Shuttle-Derived Launch Vehicle

The Shuttle-Derived Launch Vehicle, or simply Shuttle-Derived Vehicle (SDV), is a term describing one of a wide array of concepts that have been developed for creating space launch vehicles from the components, technology and/or infrastructure of the Space Shuttle program. In 2005, NASA decided to develop the Ares I and Ares V launch vehicles, based in part on highly modified Shuttle components to replace the Space Shuttle and enable exploration of the Moon and Mars.cite web | date = June 30 2006 | url = http://www.nasa.gov/mission_pages/exploration/spacecraft/ares_naming.html | title = Ares: NASA's New Rockets Get Names | publisher = NASA | accessdate = November 22 | accessyear = 2006] [cite news|first=Tariq |last=Malik |url=http://space.com/news/060630_ares_rockets.html |title=NASA Names Rockets for Moon and Mars Missions |publisher=Space.com |date=30 June 2006 |accessdate=2006-11-22] In early 2007, the agency confirmed that it was formally studying a third such vehicle, the Ares IV.

Concepts

SDV concepts were proposed even before the Shuttle itself began flying. Proposed SDV concepts have included:
* Replacing the winged Shuttle Orbiter with an uncrewed, expendable cargo pod ("side-mount style" SDV)
* Removing the Orbiter and mounting an upper stage and payload atop the Space Shuttle external tank ("inline-style" SDV)
* Adding a large cargo container to the rear of the external tank, allowing launches of bulky materials (Aft Cargo Carrier)
* Replacing the Space Shuttle Solid Rocket Boosters (SRBs) with liquid rockets, including recoverable winged "flyback" boosters
* Creating vehicles from one or more Space Shuttle Solid Rocket Boosters, usually with some kind of an upper stage
* Removing the wings of an Orbiter at the end of its useful life, permanently attaching it to a Space Shuttle external tank, and launching the combination as a space station

Two such concepts are of particular note:

Shuttle-C

Beginning in 1987, NASA actively pursued development of a vehicle called the Shuttle-C, an uncrewed cargo-only launch vehicle. Shuttle-C would have replaced the winged Space Shuttle Orbiter with an expendable cargo module. The module would have no wings, would not carry crew, and would not be recovered. It was expected to carry up to 150,000 pounds (68,038 kg) of payload to low-Earth orbit, compared to the Shuttle's nominal maximum of 65,000 pounds (29,483 kg). Budget pressures, caused in large part by the Space Station Freedom project, resulted in the official cancellation of Shuttle-C in 1990.

Mars Direct

As part of the Mars Direct plan, Mars exploration advocate Robert Zubrin utilized an "inline" SDV concept developed by engineers at NASA and Martin Marietta. The rocket consisted of a large upper stage and payload shroud mounted on top of the Space Shuttle external tank, and the Orbiter replaced by a simple engine pod. The rocket would launch crews and vehicles directly to Mars. NASA's planned Ares V vehicle would superficially resemble this vehicle due to its "inline" setup, although the Mars Direct Ares used side-mounted Space Shuttle Main Engines and a core with the Shuttle External Tank's diameter for greater commonality with Space Shuttle infrastructure.

Vision for Space Exploration

In 2005, NASA decided to pursue the design and construction of two new launchers, both based on technology and infrastructure developed for the US Space Shuttle program. These launchers would replace the Space Shuttle and supply the launch services necessary to fulfill the Vision for Space Exploration. NASA has given the name "Project Constellation" [cite news |first=Brian |last=Berger |url=http://space.com/news/060120_cev_overhaul.html |title=CEV Makeover: NASA Overhauls Plans for New Spaceship |publisher=Space.com |date=20 January 2006 |accessdate=2006-11-22] for the manned Crew Launch Vehicle project.

Requirements

In an April 29, 2005 memo, the following four requirements were given to shape the end result.

