Economics of Intra-Stellar Spacecraft

After seeing the discussion of spacecraft within our solar system in the textbook, and the impact the mission type has on the cost, I was curious to see how these discussions were reflected in actual data on these missions. So, I copied each mission from the book into Excel, and then researched each. Thanks mostly to Wikipedia and the Google search “How much did [MISSION NAME] cost?”, I came up with this table. Feel free to skip over it – the rest of the blog is more interesting.

Name	Launch Year	Cost (inf. adj.)	Launch Mass (probe)	Type	Planet Reached
MESSENGER	2004	$504 Million	1110 kg	Orbiter	Mercury
Magellan	1989	$1155 Million	1035 kg	Orbiter	Venus
Venus Express	2005	$128 Million	1270 kg	Orbiter	Venus
Spirit	2003	$1094 Million	1063 kg	Rover	Mars
Opportunity	2004	$1600 Million	1063 kg	Rover	Mars
Mars Express	2003	$472 Million	1120 kg	Rover	Mars
Mars Recon. Orbiter	2005	$928 Million	2180 kg	Orbiter	Mars
Phoenix	2007	$469 Million	670 kg	Lander	Mars
Curiosity	2011	$2798 Million	3839 kg	Rover	Mars
MAVEN	2013	$725 Million	2454 kg	Orbiter	Mars
Mars Insight	2018	$832 Million	694 kg	Lander	Mars
Voyager 1	1977	$1797 Million	825.5 kg	Flyby	Neptune
Voyager 2	1979	$1797 Million	825.5 kg	Flyby	Neptune
Galileo	1989	$2766 Million	2562 kg	Orbiter	Jupiter
Cassini	2004	$4336 Million	5712 kg	Orbiter	Saturn
Juno	2009	$1231 Million	3625 kg	Orbiter	Jupiter

Then, with all the boring data out of the way, I could make (relatively) pretty graphs to see how each part of the mission related to cost:

Cost and Mass

The most intuitive finding of this data is that more massive probes are (quite literally) exponentially more expensive:

This makes sense. Here, “mass” refers to the mass of the final probe (including propellant for any maneuvers once it’s in orbit). So, a heavier probe would need a bigger rocket to bring it to space. But this is constrained by something called the rocket equation, which (in very rough terms) says that as you increase the final mass of what you’re bringing to space, the total mass of your rocket has to increase exponentially. So it makes sense that, the more massive your final probe already is, the greater the marginal cost of another kilogram.

Cost by Probe Type

The book suggested that flybys are less expensive than orbiters which are less expensive than landers (and, presumably, stationary landers are less expensive than rovers). In practice, this isn’t reflected in the actual costs of these missions.

Rover	$1,490,865,000
Lander	$650,132,000
Orbiter	$1,471,548,000
Flyby	$1,796,605,000

Of course, none of this shows the inherent cost of each mission type. But it may indicate how much priority different projects are given. A rover will be driving all over a planet’s surface, so it makes sense to have a lot of gadgets to comb through all that data. And if the best you can do is fly by a planet, you only have one chance to collect a lot of data, so you need to make it worth it (perhaps with very expensive equipment). Landers, meanwhile, can’t see as far as an orbiter, so they can only do a handful of experiments.

Cost by Launch Year

The book didn’t discuss this directly, but I was curious if the price (adjusted for inflation) of missions within the solar system had come down. It has.

Excel’s trendline suggests that (after adjusting for inflation), the average cost of a mission within the solar system comes down by about $22 million every year. But looking at the data, a lot of this seems to be caused by the missions from 2000-2010. It’s hard to say how much of this “trend” is caused by changes in technology vs. changes in available funding vs. changes in mission designs.

Cost by Planet

We’ve sent missions to every planet in the solar system. I was curious which were most expensive.

Overall, missions to Saturn have been the most expensive on average. It’s not hard to come up with an explanation for why this could be. We’ve sent far more missions to Mars, and it’s cheaper to get back there. That means it may not be worth sticking everything you can on the ship and increasing the price. But with Saturn, it takes a lot just to get the rocket there. So if you have something going there, then everything to make the mission better – every extra hour of design, every special instrument to get more knowledge, every unique material to bring down the mass – becomes worth the cost. This doesn’t explain the trend in the opposite direction – that Mercury’s missions are cheaper than Venus’s, even though Venus is closer to Earth. That could be because we aren’t as interested in Mercury as we are Mars or Venus, but I really couldn’t say.