Moon, Mars, baseball, and footballby Jeff Foust
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| Like the NFL, Mars exploration is very event-driven, dictated in this case by orbital mechanics that open launch windows for only a few weeks every 26 months. |
Because of this relatively short season, each game becomes a big deal. With relatively few opportunities to play, and the knowledge that a team will need at least nine or ten wins to make the playoffs, each team has to make the most of every game. Lose a game, particularly against a division rival, and the sports talk radio airwaves and online discussion groups will be burning with complaints and criticism of the team in general and its coaches and star players in particular.
Baseball, by contrast, operates on a far different schedule. The major leagues play a 162-game schedule spread out over six months, effectively the opposite of football: instead of one game a week, a baseball teams gets, on average, one day off a week. This offers teams and their fans little time to celebrate a victory or stew over a loss before the next game. While there are individual games, or series of games, that will be important (such as any game between the Yankees and Red Sox), on average each game is far less important than an individual football game. This tolerance for failure extends to the playoffs: while football playoffs are single elimination, baseball playoffs are best-of-five or best-of-seven affairs.
Pigskins are from Mars
What does any of this have to do with space exploration? One can see some superficial similarities, at least, between football and NASA’s program of Mars exploration. Like the NFL, Mars exploration is very event-driven, dictated in this case by orbital mechanics that open launch windows for only a few weeks every 26 months. With launch opportunities that rare, and with NASA able to launch one or, at most, two missions each time, there’s considerable pressure to get the most out of each mission.
There are two ways NASA squeezes the most results out of each mission. One is to load as many instruments as possible on each mission, packing spacecraft with cameras, spectrometers, and other instruments. This results in large, complex spacecraft that can barely squeeze onto medium-class launch vehicles like the Delta 2 (indeed, the upcoming Mars Reconnaissance Orbiter mission is so large it will fly on an Atlas 5.) Given the scarcity of launch opportunities, though, this approach is understandable and generally quite effective.
The other way NASA gets the most out of each Mars spacecraft is with mission duration. Successful Mars missions routinely exceed their planned mission lifetimes, sometimes several times over. The twin Mars Exploration Rovers have now operated twice as long as their planned 90-day lifetimes; with a little luck they will continue to work until September and perhaps beyond. Mars Global Surveyor, which entered orbit in 1997, was designed to last for one Martian year, or about 687 days. It continues to operate today, nearly seven years after arrival, performing science and communications tasks. Part of this longevity can be explained by conservative engineering estimates, but these extended missions make sense from a programmatic standpoint: given the infrequency of launch windows, and the difficulty getting spacecraft to Mars, it makes sense to operate the spacecraft as long as possible.
| NASA’s new lunar exploration program, a critical part of the Vision for Space Exploration, appears to be heavily influenced by the Mars exploration program. |
While this approach has drawbacks in terms of cost and complexity, it has, overall, been a major success for NASA. The most notable recent failures of the Mars exploration program, the loss of Mars Climate Orbiter and Mars Polar Lander in 1999, were not failures of that philosophy but rather its implementation, the result of trying to do such missions too quickly and cheaply. (And, like an NFL team that loses two games in a row that it was expected to win, the resulting recriminations and soul-searching were particularly severe.) There is no sign NASA plans to abandon this approach to Mars exploration at least through the end of this decade.
A whole ’nuther ballgame
Given the success of this approach to Mars exploration, it’s understandable that NASA would try to apply it to other destinations, such as the Moon. NASA’s new lunar exploration program, a critical part of the Vision for Space Exploration, appears to be heavily influenced by the Mars exploration program. The initial mission, the Lunar Reconnaissance Orbiter, will closely resemble its Martian cousins: a large spacecraft, barely fitting on a Delta 2, with 100 kilograms’ worth of instruments, most likely consisting of cameras, spectrometers, and radiation detectors. While LRO has a nominal one-year primary mission, documents accompanying last month’s announcement of opportunity for LRO instruments note that such instruments should be designed to last up to five years to support an extended mission.
This mission design would make sense for a Mars orbiter, but lunar exploration is, so to speak, a whole ’nuther ballgame. As described above, the size and lifetime of Mars spacecraft are dictated by the relatively infrequent launch opportunities for such missions. That argument, however, doesn’t hold true for the Moon. Unlike for Mars, lunar launch windows are effectively continuous. Transit times are also much shorter for lunar missions: three days to reach the Moon versus six months to travel to Mars.
Rather than copying what works for Mars, NASA should consider a different approach to lunar exploration, one that more closely resembles baseball than football: a far greater number of missions, each less critical than a single Mars mission. Rather than packing a suite of unrelated instruments onto a single large spacecraft, these instruments can be split among several smaller spacecraft, whose size, orbit, and other characteristics are optimized separately. Should a single mission fail, the loss is far less catastrophic than for a single Mars, or Mars-like, mission.
| Rather than copying what works for Mars, NASA should consider a different approach to lunar exploration, one that more closely resembles baseball than football: a far greater number of missions, each less critical than a single Mars mission. |
Moreover, given the greater frequency of launches possible for lunar missions, there’s little need for such spacecraft to have long lifetimes. While it may seem fiscally prudent to eke as much data out of a mission as possible, such an approach incurs costs not only in operations but also in the initial design of a mission. Having shorter lived, but more frequent, missions also allows for the more rapid incorporation of new instruments and other technologies. Such missions can also be more rapidly tailored to follow up on the results of previous missions, which may be difficult for an existing spacecraft in an extended mission to do.
This approach has other advantages, such as allowing a larger number of companies to compete for building such missions, and opening the door to greater international cooperation. (See “Lunar science missions: the smallsat alternative”, The Space Review, May 10, 2004) The case for smaller, more frequent lunar missions becomes particularly compelling if low-cost launch options emerge in the next few years.
The temptation to stick with what has worked, despite changing circumstances, will be difficult to overcome. Yet the Moon and Mars are very different, and require exploration approaches as different as baseball is from football. For the Moon, it’s time to think of the new exploration vision as the opening day of a new baseball season, not as the kickoff of another football season. Play ball!