* Complete assessment of the top-level Orion spacecraft requirements and plans to enable the Orion to provide crew transport to the ISS and to accelerate the development of the Orion and crew launch system to reduce the gap between shuttle retirement and Orion IOC.
* Definition of top-level requirements and configurations for crew and cargo launch systems to support the lunar and Mars exploration programs.
* Development of a reference lunar exploration architecture concept to support sustained human and robotic lunar exploration operations.
* Identification of key technologies required to enable and significantly enhance these reference exploration systems and re-prioritization of near-term and far-term technology investments.

Vehicles

Ares I

The Ares I, to be used for crew launch, will use as its first stage a solid rocket derived from the Space Shuttle Solid Rocket Booster (SRB). Whereas the Shuttle SRBs use four segments of solid propellant, the Ares I first stage will use five. The shape of the central bore of each propellant segment will also be modified to produce a faster burn. [cite news|first= |last= |url=http://www.flightglobal.com/Articles/2007/01/16/Navigation/200/211501/More+powerful+vehicle+'no+threat'+to+launcher.html |title=More Powerful Vehicle 'No Threat' To Launcher |publisher=flightglobal.com |date=16 January 2007 |accessdate=2007-01-26] The Ares I will be topped by a new second stage, currently under development, that will burn liquid oxygen and liquid hydrogen.

Ares V

The unmanned Ares V vehicle, to be used to loft lunar exploration equipment into orbit to be met by human crews launched by the Ares I, superficially resembles many of the earlier proposed "inline" SDV concepts. It consists of a cryogenic, liquid-hydrogen / liquid-oxygen center stage flanked by two SRBs, topped by a new second stage. Previous "inline" SDV concepts, however, envisioned extensive use of Shuttle components such as the existing External Tank, or a "stretched" version thereof, as well as the Shuttle's existing main engines. The Ares V will use stretched five-segment versions of the SRBs; a new, larger tank using Shuttle External Tank construction and insulation technology; and newer, cheaper expendable rocket engines located at the base of the new tank.

Between T-10 seconds and T=0, five cryogenically-fueled RS-68 rocket engines located at the bottom of the Ares V core stage are ignited, similar to the fire-up sequence on the Space Shuttle. At T=0, the onboard computers, having verified that all five RS-68s are operating at full thrust and do not have any problems, will light the two five-segment solid rocket boosters (SRBs) and retract the fueling "chocks" and swing arms. The Ares V will lift off from the launch pad, perform a roll maneuver to line up the booster on its preprogrammed flight trajectory (most likely the 28.5° "due east" trajectory favored for lifting large payloads from Kennedy Space Center) and then pitch over to fly out over the Atlantic Ocean.

At an altitude of 60 kilometers (200,000 ft), the SRBs are jettisoned and fall back to Earth for a parachute recovery. These are later refurbished in Utah, and reused as either an Ares V booster or Ares I first stage. At that point, the rocket, located above most of the atmosphere, jettisons the launch shroud to reveal the Lunar Surface Access Module (LSAM), which unlike the fragile Apollo Lunar Module, can withstand any outside pressures in the upper portions of the atmosphere. The RS-68s, powered at 100% rated thrust, continue to power the core system until just a little over 8 minutes into the flight. At that time, MECO (main engine cut-off) occurs and the first stage is then jettisoned to burn up in the atmosphere over the Indian Ocean southwest of Australia and away from any known shipping lanes. The Earth Departure Stage (EDS), powered by a single J-2X engine, then maneuvers the LSAM into a circular orbit which will then be retrieved by a separately-launched Orion spacecraft within a month.

After the Orion spacecraft docks with the LSAM/EDS, the EDS then fires its J-2X motor again to thrust the Orion/LSAM stack towards the Moon. After shutdown, the EDS is jettisoned and goes into either a solar orbit or like the S-IVB stages from Apollos 13 to 17, can be deliberately crashed into the lunar surface to calibrate any future instruments left behind by astronauts.

The Ares V can carry up to ~130 tons (~118 t) into a 28.5° Low Earth Orbit, making it suitable for launching very large payloads like a modernized version of either the Skylab or Mir space stations, or up to 100 tons (90 t) into an International Space Station (ISS)-type orbit, making the Ares V a viable heavy-lift launcher for possible ISS modules and repair parts after the retirement of the Shuttle in 2010, or, after the ISS is retired in 2020, a replacement manned or unmanned microgravity station similar to the modular Mir space station. With either a Centaur upper stage augmented with the EDS, or a new cryogenic stage based on the LSAM, it can launch heavyweight probes similar to the Galileo spacecraft or the Cassini-Huygens probe to the outer Solar System using Voyager-like direct trajectories with gravity assists using either Jupiter, Saturn, or both.

