---
title: "Constellation program"
chunk: 3/6
source: "https://en.wikipedia.org/wiki/Constellation_program"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T12:41:43.933180+00:00"
instance: "kb-cron"
---

NASA planned to use the first vehicles developed in the Constellation Program for Earth-orbit tasks formerly undertaken by the Space Shuttle.  But unlike the X-33 and other programs intended to replace the Shuttle, Constellation reused concepts from the Apollo and Space Shuttle programs.
The shape of the Orion command module closely resembles the aerodynamic shape of the Apollo command and service module. However, in other areas Orion employs updated technology.  The design of the launch vehicle taking Orion into orbit, the Ares I, employs many concepts from the Apollo program.
The design of the J-2X engine intended for use on the Ares V booster rocket was originally to be similar to the J-2 engine of the Apollo-era Saturn V and Saturn IB rockets. In designing the J-2X, NASA engineers visited museums, searched for Apollo-era documentation and consulted with engineers who worked on the Apollo program. "The mechanics of landing on the Moon and getting off the Moon to a large extent have been solved," said Constellation program manager Jeff Hanley. "That is the legacy that Apollo gave us."  However, as the J-2X program progressed, it became apparent that, because of revised safety requirements and the growing mass of the upper stage, it was necessary to scrap the original J-2 design completely and use a completely new design for the J-2X.
Like Apollo, Constellation would have flown a lunar orbit rendezvous mission profile, but unlike Apollo, Constellation would have also employed Earth orbit rendezvous, conveying the crew to the vehicle. The lander, known as Altair, would have been launched separately on the Ares V rocket, a rocket based on both Space Shuttle and Apollo technologies. Orion would have been launched separately and would have linked up with Altair in low Earth orbit. Also, unlike Apollo, Orion would have remained uncrewed in lunar orbit while the entire crew landed on the lunar surface. Toward the end of the mission, the Altair spacecraft would have launched into lunar orbit to link up with the Orion spacecraft in lunar orbit rendezvous.  Like Apollo, the Orion capsule would then have returned to Earth, re-entering the atmosphere and landing in water.

== Missions ==

Like those of the Apollo Program, Constellation program missions would involve its main vehicle, the Orion spacecraft, flying missions in low Earth orbit to service the International Space Station, and in conjunction with the Altair and Earth Departure Stage vehicles, on crewed flights to the polar regions of the Moon. There were no well-defined plans at the time of cancelation for a crewed flight to Mars, the ultimate goal of the project, but a mission to a Near-Earth asteroid was in the initial planning phase as of 2008.

=== International Space Station and low-Earth orbit flights ===

After being manufactured at private plants, the parts of the Ares I/Orion stack would be tested and assembled at the Vehicle Assembly Building at the Kennedy Space Center. Once assembly was completed and a launch date was set, the crawler-transporter would transport the completed stack, along with the launch support tower and the Mobile Launcher-1, out to LC-39B. Once the crawler-transporter reached the pad, the stack and the Launcher Platform would be left in place and the crawler-transporter removed to a safe distance.
After final safety checks, the ground crew would fill up the second stage with liquid hydrogen (LH2) and liquid oxygen (LOX) fuel, and the crew, wearing all-purpose spacesuits, would enter the spacecraft three hours before liftoff. Once they were locked in, and after all systems were cleared by controllers at both the Cape and Mission Control in Houston, the Ares I would then launch.
After a two-day orbital chase, the Orion spacecraft, having jettisoned much of the initial stack during takeoff, would meet with the International Space Station. After getting the go ahead from Houston, Orion would then dock with the ISS. The six-man crew (at a maximum) would then enter the station in order to perform numerous tasks and activities for the duration of their flight, usually lasting six months, but possibly shortened to four or lengthened to eight, depending upon NASA's goals for that particular mission. Once completed, the crew would then reenter the Orion, seal itself off from the ISS, and then undock from the station.
Once the Orion reached a safe distance from the ISS, the Command Module (after having jettisoned the disposable service module) would re-enter in the same manner as all NASA spacecraft prior to the Shuttle, using the ablative heat shield to both deflect heat from the spacecraft and to slow it down from a speed of 17,500 mph (28,200 km/h) to 300 mph (480 km/h). After reentry was completed, the forward assembly would be jettisoned, and two drogue parachutes released, followed at 20,000 feet (6,100 m) by three main parachutes and airbags filled with nitrogen (N2), which does not combust when exposed to heat, allowing the spacecraft to splashdown. The Command Module would then be returned to Kennedy Space Center for refurbishment for a later flight. Unlike the Apollo CM, which was used only for one flight, an Orion CM could theoretically be used up to ten times under normal operating conditions.

=== Lunar sortie flights ===