5
Launch Vehicle and Spacecraft Options for Future Space Science Missions

The Constellation System is being developed to enable human exploration beyond low Earth orbit, to include the Moon and Mars. It consists of the Orion Crew Exploration Vehicle (CEV), the Altair lunar lander, and the Ares I and V launch vehicles. Primarily envisioned to deliver cargo to the Moon, the Ares V has nearly five times the lift capability of the most capable launch vehicle currently in the U.S. fleet—the Delta IV Heavy. Recognizing that this additional lift capability could enable new science opportunities, NASA has identified alternative Ares V vehicle configurations to launch spacecraft for science missions. Similarly, several notional configurations of the Ares I have been identified for missions that are at or slightly exceed the capabilities of the Delta IV Heavy.

This chapter provides a high-level overview of the Orion spacecraft and the Ares I and Ares V launch systems, as well as a comparison of the performance of these launch vehicles with that of the existing fleet of expendable launch vehicles employed by the U.S. government. The Altair lunar lander (technically the Lunar Surface Access Module) is in the very preliminary concept stage and is not discussed in this report.

THE ORION SPACECRAFT

The Orion CEV is to be launched atop the Ares I rocket and consists of a launch-abort system (capable of pulling the spacecraft and its crew to safety in the event of an emergency), the crew module (CM), the service module (SM, which houses the power and propulsion modules), and the spacecraft adapter (to connect the Orion capsule and service module to the launch systems). (See Figure 5.1.)

Orion has a configuration similar to that of the Apollo spacecraft but is significantly larger, with twice the internal volume. Orion will be 5 m in diameter and will have a mass of about 22.7 metric tons and a pressurized volume of 20 m3. Orion will boast a lunar return payload of 100 kg and a crew habitable volume of 11 m3, allowing it to support up to six crew members for low-Earth-orbit missions. The current baseline design of the service module includes a scientific instrumentation module (SIM) bay of 0.57 m3 volume, with power and data accommodations, capable of holding 382 kg.

The Orion vehicle is specifically designed to support missions to the Moon as well as to the International Space Station (ISS). The standard lunar mission would involve the launch of four crew members aboard an Orion atop an Ares I, followed by the launch of the Altair lunar lander atop an Ares V. The Orion would then rendezvous and dock with the Altair atop its Earth Departure Stage and then conduct an approximately 4-day journey to the Moon. The four-person crew would descend to the lunar surface inside the Altair, leaving the Orion uncrewed in



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5 Launch Vehicle and Spacecraft Options for Future Space Science Missions The Constellation System is being developed to enable human exploration beyond low Earth orbit, to include the Moon and Mars. It consists of the Orion Crew Exploration Vehicle (CEV), the Altair lunar lander, and the Ares I and V launch vehicles. Primarily envisioned to deliver cargo to the Moon, the Ares V has nearly five times the lift capability of the most capable launch vehicle currently in the U.S. fleet—the Delta IV Heavy. Recognizing that this additional lift capability could enable new science opportunities, NASA has identified alternative Ares V vehicle configurations to launch spacecraft for science missions. Similarly, several notional configurations of the Ares I have been identified for missions that are at or slightly exceed the capabilities of the Delta IV Heavy. This chapter provides a high-level overview of the Orion spacecraft and the Ares I and Ares V launch systems, as well as a comparison of the performance of these launch vehicles with that of the existing fleet of expendable launch vehicles employed by the U.S. government. The Altair lunar lander (technically the Lunar Surface Access Module) is in the very preliminary concept stage and is not discussed in this report. THE ORION SPACECRAFT The Orion CEV is to be launched atop the Ares I rocket and consists of a launch-abort system (capable of pulling the spacecraft and its crew to safety in the event of an emergency), the crew module (CM), the service module (SM, which houses the power and propulsion modules), and the spacecraft adapter (to connect the Orion capsule and service module to the launch systems). (See Figure 5.1.) Orion has a configuration similar to that of the Apollo spacecraft but is significantly larger, with twice the internal volume. Orion will be 5 m in diameter and will have a mass of about 22.7 metric tons and a pressurized volume of 20 m3. Orion will boast a lunar return payload of 100 kg and a crew habitable volume of 11 m 3, allow- ing it to support up to six crew members for low-Earth-orbit missions. The current baseline design of the service module includes a scientific instrumentation module (SIM) bay of 0.57 m3 volume, with power and data accom- modations, capable of holding 382 kg. The Orion vehicle is specifically designed to support missions to the Moon as well as to the International Space Station (ISS). The standard lunar mission would involve the launch of four crew members aboard an Orion atop an Ares I, followed by the launch of the Altair lunar lander atop an Ares V. The Orion would then rendezvous and dock with the Altair atop its Earth Departure Stage and then conduct an approximately 4-day journey to the Moon. The four-person crew would descend to the lunar surface inside the Altair, leaving the Orion uncrewed in 

