Constellation program
Project Constellation is NASA's current plan for space exploration.
It consists of a family of new spacecraft, launchers and associated hardware that allow for 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 the key hardware, the Orion Spacecraft (formerly known as the "Crew Exploration Vehicle" or CEV), is heavily influenced by the earlier Apollo Spacecraft, using a two-part crew and service module system.
The new transportations system, which uses both an Earth Orbit Rendezvous and a Lunar Orbit Rendezvous technique, can be broken down into three parts: The Orion Crew & Service Modules, the Lunar Surface Access Module, and the Earth Departure Stage. The rockets to be used for launching of the different components consists of the unmanned Ares V (for launch of the Earth Departure Stage and either the LSAM or cargo), and the manned Ares I for launch of the Orion Spacecraft.
Orion Crew & Service Modules
The Orion Crew & Service Modules (CSM) consists of two main parts--a conical crew module shaped similarly to the Apollo Command Module (a truncated 70° cone), and capable of holding four to six crew members, and a cylindrical service module which will hold the spacecraft's onboard supplies. The Orion CSM will be built on the designs of the Apollo CSM, but with the technologies introduced on both the Space Shuttle and in the private sector in the past 30 years since the last Apollo flight in 1975. Such technologies will include, but are not limited to, the "glass cockpit" technologies, improved waste management (the use of a miniaturized camping-style toilet and unisex "relief tube" instead of the much-hated plastic bags), and an oxygen-nitrogen atmosphere at sea level or slightly reduced pressure instead of a pure oxygen atmosphere, the latter being extremely flammable as was the case in the tragic Apollo 1 fire in 1967. The main feature that will be introduced in the new crew module will be a new recovery system that will employ the use of a combination of parachutes and airbags for capsule recovery. This will allow NASA to retrieve the CEV crew module on land, much like the retrieval of either the Russian Soyuz or Chinese Shenzhou descent module, and eliminate the need for an expensive naval recovery fleet employed on previous pre-Shuttle manned missions. A docking hatch and transfer tunnel, based on the Russian docking assembly for the Shuttle/Mir, and later Shuttle/ISS missions, eliminates the Apollo-era "probe and drogue" (male/female) system, and can allow, in extreme emergencies, for an in-space rescue without the need for an EVA transfer (as the two spacecraft would have the same docking adapter that was first demonstrated on the Apollo-Soyuz Test Project).
Another feature will be the partial reusability of the Orion crew module. Each crew module will be able to be reused for up to 10 flights, thus allowing NASA to construct a fleet of Orion CMs like that of the current Shuttle fleet. Part of this reusability will come from the landings made on solid ground, as the heat shield is discarded to expose the landing airbags, and that seawater, as evident on the pre-Shuttle splashdowns and current recovery operations of the Solid Rocket Boosters, is corrosive and difficult to remove (despite that the Mercury 4 Liberty Bell 7 capsule, which sunk into the Atlantic Ocean near The Bahamas in 1961, remained mostly undamaged due to the capsule being made primarily of titanium). Most of the non-critical areas of the Orion CM will be covered with nomex felt-like blankets and the Orion CM will be constructed of an aluminum/lithium (Al-Li) alloy to make the spacecraft lightweight and to keep production costs down.
The Orion service module (SM) is identical in shape (but not in size) to its Apollo predecessor, but unlike the Apollo SM, the new Orion SM will be shorter in height, lighter in weight (it too will be constructed of the same Al-Li alloy), and will feature a pair of deployable solar panels, eliminating the need to carry malfunction-prone fuel cells and its associated hardware (liquid hydrogen tanks). For propulsion, the Orion spacecraft will be fueled by the same hypergolic fuels used on every manned spacecraft since Apollo. Although this was not NASA's first choice, due to the corrosive nature of hypergolic chemicals (as evident on debris recovered from the Columbia accident), NASA wanted to originally use liquid oxygen (LOX) and liquid methane (LCH4) as the primary propellants, but due to the infancy of LOX/LCH4 rocket technology, and the need to launch the first manned CEV by 2012, the agency decided to use hypergolic technologies on the CEV and LOX and liquid hydrogen (LH2) for the Lunar Surface Access Module (LSAM).
