The Mars Geyser Hopper (MGH) was proposed in 2012 as a NASA design reference mission for a Discovery-class spacecraft concept that would investigate the springtime carbon dioxide Martian geysers found in regions around the south pole of Mars. The power technology that MGH proposed to use was the Advanced Stirling radioisotope generator (ASRG). NASA finished the ASRG design and made one test unit of the device but the program was concluded by the mid-2010s. Neither InSight nor any of the next Discovery's semi-finalists use the ASRG or an RTG due to high demand and limited supply of the type of plutonium it relies on.
Background
The Discovery program was started in the 1990s following discussions at NASA for a new program, and has achieved such missions as Genesis, Deep Impact and Kepler among others; this is the program this mission was designed for selection in, at least initially. One of the first unmanned robotic spacecraft to do a hop was Surveyor 6 lunar lander, which successfully soft landed on the Moon 1967 and conducted a post-landing hop. Another possibly for a hopper mission may be Saturn's moon Enceladus. Hoppers are noted for their ability to potentially visit different landing sites. Another hopper-type mission was the Comet Hopper, which won a Discovery semi-finalist award to study a hopping mission to the Comet 46P/Wirtanen. There was some speculation in 2012 that the Geyser Hopper mission could be flown after the InSight Mars lander.
Mission overview The mission was projected to cost US$350 million and to meet a cost cap of no more than US$425 million, not including the launch cost. In order to reduce the cost and minimize risk, the spacecraft concept is based on a previous spacecraft design, the Mars Phoenix lander, which has a demonstrated flight heritage that incorporates soft landing capability and incorporates a restartable rocket propulsion system, suitable to be repurposed for this mission requirements. The spacecraft would land at a target landing area near the south pole of Mars, where geysers exist over a stretch of several hundred kilometers with densities of at least one geyser every 1 to 2 kilometres (0.62 to 1.24 mi) and have the ability to "hop" at least twice from its landed location after a summertime landing to reposition itself close to a geyser site, and wait through the winter until the first sunlight of spring to witness first-hand the Martian geyser phenomenon and investigate the debris pattern and channel.
Martian geysers are unlike any terrestrial geological phenomenon. The shapes and unusual spider appearance of these features have stimulated a variety of scientific hypotheses about their origin, ranging from differences in frosting reflectance, to explanations involving biological processes. However, all current geophysical models assume some sort of geyser-like activity. Their characteristics and formation process are still a matter of debate. The seasonal frosting and defrosting of CO2 ice results in the appearance of a number of features, such dark dune spots with spider-like rilles or channels below the ice, where spider-like radial channels are carved between the ground and ice, giving it an appearance of spider webs, then, pressure accumulating in their interior ejects gas and dark basaltic sand or dust, which is deposited on the ice surface and thus, forming dark dune spots. This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology – especially for Mars.
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