Project Constellation

Project Constellation is a NASA program to create a new generation of spacecraft for human spaceflight, consisting primarily of the Ares I and Ares V launch vehicles, the Orion crew capsule, the Earth Departure Stage and the Altair lunar lander.^[1] These spacecraft will be capable of performing a variety of missions, from Space Station resupply to lunar landings. Most of the Constellation hardware is based on systems originally developed for the Space Shuttle, although Orion's two-part crew and service module system is heavily influenced by the earlier Apollo Spacecraft, and it uses engines derived from the Saturn V and Delta IV rockets. Proposed Constellation missions may employ both Earth Orbit Rendezvous and Lunar Orbit Rendezvous techniques.

Constellation Program

NASA has formed the Constellation Program to achieve the objectives of maintaining American presence in low Earth orbit, returning to the Moon for purposes of establishing an outpost, and laying the foundation to explore Mars and beyond in the first half of the 21st century. The Constellation Program's heritage rests on the successes and lessons learned from NASA’s previous human spaceflight programs: Mercury, Gemini, Apollo, Space Shuttle and the International Space Station (ISS).

Spacecraft

Main article: Orion (spacecraft)

Orion will consist of two main parts, a Crew Module (CM) similar to the Apollo Command Module capable of holding four to six crew members, and a cylindrical Service Module (SM) containing the primary propulsion systems and consumable supplies. The Orion CM will be reusable for up to 10 flights, allowing NASA to construct a fleet of Orion CMs. Current plans call for the phased introduction of Orion variants tailored for specific missions. The Block I Orion will be employed for ISS crew rotation and resupply and other Earth orbit missions, while the Block II and III variants will be designed for deep-space exploration.

Launch vehicles

Main articles: Ares I, Ares IV, and Ares V

Conceptual drawing of the Ares I launch vehicle leaving Earth's atmosphere.

As currently envisioned, the Orion spacecraft will be launched into a low earth orbit using the proposed Ares I rocket (the "Stick"). Formerly referred to as the Crew Launch Vehicle (CLV), the Ares I consists of a single Solid Rocket Booster (SRB) derived from the boosters used in the Space Shuttle system, connected at its upper end by an interstage support assembly to a new liquid-fueled second stage powered by an uprated Apollo-era J-2X rocket engine. The Orion spacecraft would be lifted into orbit atop this "stack", while a larger launch vehicle (the proposed Ares V) would be used to launch the heavier Earth Departure Stage and Altair. In January 2007, NASA announced that a different launch vehicle design, the Ares IV, was actively under consideration for the program. If chosen, the Ares IV might replace both the Ares I and the Ares V launch vehicles for some Constellation launches at later dates, or all of them altogether.

Altair

Main article: Altair (spacecraft)

Altair

Altair (formerly known as the Lunar Surface Access Module, LSAM) will be the main transport vehicle for lunar-bound astronauts. Like its Apollo Lunar Module (LM) predecessor, Altair consists of two parts: an ascent stage which houses the four-person crew, and a descent stage which has the landing legs, the majority of the crew's consumables (oxygen and water), and scientific equipment. Unlike the Apollo LM, Altair is to touch down in the lunar polar regions favored by NASA for future lunar base construction.^[2] Altair, like its Apollo predecessor, is not reusable and is discarded after use. The Altair descent stage will be powered by four RL-10 rocket engines that are currently used for the Centaur upper stage used on the Atlas V rocket . Unlike the current RL-10 engines in use, the newer RL-10s would be able to throttle down to as low as 10% rated thrust (the current specifications allow for 20%), thus allowing the use of Altair for both the lunar orbit insertion (LOI) and landing stages of the lunar mission. The ascent stage will be powered by a single engine, likely a hypergolic engine similar or identical to the main engine of the Orion CSM, using the descent stage as a launchpad, and as a platform for future base construction. There remains a small possibilty that the original plan of using LOX/CH4 - fueled engines onboard the Block II (lunar) Orion CSM and Altair ascent stage will come to pass; however, this appears very unlikely.