The use of LOX/LCH4 would allow NASA to develop the technologies that would be needed to convert, "in situ" any methane found on Mars, the lunar polar regions, and on any methane-rich body in the Solar System, especially Titan, Pluto, similar dwarf planets, and most smaller trans-Neptunian objects and even comets in the outer solar system (Kuiper Belt, Scattered Disc, and Oort Cloud). The Reentry Control System (RCS) on both the Orion CM and SM, identical in arrangement to the Apollo RCS, will use the same hypergolic fuels as that of the main propulsion system, but will be powerful enough to propel the Orion spacecraft back to Earth in the event of a main engine failure. The main engine on the CEV SM is the same engine used on the second stage of the Delta II rocket and will be built by Aerojet.
The Orion spacecraft will be launched into a low earth orbit using the new Ares I rocket (formerly referred to as the Crew Launch Vehicle or CLV). Based on the Shuttle's SRBs and Space Shuttle External Tank (ET), the Ares I will consist of a solid-fueled first stage, built using a modified SRB with five segments instead of four and with a new interstage assembly, and a liquid-fueled second stage fueled with LOX and LH2 and powered by an uprated Apollo-era J-2X rocket engine. Originally, the Ares I would have used a slightly modified 4-segment SRB and a second stage using a single throw-away version of the Space Shuttle Main Engine, but the expense of designing and constructing an air-startable, throwaway version of this engine (the current SSME is a ground-started engine) forced NASA to redesign the booster to incorporate the newer J-2X engine.
During the first two minutes of launch, abort capability is provided by a launch-escape system (LES), a standard for manned space capsules. The LES, based on the Russian Soyuz and Chinese Shenzhou LES systems, is bolted directly atop of a fiberglass "boost protective cover" (BPC), which is then in turn bolted to the Orion CM. The BPC, identical to that used on the Apollo spacecraft, is designed to protect the Orion CM and its nomex thermal protection system during the first 2½ minutes of powered flight (first stage or SRB operations) and is discarded along with the LES after second-stage ignition.
NASA also has plans to build two unmanned variants of the CEV. One version will be identical in design and construction to the manned CEV, but with the pressurized crew module stripped of all crew-required equipment, and replaced with storage lockers that would bring up fresh supplies from Earth. This version, which can be recovered, will allow astronauts to return old experiments, or results from on-going experiments on a regular basis; a feature not possible on the current unmanned Progress spacecraft used by Russia. Another variant, which has the crew module completely replaced with an enlarged CEV SM and docking system, will allow NASA to boost the ISS into a higher orbit than that currently possible with the Progress vehicle or the unmanned Orion Cargo CSM, which has limited fuel supplies for reboosts. This will allow NASA to reduce the need for reboost flights from three times per year to only once or twice per year, depending upon the 11-year solar activity period.
Lunar Surface Access Module
The Lunar Surface Access Module (LSAM) is the main transport vehicle for lunar-bound astronauts and has its heritage from the Apollo Lunar Module (LM). Like its Apollo predecessor, the LSAM consists of two parts, a sideways cylindrical ascent stage which houses the four-person crew, and an octagonal descent stage which has the landing legs, the majority of the crew's consumables (oxygen and water), and scientific equipment. The LSAM, like the LM, descends from lunar orbit on the descent stage, and uses the same stage as a launchpad when the ascent stage departs from the Moon. Unlike the Apollo LM, the LSAM will play a major role in braking the Orion/LSAM stack into lunar orbit, which can be an Apollo-like (0 to 30-degree) equatorial, or an ISS-style (55 to 60-degree) inclinational orbit, allowing the LSAM to touch down in the lunar polar regions favored by NASA for future lunar base construction. [1]. This "lunar orbit insertion" (LOI) technique is similar to the former Soviet Union's lunar mission profile in which the Zond orbiter (a modified two-man Soyuz) and lunar lander, attached to the "Block E" stage of the N-1 rocket, would enter lunar orbit, allowing a spacesuited cosmonaut to make a transfer spacewalk to the lander, which only then the Soyuz and lunar lander would separate and then proceed with the lunar landing.
This use of the LSAM for braking the stack into lunar orbit will be accomplished by the use of 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 the LSAM for both the LOI and landing stages of the lunar mission.