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 LAUNCHING SCIENCE Crew Module (JSC) Crew and cargo transport Launch Abort System ( LaRC) Emergency escape during launch Spacecraft Adapter (GRC) Structural transition to Ares launch vehicle Service Module (GRC) propulsion, electrical power, fluids storage FIGURE 5.1 The Orion spacecraft. The overall configuration is similar to that of the Apollo spacecraft. NOTE: GRC, Glenn Research Center; JSC, Johnson Space Center; LaRC, Langley Research Center. SOURCE: Courtesy of NASA. Figure 5.1.eps low lunar orbit for up to 180 days. At the end of the lunar phase of the mission, the Altair would launch from the Includes low resolution bitmap image surface and rendezvous with Orion for the return to Earth. The command module would perform direct or skip reentry and make a precision water landing off the coast of California. The core capabilities for the ISS mission are launch by way of Ares I for a crew of up to six, automated rendezvous and docking with relative navigation sensors, and a low impact docking system (LIDS). Orion then remains at ISS for up to 180 days and undocks for return to Earth. Additional capabilities are available with further small- or large-scale design work. These include the delivery of unpressurized cargo to the ISS with volume of up to 2.92 m3 and mass up to 600 kg, the ability to configure the service module as a stand-alone element (ability to deliver a payload to a particular location), and the capability of being used in a modular fashion. OPPORTUNITIES FOR SMALL SPACE SCIENCE PAYLOADS ABOARD CONSTELLATION Although the Orion spacecraft is still in a relatively early stage of development, NASA has reserved payload space and mass at the rear of the vehicle for potential science payloads (see Figure 5.2). These could include both attached payloads and small deployable satellites. The committee did not receive any such small-payload propos- als in response to its request for information (all of the mission proposals that the committee evaluated are large, multiton experiments), but this payload capability offers the potential for interesting and worthwhile science to be conducted on Orion flights. This would enhance Orion’s capabilities. As of the writing of this report, opportunities appear to exist to attach experiments to the service module on lunar missions. Studies and analyses to evaluate various options are in progress. The Orion designers currently

