Lander vs. Rover

How much should be invested in highly-accurate landers vs. more capable rovers?

This case study compares the impact of investments in precision landing and long-range roving technologies on a hypothetical mission to Mars. We show how to develop an optimal investment strategy that minimizes mission risk, given a fixed total technology investment budget.

The baseline mission scenario for this study is a Mars 2009-class mission with precision landing capability and a long-range rover. There are three preselected science sites, including the target-landing site, with a total traversal distance of six kilometers. Total mission time is 90 sols (Martian days), with 50 sols allocated to traversal.

The results are shown below.

In this graph, investment in lander technology is shown on the horizontal axis, and investment in rover technology is shown on the vertical axis. The dollar amounts on the two axes are connected by diagonal "isobudget" lines. Every point along the straight line that connects $40M on the lander axis with $40M on the rover axis, for example, indicates a combined investment of $40M.

The curved lines represent levels of risk of mission failure. The top curved line, for instance, represents a 10% chance that the mission will fail (or, to put it more optimistically, a 90% probability of success).

The uppermost "risk" curve that is intersected by any given "budget" line indicates the lowest risk level that budget can buy. The point of intersection reveals what combination of investments in lander and rover technology will achieve that lowest possible risk.

For example, if you have $40M to spend, you look along the $40M diagonal line until you see where it intersects the highest risk curve. $40M doesn't intersect the very top curve, which indicates a 10% risk of failure, but it does intersect the 20% curve. So the least amount of risk you can have for a $40M budget is 20%. And by seeing where that intersection point falls on the two axes, you can determine how that $40M budget should be divided between lander and rover technology. In this case, you'd spend about $13M on lander technology and about $27M on rover technology to achieve the lowest possible risk for that budget: 20%.

If risk level is more important to you than dollar amount, you can use this graph to see how much you have to spend -- and where you should spend it -- to achieve that level of risk. For example, if nothing greater than a 10% risk (that is, nothing less than a 90% probability of success) is acceptable, you can see that the least amount you can budget is $50M. And $26M of that should be spent on lander technology, while $24M should be spent on rover technology.

Another method of visualizing the results from this study is shown below.

On this graph, total budget levels vary vertically. The minimum mission risk achievable at each budget level is shown on the left (in red), while the corresponding technology portfolio appears on the right.