Space Launch System — NASA’s Ride to the Moon and Mars?

Back in 2014, NASA awarded aerospace and defense contractor Boeing a $4 billion dollar contract to construct the core rocket designed to ferry NASA astronauts to the moon and Mars for decades to come. Some say that the future of this rocket, dubbed the Space Launch System (SLS), may be in danger.

(📷: NASA)

While admittedly not as sexy-looking as a Falcon Heavy or Delta IV, SLS promised to be an extremely capable heavy-launch vehicle. A good measure of rocket performance is the amount of cargo it can carry into low-earth orbit — below is a summary of common rockets and their payload capacity.

United Launch Alliance (ULA) is a joint venture between Boeing and Lockheed Martin. The US government effectively created ULA when they forced the space divisions of these two companies to merge, and has since showered billions of dollars of launch contracts on ULA. ULA also launches numerous private satellites. ULA’s flagship heavy-launch vehicle, the Delta IV Heavy, can loft 29,000 kg into low Earth orbit (LEO). It can also place 8,000 kg in a Mars transfer orbit.

The Delta IV heavy carrying NASA’s Parker Solar Probe. (📷: ULA)

SpaceX also has a flight-tested heavy-lift rocket. Its Falcon Heavy can place 63,800 kg in LEO and 16,800 kg in Mars transfer orbit. Additionally, SpaceX is developing the Big Falcon Rocket (BFR). While not remotely ready to launch, the BFR should be able to place 130,000 kg in LEO, and a similar amount in Mars transfer orbit with orbital refuling. This isn’t exactly a direct comparison due to the in-orbit refueling, but it’s still interesting nonetheless.

SpaceX rocket comparison. (📷: SpaceX)

Now we come to the Space Launch System. The SLS contract is broken into three phases or “blocks:” block 1, which is currently being developed and is projected to be completed in 2020, will be capable of lofting 25,000 kg to Mars or the moon. Block 2, not slated for completion until 2028, should be able to send a whopping 45,000 kg to the moon and 37,000 kg to Mars.

(📷: NASA)

This all sounds well and good, right? NASA’s goal is to put humans on Mars in the 2030s, and return humans to the moon in the 2020s, with SLS being the rocket that NASA plans on using to accomplish these tasks.

Well, not so fast. Boeing is almost $4 billion over budget and 3 years late on the delivery of the core stage (the main body of the rocket). Naturally, Washington is upset. NASA’s inspector general released a scathing review of Boeing’s performance in an October 2018 report. I highly recommend reading this document; it’s very easily digestible and gives a great summary of where things stand with SLS.

(📷: NASA)

In a recent speech, vice-president Mike Pence directed NASA to put boots on the moon by the end of 2024. This timeline is no accident — it coincides directly with the end of the next presidential term. If Donald Trump is reelected, this feat could be a lasting legacy for the administration. Pence’s speech, however, provides few details about how this might be accomplished.

NASA’s current plan is to run the first test of SLS in June 2020, with Exploration Mission 1 (EM-1). EM-1 is a 25-day spaceflight that will send SLS’s crew stage, the Orion capsule, around the moon. This will serve as the first integrated test of all of SLS’s components. Orion is already completed and flight-tested — it flew aboard a Delta IV Heavy all the way back in 2014 on its first flight test.

At the request of the Trump administration, NASA analyzed the feasibility of including astronauts on EM-1. They ultimately decided to stick with the original plan, even though EM-1 has already suffered years of delays (the original launch date was scheduled for 2018).

(📷: NASA)

As it stands, astronauts setting foot on the moon by 2024 seems highly unlikely. This is years ahead of NASA’s schedule — NASA originally planned to construct a space station in orbit around the moon before any surface operations commence.

Lockheed Martin, the company responsible for constructing most of the crewed aspects of these missions, thinks that the accelerated 2024 timeline is possible. Therefore, the rate-limiting step in this entire process appears to be Boeing and SLS.

This leads to a central question about ensuing missions to the moon and Mars: will NASA cancel SLS? My answer is no.

SLS is the key component to NASA’s long-term crewed missions. Having a consistent and capable launch vehicle is absolutely crucial for NASA in this respect. NASA administrator Jim Bridenstein went so far as to say this directly:

If NASA were to cancel SLS, the only other option would be to rely on commercial rockets. Neither the Delta IV heavy nor the Falcon Heavy can loft enough mass for mission specs, so the only feasible way to complete NASA’s missions would be to launch parts of the systems separately and assemble them in space. For EM-1, this might involve launching the Orion module on one rocket then launching a fueled upper stage (the propulsion system that Orion uses to travel in deep space) on another rocket.

This would still be extremely expensive (a Delta IV Heavy costs $350 million per launch), and would push the mission timelines back months or years as engineers now need to figure out how to get these stages to meet and dock in orbit.

In short, NASA needs SLS. SLS is more than just a series of rockets; SLS will be the backbone of NASA’s moon and Mars ambitions for many years to come. The 2020s promise to be an extremely exciting decade for space exploration, as we will see the first crewed deep-space missions since the Apollo program. With any luck, these astronauts will blast off atop SLS.

I'm a Harvard student, maker, and radio enthusiast. Check out my book on radio communications at and my website at

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