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 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS Service module includes a scientific instrumentation module (SIM) bay – 0.57 cubic meter volume – Capable of holding 382 kg – Power and data accommodations FIGURE 5.2 NASA has reserved space on the Orion spacecraft for a scientific instrumentation module. This could carry instruments as well as small deployable payloads. Figure Courtesy of NASA. SOURCE: 5.2.eps Includes low resolution bitmap image envision relatively simple interfaces between such experiments and the service module. The experiments could ride along with the service module into orbit with the spacecraft, could be separated from the service module, or could also be propelled into a different orbit by a self-contained rocket motor. 1 There may be similar opportunities for additional secondary payloads aboard the other elements of Constel- lation such as Orion and Altair and even the Ares V.2 Historically, as space launch systems mature, opportunities develop for secondary payloads to ride into space in addition to primary payloads. This has been the case for Atlas, Thor, Delta, and Titan, and one can expect a similar evolution as the Constellation System matures. Secondary experiments were carried aboard the Apollo program. Subsatellites were released during the Apollo 15 and 16 missions and orbited the Moon for periods much longer than the Apollo excursions to the lunar surface. (See Figure 5.3.) Similarly, many secondary payloads were carried into orbit aboard Department of Defense boost- ers. Such secondary experimental payloads had the virtue of being relatively inexpensive and provided flexible, quick-turnaround, rapid-response capabilities to seize scientific opportunities. For example, assuming that lunar missions are launched twice a year and assuming that secondary experiments capabilities also become available aboard Altair and Orion, there would be multiple opportunities each year for appropriate experiments to fly. Recommendation: If NASA wishes to use the Constellation System for science missions, it should preserve the capability for Orion to carry small scientific payloads and should ensure that the Ares V development team considers the needs of scientific payloads in system design. ARES I The Ares I will lift the Orion into low Earth orbit, either to dock with the ISS or to mate with the Earth Depar- ture Stage (EDS) for transport to the Moon (Figure 5.4). The Ares I is a two-stage, human-rated launch vehicle that employs proven technologies and hardware designs to increase vehicle safety and reliability and significantly reduce development cost and time. The first stage is a five-segment reusable solid-rocket motor derived from the four-segment Reusable Solid Rocket Motor (RSRM) currently used to boost the space shuttle into orbit. The upper stage is a liquid oxygen/liquid hydrogen (LOX/LH2) system using a single J-2X engine. (See Figure 5.5.) 1 Flights to the International Space Station could accommodate a mass of about 600 kg and a volume of about 3 m 3. 2 One possibility discussed for Ares V is the inclusion of a device similar to that developed for the Evolved Expendable Launch Vehicle (EELV) family and known as the EELV Secondary Payload Adapter, or ESPA ring. This device enables small satellites to be carried and deployed. However, no formal proposal for such a device was presented to the committee, and there is no indication that NASA is actively considering such a device at this early stage of Ares V development.

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00 LAUNCHING SCIENCE FIGURE 5.3 Artist’s impression of an Apollo spacecraft launching a subsatellite while in orbit around the Moon. The Orion spacecraft could have a similar capability. SOURCE: Courtesy of NASA. This engine is a derivative of the J-2 used on the Saturn IB and Saturn V rockets during the Apollo program. The modern version incorporates technologies developed for the J-2S, a simplified version of the original J-2, and the XRS-2200 aero-spike engine developed for the X-33 Advanced Technology Demonstrator program in the late 1990s. It also employs modern manufacturing processes used for the Delta IV RS-68 engine. The first develop- ment test flight of a dynamically similar test version of the Ares I (designated the Ares I-X) is scheduled for the fall of 2009. The first flight validation test is scheduled for 2012 or 2013. To meet the needs of science missions, the Orion CEV and Encapsulated Service Module could be replaced with a 5-m shroud, derived from either the Atlas V or Delta IV composite fairing. This version could be used to place satellites into low Earth orbit. For higher orbital altitudes and interplanetary missions, a dual-engine Centaur (Centaur V2) could be added. Using heritage systems again reduces development costs and time. The primary development would focus on system integration and the interfaces between the Ares I booster and the Centaur or payload.

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0 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS FIGURE 5.4 Artist’s conception of the Ares I launch vehicle on its pad. SOURCE: Courtesy of NASA. Figure 5.4.eps Bitmap image

