Bill Workman as Branch Lead, to create the Long Range Plan (LRP) at the beginning of the observing cycle. Once in place, SMSB also creates the weekly flight schedule and the instructions that get uplinked to the telescope.
The LRP (Long Range Planning) Group—Dave Adler, Brigette Hesman, and Ian Jordan—has two main tasks. First, they create an observing plan that enables Hubble to be scheduled as efficiently as possible. These observing plans typically span ~18 months, to give some flight-ready material for the transition to the next observing cycle, and include 2000–2500 individual science "visits," generally spanning from 1–5 orbits (1.5–7.5 hours) each. Time is money, as the saying goes, so the more time Hubble is observing, the better. With the four science instruments having varied observing characteristics, and targets spread throughout the sky requiring spacecraft slews, all factors are considered when creating the LRP. Most science observations don't require specific timing or telescope orientation, and can be scheduled throughout the observing cycle. But some observations have precise period/phase requirements (i.e., transiting exoplanets), or are coordinated to observe specific events (such as Juno orbital passes of Jupiter, or Europa's flaring plumes). With a lot of recent interest from the astronomical community in regards to specifically timed events, the percentage of highly constrained Hubble observing time has risen in recent years. The LRP group sorts these out to avoid scheduling conflicts, and consults the Hubble Mission Office for priorities as needed.
Second, the LRP group maintains the observing plan by making adjustments, as needed, on a daily basis. That's right, the LRP isn't static—it's a living, breathing entity! Target-of-Opportunity programs can interrupt an executing timeline; failed visits and new material (Director's Discretionary time, mid-cycle programs) get added back to the LRP as soon as possible. When there's a spacecraft anomaly, the LRP group determines the observing priorities and helps get the spacecraft back online as quickly as possible.
The LRP group also looks for ways to increase productivity. In 2009, right after Servicing Mission 4, they changed the planning process to better take advantage of Hubble science that could schedule through the South Atlantic Anomaly (SAA). That efficiency gain allowed 3–4 more science orbits to be completed each week, i.e., up to 200 orbits (300 hours) of extra Hubble science per year. Those gains have been maintained to this day.
Along with ongoing Hubble operations, the LRP group is creating and testing tools for the James Webb Space Telescope science observing plans. The concept is mostly the same, but specifics certainly differ. For instance, Webb orbiting L2 means there are no concerns from the SAA as with Hubble, but on the flip side, spacecraft momentum will have to be actively managed. The different field of view, due to sunshade placement and pointing constraints, also create a challenge of how often a specific target is visible throughout an observing cycle. Through it all, the goal for Webb will be the same as for Hubble—maintain the highest observing efficiency possible.
Each week, the Short-Term Schedulers (STS)—Gary Bower, Jim Caplinger, Bill Hathaway, RJ Lampenfield, Ryan Logue, and Kristen Wymer—query the Hubble LRP for the next week of observations, starting 11 days before the one-week flight products start executing. The exact order of the science and calibration visits isn't determined ahead of time; these "calendar builders" put things together to create the most efficient schedule as possible. In addition to the observations, they take into account things like spacecraft slews, guide star acquisitions, target acquisitions for positioning in the appropriate aperture, and communications with the TDRS satellites (for Hubble). STS is ably supported by software developers Don Chance and Danny Jones.
While Webb has yet to launch, there will be a similar process in place to proceed from querying the LRP for the mix of science, to building short-term schedules, to producing flight products that will be uplinked to the telescope using the Deep Space Network. In anticipation of Webb operations, both the LRP and STS groups have been involved in numerous Science Operations Rehearsals, and participated in the NASA operational exercises.
For the past ~30 years, SMSB has been planning and scheduling a single telescope. The dawn of a multi-mission environment—with more missions yet to come—will be a challenge, but SMSB is ready for this exciting time at the institute.