Earth Departure Stage

Main article: Earth Departure Stage

The Earth Departure Stage

The Earth Departure Stage (EDS) is the main propulsion system that will send the entire Orion/Altair stack from low Earth orbit to the Moon. It will be launched on an Ares V rocket; Orion spacecraft will launch separately, rendezvous and dock with the EDS/Altair combination, which will then be configured for the journey to the Moon. This method, known as Earth orbit rendezvous, was considered by NASA for the Apollo program in the early stages of planning, but was dropped in favor of the lunar orbit rendezvous approach.

Mission profiles

See also: List of Constellation missions

Like that of the Apollo Program, Project Constellation will involve the Orion CSM flying near-Earth orbit missions, with the emphasis on servicing the ISS, and lunar orbit and landing flights. Currently (as of 2006), there are no immediate plans on the type of mission profile that would be flown to Mars, a mission which will not take place until after 2020.

Low-earth orbit and ISS service flights

The Orion CSM and Ares I will be assembled on a new lightweight Mobile Launch Platform II (MLP-II) in the Vehicle Assembly Building (VAB) at the Kennedy Space Center in Florida. After the Orion/Ares I launch stack is assembled, it is then transported to either Launch Pad 39A or 39B (currently envisioned to be LC-39B as it will be taken off-line in 2007, but both pads will be made identical to each other by placing the service tower on each MLP-II) where the second stage is fueled with LOX and LH2 and the Orion CSM is filled with hypergolic propellants. Once the crew is secured inside of the spacecraft and all systems are cleared for launch, the solid-fueled first stage of the Ares I is ignited, at the same time the access arms are retracted. This is followed by the detonation of the hold-down posts, allowing the Ares I to "spring" off of the pad (much like that of the Shuttle, and to a lesser extent, the Saturn IB; as the Saturn V had to "lumber off" the pad and take 8 seconds to "clear the tower"), followed by a roll maneuver to place the Ares I onto the proper trajectory, either a due-east trajectory for solo LEO flights or a trajectory with inclination of 51.5 degrees for flights to the ISS. Two minutes into the flight, the depleted solid first stage is jettisoned to fall into the Atlantic Ocean for recovery and reuse in the same manner as the Shuttle's SRBs. The single J-2X engine on the liquid-fueled second stage is then fired. Also at this time, the launch escape system and protective cover atop the spacecraft are jettisoned to expose the docking ring and crew windows (as the spacecraft is above most of the atmosphere, and thus chances of damage to the thermal protection system is minimized). The second stage burns for four minutes, shutting down at 6½ minutes mission-elapsed time and placing the Orion spacecraft, at that point, into a roughly 80 km × 560 km (50 mi × 350 mi) elliptical orbit. This orbit is then circularized with the second firing of the second stage engine 45 minutes later, following with the Orion spacecraft separating from the second stage to allow for it to fall back into Earth's atmosphere to burn up. After separation, the twin solar panels on the Orion SM unfurl, providing the spacecraft with the electricity needed to support spacecraft systems. On solo flights, the four-man crew will carry out Earth observation and other experiments. The Orion CSM is designed to support a four-man crew for 14 days, but the usual flights will last approximately 8 to 10 days, much like that of the early Apollo flights. For flights to the ISS, after orbital circularization and separation from the Ares I, the Orion CSM will fly for at least 2 days to catch up with the ISS, during which it will trim its trajectory to match that of the ISS. Upon reaching the space station, Orion will dock at either the main node docking port (currently used by the Space Shuttle) or the auxiliary docking port originally planned for use by the cancelled X-38 rescue ship, and is currently planned to be the primary port for unmanned Orion-derived supply spacecraft. During the stay on the ISS, the 6-person American crew (or one with one or more foreign nationalities aboard) would operate onboard experiments and even host "guest" flights from either Russia, the European Space Agency, or even Bigelow Aerospace, while at the same time, receive unmanned Orion cargo ships that would help supply the Earth-orbiting outpost. After a stay of 6 months (the usual length of time for an ISS Expedition), the crew would then reactivate the Orion they were launched in, and then undock from the ISS. Once the Orion reaches a safe distance from the ISS, the spacecraft will turn around so the main engine faces forward and fire its single Aerojet AJ-10 engine. After the deorbit burn has been completed, the service module will then be jettisoned, which will burn up in the atmosphere while the crew module re-enters 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 28,000 km/h (17,500 mph or Mach 25) to 480 km/h (300 mph or Mach 0.5). After reentry is completed, the forward assembly is jettisoned, and two drogue parachutes will be released, followed at 20,000 feet by three main parachutes and airbags filled with nitrogen (N2), which does not combust when exposed to heat, allowing the spacecraft to splashdown.^[3] The Orion CM is then 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 can be used up to 10 times under normal operating conditions.