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0 LAUNCHING SCIENCE Instrument Unit Stack Integration • Primary Ares I control • 927.1 mT (2,044.0K lbm) Module (ESM) Panels avionics system gross liftoff mass • NASA Design / • 99.1 m (325.0 ft) in length Boeing Production ($0.8B) • NASA-led Orion CEV First Stage • Derived from current Interstage Shuttle RSRM/B • Five segments/Polybutadiene Acrylonitrile (PBAN) propellant Upper Stage • Recoverable • 137.1 mT (302.2K lbm) LOX/LH2 prop • New forward adapter • 5.5-m (18-ft) diameter • Avionics upgrades • Aluminum-Lithium (Al-Li) structures • ATK Launch Systems ($1.8B) • Instrument unit and interstage • Reaction Control System (RCS) / roll control for first stage flight • Primary Ares I control avionics system • NASA Design / Boeing Production ($1.12B) Upper Stage Engine • Saturn J–2 derived engine (J–2X) • Expendable • Pratt and Whitney Rocketdyne ($1.2B) FIGURE 5.5 Ares I configuration. The first stage is derived from the space shuttle’s solid-rocket booster. The upper stage will use the J-2X engine. NOTE: RSRM/B, Reusable Solid Rocket Motor/Booster; lbm, pound-mass; LOX/LH 2, liquid oxygen/liq- Figure 5.5.eps uid hydrogen. SOURCE: Courtesy of NASA. Includes low resolution bitmap image Lines are squiggly ARES V The Ares V provides significant increased capability over the existing fleet of U.S. government launch vehi- cles, both in terms of payload mass and available payload volume. It is being designed to transport cargo to the Moon as well as to deliver the Earth Departure Stage to low Earth orbit to rendezvous with the Orion spacecraft for missions to the Moon. The Ares V consists of a pair of 5.5-segment solid-rocket boosters (SRBs) strapped to an LOX/LH2 core stage, and an EDS. The SRBs are common to the first-stage motors used on the Ares I, with direct heritage to the shuttle RSRMs. The core stage will be propelled by six RS-68B engines derived from the RS-68 engines developed for the Delta IV launch vehicle. The EDS will employ the J-2X engine being developed for the second stage of the Ares I, as well as the Ares I instrumentation unit. (See Figure 5.6.) Given the use of hardware and systems being developed for Ares I, the development risks of the Ares V are significantly reduced. The first test flight of the Ares V is projected to occur in the 2018 time frame, with the first opportunity for a lunar mission occurring by 2020. The standard Ares shroud can be used for science missions. It has a usable volume of 860 m 3, which is more than three times the volume of the Delta IV fairing. For larger payloads, the cylindrical portion of the baseline shroud could be extended by 9 m, to provide usable volume of 1,410 m 3. To enhance the usefulness of Ares V for deep space missions, the Constellation System has identified a notional configuration that includes a dual-engine Centaur to improve mission capability.

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0 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS Composite Shroud Launch Abort System Altair Lunar Lander Earth Departure Stage Orion Crew Exploration Vehicle LOX/LH 2 (Crew Module / Service Module) 1 J –2X Engine Encapsulated Service Al -Li Tanks Module Panels Composite Structures Instrument Unit Loiter Skirt Upper Stage Interstage J–2X Upper Stage Engine Interstage Core Stage Forward Frustum LOX/LH 2 6 RS–68 Engines Al-Li Tanks/Structures First Stage (5-Segment RSRB) 2 5.5-Segment RSRBs Ares I Ares V 25.5 mT (56.2K lbm) to 71.1 mT (156.7K lbm) to TLI (with Ares I) Low Earth Orbit (LEO) 62.8 mT (138.5K lbm) to TLI ~187.7 mT (413.8K lbm) to LEO FIGURE 5.6 Comparison of Ares V and Ares I configurations. Although significantly larger than the Ares I, it is planned that the Ares V will use a number of the Ares I components. NOTE: RSRB, Reusable Solid Rocket Booster; lbm, pound-mass; Figure 5.6.eps LOX/LH2, liquid oxygen/liquid hydrogen. SOURCE: Courtesy of NASA. Includes low resolution bitmap images DELTA IV The Delta IV is currently in service, primarily carrying national security payloads. (See Figure 5.7.) The Delta IV family of vehicles consists of five different configurations. The smallest is the Medium Launch Vehicle (MLV; referred to in several of the Vision Mission studies as a Delta 4040). It consists of a Common Booster Core, with a 4-m upper stage and payload fairing. A variant of this configuration includes the addition of two solid-rocket motors and is referred to as a M+(4,2) (or Delta 4240 in the various studies). The next variant uses either two or four solid-rocket motors with a 5-m upper stage and payload fairing. These variants are referred to as M+(5,2) and M+(5,4) vehicles, or Delta 4250 and 4450, respectively. The largest variant of the Delta IV is the Heavy Lift Vehicle (HLV). It consists of three boosters and a 5-m upper stage and payload fairing. (It is the variant identi- fied in the majority of the Vision Mission studies and is referred to as the 4050 or 4050H.) The first Delta IV was launched in November 2002, with the first Heavy configuration launched in December 2004.

