Mars Exploration Program
[5] NASA also has goals of collaborating with the European Space Agency (ESA) in order to conduct a mission involving returning a sample of Mars soil to Earth, which would likely cost at least $5 billion and take ten years to complete.
As a result, if a landing craft were to descend into Mars' atmosphere, it would decelerate at a much lower altitude, and depending on the object's mass, may not have enough time to reach terminal velocity.
Frequently-occurring dust storms increase lower atmospheric temperature and lessen atmospheric density, which, coupled with the extremely variable elevations on Mars' surface, forces a conservative selection of a landing site in order to allow for sufficient craft deceleration.
These thrusters must be designed so that they only need to be active for an extremely short amount of time; if they are active and pointed at rocky ground for more than a few milliseconds, they start to dig trenches, launch small rocks up into the landing gear, and cause destabilizing backpressure to be forced upon the lander.
The technology to accurately determine rock size under 0.5 meters in diameter from orbit has not yet been developed, so instead rock size distribution is inferred from its relationship to thermal inertia, based on thermal response of the landing site measured by satellites currently orbiting Mars.
[14] Along with the possibility of the lander tipping over on sloped surfaces, large topographical features like hills, mesas, craters and trenches pose the problem of interference with ground sensors.
[14] While it was observed in ancient times by the Babylonians, Egyptians, Greeks, and others, it was not until the invention of the telescope in the 17th century that Mars was studied in depth.
The mission ended in August 1993 when communications were lost three days before the spacecraft had been scheduled to enter orbit.
The first robotic spacecraft in this program was Phoenix, which utilized a lander originally manufactured for the canceled Mars Surveyor 2001 mission.
[35][36][37] The purpose of the MPPG was to develop foundations for a program-level architecture for robotic exploration of Mars that is consistent with the Obama administration's challenge of sending humans to Mars orbit in the decade of the 2030s,[34] yet remain responsive to the primary scientific goals of the 2011 NRC Decadal Survey for Planetary Science.
[34] At a budget envelope of $700 million USD, including a launch vehicle, it was presumed that the mission would be limited to an orbiter.
[34] Concept missions that were studied that fit the budget requirement of US$700 million to US$800 million included the Next Mars Orbiter (NeMO) to replace aging satellites' telecommunication services, and a stationary lander to investigate and select samples suitable for a later return to Earth.
