v1.2.2 / chapter 8 of 19 / 01 feb 08 / greg goebel / public domain
* Although the mixed results in Mars exploration during the 1990s led to a reconsideration of tactics, enthusiasm for Mars exploration remains high. Missions were launched in the 2001, 2003, and 2005 Mars launch windows, and further missions are in planning.
* The failure of MCO and MPL resulted in a complete reassessment of the ambitious Mars exploration missions NASA had planned. In late October 2000, NASA released a preliminary revised Mars plan. The most significant feature was that the goal to send both orbiter and lander missions to Mars in each launch window was abandoned, with the focus now on performing orbiter and lander missions in alternating launch windows. The revised plan envisioned launch of a "Mars Odyssey Orbiter" in the 2001 launch window, two "Mars Exploration Rovers (MERs`)" in the 2003 window, and a "Mars Reconnaissance Orbiter (MRO)" in the 2005 window.
* The Mars Odyssey Orbiter was originally given the working name of "Mars Surveyor 2001" when formal work on the spacecraft began in 1998. The name of "2001 Odyssey" was inspired by Stanley Kubrick's classic science-fiction film, 2001: A SPACE ODYSSEY. NASA carefully avoided use of the acronym "MOO".
Originally, a lander was also planned for the 2001 launch window, but as mentioned that program was scrapped after the MCO / MPL fiasco, even though the lander was almost complete. Money saved by scrapping the lander project was used to boost the Odyssey budget. Since development of the Odyssey spacecraft was almost complete at that time, the additional funds were used to implement enhanced oversight and testing programs to increase chances for mission success. The nearly complete lander was mothballed but not scrapped.
Odyssey was intended to observe Mars for two Earth years. Its main mission was to obtain a global map of the elemental composition of the Martian surface, particularly for hydrogen, which would be associated with the presence of water. Odyssey also measured surface radiation levels. Both these objectives were to provide useful data for a potential manned Mars mission in future decades.
Odyssey was launched on 7 April 2001 on a Delta II 7925 launch vehicle. The interplanetary cruise phase went without major trouble, and Odyssey was inserted into Mars orbit on 24 October 2001. This was a great relief after the MCO/MPL fiasco. The NASA Odyssey website featured music composed for the mission by the Greek electronic music composer Vangelis in celebration.
The spacecraft used aerobraking to attain its final Mars orbit, skimming the atmosphere in 273 orbits, while the mission team took preliminary observations to validate the spacecraft's instruments and provide some publicity. The probe was finally placed at an altitude of 400 kilometers in a near-polar Sun-synchronous orbit, with a period of 2 hours. Its orbit brought it over targets in late afternoon on the day side of the planet and shortly before dawn on the night side of the planet.
Odyssey had a launch weight of 758 kilograms. The spacecraft's instrument payload included:
The high resolution of THEMIS translated to high data rates. Some data processing was performed on board the spacecraft, but most of the data was collected for daily data dumps and compressed before download to Earth stations at rates varying from 14 to 110 kilobytes per second.
Odyssey was damaged by an intense solar storm that occurred on 28 October 2003 that knocked out the MARIE instrument, but the rest of the spacecraft remained operational, and by the summer of 2004 the orbiter had completed its primary mission. It continues to perform observations.
* On 10 June 2003, a Boeing Delta II 7925 booster launched the first "Mars Exploration Rover (MER-A)", named "Spirit", on a mission to land on and explore the surface of Mars. The lander set down on 3 January 2004 near Gusev Crater, 15 degrees south of the Martian equator. MER-A was followed into space on 8 July 2003 by "MER-B", named "Opportunity", which landed on Mars on 24 January 2004, setting down in Meridiani Planum, two degrees below the Martian equator and on the other side of Mars.
Each MER flew to Mars in a planetary cruise stage similar to that used by Mars Pathfinder / Sojourner, but larger. The cruise stage was about 2.6 meters in diameter and 1.6 meters tall, with solar panels and communications antennas on one side, and two hydrazine fuel tanks and an entry aeroshell on the other.
The cruise stage spun at about 2 RPM, which provided a little "artificial gravity" to allow fuel to flow to thruster assemblies on each side of the cruise stage. Each assembly had four thrusters, with the two working together to provide pitch-yaw-roll control and minor course corrections. The rim of the cruise stage was also fitted with a Sun sensor and a star sensor for orientation and navigation.