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0 LAUNCHING SCIENCE FIGURE 5.7 Launch of a Delta IV Heavy launch vehicle carrying a military payload. Most of the Vision Mission concepts evaluated in this report used the Delta IV Heavy. SOURCE: Courtesy of U.S. Air Force.

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0 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS The launch vehicle performance estimates used in each of the Vision Mission studies were based on the original Delta IV Payload Planners Guide, published in 2000 and updated in 2002.3 United Launch Alliance (a joint venture formed by the Boeing Company and Lockheed Martin Corporation) released an updated version of the Payload Planners Guide in September 2007.4 The updated performance estimates for low Earth orbit are slightly lower (∼6 percent) than the 2002 estimates. The vehicle performance estimates across the reported range of C3 (hyperbolic excess speed over escape velocity) increased by 10 to 15 percent. Performance comparisons and assessments in the remainder of the discussion are based on the most recent values. The government is currently funding an upgrade program for the RS-68 engine used on the first stage of the Delta IV. The upgraded engine, known as the RS-68A, is projected to be completed to support a launch in the 2010 time frame. Various improvements will increase both the thrust and specific impulse (Isp) of the engine, increasing the overall vehicle performance. Since the results of the upgrade are not yet documented, the benefits of the performance improvements are not considered in this evaluation. A slightly modified version of the RS-68A engine, designated the RS-68B, is to be used on the Ares V launch vehicle. The modifications are intended to (1) take advantage of the performance enhancements currently in development, (2) reduce the use of helium for the five engines to levels comparable with the levels used by the three space shuttle main engines, and (3) minimize the hydrogen flame that rises around the Delta IV during the engine start sequence. ATLAS V As with the Delta IV, the Atlas V consists of multiple vehicle configurations. All configurations use a standard common core booster, with up to five strap-on solid-rocket boosters, and a Centaur upper stage. The Centaur can be ordered with either a single or a pair of RL10 engines. A three-digit naming convention is used to identify the specific configuration of the highly modular Atlas V vehicle. The first digit indicates the payload fairing size (4- or 5-m), the second identifies the number of strap-on solid-rocket motors (from 0 up to 5), and the third identifies the number of RL10 engines (1 or 2). The Atlas V is currently in service carrying military, civilian, and commercial payloads, as illustrated in Figure 5.8. The first Atlas V flew in August 2002. The 400 and 500 series configurations provide a broad range of payload capabilities, bridging the gap between the M+ and Heavy configurations of the Delta IV. An HLV configuration of the Atlas V is currently under development but does not have a planned launch date. (The Super Heavy con- figuration identified in several of the Vision Mission studies is a notional growth option for the Atlas family and does not currently exist, nor is any work underway to develop it.) ARES DEVELOPMENT RISKS Engines generally provide the greatest technical risks for launch systems. To address this risk, NASA is employing and enhancing engines with significant flight and development history (see Figure 5.9). A second significant risk is mass growth of the launch vehicle. This is a continual challenge during the development phase and often leads to engine performance upgrades or structural weight-saving measures. The RS-68 has a modest flight history (8 flights, 12 engines) and significant development history. The govern- ment is currently upgrading the performance of the engine to address unique requirements of a mission scheduled to fly in the 2010 time frame. NASA will use this upgraded engine, the RS-68A, as the foundation for the RS-68B to be used for the Ares V. The modifications planned for this upgrade are not necessarily simple modifications, but they are much simpler than a complete engine development activity, or even the performance upgrades currently in work by the U.S. Air Force and the National Reconnaissance Office. 3 Delta IV Payload Planners Guide, The Boeing Company, Huntington Beach, Calif., 2002. 4 Delta IV Payload Planners Guide, 06H0233, United Launch Alliance, Littleton, Colo., September 2007, available at http://www.ulalaunch. com/docs/product_sheet/DeltaIVPayloadPlannersGuide2007.pdf.

