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Shackleton Crater to Malapert Mountain and Back

What are the most important drivers of results on hypothetical 7-day and 14-day missions to the Moon's Malapert Mountain?

Malapert Mountain is an attractive candidate for field work located about 130 km from a likely landing spot at Shackleton crater near the lunar south pole. Our team scientist assembled a list of targeted tasks -- derived from the science goals stated in NASA's lunar roadmap -- and proposed a 3-day round-trip mission to this destination from a presumed outpost at Shackleton crater. Two pairs of astronauts, each driving a pressurized rover, conduct science activities at up to 11 stops in this hypothetical expedition, including sites at Shackleton crater, Shoemaker crater, and Malapert crater.

Possible exploration route from Shackleton to Shoemaker to Malapert Mountain and back. Major stops are marked by triangles, camping sites by black circles.
Possible exploration route from Shackleton to Shoemaker to Malapert Mountain and back. Major stops are marked by triangles, camping sites by black circles.

Our initial analysis found that, given the assumed speed of the rovers (10 km/h), a 3-day mission would allow only enough time to drive to Malapert, install a science station, and drive back, with virtually no time remaining to conduct science investigations at the 11 stops. We therefore hypothesized a 7-day mission with constraints derived from previous experience with sortie models, the most important of which is that astronauts would be permitted 8 hours of extravehicular-activity (EVA) time per day for a mission total of 56 EVA hours, during which all science work is to be conducted.

In consultation with NASA mission architects we learned that, while 8 EVA hours per day were permitted for models of sorties, longer missions would be restricted to 24 hours per week, with a rest day after each 6-day work period. The mission length, however, could be as long as 14 days. In response, we modeled a 14-day mission to Malapert in which astronauts would conduct 4 hours of EVA work per day for two 6-day periods separated by a rest day, for a mission total of 48 EVA hours. All other constraints remained as they had been for the 7-day mission, except that ingress into and egress from the pressurized rover, each of which was modeled at 10 minutes for the 7-day mission, was changed to a constraint of 15 minutes each.

We compared the results of the 7-day and 14-day scenarios to determine the impact of the changes in the EVA and ingress/egress constraints, and then went on to determine the sensitivity of the results to other parameters.

Table 1. Comparison of the results of 7-day and 14-day scenarios with targeted results

  Times done Summed value of activities Mass of samples (kg)
Activity Target 7-day 14-day Target 7-day 14-day Target 7-day 14-day
Panoramic survey 164 488 358 820 2440 1790 0 0 0
Structure survey 138 135 135 690 675 675 0 0 0
Soil sample 123 952 600 1230 9520 6000 246 1904 1200
Rake sample 125 946 601 1250 9460 6010 62.5 473 300.5
Rock sample 138 135 135 1380 1350 1350 262.2 256.5 256.5
Drive tube 137 961 616 1370 9610 6160 95.9 672.7 431.2
Gravimeter 45 45 45 90 90 90 0 0 0
Drill core 20 22 22 84 92 92 18 19.8 19.8
Stow core 20 22 22 16 18 18 0 0
Active crustal 6 5 5 30 25 25 0 0 0
Deploy science station 1 1 1 2715 2715 2715 0 0 0
Continuous mapping 1 1 1 1086 1086 1086 0 0 0
TOTAL 918 3,713 2,541 10,762 37,081 26,011 684.6 3,326 2,208

The number of times each activity is conducted, as listed under the "Target" column in Table 1, is considered the "enabling" number. Our optimization tool, HURON, was instructed to fill the schedule at each of the 11 stops with the enabling number of all activities and then, if allowable EVA time remained for that location, to fill the remaining time with additional repetitions of selected activities, which would be considered "enhancing." Each activity was assigned a value, which HURON was to consider in making its scheduling decisions.

As can be seen in Table 1, both the 7-day and 14-day scenarios achieve -- and in some cases, significantly exceed -- the targets. (For a few activities -- structure survey, rock sample, and active crustal -- the scenario numbers don't quite measure up to the targets, but the differences are considered to be within the noise of uncertainty and thus insignificant.) However, in all three categories, the 14-day scenario achieves only about 2/3 as much as the 7-day scenario, despite the fact that the amount of EVA time each allows differs by only about 15%.

We next analyzed the effects of varying rover speed, the EVA constraint, and the amount of time needed for ingress into and egress from the rover's pressurized cabin.