The solar arrays on the cruise stage provided about 600 watts at the beginning of the flight and 300 watts at the end. The rover's computer system ran the cruise stage, and the cruise stage included a cooling system to keep the computer operational inside the aeroshell. The freon-based cooling system consisted of a loop of pipe running from inside the aeroshell to rim-mounted radiators.
The aeroshell was used to protect the system during entry into the atmosphere of Mars. After entry, the aeroshell was discarded and the lander system deployed a parachute with a diameter of about 15 meters. The lander was also similar to that of Pathfinder / Sojourner, with a tetrahedral assembly that inflated six airbags on each face before landing. The airbags were made of cloth woven from tough Vectran polymer, which is also used for bowstrings for archery and for tennis-raquet strings. The lander used a radar altimeter to determine when to cut the parachute loose, allowing the airbag-protected lander to drop to the surface. After bouncing to a stop, the lander system deflated the airbags; tucked the airbags under the lander; and then opened up its petals, righting itself. The petals could be adjusted to level the lander, making it easier for the rover to roll off.
The lander also included communications subsystems to relay telemetry on the landing back to Earth. The lack of a landing telemetry system was recognized as one of the problems with the Mars Polar Lander. In fact, the entire MER program was conducted in a substantially more robust fashion than the MCO / MPL effort, and ended up with an appropriately higher pricetag.
The MER rovers themselves were similar in configuration to the Sojourner rover carried by Mars Pathfinder, being six-wheel-drive robot vehicles, but much larger, 1.6 meters long and weighing 174 kilograms. Each MER was controlled by a single processor, with 128 megabytes of RAM and 256 megabytes of nonvolatile flash memory. As noted, this processor was also used to control the interplanetary cruise stage.
The science payload of the MERs was based on the "Athena" system originally designed for a NASA Discovery mission that didn't make the cut. The science suite included:
Each MER carried a DVD storing four million names of people who responded to a NASA campaign to name the rovers.
* The landings of the two MERs attracted a great deal of public attention. One cartoonist had the rovers returning images of rocks and landscapes from Mars -- as well as elusive master terrorist Osama bin Laden. Communications were lost with Spirit for a day or so in late January during its preliminary checkout period, but telemetry was finally regained, with ground controllers putting the rover in a troubleshooting mode to make sure it didn't decide to go out to lunch again. The trouble was a software error that accumulated trash data in the flash memory system; a fix was carefully designed and implemented.
The rovers were able to move up to 100 meters of terrain during daylight hours, over a total range of about a kilometer, and had a semi-autonomous navigation system that allowed them to get around without continuous control from Earth. Power was provided by a "roof" panel tiled with gallium arsenide solar cells, with a maximum power output of 120 watts and a lithium battery energy storage system. Small radioisotope heaters were included to help keep critical systems from freezing up.
The rovers went to "sleep" during each night. At the beginning of each martian day, or "sol", commands and data were transferred directly to Earth over an X-band communications link. Each rover also had a UHF antenna to relay the greater volumes of science data through the Mars Global Surveyor and Mars Odyssey orbiters twice each afternoon. JPL operated two shifts, with each shift dedicated to one rover; the shifts had gradually sliding work schedules since the Martin sol isn't exactly the same length as the Earth day.
As it turned out, the choice of landing sites worked out well. Opportunity's landing site in Meridiani Planum was a small crater whose floor was littered with small mineral spheres. Very fortunately for the science team, there was an outcropping of bedrock, the first to be available for inspection by any Mars mission, and the outcropping was embedded with large numbers of these "blueberries" as well. Careful analysis showed the blueberries were made of a high proportion of salts and were almost certainly concretions from liquid water, which had been widespread in the region in the distant past.
Spirit's landing site, Gusev Crater, had been selected since there was some thought that it had been an ancient lake. No evidence was found of water activity there, but on inspection the area seemed like fairly typical Martian terrain, making it a good "control" for Opportunity's observations.
The MERs celebrated their first (Earth) year in operation in January 2005, with both rovers still in very good operating condition. Given the harsh Martian environment, their survival was a testimony to sound engineering, proving NASA had successfully come a long way from the MCO / MPL fiasco.
