But when is enough, enough? There are so many places to go, so much to do and so little money to spread around; new missions are waiting their turn. Once a mission completes its defined job, shouldn’t we accept that it’s over and move on to the next one? What reasoning guides NASA’s continued support for extended missions?
There are several strong arguments in favor of continuing extended missions. The most obvious one is that an extended mission takes advantage of a proven asset already in place and working. Spaceflight remains a risky business and it’s amazing that after 50 years of experience with it, seemingly minor malfunctions or glitches can and do destroy the well-laid plans, work and dreams of hundreds of scientists and engineers. Every launch of a spacecraft is a heart-stopping moment for the people who have worked (often for years) on the mission – a hope against hope that somehow, their “baby” will survive this baptism of fire and safely navigate the treacherous shoals of interplanetary space. Most malfunctions occur early in flight, either in launch failures or during the deployment of structures, such as antennas and solar arrays. With those early events safely behind them, the mission team can breathe easier and begin data collection.
Once the nominal mission data is “in the can,” the mission team has safely cleared another hurdle and eagerly looks forward to the collection of additional data. In some cases, spacecraft are flexible enough to be programmed to collect data or conduct experiments that were not thought about prior to flight. In other cases, spacecraft designed to collect partial data for a planet can end up collecting global data sets, or at least greatly improve an existing data product through repeated additional observations. In the 1970s, the Viking Orbiters had imaging systems much improved over the previous Mariner 9 camera, but the mission was not designed to make a global map of Mars. Nonetheless, the Viking Orbiters ended up mapping the entire planet in unprecedented resolution and image quality during their extended missions.
Another reason for continuing an extended mission is if there are no immediate plans for any future missions to the object of study. For example, the Cassini mission has been extended repeatedly not only for the excellent science it is producing, but also because no future missions to Saturn are currently planned by any space faring nation. In the case of LRO, it is the last remnant of what was to be a series (now cancelled) of robotic missions to the Moon. Moreover, the LRO spacecraft is in a stable “frozen” orbit that requires no maintenance; its instruments continue to work superbly and we are conducting new and innovative experiments, such as using the large radio dish antenna at Arecibo (Puerto Rico) to undertake “bistatic” radar measurements of various locales and geological units, including most interestingly, polar deposits. Bistatic radar measurements of diffuse backscatter can distinguish between those caused by rocky surfaces and ice; this particular experiment was not planned when LRO was launched five years ago. We have obtained new data that portrays a moon unlike the one we thought it to be. This “new” Moon is drawing the attention of the world’s space powers.
The camera on LRO constantly returns detailed, high-resolution images of astonishing beauty and utility. We have completely mapped the Moon at medium resolution (about 100 meters per pixel); the Narrow Angle Camera on LRO can resolve objects on the surface as small as one meter (pixel size 25-100 cm). These data have given us spectacular views of fresh flows of impact melt (twisted landforms caused by the flow of liquid, shock-melted rock), entrances to subterranean (sublunarian?) voids (possibly intact lava caves), unusual and enigmatic landforms that may be created by recent and violent venting of gas from the lunar interior, and newly formed impact craters, known to be new because previous images show nothing at these sites. Virtually all of these features were completely unknown prior to being imaged by the LROC. Thus, ongoing extended missions can and often do make new and unexpected discoveries, in some cases discoveries that could not even have been anticipated prior to flight.
At a recent meeting, NASA Administrator Charles Bolden claimed that extending old missions was “not as invigorating” for young scientists than starting new ones. Nothing could be further from the truth. Most students in planetary science and space engineering cut their teeth by working on extended missions. Students and young investigators get few opportunities to work directly on new missions – most mission teams are made up of experienced scientists and engineers (read: greybeards). It is only during the extended mission that the less experienced people get their chance (“It’s done its job – let the kids play with it!”). Moreover, for ongoing missions like LRO, student workers are a critical and large part of the team for ongoing operations. They plan data collects, monitor the downlinks and store and archive the data. The loss of an extended mission asset doesn’t increase opportunities for students – it decreases them.
We do not yet know how the Senior Review will turn out. NASA is famous for wanting to “move on” to the next thing and often abandons working spacecraft. A bird in the hand is worth two in the bush but as things currently stand, there isn’t much in the mission pipeline to move on to. Planetary Science has taken several massive budgetary hits in the past few years, with more on the way.
The termination of LRO and MER will not help move new missions off the drawing board. Money not spent on these extended missions will probably slide into SMD’s Black Hole of Funding (the James Webb Space Telescope) or be dissipated on new paperwork, committee meetings and concept studies. It would be both fiscally prudent and programmatically responsible for NASA to fund and retain these working and still productive extended missions.
The community of planetary scientists is abuzz over the upcoming “Senior Review” of the Science Mission Directorate (SMD), as managers at NASA decide which ongoing robotic science missions will receive necessary funding to continue their extended missions. Up on the chopping block are missions that cover a wide range of targets and levels of effort. Some, like the MESSENGER mission currently orbiting Mercury, are nearing the end of their useful lifetime (MESSENGER is running low on propellant to maintain a stable orbit). Others, such as the Cassini spacecraft currently orbiting Saturn, have momentum by virtue of their stability; it has little need for propulsive maneuvers and runs on a long-lived (nuclear) power source.
The two missions most vulnerable to termination are the remaining functioning Mars Exploration Rover Opportunity and the venerable Lunar Reconnaissance Orbiter (LRO) currently circling the Moon. Both of these missions require very little in the way of spacecraft maintenance, merely operational costs. These costs pay for tracking the spacecraft, commanding it to take measurements and observations, and then collecting, validating and archiving the data. The mission ops teams also serve the scientific community by fulfilling requests for specific or unusual observations besides the regular ones already scheduled.
Missions have well defined life cycles of planning, design, fabrication and flight. NASA assigns letters (A-E) to designate which phase a given mission is in at any time. Phases A and B are the design and mission definition stages. Phase C and D make up the actual building, test, delivery and launch of the spacecraft. Phase E consists of mission operations. This last phase is usually defined at the very beginning of a project, eventually playing out as a baseline mission (the minimum acceptable level of return needed to declare success), a nominal mission (the former level plus additional measurements that enhance and fully define a successful mission), up to an extended mission (additional data collection and operations beyond the original expectations). Both Opportunity and LRO are in their extended mission phase.