Table 2. Effects of varying rover speed, EVA constraint, and ingress/egress time

  7-day baseline1 7-day
5 km/h rover speed
7-day
15 km/h rover speed
7-day
24 h/wk max EVA
7-day
15 min ingress/ egress
14-day scenario2
Importance-weighted accumulated measurements (normalized) 1 0.24 1.04 0.226 0.923 0.687
Mass of acquired samples in kg (normalized) 1 0.20 1.05 0.177 0.920 0.664
Productivity (normalized) (science return per weighted ops time (hours) needed for plan completion) 1 0.30 1.04 0.305 0.923 0.453
  1 7-day baseline:
EVA: 8 h/day (56 hours total) Ingress/egress: 10 min each
Rover speed: 10 km/h
2 14-day scenario:
EVA: 24 h/week (24 hours total) Ingress/egress: 15 min each Everything else same as 7-day

As might be expected, reducing EVA time to 24 hours has the greatest impact, reducing importance-weighted accumulated measurements to less than a quarter of what they are with 56 hours of EVA time, and shrinking productivity to about a third of the baseline value. Reducing rover speed to 5 km/h, which doubles the driving time, is nearly as effective in slashing mission results.

Interestingly, speeding up the rovers to 15 km/h has a negligible effect since virtually all of the available EVA time is consumed in the baseline scenario in which rover speed is 10 km/h. The astronauts would reach each of the localities faster at 15 km/h, but they would have almost no additional EVA time for productive work.

Increasing ingress/egress time by 50% has a mild negative effect on mission results. The 14-day scenario, in which total EVA time is reduced from 56 to 48 hours and ingress/egress time is increased by 50% to 15 minutes each, shows a strong negative impact, with importance-weighted accumulated measurements and total collected mass each reduced by about a third, and productivity cut to less than half of what it is in the 7-day baseline scenario.

Table 3. Sensitivities of 14-day scenario results to changes in EVA limit, rover speed, and time needed for ingress into or egress from the rover's pressurized cabin.

Variable Importance-weighted accumulated measurements (normalized) Productivity (science return per weighted ops time (hours) needed for plan completion (normalized) Mass of acquired samples in kg (normalized)
EVA limit = 30 h/week 1.47 1.39 1.53
Egress/Ingress time = 5 min each 1.36 1.37 1.41
Mission duration = 16 days 1.26 1.03 1.30
Rover speed = 15 km/h 1.00 1.01 1.00
BASELINE* 1.00 1.00 1.00
Mission duration = 12 days 0.91 0.99 0.91
Rover speed = 5 km/h 0.88 0.90 0.87
Egress/Ingress time = 25 min each 0.66 0.66 0.62
EVA limit = 18 h/week 0.54 0.56 0.48

*Baseline:
EVA limit = 24 h/week
Egress/Ingress time = 15 min each
Rover speed = 10 km/h

Finally, we looked at the impact of these variables on the14-day scenario. As displayed in Table 3, maximum allowed EVA time is the most important driver of results. Increasing EVA time from 24 to 30 hours per week (i.e., increasing mission total from 48 to 60 hours) has the greatest impact. This 25% increase in EVA time yields about a 50% increase in importance-weighted accumulated measurements and total acquired mass, and nearly 40% more productivity than the baseline scenario. Shrinking EVA time from 24 to 18 hours per week, a 25% reduction, has a similarly disproportionate impact. It cuts mission results in half in all three categories.

Cutting ingress/egress time by 2/3 (from 15 to 5 minutes each) produces only about a 1/3 improvement in each category.

Adding 2 days to the mission (a 14% increase) precipitates a 26% increase in importance-weighted accumulated measurements. Productivity -- the ratio of value to cost -- remains about the same. That there is any increase at all in productivity is because the extra 2 work days do not come with the penalty of an unproductive rest day. Conversely, removing 2 days from the baseline scenario has a smaller impact since one of the extracted days is a rest day.

As in the 7-day scenario, increasing rover speed by 50% has no impact since EVA time is saturated in the baseline version of the mission. The astronauts can reach their experiment sites faster, but cannot spend any additional time conducting experiments. A 50% reduction in rover speed (i.e., doubling the driving time) cuts mission results by only about a tenth -- very different from the devastating effect this change has in the 7-day scenario. So little EVA time is permitted at the work sites in the 14-day scenario (just 4 hours per day) that you might as well take your time getting to them.

For more information, contact Joseph Mrozinski at Joseph.J.Mrozinski@jpl.nasa.gov.



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