Lunar flights

Artist's conception of the Orion Spacecraft in lunar orbit

Unlike the Apollo flights, when both the Apollo Command/Service Module and the Apollo Lunar Module were launched together on the Saturn V rocket, the first phase of a lunar mission will occur with the launch of the Shuttle-derived Ares V. Like the Ares I, the Ares V will be assembled at the VAB and then transported to the launch pad, which will likely be LC-39A, although NASA may use LC-39B as a backup. Upon giving the clearance to launch, the five RS-68 engines will ignite and upon verification by the on-board computer, the twin five-segment SRBs will ignite. At the same time, the EDS swing arms and Ares V core stage collect "chocks" will retract, and the booster will then lift off from the pad. After clearing the tower, the Ares V will perform a roll maneuver and travel due east from the launch pad so that the orbital inclination is the same as the latitude of Cape Canaveral, 28.5 degrees. This launch profile has the twin SRBs jettison at 2 minutes into the flight and the main engines shutting down approximately 8½ minutes later, followed by the jettisoning of the core stage and launch shroud. The spent core stage and its RS-68 engine cluster will then burn up in the atmosphere over the Indian Ocean west of Australia. The EDS, powered by its single J-2X motor, will steer the Altair/EDS combination into a stable 360 km (approx. 225 mi) high circular orbit. Approximately 90 minutes after the Ares V launch, the Orion/Ares I stack will lift off from the adjacent launch pad at the same orbital inclination, allowing the manned Orion CSM to dock with the Altair/EDS combination already in low-Earth orbit. After the systems are configured for lunar flight, the EDS will fire for the five-minute translunar injection (TLI) burn, which will accelerate the spacecraft stack from 28,000 km/h (17,500 mph) to 40,200 km/h (25,000 mph). Unlike the Apollo/Saturn TLI burn, the Orion/Altair/EDS TLI burn will be done in the same "eyeballs out" fashion (with the astronauts being "pulled" from their seats) similar to that envisioned with the Manned Venus Flyby missions planned during the Apollo Applications Program in the late 1960s. After the TLI burn, the EDS is jettisoned, and either enters into an orbit around the Sun or steers into a slightly different trajectory to crash into the lunar surface (similar to that employed by the S-IVB stages from Apollos 13 to 17). During the remaining Orion/Altair combination's trans-lunar coast, which will last 3 days, the four-man crew will monitor the Orion's systems, inspect their Altair and support equipment, and, if necessary, change their trajectory to allow the Altair to land in a near-polar landing site suitable for a future lunar base. Three days after TLI, the Orion/Altair combination, approaching the lunar far side, will orient the Altair's engines in the proper direction for the lunar orbit insertion (LOI) burn to begin. Once in orbit, the crew will refine the trajectory and configure the Orion CSM for unmanned flight, then all crew members will transfer to the Altair, undocking from the Orion CSM after receiving clearance from Houston. Ground controllers will next perform an inspection of the Altair using a remote, near-time (a signal takes approximately 3 seconds total to go to and from the Earth and Moon due to the distance) TV camera; formerly this was performed by the Apollo Command Module Pilot (CMP). Once the subsequent separation maneuver is completed, the unmanned Orion CSM is placed in a 95 to 110 km (approx. 60 to 70 mi) high circular orbit to wait for the Altair's return. After the crew receives approval from Houston, the four RL-10 engines on the Altair's descent stage will fire again, and like that of Apollo LM, the crew will land their Altair in a pre-determined landing spot that was scouted out before by unmanned spacecraft. Upon landing, the crew will don their moonwalking spacesuits and commence the first of five to seven lunar EVAs collecting samples and deploying experiments. After completing their lunar deployment operations, the crew will enter the Altair's ascent stage and lift off from the Moon's surface, powered by a single ascent engine, likely a hypergolic engine similar to that used on the Orion CSM, using the descent stage as a launchpad (and as a platform for future base construction), then dock with the Orion CSM in lunar orbit. Once the crew transfers the samples and photographs over to the Orion CSM, the Altair will be jettisoned to crash into the lunar far side, and the Orion CSM will then ignite its single engine (Trans Earth Injection – TEI) for the return trip to Earth. Upon reaching Earth, the service module is jettisoned and a special reentry trajectory is established; the reentry trajectory is designed to both slow the vehicle from its speed of 40,200 km/h (25,000 mph) to 480 km/h (300 mph) and allow for a West Coast landing. The Orion CM will then splashdown in the same manner as an ISS/solo Orion flight. Like that of the ISS/solo missions, the Orion CM will be flown back to KSC for refurbishment and reuse on another flight, while the lunar samples are flown to JSC for analysis at the Lunar Receiving Laboratory.

