SLS vs Starship: Rockets Compared as NASA, SpaceX Eye Moon and Mars

This year is set to be exciting for spaceflight, with two entirely new deep space rockets set to make their first voyages.

NASA is on Thursday, March 17, set to roll its hulking Space Launch System (SLS) rocket to a launch pad at the Kennedy Space Center in Florida. Until now the rocket has been under construction in NASA's Vehicle Assembly Building.

The rocket is the backbone of NASA's new human spaceflight program, Artemis, which is currently aiming to put humans back on the moon by 2025.

At the same time, private U.S. space company SpaceX is working on ambitious plans of its own. Over the past year or so, the world has watched as its upcoming rocket Starship has taken form, going through several prototypes on sometimes explosive test flights.

Like NASA's SLS, Starship is the foundation of SpaceX's plans for human spaceflight missions to the moon and Mars within the decade. Below are the stats on how the two rockets compare.

SLS vs Starship: Size and Power

One thing the two rockets have in common is that nothing like either of them has been seen since the mighty Saturn V rocket which enabled the historic Apollo missions.

SLS is slightly complicated in that it is expected to come in various combinations. Its first variation, Block 1, will stand at 322 feet tall and weigh 5.75 million pounds. When it launches, Block I will produce 8.8 million pounds of thrust, which is 15 percent more than Saturn V produced. It will be able to send more than 27 metric tons or 59,500 pounds into orbits beyond the moon.

In its Block 2 configuration, SLS will produce 9.5 million pounds of thrust and will be able to lift more than 46 metric tons or 101,400 pounds to deep space.

Starship is set to be taller than SLS, standing at 394 feet with its cargo and booster stage combined, according to SpaceX. Its Super Heavy booster stage will be able to provide 17 million pounds of thrust.

Orbital capacity figures publicly available on the NASA and SpaceX websites aren't directly comparable. For example, NASA says SLS will be able to launch 46 metric tons to "deep space", while SpaceX says Starship will be able to launch more than 100 metric tons into Low Earth Orbit (LEO).

A NASA spokesperson told Newsweek that "deep space" is defined as anything from the moon onward. They added that the SLS block 1 configuration can send 95 metric tons or about 210,000 pounds to LEO.

This is complicated by the fact that SLS is intended to go straight to its destination while there are plans for Starship to reach Earth orbit, refuel via another Starship, and then continue its journey, which would boost its range and payload capability.

Both SLS and Starship are intended to deliver humans or cargo to the moon, Mars and possibly even further.

NASA intends for SLS to launch the upcoming Artemis moon missions later this decade, although NASA has selected SpaceX to use Starship for the lunar descent phase, which will actually deliver astronauts to the moon's surface.

Difference in Costs

In terms of cost, there are a lot of uncertainties and ambitious figures flying around. SpaceX CEO Elon Musk expects Starship to be far cheaper than SLS in the long run. In a press briefing in February he said he was "highly confident" that within a few years Starship launches could cost less than $10 million. This would be a very low launch cost even compared to the price to launch its much smaller Falcon 9 rocket, which is $67 million, but it's unclear how achievable it is.

The cost per launch of SLS is also unclear, but in 2019 it was estimated by the White House Office of Management and Budget to be "over $2 billion," though NASA has proposed to halve launch costs, and in March this year NASA Inspector General Paul Martin said it could cost $4.1 billion for an Artemis mission, Ars Technica reported.

Cost is also tied into the fact that SpaceX intends Starship to be reusable while the SLS isn't intended to be reusable.

Update, 3/17/22, 12:23 p.m. ET: This article was updated to include a NASA comment on the SLS payload to LEO capability.

SLS (L) and Starship
A photo of the SLS rocket in NASA's Vehicle Assembly Building at the Kennedy Space Center in Florida on March 16, 2022, and a photo of a Starship prototype at SpaceX's Starbase facility in Texas on February 10, 2022. Both rockets are set to be used on human spaceflight missions to the moon and Mars. NASA/Joel Kowsky/Jim Watson/AFP/Getty