There was a bit of a scare on 26 April 2005, when Opportunity ran into a sand dune and ended up bogged down, spinning its wheels. The mission team spent a month very carefully withdrawing the rover from its "sandtrap", and it finally freed itself on 3 June. Procedures were developed to help prevent running into a similar trap in the future. They were still working effectively in early 2007, and in fact featured some improvements, with new software having been downloaded in 2006. The software allowed them to spot clouds and dust devils in their imagery, then pass the relevant images on to Earth. Previously, researchers had to wade through streams of imagery to hunt for such phenomena.
* One of the footnotes to the MER landings was that they provided clues to the fate of the unlucky Mars Polar Lander. After loss of the MPL in late 1999, the Mars Global Surveyor imaged MPL's landing zone, finding a white patch that might be a parachute and what looked like a disturbed spot with a bright dot at the center where the lander came down, but the imagery was ambiguous. MGS observations of the MER landing sites yielded images that were consistent with the supposed MPL images, with surface feature corroboration by the MER rover observations. The MGS team has developed a new high-resolution imaging scheme and wants to take more shots of the MPL landing area.
* Days before the launch of the two MER rovers, the ESA had begun Europe's first Mars mission, named "Mars Express (MEX)", launched on 2 June 2003 by a Russian Soyuz Fregat booster from Baikonur. MEX consisted of an orbiter and a small British-built lander named "Beagle 2".
MEX was the first ESA "Flexi" project. Flexi projects are defined as fast track, low cost missions, and at 150 million Euros ($127 million USD), the MEX orbiter was the cheapest Mars spacecraft made to that time. It leveraged heavily off the ESA "Rosetta" comet probe, discussed in a later chapter; featured instrument designs from the ill-fated Mars 96 probe; and used off-the-shelf components whenever possible. The Beagle 2 lander cost an additional 50 million Euros ($43 million USD). Total system launch weight was only 1,070 kilograms.
MEX successfully went into Mars orbit on 25 December 2003. The probe was placed in a highly elliptical polar orbit with a perigee of 250 kilometers, an apogee of 10,240 kilometers, and a period of 6.7 hours. From orbit, it performed observations to search for water, as well as signs of present or past life. Despite its low cost, MEX was a highly sophisticated spacecraft, with a payload of seven instruments:
MEX was to provide communications relay services for the Beagle 2 lander. MEX had a 12 gigabit data buffer to allow accumulation of data between Earth downloads. The orbiter was designed for a two-Earth-year mission, but was expected to operate as a communications relay for substantially longer.
* The British Beagle 2 lander was something unusual for Britain, which has traditionally given space a low funding priority. Money for the project was obtained from the scientific and academic community with some corporate sponsors. The idea was conceived in 1997 by Professor Colin Pillinger of the Open University at Milton Keynes in the UK. He promoted the idea at an ESA meeting, and then a meeting of the British Royal Society in London. The project was approved by the ESA in 1999 and implemented by a team at the Open University.
The lander's name, of course, was in honor of the HMS BEAGLE, the British Royal Navy sailing ship that took Charles Darwin on his epic voyage of discovery in the 19th century. Beagle 2 was designed to search for water and signs of life. The original design concept was a truncated pyramid with a system launch weight of 100 kilograms, but it was redesigned into a flat disk configuration with a system launch weight of 60 kilograms. The lander itself weighed 32.7 kilograms, with almost a third of that instrument payload, an unusually high ratio.
The Mars Express orbiter ejected Beagle 2 on 19 December, and on 25 December the probe fell into the Martian atmosphere, protected by an ablative aeroshell built by the European Aerospace & Defense Systems (EADS) company. It was to deploy a pilot parachute to slow down, discard the aeroshell, then deploy a main parachute. It would touch down using an airbag system, then deploy itself.
In deployed configuration, Beagle 2 resembled a flower with five petals, one of the petals being the main lander bus, and the other four petals and the central element being covered with solar panels. Beagle 2 carried a capable ultraminiaturized science payload:
Beagle 2 had a small communications system to communicate with Earth through relay systems on the NASA Odyssey Orbiter and the MEX orbiter.
Unfortunately, contact with Beagle 2 was lost after it entered the Martian atmosphere on Christmas Day 2003, and the probe was a loss. Although the design team had proudly announced how the project had been put together on a shoestring with considerable non-governmental backing, in hindsight that didn't turn out to be a virtue. A study on the project concluded that Beagle 2 had been overpromoted, underfunded, and undermanaged -- the report was scathing, stopping just short of calling it a "science-fair project". The recommendations were for a more robust approach to any follow-on.
