A version of this article appears in the September 8 issue of Aviation Week & Space Technology.
Scientists and spacecraft controllers in Denver, Bangalore and many points in between are preparing for a rush of activity at the planet Mars, where two new spacecraft designed to study its atmosphere will arrive later this month, followed shortly thereafter by a rare Oort Cloud comet.
If all goes as planned, the two orbiters and the comet Siding Spring should add volumes to human knowledge about where most of the red planet’s water went, and perhaps about how it got there in the beginning.
NASA’s only Mars mission in the current launch window—the $671 million Mars Atmosphere and Volatile Evolution (Maven)—is expressly designed to investigate whether the water that once ran on the surface escaped into space. India’s Mangalyaan Mars Orbiter Mission (MOM)—its first flight to the red planet—can address some of the same questions (see page 42).
And Siding Spring’s flyby of Mars will be the equivalent of a free trip to the Oort Cloud, the mysterious realm of icy planetesimals 5 trillion miles from the Sun, which might have showered the inner Solar System with primordial water and perhaps even the building blocks of life.
Mars being Mars, there is also a risk of spacecraft failure, compounded by the danger posed by high-speed comet debris. At 34 mi./sec.—the closing speed as Siding Spring crosses the orbit of Mars—even a dust mote could damage or destroy a delicate instrument or critical piece of spacecraft hardware. So Maven and MOM will interrupt their planned checkout periods to hunker down as the comet passes only 80,000 mi. from the planet they, hopefully, will be orbiting.
Recent ground observations of Siding Spring’s path and coma suggest the comet will not pose as big a threat as originally feared, and mission scientists on all of the spacecraft at Mars are planning to take maximum advantage of the opportunity for observation that it represents (see page 42). But the guiding principle of spacecraft operation remains “safety first,” particularly after the programs have spent 10 months and plenty of money getting to their objective.
“Safety and health of the spacecraft and instruments absolutely come first,” says Bruce Jakosky, a planetary scientist at the University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP) who is the Maven principal investigator. “There is no question about that. So if there is something that happens in the run-up to the comet, we’re going to make sure we’re safe. We want to survive and do our mission.”
Siding Spring will pass closest to Mars on Oct. 19. Maven will arrive there on Sept. 21, followed by MOM on Sept. 24. For Jakosky, who has managed the Scout-class mission from the beginning, the first order of business will be ensuring his spacecraft gets safely into orbit. Maven controllers have been in a 60-day “command moratorium” since the end of July that was designed into the Mars orbit-insertion (MOI) sequence to circumvent any action that might go wrong and cause problems.
“We just finished our last operational readiness test for orbit insertion,” he said Aug. 11. “It’s basically a rehearsal, and the team went through everything we’re going to be doing on MOI day to make sure we knew the procedures, knew what we had to do and were prepared. So we’re doing everything we can to be ready to ensure a success.”
With a 12.5-min. one-way speed-of-light delay in radio signals between the Maven spacecraft and its controllers at the Lockheed Martin facility near Denver, where it was built, the actual MOI will be completely autonomous.
Nominally, the MOI is a three-day sequence leading up to a 34-min. burn beginning a little before 10 p.m. EDT on the 21st—a Sunday—that will slow the spacecraft enough to enter orbit. But there is plenty of redundancy built into the flight-computer programming in case something goes wrong.
“If it goes correctly we go into orbit; if it doesn’t, we don’t,” says Jakosky. “In order to ensure it goes correctly, we have engine-out capability, so that if we lose one of the six thrusters we’re using, we can still get into orbit on five of them. We also have a computer-reboot capability, so if something happens during the burn, we designed it so that we could have a 13.5-min. outage, and that’s enough time for the computer to reboot, decide it still has a problem, swap sides, realize it’s supposed to be in the middle of its burn, reacquire attitude, resume the burn and get into orbit.”
Maven navigators are working with NASA’s Deep Space Network to track the spacecraft very precisely, and may decide to conduct one more trajectory correction maneuver (TCM) nine days before MOI. Jakosky says a course-correction burn planned for the end of July was canceled because it was not needed. The aim-point is a 100-by-200-km box in the sky, and so far Maven is inside the box if not headed straight for the bull’s-eye.
“Whether we do [the final TCM] will depend on what the tracking shows our trajectory to be, relative to our target point,” he says.
Mindful of the September 1999 loss of the Mars Climate Orbiter, the Maven MOI sequence also has provisions for an emergency orbit-raising maneuver at 24 hr. and then again at
6 hr. before insertion. The earlier spacecraft plunged too deeply into the atmosphere on arrival at the planet and disintegrated because of a mix-up between English and metric units of measurement (AW&ST Oct. 4, 1999, p. 40).