Ares IV

In early 2007, NASA confirmed that it was studying a third, crew-capable, launch vehicle concept. The Ares IV would use the Ares V first stage core and side-mounted SRBs, but with the planned Ares I second stage atop that to carry the Orion crew vehicle. Advantages over the Ares I would probably include reduced development cost and time, common launch pad infrastructure and providing more than adequate lift for the Orion, while disadvantages would include increased per-launch cost over the use of a single SRB for the first stage. According to NASA, potential uses of the Ares IV would include sending the Orion spacecraft on early "shakeout" missions into lunar orbit only, as well as testing high-speed "skip" reentries in which the capsule would skip in the Earth's atmosphere before landing, rather than making a relatively direct descent. [cite news|first=Brian |last=Berger |url=http://space.com/news/070126_ares_moon.html |title=NASA Studies Early Moon Shot for New Space Capsule |publisher=Space.com |date=26 January 2007 |accessdate=2007-01-26]

Ares / Orion risk reduction

Proponents of NASA's planned Ares and Orion vehiclesWho|date=August 2007 claim that a primary benefit of the proposed Ares system would be a risk reduction of an estimated ten to one hundred times for Orion crews compared to the present Shuttle system. This would be for two main reasons, as reflected in the two causes of the "Challenger" and "Columbia" disasters:

* Ares I does not have an SRB positioned next to a liquid fuel tank, as is the case with the Shuttle, so any future incidents of O-ring failure and "blow-by" (a term coined by Morton Thiokol engineers for any hot gases that escape through the field joints) could not trigger a catastrophic rupture of the liquid tankage, as it did with "Challenger". Such blow-by could also be detected by means of lower internal pressure in the booster, soon enough for the Orion launch escape system to pull the Orion CM off of the malfunctioning booster. This would negate the form of failure seen in the "Challenger" accident. (The crewed Ares IV and unmanned Ares V would not have this benefit.)

* The Orion Command Module, a space capsule like the Apollo and Soyuz, is positioned above the cryogenic tankage, eliminating the chance of damage to reentry or pressurization systems by falling ice or insulation foam. This would negate the form of failure seen in the "Columbia" accident, in which debris shed by the tankage struck the Orbiter's exposed reentry heat shielding. In addition, the Orion's Command Module heat shield is fully enclosed by its Service Module, as with Apollo spacecraft. The Orion heat shield is thus protected from debris until the Service Module is jettisoned prior to reentry. The Orion Command Module itself would also be protected by a fiberglass "boost protective cover" that shields the spacecraft during the initial launch phase and would be jettisoned, along with the launch escape system, after the first stage is jettisoned. As a result, debris impingement risks during ascent would be all but eliminated.

Criticisms

A shuttle-derived vehicle would utilize support personnel who currently work on the shuttle program. However, since the large support crew constitutes the major component of the Shuttle's operational cost, some feel that an architecture not tied to the Space Shuttle would be significantly less expensive.

Instead of a single heavy lift cargo launcher, it is possible that smaller rockets (though with smaller mass fractions) would allow lower up-front fixed expenditures (development costs, infrastructure, etc.) that could be spread out over more launches. Although more fuel would be used per kilogram of payload launched in a smaller rocket, these are marginal expenses compared to the costs of other aspects of the program. From this standpoint, a smaller rocket might be more adaptable to future missions, as well as more cost-efficient.