* On 12 August 2005, the NASA Mars Reconnaissance Orbiter (MRO) was launched from Cape Canaveral on an Atlas 5 booster. The MRO was substantially larger than the Mars Global Surveyor and Mars Odyssey Orbiter. It had a launch mass of 2,175 kilograms, twin solar arrays with a width of 6 meters each and spanning 13.4 meters across the spacecraft bus, and an instrument payload of unprecedented sophistication:
Since the orbits of both Earth and Mars are slightly elliptical, not all Mars launch windows are equally favorable. The most optimum windows are when Earth is at its perigee, or farthest part of its orbit, at mission launch, and Mars is at its apogee, or nearest part of its orbit, at mission arrival. The least optimum windows are when the circumstances are reversed. The relatively large Atlas 5 booster was needed since the 2005 launch window was less optimal than average.
The probe arrived at Mars in early March 2006 and went into a 48,000 x 300 kilometer preliminary orbit. The spacecraft used an unusual "Mars Orbit Injection (MOI)" engine system. Traditionally, space probes have used a single big "bipropellant" engine burning hydrazine and nitrogen tetroxide for orbital injection, but the MOI consisted of six smaller "monopropellant" engines, burning hydrazine broken down by a catalyst, aided by the smaller spacecraft monopropellant thrusters. The MOI weighed more than a bipropellant system because monopropellant propulsion isn't as efficient in generating thrust, but the monopropellant system is much simpler and more reliable.
After orbital injection, MRO used aerobraking over the next six months to descend into its 225 x 320 kilometer operational orbit, with the big solar arrays reinforced to permit their use as drag panels. This was an unusually low orbit, providing maximum resolution for MRO's instruments. The spacecraft's signals and orbital path were monitored to provide gravitational and upper atmosphere data. The spacecraft reached final orbit on 11 September 2006, and was returning low-orbit pictures of unprecedented detail with the HIRISE camera by the end of the month. MRO has fuel to keep it operational up to at least 2014.
In all, the MRO will send ten times as much data back to Earth as any Mars orbiter before it. To support the high data rates, the probe is fitted with a high-bandwidth communications system featuring a 3 meter dish antenna, capable of providing data rates of up to 5.6 megabits per second, one to two orders of magnitude greater than the previous generation of probes. The MRO will also provide communications relay support for future Mars lander missions.
* NASA has also been interested in conducting low-cost "Scout" missions to support Mars exploration. The first Scout mission, a Mars lander named "Phoenix", was selected in the summer of 2003. The name was selected because the lander was the same one that had been built to be launched in 2001, only to be cancelled. Lockheed Martin had kept the nearly-complete lander in environmentally-controlled storage since that time.
Phoenix was launched by a Delta II 7925 booster and was to land near the Martian north pole on 25 May 2008. The science payload included:
The stereo panoramic camera and thermal evolved gas analyzer were improved versions of those flown on the ill-fated MPL, and like the MPL, Phoenix used a conventional retrorocket system, not an airbag system, to perform its landing. Of course, improvements were added, such as a "smart" landing system that allowed it to navigate its landing away from obstacles.
NASA had considered sending a small drone aircraft to Mars for surface exploration to commemorate the centennial of the first flight of an aircraft by the Wright Brothers in 1903, but the program was delayed and then suspended in the wake of the MCO/MPL fiasco. The French CNES space agency, which is also interested in small Mars missions, had planned to send a balloon to Mars on the ill-fated Russian Mars 96 probe to perform long-range surface exploration, but it didn't make the payload manifest, which was just as well. NASA is now working on plans for a Scout mission in the 2013 Mars window.
* There are plenty of plans and ideas for other Mars missions. NASA had wanted to send a large rover named the "Mobile Science Laboratory (MSL)" in the 2007 launch window, but budget constraints have slipped this mission out to 2011 window.
The MSL would be the next step up in rover capability. Current concepts envision a vehicle as large as a Jeep, weighing about 900 kilograms, but mission planners are trying to see if it can be cut down to about the size of a dune buggy, with a weight of about 400 kilograms, since the reduced weight would simplify the mission all up and down the line. It would be able to roam over the Martian surface for about two Earth years. Costs are appropriately greater, given as about $1.5 billion USD.
One of the interesting options being considered for the MSL is use of a "skycrane" landing system instead of airbags. The skycrane platform would descend to about 5 meters altitude and hover on thrusters while it lowered the rover on a tether. The platform would then boost away from the landing area and crash. The airbag scheme has proven highly successful, though there are questions on whether it can be properly scaled up to work for a big item like the MSL, and the skycrane might be a more appropriate solution.