Like the Orion Spacecraft, the ascent stage was originally planned to use an RL-10 type engine fueled by the same LOX/LCH4 mixture originally planned for the CEV, but this has since been replaced with a single RL-10 fueled by the same LOX and LH2 mixture. Despite the change in the type of fuel to be used for the LSAM, the vehicle will feature the same equipment as planned for the Orion Spacecraft itself, but will have provisions for the LSAM to be powered by either solar batteries or with fuel cells (using leftover hydrogen in the descent stage's tanks), eliminating the extra weight and space created by batteries needed for a seven-day lunar stay. It would also have an airlock, a feature not found on the Apollo LM, that would allow the LSAM to remain pressurized during a lunar EVA, and minimize the dust transfer from the lunar surface to the cabin. The LSAM, like its Apollo predecessor, is not reusable and is discarded after use.
Earth Departure Stage
The Earth Departure Stage (EDS) is the main propulsion system that will send the entire Orion/LSAM stack from low Earth orbit to the Moon. It will be launched on the Ares V rocket (formerly referred to as the Cargo Launch Vehicle or CaLV), an in-line Shuttle Derived Launch Vehicle roughly based on both the in-line Magnum (U.S.) and piggy-back Energia (U.S.S.R./Russia) boosters. The Ares V will incorporate five RS-68 engines (five Space Shuttle Main Engines were originally planned for the Ares V, but the RS-68 engines are more powerful and less expensive than the SSMEs) with assistance from a pair of five-segment SRBs. The Ares V will fly for the first eight minutes of powered flight, while the EDS will place itself and the LSAM into low Earth orbit while awaiting the arrival of the Orion. Like that of Skylab, the manned Orion Spacecraft will be launched separately (at least 2 to 4 weeks after the Ares V launch, depending upon the lunar phase) and then rendezvous and dock with the EDS/LSAM combination. After configuring the system for the journey to the Moon, the EDS will then fire its engines to propel the Orion/LSAM stack to the Moon.
Based on the S-IVB upper stage of the Saturn V rocket, the EDS is in essence an enlarged S-IVB with larger LOX/LH2 tanks and is powered by the same J-2X engine already being planned for the Ares I. The EDS, while primarily being designed for its lunar role (and eventual Mars role), can also launch large modules that cannot be launched with the Russian Proton booster in support of the International Space Station, or even a Skylab-class or Mir-class space station in an ISS-like orbit. It can also, with the LSAM removed and a docking collar added, allow a CEV to change its orbital inclination (either the standard 29-degree orbit or the 57.5-degree ISS orbit) to that of a Sun-synchronous, Clarke, or near polar orbit in a manner originally planned for the Apollo Applications Program. The EDS, teamed with a LSAM-derived or even a Centaur upper stage, could also be used to launch large space probes in the same weight class as Galileo and Cassini-Huygens to Uranus, Neptune, and any trans-Neptunian object (TNO) using direct-trajectory profiles similar to that used on the Voyager spacecraft. For instance, it could have easily launched the now canceled JIMO mission directly to the moons of Jupiter.
It could also support a Mars Sample Return mission with direct descent and ascent from Mars surface, without the complication and technical challenge of a rendezvous in Mars orbit.
Mission Profiles
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 2030.
Near-Earth Orbit & ISS Service Flights
The Orion CSM and Ares I are assembled on a modified Apollo/Shuttle-era Mobile Launcher Platform in the Vehicle Assembly Building (VAB) at the Kennedy Space Center in Florida. After the Ares I/CEV launch stack is assembled, it is transported to either Launch Pad 39A or 39B (currently envisioned to be LC-39B as it will be taken off-line in 2008, but both pads will be made identical to each other by placing the service tower on each MLP) where the second stage is fueled with LOX and LH2 and the Orion CSM is filled with hypergolic propellents.
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, followed by a roll maneuver to place the Ares I in the proper trajectory, either on a due-east pattern for solo NEO flights or the 57.5-degree inclination for ISS flights.
