Drive me to the moon
Let me cruise among the stars.
Let me see what gas sells for
On Jupiter and Mars.
“Are we there yet?”
No we’re not.
Those are not quite the right words, are they?
However, I have been fortunate enough to own a car that has driven my family all the way to the moon — 238,900 miles. I keep a spreadsheet of my fill-ups and gas mileage (gas mileage is like the blood pressure of a car; keep track of it and you can see automotive health problems coming), and that allows for some very practical ways of visualizing distances in space.
The 238,900 mile figure is the radius of the moon’s orbit. That measurement is from the center of the Earth. Were our family driving to the moon, we would be leaving from Earth’s surface. Earth has a radius of 4000 miles. We bought the car, a 2009 Toyota Yaris, in May of 2009. Liftoff! We are headed to the moon, with starting distance of 4000 miles from the center of the Earth.
Our first fill-up in the Yaris was May 26, 2009. At that point there were over 400 miles on the odometer — 400 miles on our way to the moon, and 4400 miles from the center of the Earth. At that point we were already well past the orbit of the International Space Station (ISS), which orbits at an altitude of roughly 250 miles (an easy day’s drive).
Satellites in geostationary orbits circle the Earth once every 24 hours, riding along above the equator. Thus they are synched to Earth’s rotation, and seen from Earth they stay fixed in one place in the sky. Those dish-type satellite TV receivers point at a geostationary satellite. The radius of a geostationary orbit is about 26,200 miles. We drove past those dish TV satellites around the start of April, 2011.
Then it was a long, long trip. The radius of the moon’s orbit may be 238,900 miles, but that is just an average figure. The moon’s orbit is slightly elliptical, so the moon draws as close to Earth as 226,000 miles (center-to-center). This is the moon’s perigee distance — the distance it has at those “super moons” we hear about. We crossed the perigee point around October 10, 2023. The radius of the moon is about 1000 miles, so we actually could have hit the surface of the perigee moon (at 225,000 miles) in mid September of 2023.
We finally reached the moon’s average orbital distance, 238,900 miles (the distance you get if you “Google” the distance to the moon), on July 24 of this year. The Yaris drove us to the moon in 15 years and 2 months!
Driving to the moon well illustrates the vast distances in space. We were past the ISS in no time, but the moon took years to reach. The moon’s orbit looks circular (see below, where the red line is Earth’s orbit), and yet crossing the range of lunar distances caused by the slightly elliptical nature of the lunar orbit, from the perigee distance to the average distance, took almost a year. It will presumably take almost another year to get past the apogee distance (the other extreme of the lunar distance range). The Yaris is one finely engineered vehicle — it made it all the way to the moon needing nothing but routine maintenance like tires, batteries, and oil changes and having no breakdowns of any sort — but it is now showing signs of tiring out and may not make it to apogee. Space is so big that even the variation of the moon’s distance makes for a very long trip.
And yet the distance to a nearby planet, like Mars or Venus, makes the distance to the moon vanish by comparison — literally, as seen below. No car is going to get you to Jupiter and Mars. Judging from the challenges we face today in just getting up and down to the ISS, no crewed vehicle is going to take us to those places in the foreseeable future. Driving to the moon also helps us better appreciate the achievement that was the Apollo program, and the practicality of sending robots, rather than people, to explore space. Robots don’t get bored or hungry, they don’t need to go to the bathroom, and they don’t ask if we are there yet.