Science payload for the MSL is still being defined, but the expectation is to provide an order of magnitude greater capability than featured by earlier rovers. The Italian ASI intends to provide a drill system that will be able to take samples from two meters or more below ground. There is currently a debate over how the MSL will be powered: solar cells or RTGs. The weight of a solar cell and power storage system would be painful, and a solar cell system would not work very well at low Martian latitudes or in dusty conditions. The drawback is that if the MSL crashed the RTGs might disturb the Martian environment.
The RTG approach is currently favored. NASA is now pushing for a new space nuclear power research effort to develop advanced, efficient RTGs. The RTGs would provide from 80 to 100 watts, possibly using a Stirling-cycle heat engine instead of thermoelectric junctions, as used on the RTGs carried by the Viking landers. As with the Viking lander RTGs, the MSL's RTGs would have a thermal radiator system specially designed for operation in a planetary atmosphere.
MSL will be set down on the Martian surface using a new NASA high-precision entry, descent, and landing (EDL) system that will place it to within 6 kilometers of an intended target, in contrast to the 150 kilometer error for current landing systems. The EDL system would have an aeroshell with a small trim tab at the base for guidance during the entry phase, which would be followed by deployment of a two-stage parachute system and discard of the aeroshell.
The rover would be on a "pallet" with a retrothruster system. The pallet would have a laser or radar altimeter, working in conjunction with a mapping system to allow the pallet to select its precise landing area in order to avoid hazards. The pallet would either use airbags or a "crushable" design to permit a safe landing. The MSL lander and rover will be launched by an Atlas V or Delta IV medium class booster.
There has been some brainstorming about having a Mars rover carry a small legged robot that could walk into terrain too difficult for the rover itself to negotiate, with the robot returning images and taking samples. There is no plan at present to include such a robot on the MSL, but the idea remains an interesting option for later rovers.
* NASA had planned to launch a "Mars Telecommunications Orbiter (MTO)" in the 2009 launch window; it was to have been the first communications satellite (comsat) to be sent to another planet.
The idea of a Mars comsat has many attractions. If a Mars orbiter imaged the entire surface of Mars with 1 meter resolution, comparable to the capabilities of the latest commercial Earth-imaging satellites, the complete map would take up 5,000 terabits of uncompressed data storage. With Mars data transfer rates for current spacecraft on the order of 50 kilobits per second, transferring this amount of data back to Earth would take over 3,000 years.
Comsats will be handy for dealing with probes that have much smaller data rates as well. Such probes could be fitted with smaller and cheaper transmitter systems, since they would only have to transmit to Mars orbit, instead of back to Earth. The comsats would also help ensure that telemetry is returned from all phases of a probe's mission, allowing correct understanding of a failure if a probe is lost.
A "geostationary" comsat network would use three satellites to provide a continuous data connection to Earth from almost any location on Mars, but the satellites would be at high altitude, requiring greater probe transmitter power and larger comsats. A low-altitude comsat network would minimize probe transmitter power and comsat size, at the expense of requiring a large number of satellites to ensure guaranteed communications.
Since there was to only be one comsat, MTO was to be placed in a circular polar orbit with an altitude of 4,000 kilometers or so. The high orbit would allow MTO to provide four or five communications sessions per day with a lander or rover, with each session lasting from an hour to an hour and a half. In comparison, the communications sessions between the MGS and Odyssey with the MERs only last a maximum of ten minutes, with only one session per orbiter per day.
MTO was to have a X-band datalink with a bandwidth of 10 to 20 gigabits of data per day, a Ka-band datalink providing 300 to 500 gigabits per day, and an experimental laser communications link. A laser communications link could in principle provide much greater data bandwidth, but nobody's ever used lasers for deep-space communications before. MTO was also to serve as a navigational reference for other Mars spacecraft. However, MTO was quietly cancelled in the summer of 2005, since NASA was shifting focus to the Moon-Mars effort, discussed earlier. Thinking has moved on to a "hybrid" orbiter that performed both scientific and communications relay functions.
NASA and its partners would still eventually like to have a full comsat network in orbit around Mars to support high-bandwidth communications, provide precision navigation signals, and perform secondary scientific observations. Ultimately, NASA researchers envision an entire communications network spanning the Solar System, using lasers to establish an "Interplanetary Internet".
