I was thinking about NASA’s new launch vehicle plans, and I decided to dig through some of the data in the public record and crunch a few numbers on launch vehicle performance. Specifically, payload mass to orbit.
I am proceeding from my favorite space-system-engineering assumption, which is that we can take more than one launch to build a spacecraft. Thus, the payload mass to orbit on a single launch is not the most important metric for a launch vehicle. I care equally about how frequently the launcher flies. So I crawled through launch dates and came up with numbers for the average (and peak) payload masses various launch systems delivered to low Earth orbit on an annual basis. (For example, between January and November 1985, the Space Shuttle launched a total of nine times, and in no continuous one-year period did the Shuttle launch 10 or more times, so I multiplied the Shuttle’s payload capacity by 9 to get the peak annual payload to orbit figure.)
Here’s what I came up with:
|Launch System||Mass to LEO,
|Mass to LEO,
|Mass to LEO,
|Delta IV Heavy||23,000||15,119||23,000|
|Ariane V ES/ECA||21,000||47,049||147,000|
|Space Launch System||170,000||170,000||170,000|
All masses are in kilograms, and for the SLS I used the “evolved” 2021 configuration of the vehicle and the projection that it will likely fly once per year. Averages are over the course of the entire available service lifetime for the vehicle.
My points are these:
- While the Saturn V is still the behemoth of launch no matter how you slice it, some of the other systems come surprisingly close in certain metrics. Even though SLS will boost more than the venerable Saturn, it’s more of an incremental improvement – and the Saturn launched more frequently in its heyday than SLS is likely to. Cost information on the Saturn V (either total cost per launch or cost per kilogram) is a little tricky to come by; I don’t think there are good estimates, so it’s hard to see how that stacks the deck. I suspect that the Saturn V’s cost per launch would hurt it in this comparison.
- Historically, the Space Shuttle has already outperformed the projected mass to LEO of the fully evolved SLS. It didn’t always, but there were a couple year-long periods when I did count 9 STS launches/year. By the peak annual mass to LEO metric, then, SLS is a step back from the Shuttle.
- The commercial Atlas V is essentially already as good at putting mass in orbit as the SLS will be, on average. And its peak annual mass to LEO is 35 metric tons higher.
My biggest point, however, still is that if you count cumulative launch capacity over several launches, you can get enough material into orbit to build some really big things. We could have NASA developing self-contained habitats and interplanetary spacecraft without developing any new NASA launch systems.