Two minutes into the flight, the solid-fueled first stage, now completely out of fuel, is jettisoned to fall into the Atlantic Ocean for recovery and reuse, while at the same time, the single J-2X on the liquid-fueled second stage is fired and the launch-escape system and boost protective cover is jettisoned to expose the docking adapter ring, as well as the crew's windows. The second stage burns for four minutes, than shuts off at 6½ minutes into the flight, placing the spacecraft into a roughly 80 km × 560 km (50 mi. × 350 mi.) elliptical orbit. The orbit is circularized with the second firing of the engine 45 minutes later. After the second firing, the Orion CSM is separated from the second stage of the Ares I, which is allowed to fall back into Earth's atmosphere to burn up. Upon separation from the Ares I, the twin solar panels for the Orion CSM will unfurl, and allow the spacecraft to collect the electricity needed to support spacecraft systems.
On solo flights, which most likely will occur early in the program, the onboard three to four-man crew will carry out Earth observation and other experiments reminiscent to that of the early days of NASA and all pre-ISS Space Shuttle flights. 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.
For flights to the ISS, the Orion CSM, after its orbital circularization burn and jettison of the Ares I, will fly for at least 2 days to catch up with the ISS, at the same time it will trim its trajectory to match that of the ISS. Upon reaching the ISS, the Orion CSM will dock, depending on the mission, at either the main U.S. front docking adapter (currently in use by the Space Shuttle) or on the auxiliary (X-33) docking adapter that will either have a manned CEV (in the case for an emergency escape from the ISS) or an unmanned CEV supply spacecraft.
During the 7 to 14-day stay at the ISS, the U.S. crew elements are exchanged (the fourth person, either from JAXA (Japan), Canada, or the European Space Agency would fly as a "guest" astronaut, borrowing an element from the Russian Soyuz Program) and old experiments are loaded from the ISS to the Orion CSM. Following the same precedence as Russia, the most recently-launched Orion CSM will remain with the new U.S. crew members while the old CEV will go back to Earth with the old U.S. crew. If the new Orion CSM is required to be moved due to the need for a reboost ship (an unmanned Orion Cargo Spacecraft with the pressurized crew capsule replaced with a docking ring attached to an enlarged service module), the spacecraft will then be "rotated" to the auxiliary adapter after the old CEV departs from the station.
Once the Orion CSM undocks from the ISS, or at the end of a solo Orion flight, the spacecraft will then turn around so that the main propulsion engine faces forward. After the reentry burn commences, the service module is then jettisoned to burn up in the atmosphere while the crew module makes an Apollo-like entry, using the heat shield to both shield and to slow down the spacecraft from 28,000 km/h (17,500 mph) to 480 km/h (300 mph). After reentry is completed, the forward assembly is jettisoned to release a pair of drogue parachutes, followed at 20,000 feet by three main parachutes and airbags (which are filled with nitrogen (N2), as it does not combust in high-heat situations), allowing the spacecraft to touchdown at a landing site in the western United States, most likely Edwards Air Force Base in California or White Sands Missile Range in New Mexico. The Orion CM is then returned to Kennedy Space Center for refurbishing and reuse (it can be reused up to 10 times under normal situations) for a later flight.
Lunar Flights
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 LSAM/EDS combination into a stable 360 km. (approx. 225 mi.) high circular orbit.
Approximately 2 to 4 weeks 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 mannned Orion CSM to dock with the LSAM/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/LSAM/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 1960's. 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/LSAM combination's trans-lunar coast, which will last 3 days, the four-man crew will monitor the Orion's systems, inspect their LSAM and support equipment, and, if necessary, change their trajectory to allow the LSAM to land in a near-polar landing site suitable for a future lunar base.
Three days after TLI, the Orion/LSAM combination, approaching the lunar far side, will orient the LSAM'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 LSAM, undocking from the Orion CSM after receiving clearance from Houston. Ground controllers will next peform an inspection of the LSAM 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 LSAM's return.
After the crew receives approval from Houston, the four RL-10 engines on the LSAM's descent stage will fire again, and like that of Apollo LM, the crew will land their LSAM 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 LSAM's ascent stage and lift off from the Moon's surface, powered by a single RL-10 engine and 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 LSAM will be jettisoned to crash into the lunar far side, and the Orion CSM will then ignite its single engine (transearth 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 land on Earth in the same manner as that of 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.
See also
- Exploration Systems Architecture Study
- NASA's Vision for Space Exploration
- Advanced Crew Transportation System (ACTS), European-Russian counterpart of the CEV and the Vision of Space Exploration
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