Shuttle-Derived Launch Vehicle

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Comparison of the Saturn V, Space Shuttle, Ares I, and Ares V.
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Comparison of the Saturn V, Space Shuttle, Ares I, and Ares V.

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 two SDVs to replace the Space Shuttle and enable exploration of the Moon and Mars. It has been announced that the new name for the rocket system will be Ares.[1][2]

Contents

[edit] Vision for Space Exploration

Main article: 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"[3] for the manned Crew Launch Vehicle project.

[edit] 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.

[edit] Vehicles

[edit] Ares I

Main article: Ares I
Ares I at launch.
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Ares I at launch.

At liftoff, the solid first stage would power the vehicle up to approximately 60 kilometers (200,000 ft) and a velocity of about 2000 meters/second (6,700 ft/s). At that point, the first stage is jettisoned and the liquid-fueled second stage would take over, burning for about 3½ to 4 minutes to place the Orion spacecraft on a suborbital trajectory with a 354 kilometers (220 mi) perigee and then firing again about 45 minutes later to perform orbit circularization. The J-2X, the engine used for the second stage, would be throttled to maintain 4 g (40 meter/sescond² (131 ft/s²)) acceleration. This is nearly identical to the "direct insertion" profile used on earlier U.S. spaceflights and most Space Shuttle flights.

The first stage SRB could in theory be recovered and reused as they are with the shuttle program, but the uncertain cost benefits of SRB recovery may preclude this. While the shuttle boosters are retrieved and re-used, the actual savings are negligible. Additionally, the lack of the nose cap would require the development of a new interstage assembly to hold the parachutes, adding expense and weight to the design.

After allowing for a 9,000 pound (4000 kg) escape system, the original Ares I concept was expected to deliver approxmiately 59,999 pounds (27,000 kg) into a 220x200 mile (350x350 km) orbit at 28° inclination. However, issues with weight growth and underperformance have reduced this and the current payload is expected to be around 48,400 pounds (22,000 kg) into a much lower -30x160 mile (48x258 km) orbit. The higher inclination of the ISS orbit lowers this payload significantly. With the Orion spacecraft having a mass of around 55,000 pounds (25,000 kg), it will have to use its own propulsion system to complete the ascent and to circularize the orbit. For these reasons, Ares I will be very unsuitable for launch of any other payload than the Orion itself.

Noteworthy is the relatively brief flight time, just over 6½ minutes, compared to the much longer burns characteristic of EELV derived launchers with their low-thrust, long-burn upper stages. Thiokol appears to be actively promoting this quick flight as minimizing the length of time during which a crew is at risk. The original planned re-engineering of the SSME to be restartable was to be significant, but with the decision to use the J-2X, the problems of developing a restartable engine was significantly reduced, as the original Apollo-Saturn J-2 was designed to be restartable, in both the air and in a near-vacuum from the beginning.

[edit] Ares V

Main article: Ares V
Ares V jettisons solid rocket boosters.
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Ares V jettisons solid rocket boosters.

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 then 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, continues 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.

[edit] Risk reduction

One of the primary benefits of the proposed system is that it is estimated to be ten to one hundred times safer for Orion crews than the present Shuttle system. This is for two main reasons, that are reflected in the two causes of the Columbia and Challenger 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 explosion and would be detected by means of lower internal pressure soon enough for the Orion launch escape system to pull the Orion CM off of the booster. This would negate the form of failure seen in the Challenger accident.
  • The Orion Command Module, a space capsule like the Apollo and Soyuz, is positioned above any cryogenic fuel tank architecture so the chance of damage to reentry systems or pressurization systems by ice or foam falling from fuel tanks is eliminated entirely, thereby negating the form of failure seen in the Columbia accident. In addition, the Orion Service Module fits snugly across the entire base of the heat shield, like that of the Apollo spacecraft, and demonstrated on the Apollo 13 flight when engineers decided to retain the nearly-destroyed Apollo Service Module due to the possibility of a crack in the heat shield. Although not originally intended, the Orion Command Module will also be protected by a fiberglass "boost protective cover" that will shield the spacecraft during the initial launch phase and would be jettisoned, along with the launch escape system, after the first stage is jettisoned.

[edit] Criticisms

Further information: Exploration Systems Architecture Study

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.[4][5] One major assumption is that if smaller rockets were used, it would only be possible to prepare for one launch at a time.

[edit] Past proposals

Proposed SDV concepts in the past have included:

  • Replacing the winged Shuttle Orbiter with an uncrewed, expendable cargo pod
  • Removing the Orbiter and mounting an upper stage and payload atop the Space Shuttle external tank
  • 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

SDV concepts were proposed even before the Shuttle itself began flying. Three concepts were of particular note.

[edit] Shuttle-C

Main article: 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.

[edit] Mars Direct

Main article: 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 Marrietta. 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.

[edit] DIRECT

Main article: DIRECT

A more recent proposal is the "Direct Shuttle Derivative" or DIRECT launch vehicle (unrelated to the "Mars Direct" plan), and made by a grassroots group of engineers and other spaceflight enthusiasts. DIRECT would utilize a ET-derived core stage powered by two regeneratively cooled versions of the RS-68 engine, plus a pair of standard four-segment SRBs, and be able to deliver more than 70 metric tons (77.2 tons) to orbit. An upper Earth Departure Stage would increase this payload to around 96 metric tons (105.8 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, and hence Ares I would not be needed.

[edit] References

  • Jenkins, Dennis R. (2002). Space Shuttle: The History of the National Space Transportation System. Stillwater MN: Voyageur Press. ISBN 0-9633974-5-1.

[edit] Notes

  1. ^ Ares: NASA's New Rockets Get Names. NASA (June 30, 2006). Retrieved on November 22, 2006.
  2. ^ Malik, Tariq. "NASA Names Rockets for Moon and Mars Missions", Space.com, 30 June 2006. Retrieved on 2006-11-22.
  3. ^ Berger, Brian. "CEV Makeover: NASA Overhauls Plans for New Spaceship", Space.com, 20 January 2006. Retrieved on 2006-11-22.
  4. ^ Goff, Jonathan (12 September 2006). ESAS Issues Part One. Selenian Boondocks. Retrieved on November 22, 2006.
  5. ^ Launch Vehicles and Earth Departure Stages (PDF). NASA. Retrieved on November 22, 2006.

[edit] External links

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Space Shuttle Program
Space Shuttle Insignia Main Articles: Space Shuttle program | Space Shuttle
Components: Orbiter | SRB | External Tank | SSME | OMS | Crawler Transporter
Orbiters: Enterprise | Columbia | Challenger | Discovery | Atlantis | Endeavour
Launch Sites: Kennedy Space Center LC-39 | Vandenberg Air Force Base SLC-6
Developments: Shuttle-Derived Launch Vehicle | Shuttle-C | Ares I | Ares V
Test Articles: Pathfinder
Misc: Missions | Cancelled Missions | Decision | Crews | Abort modes | In Fiction
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