“The hooks are in there so we can do it if we need it,” Jakosky says. “We don’t expect to need it.”
Five orbital-adjustment maneuvers are planned to put Maven into its 6,200 X 150-km (3,850 X 93-mi.) science orbit. Instrument checkout will run until the end of October, when the spacecraft is scheduled to begin a year-long data-collection session designed to help scientists understand the interactions between the upper Martian atmosphere, the solar wind and other elements of the space environment.
A primary objective is to test the theory that the liquid water that once flowed on the planet’s surface was lost when the solar wind and ultraviolet radiation in sunlight stripped away the heavy, wet primordial atmosphere (AW&ST Aug. 26, 2013, p. 40).
The instrument suite designed for the job consists of the Solar Wind Electron Analyzer (SWEA) to measure solar winds and electrons in the Martian ionosphere; the Solar Wind Ion Analyzer (SWIA), to measure solar wind and ion density and velocity in the planet’s magnetosheath; the Suprathermal and Thermal Ion Composition (Static) instrument, which will measure ions in the atmosphere of Mars, including moderate energy escaping ions; and the Solar Energetic Particle (SEP) instrument to measure the impact of the solar wind on the planet’s upper atmosphere.
Also on board are the Langmuir Probe and Waves (LPW) instrument, which includes an extreme ultraviolet sensor, to measure properties of the ionosphere, wave-heating in the upper atmosphere and extreme ultraviolet inputs into the atmosphere from the Sun. Rounding out the package is a magnetometer, which will measure interplanetary solar wind and magnetic fields in the ionosphere; a Neutral Gas and Ion Mass Spectrometer to measure the composition and isotopes of ions and thermal neutrals in the atmosphere; and an Imaging Ultraviolet Spectrograph for global remote sensing of the upper atmosphere and ionosphere at Mars.
Maven scientists designed the instruments to work across the entire range of the spacecraft’s elliptical orbit, making in-situ measurements of the upper atmosphere at the lowest altitudes and then backing off for remote-sensing measurements that will allow researchers to extrapolate the low-altitude data out to global processes.
The arrival of a comet from the distant Oort Cloud, on a multimillion-year orbit that will reach its closest approach to the Sun five days after it passes Mars, is pure serendipity for comet experts. While the Maven team plans to switch off instruments that could be damaged if they are hit with debris while they are active, and to turn the spacecraft into the orientation that affords the greatest protection from any oncoming dust from Siding Spring, controllers also will interrupt instrument checkout and calibration to make observations of the event.
Still, safety comes first so at the point of greatest danger from the comet, plans call for Maven—and the other orbiters circling Mars that day—to be on the other side of the planet. Once its early orbital parameters are established, Jakosky says, controllers will adjust the orbit to minimize the danger by using Mars as a shield.
“We can get about 20 min. of hiding behind the planet, and the time of peak risk of the dust is thought to be between 30 and 60 min., so that is a significant risk reduction right there,” he says.
Jakosky’s counterparts at the Indian Space Research Organization are facing the same problems, and are considering the steps they can take to prepare the MOM spacecraft for the encounter. They are also working with Jakosky and his colleagues on possibly coordinating some scientific observations while the two orbiters are measuring the upper atmosphere.
“We’re going to meet with some of the Indian investigators before our science mission starts to talk about what’s possible,” Jakosky says. “There is a strong desire to collaborate, and I don’t know where it’s going to head.”
Of particular interest to the Maven scientists are the Lyman-alpha photometer and mass spectrometer on MOM. Maven, too, carries a mass spectrometer to measure chemical composition and coordinated observations at the same time from different locations which “allow you to separate out temporal and spatial variability,” Jakosky says.
However, because the Maven and MOM teams are just beginning detailed discussions, the most likely outcome will be joint data analysis at the end of the science missions, he says. Maven scientists have also been working with scientists on the European Space Agency’s Mars Express mission, which carries several instruments that can complement the Maven suite, so coordinated observations with that team are more likely. Joint data analysis with the Europeans is also in the cards, Jakosky says.
With the five-day delay in commissioning caused by the comet encounter, Maven probably will not be able to start its science mission until the second week in November. Jakosky says the annual American Geophysical Union meeting Dec. 15-19 in San Francisco is well timed for release of data on the comet encounter two months earlier.
“We think it is going to take about three months for us to come out with real, preliminary results about what Maven is telling us about Mars,” Jakosky says of the primary mission objectives. “Before that, we’re going to do everything we can to get data out and show people the types of things we’re measuring; but in terms of grand pronouncements of what it all means, at least [for the] preliminary pronouncements, we’re thinking about mid-to-late winter.”
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