It has also been asserted that the Exploration Systems Architecture Study, which was largely responsible for the decision to use a shuttle-derived heavy-lift launcher instead of smaller rockets, relied on a number of potentially faulty assumptions. [cite web | last = Goff | first = Jonathan | date = 12 September 2006 | url = http://selenianboondocks.blogspot.com/2006/09/esas-issues-part-one.html | title = ESAS Issues Part One | work = Selenian Boondocks | accessdate = November 22 | accessyear = 2006] [cite web | url = http://www.nasa.gov/pdf/140637main_ESAS_06.pdf | title = Launch Vehicles and Earth Departure Stages | format = PDF | publisher = NASA | accessdate = November 22 | accessyear = 2006] One major assumption is that if smaller rockets were used, it would only be possible to prepare for one launch at a time.

DIRECT

A recent proposal put forward as alternative to the NASA Ares vehicles is the "Direct Shuttle Derivative" or DIRECT launch vehicle (unrelated to the "Mars Direct" plan), made by a grassroots group of engineers and other spaceflight enthusiasts. DIRECT would utilize an ET-derived core stage powered by two man-rated versions of the RS-68 engine, plus a pair of standard four-segment SRBs, and be able to deliver more than 50 metric tons to orbit. Adding a third RS68 and an upper Earth Departure Stage engines would increase this payload to around 100 metric tons.

Proponents argue that development costs of this vehicle would be significantly lower than those for the Ares V because of its greater commonality with the existing shuttle, and because the system would be man-rated by default. Further, whilst the larger version of the rocket would take on the role of Cargo Launch Vehicle, the smaller version would be used as the Crew Launch Vehicle; hence, Ares I would not be needed.

References

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Notes

External links

* [http://www.nasa.gov/mission_pages/exploration/spacecraft/index.html NASA Official Project Constellation Homepage]
* [http://www.nasa.gov/mission_pages/exploration/spacecraft/ares_naming.html NASA Official Ares Rocket Website]
* [http://space.com/news/060630_ares_rockets.html Ares Rocket at Space.com]
* [http://www.astronautix.com/lvfam/shuttle.htm Shuttle-Derived Vehicles]
* [http://www.astronautix.com/lvs/shuttlec.htm Shuttle-C]
* [http://www.globalsecurity.org/space/systems/sdv-hllv.htm SDV Heavy Lift Launch Vehicles]
* [http://www.globalsecurity.org/space/systems/srb-x.htm SRB-X Launch Vehicle]
* [http://chapters.nss.org/ny/nyc/Shuttle-Derived%20Vehicles%20Modified.pdf SDV Presentation]
* [http://www.cnn.com/2006/TECH/space/03/03/cev.vs.apollo/index.html CEV vs Apollo]
* [http://img375.imageshack.us/img375/3017/clvcev7we.jpgAres I-Crew Exploration Vehicle]
* [http://www.safesimplesoon.com/ (Advocacy site by ATK, Inc.)]
* [http://www.spaceref.com/news/viewsr.html?pid=16512 Internal Letter from NASA Administrator Griffin: Exploration Systems Architecture Study Support]
* [http://www.spaceref.com/news/viewnews.html?id=1040 NASA Plans to Build Two New Shuttle-derived Launch Vehicles]
* [http://www.spaceref.com/news/viewnews.html?id=1055NASA'ss New CEV Launcher to Maximize Use of Space Shuttle Components]
* [http://www.spaceref.com/news/viewnews.html?id=1057NASA'ss New Launch Systems May Include the Return of the Space Tug]
* [http://www.spaceref.com/news/viewnews.html?id=1087 NASA Encounters Possible Problems With Crew Launch Vehicle Design] Spaceref, January 17, 2006)
* [http://www.space.com/adastra/adastra_mega-modules2_051013.html The Mega-Module Path to Nowhere (Or: How to Eliminate Human Space Flight With an HLV)] (Ad Astra, 13 October 2005)
* [http://www.nasaspaceflight.com/content/?id=4333 NASA closing in on naming new fleet] (NASASpaceFlight.com; 2/27/2006 8:55:00 AM)
* [http://www.nasawatch.com/archives/2006/08/vse_launchers_w.html VSE Launchers: Why Recreate Something You Can Already Buy?] (NASA Watch, August 29, 2006)
* [http://www.directlauncher.com The 'Direct' Shuttle Derived launch vehicle proposal]
* [http://www.tallgeorge.com/projectconstellation.php A Visual History of Project Constellation]