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0 LAUNCHING SCIENCE FIGURE 5.8 Launch of an Atlas V launch vehicle carrying NASA’s New Horizons spacecraft. SOURCE: Courtesy of NASA.

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0 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS 122 m (400 ft) Crew Altair 91 m Lunar Orion (300 ft) Lander Earth Departure Stage (EDS) (1 J –2X) Overall Vehicle Height, m (ft) 253.0 mT (557.7K lbm) LOX/LH2 S–IVB (1 J–2 engine) Upper Stage 108.9 mT (1 J –2X) (240.0K lbm) 61 m 137.1 mT (200 ft) LOX/LH2 (302.2K lbm) LOX/LH2 S–II (5 J–2 engines) 453.6 mT Core Stage 5-Segment (1,000.0K lbm) (6 RS–68 Engines) Reusable LOX/LH2 1,587.3 mT Solid Rocket 30 m (3,499.5K lbm) Booster (100 ft) S–IC (RSRB) LOX/LH2 (5 F–1) 2 5.5-Segment 1,769.0 mT RSRBs (3,900.0K lbm) LOX/RP–1 0 Ares V Saturn V Space Shuttle Ares I Height: 56.1 m (184.2 ft) Height: 99.1 m (325.0 ft) Height: 116.2 m (381.1 ft) Height: 110.9 m (364.0 ft) Gross Liftoff Mass : Gross Liftoff Mass: Gross Liftoff Mass : Gross Liftoff Mass : 3,704.5 mT (8,167.1K lbm) 2,041.1 mT (4,500.0K lbm) 927.1 mT (2,044.0K lbm) 2,948.4 mT (6,500K lbm) Payload Capability: Payload Capability: Payload Capability: Payload Capability: 25.0 mT (55.1K lbm) 25.5 mT (56.2K lbm) 71.1 mT (156.7K lbm) to TLI (with Ares I) 44.9 mT (99.0K lbm) to TLI to Low Earth Orbit (LEO) to LEO 118.8 mT (262.0K lbm) to LEO 62.8 mT (138.5K lbm) to TLI ~187.7 mT (413.8K lbm) to LEO FIGURE 5.9 Ares I and Ares V use flight-proven technologies adopted from other vehicles, including the space shuttle and Delta IV. NOTE: lbm, pound-mass; LOX/LH2, liquid oxygen/liquid hydrogen; LOX/RP-1, Rocket Propellant-1. SOURCE: Figure 5.9.eps Courtesy of NASA. Includes low resolution bitmap images The space shuttle SRB has significant flight history and demonstrated reliability. Nonetheless, increasing the number of segments and increasing the chamber pressure are significant modifications. A planned series of development and qualification test motors should provide confidence in the design, leading up to the first flight test of the five-segment variant by 2013. This development activity is well ahead of the need for the Ares V and therefore represents a low risk for the future superheavy lift booster. The most challenging engine development activity is the J-2X, which is a second-generation version of the J-2 engine last flown on the Saturn V. Although there is pedigree to the Saturn IB and Saturn V engines, the new design incorporates design features and manufacturing processes developed for various engines over the past 30 years. As such, this represents a significant development effort. Pratt & Whitney Rocketdyne is utilizing its proven development philosophy of incremental component, subsystem, and engine system testing, coupled with early identification and elimination of development risks. The first test flight of the J-2X is scheduled for 2012. Again, the development activity is well ahead of the need for the Ares V and represents a low risk for that vehicle. One of the most significant residual technical risks associated with the Ares V will be the mass of the tank structure/airframe, electronics, controls systems, and so on. If the mass exceeds expectations, the engines will require upgrades or mass will need to be shaved off the vehicle. Standard mass growth allowances are being used for the design, which should mitigate this concern.

