What do the Atlas V numbers like '401' or '551' mean?

They describe the configuration: the first digit is the fairing diameter in metres, the second is the number of strap-on solid rocket boosters, and the third is the number of engines on the Centaur upper stage.

What engine powers Atlas V?

The first stage uses a single Russian-built RD-180 engine burning kerosene and liquid oxygen; the Centaur upper stage uses one or two Aerojet Rocketdyne RL10 engines burning liquid hydrogen and oxygen.

Is Atlas V being retired?

Yes — ULA is phasing out Atlas V in favour of its new Vulcan Centaur rocket, flying out the remaining Atlas V vehicles already on its manifest.

What notable missions has Atlas V launched?

Atlas V has launched NASA flagship science missions including New Horizons (to Pluto), Juno (to Jupiter), Curiosity and Perseverance (to Mars), plus many national-security and commercial satellites.

Rockets

Medium/heavy-lift launch vehicle · ULA

Atlas V

A versatile, highly-reliable expendable rocket flown in many configurations since 2002.

OperationalUnited Launch Alliance

109

Total launches

100%

Success rate

109

Successful

Consecutive successes

Overview

About Atlas V

Atlas V is an expendable launch vehicle operated by United Launch Alliance (ULA), with a first stage powered by the Russian-built RD-180 engine and a cryogenic Centaur upper stage. Since its 2002 debut it has built one of the strongest reliability records of any modern rocket, launching US national-security, NASA science and commercial payloads.

Atlas V flies in a range of configurations described by a three-digit code: the fairing size, the number of strap-on solid rocket boosters, and the number of Centaur engines. It is being phased out in favour of ULA's Vulcan Centaur as remaining vehicles work through their manifest.

Evolution

Configurations

The 'XYZ' code
e.g. 401, 411, 541, 551
The first digit is the payload-fairing diameter in metres (4 or 5), the second is the number of strap-on solid rocket boosters (0–5), and the third is the number of Centaur upper-stage engines (1 or 2).
Atlas V 401
Baseline
No solid boosters, 4-metre fairing — the most-flown configuration, used for many science and government payloads.
Atlas V 551
Most powerful
Five solid rocket boosters and a 5-metre fairing — the heaviest Atlas V, used for missions like New Horizons and Juno.
Atlas V N22
Crewed
A boosterless, dual-engine-Centaur variant with no fairing, configured to launch Boeing's Starliner crew capsule.

Cadence

Flight history

Busiest year

2015 · 9

Last 12 months

Total flown

109

Most recent

May 29, 2026

'02

'04

'06

'08

'10

'12

'14

'16

'18

'20

'22

'24

'26

Good to know

Frequently asked questions

Specifications

Height: 58.3 m
Diameter: 3.8 m
Launch mass: 590 kg
Payload to: 9,050 kg
Payload to: 4,950 kg
Payload to: 6,670 kg
Thrust at liftoff: 3,827 kN
Cost per launch: $115M
Reusable: No

Milestones

Key dates

First flight: Aug 21, 2002

Learn more

Official links

Atlas V launches

Every upcoming and past Atlas V launch — live countdowns, mission details and launch history.

Upcoming Launches

TBD

Amazon Leo (LA-08)

Jul 31, 2026, 12:00 AM

ULA

Atlas V 551

Cape Canaveral SFS, FL, USA

Atlas V

Flight record

About Atlas V

Configurations

The 'XYZ' code

Atlas V 401

Atlas V 551

Atlas V N22

Flight history

Frequently asked questions

What do the Atlas V numbers like '401' or '551' mean?

What engine powers Atlas V?

Is Atlas V being retired?

What notable missions has Atlas V launched?

Specifications

Key dates

Official links

Upcoming Launches

Amazon Leo (LA-08)

Starliner-2

Starliner-1

Starliner-3

Starliner-4

Starliner-6

Starliner-5

Previous Launches

Amazon Leo (LA-07)

Amazon Leo (LA-06)

Amazon Leo (LA-05)

Amazon Leo (LA-04)

ViaSat-3 F2 (ViaSat-3 EMEA)

Amazon Leo (KA-03)

Amazon Leo (KA-02)

Amazon Leo (KA-01)

USSF-51

CST-100 Starliner Crewed Flight Test

Amazon Leo (Project Kuiper) Protoflight Mission

NROL-107 (Silent Barker)

More rockets

Vulcan Centaur

Delta IV Heavy

Falcon 9