Alternatives

The choice to accept the ESAS-recommended Ares launchers is not without controversy, and two major alternative launch architectures have been suggested to fill the Ares role: The DIRECT launch vehicle concept, which uses existing shuttle components, such as the solid rocket boosters and the external tank, with minimal development of new hardware. The original VSE architecture supported the use of manrated versions of the current EELV launchers to lift a modified CEV, as well as the components required for lunar exploration into Low Earth Orbit.

See also

• Exploration Systems Architecture Study
• NASA's Vision for Space Exploration
• Crew Space Transportation System (CSTS), European-Russian counterpart of the CEV and the Vision of Space Exploration

References

External links

• Official Constellation NASA Web Site
• Official Orion NASA Web Site
• Official Ares Web Site
• A Visual History of Project Constellation

•  • e Project Constellation
Sub-orbital	Ares I-X · Ares I-Y
Earth orbital	Orion 1 · 2 · 3 · 4 · 5 · 6 · 7 · 8 · 9 · 10 · 11 · Ares V-Y · Orion 12 · 14 · 16 · 18 · 20
Lunar	Altair 1 / Orion 13 · Altair 2 / Orion 15 · Altair 3 / Orion 17 · Altair 4 / Orion 19 · Altair 5 / Orion 21
Solar System	Orion Asteroid Mission · Orion Mars Mission
Components	Orion · Ares (I • IV • V) · Earth Departure Stage · Altair · J-2X · RS-68
Launch sites	Kennedy Space Center LC-39
Abort	Orion abort modes · In-flight aborts and rescue options · Orion Abort Test Booster · Launch Abort System (LAS) · Max Launch Abort System (MLAS)
Other	Vision for Space Exploration · Exploration Systems Architecture Study
List of missions

•  • e United States government human spaceflight programs
Active	Space Shuttle · ISS (joint)  · Project Constellation (future)	Spaceflight Portal
Previous	X-15 (suborbital) · Mercury · Gemini · Apollo · Apollo-Soyuz Test Project (with USSR) · Skylab · Shuttle-Mir (with Russia)
Canceled	MISS · Orion (nuclear) · Dyna-Soar · Manned Orbital Laboratory · Space Station Freedom (now ISS) · Orbital Space Plane