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0 LAUNCHING SCIENCE Vehicle Performance Comparison LEO Missions 25 20 Payload (tonnes) 15 10 Ares I Delta IV HLV 5 Delta IV M+(5,4) Delta IV (M+4,2) Delta IV MLV 0 200 300 400 500 600 700 800 900 1000 Circular Orbit Altitude (km) FIGURE 5.10 Comparison of Ares I and Delta IV family vehicle performance. Figure 5.10.eps VEHICLE PERFORMANCE COMPARISONS Ares I The capability of the Ares I is roughly equivalent to, and perhaps slightly greater than, that of the Delta IV Heavy to a low Earth orbit of 200 km. However, the performance of the Ares I drops off more dramatically with altitude than does the performance of the Delta IV. Figure 5.10 provides a comparison of the payload capability of the Ares I and the various Delta IV configurations, based on the data provided to the committee by NASA’s Exploration Systems Mission Directorate and the Delta IV Payload Planners Guide released in 2007.5 This figure shows that the Ares I does not provide any benefit over the current fleet of Evolved Expendable Launch Vehicle (EELV) vehicles for low-Earth-orbit missions. Figure 5.10 also shows that because Ares I is optimized to deliver the heavy Orion spacecraft to low Earth orbit, Ares I capability falls off rapidly above low Earth orbit. The per- formance of the Atlas V is not included in this figure, since the various Delta IV configurations envelope the lift capability of the Atlas configurations. In general, a dual-engine Centaur would be used to maximize performance for low-Earth-orbit missions, with the 532, 542, and 552 configurations filling in the gap between the Delta IV M+(5,4) and Heavy configurations. As indicated above, the Ares I/Centaur V2 configuration can be used to augment performance to low Earth orbit; however, its primary purpose is to provide capability for interplanetary missions. A comparison between the Delta IV Heavy and the Ares I is provided in Figure 5.11. The performance of the Ares I/Centaur and the Delta IV Heavy are roughly equivalent for C3 values up to roughly 20 km2/s2. However, the Ares I appears to provide a greater lift capability for higher C3 requirements. The Atlas V 551 can be fitted with a Star 48V Orbit Insertion 5 Delta IV Payload Planners Guide, 06H0233, United Launch Alliance, Littleton, Colo., September 2007, available at http://www.ulalaunch. com/docs/product_sheet/DeltaIVPayloadPlannersGuide2007.pdf.

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0 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS Vehicle Performance Comparison Interplanetary 12.0 10.0 Ares I - Centaur Delta IV HLV Atlas V 551 w/ Star 48 8.0 Atlas V 551 Payload (Tonnes) 6.0 4.0 2.0 0.0 0 20 40 60 80 100 120 140 C3 (km2 /s2) FIGURE 5.11 Comparison of escape performance of the Delta IV Heavy, Atlas V, and Ares I/Centaur V2. Figure 5.11.eps Stage. In this configuration, it provides capability equivalent to that of the Delta IV for a C3 of 100 km 2/s2 and approaches that of the Ares I with a Centaur for C3 values greater than 120 km 2/s2. Since the Ares I would use the Atlas V extended payload fairing configuration with the dual-engine Centaur, the usable volume in the payload fairings are roughly equivalent for the Delta IV and Ares I. The available volume for the Atlas V 551 with the Star 48V will be reduced slightly to accommodate the Orbit Insertion Stage. This is a notional, nonstandard configuration for the Ares I and is not part of the Constellation System baseline. The performance estimates should therefore be used with caution. Nonetheless, the Ares I with a Centaur V2 may be a potential alternative to the Delta IV Heavy and Atlas V 551/Star 48V. Finding: The Ares I will not provide capabilities significantly different from those provided by existing launch vehicles. Ares V The Ares V provides significantly greater launch mass and C3 performance over the existing fleet of expend- able launch vehicles in the U.S. inventory (Figure 5.12.). Figures 5.13 and 5.14 provide a comparison of the low Earth orbit and C3 performance for the Ares V, Ares I, and Delta IV.6 For low-Earth-orbit missions, the Ares V provides four to seven times the mass to orbit of the other systems. Similarly, the Ares V, with or without the Cen- taur, offers dramatically greater performance for interplanetary missions than does either the Delta IV or Ares I. 6The performance curves for the Ares V are based on the latest data available to the committee and refer to the earlier Ares V version with five RS-68 engines and five-segment solid-rocket boosters. NASA has indicated that the performance of the latest baseline of the Ares V will be higher, but has not produced the data yet.