* Although the Russian interplanetary exploration effort all but collapsed after the fall of the Soviet Union, the Russian state is making money from oil exports and the planetary exploration effort is now reviving. Along with plans for Moon probes, discussed in a previous chapter, the Russians are working on a sample-return flight to Phobos, to be launched in October 2009, with the samples returned to Earth in 2012.
The new "Phobos-Grunt" sample return probe -- "Grunt" means "soil" in Russian -- will weigh about two tonnes, making it less than half as big as the ill-fated Phobos 1 & 2 probes of the late 1980s. It will consist of a four-legged cruise / lander stage, which will take a core a meter deep into the surface of the little moon, then put the core into a return stage mounted on top of the lander, which will take the core sample back to Earth.
The lander will also have a suite of about 20 instruments, provided by an international team of researchers. The Chinese are planning to contribute an orbiter, the "Yinghuo-1 (FireFly 1)", which will be a smallsat carried along with the Phobos-Grunt spacecraft. The Finns also plan to contribute two "MetNet" small Mars landers, which will be small spikelike weather stations that will fall to the surface using "ballute (balloon-parachute)" "retarders" to slow down their impact. The Russians are thinking about follow-on efforts, such as Mars rovers and Mars sample return missions.
* While the ESA MEX orbiter was highly successful, the Europeans seem to be stalled for the moment on their next step towards Mars exploration. The French CNES space agency did come up with a plan for a large Mars orbiter, with the entire spacecraft featuring an aeroshell to allow it to use aerobraking for orbital insertion, not just for circularizing its orbit as did MGS and Odyssey. The probe was envisioned as carrying four "Netlander" soft-landing probes, similar in overall concept to the British Beagle II lander and built by a collaboration of European research organizations. Preliminary design studies were conducted but the program was then suspended.
In 2001, the ESA established a planetary exploration program named "Aurora" to send probes to Mars, the Moon, asteroids, and other worlds in the solar system. In principle, Aurora's first major mission was to be "ExoMars", envisioned as a Mars orbiter carrying lander or rover systems to be launched in the 2009 Mars window.
By the spring of 2005, ExoMars had been judged overly ambitious, with revised plans focusing on an ExoMars lander mission for the 2011 Mars window. The lander would be launched by a Russian Soyuz booster and would carry a rover. However, almost unsurprisingly, plans for this configuration began to creep back up to including a functional orbiter, with a data-relay system to support the lander and a simple instrument package, for a total payload weight of about 30 kilograms. The next year the program was rescheduled for flight in the 2013 launch window on an Ariane 5 or Proton booster, which would provide enough lift capacity to carry an orbiter along as well -- though doubts then set in about committing to the orbiter.
The 2013 mission is expected to lead to a "Mars Sample-Return (MSR)" mission. As currently envisioned, a Mars orbiter with an Earth-return capsule will be launched in one Mars launch window, followed by a lander probe with a "Mars Ascent Vehicle (MAV)" in the next window. The lander would take samples with a drill and possibly a surface scoop and then place them in the MAV, which would then blast off from Mars and rendezvous with the orbiter. The orbiter would load the samples into the Earth-return capsule and then shoot it back to Earth, where it would be recovered by parachute. The capsule would be rugged enough to survive even if the parachute failed, ensuring that the samples were recovered.
NASA has also come up with various scenarios for an MSR mission, featuring interesting concepts such as a sample-return orbiter with a high-efficiency electric-ion engine, or having the MAV rendezvous with a spacecraft in an orbit around the Sun that flies by Mars to pick up the capsule and then swings back to Earth. The sample capsule might then be recovered in Earth orbit, eliminating the need for a heatshield and reentry systems. The expense of an MSR mission gives the ESA and NASA a strong incentive to collaborate, but so far MSR remains on the "wish list".
Both China and India are discussing Mars missions as follow-ons to their current Mars efforts, but no specifics are available yet. In fact, anybody who tracks Mars exploration plans soon learns to recognize that all future Mars missions not currently in advanced development have to be regarded as strongly subject to change. It does seem likely that there will be a Mars sample-return mission in the 2020s. Once that is done, a manned Mars mission would seem like the next step up, and in early 2004 US President George W. Bush proposed such a mission as a long-term goal for NASA. There are plenty of ideas for making such a mission happen, which are discussed in the next chapter.