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0 LAUNCHING SCIENCE FIGURE 5.12 Launch of an Ares V rocket. SOURCE: Courtesy of NASA. CONCERNS REGARDING THE ARES V SHROUD Although the Ares V offers the greatest potential value to science, the launch vehicle has to be capable of accommodating science payloads. Astronomy and astrophysics payloads will require cleanliness and vibration and noise levels at least as low as the space shuttle. Ares V design goals currently include these cleanliness and vibration and noise-level targets. Planetary missions will require a method of removing waste heat from radioisotope power sources on space- craft underneath the payload shroud and will also require late (i.e., prelaunch) access to the payload through the shroud. Science missions are more likely to take advantage of the Ares V if these capabilities are designed in to the vehicle rather than being added later.

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 LAUNCH VEHICLE AND SPACECRAFT OPTIONS FOR FUTURE SPACE SCIENCE MISSIONS Vehicle Performance Comparison LEO Missions 160 Ares V Ares I 140 Delta IV HLV 120 100 Payload (tonnes) 80 60 40 20 0 200 300 400 500 600 700 800 900 1000 Circular Orbit Altitude (km) FIGURE 5.13 Comparison of payload capability to low Earth orbit for the Ares V, Ares I, and Delta IV Heavy Launch Ve- Figure 5.12.eps hicle. Vehicle Performance Comparison Interplanetary 70.0 60.0 Ares I - Centaur Delta IV HLV 50.0 Ares V Ares V / Centaur 2 Payload (Tonnes) 40.0 30.0 20.0 10.0 0.0 0 20 40 60 80 100 120 140 C3 (km2 /s2) Figure 5.14.eps FIGURE 5.14 Comparison of escape performance for Delta IV Heavy, Ares I/Centaur V2, and Ares V with and without an upper stage.

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 LAUNCHING SCIENCE A potentially more serious issue for using Ares V for planetary missions concerns the need for a dedicated upper stage to provide high excess escape velocities for spacecraft (known as C3). Several of the mission con- cepts evaluated in this report, including Solar Probe 2, Interstellar Probe, Solar Polar Imager, Neptune Orbiter with Probes, and Titan Explorer, would require some kind of upper stage. The current most likely upper stage, the Atlas V Centaur III Dual Engine Configuration, is relatively tall and thin compared with the Ares V. When placed under the current baseline launch shroud, it would leave relatively little room for a spacecraft (Figure 5.15). An extended shroud would provide more room, but it is unclear if this would be sufficient for many of these mission concepts. The Titan IV Centaur was shorter and wider than the current Centaur but has long been out of produc- tion. Neither upper stage takes advantage of the increased diameter of the Ares V payload shroud. Planetary mis- sions could better use an upper stage that is shorter and takes advantage of the full width of the Ares V; however, development of such a stage could be expensive. In order for Ares V to be attractive for future science missions, vehicle designers will have to consider the requirements of potential science missions. 4.44 m [ 14.6 7.50 m [ 24.6 12.4 m [ 40.8 ft] 9.70 m [ 31.8 8.80 m 8.80 m [ 28.9 [ 28.9 ft] Baseline Extended Shroud Shroud FIGURE 5.15 Two possible configurations of the Ares V shroud—the current baseline shroud and a proposed extended shroud. Shown inside the shrouds are two possible Centaur upper-stage configurations: the Titan IV Centaur (left) and the Atlas V Centaur III Dual Engine Configuration (right). Any spacecraft carried atop an upper stage would have severely restricted volume constraints. Neither shroud option takes advantage of the width of the Ares V shroud. SOURCE: Adapted; courtesy of NASA.